Are the implications of MWI really this horrifying?

[PeterDonis]

My opinion is, like others already explained in this thread, that there is basically no impact that MWI has on those reasonable pragmatic answers.

That's fine, but it's very different from what you said in your previous post.

Also, please be aware that this is not a philosophy forum and general issues of philosophy are off topic here.

 

[PeterDonis]

I would say branching is just an approximate and convenient description; only the universe as a whole is independently consistent.

Does this include your conscious experience? You are aware, I take it, that according to the MWI, "you" have different conscious experiences in each individual branch, and that must be the case even though "you" do not have a definite state in each individual branch.

 

[Grinkle]

according to the MWI, "you" have different conscious experiences in each individual branch,

Does MWI require (I think the answer is yes, but I am not asking rhetorically, I may be incorrect) that any conceivable state of mind of the human race be allowed?

For instance, does MWI insist that there is a branch somewhere in which immediately after I post this reply I will spontaneously become an ardent advocate of flat Earth and instead of being banned from PF for nonsensical postings I will be hailed as a visionary by all of the PF mentors?

Absurdity may not be a barrier to something being real, but MWI seems to require so much to exist that its very hard for me to accept it as possible. My example is intended both tongue-in-cheek and also as a serious question - do such branches exist, according to MWI?

Sort of poking Occam right in the eye, if so.

 

[PeterDonis]

Does MWI require (I think the answer is yes, but I am not asking rhetorically, I may be incorrect) that any conceivable state of mind of the human race be allowed?

No, only ones that correspond to something with nonzero probability amplitude in the wave function.

For instance, does MWI insist that there is a branch somewhere in which immediately after I post this reply I will spontaneously become an ardent advocate of flat Earth and instead of being banned from PF for nonsensical postings I will be hailed as a visionary by all of the PF mentors?

Only if there is a nonzero probability amplitude in the wave function for that transition. You would be a better judge than I am of whether that is the case.

 

[Grinkle]

You would be a better judge than I am of whether that is the case.

Ha! I've likely made more ridiculous posts with far less awareness. ;-)

Only if there is a nonzero probability amplitude in the wave function for that transition.

OK - this can potentially rescue MWI for me. I can imagine that human minds operate to some degree as equilibrium restoring machines, and this mechanism will drive the probability of flatly absurd human behavior scenarios to zero. Like the laws of physics driving the probablility of impossible physics branches to zero.

 

[akvadrako]

Does this include your conscious experience? You are aware, I take it, that according to the MWI, "you" have different conscious experiences in each individual branch, and that must be the case even though "you" do not have a definite state in each individual branch.

In terms of consciousness, I don't see why according to the MWI anything would be different. I can just guess what must be required to explain it; maybe it can't be described as a classical state or even one branch, but the experience of continuously branching must be taken into account.

 

[Quantumental]

In terms of consciousness, I don't see why according to the MWI anything would be different. I can just guess what must be required to explain it; maybe it can't be described as a classical state or even one branch, but the experience of continuously branching must be taken into account.

In your view, what does this mean?

Either Person A becomes Person B and C, or they don't. There is literally no other option. If both outcomes (persons) are equally real, how can you say that either of them is 'more likely' to experience a certain outcome? This is where MWI has not progressed since my decade-old post which was quoted in this thread.

Since we cannot rely on branch counting, how can you logically defend X over Y outcome in any quantum mechanical probabilistic scenario? If both outcomes are equally real, by definition, there cannot be a 'preferred' outcome...

 

[PeterDonis]

In terms of consciousness, I don't see why according to the MWI anything would be different.

We have no actual theory of consciousness in physical terms, so of course we don't know, but one thing that would seem to be required is that a physical system that is having some definite conscious experience should be in some definite physical state. And that is not true of an individual branch of the wave function in the MWI.

maybe it can't be described as a classical state or even one branch, but the experience of continuously branching must be taken into account.

But nobody has any such experience of continuously branching.

 

[akvadrako]

But nobody has any such experience of continuously branching.

I don't know how you can know this; I certainly don't know it about myself. But I think the lack of any model for consciousness means it isn't a good avenue for discussion.

 

[akvadrako]

In your view, what does this mean?

Either Person A becomes Person B and C, or they don't. There is literally no other option. If both outcomes (persons) are equally real, how can you say that either of them is 'more likely' to experience a certain outcome? This is where MWI has not progressed since my decade-old post which was quoted in this thread.

Since we cannot rely on branch counting, how can you logically defend X over Y outcome in any quantum mechanical probabilistic scenario? If both outcomes are equally real, by definition, there cannot be a 'preferred' outcome...

I find several of the models for weighing outcomes satisfactory, but think it's a bit off-topic so won't get into it. Research hasn't stopped along these lines either; for example there is a paper from November which proposes an alternative way to count: Branch-counting in the Everett interpretation of quantum mechanics from Simon Saunders.

 

[PeterDonis]

I don't know how you can know this; I certainly don't know it about myself.

It seems obvious to me.

I think the lack of any model for consciousness means it isn't a good avenue for discussion.

Yes, fair point.

 

[hungrybear]

Thanks for the replies again.

I don't think you can avoid a model in which if Person A splits then they are the same as the two people they split into, even though those two people are now separate from each other, and don't experience each others perceptions. From person A's perspective, upon being split they either cease to exist or they become two separate selves, there's no reason why they would become only B or C. From the perspective of person A thinking about their future, they will become two separate entities and their future is both futures even though those entities will not experience each other once the split occurs. For person A to think of their future "I wonder if I will become person B or C?" doesn't make sense ontologically if B and C are made from directly splitting A.

If you're coming from an materialist perspective, this works just as well with particles. If you literally split an electron, it doesn't make sense to say which half of the electron will the original electron become? If you split the particles you are made of, from a materialist viewpoint you would become both people.

But you're right we're straying into philosophy here.

Peter I think if I'm following you when you say nothing splits and MWI is a temporal unity, does that mean that many world theories effectively require a block universe, with no flow of time? This is what David Deustch advocates.

In this case my scenarios become different again. An electron spin is measured and:

1. In scenario one, I am a unified person in one unified world and after the experiment there are two people like me, each of which experiences a different outcome. There has been no split because all times exist simultaneously so the me in the first timeframe and the two people in the next time frame have in some sense always existed but don't move through time.

2. In scenario two, there are already two versions of me but their experiences have been identical, after the experiment there are two further people like me, each of which experiences a different outcome. There is no progression of time but each possible past and future was already a separate world so in a sense there are four version of me, two before the experiment, two after, it's just the two versions after the electron experiment are not in identical universes, one experiences spin up, one experiences spin down.

Another question - does MWI mean there could be an extremely unlikely universe in which there is perpetual motion / no end of the universe scenario? My understanding is quantum events can extremely rarely disobey the laws of thermodynamics?

 

[PeterDonis]

if I'm following you when you say nothing splits and MWI is a temporal unity

I said nothing splits. I didn't say anything about MWI being "a temporal unity". I don't know what that means.

does that mean that many world theories effectively require a block universe

No.

In scenario one, I am a unified person in one unified world and after the experiment there are two people like me, each of which experiences a different outcome.

The MWI can be interpreted to say this, if you're willing to accept the implicit claim that each branch of the entangled wave function after measurement can contain a person that experiences a definite outcome at all, since neither branch has a definite state by itself. However:

There has been no split because all times exist simultaneously so the me in the first timeframe and the two people in the next time frame have in some sense always existed but don't move through time.

No. The MWI doesn't say anything like this. The MWI says there has been no split because the time evolution is always unitary, and a unitary operation can't "split" or "copy" anything. All that has happened is entanglement. That's it.

In scenario two, there are already two versions of me but their experiences have been identical, after the experiment there are two further people like me, each of which experiences a different outcome.

The MWI can also be interpreted to say this, with the same caveat as I gave for scenario one above. In other words, the MWI doesn't really see any difference between the two.

There is no progression of time but each possible past and future was already a separate world so in a sense there are four version of me, two before the experiment, two after, it's just the two versions after the electron experiment are not in identical universes, one experiences spin up, one experiences spin down.

The MWI doesn't say anything like any of this.

 

[Grinkle]

@hungrybear I don't think Unitary means what you are interpreting it to mean, but I'm not sure what your interpretation is.

 

[PeroK]

Another question - does MWI mean there could be an extremely unlikely universe in which there is perpetual motion / no end of the universe scenario?

MWI is not about unlikelihoods in that sense. The laws of physics remain as they are, except that every probabilistic outcome is realized (in some sense). There would be no branch in which you could rely on unlikely outcomes to continue.

This raises the question about the physical significance of these branches compared to the "normal" branches. To take an example:

You park your car overnight and wake up the next morning. There are, let's say, two reasons that your car is not there.

1) It's been stolen. That has a probability of, say, 1/10,000. Which corresponds to an overnight theft every 30 years.

2) It's vanished due to "an improbable sequence of quantum events". I can't write down a probablity for that because it's too small.

Leaving MWI aside, what is the physical significance of 2)? And, in MWI, what is the physical significance that in some sense a branch exists where your car has vanished into thin air overnight? You'd just assume it was stolen in any case!

 

[stevendaryl]

MWI is not about unlikelihoods in that sense. The laws of physics remain as they are, except that every probabilistic outcome is realized (in some sense). There would be no branch in which you could rely on unlikely outcomes to continue.

This raises the question about the physical significance of these branches compared to the "normal" branches. To take an example:

You park your car overnight and wake up the next morning. There are, let's say, two reasons that your car is not there.

1) It's been stolen. That has a probability of, say, 1/10,000. Which corresponds to an overnight theft every 30 years.

2) It's vanished due to "an improbable sequence of quantum events". I can't write down a probablity for that because it's too small.

Leaving MWI aside, what is the physical significance of 2)? And, in MWI, what is the physical significance that in some sense a branch exists where your car has vanished into thin air overnight? You'd just assume it was stolen in any case!

I don’t have an answer, but I would like to point out that there could be a “many worlds” interpretation of classical probability, as well. To simplify things, let’s assume a world that is deterministic except for one thing: There is a coin that can be flipped so tgst the outcome, heads or tails, is completely unpredictable, with a 50/50 chance if heads or tails.

Now, suppose that every time that you flip this coin, what really happens is that two copies of the universe are created. In one copy, the result is heads, and in the other, the result is tails.

Now there are two universes, slightly different. Any time that a coin is flipped in any universe, that universe is copied and made different by the results of that coin flip.

As far as someone living in the original universe is concerned, the existence of the alternate universes makes no difference. He might as well think of his as the only one. Of course, absolutely any universe can equally well consider itself to be the original.

So in this many-worlds model, the multiverse evolves deterministically, while each universe appears to its inhabitants to evolve nondeterministically.

 

[Nugatory]

It strikes me that most other interpretations keep shy of making outlandish unverifiable claims.

They all make unverifiable claims - that's what makes them interpretations. To the extent that they help us develop a mental model what the math is telling us in any given problem that's OK - it's what interpretations are for.

"Outlandish" is very much in the eye of the beholder (or as I've said many times before there is something to dislike about every interpretation). They all resolve the measurement problem with some form of "and then a miracle happens". MWI provides a consistent mathematical treatment of the miracle, unlike - for example - the relativity-defying unmotivated magical abandonment of unitary evolution that we find in collapse interpretations. Which do you find more outlandish? And is that not basically an aesthetic judgment?

 

[CoolMint]

They all make unverifiable claims - that's what makes them interpretations. To the extent that they help us develop a mental model what the math is telling us in any given problem that's OK - it's what interpretations are for.

"Outlandish" is very much in the eye of the beholder (or as I've said many times before there is something to dislike about every interpretation). They all resolve the measurement problem with some form of "and then a miracle happens". MWI provides a consistent mathematical treatment of the miracle, unlike - for example - the relativity-defying unmotivated magical abandonment of unitary evolution that we find in collapse interpretations. Which do you find more outlandish? And is that not basically an aesthetic judgment?

Yup. It is. Still people have been trying to harness the quantum weirdness and use its potentials. If what I have been reading is right, quantum computing has now been proven feasible. Quantum states, for all practical reasons, appear to have a reality of their own. Its major hurdle is what is perceived as 'decoherence' which like measurement also appears irreversible. If they can cool down the qubit and isolate it well enough, the future is quantum. From computers to tv's simulating virtual reality via goggles in highest resolution to cars and the internet. I am modestly optimistic that the future of the human race is quantum and with its endless practical applications, interpreting its essence will likely be easier.

 

[physika]

But, as a realist, the only objectively real world is the one experienced. Why should any alternative reality concern me based on my concrete experience?

Experencied by another "one".

 

[hutchphd]

Quantum states, for all practical reasons, appear to have a reality of their own.

What does that mean? They describe only themselves? This would not seem useful.

I am modestly optimistic that the future of the human race is quantum

I am equally modestly certain that the past has also been quantum. With respect, I find these pronouncements meaningless .

 

[CoolMint]

What does that mean? They describe only themselves? This would not seem useful.

No.

I am equally modestly certain that the past has also been quantum. With respect, I find these pronouncements meaningless .

One sentence can be meaningless when you remove the relevant context.
You should quote the whole comment I made(as I do with your comments) without removing the context so that it makes sense. The context can make a world of difference.

 

[hutchphd]

OK

Yup. It is. Still people have been trying to harness the quantum weirdness and use its potentials. If what I have been reading is right, quantum computing has now been proven feasible. Quantum states, for all practical reasons, appear to have a reality of their own. Its major hurdle is what is perceived as 'decoherence' which like measurement also appears irreversible. If they can cool down the qubit and isolate it well enough, the future is quantum. From computers to tv's simulating virtual reality via goggles in highest resolution to cars and the internet. I am modestly optimistic that the future of the human race is quantum and with its endless practical applications, interpreting its essence will likely be easier.

I find the highlighted text meaningless word salad . Please elucidate.
.

 

[hutchphd]

I have recently remembered this bit of Feynman wisdom. I believe it is part of the Cornell Messenger Lectures:


Drop the Mic.

 

[CoolMint]

OK
I find the highlighted text meaningless word salad . Please elucidate.
.

You need to understand the developments in quantum computing.
Quantum computers store the non-binary information in quantum states. You can find further info in the links provided in the wiki article. https://en.m.wikipedia.org/wiki/Quantum_computing

 

[hutchphd]

All computers store information in quantum states.
I was hoping you could make sense out of a statement that makes no sense to me. It was, after all, your statement.
I have taught both undergrad and graduate quantum mechanics courses. Yet there are parts of quantum computing I do not think I understand, so I already know that I need to "understand" it.

 

[CoolMint]

All computers store information in quantum states.
I was hoping you could make sense out of a statement that makes no sense to me. It was, after all, your statement.
I have taught both undergrad and graduate quantum mechanics courses. Yet there are parts of quantum computing I do not think I understand, so I already know that I need to "understand" it.

Computers based on transistors like yours store binary information in the transistors' gates. Not in quantum states. The computers of today do not employ quantum mechanics, but rather try to prevent it. E.g. leaking 2nm transistors due to quantum tunneling.

https://en.m.wikipedia.org/wiki/2_nm_process

The separation between gates and insulation becomes too small and quantum tunneling is very hard to prevent.

 

[PeterDonis]

Computers based on transistors like yours store binary information in the transistors' gates. Not in quantum states.

If you adopt a realist interpretation of quantum states (which is implied by your statement that "quantum states have a reality of their own"), then the states of the transistor gates are quantum states, since the state of any real object is a quantum state. So your statement above would be false as you state it.

The computers of today do not employ quantum mechanics, but rather try to prevent it

This is also false as you state it, since "quantum mechanics" underlies the behavior of everything, including transistors and computers.

I think you need to be more careful in how you state things. It would be valid to state that today's digital computers do not depend on any quantum interference effects, and try to prevent things like quantum tunneling from happening, since those things reduce the accuracy and reliability of the computers. But that is not what either of the statements of yours that I quoted above say.

 

[CoolMint]

If you adopt a realist interpretation of quantum states (which is implied by your statement that "quantum states have a reality of their own"), then the states of the transistor gates are quantum states, since the state of any real object is a quantum state. So your statement above would be false as you state it.This is also false as you state it, since "quantum mechanics" underlies the behavior of everything, including transistors and computers.

I think you need to be more careful in how you state things. It would be valid to state that today's digital computers do not depend on any quantum interference effects, and try to prevent things like quantum tunneling from happening, since those things reduce the accuracy and reliability of the computers. But that is not what either of the statements of yours that I quoted above say.

Quantum theory was never relevant to classical computers until the time when tunneling become a problem. Clearly everything is quantum in nature but that doesn't mean that a kitchen knife uses quantum mechanics. Even if its constituents are quantum in nature.
There is still a field of physics known as classical physics and it is no more false than a knife being a quantum object. A classical computer is not a quantum object unless weird discussions among interpretations are concerned.

 

[PeterDonis]

Clearly everything is quantum in nature but that doesn't mean that a kitchen knife uses quantum mechanics.

According to your idiosyncratic definition of what "uses quantum mechanics" means, perhaps. But as you can see from others' responses in this thread, your idiosyncratic use of language just makes it difficult for other people to understand what you are saying. That is why I said I think you need to be more careful.

 

[gmax137]

Has anyone done an estimate of how many worlds there are now? If the universe is made of say,10^80 protons and electrons that have been interacting for about 14 billion years, what does the number come to? Isn't it unimaginably huge?

How many bifurcations does an individual human experience every day? Asking for a friend :)

 

[PeroK]

Has anyone done an estimate of how many worlds there are now? If the universe is made of say,10^80 protons and electrons that have been interacting for about 14 billion years, what does the number come to? Isn't it unimaginably huge?

How many bifurcations does an individual human experience every day? Asking for a friend :)

I'm not sure there is a consensus on whether the number of branches is finite, countable or uncountable. I believe Everett himself postulated bifurcation into uncountably infinite branches.

 

[gmax137]

I believe Everett himself postulated bifurcation into uncountably infinite branches.

Well then in nearly all of them, the OP is not there. So the OP worrying about how things are going for him/her in these other worlds seems to miss the point. On the other hand, maybe there are some worlds where he/she is the king. And lives for ten thousand years. It's a glass half full thing.

 

[PeroK]

Well then in nearly all of them, the OP is not there. So the OP worrying about how things are going for him/her in these other worlds seems to miss the point. On the other hand, maybe there are some worlds where he/she is the king. And lives for ten thousand years. It's a glass half full thing.

Sure, especially if we believe that the origin of the galaxies is a series of quantum events in the early universe, then "most" branches do not have the Milky Way, Sun or Planet Earth, let alone an individual whose birth depended on a very specific set of macroscopic circumstances, which themselves were heavily dependent on quantum mechanical outcomes.

Taking about "being king" or "living for ten thousand years" may be missing the point. Even if there are such branches, then they must be statistically dominated by more normal outcomes.

That said, I'm not sure any of us has the capacity to make much sense of MWI from any sort of "human" perspective.

 

[stevendaryl]

I'm not sure there is a consensus on whether the number of branches is finite, countable or uncountable. I believe Everett himself postulated bifurcation into uncountably infinite branches.

Everett’s original paper on what came to be known as the “Many-Worlds Interpretation” didn’t talk about branching. It talked about the state of the rest of the world relative to the state of the observer.

 

[stevendaryl]

Everett’s original paper on what came to be known as the “Many-Worlds Interpretation” didn’t talk about branching. It talked about the state of the rest of the world relative to the state of the observer.

The original paper can be found here: http://jamesowenweatherall.com/SCPPRG/EverettHugh1957PhDThesis_BarrettComments.pdf