I Are the implications of MWI really this horrifying?

[akvadrako]

These two scenarios are very philosophically different, because in version two I can only ever experience one timeline, but in version one, I am continually literally splitting and experiencing every possible future. If the first version is true, philosophy has a lot of work to do on what MWI means for individuals. The second one doesn’t have any huge consequences other being interesting for the imagination.

I don't think they are philosophically different, at least in terms of what you should expect to experience.

Each version of you will only experience one timeline in both the splitting and the diverging descriptions. If this wasn't true, you would already be experiencing something different. So it's a matter of degree how altruistic it is to care about those other "yous" vs other people in the current world, because once the split has happened, you are different beings.

It's hard to explain this in normal language, but there is a classical analogy which I think captures the essence of it pretty well. Imagine we had perfect cloning machines. Each night you enter the machine, the original body is removed, and say a million perfect copies wake up in different rooms which will never interact until the end of the universe. Most of those copies are giving a very typical room, some are given bad rooms, and some good rooms.

From then on they live their own lives – they are not the same person. So even though there is no randomness involved from an objective (god or bird's eye) viewpoint, there is something like a random expectation from a subjective viewpoint, just like in non-MWI theories. In either case, over repeated iterations, to maximize your expected payout, the best strategy is to place bets in accordance with expecting to become one of the typical copies.

Expecting to become all of the copies does not make sense – it just comes about from a limitation of our language in describing such a situation.

 

[PeterDonis]

Imagine we had perfect cloning machines.

Note that, by the quantum no-cloning theorem, this is not possible. So this aspect of the analogy does not carry over to the quantum case. That should be kept in mind when interpreting it.

 

[akvadrako]

Note that, by the quantum no-cloning theorem, this is not possible. So this aspect of the analogy does not carry over to the quantum case. That should be kept in mind when interpreting it.

Are you saying that the versions of each "future you" in the different branches cannot be perfect copies?

 

[PeterDonis]

Are you saying that the versions of each "future you" in the different branches cannot be perfect copies?

In the sense of your classical analogy, they can't be perfect copies. In quantum terms, "you" are entangled with what you are observing, and each "future you" is the "you" degrees of freedom in one particular branch of the entangled wave function. So strictly speaking, none of the "future yous" have a definite state at all; only the overall entangled wave function is in a definite state. (Note that this is one of the issues with the MWI, explaining how we experience definite outcomes even though no individual branch of the wave function has a definite state at all.) Certainly no "copying" is going on in the quantum wave function; as I have already said, unitary evolution can't do that.

Even if we assume there is some way of getting around that difficulty, each "future you" experiences a different result of whatever measurement we're talking about, so they aren't perfect copies in that sense either.

 

[akvadrako]

Even if we assume there is some way of getting around that difficulty, each "future you" experiences a different result of whatever measurement we're talking about, so they aren't perfect copies in that sense either.

Indeed, better not to say they are perfect; but a clone that's good enough so it can reasonably think it's a future you.

And better not to say copies, but perhaps more future versions. Even though there is no copying going on, it's the orthogonal differences between the different branches that let's us say the branching tends to give us more branches in the future compared to the past, even assuming a diverging view.

 

[PeterDonis]

Even though there is no copying going on, it's the orthogonal differences between the different branches that let's us say the branching tends to give us more branches in the future compared to the past

As long as you're willing to ignore or hand-wave the fact that none of the branches individually has a definite state at all, yes.

 

[Moes]

These two scenarios are very philosophically different

You are getting into many philosophical questions, many which we already are confused about. It’s not even clear whether your two scenarios are at all philosophically different.

If there are two identical versions of you are there two of you or one?

Expecting to become all of the copies does not make sense – it just comes about from a limitation of our language in describing such a situation.

I don’t think it makes any more sense to expect to become only one of the copies.

If the first version is true, philosophy has a lot of work to do on what MWI means for individuals

Even without MWI philosophy has a lot of work to do. Why should you care about your future self/selves? Even if you do care about it why should you care about your own future self more than you care about anyone else’s? What makes you the same you today and tomorrow?

Before we have answers to all these questions I think it’s pointless to ask specifically about MWI.

 

[PeterDonis]

Even without MWI philosophy has a lot of work to do. Why should you care about your future self/selves? Even if you do care about it why should you care about your own future self more than you care about anyone else’s? What makes you the same you today and tomorrow?

Even if philosophy hasn't come up with what it believes to be good answers to all these questions (and I'm not sure all philosophers would agree with that--I think some think they, at least, do have good answers to them), our ordinary everyday view of things has reasonable pragmatic answers to them. Given that, it's reasonble to ask what, if any, impact the MWI has on those reasonable pragmatic answers. That is what I take the OP to be doing in this thread.

Before we have answers to all these questions I think it’s pointless to ask specifically about MWI.

Since this is your opinion, please do not post further in this thread, since you are basically saying the thread is pointless. Others may disagree, and they are the ones who should be posting here.

 

[Moes]

since you are basically saying the thread is pointless

Sorry if this is what it sounded like I was saying, its not at all what I was trying to say.

our ordinary everyday view of things has reasonable pragmatic answers to them. Given that, it's reasonble to ask what, if any, impact the MWI has on those reasonable pragmatic answers

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

 

[akvadrako]

As long as you're willing to ignore or hand-wave the fact that none of the branches individually has a definite state at all, yes.

I am willing to do that since I would say branching is just an approximate and convenient description; only the universe as a whole is independently consistent.

 

[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 .