THE UNIVERSE AS A WHOLE
By Roland Watson
I will now move on to consider the universe in its entirety. This brings us to the study of what is known as cosmology.
By way of introduction, we have seen that the universe is believed to have begun in a Big Bang. Further, under the account provided by the cosmological theory of "inflation," this was followed by a brief, but extremely rapid, period of expansion. And, the universal expansion continues today, although at a much slower rate.
The arguments for inflation are strong, and it is generally accepted to be true. What this means is that while nothing within the universe can exceed the speed of light, the universe itself, as a whole, apparently did so during its inflation. This implies that during this period, gravity was not operative. It only came into being, perhaps as a consequence of another symmetry breaking, at the end of the inflationary period. Subsequently, and through this, the speed of light - inside the universe - was established as the velocity limit.
However, all of this raises the question: why is the universe expanding? None of the earlier mentioned forces account for this. Indeed, one would assume that there is also another force responsible for the universe's initial explosion, and subsequent expansion.
The end of the universe?
A number of different long-term outcomes for the universe have been proposed. The first is that it will continue to grow until at an infinite point in the future it approaches zero density. This is the "open" theory of the universe, and it is also linked to the idea that the universe, in its entirety, is "flat." What this means is that the density of the matter in the universe is just below the level that would be required to initiate a gravitational collapse.
The second possibility, that of a "closed" universe, applies if the rate of universal expansion is slowing. Under this view, the expansion eventually will end, and this will be followed by a contraction back to a singularity. But, the likelihood of such a contraction has not been demonstrated, since the universe does not appear to contain enough matter to cause it. It is for this reason - among others - that there is a search for dark matter. Also, if the universe did stop expanding, at the actual point before it began to contract, it would be static. But this, seemingly, is inconsistent with energy's dynamic nature, and also the provision from relativity theory that there can be no absolute non-motion.
This view is also in conflict with the astronomical evidence that suggests that the rate of expansion is actually increasing. However, if inflationary theory is correct, it has already slowed dramatically. The process envisioned is of a very brief explosive expansion, followed by a deceleration to a much more sedate rate of expansion, but which deceleration has now been reversed such that the rate of expansion is speeding up.
A final possibility is that, quoting Stephen Hawking, "the universe is not infinite in space, but neither does space have any boundary. Gravity is so strong that space is bent round upon itself." In other words, if you could travel across the universe, you would eventually return to the same spot - without ever reaching an "end." This view is also associated with the idea that the universe will eventually stop expanding, and then contract back to a singularity again. However, current evidence suggests that it never will stop expanding, and that it is, or will become, infinite in time and space.
The difficulty, of course, is in evaluating the rate of expansion, and any change in this rate over time. For the former, the shifting of the spectrum which is observed for the light which comes from distant galaxies, enables the calculation of the rate of relative motion between such galaxies and our own. Indeed, this was actually how we learned that the universe was expanding. The light from other galaxies is shifted towards the red end of the spectrum. They are all moving away from us.
However, for the latter - the change in the rate of universal expansion - our observations, even over the entire history of astronomy, still amount to a single snapshot relative to the universe's age. But, experimental evidence regarding the background microwave radiation that fills the universe, which is a remnant of the Big Bang itself, has suggested that space-time cannot be completely curved onto itself, and that there will never be a Big Crunch. The universe is flat, and open, and it will expand forever.
The universe is believed to be about fourteen billion years old. This is the duration of its expansion so far. Said another way, though, the universe is young. One way to grasp this is to consider our galactic disk, which is estimated to revolve one complete turn every two hundred million years. Subtracting a billion years to allow sufficient time for the galaxy to have formed, this means its total number of rotations, so far, is about seventy. It doesn't seem to be such a large number. One could easily imagine that the galaxy's structure could stay intact through a far greater number of revolutions; indeed, that it has just begun to spin.
As to the universe's current size, the most distant objects observed, quasars, which actually are one of the main sources of evidence about its age, range up to fourteen billion light years away. We know the universe has to be at least this old, to allow such distant light sufficient time to reach us. One light year is approximately six trillion miles, so fourteen billion light years is roughly eighty sextillion miles.
This is a first approximation of the scale of the universe, but it is imperfect. Consideration must also be given to its shape, which has been likened to an expanding balloon, as the explosion of the Big Bang continues to blow out in all directions. All matter is viewed as being on the edge of this expansion.
Further, and as I just said, everything is moving away from everything else. Like the increasing distance between two points on the surface of a real balloon, as it is blown up, all matter is moving away from all other matter, as the universal expansion continues.
This, in turn, raises a number of problems. First, what is inside the universal sphere or balloon? Is it a void, left behind? Or, in some way involving the curvature of space - some way that does not conflict with the fact that as far as the distribution of matter is concerned space is flat - is there only the edge of the sphere, the expanding edge of the universal envelope?
Calculations of universal scale get involved in all sorts of complexities. For example, the light from the quasars is not only coming from up to eighty sextillion miles away; it also is up to fourteen billion years old. Where are the quasars now? How much have they moved; or, do they still even exist?
As the universe expands, it further is undergoing "entropy," or seeking a less-ordered state. This results from chance disorganization, and also from reorganization that occurs in reaction to relative differences in temperature - and therefore also in motion - through which such relative differences are eliminated. For instance, if you mix a glass of cold water with one that is hot, the combination will move to an average temperature. In this case, the order represented by the two separate systems, in distinct states, is eliminated.
The only exceptions that exist to universal expansion, and entropy, are gravity, and life.
The source of universal flux
Also, we should not overlook one other implication of the universe's expansion, which is its underlying dynamism. The universe is in flux. Its component systems may be seeking equilibrium, but even in the rare cases where this is achieved, change remains a constant. One could take the view that this flux is the composite effect of all of the forces and principles that I have described, and their interactions with energy. However, you can also look at it in reverse. Such flux actually constitutes an underlying tension from which everything else derives. Without it, the universe would be dead.
What is the source of this tension? Could it result from the interaction between universal expansion - the force behind the Big Bang, and gravity?
Related to this, the expansion of the universe has implications for our understanding of time. Time appears to be unfolding in parallel with universal expansion. Some physicists even believe that time moves forward because the universe is expanding, and that if the universe ever contracts, its direction will reverse as well.
The end of time
Another view, though, is that time is a direct consequence of entropy. I might add, this reaffirms the perspective that space-time does not have an independent existence. When the universe reaches a state of complete entropy, when there are no heat or motion differentials left to trigger activity between particles of matter, time will cease.
The universe is a collection of energy, but such energy takes many forms. The initial source of universal energy was the Big Bang explosion, but through a process akin to symmetry breaking this undiluted, or pure energy, rapidly evolved into the variety of types that we observe today. A basic distinction, though, is between kinetic and potential, the energy involved in motion and that which is locked up in matter: that is matter. Of course, these forms do interact. The one moves the other. Also, as in an atomic explosion the energy of motion can cause the energy of matter to release itself, to become, partially at least, energy of motion as well. But, universe-wide there is a limit to such interactions, and this is defined by entropy.
The energy of motion represents "available" energy. But as this energy is disseminated, and relative differences are eliminated, it is in a sense used up. The energy still exists - the conservation of energy still holds, but it is no longer able to interact. All available energy is averaged out. It ends up evenly distributed. It evolves into - it will evolve into, over a fantastically long period of time - an unorganized fluid, with a consistent temperature and no motion, in which all of the energy locked up as matter will itself be evenly distributed. Indeed, the proof that such a state is not empty space, that it contains - or will contain - the unorganized remnants of all available energy, is that it should have a positive temperature. It should be above, if only slightly, absolute zero.
Such a state will constitute the end of time. In addition, it will represent the end of the universe's life. All space will be dark. It will be the one true, and final, equilibrium.
A final question is: will the end of time also signify the end of the expansion of space? If all available energy is used up, there seems to be no reason why it would continue to manifest space-time. However, if space and time are distinct from matter and energy, it is possible that another symmetry breaking will occur - between space and time. Said another way, if the expansion does cease, what will cause it to stop?
In the next article, I want to consider paradox. The multitude of difficulties and questions that I have described reflect different types of paradox. In there a deeper significance that we can understand from this?
© Roland Watson 2015