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NancyLebovitz comments on Harry Potter and the Methods of Rationality discussion thread, part 21, chapters 91 & 92 - Less Wrong Discussion

4 Post author: NancyLebovitz 04 July 2013 11:49AM

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Comment author: NancyLebovitz 05 July 2013 09:49:13PM 2 points [-]

This problem is fundamentally equivalent to time travel: if you can time travel, you can just go back and copy the original, and if you can reverse information-theoretic death, you can "resurrect" the visible universe at whatever time and put yourself in, essentially, a simulation of a prior time.

A person is a good bit smaller than the visible universe.

Comment author: linkhyrule5 06 July 2013 12:30:02AM 0 points [-]

Well, yes. But that's a practical/engineering problem. It is a useful and interesting fact that you can simulate any computer and execute any game by using a Conway's Game of Life Board of sufficient size; this does not mean that making a square-kilometer Board and hiring a few million people to update it is at all practical.

Comment author: Decius 06 July 2013 03:17:26AM 0 points [-]

The machine required to make the universe would be larger than the universe; the machine to make a brain or person need only be bigger than the person.

There's a qualitative difference at some point along the line.

Comment author: linkhyrule5 06 July 2013 05:48:26AM 0 points [-]

Not at all. Humans are much smaller than skyscrapers, but we can design, simulate, and build skyscrapers.

Comment author: Decius 06 July 2013 10:11:13PM 0 points [-]

I think you meant to say that humans can operate machinery which can do those things. The crane must be taller than the skyscraper, but we can't design a crane large enough to lift the counterbalance for a space elevator, much less actual stellar-scale engineering. There's a qualitative difference somewhere between a skyscraper and the altitudes of stable orbits.

Comment author: linkhyrule5 07 July 2013 12:44:20AM 0 points [-]

... No?

Intelligence and creativity can replace brute force. You don't need a crane taller than a skyscraper, you just need to get taller than the skyscraper somehow - a skycrane, a ladder made of constructor robots, a collapsible crane taller than a single floor that you carry from floor to floor, so on. You definitely don't need a crane for a space elevator, you use a rocket.

Comment author: Decius 07 July 2013 01:39:01AM 1 point [-]

Now build a skyscraper with a rocket; the two are qualitatively different. Making a person is qualitatively different from making a planet, which is qualitatively different from making a galaxy, which is qualitatively different from making a universe.

Comment author: linkhyrule5 07 July 2013 03:52:20AM 0 points [-]

... Okay, so we're talking past each other. Define "qualitatively different," please.

Comment author: Decius 07 July 2013 05:57:46AM 1 point [-]

Two things are qualitatively different if no amount of either one can serve as a viable substitute for the other; TNT and U-235 are qualitatively different explosives mostly because TNT does not generate neutrons.

The construction project that makes a planet be scaled down to make one person, and the project which makes a galaxy cannot be scaled down to make a planet even though creating galaxies involves creating planets: The process by which a galaxy is created cannot be scaled down to make a single planet.

Comment author: linkhyrule5 07 July 2013 08:53:45AM 0 points [-]

Oh, I see. Fair enough.

When I say that two processes are identical, I'm talking about a theoretical or mathematical identity, not a practical identity. If you can reverse information-theoretical death, then, at least in theory, time travel is possible; he same device may not be able to do both, but the one implies the other.