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Not even wrong: Why does nobody like pilot-wave theory? [pdf]

tcm.phy.cam.ac.uk

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Re: Not even wrong: Why does nobody like pilot-wave theory? [pdf]

#61

Post by jamesrcole »

Qwertious wrote: post #54
jamesrcole wrote: post #49

Earlier quoted context omitted.

There's two kinds of probability in question. One concerns a lack of knowledge, like in your cards example. In that case, the probability is an expression of your state of understanding of the deck, and is not a property of the deck itself. The physical details of the deck and the situation it is part of could be entirely deterministic and we could still talk about this kind of probability. In this case your knowledg…

Or to give a slightly better example, suppose you're playing russian roulette with a six-shot revolver. You empty the revolver of bullets, then put one bullet in, spin the barrel, point it at your head and fire. What is the chance that you're shot? Is it 1/6? What about if you open it up and look in the barrel to see if there's a bullet there?

Nothing about the location of the bullet has changed.

Are you suggesting this example somehow shows that changing knowledge/probabilities determine whether what's going on there is deterministic or not, as is the issue under discussion?

Re: Not even wrong: Why does nobody like pilot-wave theory? [pdf]

#62

Post by AgentME »

stephengillie wrote: post #34
olegkikin wrote: post #9

I have an unrelated question to the physics nerds. Is it even possible to determine whether the universe is deterministic or not from inside the universe? Let's imagine a simplified example. I give you two sets of numbers (let's pretend they are atom coordinates). One set is purely random, another one is generated with a very simple formula (example: f(n) = SHA256(N + salt)). I will give you as many of the numbers as…

Going to piggyback with a question unrelated to yours but tangental to the topic: What about the universes in the multiverse where 'multiverse theory' is wrong, and there is no multiverse? Are they islands? Are they like multiverse 'diodes' which may allow only one-way travel into that universe, but from which return to the larger multiverse is impossible?

Just to clarify something: the standard many-worlds interpretation (such as discussed in the original article and elsewhere in this thread) doesn't contain anything about other alternate branches having different physical laws or being fundamentally different, and in MWI the only way that branches interact with each other is that probabilities are affected when multiple branches have their physical states match up completely (after possibly taking different paths) -- there's no way for intelligent beings to interact with meaningfully different branches for example. The many-worlds interpretation isn't a baseless what-if-there-are-alternate-universes thought experiment that anything could happen in, but instead is arguably the straight-forward interpretation of what we know about quantum mechanics.

Re: Not even wrong: Why does nobody like pilot-wave theory? [pdf]

#63

Post by goatlover »

QAPereo wrote: post #40
olegkikin wrote: post #9

I have an unrelated question to the physics nerds. Is it even possible to determine whether the universe is deterministic or not from inside the universe? Let's imagine a simplified example. I give you two sets of numbers (let's pretend they are atom coordinates). One set is purely random, another one is generated with a very simple formula (example: f(n) = SHA256(N + salt)). I will give you as many of the numbers as…

Real physics nerd, non-popsci answer: everything that is obersed rather than conjectured about the universe implies that it has no "outside" and your question is a bit like asking what is North of the North Pole. It just isn't a meaningful concept, like "before the big bang" or "what did the universe expand into."

Unless there are other universes and there was a time before the big bang.

Re: Not even wrong: Why does nobody like pilot-wave theory? [pdf]

#64

Post by AgentME »

XorNot wrote: post #51
AgentME wrote: post #47

Earlier quoted context omitted.

Why do you say that quantum randomness is a problem in MWI? I thought it was one of the neat things of MWI that it doesn't require randomness. There are no random events: instead you have a branch for each outcome. The only randomness is which branch you find yourself in as an individual.

It's a problem because it closes off further investigation - same as the anthropic principle. It's an answer for everything, but doesn't tell us anything about where to look next. So if it's right, it needs to rigourously exclude everything else.

MWI doesn't mean anything and everything can happen because there's infinite universes. The equations of quantum mechanics describe the ways that worlds can branch apart and the proportions of those branches.

Sorry if I'm underestimating your familiarity with MWI here; if I am, szemet has a much better response. I'm just a little concerned that some people in the thread don't realize MWI refers to something much more specific and grounded than what-if-multiple-universes, and I wanted to dispel that notion.

Re: Not even wrong: Why does nobody like pilot-wave theory? [pdf]

#65

Post by justinpombrio »

jamesrcole wrote: post #52
justinpombrio wrote: post #50

Earlier quoted context omitted.

There's a third kind -- indexical randomness, or not knowing who you will be -- that appears in many-worlds. Many worlds is in some sense completely deterministic. Yet with indexical uncertainty you still cannot possibly ever know which way you will see a photon go in a half-silvered mirror. Is that fundamental randomness or not? http://lesswrong.com/lw/jlb/logical_and_indexical_uncertaint...

> Is that fundamental randomness or not? I would say, not. There's no actual randomness from an objective point of view, it's just a lacking in your understanding of things. I think that map/territory confusions are the source of so many problems and should be rigourously avoided. I think it would be a map/territory confusion to consider it a kind of actual randomness.

> I think it would be a map/territory confusion to consider it a kind of actual randomness.

Even though it makes perfect sense to apply probability theory to it? We found a perfect coin, one that we know that you can't predict in advance even in principle, and you want to avoid considering it a kind of randomness? Why does the mechanism by which the universe implements randomness -- in this case via determinism -- matter?

Re: Not even wrong: Why does nobody like pilot-wave theory? [pdf]

#66

Post by jamesrcole »

justinpombrio wrote: post #65
jamesrcole wrote: post #52

Earlier quoted context omitted.

> Is that fundamental randomness or not? I would say, not. There's no actual randomness from an objective point of view, it's just a lacking in your understanding of things. I think that map/territory confusions are the source of so many problems and should be rigourously avoided. I think it would be a map/territory confusion to consider it a kind of actual randomness.

> I think it would be a map/territory confusion to consider it a kind of actual randomness. Even though it makes perfect sense to apply probability theory to it? We found a perfect coin, one that we know that you can't predict in advance even in principle, and you want to avoid considering it a kind of randomness? Why does the mechanism by which the universe implements randomness -- in this case via determinism -- ma…

The many worlds case I was responding to is different to the coin case you are taking about. In the MW case we know enough to see that the situation is not at all random. In your example you're postulating a coin that may well actually be random.

Re: Not even wrong: Why does nobody like pilot-wave theory? [pdf]

#67

Post by n4r9 »

AgentME wrote: post #47
millstone wrote: post #42

Earlier quoted context omitted.

The "nonsense news headline" and followup discussion are less critiquing MWI than poking fun at David Deutsch. This is because Deutsch is a prominent critic of PWT. The arguments against MWI from Occam's Razor are indeed weak. The stronger critiques are the difficulty of deriving the Born rule, or indeed quantum randomness at all, from the deterministic MWI. This is presumably what the authors hint at in their "doubt…

Why do you say that quantum randomness is a problem in MWI? I thought it was one of the neat things of MWI that it doesn't require randomness. There are no random events: instead you have a branch for each outcome. The only randomness is which branch you find yourself in as an individual.

In short the problem is that there's no explanation for why you only experience a single branch, and no explanation of why the probabilities associated with those branches are given by the Born rule.

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.

Re: Not even wrong: Why does nobody like pilot-wave theory? [pdf]

#68

Post by kybernetikos »

AgentME wrote: post #64
XorNot wrote: post #51

Earlier quoted context omitted.

It's a problem because it closes off further investigation - same as the anthropic principle. It's an answer for everything, but doesn't tell us anything about where to look next. So if it's right, it needs to rigourously exclude everything else.

MWI doesn't mean anything and everything can happen because there's infinite universes. The equations of quantum mechanics describe the ways that worlds can branch apart and the proportions of those branches. Sorry if I'm underestimating your familiarity with MWI here; if I am, szemet has a much better response. I'm just a little concerned that some people in the thread don't realize MWI refers to something much more…

I hear a lot that MWI implies that everything that can happen does happen. What I find frustrating is that the obvious next interesting question then is 'well what can happen?', and people don't seem to talk too much about that.

Re: Not even wrong: Why does nobody like pilot-wave theory? [pdf]

#70

Post by QAPereo »

goatlover wrote: post #63
QAPereo wrote: post #40

Earlier quoted context omitted.

Real physics nerd, non-popsci answer: everything that is obersed rather than conjectured about the universe implies that it has no "outside" and your question is a bit like asking what is North of the North Pole. It just isn't a meaningful concept, like "before the big bang" or "what did the universe expand into."

Unless there are other universes and there was a time before the big bang.

While that is a nice thought it's in no way supported by any evidence or observation, or really any hope of evidence for observation. MWI or some other multi universal theory could have merit, but in their current formulation they're not even falsifiable.
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