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shminux comments on Debugging the Quantum Physics Sequence - Less Wrong Discussion

32 Post author: Mitchell_Porter 05 September 2012 03:55PM

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Comment author: shminux 06 September 2012 04:42:39PM 1 point [-]

The QM sequence was a case study.

Ah, I see. Yes, it was a case study, just not a good one, given the controversy that distracts from the point. There are better examples.

The implementation of the simulation is classical digital. The simulated world is quantum, just like you said.

I don't follow. What's the difference between the implementation and the simulated world?

Comment author: Luke_A_Somers 06 September 2012 08:58:13PM *  2 points [-]

In two simulations I ran once, the 'world', such as it was, was an FCC lattice each containing one of 2 kinds of atom, or vacuum, and the dynamics were ruled by a Monte Carlo algorithm.

It had two separate implementations, with very different MC engines. One was in Fortran77 and used the Metropolis algorithm; another was in C++ and used the Bortz-Kalos-Lebowitz MC algorithm. Both of these had effects on how dynamics progressed. They would be detectable by examination of the state of the world.

But which computer I chose to run it on would not. I put it on a Solaris machine; I put it on a Linux machine. the results were bitwise identical.

If you scale this notion up into the point that it could contain agents, and let these two swap save-files every so often, an agent inside could in principle tell which program was running at that time. But no agent could tell whether I'd changed from a Solaris box to a Linux box. So, the Metropolis vs BKL distinction is an element of their physics. The Solaris vs Linux distinction is not.

Accordingly, if we're in a simulation, and the simulation is pure quantum, but it's implemented in classical computers, it's not wrong to say MWI is correct. The referent is the implementation of quantum mechanics in those classical computers.

Comment author: shminux 07 September 2012 03:26:34AM *  0 points [-]

Accordingly, if we're in a simulation, and the simulation is pure quantum, but it's implemented in classical computers, it's not wrong to say MWI is correct.

OK, I think I understand and mostly agree. Though I would make a weaker, interpretation-agnostic statement: "it's not wrong to say QM is correct". I don't think that it invalidates my original point, however, that it is likely possible to simulate human-like agents discussing rationality using, say, Newtonian physics, and such agents will have no need for QM.

Comment author: Luke_A_Somers 07 September 2012 02:39:21PM 0 points [-]

Well, yes, but I don't see how that has anything to do with the QM sequence.

Comment author: shminux 07 September 2012 04:15:12PM *  1 point [-]

Again, my (and others') long-standing point has been that the QM sequence as a case study is not a good one. Given that the same rationality-related arguments can likely be made in a world without QM, and that the MWI discussion sparks too much controversy that detracts from the point (whatever it might be), it stands to reason that a different case study would serve this goal better (it can hardly be worse).

Comment author: Luke_A_Somers 07 September 2012 04:55:00PM 0 points [-]

If the case-study pertained to banana custard stands, certainly rationality-related arguments would be devisable in a world without banana custard stands.

That aside - MWI being controversial is a fair point, which is why I didn't have anything to say about it in the post with the simulation analogy. I suppose I should have explicitly acknowledged that then, so you would not feel the need to raise it again. Sorry about that.

Comment author: shminux 07 September 2012 06:23:37PM 0 points [-]

BTW, I hope you are not the one who immediately downvotes almost all my QM-related posts.

Comment author: Luke_A_Somers 07 September 2012 11:32:56PM *  2 points [-]

I am not. I have a batch of -1 posts elsewhere on this page myself, and I trust you're not behind them.

edit: oh come ON. How could this get upvoted? sheesh people. Maybe this could have been done in PM, but if it should have, then nail us both for it.

Comment author: shminux 07 September 2012 11:40:48PM *  0 points [-]

Just checked... No, not a single one is mine, though I did upvote a couple earler.