I do not find the article on 3D space terribly convincing either—and I am the author of it—so I would have to be understanding if you don’t. It is generally my policy, though, that my articles reflect how I think of things at the time I wrote them and I don’t remove them if my views change—though I might occasionally add notes after. I do think that an anthropic explanation still works for this: I just don’t think mine was a particularly good one.
It’s a difficult topic. Life (e.g. self-replicating CA) exist fine in 2, 3 and 4 dimensions, though there is still the issue of evolving intelligence. Some say that three dimensions is the only number that permits you to tie knots, though the significance of knots is unclear. I am not convinced that 3 is terribly special—and I’m not sure we know enough about physics and biology to coherently address the issue yet.
With physical laws of character similar to ours (not a CA), though, there are further reasons to think life requires 3 space dimensions (and 1 of time).
I don’t really see how you can build an anthropic argument out of that, though. The idea that if you make a radical mutation in one aspect of a life-supporting universe, then it no longer supports life is probably not particularly unusual. For example, if you make the game of life 3D using the same totalistic rule then it no longer supports life either. That is just a consequence of dead universes being more common than living ones, and doesn’t have anything to do with there being something special about the dimensionality of our space-time.
And cellular automata don’t select for intelligence, so it is at least reasonable to conjecture that most observers evolve under physical laws of character similar to ours (and therefore, by the orbit stability argument, in three dimensions of space).
I do not find the article on 3D space terribly convincing either—and I am the author of it—so I would have to be understanding if you don’t. It is generally my policy, though, that my articles reflect how I think of things at the time I wrote them and I don’t remove them if my views change—though I might occasionally add notes after. I do think that an anthropic explanation still works for this: I just don’t think mine was a particularly good one.
It’s a difficult topic. Life (e.g. self-replicating CA) exist fine in 2, 3 and 4 dimensions, though there is still the issue of evolving intelligence. Some say that three dimensions is the only number that permits you to tie knots, though the significance of knots is unclear. I am not convinced that 3 is terribly special—and I’m not sure we know enough about physics and biology to coherently address the issue yet.
With physical laws of character similar to ours (not a CA), though, there are further reasons to think life requires 3 space dimensions (and 1 of time).
Max Tegmark: On the dimensionality of spacetime [PDF]
I don’t really see how you can build an anthropic argument out of that, though. The idea that if you make a radical mutation in one aspect of a life-supporting universe, then it no longer supports life is probably not particularly unusual. For example, if you make the game of life 3D using the same totalistic rule then it no longer supports life either. That is just a consequence of dead universes being more common than living ones, and doesn’t have anything to do with there being something special about the dimensionality of our space-time.
And cellular automata don’t select for intelligence, so it is at least reasonable to conjecture that most observers evolve under physical laws of character similar to ours (and therefore, by the orbit stability argument, in three dimensions of space).
I think Max Tegmark made an argument for that—and I find it more convincing.