2 replies to this topic

[Futurist1000]

Interesting article by a top string physicist. (leonard susskind)

Let us begin with the DNA of a universe. What is it and why do we believe such a thing makes sense? String theory is the key. It supposes that at extremely small distances space is a complicated higher-dimensional manifold with many — typically six — tiny “extra” dimensions in addition to the three we see in everyday life. If we could look at the universe through a super-powerful microscope, we would see that it is composed of “Tinkertoy” elements called fluxes, branes, moduli, orientifolds (and more) all arranged on a tiny knot of higher-dimensional space called a Calabi–Yau manifold. The Calabi–Yau manifold is like the basic spine of the DNA molecule, and the other elements can be arranged and rearranged in a huge variety of ways; perhaps as many ways as a real DNA molecule.

Just as the details of DNA determine the biological details of a living organism, so the details of the fluxes, branes and other elements determine the properties of the universe. Again, the numbers are so staggering that even if the world as we know it seems extremely unlikely, there will be many ways of arranging the elements to make the constants of nature consistent with life. In particular, there will be many configurations in which the cosmological constant will be fine-tuned to 123 decimal places.

What about reproduction and mutability? Here is where the inflationary theory of cosmology comes into play. There is much evidence that during the earliest epoch of the universe space itself expanded exponentially. Inflation was a process in which space grew like the surface of an inflating balloon, but instead of thinning out, as the rubber of the balloon would, new bits of space were created to fill the gaps.

For the most part, the new bits of space had the same DNA as the regions surrounding them, but every so often a mutation occurred. A bit of space with new properties, new constants and a new value for the cosmological constant was created. According to standard general relativity, that tiny bubble grew and eventually became a new inflating universe, reproducing and mutating. This whole process is called eternal inflation and it produced a grand multiverse as rich and varied as the tree of life, each with its own laws of physics, constants of nature and elementary particles. Here and there a very rare branch was created that had the special properties that would allow complex life.

Another physicist gives a critique of the article.

Edited by Futurist1000, 13 July 2009 - 12:29 AM.

[Reno]

Sounds like a good book idea. Looks like the guy is making a bunch of assumptions and wrapping them up tight with a little fact.

Edited by bobscrachy, 13 July 2009 - 11:16 PM.

[Futurist1000]

I like this theory. The idea that the universe is sort of like endless inflationary bubbles. Some bubbles give rise to new bubbles that have differing laws of physics. Certain inflationary bubbles spawn more universes than others. So there is a sort of selection pressure. Maybe it looks like a fractal pattern of soap bubbles.

It also explains how physics could get more complex over time. You could start with a very simple thing (a calibi yau manifold), but it could develop increasing complexity. Eventually culminating in a universe like ours where the laws of physics are complex enough to support life.

Also I posted another speculation on my blog. Here's the excerpt.

I think the fact that our universe allows brains to evolve to the size they do may be an example of the anthropic principle. First, there is the rare earth perspective of life. Our planet is situated in a near perfect distance from the sun and is neither too hot nor too cold to sustain life. The gravitational pull of our planet may be at nearly the right level that allows a larger brain to evolve. Also our solar system is located far enough from the center of the galaxy so as to avoid excess radiation. These are only a few examples of our special situation in our own galaxy/universe. String theory predicts that our universe is merely one region out of a larger multiverse. In the multiverse there are different vacua that may have varying constants. A majority universes in the multiverse may not be able to sustain any life at all. Some universes may contain selfish replicators, but they never be able to evolve a nervous system or the capacity for sentience. Perhaps in an even smaller subset of vacua in the multiverse, a brain/nervous system can evolve, but maybe it cannot attain a complexity greater than that of a mouse's brain or an insect's or even less. There might be too many design constraints inherent to that specific universe for it to get any bigger. The physics of our own universe is perfectly suited to developing a human level intelligence.

Edited by Futurist1000, 17 July 2009 - 04:22 AM.