Thursday, June 28, 2007

The Universe as a Computer II

I like to use the topic of my last post and tie it back to the very first post I made to this blog.

In my first post I claimed that life is defined as something that resists the 2nd Law of Thermodynamics. Now this is more of a poetic statement than a scientific one so allow me to clarify. The 2nd law is a statistical fact that must be true about any large collection of discrete things (such as atoms and molecules or even the items on top of my desk). It basically says that there is a higher probability of such collections moving to a state of increased disorder (entropy) than increased order. So when I say that life resists the second law I am really stating that life has the property of expending energy to resist decay. It does this, of course, at the expense of those things in its immediate environment (including other life forms) so that on the whole the 2nd law is not violated.

Returning to the ideas expressed in my previous post and the New Scientist article, I think it is safe to say that if any law must be true in all possible universes, the 2nd law is as good a candidate as you are going to get. Given this, one must not ask why our universe is so tuned to support life. Such a statement implicitly assumes life as that which is composed of atoms and molecules. My definition of life is much more general. It does not require that there be such a thing as electric charge, for instance. It only requires that there be:

1) Some collection of discrete things
2) Some way for those discrete things to interact (i.e. at least one force)
3) Some emergent complex dynamics that can arise due to combinatorial configurations of discrete things and forces (this probably means the force must not be too weak or too strong and that it vary with distance).

Given such a system, I believe there is a high probability that in the course of large spans of time a configuration could evolve that resists the second law through actions such as replication and metabolism. It may even be inevitable for a much larger class of systems than we can consider simply by permuting the laws or constants of our own universe. For example, there may be deserts of non-life in the immediate vicinity of our universe's configuration of laws and constants but a a majestic bounty of life forms in the space of all possible laws.

Here again computers provide a wonderful analogy. Imagine a piece of working software. Almost any mild permutation of that piece of working software will lead to a broken piece of software. In fact, the probability of a crashing a program by flipping a single bit in its executable section is fairly high. However, it does not follow form this observation that all working programs must look almost exactly like this particular program. There are an infinite number of amazingly rich and varied programs in the vast space of all possible programs. So too, I believe there are a vast richness of life forms in the space of all possible universes.

The law that entropy always increases, holds, I think, the supreme position among the laws of Nature. If someone points out to you that your pet theory of the universe is in disagreement with Maxwell's equations — then so much the worse for Maxwell's equations. If it is found to be contradicted by observation — well, these experimentalists do bungle things sometimes. But if your theory is found to be against the second law of thermodynamics I can give you no hope; there is nothing for it but to collapse in deepest humiliation. ”
--Sir Arthur Stanley Eddington, The Nature of the Physical World (1927)

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