Thursday, July 5, 2007

Does The Universe Start Every Trillion Years?

How did the universe begin? Did it have a beginning at all? These questions may have been the subject of speculation and debate for millennia, but they have not been widely discussed for the past forty years. Ever since the discovery of the cosmic background radiation in 1965, the overwhelmingly predominant view has been that our universe began about 14 billion years ago in a cosmic fireball known as the "big bang" and that it has been expanding, cooling, and evolving ever since. Recently, though, a small but growing number of theorists have begun to challenge this conventional belief and to pursue a radical new history of the universe. According to this new idea, there was a big bang, but this was not the beginning of space and time. In fact, in the version proposed by Neil Turok and myself, the big bang has occurred myriad times in our universe's past, repeating at regular intervals during which galaxies, stars, planets, and life form anew. The result is a "cyclic universe" in which cycles extend far into the past and into the future—and perhaps forever.

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A challenge to the reigning paradigm of cosmology may seem ill-conceived at this time. One reads almost daily how astronomers have been able to verify the expansion and cooling predicted by the big bang model with great precision all the way back to the first second after the universe's creation and have produced detailed portraits of the various stages of its subsequent development. It is important to understand, though, that all these astronomical observations do not prove that the big bang was the beginning. This notion comes from a theoretical extrapolation back to a time beyond what can be observed using the equations of general relativity, Einstein's theory of gravity that is used to calculate how the expansion of the universe changes with time. The big bang is formally defined as the moment when the equations say that the temperature and density of the universe became infinite, and it is impossible to extrapolate back any further. Concluding that this represents the beginning of all space and time is suspect, however, as Einstein himself once pointed out. Properly construed, finding that the temperature and density become infinite is an indication that the mathematical equations underlying general relativity have become invalid, not that this is when the universe began.

To understand what really happened 14 billion years ago, it is first necessary to have an improved, complete theory of gravity, probably one that incorporates the laws of quantum physics, which Einstein's theory does not, and a precise understanding of the behavior of matter at high temperatures and pressures. String theory is the leading candidate for such an improved theory of gravity, but it has not developed to the point where it can definitively answer whether the big bang is the beginning or not.
More at:http://www.seedmagazine.com/news/2007/07/a_cyclic_universe.php
Posted by Ajay :: 9:58 AM :: 0 comments

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