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Naty1
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Paul Steinhardt and Neil Turok, Princeton and Cambridge, respectively, explain their new cyclic model of the universe in THE ENDLESS UNIVERSE, 2007. Like most on this forum, I took the big bang and subsequent inflation as the best explanation for how this universe got started. I now see these guys have a great alternative THEORY; Here's a quick overview.
Perhaps the biggest surprise is that by combining Heterotic M theory (with it's two parallel branes as envisioned by Witten and Horava), a cyclic universe, endlessly repeating, can be theorized in ten dimensional space between the branes. Dark energy plays three fascinating roles at different cycle stages: it speeds up the expansion rate, as currently observed, it acts as a stabilizer by acting as a shock absorber (analogous to an automatic pneumatic door close cylinder), and it decays over long periods, shutting itself off. Dark energy is dynamic! It means the universe does NOT have to expand forever.
One of the things I clearly don't understand is how the second law of thermodynamics (entropy must increase) is not violated. But they say:
So they envision a varying, evolving dark energy rather than patching together "inflation" at one stage with "dark energy" from another stage; and unlike inflationary theory, no fine tuning is required in their model, a big plus. So far, no experimental observations can detect any differences between their cyclic and the alternative inflationary model. I did not see any specific proposed experimental differences which could prove one model over the other.
Perhaps the biggest surprise is that by combining Heterotic M theory (with it's two parallel branes as envisioned by Witten and Horava), a cyclic universe, endlessly repeating, can be theorized in ten dimensional space between the branes. Dark energy plays three fascinating roles at different cycle stages: it speeds up the expansion rate, as currently observed, it acts as a stabilizer by acting as a shock absorber (analogous to an automatic pneumatic door close cylinder), and it decays over long periods, shutting itself off. Dark energy is dynamic! It means the universe does NOT have to expand forever.
One of the things I clearly don't understand is how the second law of thermodynamics (entropy must increase) is not violated. But they say:
It has been shown that a combination of branes and an extra dimension, with regular assists from gravity and dark energy can cause the universe to repeatedly replenish itself ...at regular intervals,,,without violating the second law of thermodynamics.
"..(Brane) collisions are unavoidable and fill the branes with hot but finite and nearly uniform radiation. ..Brane kinetic energy is converted to matter and radiation. Dark energy dominates before the bang, stretching the branes making them flat,smooth and parallel…
...A key assumption of the cyclic model is that dark energy can decay..smoothly and slowly. Dark energy is in mostly a “potential energy” form at the beginning of an expansion cycle and over time turns to a mix of potential and kinetic energy while its gravitational effect on space reverses…it acquires the properties of a high pressure gas that dominates the contracting phase of the cycle model and plays the same role of solving the homogeneity and flatness problems that inflationary energy does in an expanding universe….and a surprise is that the high pressure form of dark energy can acquire the scale invariant density variations before the final contraction which are of just the right scale invariant form…but almost opposite that of the inflationary model: slow contraction with high pressure dark energy versus rapid expansion with inflationary energy..."
So they envision a varying, evolving dark energy rather than patching together "inflation" at one stage with "dark energy" from another stage; and unlike inflationary theory, no fine tuning is required in their model, a big plus. So far, no experimental observations can detect any differences between their cyclic and the alternative inflationary model. I did not see any specific proposed experimental differences which could prove one model over the other.