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Saturday, December 25, 2010

Cosmology and the Allegory of the Cave

Chapter 5F

Cosmology and the Allegory of the Cave

As I mentioned in the previous posting, the more details we know about the universe the more hints we benefit from in trying to devise new theories to explain its origin and its evolution. And of course we have seen already that space physics and space astronomy are essential if we are to attain a worthwhile understanding of the nature of the universe (cosmology), for much of the critical information is transmitted in wavelengths that our atmosphere keeps from Earth-bound instruments. And to those two space sciences we should add astro-chemistry, for this other science is necessary if we are to understand the composition of the galactic medium, for example.

Furthermore, it is not plausible to say that we have a complete idea of the nature of the universe unless we have a far better understanding of phenomena such as quasars and black holes which obviously may have great consequences for our theories of gravitation, for what decent idea of the universe would ignore the gravity that holds it together? Nor is it plausible to hold onto certain ideas of the origins of the universe without the guidance of reliable theories of gravitation. As we will see below, space science is essential not only for the study of violent events like quasars and black holes but for the more general task of transforming our theories of gravitation. Thus, since unification schemes must deal with questions of the origin and evolution of the universe, space astronomy is clearly fundamental science by even the narrowest and strictest of criteria. Much rides on the telescopes that our rockets may take into the heavens.

To summarize this point, since cosmology is essential to the completion of the program of unification in physics, it is also essential to the pursuit of fundamental physics, even by notions of pre-Dark-Matter-Dark-Energy days. Thus even if we accept the most extreme view, that particle physics is the most fundamental science, it seems that space science is unavoidable, and therefore just as fundamental. Our investigation of the microcosm eventually takes us to the stars.

Of course, there is the possibility that all present unification schemes are entirely misguided. But if that is so, space astronomy will be particularly helpful in pointing to areas of physics where new directions would be fruitful. Without that help our models of the evolution of the universe will remain far too speculative to determine the strengths and weaknesses of any potential unification of the basic forces of physics. This point supports the claim made in Chapter 3 to the effect that space science helps transform theoretical science. Science needs to rub against the world, for such friction polishes and sharpens the rough guesses that humans make about their universe.[1] And as we can see now, at the edge of the universe we find the end of a journey through space science that begins here and brings us back.

But what if we give up on the unification of the basic forces of physics? Even so space science would be as fundamental as Earth-bound physical science. One reason is the opportunity to develop several aspects of the two main physical theories of this century: quantum physics and general relativity. I will leave general relativity for a section of its own later in the chapter. As for quantum physics, it explains micro-phenomena and is thus bound to come to terms with the first few moments of the origin of the universe, when the universe was so small that quantum events would have profound effects upon its subsequent evolution. Even without the goal of unification, different ideas on the nature of fundamental particles, their creation and their ways of interaction, could be refined so as to make distinct predictions about how the universe should have turned out. In general, to the extent that microphysics decides what processes underlie the macro-phenomena of the large universe, then the study of those phenomena ought to serve as an independent testing ground for our theories of the small.

Another reason is that the possibility of studying black holes and other strange objects presents extraordinary opportunities to challenge all of physics. It has been said that in black holes all of physics comes to an end. The reason is that in a runaway gravitational collapse, which is presumably what exists in a black hole, matter and energy disappear into a single geometrical point at the center of the black hole. This point, called a "singularity," obviously contains no space. And it contain no time either since, as we will see below, time slows down in the presence of a strong gravitational field. Where the field is practically infinite, time simply does not "happen." But the laws of physics make no sense outside of time and space. Thus we seem to have a situation in which matter-energy is no longer subject to the laws of physics as we can presently conceive of them. These are strange possibilities indeed, and there is nothing like the serious consideration of strange possibilities to loosen the grip of entrenched ideas.

Moreover, another serious complication arises. As the matter and energy in the black hole collapse towards the singularity, a moment comes when they are compressed into a volume so small that quantum effects begin to dominate. This would mean, for example, that the account of the previous paragraph could not be right, since the Heisenberg uncertainty relation between position and momentum would rule out any deterministic prediction about the behavior of matter in such a small volume. Indeed, it could be thought that a similar problem may show up at the beginning of the universe. The result is that we seem to have a conflict between the two main theories of physics: general relativity and quantum physics. A future compromise, quantum gravity, has been the goal of many theoretical physicists, particularly string theories, but without any success so far.

To pass up the opportunity to enrich our cosmology so immensely would be far more than folly for the scientist who wishes to understand the universe. In the Republic, Plato describes a group of men who are chained facing the back wall of a cave. By the entrance to the cave there is a road, and beyond the road a fire that projects on the wall the shadows of the objects that pass in front of the cave. The men spend their time trying to determine what those objects are from the shapes they see before them. One day a man is set free and turned around. In reaching the outside world he is at first taken with fright, but soon he adapts to the sunlight and marvels not only at the objects whose shadows he had seen before, but at the many that had not even crossed his imagination, let alone his line of sight. And the question is, would this man go back voluntarily to his chains in the cave? Would he be satisfied with the guessing games based on what he now knows are mere shadows?

In a certain sense the atmosphere and the gravity well of our planet have been our cave and our chains. One of the great space pioneers, the Russian rocket theorist Tsiolkovsky spoke of the chains of gravity and spent his life trying to break them. He and the other space pioneers have made it possible for us to come out and see the universe as if for the first time. Perhaps even then the universe will remain a complete mystery to us. But can we as cosmologists afford to reject the chance they offer to us and take back our place in front of the cave wall?

[1] This is a highly objectionable aspect of String Theory: that it makes no contact with the universe we actually observe. Perhaps it will eventually, though.

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