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Perplexed comments on Reductionism - Less Wrong

40 Post author: Eliezer_Yudkowsky 16 March 2008 06:26AM

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Comment author: Perplexed 07 November 2010 06:53:56PM 3 points [-]

If reality were computed in reverse chronological order, what differences would you expect to see?

Suppose our universe was produced by specifying some particular final state, and then repeatedly computing predecessor states according to some deterministic laws of nature. Would we experience time backward? Or would we still experience it forward (the reverse of the direction of the simulation) because of some time assymetry in the physical laws or in the entropy of the initial vs final states?

Everyone always assumes that the simulation will proceed "foreward". Is that important? I honestly don't know.

Comment author: imaxwell 08 November 2010 04:17:14AM 4 points [-]

You can go one step further. If folks like Barbour are correct that time is not fundamental, but rather something that emerges from causal flow, then it ought to be that our universe can be simulated in a timeless manner as well. So a model of this universe need not actually be "executed" at all---a full specification of the causal structure ought to be enough.

And once you've bought that, why should the medium for that specification matter? A mathematical paper describing the object should be just as legitimate as an "implementation" in magnetic patterns on a platter somewhere.

And if it doesn't matter what the medium is, why should it matter whether there's a medium at all? Theorems don't become true because someone proves them, so why should our universe become real because someone wrote it down?

If I understand Max Tegmark correctly, this is actually the intuition at the core of his mathematical universe hypothesis (Wikipedia, but with some good citations at the bottom), which basically says: "We perceive the universe as existing because we are in it." Dr. Tegmark says that the universe is one of many coherent mathematical structures, and in particular it's one that contains sentient beings, and those sentient beings necessarily perceive themselves and their surroundings as "real". Pretty much the only problem I have with this notion is that I have no idea how to test it. The best I can come up with is that our universe, much like our region of the universe, should turn out to be almost but not quite ideal for the development of nearly-intelligent creatures like us, but I've seen that suggested of models that don't require the MUH as well. Aside from that, I actually find it quite compelling, and I'd be a bit sad to hear that it had been falsified.

Interestingly enough, a version of the MUH showed up in Dennis Paul Himes' (An Atheist Apology)[http://www.cookhimes.us/dennis/aaa.htm] (as part of the "contradiction of omnipotent agency" argument), written just a few years after Dr. Tegmark started writing about these ideas. Mr. Himes' essay was very influential on me as a teenager, and yet I never did hear of the "mathematical universe hypothesis" by that name until a few years ago. In past correspondence, he wrote that the argument was original to him as far as he knew, and at least one of his commenters claimed to also have developed it independently, so it may be a more intuitively plausible idea than it seems to be at first glance.

Comment author: Perplexed 08 November 2010 05:54:02PM -1 points [-]

at least one of his commenters claimed to also have developed it independently, so it [Tegmark's idea] may be a more intuitively plausible idea than it seems to be at first glance.

I'm pretty sure that the idea has occurred to just about everyone who has wondered whether the meanings of the intransitive verb "to exist" in mathematics and philosophy might have anything in common. Tegmark deserves some credit though for writing it down.