Friday, January 18, 2013

Cycles of Time

I've been reading Cycles of Time by Roger Penrose off and on since about Thanksgiving.  It's a very spotty book.  The main idea is interesting, but not convincing.  The organization is atrocious, with the refrain I'll explain this more fully in Chapter 3 repeated about 10 times too often, but the biggest problem with the book is that the level of detail, though greater in some chapters and lesser in others, generally falls into an awkward middle ground that will intimidate and confuse the general reader while simultaneously frustrating physicists and mathematicians that it is not specific enough to really evaluate. 

The basic problems which Penrose wants to address are

  • Why does the Second Law of Thermodynamics give time a direction -- and the same direction for everywhere in the universe, out to the most distant galaxies?
  • Did the Big Bang have a cause, and if so, what?
  • What is the ultimate fate of the universe?
  • What is dark matter?

Penrose addresses all of these issues by suggesting what he calls Conformal Cyclic Cosmology (CCC).  The gist of the idea is that in the extremely distant future, the so-called "Heat Death of the Universe" will take place, with nothing left but increasingly low-frequency photons, gravity waves (mostly from the supermassive black holes in the centers of colliding galaxies), and, ever-so-rarely, a remaining electron or positron (the antimatter counterpart of the electron).  In an almost empty world, there are fewer and fewer events; yet time is only meaningful as a measure between events.  Due to the accelerating expansion of the universe, an infinite amount of time corresponds to only a finite number of events.  After those events have happened, what then?  Does this question even have meaning?

The only way to really deal with such questions is with advanced mathematics, but a physical analogy (one that Plato would have liked) can help with the basic idea.  Imagine a kind of projector consisting of a bright lamp surrounded by a spherical shade.  Holes in the shade allow light to fall onto a nearby wall, making (perhaps) a star field, like in a planetarium.  If the holes in the shade are evenly spaced, though, they will not evenly cover the wall with "stars"; the "stars" will be denser towards the center, near the lamp, and sparser towards far from the lamp.  No matter how large the wall, though, only holes on one side of the spherical shade will cast light on it.  If all we could see were the "stars" on the wall, we still might realize that they corresponded to evenly spaced holes on the spherical lamp shade, and we might wonder if holes continued to be evenly spaced on the other side of the lamp shade. 

To translate this back to Penrose's topic, the "stars" would represent events -- the interaction of matter and energy -- and distances on the wall, measured from the point closest to the lamp, would represent time.  Distances on the lamp shade itself would correspond to "conformal time", and the two halves of the shade would be different "aeons".  

Penrose argues that the transition from one aeon to another produces what looks like, from one side, a Big Bang, and from the other side, a Heat Death.  He further claims that to make this mathematically tidy, 

  • it is necessary to introduce something that would behave like the mysterious Dark Matter;
  • it would solve the problem of the initial thermodynamic state of the universe after the Big Bang (with a high temperature but an overall low entropy that can subsequently increase, as necessary for the Second Law of Thermodynamics); and 
  • it would remove the need for Inflation in the first fraction of a second after the Big Bang.  

So far, so good; this seems to be wrapping up some loose ends.  He even claims that correlations in the Cosmic Microwave Background are suggestively similar to what might be expected from Conformal Cyclic Cosmology (CCC).  CCC also seems to require that electrons and other particles eventually become massless; on the one hand, there is absolutely no evidence for this, but on the other, it could take place over an inconceivably long time span, making the change of mass imperceptibly small over the last 13 billion years.  

Since it seems impossible to devise any experiment or observation that will add substantial support to CCC -- and without such, this is not really physics -- it's just mathematically sophisticated science fiction.  Good historical fiction stands in the same relationship to real historical research:  the research may inform the fiction; the fiction may contradict nothing which is known from the research; the fiction may be plausible and even give insight into the research; but the fiction is fiction and not research.

It is also worth mentioning that the real motivation for this book is obviously philosophical, not physical.  Penrose admits to finding the now-traditional narrative of the Heat Death of the Universe disappointingly dreary and hopeless; this is not the kind of story he or any of us want to believe.  At the same time, Penrose is very much a modern man, and modern man does not like how a creation at the Big Bang seems to imply a Creator.  This was Fred Hoyle's objection to the Big Bang (he coined the term in mockery) and his motivation for devising the Steady State Theory.  CCC differs dramatically from Steady State Theory in all the details, but the essence of it remains the same; as they said so often in Battlestar Galactica, "All this has happened before, and all this will happen again."  Both the Steady State Theory and CCC provide a model of physical reality without real beginning or real end, and certainly with no real purpose.

It is noteworthy that in a situation like this, it is the atheist who is painted into a corner by his dogma, not the Christian.  The Christian must believe that the universe has a Creator and a purpose, but he need not insist that these facts will be manifest in the structure of nature or its laws -- other than that nature should have structure and laws, which is one of the reasons modern science originated in a monotheistic culture.  The Christian would not be troubled if In principio erat Verbum, et Verbum erat apud Deum, et Deus erat Verbum were scrawled in great letters across the Cosmic Microwave Background, but neither is he troubled that it is not.  He is free to consider both possibilities.  The atheist has no such freedom.  He must eradicate every hint of a Creator, even if that means resorting to speculations about "times" before the Big Bang and "times" after a literally infinite count of centuries.

No comments:

Post a Comment