Friday 13 February 2004

Pic of the day: And I think I'm not a Sim, but we really can't know, can we?

The real matrix

I read a somewhat disturbing article in Scientific American, January 2004. The article was about Loop Quantum Gravity. (For a brief introduction to LQG, see Wikipedia article.)

The way the article in SA spins it, this theory seems to have strengthened its position at the expense of its competitor, the more famous String Theory, which is seen as multiplying entities beyond necessity with its 10+ dimensions and rows of hitherto unobserved elementary particles. (In all fairness, the Superstring Theory pretty much tries to be a Grand Unified Theory of everything, while Loop Quantum Gravity simply tries to combine the seemingly mutually exclusive theories of relativity and quantum physics.)

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The silver bullet of the Loop Quantum Gravity theory is the calculation that space and time are not continuous, but come in discrete packages at 1 Planck unit. So a unit of space can be no smaller than 1 cubic Planck length, and a unit of area can be no smaller than 1 square Planck length. Something similar applies to time. Basically the universe has clock ticks, like a computer. And it has a countable (albeit immensely large) number of space unit. (Well, the observable universe has. If the universe beyond our line of sight is infinite, then it is not computable. Otherwise it is, given a sufficiently powerful computer. Of course we are talking a universe-sized computer here, not something you have in a lab.)

The philosophical and theological implications of this theory are staggering. It certainly does not prove or even imply that the universe is a computer program. But it basically says that we will never be able to know whether it is or not, no matter how advanced our technology. (The article wisely makes no mention of any of this. From the mention of discrete units of space and time, the article ends and I take over.)

What it says is: There is no provable or disprovable difference between "I think, therefore I am" and "My thought processes are being modeled, therefore I am a model". A computerized approximation of the universe will be indistinguishable from the universe, given sufficient computing power. With continuous spacetime, we would be able to reduce this to the absurd as our technology improved and we could measure ever smaller units of space and time. With granular spacetime, we get closer and closer to observing a computable universe instead.

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It is important to realize that according to LQG theory, these units are not units of the observers choosing, like the inch or the meter. They are inherent units of the universe itself. The universe is built like this. It is inherently granular, albeit very fine grained. Time actually moves in ticks, albeit very small ticks. These grains and ticks give rise to the discrete packages of energy seen in quantum physics. Quantum physics give rise to ordinary physics through emergent behavior, basically averaging enough of the uncertainty so that the large-scale result is certain.

However, as I said, if the universe is being computed then it is done by a universe-scale computer. We do not live in a virtual reality made by intelligent machines that have enslaved humanity. Due to the sheer scale of these things, it is extremely unlikely that a cosmic computer could ever be made by a living organism. Not a global civilization, not a galactic civilization, not a civilization spanning a large clusters of galaxies. None of these would be even close to being able to make a cosmic computer. Basically an entity able to do so would be well into the realm of theology. There is no way we could understand such an entity even if it existed, and we would also be an unimaginably small part of the whole. So there is no reason to imagine that we are being played "The Sims" with either.

Even so, it is a pretty big bang as far as paradigm shifts go.