Tuesday, December 21, 2004

The Ekpyrotic Universe

Whether you believe the universe will be destroyed by The Big Rip, or in the five dimensional "brane-storm" of a Ekpyrotic Universe, it seems to me that rather than feel depressed about the possible never-ending end of the universe as we know it, we should be glad that science can give us this sort of info at all, especially 100 billion years in advance. It's a credit to man that we have scientific theory that reaches that far into the future, and if we can see the end approaching even 5 billion years in advance, why would anyone assume that we won't be able to change something or find some way to continue to exist. Personally, I thought the Ekpyrotic Theory was the most interesting.

The following description is from SPACE.com provided by the authors: (Justin Khoury, Princeton; Burt Ovrut, UPenn; Paul Steinhardt, Princeton and Neil Turok, Cambridge):
The Ekpyrotic Universe draws its name from the ancient Greek word ekpyrosis, meaning "conflagration" (disastrous fire or conflict). According to an ancient cosmological model with this name, the universe was created in a sudden burst of fire. The current universe evolves from the initial fire. However, in the Stoic notion, the process may repeat itself in the future. This, too, is possible in our scenario in principle if there is more than one brane and, consequently, more than one collision. We plan to discuss this possibility in future work, along with further speculations about what preceded the collision that made our present universe. Quantum effects cause the incoming three-dimensional world to ripple along the extra-dimension prior to collision so that the collision occurs in some places at slightly different times than others. By the time the collision is complete, the rippling leads to small variations in temperature, which seed temperature fluctuations in the microwave background and the formation of galaxies. We have shown that the spectrum of energy density fluctuations is scale-invariant (the same amplitude on all scales). The
production of a scale-invariant spectrum from hyper-expansion was one of the great triumphs of inflationary theory, and here we have repeated the feat using completely different physics. The building blocks of the Ekpyrotic theory are derived from Superstring theory. Superstring theory requires extra dimensions for mathematical consistency. In most formulations, 10 dimensions are required. In the mid 1990s, Petr Horava (Rutgers) and Ed Witten (IAS, Princeton) argued that, under certain conditions, an additional dimension opens up over a finite interval. Six dimensions are presumed to be curled up in a microscopic ball, called a Calabi-Yau manifold. The mind-bending concept does not involve multiple or parallel universes, as have been suggested by other researchers. Instead, Ovrut explains, the fifth dimension is all there, is out there, and embedded in it are multiple branes. Each end of the fifth dimension is bounded by an infinite brane. Our visible universe is one of those, and before the collision it may or may not have contained normal matter. At the other end of the fifth dimension is a brane with physics unlike ours. The branes in between, while they may contain matter, are not universes, and they do not resemble the brane we inhabit. There is no reason to assume, given this conceptual framework, that there are any other universes out there, Ovrut said. Turner, the University of Chicago cosmologist, believes textbooks a century from now will either read:A hundred years ago, people were so desperate to try to understand how to put it all together, they invented additional spatial dimensions. What were they smoking?" Or: "A hundred years ago, people were so provincial that in spite of much evidence that there should be extra dimensions they refused to accept it.


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