Where the universe is heading - the arrow of time

AstroNuclPhysics Nuclear Physics - Astrophysics - Cosmology - Philosophy Gravity, black holes and physics

Chapter 5
GRAVITATION AND THE GLOBAL STRUCTURE OF THE UNIVERSE: RELATIVISTIC COSMOLOGY
5.1. Basic principles and principles of cosmology
5.2. Einstein's and deSitter's universe. Cosmological constant.
5.3. Friedman's dynamic models of the universe
5.4. Standard cosmological model. Big Bang. Forming the structure of the universe.
5.5. Microphysics and cosmology. Inflationary universe.
5.6. The future of the universe. Dark matter. Dark energy.
5.7. Anthropic principle and existence of multiple universes
5.8. Cosmology and physics

5.6. The future of the universe. Time arrow. Dark matter. Dark energy.

An equally interesting and fundamental problem, such as the origin and early stages of the evolution of the universe, is the question of where the evolution of the universe is headed in the future ? What will happen to matter in space? If we omit improbable models such as the stationary or oscillating universe, according to the standard cosmological model, the further fate of the universe depends on whether the average h of the cosmic mass r is less or greater than the critical density r crit (5.26 ) :

Fig.5.9.
Schematic representation of the most important stages of the evolution of the universe.
For an illustrative comparison of the closed and open space evolution scenario, see below
5.2.2 a), b)

The evolution of the universe for both cases is schematically shown in Fig. 5.9, where the most important stages of evolution are also marked . If the actual density of matter does not differ enormously from the critical one, the evolution of the universe proceeds for a very long time roughly the same for the closed and open variant; only in the late stages of the dynamics of expansion and progress of astrophysical processes for both cases will vary podstan - upper part obr.5.9 ( n zorn comparing scenarios of evolution of the closed and open space below to obr.5.2' a), b) ) .

The end of time?
In 5.4, the passage " The beginning of time? ", We discussed the issues of causal relationships at the beginning of the evolution of the universe according to the standard cosmological model. We have come to the conclusion that, from the point of view of the general theory of relativity, initial singularity was not only the beginning of the universe, but also the beginning of time . What about the passage of time and causal relationships in the final stages of the evolution of the universe?
In the case of a closed universe, the situation is to some extent inversely analogous to the beginning of the universe. All causal relationships end in the vicinity of the final singularity (they cannot be extended analytically beyond this world point) - the great collapse also represents the end of time .
In the case of the open universe, from a mathematical point of view, the coordinate time continues undisturbed to infinity . However, from the real point of view of the operationalist conception of time (see 1.1, passage " Space and time "), in the final stages of open space, where there will be no more phenomena and events ("thermal death"), we have no time to measure (and in fact is not "what" to measure). In this sense, even in the open universe , the end of time effectively occurs .

The arrow of time
Before we continue to discuss the various variants of the future development of the universe, it will be useful to think about what actually distinguishes between the past and the future - what determines the
direction of time , or as it is called " arrow of time " for short . This asymmetry of time - the "arrows" that point from the past to the future - plays a crucial role in our daily experience.
All basic laws of physics have the property of
time reversibility : if these laws allow a certain causal sequence of events, then they also allow a sequence of time-reversed events. The laws of mechanics allow the reversal of every movement of a body. Similarly, the laws of electrodynamics do not distinguish between the future and the past (Maxwell's equations themselves are satisfied both by solutions in the form of usual retarded potentials and formally by "advanced" potentials - see 1.5) . In short, the laws of physics are at their deepest level symmetric in time . If we remain purely at the level of mathematically formulated laws of physics, we will find no difference between the past and the future.
   Nevertheless, we observe a strong causal direction in all the actual events in nature - natural events always take place in one particular direction, while in the opposite direction never (at least never spontaneously: the glass can roll spontaneously from the table and break, but never break the broken shards spontaneously in the original glass ...) . The observed mechanisms of this temporal direction of natural phenomena (in other words, specific "arrows of time") can be divided into four categories :

The question naturally arises as to whether all these manifestations of time are somehow connected to each other; or whether there is a "primary" or "universal" arrow of time, which is manifested by said "partial" arrows of time. So let's look at the possibilities of merging or reducing at least some of them.
   The psychological and thermodynamic arrows of time seem to be essentially the same : the psychological arrow of time is a consequence of the thermodynamic arrow, or mental processes share an arrow of time determined by thermodynamics. If we imagine (simply but concisely) the brain as a physico-chemical system of neurons performing logical operations and recording sensory sensations in memory, all these operations are irreversible for thermodynamic reasons. It is necessary to expend energy to arrange the memory elements in the brain into a certain state, while a part of it is always dissipated in the form of heat and thus increases the disorder of the whole system. According to the laws of thermodynamics, this increase in disorder is always higher than the increase in order in memory. The direction of time in which our memory records data thus agrees with the direction in which disorder grows - with the direction of entropy growth. It can even be said that the disorder (entropy) increases with time, actually because we conceive and measure time in the direction of increasing entropy.
   Finding a direct connection between the radiation (electrodynamic) and thermodynamic arrows of time is not easy. The electromagnetic arrow is in a way a manifestation of the principle (or requirement) of causality in the Minkowski spacetime of (locally) inertial systems, within which Maxwell's electrodynamics works (see 1.6 and 3.2). The thermodynamic (entropic) arrow of time is determined by the laws of statistical mechanics applied to a situation where the initial conditions imply a significantly larger number of disordered than ordered states. The laws of mechanics itself reflect, among other things, causal relationships. The idea that " field equations also determine the regularities of the motion of their resources" can also help to find connections (see 2.5); perhaps it will be ideologically possible to combine all of this comprehensively in future unitary field theory .
   As for the cosmological arrow of time, which points in the same direction as thermodynamics, it is probably just a coincidence : we live by coincidence in a stage of expanding space. , so the arrow of time is now identical with the expansion of the universe.If the universe is closed and the expansion is replaced by contraction in the future, nothing will change on the arrow of time in locally inertial systems (as well as on local laws of physics in general), but agreement with the arrow of universe evolution will turn into contradiction *).
*) Some experts (including temporarily S.Hawking) once thought that the cosmological arrow of time is the primary and that as the evolution of the universe transitions from the stage of expansion to the state of contraction, the direction of the passage of time is also reversed . Now, however, they have mostly seen the erroneous view of this view and accepted the position of Zeldovich and Novikov on the irrelevance of the cosmological arrow of time.

The arrow of time and the anthropic principle
The agreement of the thermodynamic, cosmological and psychological arrows of time can be put into a certain connection with the anthropic principle (its weak variant is enough) - cf. 5.7 and the work "
Anthropic principle or cosmic God ". We necessarily live in the "intermediate" stage of the expandingof space. In the late stages of the evolution of the universe, the conditions for the existence of life and intelligent information processing will not be suitable - there will be no one to study the connection between the expansion or contraction of the universe and the time direction in which entropy grows. In accordance with the concept of inflation expansion and the anthropic principle, the universe expands almost exactly at a critical speed, so that the shrinkage phase does not occur either at all or only after a very long time. In the meantime, all the stars will go out, the galaxies will collapse and no more free energy sources will be available. The universe will enter a state of almost maximum disorder, which will no longer increase locally - the thermodynamic arrow of time will actually disappear (cf. the above-mentioned passage " The end of time ?"). Thus, life and all orderly processing of information will disappear ....

We can therefore conclude that the common essence of all "partial" arrows of time is the principle of causality for each locally inertial frame of reference. In analyzing the various possibilities of the evolution of the universe, we are therefore entitled to proceed from the concept that there is a clear universal "arrow of time" determining the direction of evolution of physical systems in each locally inertial frame of reference. These local arrows of time are transmitted from one place to another by means of special- and general-relativistic transformational laws (1.6 and 2.4) and create a branching causal structure in the spacetime of the entire universe.
Note: Some geometrical-topological aspects of the direction of the passage of time are also discussed in 3.3, passage "Closed worldlines and time travel "and in 4.4, the passage" Black holes - bridges to other universes? Time machines? ".

The future development of the universe. Hidden-dark matter.
Let us now continue to discuss the individual eventualities of the future development of the universe. It is very difficult to decide which of the two basic branches of evolution according to Fig. 5.9 is realized in the real universe. The accuracy of measuring the deceleration parameter q is still insufficient and when determining the average density
r of matter in space, the problem of hidden matter (dark, non-radiant substances) is encountered . If we take only the "luminous" mass contained in galaxies and in clusters of galaxies, r is 10 -32 g / c m 3 , which is more than an order of magnitude smaller than r crit ( @ 5.10 -30 g / cm3 at H 50 km / s.Mpc) and would indicate an open space. However, it is likely that the "luminous" substance by far not the only matter in the universe :
Hidden-dark matter in galaxies and clusters of galaxies

When monitoring
the dynamics of the rotation of galaxies shows that real (gravitational) mass galaxies appear about one order larger than that from luminosity astronomically determined mass; according to today's observations, the galactic halo is much larger in size than previously thought and probably contains a larger portion of the total mass of galaxies. Even greater disproportion arises in galaxy clusters where the relevant difference is almost two orders of magnitude - so that at the observed relative velocities of the individual galaxies, the system-cluster of galaxies can be stably gravitationally bound.
   This is evidenced by the analysis of the motion of glowing very sparse gas around galaxies. If the mass of the galaxy were concentrated only in the visible region, the orbital velocity of the surrounding glowing gas would be inversely proportional to the square root of the distance from the center of the galaxy (according to Kepler's law). In a simplified spherically symmetric model, at a distance r from the center of the galaxy, the orbital velocity of a substance will be given by the relation v 2 = GM (r) / r, where M (r) is the mass contained in a sphere of radius r . For a constant density of matter r (r) = r then inside will be at 2  = (4/3) pr G.r 2 (orbital velocity will increase in direct proportion to the distance r ), while outside the galaxy the dependence in 2 = GM / r will apply , where M is the total mass of the galaxy. Outside the galaxy, according to Newton's laws, the orbital velocity of matter (gases) should decrease with the square root of the distance (dotted curve in Fig . 5.10) .

Fig.5.10.
Typical rotation curve - dependence of the orbital velocity of matter on the distance from the center of the galaxy.
Instead of the expected decreasing orbital velocity with distance in the halo galaxy, an almost constant rotational velocity is observed, indicative of a distributed gravitational hidden mass.

In reality, however, it is observed that up to a distance of several radii of the visible part of the galaxy, the gas orbital velocity remains roughly constant (solid curve in Fig. 5.10, which is "flat") , so that in this non-radiative region the mass density appears to be approximately the same as in the luminous areas of the galaxy. It can be said that stars in galaxies and galaxies in galaxy clusters and generally move so fast that centrifugal force and inertia would have long ago had to scatter them into space if they were not held by the gravity of some unknown hidden mass . This fact was pointed out in 1934 by F. Zwicky, who at the observatories in Mt. Wilson and Mt. Palomar observed faster movement by spectrometry galaxies at the edge of a cluster of galaxies and stars in the peripheral parts of galaxies than would correspond to the law of gravity at astronomically determined masses of "luminous" matter.
Because this problem is closely related to the virial theorem (1.2, passage " Distribution of kinetic and potential energy. Virial theorem ") known from classical mechanics (according to which the sum of potential energy and twice the kinetic energy of a stationary system of bodies is zero), it is said sometimes also about the " virial paradox ".
   In order to explain this paradox, it was necessary to assume that in galaxies a much stronger gravitational field acts than corresponds to the classical mass of electrons, nucleons, atoms, ions that form stars (with planets) and interstellar gas. There must be a large amount of some hidden and non-radiant dark matter that has gravitational effects. The measured rotational curves of ordinary galaxies show a content of at least 70 % of dark matter (up to 90% in dwarf galaxies) . Measurements of motions in large systems of galaxy clusters show that hidden matter is not only contained in galaxies, but is distributed throughout the universe (with different local densities).
  
This hidden mass should be composed of particles that are affected only by gravitational and weak interactions (the effect of which would be negligible due to the low effective cross section and short-range), but they are not affected by strong and electromagnetic interactions or electromagnets. the interaction does not manifest observationally. Hidden matter would be affected - and would affect the surrounding universe - only gravitationally (see below) .
   In short, galaxies rotate too fast to hold together visible gravity in stars and interstellar gas. So there should be a kind of hidden gravitational "glue" that holds galaxies and clusters of galaxies together so that the stars do not fly away from the rotating galaxies into the surrounding universe. Without this hidden matter, galaxies and galaxy systems would be unstable and would not hold together.
   In addition to observing the motion of stars and gas in galaxies and the motion of galaxies in galactic clusters, there are others indications of the presence of dark matter :
In addition to stars and cold interstellar gas, there are also very hot gas in galaxies , which is ionized and shines mainly in the X-ray field. Due to the high temperature of the gas, the speed of chaotic movement of electrons and atoms-ions of hydrogen and helium is quite high, exceeding the escape velocity (about 500km / s) needed to leave the gravitational influence of the galaxy. Such hot gas would dissipate in a short time and escape from the galaxy. The presence of this hot gas indicates a much stronger gravitational field than corresponds to the classical mass of stars and interstellar gas.
The gravitational field of galaxies and clusters of galaxies curves the light that passes around them - leading to an effectgravitational lenses (4.3, section " Gravitational lenses ") . From how the gravitational field of a galaxy or cluster of galaxies affects the light from more distant galaxies beyond it by the effect of a gravitational lens, the mass of that galaxy or cluster of galaxies can be determined. The masses here also come out much larger than the classical luminous mass and interstellar gas.
Cosmological evolution of the early universe according to the standard model (5.4, part " Standard cosmological model ")
:
> The course of primordial nucleosynthesis in the first about 3 minutes depended on the proportion of baryon and non-baryon matter (5.4, part "Initial nucleosynthesis ")- with greater representation nonbaryonick substances simply arise less helium. The observed amounts of primordial helium4He (25%), deuterium and3He suggests significant presence nebaryonic substances (see. Also below note the primary nucleosynthesis in the passage" From what is dark matter? "); otherwise helium would be more ...
> The formation of galaxies and galaxy clusters
in the era of matter was significantly influenced by the composition of matter in the universe
(5.4, section" Forming the large-scale structure of the universe ", section" Structure and evolution of galaxies "). "). If this substance were composed only of protons, electrons and atoms of hydrogen and helium, intense radiation (from the not too long time of the radiation era) would prevent and prevent the formation of galactic structures for a long time - the universe would remain homogeneous , smooth, without large-scale structures. The presence of dark matter , which does not directly interact with radiation , soon allowed gravitational contractions to "win" over the destructive effects of radiation. The observed faster (earlier) formation of galactic structures requires for its explanation additional (only gravitationally interacting) matter - dark matterthan would correspond to the dynamics of known matter during the expansion of the universe. This is perhaps the most important cosmological clue for hidden matter - it enabled, among other things, the formation of our Galaxy, in which the solar system, planet Earth, the evolution of life and our existence ...? ..
Note:
Some doubts about the concept of dark matter and alternative explanations are discussed. below in the passage "
Doubts of Nebaryonic Dark Matter - An Alternative Explanation? ".

Transparency and large-scale dominance of dark matter
Dark matter should be about 10 times more in galaxies and galaxy clusters than luminous (or radiation-absorbing) matter - it is dominant on a large spatial scale . The name "dark matter" could lead to the misconception that this substance will absorb light much like the dark clouds of interstellar dust. Nothing like this is observed, "dark" or rather " hidden " matter is perfectly transparent to light and other electromagnetic radiation . It does not emit, absorb or reflect electromagnetic radiation, it shows only a universal gravitational interaction and probably also a weak interaction (see below). If so,, it cannot "settle" in large numbers near the stars, its accretion is negligible. It can collect and gravitate only in huge clusters of matter such as galaxies and clusters of galaxies. It can be said that dark matter can be a kind of "backbone" or "skeleton" on which ordinary luminous matter is "wrapped".
   In addition to its gravitational influence on the motion of glowing astronomical objects (stars, galaxies), dark matter manifests itself in an attractive gravitational influence on the propagation of light - the effects of a gravitational lens
(4.3, section " Gravitational lenses ") . For the curvature of electromagnetic rays, it does not matter whether the gravitational substance is glowing or dark. In this way "gravitational lensing"(even hypothetical "dark galaxies") .

What is dark matter made of ?
The question naturally arises,
what is this hidden dark matter made of? In particular, they could be the usual forms of matter such as ionized intergalactic gas, molecular clouds, "infrared" or "brown" dwarfs similar to Jupiter (stars so light that they did not ignite thermonuclear reactions) , burnt-out stars of the 1st generation, after which left black dwarfs, neutron stars and the like. They could also be numerous smaller black holes of stellar origin (most of the degenerate matter hidden in these black holes has a baryon origin) . This component is called baryon dark matter and is not fundamentally very different from the commonly known substance composed of atoms.(more than 99.9% by weight here is made up of baryons - protons and neutrons in the nuclei of atoms) .
   Black holes of small and medium masses could generally be ideal candidates for dark matter, as they do not emit light and, due to their very small dimensions, practically do not absorb light from an astronomical point of view. An interesting hypothesis is the black holes of primordial origin , which could have formed in large numbers from the hot, extremely dense plasma that filled the universe immediately after the Big Bang. Microscopic quantum fluctuations   they increase to a macroscopic scale during inflationary expansion - regions with significantly lower and higher densities of matter and energy have emerged, from which all structures in the universe later emerged. In the very early stages of the universe, soon after the inflation period, a large amount of significant condensation could be present, which could quickly collapse into black holes. This would create a large number of primordial black holes of various weights. These primordial black holes can be considered of non- baronic origin .
   However, most
astrophysicists are inclined to believe that most of the (hidden) matter in the universe is contained in so-called " nebaryonic " matter *) such as neutrinos or some "exotic" structures formed from quarks, hypothetical gravitins, axions, s-neutrinos (also called neutralin), and the like. These exotic nature nebaryonov particles are collectively called WIMP ( W eakly I nteracting M assive P Articles - weakly interacting material particles) - see 1.5 " Elementary particles " passage " Hypothetical Model and particles " in the book " Nuclear Physics, ionizing radiation " .
*)
One of the clues for this view is based on a detailed analysis of the cosmological theory of primary nucleosynthesis, according to which the density of baryons in nucleosynthesis had to be about one order of magnitude lower than critical in order to explain the observed relative abundance of light elements (especially helium and deuterium). The observed representation of 4 He and D ( 2 H) indicates the amount of baryon mass W b 0.05 - compare with the footnote in 5.4, passage" Lepton era - Initial nucleosynthesis " . Therefore, all known atoms together (especially their nuclei composed of baryons) are not enough to explain the hidden substance, its gravitational action. If all non-luminous matter were baryon, there would be much more helium in the universe.
   First candidates for the composition of dark matter is naturally offered neutrino . If neutrinos had a non-zero rest mass greater than about 5 eV / c 2 , their total gravity could even lead to a closed universe. The rest mass of neutrinos was first measured in 1982, but then very inaccurately. Newer measurements of the mass of neutrinos (mentioned, for example, in the section " Neutrinos between particles " of the monograph " Nuclear physics and physics of ionizing radiation ") indicate the rest mass of neutrinos m o n < 2    eV. This question remains open, astrophysicists mostly doubt the substantial presence of neutrinos in the hidden matter of the universe, estimating it at a maximum of only about 1-2%. Although neutrinos are large in the universe (along with photons, they are the most abundant particles) , their rest mass is too small to explain the observed large amount of gravitational dark matter. In addition, due to the low rest mass, the neutrinos move at high speeds: such a mass of light fast particles would be too " hot "." *), so it could not form the observed gravitationally bound structures and would not explain the observed hierarchy of galaxies - the cluster of galaxies. than escape velocities from galaxies - the neutrino would soon disperse and escape from the galaxy , so dark matter should be made up of heavier, slower-moving particles.
*) According to the speed of motion of the particles that make up dark matter, it can be divided into two types :
Hot dark matter is made up of light particles moving at high speeds , comparable to the speed of light (such particles during the existence of the universe could therefore fly through a substantial part of the observable universe). Such particles leave the places of gravitational fluctuations very quickly. Thus, hot dark matter could not stimulate the formation of structures in the universe from originally small fluctuations to large units (the rapid motion of particles would rather eliminate these fluctuations). Only large structures could form - first superclusters of galaxies, of which clusters of galaxies, then galaxies. Particles of "hot" dark matter cannot be kept in gravity. fields of galaxies, their speed is many times higher than that of galaxies - they cannot create hidden matter in a galactic halo.
Cold (cryogenic) dark matter is formed by heavy particles moving at low speeds compared to the speed of light. Such slow particles of cold dark matter could be gravitationally attracted by small fluctuations in density distribution in the early universe and further increase these fluctuations. Thus, cold dark matter can stimulate the formation of large-scale structures in the universe "bottom-up": from galaxies, through clusters of galaxies, to superclusters of galaxies. It can explain the observed rotational curves of galaxies.
   Dark matter in the universe probably consists of both of these species, but most of it is its cold component. Astronomical observations (fluctuations of relic radiation, distribution of galaxies and clusters of galaxies, computer simulations) indicate the formation of a large-scale structure of the universe in a "bottom-up" direction.
   
   Neutrinos are therefore probably only a minor component of dark matter. Unfortunately, the main "candidates" for hidden matter in space remain hypothetical hitherto undiscovered particles from the WIMP group ( Weak Interactic Massive Particles ) . According to the unitary theory of sypersymmetry, there should be a " superpartner " for each particle , differing, among other things, in spin (for particles with half-digit spin, the superpartner should have an integer spin and vice versa). It is believed that a large number of these superparticles formed in the early universe. Most of them disintegrated later, but due to the disruption of left-right symmetry, (left-handed) relict superparticles could remain here - WIMP, interacting with matter only by weak and gravitational interaction. The WIMP particles do not disintegrate spontaneously, but in collisions they are transformed ("annihilated") into a pair of X particles and its antiparticles. It could be neutralina, for example (see the section " Hypothetical and model particles " in 1.5 of the above-mentioned monograph in electronic version) . Neutralins (supersymmetric particles to neutrinos) have a relatively large rest mass, estimated at about 50-200 proton masses. If there are heavy WIMPs, a relatively small number of units (% units relative to the number of baryons) would suffice to explain the gravitational effect of dark matter *); they would form the desired "cold" component of dark matter.
*) Related to it difficult detectability of heavy WIMP particles of hidden matter. While neutrinos are huge, so some of those trillions of neutrinos can sometimes be detected (
Neutrine Detection ) **), the frequency of WIMP interactions with particles of our common mass, or with each other, is so low that it is below current detectability. However, with the progress of electronics and detection technology, it is to be hoped that in the end it will succeed ...
**) But it should be noted that we can only detect high-energy neutrinos, originating from nuclear reactions in stars (from the Sun), from a supernova explosion, or from cosmic ray interactions. However, cosmological significance may be rather low-energy neutrinos (of relict, primordial origin), which we cannot detect.
  Other particles that are sometimes considered in connection with dark matter are axions - hypothetical particles introduced in quantum chromodynamics as a quantum of fields compensating for the strong interaction of CP-symmetry breaking. Axions do not have an electric charge and interact very little with matter through weak and strong interactions. They have very little mass (comparable to or less than neutrinos), so there would have to be a huge number of them in space to explain hidden matter; they could perhaps come from the processes of symmetry breaking and separation of interactions at the earliest stage of the universe. Axions could form a "hot" component of dark matter, along with neutrinos.
   The last candidate for dark matter could be the so-called mirror matter , hypothetically postulated in connection withparity symmetry and its disruption in weak particle interactions (it is also described in the
section " Hypothetical and model particles ", passage " Shadow or mirror matter - Catoptrons? ", in 1.5 of the monograph " Nuclear physics and physics of ionizing radiation ").
   In connection with the geometric theories of superstrings
(B.6. " Unification of fundamental interactions. Supergravity. Superstrings. ") There have been some sci-fi speculations that dark matter particles do not occur in our 3-dimensional space, but in another extra- dimensioni, which interacts with our universe only gravitationally; therefore they cannot be discovered by any particle experiments or detection ..? ..
Unstructuredness and spreading of dark matter
Another question is, what distribution and what structures can dark matter form? Interstellar gas composed of ordinary matter (such as hydrogen and helium) can condense by gravity to form globules, protostars, and stars
(4.1, " Star Formation " section) . At first glance, dark matter could do the same. However, contraction and collapse require the way in which the particles lose the kinetic energy generated by the adiabatic compression and slow down so that gravity prevails and the contraction can continue. In ordinary matter, this occurs loss of kinetic energy through electromagnetic interactions, radiation of electromagnetic waves. However, dark matter particles (such as putative WIMPs) do not have an electromagnetic interaction and have no way to lose energy. From this point of view, dark matter probably cannot form more complex gravitationally compressed star-sized structures.
   For similar reasons, dark matter cannot contribute significantly to accretion on compact objects. Ordinary matter trapped in the accretion disk loses kinetic energy and momentum
due to friction (caused by electromagnetic interactions) , thus moving in a spiral until it is absorbed
  
(4.8, section " Accretion disks around black holes ") . Dark matter probably does not show friction , its particles would orbit the compact object constantly in the disk. Only particles coming with a very small impact parameter can be captured - in the case of dark matter, only spherical accretion can occur , which is generally inefficient .
  According to current knowledge
(these are rather hypotheses ...) , dark matter does not create local structures, it is spread out in clouds comparable to galactic dimensions.

Doubts about non-baritone dark matter - an alternative explanation?
The concept of dark matter outlined above is now almost universally accepted in the astronomical and astrophysical community. However, there are some problems and controversial issues :
Nonbaryonic particles designed as dark matter components are purely hypothetical , not part of a standard particle model, have not been demonstrated in laboratory experiments at large accelerators, nor have they been detected in radiation coming from space. This circumstance diminishes the credibility of the nebaryonic dark matter.
The question of accuracy and interpretation of measured data - the correct determination of the amount of classical baryon mass and its distribution in galaxies and surrounding space.
Application of Newton's laws over vast distances in curved spacetime. We would see the observed effects (even without the assumption of unknown dark matter) if the gravitational force on large galactic scales decreased with distance more slowly than Newton's law (and also the general theory of relativity) . In this context, an alternative eventuality of the modification of Newton's law of gravitation is sometimes considered ("MOND - modified Newtonian dynamics", 1.2, part " Galactic modification of Newton's law of gravitation - MOND "). The observed astronomical measurements of the dynamics of the motion of stars in galaxies and galaxies in galaxy clusters, which are generally attributed to the gravitational effect of dark matter, could thus be explained by another form of gravitational law. By appropriate modeling of MOND parameters, anomalous rotational curves of galaxies can be explained quite satisfactorily (but not anomalies in galaxy clusters and galactic collisions). These efforts do not yet seem very justified and promising (Milgrom's MOND, with its accelerating dependence, is an artificial and not very convincing ad hoc theory ) ; dark matter is likely to be explained in simpler physical ways. Or even discrepancies can only be caused by a model error distribution of baryonic matter in galaxies and galaxy clusters ..? .........

The more complex dynamics of the expansion of the universe?
Some new aspects in the issue of the distant future of the universe, in relation to the mean density of matter in the observed part of the universe, are now brought about by the presumed
inflationary expansion of the early universe (5.5, section " Inflationary expansion of the universe ") . As a result of this inflationary stage, the radius of the universe would probably be many times (by many orders of magnitude) larger than the horizon, ie than the observable region of the universe. The "local" density in the observed part of the universe may then differ somewhat from the global mean. That means that even very accurate determination of the average density of matter in the observed universe can not by itself determine m efrom a closed and open universe, especially if this measured density is close to the critical density. For a sufficiently long time, the density of matter in the now observed part of the universe "mixes" with the density of matter in other parts of the universe and the total density t a can move to the "opposite side" of the r = r crit limit than now. Recall the same time, according to current quantum cosmology inflationary universe model would likely be closed, although very close to planar, as mentioned in the previous paragraph and I to it indirectly follows from the anthropic principle (5.7).
   However, see the new findings - "Accelerated Expansion of the Universe? Dark Energy?" - at the end of this chapter.

Astrophysics and cosmology: - human hopelessness?
If we reflect from our
human point of view the knowledge of contemporary astrophysics and cosmology about the evolution of the universe (and combine it with other risks) , it will inevitably evoke in us a sense of hopelessness in the ultimate perspective and the meaning of our existence - the duration of human civilization ! The danger to humanity is in several directions (listed in chronological order according to potential acuteness) :
From human society
We prepare the most acute danger ourselves. Greed, selfishness, and pride (especially among "celebrities" - the rich and powerful of this world who claim to dominate and manipulate other people) breed hatred and
murderous wars (often with religious pretexts) . Using current weapons of mass destruction, potential global wars could threaten entire human civilization. The consumer society leads to a waste of natural raw materials, waste contamination and total devastation of the environment. There is an overpopulation of people , especially unproductive individuals, who will parasitize nature and society - especially Africa and India (including Pakistan) , other Islamic countries and some problematic minorities in Western countries. Unless extensive enlightenment is provided and effective birth control, this population explosion can lead to bloody wars and the devastation of nature, threatening entire human civilization. In the interests of peaceful peaceful development, it will also be necessary to eliminate or transform unjust social systems based on human inequality, as well as to eradicate religious superstitions and prejudices (which divide people) , especially dogmatic and radical trends - many "believers" are indoctrinated (or more aptly ') criminal religious ideology in whose name they are able to kill their fellow man ..! ..
   Only when man kind in unison , " pulling together", it will hopefuly avert some terribl dangeres in the future, mentioned below ..!..

From the Earth's atmosphere
The
Earth's atmosphere plays a significant role in the appropriate climate (temperature, humidity, pressure) for various species of life, including us humans. Now there is often a discussion about increasing the concentration of so-called greenhouse gases (especially CO 2 ), which can lead to an unfavorable increase in temperature in our biosphere; in extreme cases except for temperatures incompatible with life. The extent to which human activity contributes to this is the subject of professional discussions. The Earth gradually loses its atmosphere by evaporation into the surrounding universe and could eventually end up completely without an atmosphere - a "dead planet" (cf. the atmosphere destruction scenario in the next paragraph) .
From the planet Earth 
We are also in mortal danger from our "Mother Earth". We live on a thin shell of the earth's crust (broken into a series of
lithospheric plates ), under which a hellish hearth of molten rocks rages. Earthquakes and volcanic activity occur at the junction of lithospheric plates. Under the thin shell of the earth's crust, in the earth's mantle, like a "time bomb", massive streams of hot molten rocks rise by thermal convection. If it melts to the surface, lava gushes violently under great pressure like a destructive supervolcano . Such a supervolcano can not only destroy an area of hundreds of kilometers, but the amount of volcanic gas and dust (thousands of km 3 ) can block sunlight and cause a planet-wide ecological catastrophe.with radical climate change. Yelowstone National Park in North America is considered to be one of the areas most threatened by a devastating supervolcano.
   Another risk in the distant future may be the weakening of the Earth's magnetic field , which protects it from a stream of charged particles from the Sun. The Earth's magnetic field is generated in the rotating semi-fluid outer part of the nucleus, which acts as a magnetohydrodynamic "dynamo". In the later stages of the planet's evolution, this nucleus cools and solidifies, weakening the magnetic field and eventually disappearing. For possibly. Life on the surface of a plant has two adverse consequences. Larger amounts of hard ionizing radiation, harmful to living organisms, begin to enter the biosphere from outer space. Furthermore, an intense stream of charged particles emitted by a star ("solar wind"it destroys the atmosphere and can "spray" it into the surrounding universe. The loss of the atmosphere leads to faster evaporation of water, whose steam is also carried into space by the stellar wind. The loss of the atmosphere and water would be incompatible with the continuation of life on our planet.
From near space - asteroids
In the solar system, not only well-known planets or our Earth orbit the Sun, but also a large number of smaller bodies of various sizes, from fractions of millimeters, several centimeters and meters (meteorites) to tens or hundreds of kilometers -
asteroids or asteroids (name " asteroid ", which means " star - like
" Arose from the fact that the sun illuminated by nearby bodies of ground-based telescopes look like tiny points of light, like distant stars, unlike the stars but move across the sky like planets) . Some of these objects cross the orbits of the planets can be collide with them, be captured by their gravity, and hit their surface at high speeds of tens of kilometers per second.All terrestrial planets are densely littered with impact craters after the impacts of these bodies.
   
Thousands of the above-mentioned bodies also cross the Earth's orbit. Small bodies "burn" in the atmosphere like meteors; it is estimated that such a meteor fallout represents millions of tonnes each year. We are effectively protected from small "space projectiles" by the Earth's atmosphere, in which small meteor bodies burn and do not fall to the surface at all. Even larger meteorites that hit the earth's surface do not pose a greater danger, as they lose almost all their kinetic energy by friction in the atmosphere (and most of their mass evaporates).
   Unfortunately, the orbits of larger bodies and asteroids also intersect the Earth's orbit , fortunately mostly at a time when the Earth is not in the given place. However, there is a certain probability that the asterioid will hit the collision path   with the Earth and the Earth will collide with an asteroid - " we live in a space shooting range, " astronomers say. There is a real danger from larger bodies with a diameter of tens of meters and a weight of over 1000 tons (it would cause "only" a local catastrophe) . An impact of a planet several kilometers long weighing more than 10 12 kg would suddenly release energy greater than 10 22 J, which corresponds to the explosion of more than a million thermonuclear bombs. In addition to the immediate destruction of an area of ??thousands of kilometers, this would cause (similar to the above-mentioned supervolcano) ejection of huge amounts of rocks, gas and dust into the atmosphere. The fall of molten rocks to the surface would cause fiery meteor shower, which could burn a large part of the earth's surface. Large amounts of ejected dust could remain in the atmosphere for several years, which would significantly weaken the sun's radiation for a longer period of time. This would lead to a global environmental catastrophe with radical climate change. Mankind probably wouldn't survive it! Such an asteroid crash is thought to have occurred 65 million years ago, when dinosaurs and most species of fauna and flora at the time became extinct. The Earth collided with asteroid-sized cosmic bodies several times in the past and is likely to continue to do so in the future - with fatal consequencesfor the continuation of human civilization; we do not yet have the opportunity to prevent such a cosmic catastrophe ...
How to prevent a collision with an asteroid ?
Current astronomical technology is gradually making it possible to find "risky" asteroids and predict a possible cosmic collision. There are basically two basic possible ways to avert an impending catastrophe :
1.
If we knew well in advance (several years) the future orbit of such a potentially dangerous cosmic body, we could avert an impending collision by changing its trajectory - deflecting it or changing the speed of the body so to cross the Earth's orbit when the Earth is not there. Such a deflection of the path could be effected by the application of a force, preferably perpendicular to the instantaneous direction of movement. Usage is discussed nuclear charge , the energy of which would explode would cause a "rocket effect" (primarily by ejecting molten material from the crater), leading to a deflection of the asteroid's orbit. Or shelling with high-power laser beams. The launch of a spacecraft in orbit near an asteroid is also being considered, which would gravitationally deflect the asteroid's orbit.
2. Another possibility would be to break the body of the explosion , but a number of fragments would move in their original orbit and land on Earth. The individual fragments might not cause a global catastrophe ..? .. But it is a dictable and not very optimal way.
   However, we do not yet have sufficient missile technology for any of these interventions (perhaps in 50 years? - provided that humanity does not waste its forces on senseless political and religious disputes, armaments and wars!). Meanwhile, we have to stand idly by as our asteroid "falls on the head" ...
From the distant universe - supernovae, gamma-ray bursts ,
If some of the closer or "nearby" stars within a distance of about 30 light-years across, exploded as a
supernova , n Enormous amounts of radiant energy, especially hard ionizing radiation , that would hit the Earth would probably cause a huge natural disaster which could seriously jeopardize the very existence of life here on Earth! Even from an even more distant universe, hundreds or thousands of light-years, narrowly collimated gamma-ray bursts emitted by collapsing objects — massive stars, neutron star collisions, accretion disks around black holes — can be potentially dangerous to us if their rotational axis is rotated toward us (they would affect not only the Earth, but the entire solar system ...) . From an astrophysical point of view, these high-energy events are discussed in 4.2, section " Supernova explosion. Neutron star. Pulses. " And 4.8, section " Accretion disks around black holes. Quasars. " .
   The risk of cosmic radiation from catastrophic processes in space is discussed in the treatise "
Cosmic radiation ", part " Biological significance of cosmic radiation ", passage " Deadly cosmic radiation " 1.6 monograph " Nuclear physics and physics of ionizing radiation ".
From the Sun
Even if we can avert the catastrophe of the Earth's collision with asteroids, devastating wars, survive supervolcanoes and various ecological catastrophes, protect the Earth from a massive flash of cosmic rays from a nearby supernova explosion or neutron star fusion, our life-giving star Sun will kill us. Over the next 3 billion years, the Sun will increase its current radiant power by about 40
%.. The temperature on Earth will rise by tens of degrees, the oceans will evaporate and all life will end. In about 5 billion years, the Sun will deplete the supply of thermonuclear fuel (especially hydrogen) and reach the final stages of its evolution (see 4.1, section " Late Stages of Stellar Evolution ") . The sun then "inflates" and, like a red giant, first absorbs and evaporates all the inner planets, including the Earth *), creating a "planetary" nebula and later becoming a white dwarf itself .
*) The sun in the stage of the red giant will be large enough to engulf Mercury, Venus, Earth and Mars if they orbit at the same distance as today. But Earth and Mars might be able to avoid this fate due to the following effect :
   In the late stages, with increased radiant power, the Sun will emit significantly more "solar wind", which will carry a considerable amount of the Sun's material away into space outside the solar system. This will reduce the total mass of the Sun, which will increase the radius of the planet's orbits. If the mass of the Sun is reduced sufficiently in this way, the Earth can orbit at an already safe distance, where the inflated surface of the Sun cannot reach ..? .. However, even if this favorable development took place, the Earth would be a desolate planet with a hot dried surface on which life could no longer exist!
   The only way to maintain the Earth's habitability in the long run against the rising radiant power of the Sun is to gradually increase the orbital distance. Earth around the sun. It would be enough very slowly, on the order of millimeters per year. Currently, it is sci-fi, we have no technical means to do so. In the distant future, however, our offspring are likely to have much greater energy resources. In addition, gravity and asteroid energy could in principle be used to bring the Earth into higher orbit, which could be carefully guided into a close coronary orbit with the Earth so that it gravitationally transfers kinetic energy to the Earth in the direction of orbit. In this way, at least in principle, the habitability of the Earth could be preserved by life for about 5 billion years. In the final stages of the Sun's development, however, this would already be a problem, because its radiation changes relatively quickly. The earth would be hit by high-energy gas streams from an expanding envelope. Then it would be "useful" the radiance of the Sun - the white dwarf - sharply reduced and the hard ultraviolet component would predominate in the radiation. The earth in distant orbit would freeze, it would need to be quickly moved to nearby orbit. If we moved the Earth to a very close orbit to maintain the temperature in the sci-fi concept, intense UV radiation would destroy the atmosphere and life. At that time, however, human civilization, if it survives at all, will certainly be transformed into a completely different form - see the passage "Artificial intelligence and transhumanism "work" Anthropic Principle, or cosmic God "...
For Global Evolution - extinction of the Universe
People might (?) Until manage the Earth and the solar system
escape and repopulate other appropriate objects in the universe(so far this pure sci-fi!). But what's next? If the universe were closed and collapsed it into a "fiery furnace" big crash, we should probably no hope. If the universe was open, so fatal end we would fundamentally threatened, at least not However, in an expanding and ever-cooling universe, it would be increasingly difficult to find areas of local entropy fluctuation where there are still available energy sources *) for the development and maintenance of civilization. The " thermal death of the universe " would ultimately mean the death of human civilization (discussed at the beginning of this chapter, the " Open Universe " passage ) .
*) Living matter receives food, which is an ordered form of energy, and converts most of it into a heat - disordered form of energy. Even if in the distant future there is a transformation of civilization and intelligent processing of information from the environment of living matter, eg into electronic form (as discussed in the passage "
Artificial Intelligence and Transhumanism " of work) Anthropic principle or cosmic God"), the basic thermodynamic process would not change in principle (however, the energy efficiency of information processing would increase dramatically!). the entire system; this increment disorder, according to the laws of thermodynamics always higher than the growth of order in mind. this concept would only delay the demise of civilization heat death.
   A certain, but only imaginary hope of eternal duration of life, could represent the concept of " multiverse " - an infinite number universes (5.5 " Microphysics and cosmology. Inflationary universe. ", part "Chaotic inflation"Arcade" The emergence of multiple universes ") . Although a single specific universe" die "collapse or heat death multiverse as a whole will live on - forever, with individual universes can arise a new life . But this is no hope for us .. ! ..
   In any case, we can state that the knowledge and theories of contemporary astrophysics and cosmology unfortunately do not show us any real perspective of the eternal existence and development of our human civilization ! what we do n't know yet and maybe we don't even know ... And from this ignorance of ours we can perhaps draw some hope..? ..

-------- The findings below arose only after the writing of the book "Gravity, Black Holes ...", so they were not included in the book edition -----

Cosmological Surprise:
Accelerated Space Expansion? Dark energy?
According to the standard cosmological model (5.4), the expansion of the universe is hampered by the attractive gravitational effects of matter and must therefore slow down - both in the closed universe
(where it would eventually contract) and in the open universe (where the expansion will slow down, but it never stops completely) . After all, to quantify the deceleration of the expansion of the universe, we introduced the so-called decellation parameter q in 5.3 . We now know that the gravity of dark matter in particular contributes decisively to slowing down the expansion of the universe. The cosmological constant in Einstein's gravitational equations, according to previous ideas, may have played a decisive role in the inflationary expansion of the universe at the outset (as discussed in more detail in 5.5 " Microphysics and Cosmology. Inflationary Universe. ") , But did not need to be considered for further evolution of the universe.
   As discussed in 5.1 and 5.3, the dynamics of expansion
(or contraction) of the universe, ie the time course of the scale factor or expansion function and (t) - the expansion history of the universe , can be determined by determining the relationship between the cosmological redshift Z in the spectrum of distant objects and their distances. These distances are derived from the ratio of the actual and observed (apparent) luminosity of suitable " standard candles " (4.1, passage " Determining the distances of space objects - a basic condition of astrophysics ") . For large cosmological distances, type Ia supernovae are suitable "standard beacons" (SN Ia; they are described in more detail in 4.2, section " Supernova explosion. Neutron stars. ", Passage " Supernova types and their astronomical classification "), which astronomers are currently able to observe with the help of large telescopes up to distances of more than 6 billion light-years. Supernova Ia can be identified by the shape of the spectrum, their brightness is determined from the course of the light curve - the increase, peak and decrease of the brightness of the supernova. Photometric measurements of such different distant supernovae (with different Z's) make it possible to determine how the universe expanded at different time periods. By performing multiple measurements at multiple distances, we can create a graph mapping the expansion of the universe as a function of its age.
   In 1998-99, two groups of American astronomers undertook the astronomical "mapping" of the dynamics of space expansion by photometric measurement of a large number of type Ia supernovae. The first was led by A. Reiss and B. Schmidt
(Space Telescope, Baltimore)within the project " High-Z Supernova Search " - to search for supernovae with a large redshift Z . The second group (" Supernova Cosmology Project ") was led by S. Perutter (Lawrence Berkeley Laboratory) . The original goal of these observations was to find out how big the slowdown in the expansion of the universe is .
  This accurate photometric measurements of distances supernovae type Ia *) showed that very distant supernovae type Ia
(high value Z) are less bright than would correspond to the cosmological red shift from the universe, the expansion is due to the gravitational effects of the mass slows (the dynamics expansion of the universe see 5.3). For closer supernovae with a smaller Z, the relationship between distance and redshift corresponded to the standard scenario. However, the most distant galaxies seem to have driven "something" further than the usual Fridman expansion of the universe. Respectively (which is the same thing) , these very distant galaxies, corresponding to the earlier periods of the universe, are moving away at a slower speed than would correspond to Fridman's dependence.
  From such a measured relationship between the cosmological redshift and the distance of supernovae, it was surprisingly observed that the expansion of the universe is probably not slowing down at the moment , but is accelerating on the contrary.! By default, the expansion of the universe has slowed to only about half the current age of the universe, to about 6-7 billion years, but then began to accelerate, which continues.
Photometric measurements of supernovae Ia
A supernova of type Ia arises in a close binary star consisting of a giant star and a white dwarf, where matter is transferred from the giant to a white dwarf, whose mass gradually increases. It then crosses the Chandrasekhar limit (1.4 M ) and the white dwarf collapses into a neutron star, which manifests itself as a type Ia supernova explosion - see 4.2, section " Supernova explosion. Neutron stars. " . All type Ia supernovae explode according to the same mechanism and with the same initial mass and therefore the amount of energy released is practically the same every time . Thus, from the relative observed brightness, the distance of such a type Ia supernova can be determined , independently of the spectrometrically measured cosmological redshift z = ( l - l o ) / l o of radiation from the supernova ( l o is the wavelength of a certain spectral line at time t o of transmission beam, l is the wavelength of the same line at time t of beam capture). In 5.3, a scale ( expansion ) function was introduced to describe the evolution of the universe and (t) indicating how distances in the expanding universe change with time t . For two time instants t o and t, there is a simple relation z = (a - a o ) / a o between the values of the scale function a and the cosmological redshift z , where a o characterizes the dimensions of the universe at time t o sending a ray a and the dimensions of the universe v time t of its capture. Of which a = (1 + z) .a o , so from the measured cosmological redshift we can determine how the dimensions of the universe have changed since the light beam captured today was emitted. Careful analysis of the radiation from a number of differently distant supernovae can reveal the relationship between the cosmological redshift and the distance of the supernovae, from which it is possible to "trace" how the universe expands. And it is these measurements that show the time dependence a (t) similar to the curve L> L E in Fig. 5.3c in 5.3, according to which the rate of expansion of the universe slowed down in the early stages, but is currently increasing in Fig. 5.3'c :

Figure 5.3 will be presented here again for clarity (with red markings important for this issue):

Figure 5.3. Evolution of cosmological models - time course of radius
a (scale factor) of the universe, depending on the value of cosmological constant L and mass distribution density r ( r krit is the value of critical mass density, and E and L E denote values ??of space radius and cosmological constant corresponding to Einstein's cosmological model) .
For our purpose, the graph L> L E in Fig. C) on the right is important here, which expresses the newly observed dynamics of the evolution of the universe, with late accelerated expansion.

Regression analysis of the Hubble diagram of the measured dependence of the relative magnitude of type Ia supernovae on the cosmological redshift best corresponded to the curve of the cosmological model with parameters W M = 0.29 and W L = 0.71 ( W parameters were introduced in 5.3, passage " Relative W - parameterization cosmological models ") . The analysis according to Fridman's cosmological model (equation (5.23a) in 5.3) led to the value of the cosmological constant L 1,2.10 -52 m -2 .
Dark energy
It has been hypothesized that this accelerating expansion is caused by a kind of pervasive vacuum called "dark energy " DE ( Dark Energy ) with a negative energy density is so great that their repulsivnmi effects overcomes the gravitational pull of all matter in the universe. In the simplest case, it is assumed that dark energy and emerging repulsive action is in the area of distributed roughly uniformly.
   Equation of state of dark energy can be modeled in a simple general form as an "ideal liquid"
   

p de = w. c 2 . r de , (5.59)

where p de is the pressure, r de is the dark energy density and w is the state constant.
   If the universe were filled only with the dark energy " de ", the acceleration of the scale function a (t) with time is given by substituting p
de a r de into 2. Fridman's equation (5.23b), in a simplified form: / a = - (4 p G / 3). ( r + 3p / 3). If the value of the state constant w <-1/3, this leads to a positive value of , ie to a cosmic acceleration of the expansion. And as shown in (5.28) - (5.29), from the 1st Fridman equation (5.23a) the expansion law follows for the equation of state of type (5.59) a(t) = a 0 .t 2 / [3 (w + 1)] . .........
   This mysterious hidden or dark energy is sometimes referred to as the "fifth state" or " quintessence "
(see below) . As shown in 5.2, part " Cosmological constant ", further in 5.3 and 5.5, such vacuum dark energy would equivalently generate a cosmological constant L> 0 ( case w = -1 in table (5.61) ) in Einstein's equations (5.7 ) of the general theory of relativity, leading to a negative pressure that would induce " antigravity " repulsion at cosmological distances , acting opposite to the gravitational gravity of ordinary matter. That would be the simplest explanation of dark energy ...
   In connection with the concept of dark energy, it is therefore useful in Fridman's equation (5.40) to replace the cosmological term
L and W L - to generalize ( this generalization is evident from the table (5.61) ) with dark energy density r de and its relative density W de = r de / r de-crtit - by the contribution of dark energy :

(5.60)

The "functioning" of this contribution of dark energy in the dynamics of the expansion of the universe depends on the value of the coefficient w in the equation of state p de = wc 2 . r de dark energy :

and) w> 0 => ordinary gravitational matter slowing down expansion (here irrelevant case) (5.61)
b) w <-1/3 => general dark energy accelerating expansion; quintessence
C) w = -1 => cosmological constant L , generating vacuum dark energy
d) w <-1 => "aggressive" dark energy (quintessence) accelerating expansion exponentially above all limits - "phantom" energy

These options ( except for the uninteresting case a) ) will be discussed below.
   If the dark energy density is constant over time or decreases more slowly than the density of ordinary matter (ie slower than 1 / a
3 for matter, or 1 / and 4 for radiation), the scenario of the evolution of the universe would correspond to the curve L> L E in Fig.5.3. c): after the end of the initial inflation expansion and the onset of the Fridman expansion, a period of deceleration would take a long time , when the gravitational effects of total matter (shining + hidden) prevail over the repulsive forces of dark energy and the expansion slows down. After a proper reduction in the density of the mass, a reversal would occur . For a short time, the two forces would be balanced ("indecisive universe"), then dark energy would prevail and cosmic expansion would eventually go from the deceleration stage to  acceleration - the constant acceleration of expansion, towards the "thermal death" of the universe ...

Unless a convincing alternative astrophysical explanation of the observed data *) for distant supernovae is found (eg light absorption mechanisms from supernovae in the dust component of an intergalactic substance, different evolutionary properties of early stars formed from a substance with less heavier elements, or inadequate use of existing physical models to extremely long time and space intervals, ...) , the accelerated expansion of the universe and the existence of dark energy must be taken very seriously. It would be one of the most surprising and mysterious discoveries in the history of astronomy!
*) The processing of some newer and larger sets of several hundred distant type Ia supernovae somewhat reduces the statistical significance of the data from the first observation (and perhaps does not even rule out a constant rate of expansion ..? ..) , further measurements will specify ....
Three indications for dark energy
We now have three independent indications for the accelerated expansion of the universe :

The measurement of supernovae Ia
is the most important, it is a direct indication - it has been discussed above. In addition, there are two other indirect, looser and model-dependent indications:

Inhomogeneities of relic radiation in correlation with the large-scale structure of the universe 
The small anisotropies of relic radiation reflect inhomogeneities in the distribution of matter just after the end of the radiation era. One of the possible origins of these inhomogeneities may be the so-called acoustic horizon of density waves-oscillations in the hot plasma of the lepton and radiation era
(it is discussed in 5.4, passage " Baryon acoustic fluctuations " ) . It is believed that galaxies later formed from these initial inhomogeneities, stretched by the expansion of space over long distances of hundreds of millions of light-years. Their current distribution - clustering - depends on the dynamics of the expansion of the universe.
Detailed analysis of relict radiation inhomogeneities
(performed by COBE and WMAT satellites, even more sensitive analysis of relic radiation is performed by PLANCK satellite) and itscorrelations with astronomical mapping of the large-scale distribution of galaxies suggest that the observed clustering structure corresponds to the accelerated dynamics of space expansion.
After all, even the comparisons of the density of galaxy clusters with low and high redshifts give a slight indication for accelerated expansion ...
Measurement of the dynamics of the expansion of the universe using quasars 
In addition to supernovae Ia, the dynamics of the expansion of the universe to even greater distances, ie to earlier periods, can be studied using quasars . Quasars are giant black holes in the center of galaxies that absorb a large amount of surrounding gas in a large accretion disk , part of which is ejected along the axis of rotation in massive jets (jets) - see 4.8 passage "
thick accretion disks. Quasars ." The absolute magnitude (actual radiant power) of quasars is different, but it turns out that this absolute magnitude is related to the spectrum of quasar radiation , especially to the ratio of ultraviolet and X-ray radiation (4.8, passage " Quasars as standard candles ") . Quasars with spectrometric analysis can then in principle be used as " standard candles " for measuring the greatest cosmological distances .
At present, these spectrometric measurements are performed on a large number of quasars of different distances.
Some preliminary results for the most distant quasars suggest that the density of dark energy could perhaps even increase over time ..!?. .

The influence of dark energy on the evolution of the universe
Dark energy is very dilute but ubiquitous and its effect is cumulative . It is imperceptible on terrestrial scales and within the solar system, but it may be dominant on a cosmological scale throughout the universe.
   According to current estimates, in the universe, about 70% of dark energy, about 25% of dark (hidden, non-radiant) matter, and only
4% of ordinary (" luminous "or absorbent) matter are accessible to observation(see table below, at the end of this chapter). Therefore, if the existence of dark energy (or non-zero cosmological constant) is really definitively proven, it will change our ideas about the dynamics of the evolution of the universe, which would consist of two previous stages instead of the previous two stages.3 stages :

The original Figure 5.2 from 5.3, showing the evolution of the closed universe, will be redrawn and supplemented here again, with an emphasis on the open universe and the dynamics of accelerated expansion (Fig. 5.2'c) :


Fig.5.2. Different possibilities of the dynamics of the evolution of the universe. a) Closed space. b) Open space. c) Open universe with final accelerated expansion.

Hidden (dark, non-radiant) matter and hidden (dark) energy play essentially opposite roles in the universe :
Hidden matter - holds the universe and its structures together, inhibits the expansion of the universe. The formation of large structures - galaxies and clusters of galaxies - was caused mainly by the distribution of hidden matter in the early stages of the universe (at the beginning of the matter era). And this dark matter still holds the galaxies and clusters of galaxies together by gravity.
Hidden energy - if it prevails, with its repulsive effects, on the contrary, it stops the formation of structures and forces the universe to expand faster and faster globally.
   The new cosmological model, extended by the implementation of hidden matter and energy, is sometimes referred to as LCDM - Lambda Cold Dark Matter (Lambda Cold Dark Matter), where the cosmological constant "lambda"
L indicates the acceleration of the expansion (cf. also 5.3, passage " Relative omega W - parameterization of cosmological models ") .
   In the early universe, dark energy played no role
(with the exception of the inflationary stage - 5.5) , while in the distant future it may acquire a decisive influence; it is even able to "blow" the universe and dissolve it in "nothingness" (see "The Great Burst? " below) .
   Thus, if the concept of dark (hidden) matter and energy turns out to be true, the ultimate fate of the universe in the future will be determined by the " duel " between dark matter and dark energy , between their attractive and repulsive gravitational effects. The visible glowing substance, due to its small representation, plays only a secondary role in the dynamics of the universe - it is "passively" carried away by dark matter and energy - generated by the global structure of spacetime. However, luminous matter serves as a source of electromagnetic signal, an " indicator " that allows us to map the distribution and dynamics of the motion of matter - luminous and hidden - in outer space.

The essence of dark energy ?
Dark energy probably does not have the usual material, material or particle nature, it is rather the field property of spacetime as such. Although recent astronomical observations may make it possible to specify the representation of dark energy and perhaps even estimate its " equation of state " (5.59), ie the relationship between pressure p and density
r ( cf. also 5.3) , about the very nature of dark energy , or alternative explanation of the cause of the accelerated expansion of the universe, it will be possible to speculate in the foreseeable future. So far, there are basically four possibilities (hypotheses) :
l Vacuum energy with negative pressure. In connection with the concepts of phase transitions in unitary field theories (discussed at the beginning of 5.5 " Microphysics and Cosmology. Inflation Universe. "), It was hypothesized that this is a " false vacuum " energy density of the same kind that caused a massive accelerated inflation expansion on the very beginning of the universe (5.5 " Microphysics and cosmology. Inflationary universe. ") . Even the current vacuum could be "somewhat false" according to this hypothesis, but the difference is that its energy density is many orders of magnitude lower than at the beginning and therefore causes only a "slightly" accelerated expansion of the universe. This hypothesis assumes, immutable in space and time, is not dependent on the expansion of the universe and can be equivalently expressed as the cosmological constant L in Einstein's gravitational equations (cf. 5.2, part " Cosmological constant ") , case c) in table (5.61).
l A new kind of field - the 5th interaction, sometimes also called quintessence (lat. quinta esentia = fifth essence , figuratively punished, primordial essence ) , filling the space of the universe ( case b) in the table (5.61) ). The field of this interaction will generally no longer be constant but its power may change over time and may be different in different parts of the universe. It changes as the universe expands - it should decrease with expansion (if it was initially established with a specific intensity) , albeit at a different rate than the density of matter, radiation, or hidden matter. But in general, this unknown field of the 5th interaction can be governed and developed by its own dynamics , of which we know nothing yet, but we can consider three possibilities :
- Its intensity may begin to diminish in the future , until he eventually collapsed with a "big crash", as predicted by the model of a closed universe - Fig.5.2'a (this does not seem likely now ...) .
-Or it may remain approximately constant, leading to a constant slow acceleration in a scenario similar to the vacuum energy of the cosmological constant (Fig. 5.2'b).
- Possibly. we could also imagine an increase in the intensity of the quintessence field with time, which would cause an unlimited acceleration of the expansion of the universe, at which all structures in the universe could be torn (see " Great burst? " below) , Fig.5.2'c.
l
Deviations from the general theory of relativity . The cause of the accelerated expansion could be a slightly different dynamics
the evolution of the universe at extreme cosmological distances than that resulting from the "classical" general theory of relativity, well validated at shorter "astrophysical" distances. A new theory of gravity needs to be developed ..? .. This possibility does not seem very likely, the modification of the existing OTR should not conflict with other successfully explained observations and experiments.
l Dark energy does not exist , accelerated expansion is a mere observational illusion ! What we perceive or interpret as dark energy may be due to our not entirely adequate cosmological idea of ??the large-scale structure of the universe. Global homogeneity and isotropy of expansion may not be completely absolute. We can be inside a kind of large "bubble" of slightly reduced Hubble expansion rate, so in other remote areas the expansion may seem faster ..? ..
But it would require relatively large density fluctuations, around 20% ...
  Anyway, the essence of dark energy is currently the most difficult unresolved issue in astrophysics and cosmology.

The Late Accelerated Expanding Universe
The accelerating expansion of the universe, in co-production with standard gravitational attraction, would dramatically change the appearance of the universe in the distant future compared to the current state. From a global perspective, two opposing events will take place in such a universe :
l All expanding matter in the universe - distant galaxies that are not gravitationally bound to each other - will rapidly recede until they escapefrom our sight beyond the horizon of events, visually and causally "disappears", they will be "swept" from our cosmic horizon, they will move into the "invisible". We can imagine this as new expanding space is created between distant galaxies so fast that even light appears slow to keep up with the rate of expansion - it is not enough to transport information between distant galaxies.
l Nearby galaxies, on the other hand, will continue to be attracted to each other by gravity and merge into a single huge "supergalaxy".
   In a few hundred billion years, the visible universe will be formed by a single supergalaxy, surrounded by a vast, insurmountable emptiness.. In the distant future (hundreds of trillions of years), individual parts, and eventually the entire galaxy, will collapse into a gigantic black hole; therefore, it would be one variant of the ultimate future of the observable universe ...
   
Note: Since outer space expands homogeneously, they would see the same situation or. observers ("aliens") in distant galaxies. For them, our (and close to us) galaxies would escape from sight, the surrounding galaxies there would be gravitationally reunited ...
   Let's compare this unhappy prognosis with the above-mentioned thought " Astrophysics and cosmology: - human hopelessness? ". The observational and gnoseological aspects are also worth consideringthis development. If an intelligent civilization had developed in the late acceleratingly expanding universe on a planet around a star in that supergalaxy (the Earth would no longer exist at this time) , its astronomers would come to completely different conclusions about the universe as a whole than our current astronomers. Even the largest telescopes would not see any distant galaxies whose spectral shift would reveal the expansion of the universe. Relic radiation (now microwave) is so diluted and elongated that it ceases to be measurable. Hard to say, what kind of future observers would these cosmological theories have? The idea of ??a universe created by the big bang would probably not even occur to them in a dream ..? .. Accelerated expansion will irreversibly " erase " all the evidence about the beginning of the Universe and its earlier evolution ..! ..
Note: From the point of view of the current scenario of space evolution, we can acknowledge that we are lucky to live at a suitable time when we have a good view of distant space and by analyzing astronomical observations(not only in optical and electromagnetic)we can get a realistic idea of space evolution almost to period of its origin.

A big burst ?
If the very intense (
case d) in Table (5.61) ) "phantom" dark energy continues to drive the expansion of the universe with increasing speed, in about a billion years we will not see even at the "fingertips", because everything around us will move away at super-light speed. The exponential course of expansion leads to an ever-accelerating expansion, which could theoretically approach infinite speed in the distant future. Conjecting this scenario "to the end" may lead to the idea that ever-accelerating expansion will not only absolutely delay (beyond the horizon) all distant structures in space, as outlined above in the " Late Accelerated Expanding Universe " passage , but then dark energy. overcomesall interactions and binding forces. "Antigravity" will tear apart all bound structures - gradually galaxies, planetary systems, stars. In the final phase, according to some ideas, the atoms would rupture and even the elementary particles themselves and perhaps even the structure of space-time would rupture. Such a scenario of cosmic evolution is sometimes referred to as the " big rip " ( Big Rip ). Opinions on this (purely hypothetical!) question differ :
According to the "moderate" opinion, from the point of view of standard OTR based on the principle of equivalence (2.2 and 2.3), nothing like this should happen *). Only distant objects that do not have internal integrity would be subject to accelerating expansion. Smaller bound systems develop under the influence of their internal binding forces ; we can introduce an approximate locally inertial system for them , within which the laws of physics will not be practically affected by the global cosmological gravitational field of the expanding universe. E.g. the electron orbits in the atoms do not change with the expansion of the universe : they are not bound by gravity, but electrically, while within the locally inertial system these electric forces do not depend in any way on a spread gravitational background. Even in galaxies, cosmological expansion does not occur, because the presence of matter leads to a "positive" curvature of space-time, which overcomes repulsive forces. For a comparison, see also the discussion " What actually expands and does not expand during the expansion of the universe? " In 5.4 .
*) Such a conclusion would apply under the usual assumption of a constant (or decreasing) value of the cosmological constant, or dark energy density, with the expansion of the universe. If, hypothetically, the density of dark energy (as a "quintessence") increased indefinitely over time - "phantom" dark energy - it would support the "big burst" scenario ..? ..
An alternative "radical" view, supporting the concept ", argues, among other things, by analyzing the time dynamics of the event horizon . In any case, with the expansion of the universe, the horizon of events becomes smaller and smallerpart of the whole universe. As the expansion exponentially accelerated, this effect would become increasingly dominant. The DeSitter event horizon would shrink to the size of clusters of galaxies, then galaxies whose stars would scatter into expanding space. In the final stages of expansion, the horizon would shrink sharply to the dimensions of the solar system, stars (Sun), planets. All these bound systems would disintegrate and "fly away" from each other. Even with such stable formations as black holes, the deSitter horizon would eventually "beat" the gravitational (Schwarzschild) horizon and the black hole would be destroyed. Eventually, molecules, electron shells of atoms and atomic nuclei would rupture, and the individual elementary particles would move so far apart from each other that they would no longer physically "know about themselves" and interact. Furthermore, nucleons would be torn into free quarks (repulsive forces of dark energy will surpass the law of "quark trapping"). An immensely vast Universe will still exist, but in a state of "thermal death."
   Finally, the deSitter horizon would fall below the dimensions of the elementary particles that would be torn. Immediately, the structure of spacetime in the discontinuity of the metric tensor g ik would disappear , similar to the singularity of spacetime (see 3.7, 4.9; unlike the "localized" singularity of a black hole, this singularity would be everywhere). The amorphous variety formed in the topological foam could then perhaps re-create an inflation-expanding region by quantum fluctuation, which could give rise to a new universe , as described in 5.5, passage " Chaotic inflation and quantum cosmology "). But this hypothetical "new universe" would have nothing to do with the original "our" universe ...
   This radical scenario "unlikely , because the density of dark energy, if constant or does not grow too fast, will never locally exceed the density of matter in galaxies, stars or atoms.
   In any case, these are only purely speculative questions , caused by perhaps somewhat hasty conclusions from so far sporadic astronomical observations ..? ..

From emptiness to emptiness ?
The combination of the idea of quantum cosmology of the universe by chaotic inflation and accelerated expansion in the late stages of the universe offers a scenario of global universe history from the emptiness of " thermal birth " to the emptiness of " thermal death " of the universe :
The initial state is almost empty space ; Quantum field fluctuation occurs in a certain region; There will be a rapid inflationary expansion of this fluctuation; At the end of inflation, vast outer space is filled with a more slowly expanding, almost evenly distributed primary hot gas; CAfter its cooling, the inhomogeneities condense by gravity into clusters of galaxies and galaxies in a slowly expanding universe; After a long time, dark energy prevails, accelerating expansion dilutes all scattered matter, galaxies escape beyond the horizon; The galaxy collapses into black holes, which then quantum evaporate in the radiation; Accelerating expansion infinitely dilutes all remaining radiation; The universe is again almost empty space .
And in this empty space there can again be quantum fluctuation, leading to the creation of a new universe ... Individual such universes would in this respect be only "episodes in quantum fluctuations" of the eternal basic space ..? ..
   Again, it is necessary to emphasize the speculativeness of this scenario, which is a far-reaching extrapolation of the little we know to a large area of the unknown ..! ..

The greatest mystery of nature ?
The existence of hidden or dark matter (matter) and even more "hidden", "darker" and more mysterious dark energies in the universe is a great challenge not only for astrophysics and cosmology, but also for elementary particle physics
(if we look for its source at the quantum level) . The problem of explaining a non-zero but very small cosmological constant L (corresponding to a density r L 0.5.10 -5 GeV / cm 3 , which is a few atoms per m 3 ), represents a major challenge for unitary field theories (cf. B.4"Quantum geometrodynamics "and B.6" Unification of fundamental interactions. Supergravity. Superstrings. "). In the current field based on quantum theories ofr L ~ m p .c 2 / L p 2 10 118 GeV / cm 3 (m p is the Planck mass, l p Planck length), which is more than 120 orders of magnitude higher. !?.
   To analyze this problem would perhaps have their say and the anthropic principle
(5.7 " anthropic principle and the existence of multiple universes ", see also the philosophical-naturalistic work "Anthropic principle or cosmic God '). "Anthropicly justification " coproduction with vision multiverse - huge set of different "Space", with different properties of elementary particles, fundamental interactions (and thus also bigstsvacuum energy) and evenvariousdimensions ofmyspace, could reflect, at least on a philosophical level, these hidden mysterious qualities ..? ..

What is the basic composition of universe ?
In addition to the global structure and evolution of the universe, the basic task of physical cosmology is also to clarify what matter - matter, field, particles - the universe consists of? In 5.4 " Standard Cosmological Model. The Big Bang. Shaping the Structure of the Universe. " We saw that the composition of the matter filling the universe changed significantly during its evolution . From fluctuating fields and quanta in the very early universe immediately after the Big Bang, through quarks and baryons (protons, neutrons), photons, electrons, muons, neutrinos, up to light atomic nuclei of hydrogen and helium after initial nucleosynthesis and finally all heavier atoms formed during nucleosynthesis in stars and during the supernova explosion (4.1 and 4.2). The composition of the universe was set at about 75% hydrogen, 25% helium and a smaller amount of heavier elements according to the graph on " Elements-Representation " in 4.1. All this is "ordinary" matter made up of baryons, electrons, photons.
   However, the concept of dark matter and dark energy changes significantly - it complements our earlier idea of ??the composition of the universe. According to current knowledge, the composition of matter-energy in the present universe is as follows :

         Mass: material - particle, atomic structure
field - distributed form of matter (quantized)
Matter in space:

the observed luminous + lightless - baryonic
non-radiant - dark (hidden) matter
                    
                           
           dark matter   dark energy ?
  baryonic    ?     nonbaryonic ( nonbaryonic )
According to current estimates, it is in space :
about 73% dark energy ; about 23% dark matter (hidden, non-radiant);
only
4% of ordinary matter " luminous"or absorbing, accessible to observation .

These values ?were obtained by a detailed analysis of the correlation of the LCDM model with extensive astronomical observations and sensitive measurements of intensity, spectrum and subtle fluctuations of relic microwave radiation (most recently by the WMAP and PLANCK space probes) .
   This global composition also has a strong gnoseological aspect. Until recently, we thought that by astronomical observation of glowing objects and absorbing clouds of gas and dust in optical, infrared, radio, X or gamma electromagnetic radiation, we would gradually find out everything about the universe, it would be just a matter of larger and more advanced telescopes and other instruments. It now turns out that in this way we are able to observe only about 4% of the matter in the universe. We don't know much about about 25% of dark matter yet and about 70% of dark energy is completely unknown to us. Thus, for the properties of the universe as a whole and for its evolution, stars, nebulae or galaxies are not the essential component of the universe. This luminous or otherwise astronomically observable matter in space is just the "tip of the iceberg", whose main mass is hidden from us. The universe is made up mostly of something we don't see andunknown . It's a depressing discovery of how little we know about the Universe ..!? ..

Brief and simplified final summary: Why " phantom " dark matter and dark energy ?
At the scales of galaxies and galaxy clusters, gravity appears stronger than would correspond to astronomically observed "luminous" or absorbing matter composed of electrons, protons, and neutrons. So gravitational dark-hidden matter is added .
   On the larger cosmological scales, where the universe expands, gravity, on the other hand, appears weaker than would correspond to the overall attraction of particles of ordinary and dark matter. Therefore, " dark energy "is added - a weak antigravity a force that acts against gravity and independently of matter. Current models of the universe require dark energy to explain the observed acceleration of space expansion resulting from measurements of supernova distances in distant galaxies (which appear to be more distant than they should be if the expansion of the universe did not accelerate).
   However, the issues of dark matter and dark energy are still being discussed, new measurements are being evaluated, and alternative options are being explored ..? ..

5.5. Microphysics and cosmology. Inflationary universe.   5.7. Anthropic principle and the existence of multiple universes

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

Vojtech Ullmann