So this, in turn, tells us something about Physics: a universe that has people like us must obey some conservation-like laws; otherwise nothing would last long enough to support a process of evolution. We couldn't 'exist' in a universe in which things are too frequently vanishing, blowing up, or being created in too many places. In other words, we couldn't exist in a universe that has the wrong kinds of laws. (To be sure, this leaves some disturbing questions about worlds that have no laws at all. This is related to what is sometimes called the Anthropic Principle." That's the idea that the only worlds in which physicists can ask about what created the universe are the worlds that can support such physicists.)

The Certainty Principle

In older times, when physicists tried to explain Quantum Theory, to the public what they call the uncertainty principle, they'd say that the world isn't the way Newton described it; instead it. They emphasized 'uncertainty' - that everything is probabilistic and indeterminate. However, they rarely mentioned the fact that it's really just the opposite: it is only because of quantization that we can depend on anything! For example in classical Newtonian physics, complex systems can't be stable for long. Jerry Sussman and John Wisdom once simulated our Solar System, and showed that the large outer planets would stable for billions of years. But they did not simulate the inner planets - so we have no assurance that our planet is stable. It might be that enough of the energy of the big planets might be transferred to throw our Earth out into space. (They did show that the orbit of Pluto must be chaotic.)

Yes, quantum theory shows that things are uncertain: if you have a DNA molecule there's a possibility that one of its carbon atoms will suddenly tunnel out and appear in Arcturus. However, at room temperature a molecule of DNA is almost certain to stay in its place for billions of years, - because of quantum mechanics - and that is one of the reasons that evolution is possible! For quantum mechanics is the reason why most things don't usually jump around! So this suggests that we should take the anthropic principle seriously, by asking. "Which possible universes could have things that are stable enough to support our kind of evolution?" Apparently, the first cells appeared quickly after the earth got cool enough; I've heard estimate that this took less than a hundred million years. But then it took another three billion years to get to the kinds of cells that could evolve into animals and plants. This could only happen in possible worlds whose laws support stability. It could not happen in a Newtonian Universe. So this is why the world that we're in needs something like quantum mechanics - to keep things in place! (I discussed this "Certainty Principle" in my chapter in the book Feynman and Computation, A.J.G. Hey, editor, Perseus Books, 1999.)


Why don't we yet have good theories about what our minds are and how they work? In my view this is because we're only now beginning to have the concepts that we'll need for this. The brain is a very complex machine, far more advanced that today's computers, yet it was not until the 1950s that we began to acquire such simple ideas about (for example) memory - such as the concepts of data structures, cache memories, priority interrupt systems, and such representations of knowledge as 'semantic networks.' Computer science now has many hundreds of such concepts that were simply not available before the 1960s.

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