2008 : WHAT HAVE YOU CHANGED YOUR MIND ABOUT? WHY?

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Emeritus Professor of Physics and Astronomy, UC-Irvine; Novelist, Shipstar
Evolving the laws of physics

Richard Feynman held that philosophy of science is as useful to scientists as ornithology is to birds. Often this is so. But the unavoidable question about physics is — where do the laws come from?

Einstein hoped that God had no choice in making the universe. But philosophical issues seem unavoidable when we hear of  the "landscape" of possible string theory models. As now conjectured, the theory leads to 10500 solution universes — a horrid violation of Occam's Razor we might term "Einstein's nightmare."

I once thought that the laws of our universe were unquestionable, in that there was no way for science to address the question. Now I'm not so sure. Can we hope to construct a model of how laws themselves arise?

Many scientists dislike even the idea of doing this, perhaps because it's hard to know where to start. Perhaps ideas from the currently chic technology, computers, are a place to start. Suppose we treat the universe as a substrate carrying out computations, a meta-computer.

Suppose that precise laws require computation, which can never be infinitely exact. Such a limitation that might be explained by counting the computational capacity of a sphere around an "experiment" that tries to measure outcomes of those laws. The sphere expands at the speed of light, say, so longer experiment times give greater precision. Thinking mathematically, this sets a limit on how sharp differentials can be in our equations. A partial derivative of time cannot be better than the time to compute it.

In a sense, there may be an ultimate limit on how well known any law can be, especially one that must describe all of space-time, like classical relativity. It can't be better than the total computational capacity of the universe, or the capacity within the light sphere we can see.

I wonder if this idea can somehow define the nature of laws, beyond the issue of their precision? For example, laws with higher derivatives will be less descriptive because their operations cannot be carried out in a given volume over a finite time.

Perhaps the infinite discreteness required for formulating any mathematical system could be the limiting bound on such discussions. There should be energy bounds, too, within a finite volume, and thus limits on processing power set by the laws of thermodynamics. Still, I don't see how these arguments tell us enough to derive, say, general relativity.

Perhaps we need more ideas to derive a Law of Laws. Can we use the ideas of evolution? Perhaps invoke selection among laws that penalize those laws that lead to singularities — and thus taking those regions of space-time out of the game? Lee Smolin tried a limited form of this by supposing universes reproduce through black hole collapses. Ingenious, but that didn't seem to lead very far. He imagined some variation in reproduction of budded-off generations of universes, so their fundamental parameters varied a bit. Then selection could work.

In a novel of a decade ago, Cosmo, I invoked intelligent life, rather than singularities, to determine selection for universes that can foster intelligence, as ours seems to. (I didn't know about Lee's ideas at the time.) The idea is that a universe hosting intelligence evolves creatures that find ways in the laboratory to make more universes, which bud off and can further engender more intelligence, and thus more experiments that make more universes. This avoids the problem of how the first universe started, of course. Maybe the Law of Laws could answer that, too?