- A New Contender for the Theory of Everything
- Quantum bounce could make black holes explode
- Hubble Finds Evidence of Dark Matter Around Small Galaxies - Universe Today
- Further Information
Furthermore, as already mentioned briefly, the fact that the black body temperature of this CMWBR is very smooth — varies only by one part in a , over the whole sky, once peculiar velocity effects are neglected — indicates that the density of matter at that time varies only by one part in ,, too. Temperature variations code for density fluctuations. However, these tiny density fluctuations in the primeval plasma, which were first confirmed through the positive detection of fluctuations anisotropies in the CMWBR blackbody temperature by the Cosmic Background Explorer COBE satellite in , are very significant.
They are considered to be the seeds of later galaxy formation. Without them, there would be nothing from which galaxies, clusters and superclusters of galaxies, and therefore stars, could evolve. If the density of the universe is perfectly smooth, then it remains perfectly smooth, unless some mechanism generates density fluctuations. But, if there are already slight overdensities and underdensities in the primordial cosmic material at some point, whatever their origin, then as the universe expands these overdensities and underdensities can grow to form the rich astronomical structure we now behold.
A New Contender for the Theory of Everything
The way this happens is very simple — it is due to gravity. Consider cosmic overdensities. Because there is slightly more matter in the overdensity, there will be a slightly stronger gravitational attractive force tending to draw that overdense region together. Due to this that region will expand less rapidly than the surrounding universe. Thus, its density will increase further, and its expansion rate will decrease even further. Eventually, the overdensity, or perturbation as it is often called, will reach a point where it stops expanding altogether and begins to collapse under its own weight gravity again!
As it collapses it will fragment into thousands or even millions of knots, each of which themselves will collapse, forming a cluster of stars or galaxies, depending on how big the original cloud of gas was to begin with.
- Cosmology's Only Big Problems Are Manufactured Misunderstandings.
- The Excalibur Codex.
- Light Headed (Lesbian Erotica)!
- The world after the Revolution: Physics in the Second Half of the Twentieth Century.
- A Walking Tour of Ithaca, New York (Look Up, America!);
- The Pocket Gnome?
- You are here.
And, as these regions and sub-regions collapse, they will begin to spin faster and faster, due to the conservation of angular momentum just as a figure skater spins faster and faster as she draws her arms closer to her body. Thus, the overdensities discovered by COBE in the primordial cosmic plasma are essential to our understanding of how our universe came to be the way it is today.
However, this raises a more fundamental question: Where did these overdensities and underdensities — these perturbations — come from? How can they be explained? We need to account for them.
At the same time, there is another very puzzling coincidence which needs explanation. Thus, the last scattering surface we see, from which the CMWBR originates, is, from this point of view, tiled with about 50, little regions which are causally isolated from one another. But, if they are causally isolated from one another, how then can we explain how the temperature of the material in them is practically the same, as indicated by the CMWBR measurements?!
This is a very serious problem!
Quantum bounce could make black holes explode
In the first place, it happens that inflationary expansion generates a spectrum of perturbations in a well-defined way and freezes them into the primeval plasma until such a time that they can begin to grow, after the matter in the universe decouples from the radiation. Secondly, if inflation occurred, then the ancestral region from which our observable universe originated was much, much smaller just after the Big Bang than it would have been without inflation.
This simply means that with inflation the part of the universe from which our observable universe originated was causally self-connected beforehand, and therefore remained causally self-connected thereafter, eliminating the horizon problem. It can be demonstrated that, once a region is causally self-connected, it will remain so throughout an inflationary period. There is as yet no direct confirmation that such an inflationary period actually occurred. However, at the same time, there is no evidence that is inconsistent with such an epoch, and, what is most important, there is so far no other viable alternative for solving both the perturbation and the horizon problems.
Inflation is closely related to the vacuum energy we discussed earlier see above, II. The only way in which we can imagine inflation occurring is by the driving force of a positive vacuum energy, which can be shown to induce exponential expansion. It is relatively easy to see where such a vacuum energy might be generated in the very early universe.
Two strong possibilities are: 1. These in turn broke apart at somewhat lower temperatures. In both cases it is fairly easy to account for the generation of dominant vacuum energy in small, causally connected regions of space, which under its influence would then undergo extremely rapid expansion — inflation. At the same time, however, the universe must be able to exit from this rapidly expanding state, and in this exit it must somehow be reheated the exponential expansion is accompanied by supercooling!
This can be accomplished by having the vacuum energy rapidly dissipate into heat and particles. But this should not happen too rapidly! Before that occurs the universe has to expand enough to solve the horizon problem, and also to generate the perturbation spectrum. Providing a completely satisfactory model for the inflation mechanism is a very difficult, but probably not impossible, task, and has not yet be accomplished.
Besides enabling enough expansion and adequately explaining reheating, the scalar field which is usually invoked to provide the vacuum energy to drive inflation, must also be consistent with demands of particle physics and lead to density perturbations of the observed amplitude at the time of last scattering, when the finishing touches on the CMWBR were made.
- Useful info?
- Faith That Saved My Home: THE SECRET THAT SAVED MY HOME FROM FORECLOSURE;
- Glossary of Terms.
- Glossary of Terms - The Physics of the Universe.
- Superfluid Quantum Space and Evolution of the Universe.
Finally, the inflationary period which results must also lead to a density of matter in the universe which is consistent with the one we presently observe. If this were so, and if the density turns out to be less than critical, as is still possible, inflation would be ruled out. However, it has now been established that certain types of inflationary scenarios do not necessarily lead to a nearly critical-density universe. Thus, it seems that, though an inflationary epoch is quite difficult to incorporate consistently into an adequate overall cosmological model of our observable universe and the physics which governs it, it is still both possible and promising.
Of course, as already mentioned, it is very important to find ways of determining whether or not inflation did occur, particularly positive evidence for it. If it turns out that inflation could not have happened, then cosmologists will be very much in the dark as to how very important features of the universe — the nearly constant CMWBR temperature in all directions and the galactic and stellar structure we see — are ultimately to be explained. No other reasonable alternative to inflation has appeared on the horizon.
In the course of what has already been presented, we have seen that the CMWBR provides the strongest evidence for the principal characteristics of the universe as we know it. It is the observational cornerstone of cosmology. The CMWBR has been, and is being, very thoroughly studied and measured with increasing precision on many different angular scales. Thus, together with other corroborating evidence, it compellingly indicates that, as we go back farther and farther into the past with our observations, we encounter a succession of ever hotter, ever denser phases.
We shall discuss the Big Bang and what it means more thoroughly below. Beyond that point, the physics upon which the models depend — in particular, Einstein's theory of gravity and of space-time — breaks down. In order to investigate what really happens at those enormous temperatures, a quantum theory of gravity has to be used. As yet we do not possess a satisfactory one, though superstring theories look very promising see, for example, Greene, The next most important feature of the universe and its history the CMWBR convincingly demonstrates is that there was a time when all the matter in the universe was nearly homogeneous smooth — when there were no stars or galaxies.
Along with this is the nearly incontrovertible evidence that at even earlier times the matter in the universe was ionized, in perfect equilibrium with the radiation it contains. Therefore the matter was coupled to by electron scattering , and opaque to, that radiation. As already mentioned above, the almost featureless smoothness of the density at the time the CMWBR was last scattered further indicates that there must be a presently very large length scale on which the average density is constant — that the universe is almost spatially homogeneous on that scale.
Finally, the slight perturbations, or fluctuations, of the blackbody temperature of the CMWBR — as already indicated — signal the presence of similarly slight fluctuations in the matter density at that time, providing evidence for the beginning of the formation of structure in the universe. These temperature fluctuations are presently being extensively studied on all scales, and their varying amplitudes and the patterns of their varying amplitudes tightly constrain our models of the universe and the processes important in its evolution.
For instance, the preliminary indication that these perturbations are scale-invariant — that their strength does not depend on their size — is at least consistent with their origin in a very early inflationary episode. And the placement and strength of the fluctuations on a scale of about 1 degree, which are due to acoustic oscillations sound waves in the ionized gas at last scattering, helps us constrain the mass-energy density and the baryon density — of the universe — and indirectly the amount of dark matter and dark energy.
Moving from the CMWBR, another key piece of evidence in cosmology is the abundances of helium, deuterium and lithium. Let us concentrate on helium and deuterium here. But stellar processes can account for very little of that. And deuterium, which is a fragile isotope of hydrogen with a proton and neutron in the hydrogen nucleus, instead of just a proton , cannot be manufactured by stars, only destroyed. So where did all the helium and the significant trace of deuterium come from?
All the heavier elements, like carbon, oxygen, phosphorous, copper, iron, chlorine, uranium, etc. They add weight to our simple picture of the universe — the Big Bang picture — expanding, cooling and evolving from a very dense, very hot initial state. They also strongly support the detailed but very simple FLRW models of that early stage of the universe, together with the equilibrium thermodynamics and nuclear physics we employ to describe the matter and its interactions then.
Finally, it is important to mention that even more careful and detailed measurements and interpretations of this primordial abundance data, including that of lithium, give strong evidence that only a very small percentage of the matter in the universe can be baryonic. Most of it must be nonbaryonic, as we mentioned before. Unfortunately, those data cannot by themselves constrain what sorts of nonbaryonic particles constitute that dominant component.
That remains one of the great mysteries of physics and cosmology! Finally, there is the first really key cosmologically significant observation that was made — by E. Hubble and M. Humason — the systematic redshifts of distant galaxies, which indicate that the universe is indeed expanding. The farther away a galaxy is from us, the more its light is redshifted.
It should be emphasized here that the expansion of the universe we are talking about is not the movement of the galaxies and quasars away from us within the space that surrounds them and us, but rather the expansion of space itself. During inflation, as we have seen, this expansion of space is exponentially rapid.
It can thus involve the separation of galaxies from one another at many times the speed of light. This is all right — since Einstein's special relativity only forbids massive particles moving through space more rapidly than the velocity of light.
Hubble Finds Evidence of Dark Matter Around Small Galaxies - Universe Today
It does not say anything about how rapidly space itself may expand or inflate. In considering the three key categories of observations in cosmology — the CMWBR, the primordial abundances of helium, deuterium and lithium, and the systematic redshifts of distant galaxies — we should immediately notice that they are independent of one another and strikingly support the same general conclusions — that the universe is both expanding and cooling, and that the farther we go back into the past, the hotter and denser it was.
There are also other cosmologically significant observations, such as the degree of clustering in the universe — the strength of clustering between galaxies and between clusters of galaxies on different scales. This turns out to be a very important piece of information, as it constrains models of galaxy formation and sifts out some possible nonbaryonic dark matter candidates. Galaxy number counts with distance is another general type of observation, which can help us determine the density of baryonic matter, as well as the intrinsic non-cosmological evolution of galaxy populations.
One of the great problems in observational cosmology is separating out the effects of these intrinsic evolutionary processes from those of the expanding, cooling universe itself.
Both of these problems will probably only find answers in investigations of the very early universe, in the details of the processes which dominated the Planck epoch, or the extremely short period just afterwards — around the time when inflation may have occurred. Meanwhile, our most powerful-ever telescope, the Planck satellite, has scanned the universe on the largest visible scales.
What it has revealed is equally surprising. The whole shebang can be quantified with just six numbers: the age and temperature of the cosmos today; the density of the dark energy and the dark matter both mysterious, but simple to characterize ; and the strength, and slight dependence on scale, of the tiny initial variations in the density of matter from place to place as it emerged from the big bang.
None of the complications, like gravitational waves or the more involved density patterns expected in many models, appear to be there. Again, nature has found a simpler way to work than we can currently understand. The largest scale in physics—the Hubble length—is defined by the dark energy. By accelerating the expansion of the cosmos, the dark energy carries distant matter away from us and sets a limit to what we will ultimately see.
The smallest scale in physics is the Planck length, the miniscule wavelength of photons so energetic that two of them will form a black hole. While exploring physics down to the Planck length is beyond the capabilities of any conceivable collider, the universe itself probed this scale in its earliest moments.
So the simple structure of the cosmos is likely to be an indication that the laws of physics become simple at this extreme. What is exciting about this picture is that it requires a new kind of theory, one which is simple at both the smallest and largest scales, and very early and very late cosmological times so that it is capable of explaining these properties of our world. These gravitational waves are the long-sought markers for a theory called inflation, the force that put the bang in the Big Bang: an antigravitational swelling that began a trillionth of a trillionth of a trillionth of a second after the cosmic clock started ticking.
Scientists have long incorporated inflation into their standard model of the cosmos, but as with the existence of the Higgs, proving it had long been just a pipe dream. Astronomers say they expect to be studying the gravitational waves from mountaintops, balloons and perhaps satellites for the next 20 years, hoping to gain insight into mysteries like dark matter and dark energy. The cosmic Kahuna that now dangles before astronomers and physicists is understanding what caused inflation.
Antigravity may sound like a crazy science-fiction idea, but Einstein himself introduced the notion into physics. He later abandoned the cosmological constant, calling it a mistake, but it was resurrected 15 years ago when astronomers discovered that the expansion of the universe was speeding up because of the mysterious force called dark energy. As with inflation, the repulsion is part of space itself: The bigger the universe gets, the more powerfully it pushes apart, resulting in an exponential runaway expansion.
The recently discovered Higgs field could also behave in this way. It was by playing mathematically with a version of the Higgs field in that Dr. Guth stumbled on the concept of inflation. In the years since, dozens of versions of inflation have been proposed, like chaotic inflation, eternal inflation, slow-roll inflation, hybrid inflation, supersymmetric inflation and natural inflation, based on various kinds of fluctuating hypothetical fields.
Assuming they are confirmed and they have yet to be published in a peer-reviewed journal , the Bicep2 results eliminate most of these versions, including the Higgs, according to the Stanford physicist and inflation theorist Andrei Linde.