| AstroNuclPhysics ® Nuclear Physics - Astrophysics - Cosmology - Philosophy | Gravity, black holes and physics |
Chapter 1
GRAVITATION AND ITS PLACE IN PHYSICS
1.1. Development
of knowledge about nature, space, gravity
1.2. Newton's law of gravitation
1.3. Mechanical
LeSage hypothesis of the nature of gravity
1.4. Analogy
between gravity and electrostatics
1.5. Electromagnetic
field. Maxwell's equations.
1.6. Four-dimensional
spacetime and special theory of relativity
1.1. Development of knowledge about nature, space, gravity
Gravitation is a force with which every person is in direct and constant contact from birth to life, in the form of Earth gravity - weight (Greek gravis = heavy), and humanity thus encounters gravitational phenomena from the very beginning. Nevertheless (or perhaps because of it), as with most basic natural phenomena, there have been very misconception opinions about gravity for a very long time, and we can say that the origin and essence of gravity is not fully explained even now. In this introductory part, we will very briefly summarize how views on gravity, space, time, matter, universe, and nature in general, have gradually evolved and refined from antiquity to the present day.
Science in antiquity
The origins of science in antiquity arose from
entirely pragmatic motives: to systematically and correctly solve
the problems that life brought. Such specific problems were, for
example, the construction of cult buildings and the construction
of irrigation systems, the rational management and cultivation of
land, the distribution of food or other objects and their
exchange, and so on. To solve such tasks, it was necessary to
learn to determine distances, height differences and areas, to
study and predict the weather, to count and distribute goods in
terms of quality and quantity.
The needs of exchange and distribution led to the introduction of the basic arithmetic operations of addition, subtraction, multiplication and division. These operations, which are an expression of the properties of ordinary material objects, display (model) the actual processes with real bodies. Scales - units *) have been introduced to determine the distances and sizes of objects , ie certain standard objects, which can be used to express the sizes of other objects by comparison. In other words, the amount and sizes of real bodies were assigned numbers - their number and dimensions - which were operated according to the rules of arithmetic, and the resulting numbers were converted back to the corresponding number and size of real objects. Thus mathematics appeared in human activity as the science of models and a general scheme began to be used (initially subconsciously) :
reality ® Model ® reality
n
n
mathematics
*) Units of length and time
In the past, people chose basic mechanical units
for measing distances, time, and weight (the amount of matter)
according to the environment in which they lived and using the
objects they encountered. For length, these were first human
measures such as "foot", "elbow" or
"inch", later, when the shape and approximate size of
the Earth were already known, the unit of length
"kilometer" was determined as 1/40000 of the length of
the Earth's equator, from which then "meter".
Time
was derived from the duration of one Earth orbit around the Sun -
"year", the time of the Moon's orbit around the Earth -
"moon", the time of one rotation of the Earth around
the axis - "day"; it was divided into 24
"hours", an hour into 60 "minutes", a minute
into 60 "seconds". The name "minute" comes
from lat. pars minuta - reduced part (from
hours), "second" then from pars minuta secunda
- second reduced part.
Although today
these units are defined and metrogically measured much more
accurately than by the properties of the Earth, for historical
reasons they have basically been preserved and their factual
random selection overshadows some fundamental relationships in
natural laws, where there are complex constants
whose numerical size is given by the choice of units.
Astronomical observations. Astrology,
alchemy; quackery
Already in prehistoric times, people have observed that not only
day and night but also seasons recur periodically, and there is a
close connection between these daily and annual seasons and the
movement of the Sun, Moon and planets across the sky. The need to
determine and predict the time of day and season, ie natural
conditions for agricultural and other work, therefore naturally
led to astronomical observations and the
introduction of corresponding time units: day, month, year
(measuring time both short-term - hours and long-term - calendar)
. The Babylonians and Egyptians excelled in observing the sky in
ancient times.
The study of objects outside the
Earth - in space - is dealt with by astronomy (Greek astron = star,nomos = rule,
order, law; that is, the " laws of the stars
") *), popularly stargazing.
Although current astronomy includes the study of planetary
systems, interstellar matter, and the overall evolution of the
universe (cosmology),
stars and their systems (galaxies) are still the
main objects for astronomers.
*) Originally, it was a "regularity
of star motion", because the apparent shifts of stars
and constellations in the sky were considered star motion.
Nothing was known about the very nature of the stars in
antiquity and the Middle Ages; they were
considered a sort of unchanging distant points of light - perennials,
against the background of which the moon, planets, or the Sun,
moving. The true nature of the stars was gradually revealed only
during the 19th and 20th centuries - that they are very distant
huge hot gas spheres, in the interior of which thermonuclear
reactions take place (for most of their
evolution) ; The sun is also a star, they
are a kind of "distant sun". They are not immutable and
eternal, but during their evolution they shrink and expand, they
can even explode violently, "live" for a finite time -
details are in §4.1 "Gravity and evolution of stars".
Astronomy is
sometimes considered the "queen of science",
from two points of view :
a) It is the oldest natural Science.
Astronomical observations, records and calculations of the
positions of celestial bodies in the sky have been made since
ancient times. At that time, however, it was not considered a
natural science, because it was not known that earthly and
"heavenly" nature are one and the same.
b) Everything is part of the universe, and
our Earth is a cosmic body; everything around us was formed by
astrophysical processes in the universe (§4.1
"The role of gravity in the formation and
evolution of stars" and
§5.4 "Standard cosmological model. The Big Bang.
Shaping the structure of the universe."). In the concepts of unitary field theory,
contemporary fundamental physics tries to solve the problems of
the microworld of elementary particles and the megasworld,
the origin and evolution of the universe, on the same basis (Chapter B "Unitary field theory and
quantum gravity", §B.6
"Unification of fundamental interactions.
Supergravity. Superstrings.")
.
Ancient civilizations generally had
very poor and completely distorted
knowledge of the universe. No wonder - after all, we wouldn't be
better off if we just looked around the sky without optical
instruments and without prior knowledge. There are fundamental obstacles
in the immediate visual cognition of the universe :
1. Cosmic objects are very distant. The
optical system of our eye creates such small images of these
objects on the retina that it is impossible to distinguish the
details of their structure. Very little light
comes from distant objects in space , which due to the small
diameter of the eye lens (approx. 5 mm) is usually not enough to
see them even with a relatively high sensitivity of the retina.
2. We live on the planet Earth, which rotates
("cosmic carousel" ) and orbits the Sun. These movements of us observers
(which we are not aware of) give the false impression of the
movements of observed objects in space.
3. The Earth's atmosphere absorbs a lot
of light and our eye is sensitive only to a narrow region of the
electromagnetic radiation spectrum. Other important
"windows" into space are hidden from our sight.
4.Earth's gravity binds us tightly to the
earth and prevents me from "going to take a closer
look" at cosmic objects. After all, our close connection
with terrestrial living conditions and our "snail"
slowness in overcoming vast distances in space
also prevent us from doing so.
Astrology
The observed connections between periodic natural events and the
movement of celestial bodies, the causes of which ancient
observers did not know, led to the idea that the
positions and movements of celestial bodies are related even to
other phenomena on Earth *) - various catastrophes, wars and even
human destinies. From this false notion
developed astrology, which until the end of the
Middle Ages was the main motive for astronomical observations.
However, already Copernicus' and Kepler's findings about
planetary movements made astrological claims highly unlikely:
individual planets, when viewed from another planet - Earth - are
randomly projected into different constellations as they
move.(also randomly projected) in the starry sky; there is no reason to attribute to
these random projections any real influence on the course of
events. Indeed, since then, educated people have mostly not
believed in astrology; let us remember only the words of
J.A.Komenský: "Astrologers
- they are not astronomers, but liars from the stars!". Other scientific findings have confirmed this
view even more certainly. It is hard to imagine that the apparent
projections of sunlit planets on random constellation patterns in
the sky could somehow affect the complex structure of DNA
macromolecules inside homo sapiens germ cells on one of
the other planets orbiting the Sun! No distant cosmic bodies can
affect on the personality characteristics of people or
on their fate. So astrology is no longer a science,
but it can be a nice game using astronomical
props ...
* ) It is interesting that the ideas of
cosmic action are again encountered in modern physics in
connection with some interpretations of Mach's principle,
according to which local physical laws are determined by the
distribution and motion of all matter in the universe - see
"Appendix A". Of course, this has nothing to do with
astrological ideas!
It is similar with numerology.
Numbers fascinate many people, and some attribute magical powers
to them - that a particular number affects a certain
characteristic of a person. Astrology, numerology, chiromancy,
irodology, magic balls, card unloading ... etc., belong to the
same category of superstitious "oracle" or
"prophetic" techniques that do not work,
but many people believe them ...
Alchemy
Closely related to astrology was another false way *) to explore
nature - alchemy, which, based on some
metaphysical principles and philosophical ideas, sought to
achieve the transmutation of the elements **) - especially to
make gold - and to find a universal "sage stone". But
alchemists in their attempts (in terms of
the then required goals inevitably unsuccessful!) gathered a large amount of empirical knowledge, which
later, after abandonding alchemical misconceptions, have become
an important basis for understanding the true nature of the
chemical merging of substances - the basis for building of chemistry.
*) This critical evaluation applies only to science
page of alchemy and astrology! Some spiritual and philosophical
aspects, especially the effort for a unified conception
of being, for spiritual improvement,
the transformation for improvement, the unification of art and
science, were at a high level for their time and can still appeal
to us today. However, among current proponents of alchemy and
astrology, we often encounter misunderstandings
related to confusing and merging the misguided scientific ideas
of the past with valuable spiritual and philosophical ideas of
enduring validity.
**) However, alchemists had no idea not only about atoms and
their nuclei, but also did not recognize elements and compounds.
They judged the substances according to their external
manifestations and a few simple chemical reactions that they were
able to carry out. Today, with the methods of nuclear physics, we
can perform transmutations of elements - this is "Nuclear Alchemy".
From the turn of the
17th and 18th centuries, when feudalism and the church lost their
absolute power, the former alchemists - charlatan and often
fraudulent "gold-producers" in the service of the rich
and powerful - were gradually replaced by serious naturalists,
who no longer wanted a recipe for making gold or different
elixirs, but they tried to penetrate the essence of the
construction of matter. This eventually succeeded in
atomic and nuclear physics and chemistry (see Construction
of atoms).
Quackery versus science
For erroneous, untrustworthy or fraudulent schools of
thought and behavior of people is being called quackery
or charlatanism. According to literary sources,
the name "charlatan" comes from the Italian
word "ciarlatano", meaning the inhabitants of
the town of Cerreto, from where in the 15th century
several prominent magicians and healers came. In French, the word
"charlatan" began to be used for an
untrustworthy healer and impostor using unproven and medically
unrecognized practices. More generally for other talkers,
shaders, swindlers...
From the mental roots of astrology,
alchemy, and religion, are growing up some newer quacks
directions - a parapsychology denoting
itself by misleading name psychotronics, various
ideas about the aura, cosmic energy,
quantum consciousness, geopathogenic zones, megalytic legends, homeopathy,
alternative medicine. They are a frequent part of the line of
thought called the esotericist (cf. the passage "The
Meaning of Phenomena and Events"
in the essay "Science and Faith") . On this occasion, we will make a brief mention of
these worrying mistakes, and even frauds
, which, paradoxically, have become more and more common in
people's consciousness in recent decades.
Proponents of these ideas often
claim that our ancestors already knew in ancient times ("megalytic culture") and
used the mysterious "cosmic energy" and possessed
miraculous abilities. Today's science is accused of ignorance for
not acknowledging it... Modern charlatans equip old superstitious
ideas with new "scientific"
props, they boast the latest quantum,
holographic, relativistic physical theories - so that the lay
public can trust them. They talk without
knowing what it is, on quanta of energy, gravitons,
unified interactions, information fields, relativistic effects,
tachyons and superluminal velocities, and a number of other
concepts that, without further study and understanding, they
borrowed from the arsenal of valid theories of contemporary
science. They use computers and spread their phantasmagories with
the help of information technology ...
Most of the charlatan schools are
characterized by a misunderstanding of the way
they treat the concept of energy. There is talk
of mental, life, psychic, magnetic, cosmic, divine, etheric,
negative or positive energy, of energy zones. The physical
meaning of energy is erroneously confused with
the common folk notion of biological and mental
"energy", which is, in fact, a combinatorial and
biochemical property of the arrangement of complex molecules and
their systems in an organism; it has nothing to do with the
physical concept of energy. Not surprisingly, such confusion
often creates very bizarre nonsense . They talk
about different energy transmitters, receivers and interference
suppressors, zones, auras, "energetically active" water
and other substances, energy miraculous properties of pyramids
and other structures ...
No disguise into a modern, seemingly
scientific garb, can not change anything to the fact that all
these claims are only completely unsubstantiated
assumptions, dating from the pre-scientific period and
from misconceptions from the past. Now these
starting points have long been refuted. Nevertheless, many
trusting people, with underdeveloped critical thinking, continue
to believe in the wrong conclusions from them.
They fail to recognize that the apparent successes of alternative
medicine are due to the placebo effect, and the proclaimed
success of psychotronics is in fact only a selection
effect - from a probability of 50% to 50%, failed cases
are excluded and forgotten, while (randomly) successful cases are
glorified and widely published. Objective comparison and
confrontation (independent "blind" experiments with
subsequent statistical evaluation) is strongly opposed by
charlatans; they argue that "scientific supervision"
leads to the inhibition of their mental faculties, or disrupts
their association with the transcendent, cosmic energy, gods or
demons, and so on. If some such comparisons were still made (eg wells for finding water with dividing rot), the statistical significance of paranormal phenomena was
not proven.
Quackery and fraud
are most common in the field of health and disease, in medicine
-miraculous means and methods that can cure all
diseases, from cancer to AIDS. Whether they are pharmacological
means (universal "miracle drugs") or physical means
- various biolamps, magnets, generators of electromagnetic
frequencies or some mysterious fields, etc. The use of these
methods, as well as psychotronics and homeopathy in medicine, can
sometimes subjectively improve the health by the placebo
effect; or it may be a mere coincidence (even without treatment, the body would "help
itself")... However, in serious
diseases, their use carries the risk that there
will be a delay in waiting for the alleged
effects effective treatment, which may cause irreversible damage
to the patient's health.
Quantum
consciousness, quantum medicine
Concepts and knowledge of quantum physics are a
popular tool of fictional directions. This field of physics is
sufficiently mysterious (moreover, in
connection with the theory of relativity) and human
consciousness is also shrouded in mystery, so that in
the opinion of some people they should have something in common..?..
The common name "quantum consciousness"
or "quantum mind" means a group of
hypotheses proposing putative quantum-mechanical phenomena in the
function of the brain to explain thinking and consciousness.
Immediately after the creation of quantum mechanics in the works
of Planck, Bohr, Schrödinger, Heisenberg, Pauli and others (see eg "Quantum
Physics"), quantum
theory became an attractive option for solving the
philosophical-epistemic conflict between the
strict determinism of classical physics and our
conscious free will : quantum randomness
can open up new possibilities for free will. In most discussions
of the relationship between quantum physics and consciousness,
the basic ideas of quantum theory are accepted in a purely metaphorical
way, only as analogies, without a relevant reference to their
physical meaning. This can lead to interesting sci-fi ideas,
which are, however, unconvincing and scientifically erroneous.
Quantum-mechanical terms are often used to seek greater
persuasiveness - to add "scientific weight" to
subjective hypotheses.
The latest
hypothesis of this kind was created by R.Penrose *) and
S.Hameroff, who assumed cells or structures with "quantum
sensitivity" in the brain, through which quantum
mechanics is involved in brain activity. Hameroff
hypothesized that suitable structures for quantum behavior are microtubules
(for microtubules see eg "Cells
- basic units of living organisms", passage "Cytoskeleton -
skeleton and carrier of cell functions"),
which form the cytoskeleton of cells, including neurons, where
they could mediate synapses. Quantum vibrations could occur in
their regular lattices of tubulin protein, and coherent
superpositions of tubulin states could interfere with many
neurons. However, those skilled in the art of biochemistry,
molecular cell biology, and neurobiology are skeptical
of this microtubule function...
Simultaneous
quantum collapse of these microtubulin states is interpreted as
an "individual elementary act of consciousness".
Penrose attributes this act to "quantum gravity",
which has not yet been created. From the point of view of unitary
field theories, however, quantum gravity acts on much smaller
spatial scales than the dimensions of microtubule molecules, so
that it cannot affect any of their quantum
states at all.
More similar irrelevant constructions (such as
twistors), are being introduced here, probably to give more
"scientific weight" to these speculations...
The idea arose
that quantum information from microtubules is not lost after the
physical death of man, but they remain embedded in the
"information" structure of the universe as a kind of
"counter of consciousness"..?.. This is
already completely in the field of sci-fi..!.. The quantum
consciousness hypothesis is often (but
unjustifiably) linked to the hallucinatory experiences of
people who have undergone clinical death but have returned to
life. In fact, these frequently described typical experiences are
probably due to altered brain activity in a state of hypoxia
during circulatory arrest. The relationships between matter and
consciousness are briefly discussed in the passage "Soul and
Matter" of the work "The Anthropic Principle
or Cosmic God".
Despite
extensive treatises and great efforts by Penrose *) and Hameroff,
their hypothesis is not a convincing model of
brain function or explanation of the essence of consciousness and
mind. It is based on unverified and debatable assumptions
physical and neurobiological. Microtubules in cells probably do not
play a significant role in the function of neural networks in the
brain. It is apparently not necessary to use the
props of quantum mechanics to truly explain the human mind and
consciousness. Quantum physics works at the molecular and atomic
levels everywhere in nature, in our everyday life, but in the
behavior of macroscopic objects - which are also brain neurons
and their networks - quantum effects do not manifest
any way. Consciousness probably arises algorithmically -
combinatorially - from the enormous complexity of signal
connections between billions of neurons in the brain network...
*) Note: It
is difficult to understand, that this "flight-mistake"
happened to the excellent physicist Roger Penrose, who had
previously been very successful in research in the field of black
holes and cosmology. Together with S. Hawking, they developed
important theorems about spacetime horizons and singularities
(§3.8 "Hawking's and Penrose's theorems about singularities"). After all, this collaborator and his friend
Stephen Hawking flatly rejected the hypothesis
of "quantum consciousness"! The ways of the human mind
are unpredictable...
Other
fictitious claims of "quantum medicine"
are based on hypotheses about quantum behavior, according to
which the body is quantum composed of energy and information
influenced by quantum consciousness. Quantum healing can
therefore cure any disease based on a person's state of
mind..?.. Some charlatans even claim that they can heal
in this way even from a distance..!..
Rational approach to reports of miracles and
supernatural phenomena have already expressed the Scottish
philosopher David Hume (1711-1776) words: "No
testimony is not able to prove a miracle - it would have to be a
witness of this kind that the error of his would be more
miraculous than the event. which he is trying to witness". In other words, a mistake or a lie is more
likely than a miracle. This attitude is sometimes referred to as
"Hume's Razor", cutting off credible
information from improbable and perhaps erroneous information.
Within science itself, criteria called "Occam's razor"
and "Popper's razor" are used - see " "New" and
"Old" physics"and "Knowledge:
experience + science. Awareness
- education - wisdom." in the
monograph "Nuclear Physics and the Physics of Ionizing
Radiation".
All this would not be worth mentioning
in a physically oriented treatise, if these irrational
ideas did not spread more and more in recent years (and a lot of people believe them)..!..
For a comparison, see also the essay "Science
and Religion".
Space,
time, matter, universe
In the empirical observation of nature and finding their laws,
important abstract concepts such as space, time,
motion, matter were formed , which are certain images of the
general (universal) properties of being. Efforts were made to put
individual isolated knowledge into context, to
generalize it and to extrapolate it. Questions like "When
and how did the world (universe) come into being?",
"How big is the universe?", "What is matter
composed of?" etc., they are probably as old as people's
conscious thinking about nature.
One of the basic questions that philosophy
asks is where to find the essence of all being -
the basic "primordial matter" (the simplest and
indecomposable primordial substance) from which all things,
plants, animals and people are formed and composed. Ancient
philosophy, which could not penetrate into the true essence of
things and phenomena, naively considered to be the essence of
some superficial and purely phenomenal aspects of reality, based
on immediate sensory sensations. Thus, water (Thales *) , air
(Anaximenes) or fire (Herakleitos) were considered the basic
precursors. Later, four basic (independent and non-intertwining)
primates were postulated, or elements (natural elements) from
which the whole world is built: water (as the essence of
liquids), air (as the representative of the gaseous state), the
earth (as the carrier of solid properties ) and fire (as a cause
of mobility and variability).
*) However, in the light of today's
knowledge, it can be said that Thales was not so far from the
truth: according to current astrophysics, all elements were
actually formed in stars by nuclear reactions from hydrogen
formed from elementary particles generated during the Big Bang (see §5.4 " Standard cosmological model.
The Big Bang. Shaping the structure of the universe. ") .
This teaching
on the four basic elements of the world was developed especially
by Aristotles (384-322 BC), who supplemented it with the concept
of four basic properties (essences), which are heat, cold,
humidity and dryness. The interconnection of such
"essences" was to create individual basic elements of
the world (eg water from moisture and cold, fire from heat and
drought). Similar ideas persisted until the Middle Ages, where
they were the basis of alchemy.
Philosophers have also addressed the
question of how matter is composed of the basic elements. As for
the structure of matter, there are basically two possibilities:
either matter is continuous (infinitely
divisible), or it consists of certain small "grains"
(atoms) that are no longer divisible. In ancient
times, it was not possible to make a reliable decision between
these two possibilities, so both concepts were coined in
different philosophical schools. The science of atoms was
developed mainly by Democritos (ca. 460-370 BC), who justified
the necessity of the existence of indivisible atoms by the fact
that, with unlimited divisibility, there would be nothing left
that could carry the properties of the substance. This
speculative reasoning is based on the assumption that the
properties of substances never change by division and that the
substance itself is the bearer of all its properties (current atomic and nuclear physics already looks at it
differently...) . The philosophical thesis
of the structure of matter is almost universally accepted in the
methodology of the natural sciences.
Gravity
and the Universe in Antiquity
In the earliest times, before conscious exploration of nature
began, humans did not think about gravity at all
; it was so common and mundane that people got used to it and
ignored it. They took the gravity of the earth as a matter of
course and a natural effort of objects to fall to the ground.
Cognition of what we call gravity today was previously associated
with astronomy. Astronomy and philosophy in
general - all teaching about nature was part of philosophy at the
time - reached a particularly high level in the period of ancient
Greek culture. Some ancient philosophical schools (represented by Thales Miletsky, Pythagoras,
Aristarchus, in India by Arjabhata) at the
time had a surprisingly realistic picture of the shape, location
and motion of nearby planets (including the
Earth) around the Sun *).
*) Opinions on the true level of ancient
science sometimes differ. There are sensational claims about the
use of electricity and atomic energy and about knowledge of outer
space in ancient civilizations. However, these claims are
completely unfounded. The legacy of ancient thinkers is so rich
and extensive that among hundreds and thousands of ideas and
statements (often contradictory) one can find those that, more or
less by accident , coincide with the conclusions
of modern science. In these statements, we sometimes insert a
sense that their authors might be very surprised by ...
The
development of natural sciences, especially astronomy and the
overall worldview, for a long time significantly (and unfortunately mostly negatively)influenced the teachings of the most important
representative of Greek philosophy - Aristotle. This teaching was
the culmination of ancient natural philosophy. Aristotle came
from the basic sensory experience of earthly life, that heavy
bodies try to fall down to the ground, while "light"
objects like smoke or fire rise. Based on this, Aristotle
proclaimed the concept of " natural places "
and " natural movements": the natural place of
heavy substances (soil and water) is" to be below ",
the natural place of light substances (fire and air) is"
above ". The natural movement of earth and water is to
descend, the natural movement of air and fire is to ascend *).
All other movements are forced by an external force.
*) The philosophical thesis that
"the like goes to the like" was already expressed by
Platon, who thus explained the fact that material bodies fall to
the ground.
This concept,
together with the assumption that the Universe has only one
center of gravity, led Aristotle to the following image of the
world: in the center of the universe is a motionless
Earth, in which the heaviest matter of the universe
gathered - earth and water; the earth is composed of soil and
water located in its natural place, so it is at rest. The
universe (ie the Earth and its surroundings) consists of
individual spherical layers: earth, water, air, fire. All
celestial bodies are composed of the lightest and "most
perfect" substance - ether - and perform a
"perfect" uniform circular motion over some spheres
through which they are carried. Thus, in Aristotle's conception,
the universe is composed of two diametrically opposed parts:
earthly and celestial.
As for movementas
such, Aristotles taught that bodies move only when they are
propelled by some force - "the cart drawn by the donkey
stops, when the donkey stops towing". Aristotele did not
know inertia because he was not experimenting and could not
reduce or relieve friction enough. Regarding the fall of bodies
to the ground, Aristotle claimed that the rate of fall of a body
is proportional to its weight; this erroneous conclusion again
arose from the common experience that light sparse bodies fall
much slower than dense heavy bodies.
Aristotele's geocentric cosmology
further elaborated by Ptolemaios (ca. 100-160n.l.), who solved
the discrepancies between the assumed perfectly uniform motion
and the observed irregularities of the planets' motion together
with changes in their brightness (indicating changes in distances
between Earth and planets) by hypothesizing that real planetary
motions or more uniform circular movements, the so-called
deferent, epicycle and equant. Ptolemaios thus reached a
relatively good agreement with astronomical observations, but at
the cost of considerable complexity and sophistication.
Aristotle-Ptolemy's geocentric teaching was then canonized by the
Church and maintained as a dogma throughout the Middle Ages (the era of "intellectual darkness"); the development of astronomy and the natural sciences
has thus been hampered for more than a thousand years.
Development of
scientific astronomy and physics
Heliocentric
system
The first significant breakthrough into the long-prevailing
misconception of the structure of the universe was made by M.
Copernicus (1473-1543), who noticed that is the Sun, around which
the planets and the Earth orbit. He thus assembled a heliocentric
system and showed that the Earth is only one of the other
orbiting planets; in addition, the Earth revolves around its axis
with the diurnal period, giving the impression
that all cosmic bodies, stars and planets, orbit it. This laid
the foundation for eliminating the senseless contradiction
between "terrestrial" and "celestial" and for
bringing astronomy closer to other sciences, especially physics.
The knowledge that the Earth (and as it
turned out later, neither the solar system nor our Galaxy) has no any privileged place in the universe, it is
called the "Copernican principle" and plays an
important role in contemporary cosmology (Chapter
5, §5.1 "Basic starting points and
principles of cosmology
") .
Copernicus also realized that it was
probably not correct to assume only one center of gravity in the
universe, but that each body should have its own weight
- gravity. At Copernicus, we thus already encounter a hint of a
realistic conception of gravity as the effort of bodies and their
parts to join together into the whole, ie with a hint of the
concept of general gravity. Copernicus' conception was followed
by J.Bruno (infinity of the world in space
and time, the same nature of the perrenials-stars and the Sun) and especially J.Kepler (1571-1630), who, on the basis
of astronomical observations, formulated his three important laws
of planetary motion around the Sun (§1.2). Kepler
sensed that the cause of these planetary motions was a force
emanating from the Sun, but in the absence of mechanics he could
not come to a correct explanation; it was later filed by Newton.
Experiment
- the birth of scientific physics and natural science
Galileo Galilei (1564-1642), who can be considered the founder of
physics as a scientific discipline, made a decisive contribution
to the development of astronomy and physics. He introduced experiment
into physics as a decisive tool of knowledge. On the basis of
simple experiments with the motions of bodies, Galileo formulated
the law of inertia (which denied Aristotle's teaching on
motion), the composition of motions, and also arrived at the principle
of relativity of motion (see §1.2 and §1.6). He thus became
a pioneer in the mechanics of motion of bodies, especially
kinematics. In astronomy, Galileo was a staunch supporter of
Copernicus' heliocentric system, which he decisively supported
with his discoveries using telescopes.
Galileo was also the first scholar in
history to have made a direct and significant contribution to the
knowledge of gravitational phenomena. Through his experiments
with free-falling bodies (allegedly from the Leaning Tower of
Pisa), he arrived at the famous law
of free fall,
according to which in free fall all bodies fall to the ground
with a constant
acceleration,
which is independent of weight (mass) and composition of the body.
Hi thus refuted Aristotle's concept of natural movements upwards
or downwards: these are always the movements of bodies under the influence of
gravity, but in an environment with greater or lesser density.
The law of free fall, generalized to the principle of universality of gravitational action and the principle
of equivalence, has become one of the main starting
points of modern gravity physics - Einstein's general theory of
relativity (see Chapter 2, especially §2.2
"Universality - a basic property and the key to
understanding the nature of gravity").
Isaac Newton (1642-1727) was a decisive
milestone in the development of physics, astronomy, and the
natural sciences in general. Above all, Newton followed up on the Galileo's
findings and built mechanics, in which he formulated precisely and
mathematically expressed the three
basic laws of motion (§1.6, passage " Newton's classical mechanics "). He also discovered the basic laws of
hydrodynamics, acoustics and optics. Newton then completed his
epoch-making work by combining his and Galileo's mechanics of the
motion of terrestrial bodies with Kepler's kinematics of
planetary motion, thus arriving at his great law of general gravity and creating the dynamics of the
solar system; more on this in §1.2 "Newton's
law of gravitation".
Through the work of I. Newton,
the pre-scientific period of erroneous conjectures and dogmas
ended in human cognition, and a period of scientific
research,
precise experiments and logical thinking begins. Newtonian
physics also provided a new, more realistic view of the universe.
Observing
the universe with telescopes - telescopic astronomy
We know from everyday life that we do not see what is too far
away, we do not recognize the details and we can only guess at
the true nature of distant objects. This is even more true of
distant objects in universe. G.Galilei first looked into
space with a simple self-constructed telescope in 1610 and was surprised to see
craters on the Moon ("moon mountains"), Jupiter's
moons, the phases of Venus illumination, Saturn's rings. Larger
telescopes *) then revealed many stars invisible to the naked
eye, nebulae, new planets (Uranus r.1781, Neptune r.1846), spiral
"nebulae" - galaxies during the 19th century. New tools
placed in the foci of telescopes - photography and spectroscopy
- led to the
fascinating discoveries of previously unsuspected structures in
space, a huge number of stars and paved the way for astrophysics to study the physical properties of stars
and galaxies (see below "Electromagnetic
radiation - a fundamental source of information about the
universe ").
*) Small binoculars are often lens refractors -
the primary lens consists of a larger converging
lens with a large focal length, the eyepiece
(used as a magnifying glass to observe the image created by the
lens) is a smaller converging or diverging lens with a short
focal length. The optical disadvantage of the refractor is a color
defect (chromatic aberration) - due to the dispersion of
light, the focal length is somewhat different for different
wavelengths - colors - light. In addition, it is technically
difficult to produce quality large diameter lenses. In 1668
I.Newton assembled the first mirror telescope -
a reflector, the "lens" of which was a concave mirror
creating the image in the focal plane by means of reflection of
light. The reflector has no color defect and, in addition,
large-diameter spherical or parabolic mirrors can be precisely
ground (their deformation is prevented by mechanical
reinforcement "from behind"). That's why all large
binoculars are mirrored. Large diameter telescope (aperture)
collects more light and therefore we can observe fainter and more
distant objects. In addition, larger telescopes have better
spatial resolution, so we can recognize finer details of the
structure of multiple stars, star clusters, spiral arms of
galaxies, gas clouds.
Electrodynamics,
atomic physics, theory of relativity, quantum physics
In the middle of the 18th century, the development of mechanics
was seemingly completed. Fundamental physics focused on the study
of other physical phenomena - thermal and especially electrical and magnetic.
Electricity
and magnetism
At this point, it may be useful to briefly recapitulate the
development of knowledge about the extremely important natural
phenomena of electric and magnetic. The first
observation of electrical (electrostatic) phenomena comes
from ancient Greece. For articles made of amber, which is fossilized natural resin from
which jewelry and ornaments were made, at friction
were observed the
attraction of small light bodies - hair, feathers, yarn
(Thales Miletus in the 6th century BC described that the amber
tool used at spinning flax began to attract various small bodies,
while the flax fibers began to repel each other).
Amber is called the electron (electron) in Greek, which later gave a
collective name to all these phenomena (the
name elektricitas derived from amber was used by W.
Gilbert in the study of static electricity, although he observed
attractive forces at friction even in some other materials,
especially glass). For many centuries,
these phenomena served only as an curiosity interest and for
juggling demonstrations, nothing was known about their cause and
nature.
Only the existence of two kinds of electric charges (called conventionally positive
"+" and negative "-") has been discovered,
with charges of the same kind repelling each
other and of the
opposite kind attracting each
other. Later, the
law of conservation of electric
charge was discovered
(B.Franklin). In 1784, Ch.A.Coulomb, with the help of sensitive
torsional weights of his own construction, measured the interaction of
electric charges (Priestley and Robinson
dealt with these experiments independently) and discovered the basic law of
electrostatics - Coulomb's law (1.20b), similar to Newton's law
of gravitation (the comparison of the laws
of electrostatics and gravity is discussed in detail in §1.4
"Analogy between gravity and electrostatics").
In 1789, in his well-known
experiments with frog legs, Galvani observed muscle contraction
when touching an iron railing - indirectly observing the biological effects of discharging electric charges, ie
electric current (at that time there was
still a distinction between "galvanic" and frictional
electricity). In
1799 A. Volta first designed a source of "galvanic
current" - an electrochemical Volt
cell; this
current has been shown to be of the same nature as the
"discharge current" generated for a short time by the
conductive connection of electrostatically oppositely charged
bodies. Electrochemical sources - Volt cells assembled into batteries - made it possible to study the
continuous passage of an electric current through a conductors, to assemble the first electrical circuits.
Completely separately and
independently of electrical phenomena, other phenomena of
"mysterious" force action were observed - magnetic phenomena. It has been observed already in
ancient times, that some minerals attract or repel each
other and that they attract iron objects. Iron ore mined near the
city of Magnesia in Asia Minor was most well-known
in this respect; this ore (it is iron oxide Fe3O4)
was called magnetite, which gave the collective name
to magnetic phenomena. When placed on a cork float on water, or
when hung on a thread, this magnetic ore was always rotated in
the same direction - one end to the north and the other to the
south. Thus, two magnetic poles were marked out - north
and south; magnetic "arrows" found important use in compasses (the
Chinese used such a magnet 4,000 years ago to determine the
correct geographical direction when traveling). In
Europe, experiments with magnets were studied in detail around
1600 by the English physician W.Gilbert. As with electrical
phenomena, no one had any idea about the nature of magnetic
phenomena until the end of the 18th century
(the fluid idea vaguely spoke of northern and
southern "magnetic amounts", which, however, unlike
electric charges, cannot be separated from each other).
The first important breakthrough
into the essence of magnetic phenomena and their connection with
electrical phenomena began with the accidental discovery of
H.Ch.Oersted in 1820, who noticed during experiments with
electrical circuits, that the magnetic
needle deflects near the conductor through which the current
passes - that is, that the electric current causes a magnetic
field in the same way as if a permanent magnet had been applied
instead of the conductor with the electric current. It turned out
gradually that the mysterious magnetic action, which until then
was the domain of only natural substances, permanent magnets,
probably has an electrical origin - it is
created by the movement of electric charges. And
the magnetic field, in turn, exerts a force on the moving
charges, on the electric currents.
This was soon shown even more
certainly by the experiments of A.Ampere (1775-1889), who
discovered the law of mutual force (magnetic) action of electric
currents. In 1820, Biot and Savart measured the intensity of the
magnetic field around the conductor flowing through the el.
current, these results were further generalized by Laplace - the Biot-Savart-Laplace law (1.33a) was created, indicating
the dependence of the intensity of the magnetic field excited by
the current in the conductor element on the magnitude of the
current and on the distance. These laws led to the construction
of "artificial magnets" powered by electric current - electromagnets. The magnetism
of permanent magnets was later explained by atomistics.
Another key finding was the law of electromagnetic induction discovered in 1831 by M.Faraday,
according to which the time change of the magnetic field evokes
(induces) an electric field, whereas the induced voltage is
proportional to the rate of time change of the magnetic flux
through the surface of the considered conductor loop - relation
(1.37a). These findings became the basis not only of electrodynamics (the merger of the science of electricity
and magnetism), but also the practical application of
electromagnetic phenomena - electrical
engineering was created.
Faraday further expressed the
idea, based on his experiments, that the electric and magnetic
forces do not take place directly from one charge to another, but
spread through the environment lying between
them. He thus laid the foundations of the teaching about the electromagnetic field, which he further
elaborated, generalized and mathematically formulated by J.C.Maxwell
(1831-1879) in the 1860s. The theory of the electromagnetic
field led Maxwell to the knowledge of the finite
speed of
propagation of electromagnetic action equal to the speed of light
*), to the prediction of electromagnetic
waves and
to the hypothesis of the electromagnetic nature of light. The
experiments of H.Hertz and his followers, which proved the
existence of electromagnetic waves and found out some of their
properties, fully confirmed the correctness
of Maxwell's theory. From the physical-mathematical point of
view, the theory of the electromagnetic field is discussed in
§1.5 "Electromagnetic
field. Maxwell's equations".
The speed of light
- or the speed of propagation of electromagnetic waves, or the
speed of photons - is extraordinarily high
compared to all other terrestrial speeds (a million times the
speed of sound in air), so in earlier times it was not easy to
measure it more accurately (it was often considered infinite).
The first approximate determination was made astronomically in
1675 while observing the eclipse of Jupiter's moons (O.Roemer in1685, c~225 000 km/s).
But the real measurement of the
speed of light using terrestrial sources and optical-mechanical
means was not made by Fizeau until 1849. In this classic
experiment, a beam of light was reflected back and forth through
the teeth of a rotating gear when reflected from mirrors. As the
speed of the gear increased, it was observed that at a certain
speed the reflected beam no longer passed through the gear - the
beam that passes through the gap between the teeth of the gear
returns to the gear space after overcoming the mirror distance,
reflection and overcoming the distance back, when the wheel
rotates by such an angle, that instead of a gap there is already
a tooth in the path of the beam. If there is a distance between
the gear and the reflecting mirror d and a wheel rotating
at a frequency f has N teeth around the
circumference, between the speed of light c and the first
frequency f , when the reflected beam stops passing, a
simple relation c = 4.d.f.N (coefficient 4 arises from the fact
that the distance d is overcome twice and the rotation
time of the wheel from the gap to the tooth is 1/2.fN ). It
gets a result of c~313,000 km/s.
In 1850, J. Foucault used a rotating
mirror to determine the speed of light propagation. The emitted
light is reflected from the rotating mirror towards a stationary
mirror 18 meters away, and from it is reflected back to the
rotating mirror, which in the meantime has rotated through a
certain small angle. From the angle of rotation of the beam,
Foucault determined the speed of light to be 298,000 km/s. In
1879, A. Michelson refined the measurement using this method to a
value of c~299,909 km/s, and then in 1929 he reached a value of
299,798 km/s.
In other experiments, the
measurement of the speed of light was gradually further refined
using laser technology, and also when measuring with a laser
reflector on the Moon. The current value is c=299,792.458
km/second for vacuum.
Note
: In 1983,
metrologists at the 17th Congress on Weights and Measures
decided that the speed of light will be defined as a natural
constant of the exact value c=299,792,458 m/s.
And the meter will therefore be derived from the speed of light
in a vacuum: 1 meter is equal to the length of
the path traveled by light in a vacuum in 1/299,792,458 seconds.
Therefore, further refinement of the measurement of the speed of
light will no longer affect the value of c, but the exact
value of the distance of 1 meter.
In material environments, the speed of light - and in
general electromagnetic waves c´= 1/Öe.m - is slightly lower
than in a vacuum c = 1/Öe0.m0 , depending on the electrical permittivity e and magnetic
permeability m of the substance (it is analyzed
in §1.1, part "Electromagnetic and optical
properties of substances"
monograph "Nuclear physics and ionizing radiation
physics") and depends somewhat on
the wavelength of light (so-called dispersion ). Eg in
water the speed of light for red light is (rounded) 226 000 km/s,
for violet 223 000 km/s. It is even slower in crystals and
glass. Of all natural materials, the highest
refractive index is diamond (n = 2.42), in which the
speed of light is only 123,881 km/s - this leads to significant
optical effects of refraction and reflection of light in crystals
of diamond, which results in its aesthetic popularity as a piece
of jewelry.
The speed of light in a vacuum
does not depend on the speed of movement of the source.
Measurements of Michelson and Morley in 1881 to 1904
(measuring the speed of light in the direction and against the
direction of the Earth's motion) even showed that the speed of
light in a vacuum does not depend on the state of motion of the
source or observer - it is the same in all inertial systems, no
matter how fast they move . This fact, expressed
in the principle of constant speed of light,
became the basis of the special theory of relativity
(§1.6 "Four-dimensional
spacetime and special theory of relativity") and thus of the whole relativistic
physics.
Note: The
specific numerical value of the speed of light c is by no
means exceptional, it is basically given by units
selected for length [m] and time [s]. In §1.6 and many other
places in our explanation of the theory of relativity and
gravity, we will often use a system of units in which the speed
of light is c = 1.
The theoretical result of
electrodynamics and the special theory of relativity, that the
velocity of photons in a vacuum is exactly equal to c ,
holds for a plane unlimited wavefront of electromagnetic
radiation. However, if the radiation beam is narrowed in the
transverse direction (the wavefront is spatially limited),
quantum uncertainty relations begin to apply, leading, among
other things, to fluctuations in the velocity of
photons in vacuum (these subtle differences
are difficult to measure) .
How fast is gravity ?
- or how long does it take for a
change in the gravity of one body to take effect on another
(distant) body? We can put it simply by the example of our Earth,
which is bound in its orbit by the gravitational force of the
Sun. If, hypothetically, the Sun suddenly ceased to act its
attraction ("the devil would steal it at once"), the
motion of the Earth would change from an ellipse to a straight
line heading into distant space. But how long after the removal
of the Sun would this happen? Immediately? -
as assumed by the classical Newtonian idea of instantaneous
action at a distance, according to which gravity propagates infinitely
fast. Or in about 8 minutes, which is about the time it
takes for the sun's rays to fly to us? Or for some other end
time?
From the point of view of the speculative example outlined, this
is certainly an insignificant question. However, the value of the
speed of gravity has a fundamental influence on
phenomena in outer space - in astrophysics and cosmology
*). If the gravitational force acted at any distance immediately,
the evolution of the universe would proceed completely
differently than if gravity affected all material bodies with a
delay given by its finite velocity. We will outline this question
first at the end of §1.2, part "Modification of Newton's law of
gravitation", but mainly
in §2.5 "Einstein's equations of the gravitational field" and in
§2.7 "Gravitational waves", where
in the passage "How fast is gravity?" will be briefly discussed as well as general
questions propagation velocity changes in the gravitational field
and the possibility of its experimental determination. We will
see that the "speed of gravity" is the same as the
"rate of electromagnetism", ie changes in the
gravitational field spreads speed of light, like
a stir in the electromagnetic field .
*) In addition, perhaps in the multidimensional
"gateway" theory of superstrings
(§B.6 "Unification of fundamental interactions.
Supergravity. Superstrings.",
passage "Another dimension, M-theory,
11-dimensional theory of superstrings"), where
the assumed gravitational action between the gates cannot be
instant ..?..
Classical Faraday,
Ampere and Maxwell electrodynamics is a macroscopic and phenomenological theory - it perfectly describes
the properties of electric and magnetic fields in vacuum and in
material environments, their temporal changes and mutual
transformations. However, it does not take into account the
details of the structure of matter, the nature of its own and
basic "carriers" of electric and magnetic forces. The
first "microscopic" theory of electromagnetism was
developed in 1895 by H.A.Lorentz, but a full understanding
of the relationship between electromagnetism and the structure of
matter was made possible by the development of atomic and nuclear physics - see below.
Great stimulus for the development of physics
during the 19th century was the technical problems arising during
the Industrial Revolution. This created fundamental discoveries
that gave physics the character of a comprehensive
science .
Some methodological issues of the construction of
physics and its incorporation into other natural sciences, as
well as in the context of scientific knowledge in general, are
discussed in §1.0 "Physics -
fundamental natural science" monograph "Nuclear
physics and physics of ionizing radiation".
Microstructure
of matter - atomic and nuclear physics
At the turn of the 19th and 20th centuries, research into
electrical phenomena opened the door to an understanding of one
of the most basic unresolved issues - the structure and
composition of matter. And in turn, the discovery of the
basic building blocks of matter has made it possible to better
understand the nature and origin of electric forces.
When chemists (especially J.Dalton)
revived the idea of atoms at the end of the 19th
century, practically nothing was known about the nature and
structure of the atoms themselves. Faraday's experiments with
electrolysis in 1836 suggested that chemical fusion had much in
common with electrical phenomena. In 1895, J.J.Thomson, during
experiments with gas discharges, discovered an elementary
particle carrying a negative charge - an electron
and proposed the first idea of the atom ("pudding
model"). E.Rutheford along with Geiger and Marsden in 1911
made an important experiment with scattering particles
alpha which led to the discovery of the atomic
nucleus and created the planetary model of the
atom. In 1913, N.Bohr supplemented the planetary model
with three quantum postulates; the resulting Bohr model
of the atom is still used with certain modifications.
Atomic and nuclear physics has shown
that the origin of electric and magnetic forces
lies in the basic elementary particles that make up matter - electrons
and protons, which are carriers of negative and
positive electric charges. It also explains all electrical and
magnetic properties of substances, including the cause of the
magnetic properties of permanent magnets. Atomic physics further
explains the mechanical and optical properties of substances and
especially chemical fusion - the essence of
chemical fusion is the electrical attractive forces
between atoms, which, when sufficiently close to each
other, share part of the envelope electrons in the valence shell.
The structure of atoms and atomic nuclei is
discussed in more detail in §1.1 "Atoms and atomic nuclei" of the monograph "Nuclear
physics and physics of ionizing radiation". Research in the field of radioactivity
has played a crucial role in elucidating the properties of atoms
and atomic nuclei (discovered in 1896 by H.Becguerel) and ionizing
radiation - see §1.2 "Radioactivity" and §1.6 "Ionizing radiation" in the same treatise.
By applying laboratory knowledge of
atomic and nuclear physics to phenomena occurring in space, nuclear
astrophysics was created, which clarifies the origin of
radiation in space, evolution of stars, release of energy by
thermonuclear reactions inside stars, formation of elements by
cosmological and stellar nucleosynthesis (§4.1
"The role of gravity in origin and evolution stars"), dramatic events of
supernova explosions (§4.2 "Final
stages of stellar evolution. Gravitational collapse").
Living
Nature - Biology
In parallel with physics, astronomy, chemistry and other sciences
of inanimate nature, it has been occurring since the 18th century
to significant discoveries in biology as well - the science of living
organisms. Earlier descriptive examination of external
manifestations and often random similarities was replaced by a
systematic examination of the structure, development, metabolism,
species classification and interrelationships of living
organisms. The basis of biology has become the science of the
structure and activity of the cell as the basic
building block of organisms (in more detail "Cells - the basic units of living organisms").
An important circumstance for a
correct understanding of life was the abandonment of so-called vitalism
- the assumption that complex "organic" substances are
created by the action of some specific "vital forces"
which are inherent only in living organisms (they are different
from the forces controlling inanimate nature). Careful
physicochemical research has shown with absolute certainty that
not a single atom in any living organism is any different
from that in an inanimate "inorganic" nature. Also all
complex "organic" molecules in organisms can be (at
least in principle) prepared by synthesis of inorganic
atoms hydrogen, carbon, oxygen, nitrogen, sulfur,
phosphorus and possibly next. What makes an organism alive is not
some mysterious "life-vital force", but an amazing
combination and interplay of the myriad chemical and biophysical
processes that take place in a living organism. This is mainly
due to the ability of carbon to form an
extraordinary variety of compounds. Carbon atoms can combine with
each other and with other atoms not only into simple molecules
(linear or cyclic), but also into chains that can have hundreds,
thousands to millions of links - to form macromolecules.
During the cessation of vital functions - the death of an
organism - none of its atoms are "lost", only the
coordination of the mentioned complex processes is lost; and many
complex "organic" molecules eventually decompose into
simpler ones.
Biological processes in cells and in
the whole organism are therefore based on chemical
reactions, especially of complex organic compounds of
carbon, hydrogen, oxygen, nitrogen, sulfur, phosphorus and other
elements. The structure of the cell nucleus and the role of
deoxiribonucleic acid (DNA) as a carrier of information in cells
were recognized, and the basic features of evolutionary theory
are developed. The processes in living organisms are so complex
that much remains unknown. Nevertheless, the application of
physical and chemical knowledge at the molecular and atomic
levels makes it possible to gradually understand increasingly
complex details and contexts in biology and to integrate this
science fully into the context of other natural sciences.
Theory of
relativity, quantum physics
The physics of the 17th and 18th centuries
tried to explain all phenomena using mechanical
models - movements
of either atoms and molecules (kinetic theory of heat,
hydrodynamics, thermodynamics) or elastic "ether" *) - the carrier of electromagnetic
phenomena. At the end of the 19th century, it seemed that almost
everything in physics was basically solved; all that remained was
the problem of the ether, the ambiguity surrounding the radiation
spectrum of the "absolutely black" heated body (leading to the so-called "ultraviolet
paradox") and
some properties of the photoelectric effect. Efforts to solve the
problem of radiation of an absolutely black body, together with
research in atomistics, led to the creation of quantum physics -
see, for example, the passage "Corpuscular
- wave dualism" in
§1.1"Atoms and nuclei" monograph "Nuclear
Physics, ionizing radiation". Problems ether became a springboard to create the
theory of relativity.
*) Problems ether is
briefly discussed at the end of §1.5 "Electromagnetic
field. Maxwell's equations. ".
As tmore detailed
experimental finding accumulated, mechanistic
models and concepts of classical physics in
general, encountered increasing difficulties. It is manifested
particularly when examiningthe microworld which
began in the late 19th century. When observing the motion of fast
electrons in electric and magnetic fields (which Lorentz dealt
with in particular), it was found that classical Newtonian
mechanics is no longer consistent with the experiment. Various
partial hypotheses were stated, until finally A.Einstein built a
new and more general mechanics, well describing even very fast particle motions , within his special theory of relativity. The special theory of
relativity (§1.6 "Four-Dimensional
Spacetime and Special Theory of Relativity ") is,
together with quantum mechanics, the most important and most
versatile interdisciplinary theory of
today's physics; it is also the "springboard" of the
general theory of relativity as the physics of gravity and
spacetime.
Note:
Discrepancies in experiments and progress in scientific knowledge
Experiments that deny the current well-established knowledge are
almost always erroneous - they are often the
result of measuring errors or hidden disturbing and distorting
influences. From time to time, however, they prove to be
right - and then they open the way to significant
progress in our understanding of nature! To generalize and
clarify previous laws, sometimes to set new horizons and
concepts.
A new concept of force
in physics
The central concept in classical physics is force,
which appears in the laws of motion as the cause of dynamic
changes; allows you to predict the movements of bodies. Force
works well as a quantity in the mathematical description of
natural processes, but the "physical" definition of the
nature of force is not easy (in classical physics it is
tautological - so we didn't really know what force is ...).
Modern physics has brought two views on the nature of force :
1. The general theory of relativity
explains the gravitational force as a geometric manifestation of
curved spacetime: Each body curves spacetime around itself, and
in this "deformed" spacetime, bodies move in geodetic
paths. This gives the impression of force. E.g. the planets orbit
the Sun not because it is acted upon by a "physical"
gravitational force, but because the Sun has curved spacetime in
its surroundings, and the orbit (circular or elliptical) is the
"straightest" orbit in this deformed spacetime.
2. Quantum field theory explains the interaction
of particles by the fact that these particles are constantly
exchanging virtual intermediate "field" particles. In
the electromagnetic interaction they are photons, for a strong
interaction the field particles are gluons, for weak
interactions they are intermediate bosons W+,W-, Z0.
It is hoped that this somewhat
"schizophrenic" view of the nature of force will unite
in the future in the unitary theory of all 4
interactions - "theory of everything".
The study of the laws of the
microworld has greatly enriched and deepened knowledge of the
structure of matter. However, the physics of the microworld has
yielded very little to elucidate the properties of space and
time, as well as to understand the nature of gravity. However, it
is hoped that this will change in the future. Quantum theory of
gravitation and especially unitary
field theory, after their successful completion, will
probably combine quantum physics,
electrodynamics, nuclear and particle physics with gravity, with
the theory of space and time (Chapter B
"Unitary field theory and quantum gravity").
A wide range of sizes of objects in our world, studied by various
fields of physics and natural science using various tools
(it is discussed in more detail in §1.0
"Physics - fundamental natural science",
passage "Methods and tools of
nature research", monograph
"Nuclear physics and ionizing radiation physics")
Electromagnetic
radiation - the basic source of information about the universe
Practically all information about bodies and processes in the
universe is still obtained through electromagnetic
radiation.
Originally it was visible light, now electromagnetic waves of
other lengths also approach it - radio waves, infrared,
ultraviolet, X and gamma radiation *).
*) It is good to realize, that the light emitted from stars and other objects
in the universe is several times transformed
by radiation
originating originally from nuclear and subnuclear processes with
much higher energies, corresponding primarily to radiation g. Recently, the "observation" of
the universe using other types of radiation - neutrinos - also
seems promising (see
"Neutrinos"), protons and other particles in cosmic
rays (see "Cosmic rays"), gravitational waves
(§2.7 "Gravitational
waves").
Although these new "non-optical
" observation "windows" into space will not
captivate us with beautiful color images of nebulae and galaxies (known from large classical astronomical telescopes), but they provide us with very important information
about structures and significant processes in
outer universe that are invisible in the optical field - see below "More 'windows' into the depths of space".
Astronomical
telescopes - cosmic "time machines"
Telescopes for observing distant cosmic objects must be much
"larger" than the telescopes used in everyday life here
on Earth ("theatrical peepholes",
binoculars, hunting binoculars). In order to achieve sufficient
magnification, they must have a long
focal length
and, in order to make very distant or dimly glowing objects
visible, they must also have a high
luminosity
- a large lens diameter. Today's astronomical telescopes
usually have a lens diameter of approx. 2 - 6 meters, their lens
is usually made of a precise parabolic
mirror with a
focal length of approx....-... m. These large terrestrial
telescopes have provided since the middle of the 19th century,
during many decades , the vast array of astronomical images and
measurements on which our current understanding of the structure
of the universe is essentially based.
Terrestrial and space telescopes
However, even the most technically advanced telescopes, located
here on the earth's surface, have two
limitations
when observing cosmic objects, reducing their performance :
1. Turbulence of the
atmosphere ; distracting light
A well-known visual experience when observing the night sky is
the "twinkle" of stars - a subtle, rapid twinkling of
star brightness. In reality, however, the stars shine absolutely
calmly and stably, with a short-term constant unchanging
brightness (we do not mean variable stars
here, which occurs over long time intervals). The observed subtle changes in their
brightness are caused by atmospheric
air turbulence, which constantly gently oscillates the
rays of starlight. Therefore, even the most perfect telescope,
placed on the earth's surface, can never produce a perfectly
sharp image.
Furthermore, the scattering of
sunlight or moonlight, light from the stars, as well as light
"smog" from artificial lighting, in the atmosphere
leads to the fact that it never gets completely dark. This
adversely reduces the contrast of telescope images - limiting
the ability to observe extremely faint objects.
2.
Absorption of radiation in the atmosphere
Atmospheric air is not completely
transparent
to light and other electromagnetic radiation, some of the light
is absorbed and scattered. The wavelengths of light visible to
our eyes represent only a small fraction of the range of
electromagnetic waves in nature and space. Electromagnetic
radiation of shorter or longer wavelengths than the visible
spectrum can carry important astronomical information, but much
of it fails to penetrate the
Earth's atmosphere.
Both of these disadvantages of
terrestrial telescopes are removed by their placement
in outer space, outside the Earth's atmosphere. These space telescopes are not bothered by clouds or mists, no
turbulence in the atmosphere, no disturbing "light
smog", sunlight (alternation of day
and night). The
light background of the sky here is
completely black,
so with a sufficiently long exposure, even the faintest or most
distant objects can be recognized in the image. And they are able
to measure and display all
wavelengths,
from radio waves, through infrared and visible radiation, UV,
X-rays and gamma rays. Even those wavelengths that relatively
penetrate the atmosphere (visible, radio) are sometimes advantageous to be
detected by space probes for accurate and sensitive measurements.
Among other things, this eliminates the disturbing effects of
radiation of natural and artificial origin. An example is the
measurement of the relict microwave cosmic background CMB, which
is so weak that terrestrial microwave telescopes hardly detect it
against the background of disturbing natural and artificial
signals, but space probes (WMAP, Planck) mapped it in detail - §5.4.
passage "Microwave relic radiation - a
unique messenger of news about the early universe".
Currently, there are mainly 3
space telescopes in operation :
- Above all, it is the legendary Hubble space telescope, launched in 1990, which
examines the universe primarily in the optical and ultraviolet
spectrum. In addition to a large amount of astrophysical data, he
also provided many beautiful
astrophotographs, which helped the general public to get a
better idea of the structure of universe.
- The Spitzer
Space Telescope, launched in 2003, explores space
primarily in the infrared range.
- The James
Web Space Telescope, launched in 2022, is also sensitive
primarily to the infrared part of the spectrum.
All astronomical telescopes show
us light that was emitted in the
past -
either nearby (seconds, minutes, hours -
for objects in our solar system), or more ancient, depending on the
distance of the observed object. The more distant the object, the
earlier its light started its journey to us. They are thus a probe into the past; with a bit of exaggeration, we
can consider them as a kind of "time
machines"
that virtually return us to the ancient past of the universe -
when observing very distant objects, it can be more than 13
billion years !
Electromagnetic radiation brings
from space information of two kinds (the
third type of information, so far potential, will be mentioned
below in the section "Polarization Measurement
"), according
to the methods of its detection and analysis
:
¨ Optical display
In visible light we see hot objects in space such as stars, hot
gases and objects reflecting light of primary sources or glowing
deexcitation of electron levels of atoms. By visual observation
and optical display, we can obtain information about the position of individual objects (with a given
resolution), their relative intensity (brightness,
clarity) and
possibly some details of their structure. Based on the change in position
over time, we can monitor the movements
of bodies and
determine them speed. However, this is only possible
with the nearest cosmic bodies - planets in the solar system.
Stars, nebulae, galaxies, and other features are so distant that
direct visual observation of changes in their positions over time
and their velocities is not possible (but
see Doppler spectrometry below).
Visual, photographic
and optoelectronic imaging
In earlier times, until the middle of the 19th century,
astronomers spent nights with their telescopes, in the eyepiece
of which they observed with their eyes. Later, by the middle of
the 20th century, photographic
plates and films were placed in the focal points of
astronomical telescopes, on which even very weak objects,
completely unobservable to the naked eye, were displayed after a
long exposure (sometimes even several hours) and development. Optoelectronic image sensors (most recently based on CCD
elements) are installed in the focal points of today's large
astronomical telescopes . The image is electronically recorded in
computer memory and displayed on the screen, computer image processing is often used .
Infrared astronomy
Observing the universe through infrared
radiation
(electromagnetic waves with wavelengths greater than 700nm but
shorter than about 1mm) is important for two reasons :
1. Most objects in space are
relatively cold and according to Planck's law it
shines dominantly (or even exclusively) in the infrared field of the
electromagnetic spectrum. These are, for example, protostars, red
and brown dwarfs, nebulae. The transitions between rotational and
vibrational energy levels of molecules in cold gases are often in
the infrared range of the spectrum, and infrared
spectrometry makes it possible to know the chemical
composition of gas clouds around stars, planets, nebulae, and
interstellar gas.
2. Due to cosmological expansion of the
universe all radiation from distant objects for
observers on Earth shifts to the long-wavelength part of the
spectrum. In the most distant objects, the original physically
emitted visible light and UV radiation of the primordial stars,
and even the X-rays of the quasars, shifst so far that they reach
the infrared region.
Infrared astronomy belongs to optical
astronomy
because it uses the same optical imaging components - mirrors,
lenses. Semiconductor diodes (most often based on HgCdTe) or
superconducting bolometers (Microcalorimetric
detectors ) are used as detectors of displayed IR
radiation. For areas from 1 to 4 micrometers, the atmosphere is
relatively permeable, so observations can be made from the
earth's surface. For longer wavelengths and submillimeter waves,
the permeability of the atmosphere is very low and observations
must be made from space probes.
Radio telescopic
imaging
Visible light forms only a very narrow window in the spectrum of
electromagnetic radiation, and in addition, clouds of
interstellar dust are opaque to visible light (light is scattered
and absorbed here). In this respect, radio
waves of
wavelengths of the order of millimeters to tens of centimeters
are more preferred. This radio radiation is abundantly generated
in the environment of flowing gases (with turbulence and shock
waves) by the mechanisms of braking and synchrotron
radiation, when
moving charged particles in a magnetic field at high speed along
curved paths. Due to the expansion of
the universe, the radiation of the most distant galaxies
and relic radiation from the period of separation of
radiation from matter is also shifted into the radio
submillimeter region of the spectrum (§5.4, passage
"Microwave relic radiation
- messenger of early space messages"
are discussed ). In the millimeter spectrum, we observe cold universe such as clouds of molecules and dust
clouds.
Radio radiation is very well measurable by focused
("parabolic") antennas - radio
telescopes.
The larger the diameter of the receiving antenna, the better the
angular resolution. To observe radiation of a wavelength of the
order of millimeters (which is much longer than that of visible
light), the parabolas for sensing this radio radiation must be
much larger than that of optical telescopes, min. 100 times
larger than optical telescope with comparable resolution.
However, increasing the size of antennas has its technical
limits. However, the method of radio
astronomical interferometry is very promising: the signal is received
simultaneously by two or more "coupled" antennas,
electronically connected in coincidence, distributed in different places
at a greater distance from each other. The resulting image is
obtained by electronic reconstruction of amplitudes and phases of
signals from different antennas. The resolution of such an
interferometric system is given by the spatial distance of the
receiving antennas *), not by the actual size of these antennas
(only the sensitivity of radiowave reception depends on
the size of the antennas). When placing antennas over long
distances (interferometry with a very
long base - the
planned placement of antennas on different continents or even in
space) a very good angular resolution can be achieved.
*) Angular resolution is given by the ratio
of the wavelength of the received radiation to
the length of the base - the larger the base,
the finer details of distant objects can be displayed.
¨ Spectral analysis
Electromagnetic waves carry not only optical information about
the position and "strength" of radiation sources. No
less important information is "encoded" in the
wavelength or frequency of electromagnetic waves - in its spectrum.
Spectral analysis of visible light is performed by its
distribution in an optical prism (light
dispersion - different refractive index for different
wavelengths, ie colors) or optical grating
(bending and interference of light waves according to different
wavelengths). In both cases, a spectrum is
obtained - graphic image, where the wavelength is on the
horizontal axis, the light intensity of individual wavelengths is
on the vertical axis or brightness scale. Spectral analysis of
radiation of wavelengths other than light is performed using
appropriate methods of detection and electronic processing of the
measured signal (for high-energy radiation, see "Detection and
spectrometry of ionizing radiation").
The term spectrum was
introduced in optics by I.Newton in the 17th century, when he
discovered that white sunlight is a mixture of many colors of the
rainbow. It is based on Lat. spectrum = image, revelation,
delusion - an image of something that is not physically
present.
Chemical spectrometry
Each atom of a given element and molecule of a particular
compound has very specific, fixed and characteristic energy levels of electrons, in the excitation
of which
electromagnetic radiation of a certain wavelength l (or a photon corresponding to the energy h.c /l) is absorbed and in the deexcitation of which the radiation of this certain
wavelength is again enitted (see "Radiation
of atoms"). By analyzing the spectral lines
"light" (emission spectrum) and "dark"
(absorption spectrum) it is possible to obtain reliable
information about the atoms of elements or molecules of compounds
that emit this radiation or that absorb it as it passes - chemical analysis of substances in outer space can be
performed .
Doppler spectrometry
Since the energies (wavelengths) of the spectral lines are fixed
and precisely known, in addition to detecting elements and
compounds, spectrometry also allows the analysis
of motion -
measuring the velocities of stars, galaxies and their parts. If
there are lines, resp. a series of lines, systematically shifted in the spectrum to the red or purple end
of the spectrum, this means that there act
Doppler effect *) - a change in wavelengths causes by the the
movement of the source relative to the observer. If the
source moves away from the observer, the wavelength lengthens
(redshift), as the source moves towards the observer, the
wavelength shortens (shifts towards the purple end of the
spectrum).
The situation is more complicated in the general theory
of relativity in the presence of gravity and curved
spacetime. This can also be a gravitational
redshift (see §2.4). In cosmology, we then encounter Hubble's
redshift of very distant objects (§5.1), which is the
result of the expansion of space itself (see
the discussion in §5.4, the passage "What
expands and does not expand during the expansion of the universe?
"). From an observational point of
view, however, both interpretations of the spectral shift are
essentially equivalent.
*) The Doppler effect is a
kinematic effect arising from the relative movement of a wave
source and an observer (wave detector). It generally applies to
all types of waves. If the wave source of a certain constant
frequency fo moves towards the observer
(receiver), this observer registers a higher frequency f
than the source actually emits. Conversely, when the source moves
away from the observer, the registered frequency is lower than
the actual one. The relative difference between the actual fo and the observed f
frequency (Doppler frequency shift) increases in proportion to
the velocity V of the source relative to the observer: f =
[1 + (V/v)] fo , where v is the propagation velocity of the
given wave; Df/fo = (f-fo)/f = V/v . The same applies to the wavelength l = v/f. By
measuring the frequency difference or
wavelengths of the primary transmitted wave and received wave, we
can determine the mutual speed of movement of
the source and the observer. For electromagnetic waves, of
course, v = c. And we know the actual (primary) frequency or
wavelength of the emitted spectral lines exactly from laboratory
measurements.
Note: This rule
also applies when the source of the received wave is the reflection
of the wave from a certain moving object (including a flowing gas
or liquid). It is used in radar technology and ultrasonic
sonography.
Accurate spectrometric analysis
can measure not only the speeds of translational motions, but
also the rotation, pulsation or turbulence of gases in stars and
galaxies; these events are manifested by a corresponding
broadening or doubling of the spectral lines as a result of the
Doppler effect.
Spectral analysis of radiation coming to us even
from the remotest
observed objects in the universe shows that there apparently
to apply the same laws of classical and quantum
mechanics, electrodynamics, atomistic, thermodynamic and gravity
as here on Earth. Although this cannot be
strictly proven, this entitles us to believe that the same laws
of physics apply even where we have not yet
"looked" - and perhaps even in places we will never be
able to see ..!..
¨ Polarization
measurement
An electromagnetic wave is a transverse wave in which the
electric field intensity vectors E and the
magnetic induction B oscillate perpendicular to
each other and perpendicular to the direction of propagation .
Both of these vectors lie in a plane perpendicular to the
direction of propagation and together with the Poynting
vector P (§1.5
"Electromagnetic field. Maxwell's equations.") form a clockwise system.
In addition to the intensity (amplitude of oscillations E
and B ), frequency (wavelength) and phase, the
electromagnetic wave is characterized by the direction in which
the vectors E and B oscillate
in a plane perpendicular to the direction of propagation (since
they are always perpendicular to each other, just consider one of
them, usually the intensity of the electric field E
is chosen). If the vectors E of individual waves
(rays, photons) always have a different, essentially random
direction in the plane perpendicular to the direction of
propagation, it is non-polarized radiation. In
the opposite case, when the vectors E have the
same direction in the imaginary plane, the vertically
intersecting beam of radiation, we speak of polarized
radiation. If the vector E still oscillates in
one constant line, it is called linear polarization. If
the ends of the vector E describe a circle, we
speak of circular polarization, if more generally they
describe an ellipse, it is elliptical polarization.
Only coherent radiation - waves
of the same frequency, the same direction of oscillation and the
same phase (or phase difference) shows complete (perfectly 100%)
polarization . Coherent radiation arises mainly during stimulated
emission in the laser. In most common sources of
radiation (sun, flame, light bulb), electromagnetic processes in
a large number of atoms and electrons take place in a disordered
manner, the electrical and magnetic components of the resulting
wave randomly change direction, the resulting radiation is non-polarized.
Partial, sometimes complete, polarization of light occurs during
the reflection and refraction of light in optical environments.
Faraday twisting of polarization of electromagnetic radiation
When passing through areas where there is a magnetic
field and free electrons - it is an ionized
plasma - there
are interactions of the electromagnetic wave with electrons,
which subsequently move in circular (spiral) paths due to the
magnetic Lorentz force. This process - interaction
+ re-emission - of an electromagnetic wave leads to partial twisting of the plane of its
polarization by the angle Dj :
Dj = l2 ò
ne B cosf ds ,
where l is the wavelength of the electromagnet.
wave, ne is the local density of free electrons in
the ionized medium, B is the intensity (induction) of
the magnetic field, f is the angle between the beam and
the direction of the magnetic field, s is the path of radiation in a
given environment. Integrates n over the entire path of s
electromagnetic waves in ionized environments.
Note: The name
"Faraday" in this phenomenon comes from the
fact, that M.Faraday was generally concerned with rotation in a
magnetic field, although electromagnetic waves were not yet known
at that time.
This phenomenon is used mainly in radio
astronomy,
where waves from distant radio sources pass through large space
regions containing a sparse ionized substance - plasma - in the interstellar or intergalactic magnetic field. For different
wavelengths, the twisting of the plane of polarization is
different, so from these differences it is possible to estimate
the magnetic field and the electron density in interstellar
space. In certain cases, this effect can also be used to
determine the distance of radio sources (if known values determined in another way are used for
electron density and magnetic field value) as
an additional method in the "ladder" of cosmic
distances (§4.1, passage "Determining distances of space objects
basic condition of astrophysics") .
Polarization of relic
microwave radiation
From an astronomical point of view, perspective may be the measurements polarization
of relic microwave radiation (the origin
and properties of the relic microwave cosmic background are
discussed in §5.4, passage "Microwave relic radiation - a messenger of
early space news"). Both electromagnetic and gravitational waves have the
property of polarization. In the early universe, at the end of the
radiation era, a special kind of polarization of relic radiation
(so-called mode B) could occur due to the action
of primordial gravitational waves generated during the inflationary expansion of the very early universe (§5.5 "Microphysics and cosmology.
Inflationary universe."). This future possibility of
measurement, discussed in §2.7, passage
"Measurement of polarization of relic microwave radiation" could reveal important information from the
earliest period of the universe.
Astronomical Telescopes - " time machine "
The universe is well transparent to
astronomically used radiation (at least at the present stage), so
we gradually gain a lot of informations about the distant
universe (paradoxically, we know more about it than about
the interior of our Earth). Thanks to the known
constant speed of light, astronomical telescopes can also be
considered as a "time machine"
(in the sense of cognition), with which we can observe events in
space even many billions of years ago (about
the possibilities of "traveling in time "see the link
"Journeys through time: fantasy or physical
reality? ").
Astronomical
observations and measurements in various fields electromagnetic
radiation (visible light,
infrared, ultraviolet, X-ray, gamma) also allowed to determine the distances of various objects in space using the interconnected methods of the "ladder" of cosmic
distances - see §4.1, passage "Determining the
distances of space objects - the basic condition of astrophysics".
Other "windows" into the
depths of universe
In addition to light and other bands of electromagnetic
radiation, other types of particles and radiation come to us from
space, which can (at least in principle, or
in the future) also
be used to study structures and processes in universe.
They can serve as new observation
"windows" into space, which are so
far slowly
"opening up", but they will certainly be very promising
in the future! There are three new "windows" and we
will only briefly list them here :
l Cosmic radiation
(primary)
is high-energy radiation of cosmic origin, which is formed
mostly by protons (88%),
followed by helium nuclei (10%) and other elements (1%); the
content of the various nuclei in cosmic rays roughly corresponds
to the representation of elements in the universe, as established
by primordial and stellar nucleosynthesis. From light particles
then fast electrons and neutrinos. High-energy photons of gamma
radiation are also part of cosmic radiation . The properties and detection of
cosmic radiation, the mechanisms of its origin, as well as its
effect on life, are discussed in detail in §1.6 "Ionizing radiation", part "Cosmic radiation" in monograph "Nuclear physics and physics of ionizing radiation".
From the point of view of astronomical use, cosmic
radiation has one major disadvantage :
electrically charged particles, which we capture, on their
long journey to Earth by magnetic fields within the galaxy and in
intergalactic space, have undergone very complex curved
orbits, which unfortunately loses directional
information about the source in which they formed. Only
at very high energies is the curvature of the trajectory small
and the particles at least approximately keep their direction. Cosmic radiation detection and
spectrometry could provide us with useful information
about processes in outer space, often the most
tumultuous processes in the extinction of stars by gravitational
collapse (supernova explosions) or the accretion of matter to a
black hole (in quasars). Methods of detection and spectrometry of cosmic radiation, including the possibilities of their
astronomical use, are discussed in the section "Detection and Spectrometry cosmic
rays" in §1.6 "Cosmic radiation".
l Neutrinos
are very small particles (the rest mass
close to zero), which have no electrical
charge and did not show a strong nuclear interactions, show only
weak interactions. This is so weak and short-range, that
neutrinos hardly interact with matter and fly
freely through it. Neutrinos in huge quantities
arise in a number of processes in space - from the "big
bang" lepton era, to thermonuclear reactions in stars, to
supernova explosions. Neutrine detection and spectrometry may be
important for the study of various processes here in space.
Neutrinos, due to their extreme penetration, are the only
particles that are able to "bring out"
information about nuclear and particle processes
from the interior of massive, large or compact
objects, from which no other radiation absolutely penetrates.
Detection of the flow of solar neutrinos makes it possible to
test the instantaneous intensity of thermonuclear
reactions inside the Sun (especially the proton-proton
cycle). Even the high density and thickness of plasma in the
solar interior do not prevent neutrinos from leaving the region
of their birth almost immediately and thus "bring out"
relevant information (unlike photons, which for
hundreds of thousands of years "penetrate" plasma, with
gradual energy degradation, from interior to surface before they
radiate; they can only carry information about the surface layers
of the Sun). Neutrinos also provide important information
about turbulent processes in outer space. These are
mainly supernova explosions in which a colossal
amount of neutrinos (electron ne) is emitted. Relic neutrinos,
originating from the lepton era, can provide important
information about the dynamics of the earliest stages of the
evolution of the universe and the formation of its structure.
The main
disadvantage of neutrinos is the very difficult detection.
The wider use of the possibilities provided
by neutrinos is thus linked to the improvement of
neutrino detection techniques. The properties of neutrinos and the
methods of their detection are discussed in detail in §1.2
"Radioactivity", part "Neutrinos - "ghosts" among the particles" of the book "Nuclear physics and physics of ionizing radiation ".
l Gravitational waves
they are a
time-varying (oscillating) gravitational field that detaches from
its source and propagates into space at the speed of light.
According to the general theory of relativity, this is a ripple in the curvature of spacetime. They arise generally in any physical system with a time-varying
mass distribution. The properties of gravitational
waves, their origin and detection possibilities are discussed in
detail in §2.7 "Gravitational
waves".
The most important permanent (periodic or
quasi-periodic) sources of gravitational waves
in the universe are massive bodies that orbit each other
(orbit around a common center of gravity). Powerfull sources of
gravitational waves can be systems of compact
gravitationally collapsed objects such as neutron stars
or black holes, orbiting close to each other.
Another intense source of gravitational waves can be the gravitational
collapse of a star, if it is asymmetrical. The
"collision" of two compact objects, the extinction and
fusion of their tight binary system, as well as the strongly
asymmetric gravitational collapse, is accompanied by a massive flash
of gravitational waves, which carry away a significant
part of the total rest mass.
Detection of
gravitational waves, measurement of their frequency and
intensity, together with the display
of the direction from which they come, will make it possible to detect
important dynamic processes with compact objects, often invisible
in other ways, including the most tumultuous processes of
gravitational collapse and collisions of neutron stars and black
holes. Perhaps also about the dynamics of
the earliest stages of the evolution of the universe, when the
universe was impermeable to all other forms of radiation, but the
"primordial" gravitational waves originating
from that period could be detected in principle (interesting possibility of indirect detection of
primordial gravitational waves is mentioned in §2.7, passage
"Measurement of relic microwave radiation
polarization").
Gravitational waves are the most difficult to
detect radiation. The possibilities of future gravitational-wave
astronomy
are discussed in §2.7, in the section "Astrophysical significance of
gravitational waves".
Natural laws, models and physical theories
Let us briefly consider some general gnoseological aspects of revealing natural laws,
creating their models and formulating physical theories. Some other aspects of this kind are discussed in §1.0
"Physics - Fundamental Natural Science" of the book "Nuclear Physics and the
Physics of Ionizing Radiation".
Order and laws in nature
In ancient times, when people did not know the causes and
interrelationships of phenomena and events in nature (or in human life), they looked at everything anthropomorphically and explained all events with the help of
the gods
or demons who
control all aspects of nature and life - the gods of the Sun,
fire, sea, war, storms, etc... These gods were, in their
opinion, unpredictable, people were given
to them at their grace and disfavor (they could
possibly be reconciled by sacrifices and rituals). However, during the long
process of knowledge development (which
began in ancient Greece, around 500 BC and was mainly attended by
Thales of Miletus, Anaximandros, Democritus, Pythagoras,
Aristarchus, Archimedes), was increasingly asserted the cognition, that nature is governed by certain
unchanging rules - natural laws that can be revealed. People
began to understand that nature (the universe) has its inner order, which can be understood through observation and thinking about these observations.
That the world is recognizable and can be understood without
reference to myths, religions, and unsubstantiated assumptions,
but on the basis of reliably established and carefully
categorized knowledge.
Natural
law is a
statement that describes a certain observed phenomenon or group
of phenomena and generalizes it to other analogous phenomena on
the basis of logical conclusions. At the same time, complex
phenomena in which we do not observe direct regularity can be
understood using simpler laws and principles - the so-called reductionism (cf. below). The individual laws of nature
form a larger, interconnected system
of laws;
this system should be logically
consistent. In
contemporary science, the laws of nature are mostly formulated mathematically. Under clearly defined
conditions, it must apply without
exception.
Under changed conditions, they may not lose their validity
completely, but may apply approximately
*).
*) An example is Newton's laws of mechanics, which apply with
high accuracy in normal conditions of everyday life, but lose
accuracy when objects move at high speeds, close to the speed of
light. Or Archimedes' law applies exactly to "ideal"
fluids (in which the pressure spreads evenly in all directions),
located in a homogeneous gravitational field; in viscous liquids
it applies only approximately, in mud it does not apply at all. And, of course, it is invalid (or
pointless) in a weightless state.
Regularities and
randomness in natural events
Everywhere
in the universe, matter behaves according to the same
laws of physics and chemistry. However, the specific
behavior, the course of events and their outcome, depend on
current conditions - these have also evolved
according to these exact laws, but often through a complex
combination of circumstances, that already have the character of chance.
The relationships between
the exact physical laws and the role of random circumstances are
analyzed in more detail in §3.3, section "Determinism
- chance - chaos ?". The
role of chance in the origin and evolution of life is discussed
in the work "Anthropic
principle and/or cosmic Good
", passage "Origin
and evolution of life".
Models and physical
theories
Descriptions of phenomena, relevant physical laws and
explanations (or attempts to explain them) of their nature and
connections with other phenomena are summarized in a broader
framework of the system of opinion, learning or system of thought
- physical theory. Each physical theory is based
on a certain basic idea or image of the studied phenomena - a model of natural reality, which captures the basic
features of the studied phenomena, but abstracts from some more
secondary, accidental or disturbing influences. Physical theory
is then actually a model + set of
laws (mostly mathematically formulated) that connect this model with the results
of observations or experiments.
The importance of
idealization and models for scientific knowledge
We create models not only in science, but also
subconsciously in everyday life, so that we can reflect and
understand the complex world around us. Even when seen,
our brain receives electro-chemical signals from the optic nerves
and creates a mental image in the appropriate
brain center - a model of reality. In
fundamental science, however, it is of fundamental gnoseological
importance :
l a) Initialy, conceptually (programmatically, but
judiciously - distinguishing which phenomena are of fundamental
importance and which are marginal), we neglect
those aspects of nature (studied phenomenon) that are difficult
to understand and describe accurately.
l b)
We will examine
the remaining simpler aspects in more detail, we will
successfully solve and understand - we will create a simplified
but functional model.
l c) After we fully understand the simpler aspects, we
return to the more complex ones and try to solve
them at an improved level of knowledge, using a more
complex model .
We consider the model or theory to be correct, resp.
adequate when it meets the following 4 criteria (the fifth
criterion will be added below) :
¨ 1. It is in line with existing
observations and explains their results.
¨ 2. Provides clear predictions of future
measurements and observations. The results of these measurements
can confirm or refute the model, depending on whether they agree
or disagree with the model's prediction.
¨ 3. It contains as few arbitrary
optional parameters as possible, the values of which do not
follow from the theory and must be artificially set so that the
model corresponds to the experimental results.
¨ 4. It is logically simple,
"elegant", naturally and credibly explains the nature
of phenomena.
Not always and for all phenomena
is doing well to create such an ideal model or theory.
The above criteria of a "good" model or theory are
largely met by classical mechanics and Newton's
theory of gravitation (within its limits),
relativistic
mechanics (in
inertial frames of reference) and electrodynamics (it is even universal). It is interesting,
that some difficulties with point 3 have such a successful theory as
the standard model of elementary
particles
(discussed in §1.5 "Elementary
Particles and Accelerators" of the book "Nuclear Physics and Physics of Ionizing Radiation"); it contains dozens of free parameters (masses, charges, spins and other characteristics of
various particles),
the values of which do not follow from the theory and must be set
on the basis of experimental data so that the model corresponds
to the results of measurements and observations.
The basis of scientific thinking
is unification : in the enormous diversity of
phenomena and events to seek general
laws and a common
essence, to try to explain the diversity of phenomena on the
basis of as few basic laws as possible. Thoughtful people have
always longed for a theory that would describe and understand all
the observed complexity and diversity of nature. The ultimate (monistic) ideal
is to explain all the laws of nature using a single universal principle - to create a definitive final
theory or a unified "theory of everything".
And it is physics,
which examines the most basic laws of nature, that has the main unifying
role among all the natural sciences. A
characteristic feature of the physical view of nature is
therefore the already mentioned reductionist approach and the
effort to uniformly understand the widest
possible class of phenomena - unitarization. In
this context, we can supplement the above-mentioned 4 criteria of
adequate theory with the fifth criterion :
¨ 5. The theory should describe and
explain the widest possible class of natural phenomena on a
uniform basis.
These aspects
are discussed in more detail in §B.1 "The Process of
Unification in Physics".
Duplicity and duality
of models and theories
As models and theories gradually evolve and
improve during our knowledge of natural laws, a number of models
and theories of various phenomena and groups of phenomena have
been formulated. It happens that two different theories describe
the same phenomenon well. How to decide which one is right, or at
least "better"? Here are two examples :
l The
motion of celestial bodies - the planetary system.
Around 150, Ptolemy created a geocentric model (system)
of the distribution and motion of celestial bodies. According to
him, the Earth is spherical, motionless and lies in the center of
the universe. Stars and the planets around it at great distances
orbit evenly in circular orbits. Discrepancy between
predicted perfectly uniform motion and the observed
irregularities in the motion of the planets with changes in their
brightness (indicating changes in the distance between the Earth
and planets) resolved by hypothesis that the actual movements of
the planets are formed by folding two or more uniform circular
motion (called deferent, epicycle and ekvant). Ptolemy thus
reached a relatively good agreement with astronomical
observations, but at the cost of considerable complexity and
artificiality. The geocentric system with the motionless Earth
looked quite natural, for in ordinary life we do not feel the
Earth moving beneath our feet (no one realized then that the same
thing was happening on a ship floating evenly on the calm surface
of a lake).
In 1543, M.Koperník developed an alternative heliocentric
model according to which the immobile center of the universe is
the Sun and the planets orbit it in (approximately) circular
orbits. The earth is one of the planets that revolves
around its axis with the diurnal period, giving the impression
that all cosmic bodies, stars and planets, orbit it. The
observed movements of the Sun and the planets are thus explained
much more easily and naturally; this in itself is preferred by
the heliocentric system. Most importantly,
however, the orbit of the planets around the Sun has been
explained precisely using Newton's law of general gravity +
the laws of classical mechanics, from which Keppler's
laws of planetary orbiting follow. Thus, it can be said that
Ptolemy's geocentric system is erroneous and the heliocentric
system *) corresponds to reality - but with the clarification
that the Sun is the center only of our planetary solar system,
not the universe.
*) At present, it is sometimes believed
that the geocentric and heliocentric models are equivalent, that
it is not possible to decide which one is more adequate. We can't
agree with that! Although the introduction of other
"epicycles to epicycles" can be achieved in such a
precision that the geocentric system will satisfy even the last
accurate observations. Or, from the point of view of the
principle of relativity, we can equally use reference systems
connected to the Sun or the Earth to describe the universe, ie
from the point of view of the standing Sun or the standing Earth.
Here, however, we come into conflict with the above-mentioned
criteria 3 and 4.adequate
model. The refinement of the geocentric model is associated with
the growing complexity and need to introduce other optional
parameters, lacking credibility and explanation of the nature of
such behavior. From a purely kinematic point of view, the
Earth-related frame of reference can be used (unfortunately we
have to do so in astronomical observations from Earth, with the
introduction of complex corrections), but when analyzing the
motion of planets, their equations are much simpler in the frame
of reference as a motionless beginning. Above all, however, the
heliocentric system is supported and justified by the dynamics of
gravitational and centrifugal forces in the orbit of the planets
around the Sun - a mechanism that explains the causes
of this motion very well. In short, "such is the
truth" !
l Theory
of light.
Using Newton's older corpuscular theory (light is made
up of tiny moving particles), the rectilinear propagation of
light in "rays" and, in essence, the refraction of
light as it passes from one optical medium to another can be well
explained. However, it cannot explain the bending of light and
interference phenomena (characteristic light and dark stripes or
Newton's rings). Therefore, a newer wave theory of light
was created, which can naturally explain all the phenomena of
propagation, refraction, diffraction and interference of light.
In addition, it unites optics with electrodynamics: light is an electromagnetic
wave of very short wavelength. The wave theory of light has
been confirmed, and it would seem that the corpuscular theory is
incorrect.
However, in the early 20th century. Einstein showed thatthe
photoelectric effect can only be explained by the fact that
a quantum of light - as a particle - hits the surface of
a metal or an atom and emits an electron from it. Thus, light
behaves both as a wave and as a particle. Each of the two
theories can describe and explain some properties of light, and
neither can be said to be "better" or "more
realistic" than the other. This apparent gnoseological
contradiction was only explained in the corpuscular-wave
dualism of quantum physics, which also manifests itself in
electrons and other particles (see the passage "Particle-wave
dualism" in §1.1 of the book "Nuclear
Physics and Physics of Ionizing Radiation").
Here, the situation is completely different from that of the
geocentric and heliocentric systems. Both theories proved equally
correct and were unified in the spirit of
criterion 5 .
Based on the above criteria 1. - 5. it is
therefore possible, in
principle, to decide which of the duplicate model is
"better" and more adequate; and
under what conditions.
Accurate and effective laws of nature; reductionism
The goal of science is to constantly seek a full
understanding of reality and perfect predictions,
especially through accurate mathematical models
of the real world (in the spirit of classical Newtonian
mechanics). However, this theoretical "ideal"
encounters enormous diversity and complexity in
practice natural phenomena. At the level of the microworld, the stochastic
character of quantum regularities, corpuscular-wave
dualism, quantum uncertainty relations contribuce to
this. Therefore, in practice we usually have to resign
ourselves to absolute accuracy and in our knowledge of reality
and the ability to predict to admit more or less uncertainty...
Each body is composed of atoms, so
the exact theory describing its behavior and motion should
include movements and interactions of all individual atoms.
According to this concept, if we wanted to analyze, for example,
the motion of a thrown stone, we would have to solve all the
equations describing the gravitational action between each atom
of the stone and each atom of the Earth, with a huge number of
parameters. This is, of course, completely impossible. The mechanics
proceed differently: the stone is modeled using an idealized mass
point - center of gravity, of mass M equal to the sum of the
masses of all stone atoms and analyzes the interaction of this
mass point with the total gravitational field of the Earth,
described by gravitational acceleration g. This is incomparably
simpler - one equation with two parameters (in
this case actually only one parameter g, because due to the
universality of the gravitational action the motion does not
depend on the mass M), while we obtain the result
(path of the thrown stone) with absolutely sufficient accuracy
for the problem.
A theory that adequately models
certain phenomena without describing in detail all the processes
that participate in and lead to these phenomena is called effective
theory. Sometimes the name phenomenological theory
is used.
The whole of classical mechanics
with the concept of a material point is based on "effective
laws". The study of mechanical processes at the molecular
level has led to statistical mechanics and
thermodynamics. It is assumed here that the individual particles
move according to the exact laws of Newtonian mechanics, but in
practice their use for larger systems would be extremely complex
and impossible. Therefore, at the turn of the 19th and 20th
centuries, statistical methods were introduced, where
the positions and velocities of individual particles were
replaced by statistical averages (assuming that the probabilities
of all microstates are the same). The analytical methods used in
Newtonian mechanics have thus been replaced by probability-based
methods of statistical physics; it has proved very
successful especially in the field of gas behavior and
thermodynamics (kinetic heat theory).
Effective theories are also the science of elasticity and
strength, hydrodynamics, electrodynamics and
optics of the material environment. In all these fields of
physics, we deal with collective ones movements of atoms and
molecules and their collective electrical interactions, without
analyzing all the details of the behavior of individual atoms.
Also, much of astrophysics, which examines planetary motions, the
evolution of stars and galaxies, including relativistic
astrophysics. Here, however, there is an interesting circumstance
that in the physics of black holes the approximate
effective theory passes into exact theory (§4.5 "Theorem "black
hole has no hair" ").
An important effective theory is chemistry.
The essence of chemical reactions is physical - the sharing of
electrons of the atomic shell at close proximity of atoms and, as
a result, the formation of an attractive electric force, binding
atoms to each other, into molecules (more
details "Interaction of
atoms -
Chemical merging"). In the simplest cases, physical chemistry can
analyze the bonds of atoms into simple molecules in detail and
described them mathematically. But can not solve the equations
describing the interaction of complex atoms and molecules.
Chemistry but developed their efficient methods that
adequately describe how atoms and molecules behave in mutual
reactions and express them using chemical formulas and equations,
without having to consider all the details of electromagnetic
interactions between atoms.
In modern
biology - molecular biology- it turns out that
all events in living organisms are based on very complicated
physical and especially chemical (biochemical) reactions between
complex molecules in cells. If we wanted to describe these life
processes precisely analytically, we would have to know the
physical state of many trillion-trillion molecules in the
organism and solve a huge number of equations of their
interactions. The behavior of living organisms is the result of
such complex processes with such a huge number of parameters that
it is completely impossible to describe them exactly physically.
However, biology has its effective methods of examining
life processes at the subcellular, cellular, and whole organism
levels, without having to consider all the details of the
reactions between individual atoms and molecules.
The gnoseological process, which
tries to explain more complex phenomena by means of simpler
phenomena, is called reductionism. It is a basic
thought platform for advanced research in areas of more complex
phenomena, especially biological ones. Biological processes are
explained by chemical reactions and chemical reactions by
physical interactions of atoms. The basic laws of physics at the
classical and macroscopic level are deterministic
(from the point of view of quantum physics
it is more complicated). The behavior of
living organisms is also internally governed by the laws of
physics, but overall it is the result of such complex processes
with such a huge number of parameters that it is practically
impossible to predict (in a deterministic sense). We are
basically "biological machines" and what we call
"free will" is a mere illusion ?
Questions of determinism versus randomness
are discussed in more detail at the end of §3.3, section "Determinism
- chance - chaos?".
From the point of view of the accuracy of
the laws of nature we know, we can ask the question: What happens
when we take the laws of nature that work perfectly in the
laboratory conditions and the surrounding nature available to us
and extrapolate them to the most extreme situations? Will there
be any minor deviations, or even gross disagreement? These
questions examine experiments with particles accelerated to high
energies and astronomical observations of turbulent events in
space.
The uniqueness and
origin of the laws of physics
In the gnoseological analysis of our knowledge of natural
processes, at least three questions about the laws of physics
arise :
1. Do the same physical laws apply
throughout the Universe, now, in the past and in the future?
2. Is there
only one set of possible physical laws?
3. What is the origin of the laws
of physics?
Ad 1: Spectrometric analysis of radiation coming from the
farthest reaches of the universe shows that natural processes
taking place here on Earth and throughout the observation of the
available universe are governed by the same universal
laws of physics, gravity, electrodynamics, atomistics,
nuclear physics, thermodynamics, plasma physics, etc. We usually
assume that the laws of physics are the same over time, but
we have no direct evidence for this. In the earliest stages of
the evolution of the universe, the individual interactions may
have been separated from the basic unified interaction, for which
the hitherto unknown laws applied. Sometimes a slow change
of physical constants with time is also considered , eg
gravitational constants (see eg §A2 "Brans-Dicke's
theory of gravitation"), which has also not been proven so far...
Ad 2: More
complex is the second question, which can be metaphorically (or
theologically) formulated: "Did God have the freedom to make
natural laws when creating the world? - or did he necessarily
have to make them as they are?". From the point of view of
classical physics, it seemed that there could be only one
logically consistent set of laws of physics. However, according
to quantum physics and unitary field theories applied to
cosmology, the universe does not have only one possible history,
but there may be many different universes with different
physical laws and values of natural constants (discussed in more detail in §5.5 "Microphysics
and Cosmology. Inflationary Universe." , §5.7 "Anthropic principle and
existence of multiple universes"
and §B6 "Unification of fundamental interactions.
Supergravity. Superstrings. ').
Ad 3: The origin of physical laws
traditionally refers to the transcendent, to God
who is the creator. This is perhaps the case with the most
fundamental laws or starting points on which unitary field
theories are based. The specific physical laws
describing the phenomena around us, however, they are probably
the product of turbulent events at the beginning of the
universe, when the fundamental fields, particles and
properties of interactions between them were formed. And in
different universes it may be different (§5.5
"Microphysics and cosmology. Inflationary
universe.")...
Existence of
objective reality
Classical science is based on the so-called
objective realism: the assumption that there is a real "external" world whose
properties are given and objective - independent of the observer
who examines it. That all objects exist
independently of us and have certain given physical
properties, such as speed, mass, electrical action (charge). And
these properties will have the same objects, whether someone
observes them or not.
This fully corresponds to our
experience with all phenomena in the macroworld, described by the laws of
classical physics. A more complex situation occurs in the field
of the microworld - atoms and elementary
particles. Here the process of "observation",
respectively measurement, necessarily interferes with the
behavior of microparticles and changes their parameters. The
measurement is necessarily of a nature mutual
interactions of the measured particle with the
"test" particles. Thus, we cannot claim that the
microparticles had a certain position and velocity until the
parameters are measured. The measured quantity has acquired the
appropriate value only at the moment of measurement - and
as a result of the measurement process. However, one cannot agree
with opinions that overestimate the role of the "subjective
observer" and question the objective reality as such!
Natural processes with innumerable interactions of particles and
fields are constantly taking place in nature and their results
are independent of us. Only our occasional probes into
the events of the microworld are burdened by fundamental quantum
uncertainties. However, this is not a consequence of our
subjective intervention as an observer, but the influence of
interaction with objectively existing particles used for
observation or measurement. Quantum physics
does not deny objective reality, it just points out some of its unusual
and difficult to understand properties.
In connection with
this, it is sometimes discussed what actually means "to exist"?
Whether we can say that there are things we do not see, such as
atoms, electrons, protons, quarks. However, these particles,
which we cannot "optically" see, are an adequate
model, which explains many of the observed properties of
matter - in fact, all known properties. In everyday life, for
example, glowing dots forming an image on a television screen
(vacuum tube - cathode ray tube): we do not see individual
electrons directly, but they are "visible" by
interaction with phosphor molecules on the screen screen. Other
subatomic microparticles can also be indirectly observed,
registered or detected by modern physics, often using very
complex experimental techniques ("Detection
and spectrometry of radiation",
"Elementary particles and
accelerators"). Therefore, we rightly "believe" that these
microparticles exist - or that they are at least
a very useful adequate model...
The discussion
of "existence" sometimes gets caught up in vain
philosophizing. E.g. under normal circumstances, that there is a
desk in the room: how do we know that the desk still exists when
we leave the room and do not see it? We can go back and see him
in the same place. But what if the table disappeared (or someone
disassembled it, fell apart) when we left the room and reappeared
(folded) in the same place when we returned to the room? That
would certainly be an absurd (though in principle possible) idea
that disagrees with experience (for example with the testimony of
someone who remained permanently in the room)...
This
vain philosophizing sometimes goes even further and degenerates
into agnosticism, nihilism and subjective
idealism: There is nothing but our minds and our
thoughts, the external world is not real and objective, but only
to usit seems. This is a popular topic of
"café philosophers", beer drinkers, or
"alternatives" of various orientations. From the point
of view of Eastern philosophy, it is reflected in the treatise
"Anthropic Principle or Cosmic
God", part "Is
the world objective or subjective?". Although we cannot
exactly prove the existence of objective reality, in our lives,
practical actions and cognitions, including scientific research, objective
reality is the only possible platform !
Space
and time
Along with the development of knowledge of specific laws of
nature, the most basic physical concepts - space and time
- developed. We all
live in space and time, so we have a certain intuitive idea of what space and time are. However, we do
not have a general and precise definition of space and time,
because we lack some "higher" superior and more general
concept by which to express it. Such a "triviality" as
space and time, which we encounter constantly and within which we
live, escapes us even in a deeper analysis...
For people in antiquity and the Middle Ages, the whole
space - the whole world, the universe - was a small district of
our Earth, which could be overlooked from the nearest hill or
bypassed in a few days. Later, thanks to sea voyages, this
limited horizon expanded and the reality of the round Earth, on
the surface of which we live, became apparent. The idea of a
solar system and a vast universe inhabited by stars and galaxies
was only brought about by modern astronomy. The details of the
spatial arrangement of the interior of matter were then shown
only by contemporary atomic and nuclear physics.
And they used to perceive time cyclically
as a periodically recurring alternation of day and night
and a sequence of seasons - in a circle of ever-recurring life
cycles. This idea had natural-agrarian roots, it was derived from
four basic periods - after winter comes the time when plants
sprout and new animals are born, in summer there is a harvest.
People had the idea that this cycle, the cause of which they did
not know (they knew nothing about the rotation of the globe and
its orbit around the Sun, or the rotation of the Moon around the
Earth), is the natural and fundamental nature of the world and
the properties of time. And they considered various supernatural
beings and deities, residing in trees, water, mountains, stones,
the Sun, the Moon, and so on, to be the "driving force"
of all natural events. These deities "enlivened" the
world..
How do we humans perceive space and time ?
We obtain basic information about the surrounding world through
our senses. We perceive sound by hearing, light
by sight, temperature of objects by touch, fumes of some
substances by smell. But do we have a sense or a receptor
for the mental perception of the passage of time
(chronesthesia )? Neurophysiology shows that we
do not have a direct "time sense",
but the brain can create it additionally or virtually.
The tool is memory - a more or less stable
record in the structure of neurons in the brain. Using our
senses, the brain registers various events as perceptions
which it processes and sequentially writes them to the various
layers of the neural network. By this sequential
"addressing" of event records in neural networks, their
chronological order is encoded in the
brain. The sequence and continuity of these
records of registered events we then understand
and experience as time . The brain constantly
compares events registered by the senses as well as neural
records of past events and sorts them in terms of space and time.
Psychological arrow of time ("psychic
feeling for the passage of time"),
according to which human memory in a way reflects the part of
events that is called the past, is clearly different in
our psyche from the future. The human mind currently perceives
the present. The past, as unique and unrepeatable, is stored in
memory and can form certain ideas and expectations about the
future based on its past experience. Time is therefore a thought
structure, which we rank consecutively
one after the other the individual events and experiences.
This mental
experience of time is very subjective, time runs
"differently fast" depending on a number of external
and internal circumstances in our brain. The apparent "acceleration"
or "slowing down" of time depends on the
"density of experiences" (It
seems to us that during an interesting activity, time passes
quickly, while during a boring waiting, time drags on
endlessly...). Clocks seldom measure the
same time that flows inside us... We can imagine our perception
of time as the number of biological events taking place in our
body with a given frequency - the "biological clock".
Time is encoded in all living things. The perception of time by
organisms is often influenced by biorhythms in cells
that have evolved during evolution - the "biological
arrow of time" (circadian
clocks - the rhythm of alternating light and darkness - have
evolved in the simplest organisms). The
"arrow of time" relentlessly shows that all organisms
age and eventually die, the opposite is never the case (cf. "Time Travel: Fantasy or Physical Reality? ").
Classical physics objectively
conceives time basically like a river that from somewhere to
somewhere flows - at the time it is in principle from infinity to
infinity (yet here we do not consider the
cosmological constraints). For us humans,
however, is time some " mental dimension
" reflecting that, how we perceive the world in our brain
This is a kind of psychological arrow of time.
Further analysis is in §5.6, section "
Arrow of time".
When we determine time using the
hands of a clock, we do not actually measure time, but the
distance they traveled on the dial during their regular
movement... In later chapters of this book we will see that in
space time does not have to run everywhere fast, it can be
affected by gravity or speed, depends on the frame of reference
and the geometry of spacetime. There is no single universal
"now" (certain present), it depends on where the
observer is and how he is moving. Time is a "flexible"
quantity similar to space.
We perceive space -
spatial relations - primarily through the visual
imaging of light, mostly light reflected from material
bodies. The light image projected by the lens of our eye on the
retina is transmitted through the optical nerves as a series of
electrochemical signals to the brain center, where it is written
into the neural network. Based on this information, we create an
image of reality in the brain, including the spatial arrangement
of objects, in our consciousness. Visual perception of space is
based on the properties of electromagnetic wave propagation
(optical wavelengths) - rectilinear propagation of waves in
vacuum, air or other optically homogeneous medium, reflection of
light from bodies and refraction of light during transition to an
environment with different speed of light propagation.
In addition to optical perception,
we often supplement our spatial information with touch
(which is essentially the electromagnetic
interaction of the electron shells of the atoms of the object
under study and the atoms of the nerves of our touch) : "by touching" we get an idea of the size,
shape and spatial arrangement of bodies. This mental idea and
experience of space is established in early childhood (even
higher animals have it) and allows for orientation and targeted
movement in nature. In the actual observation, a comparison with
earlier images is subconsciously used, we have the ability to
guess, for example, the presumed missing part of the image or to
insert our knowledge "haw it should be" into the
observation. However, when observing phenomena with which we have
no experience (such as some light phenomena in the atmosphere),
optical illusions can occur ...
The material
world, which we perceive with our senses, has three
dimensions- we distinguish between width, length and
depth. We can go up - down, left or right, forward - backward;
and also combine these directions.
Space and
time in nature
In physics and other natural sciences, space and time are the
basis for the description of all phenomena. We try to explain
these phenomena by some mechanisms that work in spacetime.
However, we never see space and time itself, we rather deduce
their existence from our everyday experience. Ancient Greeks thinkers
have already tried to solve questions about the nature of space,
time, and matter through philosophical speculation. In his "Metaphysics", Aristotle
expressed the view that
matter still existed in infinite space (since the infinite past),
with "God" (the first mover) merely putting motion and
a planned order into its originally chaotic state - natural laws. Later, prevailed faith in
the creation of the world, and philosophy discussed the question
of whether space and time already existed before the act of
creation, or were created together with matter. Some philosophers
have argued that without matter, space and time could not exist (eg Aurelius Augustinius, 354-430n.l.). Others have argued that
"the existence of matter is not necessary at all for the
existence of space and time, just as the existence of the Sun is
not necessary for the existence of time, although by its motion
we usually measure time" (J.Locke,
1690).
Does space and time exist ?
It must be realized that space and time are mere abstractions used to express the state and movements
of matter. No space or time physically
- "tangibly" - exists. They are just tools that make it easier for us to navigate the world, nature, in space. The impression of time
and space is created by the distribution
and movement of matter - the shape, distribution and movement of
ordinary bodies, interactions of atoms and particles, different
values of intensities and potentials of physical fields and their
changes (including, where appropriate, a
state of rest and immutability in a certain frame of reference). In the whole universe there is
nothing "physical" but matter that moves or changes -
no time, no space; these are just the quantities we use to
describe it... Time does not exist
independently, it is always part of some movement. And space is
an expression of the positional relations of material bodies.
Let's compare the "Operationalist concept of
space and time" below.
During the long development of
natural science, space and time became the most important physical
concepts and basic physical units were
established for them. In ancient times, these units were based on
an anthropocentric concept (eg inches and
feet for length). Later, when people began
to recognize that they live on the spherical Earth, the units of
length began to be derived from the dimensions of the Earth
(the unit 1 "meter" was created). And time was
generally derived from the alternation of day and night (unit 1
day, 1 hour), from the observed phases of the Moon (1 month) and
the alternation of seasons (1 year). That is, from the rotation
of the Earth and its orbit around the Sun.
The close connection of movement
with time led to the stabilization of the phrase "passing
of time" for events when something changes, grows
old, becomes the past. This does not mean that the physical
quantity time "flows" physically, but that the given
event can be described by a certain time interval in
which it takes place, flows. It is somewhat similar to the usual
verbal formulation that "a river flows
through a certain valley or landscape":
what is meant is that water flows through the
given river bed (under the influence of
gravity gradient).
Of course, we use these used
formulations about the passage of time and the geometry
of space in many places in our treatise, but we mean their
real physical content (primarily in
classical physics and STR - including the relativity of reference
systems). The situation is more complicated
when considering the general theory of relativity, which
equates gravity with curved spacetime. According to GTR, the
gravitational field also has energy (§2.8
"Specific Properties of Gravitational Energy"), so curved spacetime takes
on a material physical nature. In some geometric unitary
field theories, spacetime is even
considered to be the basic physical "tangible"
entity from which all particles and all matter are
composed ("condensed") (chapter B. "Unitary
Field Theory", "Geometrodynamics") - matter is created from the emptiness... From
an epistemological and philosophical point of view it can be
difficult to cope with..!..
Absolute space and time
It seemed
self-evident to the ancient Greeks, that there is a state
of absolute calm, acquired by every body that is not
subject to the effects of external forces. This led to the
concept of "absolute
space", in which
it is possible be determine whether
at different points in time the events take place in the same location (point) of space, and the idea of "absolute
time".
Galilei and Newton, in principle of relativity and the
law of inertia, the concept of absolute space partially
rid of physical soil underfoot, because there is no way by
which it is possible absolute calm or motion measure mechanically. Nevertheless, even Newton recognized the absolute space
as seen from his work "Philosophiae naturalis principia
mathematica" from 1678, in which he writes: "Absolute
space, by its nature and without relation to anything external,
always remains the same and immovable".
Newton's three-dimensional absolute space
is the environment of our everyday experience. We look or move
from left to right, from east to west, from north to south, from
top to bottom, each of us, whether we move through our
environment in different ways and speeds, we perceive space in
exactly the same way. We all agree on the basic aspects of
space both intuitively and when performing
accurate measurements.
However, the concept of absolute time has remained fully preserved, ie the possibility
to absolutely determining the present of events even when
these events take place in different places in space. Absolute time
featured on Newton's laws of mechanics, flowed equally for
arbitrary moving bodies, and its value could be
determined absolutely from the "moment of creation of the world".
"Absolute or mathematical time
flows evenly on its own, without any relation to anything
external.", Newton wrote in his "Principies". So, absolute time passes just as fast
everywhere in the universe and independently of things and events
- so the whole universe would have a single identical
"cosmic" time. This universal absolute time, to which
everything is subject, cannot be influenced, accelerated or
slowed down. Creation, transformation, and extinction of all
things (including living things), all phenomena and events, are
part of this continuous stream of "cosmic time". Time
is often compared to the one-way flow of the river, where
backward movement is not possible. This idea persisted from
antiquity, through the Middle Ages until the beginning of the
20th century.
Newton's absolute
time is an expression of our daily experience with the direction
of phenomena and events. It flows relentlessly forward *) as we
age and see many things disappear, our loved ones die, other
things arise again or be born. It is a time, whose flow is
perceived equally by all people, it governs the movements of the
planets, the rotation of the Earth and the resulting alternation
of day and night, as well as the apparent movements of the stars.
*) The direction of time is discussed from
a physical and cosmological point of view in §5.6, section
"Time arrow".
Space and time used in classical mechanics have the following four basic properties :
Newton's idea of the structure of space and time was fully in line with experience and was not in doubt until the end of the 19th century. At that time, Faraday-Maxwell's electrodynamics showed that electromagnetic waves propagate at a speed of c = 300000 km/s; immediately, however, the question arose: speed relative to what? The introduction of the ether as an environment in which electromagnetic waves propagate has actually replaced absolute space here (see also the note on the ether at the end of §1.5). The famous interference experiments of Michelson and Morley between 1881 and 1887 showed that no ether existed and that light propagates at a constant speed regardless of the state of motion of the source or observer, contrary to the most basic mechanical concepts. Discrepancies between the ideas of classical mechanics and electrodynamics solved A.Einstein (1879- 1955) his special theory of relativity (STR), in which space and time are no longer absolute, but are part of a more general spacetime - §1.6 "Four-dimensional spacetime and the special theory of relativity".
However, to understand
the relationship between space and time on the one hand and matter on the other, STR has brought very
little. Spacetime continued to be a kind of "stage" on
which the motion of matter takes place, but its properties are
not affected in any way by the behavior of matter. Properties a), c) and d) have been preserved in the
special theory of relativity. In his general
theory of relativity completed in 1916, Einstein revises all the basic
properties of space and time (see chapter 2 "General
theory of relativity - physics of gravity"): spacetime not only does not have to be
Euclidean or infinite (it is Riemannian and can be closed), but
its geometric properties are directly determined by the
distribution and motion of matter. There may be a different
course of time in different places in space, the geometry of
space can change over time. At the same time, the general
theory of relativity marked a fundamental change in views on the
nature of gravity - gravity becomes a
manifestation of the curvature of
space-time.
In conceiving the general theory of
relativity, Mach's views on the cosmic origin of inertial forces
had a significant (mostly positive) influence on Einstein (see
Appendix A).
According to the theory of
relativity, space and time are relative and
depends on weight and speed. Different moving matter can
"create" different space and time - space and time are
the result of certain physical processes. And the very reason for
introducing the concepts of space and time
is to be able to assess the motion of matter -
the motion of particles and changes in fields.
An deep revision of the concepts of space and
time in Einstein's special and general theory of relativity
stemmed from a careful analysis of the measurement process in physics. The definitions of
the terms space and time and their properties must follow from
the knowledge gained by physical measurements. If space and time
are attributed to properties that do not inevitably result from
physical measurements, we easily find ourselves on the path (astray) of
metaphysics. Mathematical theory, which seeks to claim physical
content, must be based on basic concepts that reflect natural reality. For a long time, the terms
"space", "time", "matter" have been claimed by philosophy (sometimes we still meet it
today). However, the history of scientific knowledge shows that
philosophy can ask important fundamental questions, but it is not
able to answer them reliably and definitively. With the help of
various philosophical speculations, it is possible to reach
completely contradictory conclusions and theses. Only fundamental
natural sciences (especially physics) that dialectically combine
speculative and experimental cognitive methods, theory and
practice, can help find a realistic answer to basic
philosophical questions such as the nature of space, time and
matter, and perhaps to the problems of the relationship between
being and consciousness or matter and "spirit". And the
study of gravity has significantly contributed (and continues to
contribute) to this knowledge.
Twoo
concept of space and time
To summarize, from a general scientific and
philosophical-gnoseological point of view, the categories of
space and time can be conceived in two ways
:
Exact
(ideal) measurement of space and time
For accurate measurement of physical quantities, it is necessary
to use such methods, aids and devices that are sensitive enough
to the measured quantity and are not affected by
other influences and circumstances of measurement. If this is not
the case, at least an accurate correction for
these disturbances and distortions must be possible .
Idealized clocks and measuring rods are
introduced for measuring space and time in fundamental physics,
especially in the theory of relativity :
Ideal clocks
are those calibrated clocks whose speed (frequency of the
periodic events used) is not affected by any non-universal
influences such as temperature or forces
acting. Thus, a pendulum or hourglass clock would be completely
unusable here (whose running speed is directly determined by
gravity, it stops in a weightless state); similarly, other
mechanical clocks could be affected by mechanical deformations of
their components. Electronic oscillators and atomic
clocks are considered to be the most suitable in this
respect.
Ideal measuring rods
are length-calibrated scales whose length is not affected by any non-universal
influences such as temperature or forces acting. Ideal
measuring rods should therefore be made of a non-thermally
expandable material, sufficiently strong and rigid.
If the influence of non-universal factors
cannot be avoided, a correction must be made for
these non-universal influences. In practice, "clocks"
and "rods" are usually not used directly to measure
times and lengths, but more complex methods using electromagnetic
radiation - optical and radar
methods.
With the deepening and
refinement of scientific knowledge and their extension into the
microworld and mega-world, the concept of absolute space and time
came into conflict with the results of observations and
experiments. On the contrary, the operationalist conception of
relative space and time made it possible to understand and
mathematically describe even such phenomena that would be
incomprehensible to our classical experience. In §4.3-4.9 and
§5.2-5.7 we will see that especially in extreme situations
around black holes or the beginnings of the universe, where all
our usual ideas and methods of measuring space and time fail, the
operationalist approach allows us to use new and unusual methods
of measuring space and time, proportionate to the conditions; it
is probably the only way to reflect on these exotic phenomena.
In a dynamically evolving and
ever-changing universe, only "flexible" space and time,
whose properties derive from ongoing events, can adequately
capture the structure and evolution of the universe on a global
scale and in the scale of locally ongoing processes. Material
bodies - in general every distribution
of fields, matter, energy - in their surroundings co-create
(complete) the properties of the
space in
which they move (§2.5 "Einstein's
equations of the gravitational field").
The
beginning and end of time?
Abstract, mathematical or absolute time has an eternal infinite duration from - ¥ to
+ ¥. In the physical, operationalist
conception, however, time has a finite
duration.
In §5.4 "Standard Cosmological Model. The Big Bang" we will see that the
beginning of the universe in the Big
Bang is also
the beginning of time. And in §5.6 "The
Future of the Universe. The Arrow of Time" it will be shown that the
future evolution of the universe will lead to the actual end of time - either in great
collapse or in
the thermal death of the universe...
In addition to this "global" end of time, a situation
where the "local" end of time occurs - only for certain
observers or worldlines. In §3.4
"Schwarzschild geometry" and in §4.9 it will be shown that an
observer who passes through the event horizon of a black hole, in the final interval of his own time he arrives at a singularity, which
represents a kind of "local
end of time".
Quantum
"atoms" of space and time?
In general, space and time are considered a smooth
continuum.
However, in §B.4 "Quantum Geometrodynamics" it will be shown, that the
quantum approach to gravity and spacetime leads to the idea of quantum fluctuations in spacetime . This effectively creates the
smallest, elementary, spatial cells with a Planck
length ~10-33 cm and the smallest meaningful time
intervals with a Planck time ~10-43 sec. From a quantum point of
view, the classic notion of a smooth flow of time is thus
replaced by the notion of jumping discrete mini-intervals, so a bit reminiscent
of the falling grains of sand in an hourglass. Only on larger
space-time scales do chaotically bouncing time micro-intervals
fold into a continuous one-way flow of time and the spatial
"foamy" microstructure is smoothed into a continuous
space with a certain metric.
Cf. also the discussion "Is
the world continuous or discrete at the deepest level?" in §1.1 "Atoms and atomic nuclei " of the monograph "Nuclear physics and physics of ionizing
radiation".
We live in
the curved spacetime of the evolving universe
By creating a general theory of relativity (GTR) and experimentally confirming
its basic predictions (especially the deflection of light rays in
the gravitational field of the Sun measured in 1919 by an
expedition to observe a solar eclipse), people were confronted with reality that they live in curved spacetime. Practical importance of general
relativity, however, long after its creation has not been fully
appreciated, because it was thought that the gravitational fields
in nature can never be strong enough to significantly exhibited
specific relativistic effects and deviations from Newtonian
theory. Far greater interest was aroused by quantum physics,
which celebrated immediate success in elucidating the laws of the
microworld and the structure of matter.
The first success of the general
theory of relativity came in the 1920s in cosmology (Chapter 5 "Relativistic
Cosmology"). A.Fridman found that Einstein's
gravitational equations allow a solution describing a spatially
homogeneous and closed universe that expands over time, which
fully agreed with E.Hubble's discovery that the wavelength of
light from distant galaxies is systematically shifted to red the
more the galaxy is farther away.
The first indication that compact
bodies with strong gravitational fields may exist in space
appeared in the 1930s. At that time, Chandrasekhar and Landau proved
using Newton's theory of gravitation that the stars must be a
certain maximum weight is to be at the end of their development
achievable some state of equilibrium. Oppenheimer and Snyder then
shortly (in 1939) used the previously found Schwarzschild's exact
solution of Einstein's equations and came to the conclusion that
a sufficiently massive object would collapse indefinitely under
the influence of its own gravity. However, these conclusions did
not arouse wider interest at the time.
At the turn of the 1950s and
1960s, significant astronomical
discoveries
became a powerful stimulus for the
development of the general theory of relativity and interest in it. Above all, it was
the discovery of pulsars (see §4.2 "Final stages of stellar
evolution. Gravitational collapse") and
mainly quasars (see §4.8 "Astrophysical significance of
black holes"), for which large concentrations
of matter and strong gravitational fields could be expected.
Furthermore, Fridman cosmological models were decisively supported by the discovery of microwave radiation of the thermal spectrum corresponding to a temperature
of 2.7 °K, was interpreted as a remnant of a very hot and dense
phase of the evolution of the universee -
relic radiation. At this time, a likewise relatively well
developed astrophysics of stars evolution, which showed that in the final
phase of its development may star undergo gravitational
collapse,
that for sufficiently massive stars can be fully relativistic.
This should create extraordinarily strange compact
objects
called collapsers or black holes.
Thus, in the 1960s and 1970s, an important discipline of the
general theory of relativity and relativistic astrophysics
developed - the physics of black holes (Chapter 4 "Black
Holes").
The development of electronics,
measuring and experimental techniques has made it possible to re -establish the contact of the general theory of relativity with experiments and astronomical observations at a much
more accurate level. In 1960, Pound and Rebek accurately measured
the gravitational redshift using the Mösbauer effect (see §2.4 "Physical Laws in Curved Spacetime", passage "Gravitational Frequency Shift").
Accurate measurements of subtle relativistic effects on the
motion of planets and artificial satelits
in the solar system are being performed or planned. With the help of sensitive experimental
and electronic methods, the Ëtvös experiment, proving the
equivalence of inertia and gravity, was repeated again and with
high accuracy. Another interesting area of gravitational physics
is the study of the properties of gravitational
waves and attempts to experimentally confirm them (§2.7
"Gravitational waves"). In many places in this book, the relevant
theoretical concepts and findings are supplemented by a brief
description of their experimental verification. A brief
systematic overview of experiments in the field of the theory of
relativity and gravity is in §2.10 "Experimental
verification of the theory of relativity and gravity", where there are references to the relevant
passages in the individual chapters in which the experiments are
discussed.
The path of knowing gravity is extremely interesting. It turns out to be the key to understanding the properties of space, time, matter and its motion, the key to the secret of the construction of the universe.
| Gravity, black holes and space-time physics : | ||
| Gravity in physics | General theory of relativity | Geometry and topology |
| Black holes | Relativistic cosmology | Unitary field theory |
| Anthropic principle or cosmic God | ||
| Nuclear physics and physics of ionizing radiation | ||
| AstroNuclPhysics ® Nuclear Physics - Astrophysics - Cosmology - Philosophy | ||
