The Many-Worlds Interpretation Has Many Problems • Hacker News Board

Re: The Many-Worlds Interpretation Has Many Problems

#41

Post by Jweb_Guru » Fri, Oct 19, 2018, 8:01 AM UTC

spiritcat wrote: post #31

jhpriestley wrote: post #27

MWI seems more elegant than Copenhagen in many formulations because the problem of the relative magnitudes of the worlds is swept under the rug. If I perform a quantum coin-flip with 2/3 possibility of heads, then it creates two worlds - but I end up in one of them twice as often - why? The only solutions I've seen to preserve the relative probabilities are: 1) sufficiently unlikely worlds sometimes just disappear, o…

Or it actually creates three worlds, two heads worlds and one tails.

Being able to count worlds in the manner you describe is apparently not easy to justify. If I recall correctly, this is actually a pretty thorny epistemological problem with the theory. IIRC the current response among Many Worlds people is that either (1) it doesn't really matter because there is no reason to believe that probabilities are "real" in the first place, or (2) attempting to show that if you did insist on finding a metric that looked like probability, it would provably have to be the Born probability (see https://arxiv.org/abs/1405.7577). All this stuff is way over my head so I have no way of evaluating whether it's persuasive or not, but it does at least seem to be contentious among physicists.

Re: The Many-Worlds Interpretation Has Many Problems

#42

Post by comex » Fri, Oct 19, 2018, 8:15 AM UTC

tbabb wrote: post #35

ZhuanXia wrote: post #4

>What can you do with this power to generate worlds and selves? You could become a billionaire by playing quantum Russian roulette. Quantum suicide isn't exploitable, for reasons I went over in a thread on reddit: >One thing about these quantum immortality (or modal realism, dust theory, etc.) arguments is they imply one should expect to end up in those proportion of worlds that have the highest measure in which "you…

I think there is a still more straightforward and robust argument against quantum immortality: The same reasoning predicts you can never fall asleep. If futures where you are not conscious are inaccessible by the anthropic principle, then dreamless sleep cannot be in your future. Most sleep is dreamless. At 4:00am this morning I will almost certainly be in this state. But being unconscious is not an experience I can…

I don't think that's accurate. The many worlds interpretation is fundamentally an interpretation of something unobservable; if there were a way for you to observe it (by noticing you haven't been able to sleep) and 'report back' to all/most universes, it wouldn't be an interpretation anymore. (If you did a quantum suicide experiment, you might be able to 'report back' to the subset of universes where you still exist, like in Permutation City. I'm not sure that would actually be a valid demonstration of many worlds – the classical equivalent is just "something unlikely happened", and you can justify that with the anthropic principle. But in any case, that's very different from reporting back to all universes.)

As for the diagram… Even in a classical universe (or just a non-many-worlds one), if you set a mechanism to have a 50% chance of killing you, you should expect to 'find yourself' alive afterwards – in the sense that if you 'find yourself' anything, that anything can only be alive. It's just that you have an equal chance of not having any further conscious experience. That doesn't apply to sleep or even temporary death, since the resulting universe would still be observable by you at some point in the future. Now, even in a classical universe, there is a possible set of values under which participating in a 'suicide lottery' could be rational! That would be, "I fundamentally don't care whether I exist or not, but I do prefer existing while being rich to existing while being poor". The many-worlds interpretation just lets you amend that to: "I don't care whether I exist or not in 'my' future, as long as someone else identical to me exists in an alternate universe." There is no reason you must or should care about someone benefitting in an inaccessible universe just because they're (very) similar to you; but there is also no reason you must not. To whose benefit you strive is an arbitrary choice, after all.

Re: The Many-Worlds Interpretation Has Many Problems

#43

Post by kaoD » Fri, Oct 19, 2018, 8:24 AM UTC

tbabb wrote: post #35

ZhuanXia wrote: post #4

>What can you do with this power to generate worlds and selves? You could become a billionaire by playing quantum Russian roulette. Quantum suicide isn't exploitable, for reasons I went over in a thread on reddit: >One thing about these quantum immortality (or modal realism, dust theory, etc.) arguments is they imply one should expect to end up in those proportion of worlds that have the highest measure in which "you…

I think there is a still more straightforward and robust argument against quantum immortality: The same reasoning predicts you can never fall asleep. If futures where you are not conscious are inaccessible by the anthropic principle, then dreamless sleep cannot be in your future. Most sleep is dreamless. At 4:00am this morning I will almost certainly be in this state. But being unconscious is not an experience I can…

I don't see how this refutes anything.

You cannot experience being asleep, but what you experience is waking up, having been asleep. I find this consistent with the fact that approximately 100% of the time I experience is me being awake.

Having been unconscious is also an experience with p>0. It's only having been dead where (as far as we know) p=0. Not temporary dead: dead, dead; since it's defined as having been conscious (even if on and off) and then never being conscious again.

It's similar to being born: you don't experience anything before, but it's p=1 for you being born if you're experiencing it.

It's not refuting anything, only changing the axioms.

Re: The Many-Worlds Interpretation Has Many Problems

#44

Post by TheOtherHobbes » Fri, Oct 19, 2018, 8:44 AM UTC

comex wrote: post #42

tbabb wrote: post #35

Earlier quoted context omitted.

I think there is a still more straightforward and robust argument against quantum immortality: The same reasoning predicts you can never fall asleep. If futures where you are not conscious are inaccessible by the anthropic principle, then dreamless sleep cannot be in your future. Most sleep is dreamless. At 4:00am this morning I will almost certainly be in this state. But being unconscious is not an experience I can…

I don't think that's accurate. The many worlds interpretation is fundamentally an interpretation of something unobservable; if there were a way for you to observe it (by noticing you haven't been able to sleep) and 'report back' to all/most universes, it wouldn't be an interpretation anymore. (If you did a quantum suicide experiment, you might be able to 'report back' to the subset of universes where you still exist,…

If something is unobservable, and has no observable properties - in fact cannot have observable properties, by definition - it's metaphysics, not science.

Re: The Many-Worlds Interpretation Has Many Problems

#45

Post by n4r9 » Fri, Oct 19, 2018, 8:47 AM UTC

Philip Ball has previously written very similar articles on his objections to Many Worlds:

https://aeon.co/essays/is-the-many-worlds-hypothesis-just-a-...

Whilst I share his frustration with how readily it is being taken up and the dogmatic glamour surrounding it, I feel like he consistently misses the primary issues with it.

Copy-pasting a previous comment trying to describe succinctly what I see as the central problem:

> Although there are many versions of MWI, the general claim is that a single axiom (a unitarily evolving wavefunction) is sufficient to explain our observations of the universe. Without getting into what it means to "explain" something, it seems fair to demand that a sufficiently intelligent agent with no prior knowledge of our physics should be able to predict what the theory says about their future observations. However no one would be able to make any experimental predictions based on the above axiom. There's nothing there to suggest that if the agent becomes entangled with a quantum system then they would only experience a single branch of the entanglement. Even if you add that in, there's nothing to suggest which branch the agent will experience (this is roughly the preferred basis problem). Even if you add that in, there's nothing to suggest with what probability the agent will experience that branch.

> You could always add in the above as additional axioms. You could postulate some physical content to the Born-rule, or to something weaker from which to deduce the Born rule. But this would break the illusion that MWI requires fewer axioms. Instead, a great deal of energy has been expended into deducing the Born rule purely from that single axiom. There have been many very clever attempts at this, but none convincing enough to settle the matter.

If you're interested in reading more, Adrian Kent has written some fairly thorough critiques on arxiv:

https://arxiv.org/abs/0905.0624

Re: The Many-Worlds Interpretation Has Many Problems

#46

Post by int_19h » Fri, Oct 19, 2018, 8:49 AM UTC

JProthero wrote: post #24

wildermuthn wrote: post #10

Quantum suicide is a fascinating thought experiment. If consciousness is a property of a certain type of brain (or calculation?), then the concept of ‘’’me” is just a variation of the anthropic principle: I believe my subjective experience to be something unique, but there’s nothing unique or special about a human brain and the conscious experiences it produces. So even if there are billions of worlds, there aren’t b…

>One consciousness is simply extinguished forever. The other continues. If there is one instance of a widely-distributed program installed on a particular computer, and the instance of the program on that particular computer is deleted, but the program continues to exist in identical form on many other computers, then the program continues to exist in spite of the fact that one of its instances has been deleted. If c…

For any of this to have meaning, you need to define what "consciousness" even is. I'm not aware of any definition that is not hopelessly metaphysical.

Re: The Many-Worlds Interpretation Has Many Problems

#47

Post by rain1 » Fri, Oct 19, 2018, 8:53 AM UTC

n4r9 wrote: post #45

Philip Ball has previously written very similar articles on his objections to Many Worlds: https://aeon.co/essays/is-the-many-worlds-hypothesis-just-a-... Whilst I share his frustration with how readily it is being taken up and the dogmatic glamour surrounding it, I feel like he consistently misses the primary issues with it. Copy-pasting a previous comment trying to describe succinctly what I see as the central prob…

> there's nothing to suggest which branch the agent will experience

isn't this accurate modelling though? as far as we can tell the collapse picks a branch at random. I just don't see how this is a problem of the model.

Re: The Many-Worlds Interpretation Has Many Problems

#48

Post by r_c_a_d » Fri, Oct 19, 2018, 8:53 AM UTC

JProthero wrote: post #16

jblow wrote: post #9

Of course it seems weird to think of Many Worlds as somehow manufacturing universes for each fluctuation. That seems weird and wrong ... because it probably is. A better way to think of it is as the equivalent of the relativistic block universe. All these different spaces already exist in some superspace, and ‘random’ events take you from one space to a neighboring one. Nothing is manufactured.

Well put; this is more or less what Everett actually proposed, and it's the interpretation that mainstream Everettians like Sean Carroll and Max Tegmark subscribe to.

Yes, before reading Tegmark I thought that MW was silly because "splitting" the whole universe for every tiny event just seemed crazy. Thinking of the multiverse as more like a probability distribution where everything exists in a kind of overlay seemed to make sense.

Re: The Many-Worlds Interpretation Has Many Problems

#49

Post by TheOtherHobbes » Fri, Oct 19, 2018, 8:56 AM UTC

JProthero wrote: post #15

EGreg wrote: post #8

Earlier quoted context omitted.

People ridicule the nonlocality of Pilot Wave theory. But I’d rather question locality than embrace Everett’s many-worlds theory. If you need to postulate such amazing complexity just to say basically nothing in terms of realism, then you’ve already lost. Meanwhile as one good physics professor pointed out, none of these alternatives to PWT even rule out nonlocality. So why not just assume it and be done with the wei…

>If you need to postulate such amazing complexity just to say basically nothing in terms of realism, then you’ve already lost. Defenders of the Many-Worlds Interpretation, and some other types of multiverse theory such as Eternal Inflation, would actually say that the multiverse idea is the simpler alternative, not the more complex one. Multiverse theories produce an abundance of universes, but the underlying descrip…

This is only true if you ignore the fact that there's no explanation, in detail, of how quantum splitting generates an entire universe - never mind why it happens for observed events only, and not for unobserved quantum events. (Is that how it works, or not?)

The photon bounced off a beam splitter - did that generate a new universe? How about if the photon moved one Planck distance through spacetime? The photon hit a detector? Okay - a universe. Yes? Or do you only get a new universe when the result is observed? By someone who's awake? And not on drugs, so they might be hallucinating?

The argument seems to be based on "Obviously it just does, because how else do you explain this weird math, QED, isn't our explanation great?" - which I personally don't find very convincing.

Re: The Many-Worlds Interpretation Has Many Problems

#50

Post by int_19h » Fri, Oct 19, 2018, 9:01 AM UTC

Veedrac wrote: post #3

Here's the article in short. 1. "Roland Omnès says the idea that every little quantum “measurement” spawns a world “gives an undue importance to the little differences generated by quantum events, as if each of them were vital to the universe.” This, he says, is contrary to what we generally learn from physics: that most of the fine details make no difference at all to what happens at larger scales." 2. "What can it…

It occurs to me that a lot of these arguments revolve around the author's preferred definition of consciousness, which is essentially arbitrary. There's no physical phenomenon that is consciousness - it's a term that we came up with for the subjective feeling that we experience as we function. You don't really know if someone is conscious or not unless you ask, and you don't really know if the answer is true or not anyway (because they might be conscious but unable to communicate, or because it might be an unconscious automaton that's programmed to answer that it is conscious) - so there's no way to define it experimentally.

I can't help but think that "consciousness" is really just a modern atheistic version of the "soul" concept, nothing more. Basically, we just gave up on immortality, and accepted that there are some physical processes underneath that cause it to start and stop - but we're still clinging to that self-perception of ourselves as a singular entity that drives self, as something that meaningfully exists in the physical world. But it is recursive - we think that we're conscious as a function of conscious, basically. You can't really distinguish consciousness from unconsciousness per se, because when you're unconscious, you do not observe or reason. In others, you can only observe the lack of prerequisites of consciousness (e.g. brain activity), or the lack of its side effects (communication etc), but you can't observe unconsciousness as such.

From that perspective, the idea of consciousness has no more place in science (or criticism of science) than soul does.