It's turtle's all the way down

New Scientist SPACE - Breaking News - 'Cyclic universe' can explain cosmological constant

I will expand on this post later.

Update: I think that the news@nature version of this story is much clearer than the New Sdientist one above. (It's a pity that news@nature links are not good for very long.) From the Nature story:

A bouncing universe that expands and then shrinks every trillion years or so could explain one of the most puzzling problems in cosmology: how we can exist at all...

In Steinhardt and Turok's cyclic model of the Universe, it expands and contracts repeatedly over timescales that make the 13.7 billion years that have passed since the Big Bang seem a mere blink. This makes the Universe vastly old. And that in turn means that the mysterious 'cosmological constant', which describes how empty space appears to repel itself, has had time to shrink into the strangely small number that we observe today.

In 1996, it was discovered that the universe is not only expanding but is also speeding up. The cosmological constant was used to describe a force of repulsion that might cause this acceleration. But physicists were baffled as to why the cosmological constant was so small.

Quantum theory suggests that 'empty' space is in fact buzzing with subatomic particles that constantly pop in and out of existence. This produces a 'vacuum energy', which makes space repel itself, providing a physical explanation for the cosmological constant.

But the theoretically calculated value of vacuum energy is enormous, making space far too repulsive for particles to come together and form atoms, stars, planets, or life. The observed vacuum energy, in contrast, is smaller by a factor of 10120 - 1 followed by 120 zeros. "It is a huge problem why the vacuum energy is so much smaller than its natural value," says Carroll.

The "cyclic universe" idea gives lots of time for the vacuum energy to have decayed to its current strength.

What I don't understand is how the collapse of the universe starts in this theory.

I still have a soft spot for Frank Tipler's Omega Point theory, expounded in detail in "The Physics of Immortality." How the cyclic universe idea fits into that, I am not sure. Tipler has not given up on his ideas either, as this relatively recent interview shows. Tipler believes that it is life itself that will cause the slow down in the current acceleration of the expansion of the universe:

So, if the observed acceleration were to continue forever, the Omega Point Theory would be refuted. But the expansion of life to engulf the universe is EXACTLY what is required to cancel the positive cosmological constant (a.k.a. the Dark Energy): as life expands outward, life willl require energy, and before the collapse of the universe provides gravitational collapse energy, the energy source will be the conversion of baryons and leptons into energy via electroweak quantum tunnelling, a process I describe in Section N (relativistic spacecraft) of the Appendix for Scientists. What I did not realize when I wrote my book a decade ago is that this electroweak process would also act to cancel any positive cosmological constant today, and that the net baryon number in the universe would REQUIRE such Dark Energy today.

The weakest part of Tipler's ideas is his suggested method of "resurrection" which (as I recall it) requires every possible version of every person in all of the "many worlds" being re-created by the super advanced computing thing-y that is God at the end of the universe. I had a thought while having a shower recently which seemed a better idea, but it is only a rough idea which I don't want to reveal for now.

I don't always have deep thoughts in the shower.

By the way, for those who may not know, the title of this post is explained at Wikipedia. (I am amazed at what you can find there now.)

UPDATE: The Nature article has links to some more detailed papers about the cyclic model. One I have read quickly is here. It does explain the model more clearly, even though there is much terminology there that is way above my head. Importantly, it seems that the model does not mean the universe shrinks to anything like an Omega Point (a total "Big Crunch") before the next bang happens. (There's some confusing stuff about black holes mentioned in the paper too.) Having read this, it made me realise I had something about this model some time ago in New Scientist.

It's all speculative fun, but at least does seem capable of some testing.