Vaniver comments on What I've learned from Less Wrong - Less Wrong

79 Post author: Louie 20 November 2010 12:47PM

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Comment author: Vaniver 21 November 2010 07:21:10PM *  1 point [-]

Have you read that and considered it convincing?

They use four supports, all of which collapse under examination (I don't number them the way they do, because they seem confused about what are separate supports):

  1. Though it makes the same predictions about our world as de Broglie-Bohm, they have different philosophical implications. Believe in something because of math, not philosophy.

They list three predictions made MWI, all of which are already disproved or nonsense:

  1. If memory is reversible, it's not memory because thermodynamic fluctuations make it unreliable. Beyond that confusion, the crux of this argument is whether or not a spin measurement can be reversed- if so, it should work for any flavor, and not depend on whether or not you also erase what's in memory.

  2. Their discussion of quantum gravity serves to make MWI not more plausible, as it supposedly requires quantum gravity, while other flavors function whether gravity is quantum or classical.

  3. Their discussion of linearity is flat-out bizarre. Paraphrased: 'We're pretty damn sure that QM is linear, but if it weren't and MWI were true, aliens would have teleported to our dimension, and that hasn't happened yet.' Why they think that is evidence for MWI is beyond me- using Bayesian logic, it strictly cannot increase the probability of MWI.

Comment author: nshepperd 22 November 2010 01:50:05AM 0 points [-]

I don't think the intention was to offer these as evidence for MWI. The evidence for MWI is that it has one less postulate (and therefore is "simpler"). They're just showing what MWI rules out. That these predictions are different correctly justifies saying "MWI is not just an interpretation".

Comment author: timtyler 21 November 2010 07:40:03PM *  0 points [-]

It is best not to use quotation marks - unless you are actually quoting - or otherwise make it very clear what you are doing. The resulting self-sabotage is too dramatic.

I read that - and your incorrect comments about reversible memory - and concluded that you didn't know what you were talking about.

Comment author: Vaniver 21 November 2010 07:54:04PM 0 points [-]

At your suggestion, I've revised my comment to make clear that I'm paraphrasing my interpretation of their comment instead of quoting it directly.

I was least sure about my reversible memory objection, and was considering placing a disclaimer on it; however, I feel I should stand by it unless given evidence that my understanding of information entropy is incorrect. My statement is in accord with Landauer's Principle, which I see is not known to be true (but is very strongly suspected to be). There appears to be a fundamental limit that their trend is bucking up against, and so I feel confident saying the trend will not continue as they need it to.

Even if we shelve the discussion of whether or not memory can be reversible, the other objection- that any process which reverses a measurement can be understood by both MWI and Copenhagen- demolishes the usefulness of such an experiment, as none of the testable predictions differ between the two interpretations.

Comment author: timtyler 21 November 2010 09:59:20PM 0 points [-]

If it helps, this seems relevant: http://en.wikipedia.org/wiki/Reversible_computing

Landauer's Principle doesn't seem particularly relevant - since in reversible computing there is no erasure of information.

Comment author: Vaniver 21 November 2010 11:26:53PM 0 points [-]

I don't see the relevance- the description of the experiment linked purports to hinge on the reversibility of information erasure. It sounds like both of us agree that's impossible.

(It actually hinges on whatever steps they take to 'reverse' the measurement they take, which is why it's not an effective experiment.)

Comment author: timtyler 22 November 2010 06:34:37PM 1 point [-]

It seems relevant to the comment that "if memory is reversible, it's not memory". Reversible computers have reversible memory.

Comment author: Risto_Saarelma 22 November 2010 07:33:48PM 0 points [-]

Reversible computer designs people actually consider building do a small bit of irreversible computation copying end results of the reversible computations into irreversible memory before rolling back the reversible computation. Perfectly reversible computations are a bit useless since they erase their results when they start rolling backwards.

Comment author: wnoise 22 November 2010 08:01:30PM 0 points [-]

You can erase some of their results without erasing others, of course.

Comment author: timtyler 22 November 2010 07:41:30PM *  0 points [-]

Nobody says you have to run a reversible computer backwards.

A big part of the point is to digitise heat sinks and power management. For details about that, see here.