timtyler comments on Request For Article: Many-Worlds Quantum Computing - Less Wrong

5 Post author: pre 19 November 2009 11:31PM

You are viewing a comment permalink. View the original post to see all comments and the full post content.

Comments (55)

You are viewing a single comment's thread. Show more comments above.

Comment author: [deleted] 20 November 2009 06:30:50PM *  2 points [-]

Voted down for being off-topic. Feel free to delve into a deep discussion about the merits of doing this and what should be considered off-topic. Meanwhile, I'll say what I have to say anyway. Feel free to delve into a deep discussion about the merits of doing this as well.

The thing is, quantum mechanics looks like the Copenhagen interpretation. That's why Copenhagen hasn't been falsified. We've barely managed to produce any evidence against it. (I'm not considering its low-ish prior probability to be evidence, of course.) Therefore, if you want to explain an observed phenomenon, it's perfectly valid to explain it in terms of wavefunction collapse.

Note to self: ponder, and write something about, when it makes sense to explain something in terms of a mechanism you don't know exists.

Saying that a quantum algorithm is "simultaneously sampling all possibilities and choosing the best one" has always been, I've found, a strange way of putting it, since it suggests that quantum computing can do a lot more than it actually can. (Quantum superintelligence: simultaneously sample every possible process of reasoning and choose the most interesting one. Unfortunately, you can't actually do that.)

A quantum algorithm such as Grover's algorithm simply works by changing the probability amplitudes (i.e. the heights of the wavefunctions, the things that can interfere constructively and destructively, the things that determine the probability of each outcome) in such a way that the probability of the desired answer is much higher than the probability of any other answer. ("Probability" here is just a specific function of probability amplitude, which happens to be consistent with both quantum evolution and the laws of probability.) When you perform the observation, then, the majority of Bornstuff goes to the world where the answer observed is the desired one.

How does Grover's algorithm work, specifically? Well, there's a plane where one line is the algorithm's starting point, and another line is the correct answer; it uses reflections to rotate the point for a certain amount of time, until it's very close to the correct answer. I dunno. For details, see Wikipedia.

Comment author: timtyler 20 November 2009 06:43:28PM 1 point [-]

Using the same logic:

That's why Russel's teapot hasn't been falsified. We've barely managed to produce any evidence against it. Therefore, if you want to explain an observed phenomenon, it's perfectly valid to explain it in terms of Russel's teapot.

http://en.wikipedia.org/wiki/Russell's_teapot

Comment author: [deleted] 21 November 2009 09:59:56PM 1 point [-]

That's why Russel's teapot hasn't been falsified. We've barely managed to produce any evidence against it. Therefore, if you want to explain an observed phenomenon, it's perfectly valid to explain it in terms of Russel's teapot.

Though I think you could have picked a better analogy (specifically, one that makes significant predictions about the future), I agree with what you're saying. Let me say what I should have said:

The thing is, quantum mechanics looks like the Copenhagen interpretation. The Copenhagen interpretation and the many-worlds interpretation are practically identical in the predictions they make. Therefore, if you want to explain an observed phenomenon, it's perfectly valid to explain it in terms of wavefunction collapse.

Comment author: Cyan 20 November 2009 07:17:57PM *  0 points [-]

The same "logic" would actually be:

The thing is, the Universe looks like it could contain a teapot in interplanetary space. That's why Russel's teapot hasn't been falsified...

Analogy fail.

Comment author: timtyler 20 November 2009 08:43:06PM *  0 points [-]

Um, I did substitute directly into the text of the post I was quoting from.

I shouldn't need to spell this sort of thing out - but the main problem with both the Copenhagen interpretation and Russel's teapot is that they violate Occam's razor - not that there is observational evidence against them.

Comment author: Cyan 20 November 2009 08:58:29PM 0 points [-]

Um, I did substitute directly into the text of the post I was quoting from.

Your analogy fails to, well, be analogous if you include the first sentence of Warrigal's full argument. I don't disagree with you about Occam's razor; I just think you argued the point poorly.