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03/20/2014

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Brian

In regard to the statement "...in order for reality to be a digital peer-to-peer simulation, reality must, at the very least, be digital", I don't see quantum gravity as being necessarily helpful.

Just because gravity is quantized, doesn't imply that space is quantized. I would think that wave-functions will still be "fuzzy", and on their own can spread out in seemingly continuous space.

Also, I'm surprised this observation didn't support the anthropic principal. Interesting. I personally am uncomfortable with scientists invoking this apparently untestable hypothesis.

Marcus Arvan

Brian: Thanks for your comment.

On your first worry: if gravity is quantized, then space-time *must* be quantized -- for gravity just is the metric which defines space-time (i.e. it *is* space-time). The idea that space is something beyond gravity and the objects in it is precisely what the Theories of Relativity refute. Space-time *just is* that stuff, so if the stuff is quantized, all of space-time is quantized.

On your second worry: the anthropic principle as physicists use it *is* falsifiable. Physicists have a testable conception of "naturalness" -- i.e. what it would be for the universe to be fine-tuned or not. Very roughly, they do this in terms of different parameters, and how naturally they fit together.

So, for instance, the "hierarchy problem" in the Standard Model of particle physics is that there appears to be no natural physical explanation for why there is such an incredible difference between the masses of different particles, as well as the enormous difference between the Planck mass. The Standard Model also has something like a couple dozen independent parameters that lack any natural explanation. Physicists will tell you that these things not only didn't have to be this way: the way these various parameters are tuned, and essentially disconnected from one another (rather than emerging naturally from deeper laws), is very unnatural.

Here's an analogy. Suppose it turned out that Ptolemy was right, and instead of simple elliptical orbits, heavenly bodies orbited around incredibly fine tuned *epicycles* nested on circular orbits. This would be astounding! Each heavenly body's orbit would "obey its own laws", without any deeper law explaining why.

This is roughly the situation in physics, and because it is so unnatural -- or gerrymandered -- it cannot be easily explained in terms of any *natural* phenomena.

Anyway, as physicists understand it, these anthropic considerations can be tested. If the universe turns out to be natural -- to have deeper explanations unifying these apparently disconnected "fine tunings" -- then, from a physics point-of-view, that confirms anthropic reasoning. If, however, the Universe turns out the way it appears to actually be -- incredibly finely tuned, with no deeper explanation(s) of why -- this is taken as a kind of disproof of anthropic explanation. Why? Because, again, it would follow that the incredible fine-tunings would have *no* natural explanation.

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