I started a new painting at Montgomery Hill park in East San Jose yesterday, next to Evergreen Valley Community College; the park is named after aviation pioneer John Montgomery who died when his glider, The Evergreen, crashed here in 1911. Sylvia suggests that I might add a painting of a UFO-type Flying Wing to a painting of this hill, like the one I wrote about in my novel, The Secret of Life. By the way the image above is an High Dynamic Range image fused from three exposures.

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As regular readers of this blog know, I’m currently interested in a new cosmological model called the Cyclic Universe and have posted on it before. The theory has been popularized by the scientists Paul Steinhardt and Neil Turok in their very readable book, The Endless Universe. The basic idea is that our cosmos consists of two parallel sheets of space which are called branes.

Every so often (one guess is every trillion years), the branes slam together, which fills them with energy that can be in some sense gotten for free from the boundless riches of the gravitational field. This space-filling Big Splat replaces the point-like Big Bang. While the branes are apart, they expand, with the galaxies moving apart over the years. And eventually they embrace once again. It could be that there are an endless number of cycles in the past and in the future, and that the spaces involved are infinite.

The theory of the Cyclic Universe is controversial and some well-entrenched phycisists such Stanford’s Andrei Linde (whom I interviewed for Wired , years ago) and his wife Renata Kallosh are fighting against the theory with what I would call excessive or even hysterical or persecutional zeal. You can (vaguely) follow the battle on the boffin-zone arXiv.org site (see this Wikipedia entry on arXiv to learn what arXiv is all about).

In my amateur outsider’s opinion, Steinhardt’s camp is right. LInde’s inflationary theory is falling apart. One of the nicest things favoring Steinhardt’s side is that the Cyclic Universe theory only requires for there to be one (two-braner) universe, whose parameters are what they are due to certain underlying mathematical reaons. The Lindean inflationary camp claims there are perhaps googolplex universes and the one we’re in just happens to have the particular values we observe. Hopefully some new measurements of the cosmic microwave background radiation can help resolve the dispute experimentally before too long.

In any case, I decided I might write some science fiction about the Cyclic Universe, and I sent Paul Steinhardt a few questions about the theory via email. He answered them and kindly offered to talk on the phone so that I could ask some follow-up questions. The following is a distillation of the email and phone conversations. As it’s been edited by me, any errors should be ascribed to Rudy rather than to Paul.

(R1) It would be cool if a story’s main character finds out that the Big Splat of the recolliding branes is going to be TOMORROW, rather than in a trillion years.

(P1) According to our current models, the soonest the next splat could really happen is in ten billion years. The reason is that it takes nearly ten billion years for the branes to move back together, and as soon as they start approaching each other we can notice subtle changes. So if the branes were on the road to colliding, we would have noticed by now.

(R2) What are the kinds of observational evidence that tell you the tenth-dimensionsal separation between branes is dwindling? As I understand it, our universe itself will continue to seem like it’s expanding, so how might we notice the impending splat?

(P2) You’ll like this: as the branes begin to move towards one another, nature’s fundamental “constants” begin to change— Newton’s gravitational constant, the fine-structure constant that controls the strength of electricity and magnetism, etc. And the rate of change picks up the closer the branes get. It would seem like the laws of physics are changing faster and faster.

In the earliest stages, the first thing we’d notice would be slight variations in the spectral lines between nearby atoms and distant (older) atoms. Later on, the changes would be more dramatic. We’d notice the positions of spectral lines in a single sample of matter changing over the course of a day.

Later on, atoms might get larger, but you’d have other effects mixed in as well. It would become in some sense hard to say what size anything is, as our definitions of size are ultimately based on the fundamental constants.

(R3) Presumably any humans would be destroyed at some point; our molecules would fall apart, and so on. And then, of course, you’d have the Big Flash. Might we have any hope of surviving to the next cycle?

(P3) We might draw on the fact that the collisions between the branes only occur in places where the universe is nearly empty — which is ALMOST everywhere. But where there are black holes, their gravitational field is strong enough that the collisions do not occur near them. It is as if the black hole pins the branes together in those places where they lie, and that means there are no collisions.

If an advanced civilization could figure out how to create/manipulate black holes so that they are surrounded by them but do not fall into them and if they could protect themselves from the intense radiation of the collision (about 10^10 times the temperature of the sun), they could survive into the next cycle. One problem here is that, because of all the stretching of space that occurs from cycle to cycle, surviving black holes are spread out to an enormous degree — so the chances are that, by the time the Splat approaches, there are no black holes within mankind’s observable horizon. So, even if a civilization managed to do this, they would not likely be anywhere we could see them.

(R4) I like that idea. Maybe a science-fictional civilization could manufacture black holes! Of course it would be tricky to surround our planet with them and not have the holes collapse together. Maybe they could be furiously orbiting in some chaotic dance.

On a slightly different topic, I’m intrigued by the notion of finding some way to perceive that space is infinite. But we’re to some extent limited by that big flash that happened 14 billion years ago. If the universe is spatially infinite, might there perhaps be SOME kind of signal that makes it through the haze of the Big Flash, reaching us from distances larger than the light horizon? I’m thinking, for instance, of gravitons that started on their way before the last Splat, or even from several Splats ago.

(P4) Yes and no. There would be gravitational waves produced just before the last bang that we could detect in the present universe. But the signal is very, very weak. And I suppose a civilization that existed just before the end could send that signal. But the bigger problem with the gravitational waves and photons from earlier cycles, is that their wavelengths will have been stretched by the expansion of space. The 14 billion light year diameter sphere that we see around us began as a region less than a meter across. A meter-long gravity wave from those times would now span the visible universe. There would be no way to construct an apparatus to detect it.

(R5) So there’s no way to pass information from one cycle to the next?

(P5) One very speculative idea is that you might store information inside a black hole. Although we think of the two branes as parallel with a tiny separation, in the neighborhood of a black hole, as I mentioned before, the two branes dimple out and touch each other, merging into a single brane. So there’s not going to be an big splat and radiation burst inside a black hole.

Of course the hard part about storing information inside a black hole is getting it back out. There’s an ongoing debate among physicists about whether information that goes into a black hole disappears for good, or whether it might be retrievable if the black hole spontaneously evaporates. Or perhaps if you scatter some object off of the black hole. In the scattering case, it may be that you need something like an encryption key to retrieve the information, that is, you have to in some sense know what the black hole has eaten so far.

(R6) In terms of a smooth motion, it seems like it would be nicer if the two branes could pass through each other, rather than splatting and rebounding. Is that a possibility?

(P6) Sure, I like to think of it that way myself, as then you feel less worried about the branes getting stuck together. Whether we say they bounce or pass through each other is really just a matter of how we set up our coordinate system.

(R7) Might there be life on the other brane?

(P7) We think of the other brane as probably not being something like a mirror of our world, so it would be a very different kind of place. One might not have atoms or particles there in the usual sense.

This entry was posted on Wednesday, May 14th, 2008 at 7:52 am and is filed under Rudy's Blog. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.