Why does nothing happen in MWI?

[Demystifier]

That's part of the argument about it isn't it. They look pretty natural to me though.

Well, they don't look natural to me. See e.g.
https://www.physicsforums.com/threads/why-mwi-cannot-explain-the-born-rule.364063/
especially posts #1 and #2.

 

[Demystifier]

Please help me understand: how can it matter whether we "consider" the representations to be the same object? If there is one valid basis according to which the vector contains us and our classical observations, then isn't that fact a property of the overall vector?

Let me use an analogy from everyday life. Consider a rough piece of stone. A skillful sculptor can remove a part of the stone material from it to get a beautiful sculpture. Thus, referring to the removed part as "garbage", we can write
sculpture=stone-garbage
or equivalently
stone=sculpture+garbage
But of course, from the same piece of stone the sculptor may choose to make a different sculpture, called "sculpture2", so we can also write
stone=sculpture2+garbage2

Now I am asking you: Is it the fact that the overall stone contains the sculpture? And is it also the fact that the same overall stone contains the sculpture2? And do you get the analogy?

 

[bhobba]

Well, they don't look natural to me.

The equivalence principle, informally is (page 172 of Wallace's text):
'If two acts assign the same weight to each reward the agent must be indifferent to them'

That seems pretty reasonable to me.

But its validity isn't based on how reasonable it is - the formal statement of it is proved section 5.7 page 182 from the decision theoretic foundations his method is formally based on. I have read the book - its pretty dense with theorem proof, theorem proof etc, and while I didn't go though them with a fine tooth comb the math looks tight to me. And I haven't seen anyone challenge it on those grounds so I suspect it's valid. The issue isn't the math - its if you accept a decision theory approach is a valid way to proceed.

Thanks
Bill

 

[Demystifier]

The equivalence principle, informally is (page 172 of Wallace's text):
'If two acts assign the same weight to each reward the agent must be indifferent to them'

That seems pretty reasonable to me.

Here is a counterexample from the classical world. Consider two human twins, one weighting 70 kg and another 80 kg. (The second one eats more, so weights more.) Is it reasonable to conclude that the second twin is therefore more probable than the first twin? And what does it even mean, especially from the point of view of the twins themselves?

 

[bhobba]

Is it reasonable to assume that the second twin is therefore more probable than the first twin?

What do you mean by more probable? If its more probable of existing then the augment is tautological. You assume they exist and have those properties - those properties have nothing to do with them existing in the first place - you have assumed it to begin with.

I think people are getting a bit confused about what's going on here.

In MW there is no way you can decide what world you as a rational agent will experience. That immediately raises all sorts of issues such as is what a rational agent would experience a valid way to proceed. If you assume that, is a decision theoretic approach using the formal axioms of decision theory as used by actuaries and other risk professionals valid? Once you reach that point then we have axioms and tight theorem proof consequences. At that point it looks pretty unassailable.

If you want to challenge it you need to challenge it before it reaches the theorem proof stage.

My take is it all looks reasonable to me - but if you find it unpalatable - I have no issues. I personally do not hold to MW - but for other reasons.

Thanks
Bill

 

[Demystifier]

What do you mean by more probable?

I don't know, you tell me by applying the decision theory or whatever you use to explain probability in MWI. My point is that the twins (which both exist) are analogous to the two branches of the wave function in MWI.

 

[Demystifier]

I personally do not hold to MW - but for other reasons.

What reasons?

 

[bhobba]

I don't know, you tell me by applying the decision theory or whatever you use to explain probability in MWI. My point is that the twins (which both exist) are analogous to the two branches of the wave function in MWI.

If you want to challenge this here is how to do it:

1. You can't have a theory where probabilities are determined by rational agents. Science is about objective truth - not what rational agents would conclude.
2. Even if you accept point one why do you use the axioms of decision theory? Science isn't a betting strategy like actuaries use to decide the costs their clients would incur for a particular action.

They, or similar criticisms are where its vulnerable - once it reaches where, say the equivalence principle is used, then you have all these formal proofs to support it - it must be attacked prior to that.

If you go down that path I am with you - I may not agree - but its a reasonable criticism. Others I have seen are IMHO missing the point.

Thanks
Bill

 

[bhobba]

What reasons?

Its this exponential dilution of energy - in any normal process we would say it quickly decays to zero - but not here. Its a bit too weird for me.

However the specific question was asked - how is the Born Rule justified. Its justified on decision theoretic grounds.

Thanks
Bill

 

[Jimster41]

Here is a counterexample from the classical world. Consider two human twins, one weighting 70 kg and another 80 kg. (The second one eats more, so weights more.) Is it reasonable to assume that the second twin is therefore more probable than the first twin? And what does it even mean, especially from the point of view of the twins themselves?

I'm still trying to read this thread. Great discussion.
The "onion" structure of AdS/CFT (my favorite) does seem to imply hidden dimension(s), and so in some sense says the world as we experience is not sufficient to explain itself... That said, if ever there was navel staring... extending that somewhat unsurprising result to the idea that no observer is privileged (because how could we be?) and so all observers exist (because we exist), and so all realities exist (because ours exists)... wow.

So, I hat MWI because it just sounds like infinity = everything = nothing.

Personally, I'd just like to see some concrete (viscerally convincing) evidence of something like AdS/CFT.

irregardless...

The equivalence principle, informally is (page 172 of Wallace's text):
'If two acts assign the same weight to each reward the agent must be indifferent to them'

This sounds like a line from an evolutionary dynamics text. So I'm not following the literal interpretation vis-a-vis the heavier vs. lighter twin. And I'm missing the sequitur. We are agents (it is an unfortunate fact - not even axiomatic) and we have a preferred basis, and from it our reality is formed, and in that we must act (for where-else) according to the fitness function (the weighting of action) it presents.

The Work Fluctuation Theorem, seems to describe exactly the decision engine we inhabit, I think.

To repeat myself more precisely (I hope), I would just like to know totally how that works, Quantum mechanically, whether or not it is one and the same as the emergence of space-time from some larger context and process - a context and process with clear as well as surprising (like maybe non-local) structure. This understanding, if it could be held at gut level, could place experience inside a real thing (that may be made of many things) - upon which information is inscribed. A thing we can know is not equivalent to us even though it contains us, because it is connected to things we, at least while here, are not (like non-local dimension), and because it behaves according to rules that do not apply to us (like superposition), at least while we are here - That is a feeling that might alleviate some fear of oblivion.

I want to be the cat. That would be better. Or at least I want to believe I may be the cat.

 

[Demystifier]

I want to be the cat.

Then you may want to read this:
http://lanl.arxiv.org/abs/1406.3221 [Eur. J. Phys. 36 (2015) 045003]

 

[Demystifier]

The "onion" structure of AdS/CFT (my favorite) does seem to imply hidden dimension(s)

Note that we live in a world where gravity is directly experienced, while the onion structure and hidden dimension (according to the mentioned theory) exists only in the dual CFT theory without gravity.

 

[Jimster41]

Note that we live in a world where gravity is directly experienced, while the onion structure and hidden dimension (according to the mentioned theory) exists only in the dual CFT theory without gravity.

I think I understand. I do wonder what those onion people call the information that gives us gravity.

 

[Derek Potter]

Here is a counterexample from the classical world. Consider two human twins, one weighting 70 kg and another 80 kg. (The second one eats more, so weights more.) Is it reasonable to conclude that the second twin is therefore more probable than the first twin? And what does it even mean, especially from the point of view of the twins themselves?

Yes, but the fundamantal postulate of QM is that the state is a vector in Hilbert space, not a human twin, so all the theorems of vector spaces apply, in particular Gleason's. There is no a priori reason why probability should depend on amplitude without that postulate.
Agreed, though, that the self-probabilty is always unity. Which is why it doesn't matter that the bundle of worlds that you and I inhabit right now have such a small amplitude that there isn't a word for it. Our world is real "to us".

 

[maline]

Now I am asking you: Is it the fact that the overall stone contains the sculpture? And is it also the fact that the same overall stone contains the sculpture2? And do you get the analogy?

I'm afraid I don't see the analogy. The only reason I see that the stone does not contain sculptures is that sculptures are defined by their shape, and the shape of an object is defined by the boundary between the object & the surrounding medium. Is there some analogous requirement which, in MWI, should prevent us from experiencing reality the way we do? And if so, how would "considering" representations as separate objects help?

 

[bhobba]

Yes, but the fundamantal postulate of QM is that the state is a vector in Hilbert space

Not necessarily. But it is the fundamental axiom of MW.

Thanks
Bill

 

[Derek Potter]

I think I understand. I do wonder what those onion people call the information that gives us gravity.

In our language it would be "xrtlwqngfffd". In theirs they probably call it flavour. They probably enjoy hamburgers and gravity.

 

[Derek Potter]

Its this exponential dilution of energy - in any normal process we would say it quickly decays to zero - but not here. Its a bit too weird for me.

I may be able to help you there. MWI in the deWitt picture involves splitting the universe, but it is a terrible picture. Far better to regard the universe as behaving quite nicely, conservation of energy etc but getting more complicated and thus generating new worlds in the sense of outcome-observer entanglements. The fact that you live in a world which, as part of the whole is of so low an amplitude that the number hasn't even got a name is irrelevant - the only things that interact with bhobba are things in bhobba's world(s), thus justifying normalising your state from your PoV.

 

[Derek Potter]

I want to be the cat.

Good idea as long as it's a Schrodinger cat. Schrodinger's cat has a serious flaw. Cats have nine lives so a typical cat will be alive every time - at least until the eighth repeat and generally about 17 of them. This is a kind of superselection. As far as I know it only applies to cats and the |alive> state, though maybe Schrodinger's Toast always falls butter-side up for a similar reason.

 

[Derek Potter]

I'm afraid I don't see the analogy. The only reason I see that the stone does not contain sculptures is that sculptures are defined by their shape, and the shape of an object is defined by the boundary between the object & the surrounding medium. Is there some analogous requirement which, in MWI, should prevent us from experiencing reality the way we do? And if so, how would "considering" representations as separate objects help?

Not sure who's saying what, but in MWI (the sort that makes sense, MMWI) that is exactly what happens, the state contains this world and Harry Potter's world in equal measure except that internal inconsistencies in HP make it impossible to say anything intelligible about it.

 

[atyy]

Good idea as long as it's a Schrodinger cat. Schrodinger's cat has a serious flaw. Cats have nine lives so a typical cat will be alive every time - at least until the eighth repeat and generally about 17 of them. This is a kind of superselection. As far as I know it only applies to cats and the |alive> state, though maybe Schrodinger's Toast always falls butter-side up for a similar reason.

How about superposition?

 

[Derek Potter]

How about superposition?

Superselection trumps superposition.

 

[Dale]

Closed pending moderation.

Edit: this thread will remain closed. I encourage all participants to review the forum rules on philosophy and speculation.