I Are the implications of MWI really this horrifying?

[hungrybear]

TL;DR Summary

The implications of MWI theory seem to me to be horrifying for each us individually. Am I getting something wrong?

Please excuse my massive ignorance but I find this really troubling and I would hugely appreciate some input from people who know more than me.

The implications of the many-worlds interpretation of quantum mechanics seem to be awful for individuals. Am I getting something wrong?

As I understand it, many worlds means that for us, the observer, we split into multiple copies which experience every possible outcome of quantum measurement. A number of physicists have stated MWI means all physically possible realities exist.

The implications of this seem really disturbing to me. It means that with 100% certainty each of us sitting here reading this forum will experience the most distressing and painful possible outcomes. Yes it will be split parts of us but it seems we must think of these split selves as us or the alternative is that we cease to exist and new copies of us are created, which also isn't great.

If each possible human movement causes a new world to split off, then it seems like there are some really bizarre consequences. Is that right? Or are human beings on a macro scale not able to cause quantum splits?

If I make a decision to get on a plane, does it mean there is 100% certainty that I will experience the terror of a plane crash through human error. Yes millions of copies of me won't crash, but from the viewpoint of me right now making the decision to fly, the future self that crashes is also me.

In at least some worlds incredible technologies would be possible just from random movements humans make. This sounds insane but it seems like it follows there must be worlds where we are kept alive by technology and tortured, if all possible human actions occur in all possible orders.

People often talk about many-worlds in the sense of "oooh cool, in another world you're the lead singer in a band!" but it doesn't seem like the disturbing philosophical implications have been explored enough.

As I understand it, some physicists claim the world doesn't actually split, but all possible worlds exist along side each other at all times, and they become 'discreet', unreachable from each other, when quantum states split. So it's not that we literally split, but that multiple copies of us exist all along and the timeline of their experiences splits. This seems more bearable to us individually, as we're unlikely to be on the timeline with the worst possible outcomes.

I really genuinely appreciate any help with understanding this as it scares the hell out of me to be honest.

 

[A. Neumaier]

MWI has no observable consequences beyond the standard consequences of quantum mechanics. Hence there is nothing horrifying to worry about.

 

[PeroK]

Summary:: The implications of MWI theory seem to me to be horrifying for each us individually. Am I getting something wrong?

If MWI is correct, then the consequences are already happening. Whatever horrors you might fear are already with us.

 

[CoolMint]

There's only one you. The other you's aren't you any more than Joe Biden is you. Horrors do happen for whatever reason to each and all of us all the time but this is on an individual basis.

 

[DaveE]

As I understand MWI there is absolutely no ability to communicate or know about any of the worlds except the version you inhabit. Those worlds only exist as a theoretical construct. My view is that they simply can't be real in any current world context. Perhaps there are many worlds, but you can only ever be in one. Your existence is what you experience, also what you think, both of which are only in your present world.

Also, yes, you might die tomorrow (hit by a meteorite, massive undiagnosed aneurysm, quickly, slowly, whatever), even in your present world; for real. If that doesn't terrify you, I can't imagine why dying in a world you'll never know about would.

 

[Keith_McClary]

Also, yes, you might die tomorrow (hit by a meteorite, massive undiagnosed aneurysm, quickly, slowly, whatever)

There was a sci-fi short story where the main character experienced the branches where he didn't die, for increasingly unlikely reasons (one involving aliens).

 

[PeterDonis]

As I understand it, many worlds means that for us, the observer, we split into multiple copies which experience every possible outcome of quantum measurement.

This is the basic idea, yes. (Note, however, that if you actually try to match this up with what the math of QM says, there are plenty of issues lurking: for example, there is no "split into multiple copies" in the math--the time evolution is unitary, and unitary evolution can't create or destroy anything.)

it will be split parts of us but it seems we must think of these split selves as us

That's a question of philosophy, not physics: what you think counts as "you". On at least one obvious viewpoint, that "you" are defined by the exact sequence of experiences you have had, then the other "selves" in the MWI are not "you", because they have experienced different results of measurements.

If I make a decision to get on a plane, does it mean there is 100% certainty that I will experience the terror of a plane crash through human error.

No. One "branch" of the wave function will only include the plane crashing if some event with quantum uncertainty has a nonzero probability of making the plane crash. MWI proponents often wave their hands and assume that every event you can possibly imagine has some nonzero probability, but that is not at all obvious when you actually look at the math.

if all possible human actions occur in all possible orders.

The MWI does not necessarily imply that. More precisely, "all human actions that somebody can imagine" is not the same as "all human actions that have nonzero probability given the initial wave function". The latter is the only thing the MWI says anything about.

they become 'discreet', unreachable from each other

That is correct. In more technical language, the different "branches" of the wave function in which different outcomes occur are decohered, so they cannot interact with or communicate with each other. So from the standpoint of anyone single "branch", the other branches might as well not exist.

 

[valenumr]

My personal opinion is that MWI is sensationalist. It's an entirely philosophical view point I suppose. But I think QM interpretations fit into the "other" category for discussion.

 

[DaveE]

But I think QM interpretations fit into the "other" category for discussion.

So one vote for "shut up and calculate" then?

 

[valenumr]

My personal opinion is that MWI is sensationalist. It's an entirely philosophical view point I suppose. But I think QM interpretations fit into the "other" category for discussion.

So one vote for "shut up and calculate" then?

I wouldn't put it that way. It is very much a scientific question how perceived reality arises from quantum principles. But to date, all we can do is conjecture from a philosophical point of view. No opinion is even wrong.

 

[Demystifier]

MWI has no observable consequences beyond the standard consequences of quantum mechanics. Hence there is nothing horrifying to worry about.

It is legitimate to be horrified by non observable consequences. For example, the idea that billions of people suffer in an unobservable parallel universe can be quite horrifying.

A religion analogy: Someone who believes in paradise and hell in afterlife can be horrified by all those souls that will suffer in hell, even if he believes that his own soul will end up in paradise and hence never observe the hell.

 

[Drakkith]

I really genuinely appreciate any help with understanding this as it scares the hell out of me to be honest.

Right now in our world there are people being worked to death as slaves, drowning, dying in fires, being murdered, or experiencing one of a million other terrible things. I find them to be far more worrisome than some parallel universe. That is, I think it's tragic but it doesn't bother me nearly as much as it should.

There's no reason to be more horrified about MWI's implications than about some kid being worked to death in a mine somewhere in the world today. I at least have the potential to change one of these.

 

[A. Neumaier]

It is legitimate to be horrified by non observable consequences. For example, the idea that billions of people suffer in an unobservable parallel universe can be quite horrifying.

It is legitimate to be horrified about anything, even about the death of simulated people in a computer game. But for those who don't want to be horrified, the cure is to constrain their fantasies.

A religion analogy: Someone who believes in paradise and hell in afterlife can be horrified by all those souls that will suffer in hell, even if he believes that his own soul will end up in paradise and hence never observe the hell.

Paradise and hell are quite different from parallel universes. In the former.
Each observer on Earth is supposed to end up in either heaven or hell. Hence heaven and hell are part of the present universe in the sense of MWI, rather than being parallel universes.

 

[Demystifier]

But for those who don't want to be horrified, the cure is to constrain their fantasies.

The issue here is whether the parallel worlds are a fantasy or real. If they are real, then being horrified is justified. The religion analogy is useful because there one can also ask whether heaven and/or hell is a fantasy or real.

 

[valenumr]

The issue here is whether the parallel worlds are a fantasy or real. If they are real, then being horrified is justified.

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?

 

[Demystifier]

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?

There are 7+ billion people in the world. Most of them I will never see or experience in any way. Should I worry about them?

 

[valenumr]

There are 7+ billion people in the world. Most of them I will never see or experience in any way. Should I worry about them?

Well, solipsism is one line of thought...

 

[akvadrako]

As I understand it, some physicists claim the world doesn't actually split, but all possible worlds exist along side each other at all times, and they become 'discreet', unreachable from each other, when quantum states split. So it's not that we literally split, but that multiple copies of us exist all along and the timeline of their experiences splits. This seems more bearable to us individually, as we're unlikely to be on the timeline with the worst possible outcomes.

Indeed, that is another way of looking at it, called the diverging worlds view. If you want to read more on that a good starting point is Branching and Uncertainty by David Wallace. Both branching and diverging views are compatible with the math of MWI, so either could be true.

Or perhaps neither really gives a good sense of what it would be like to live in such a reality, because it's trying to describe a quantum system in classical terms which is essentially impossible. If we could describe it better in everyday language maybe you wouldn't find it so horrifying.

 

[valenumr]

Indeed, that is another way of looking at it, called the diverging worlds view. If you want to read more on that a good starting point is Branching and Uncertainty by David Wallace. Both branching and diverging views are compatible with the math of MWI, so either could be true.

Or perhaps neither really gives a good sense of what it would be like to live in such a reality, because it's trying to describe a quantum system in classical terms which is essentially impossible. If we could describe it better in everyday language maybe you wouldn't find it so horrifying.

I keep myself sane by thinking of it as, well basically the law of large numbers. On a macro scale, if we take a huge number of more or less normal random samples with a tiny standard deviations, we shouldn't notice anything other than the mean. When we craft intricate experiments to observe such behavior on very microscopic scales with low sampling rates we can see it.

 

[PeroK]

There are 7+ billion people in the world. Most of them I will never see or experience in any way. Should I worry about them?

No man is an island entire of itself; every man
is a piece of the continent, a part of the main;
...
any man's death diminishes me,
because I am involved in mankind.
And therefore never send to know for whom
the bell tolls; it tolls for thee.

 

[PeroK]

PS having quoted John Donne, I admit that I don't necessarily agree with him!

 

[Demystifier]

any man's death diminishes me

So does the death of my copy in the quantum Russian roulette suicide diminish me?

 

[valenumr]

So does the death of my copy in the quantum Russian roulette suicide diminish me?

Well, the quantum suicide argument may be intersecting, but I'm not going to test it.

 

[valenumr]

Well, the quantum suicide argument may be intersecting, but I'm not going to test it.

Interesting...

 

[PeroK]

So does the death of my copy in the quantum Russian roulette suicide diminish me?

I suspect John Donne was not familiar with the MWI interpretation of QM.

 

[Demystifier]

Interesting...

Are you discussing with your copy?

 

[martinbn]

So does the death of my copy in the quantum Russian roulette suicide diminish me?

I have a copy in one of the universes that worries about these things so that I don't have to.

 

[atyy]

A religion analogy: Someone who believes in paradise and hell in afterlife can be horrified by all those souls that will suffer in hell, even if he believes that his own soul will end up in paradise and hence never observe the hell.

That is not correct. Hell can be observed from paradise. OK, I guess you can say it's Abraham's bosom, so strictly speaking it's not clear if that's equivalent to paradise or not.
https://en.wikipedia.org/wiki/Rich_man_and_Lazarus

 

[PeroK]

That is not correct. Hell can be observed from paradise. OK, I guess you can say it's Abraham's bosom, so strictly speaking it's not clear if that's equivalent to paradise or not.
https://en.wikipedia.org/wiki/Rich_man_and_Lazarus

So, part of the reward of being in Heaven is to get to watch those in Hell be eternally tormented?

Come to think of it, just knowing that your parents or children, say, hadn't made it to Heaven would take the shine off your own eternal paradise, I would have imagined.

 

[martinbn]

I think what believers in MWI should worry about is that there is a chance they happened to be in an universe in which the MWI is wrong.

 

[MathematicalPhysicist]

You shouldn't be terrified as a new theory is around the corner to replace Quantum Physics...

Just need to wait for it until 2100...

 

[Drakkith]

I choose not to worry about most things which I find silly. And I find MWI silly.

 

[StevieTNZ]

Sounds more like a psychiatric/psychological issue than a quantum mechanical issue.

 

[phinds]

I choose not to worry about most things which I find silly. And I find MWI silly.

 

[CoolMint]

How can just one universe be real in the MWI? It makes no sense. It's more appropriate to call it OWI(one world interpretation).

 

[PeterDonis]

How can just one universe be real in the MWI?

In the MWI, the wave function is what is real; that is "the universe"; and there is just one wave function.

 

[CoolMint]

In the MWI, the wave function is what is real; that is "the universe"; and there is just one wave function.

Yes but the issue is that we always find the electron at one single location.

 

[dextercioby]

Is the „split into multiple worlds” : A) observer/ frame dependent and B) only caused by measurement, i.e. in the absence of measurement there is only one world...?

 

[mitchell porter]

The most advanced version of many worlds is the "consistent histories" or "decoherent histories" formalism of Hartle, Gell-Mann, Omnes, etc. Each individual history is specified as a time series of properties, and then the overall formalism allows you to take a set of such histories, and assign them each a probability, given a wavefunction of the universe.

This formalism does not inherently require that "all" possible histories happen. Instead, it has a limit on how similar two of the histories can be: all the histories must "decohere" from each other, for the ensemble of worlds to be well-defined. It has occasionally been suggested that if there is a quantum multiverse, it might consist of a Hartle multiverse ensemble that is as tightly packed as possible, within the constraint of mutual decoherence.

Since the question is worrying about the possible reality of hellish universes in the multiverse... Such worlds probably exist in a maximal Hartle ensemble of worlds, but if they rely on extreme bad luck to take place, they will have a very low probability. And this brings us to one of the recurring problems for the many worlds interpretation - what it means for one world to have a lower probability than other worlds, if all worlds are equally real. (Hartle himself, as far as I know, does not regard his formalism as a theory of many actual worlds, instead it's a way to get a probability for one world, without having an external observer.)

The essence of the problem of probability in many worlds, is that if all the worlds are equally real, they should each have an equal prior probability of being the world that you are in; and that gives you probabilities inconsistent with the Born rule of quantum probability, which is the rule that actually works empirically. I only know of two ways around this. One is: if there is an uncountable number of quantum worlds, then counting them is problematic, you need a "measure" in the sense of integral calculus, and perhaps the Born probability could be the measure. The other is: if there is a countable number of quantum worlds, perhaps there are multiple copies of the different possible histories, and this is how the worlds can have the unequal prior probabilities required by the Born rule.

 

[PeterDonis]

Yes but the issue is that we always find the electron at one single location.

Not according to the MWI. According to the MWI, all possible measurement results occur. The branches of the wave function in which they occur are decohered so they can't interfere with or communicate with each other. But all of the branches are real according to the MWI.

You might not agree with the MWI; many people don't. But you can't use the fact that we observe a single result for measurements to refute it, since the MWI already accounts for that.

 

[Quantumental]

And this brings us to one of the recurring problems for the many worlds interpretation - what it means for one world to have a lower probability than other worlds, if all worlds are equally real. (Hartle himself, as far as I know, does not regard his formalism as a theory of many actual worlds, instead it's a way to get a probability for one world, without having an external observer.)

These videos makes it very clear that Hartle and his Consistent/Decoherent Histories are just a synonym for Everettian Many Worlds:

1

2

 

[mitchell porter]

These videos makes it very clear that Hartle and his Consistent/Decoherent Histories are just a synonym for Everettian Many Worlds

I looked for Hartle's own opinion on the reality of other worlds, and found on page 9 here, the statement that "words like ‘all the other histories are equally real’ can be dispensed with without affecting the experimental implications of the theory". In the same paper, in a section on "reality", he talks about the different realities of schizophrenics and UFOlogists, and also about consensus among "information-gathering-and-using systems", and "realms" within the universal wavefunction. It's almost as if he thinks, not that there are "worlds" within the multiverse, but rather "realms" defined by agreement on observations among multiple observers - but I didn't have the patience to confirm that he has actually committed himself to such a peculiar ontology.

 

[Demystifier]

I think what believers in MWI should worry about is that there is a chance they happened to be in an universe in which the MWI is wrong.

Can this probability be computed from the Born rule?

 

[hungrybear]

Thanks, I genuinely appreciate all the replies.

Yes in a sense this is a philosophical issue (as you might guess I'm coming from a philosophical, not a science background, both help us to understand what is real). From what I understand, it's not as simple as "the worlds don't interact so you are not in them" because we are talking about your future.

If you in the present moment split into multiple worlds, then although these selves won't experience each other, from the perspective of you in the present moment wondering what your future will be, it will be all the futures. It's not the case that 'the real you' splits into one world in particular. So it is different from worrying about the suffering of people who aren't you.

You exist in the present moment, you wonder what your future will be. Everything that makes up you, all the particles in your body, split into multiple worlds so your future fate is whatever happens to each self.

This is discussed here:
https://www.quantamagazine.org/why-...quantum-mechanics-has-many-problems-20181018/

It doesn't make sense to say that you are only one of those versions of yourself when the world splits, unless all along there were multiple yous and multiple worlds and they only become separate by having different events in them, rather than literally splitting from one single reality.

It relates to this topic here: https://www.physicsforums.com/threa...many-worlds-everettian-interpretation.616019/

The other question I have is in the Many Worlds Interpretation, what causes the many worlds not to interact with each other? As I understand it, each world is in the same space-time and each particle has the same properties that would previously have caused them to interact but after decoherance they don't interact. Is there a physical / ontological justification for why they don't interact or is it just an assumption based the maths?

Thanks again for any replies!

 

[hutchphd]

Is there a physical / ontological justification for why they don't interact or is it just an assumption based the maths?

You are assuming there is a physical justification for any of it. There is not.

At least with matters of religion one can rely on Pascal's Wager to provide a rational framework.

 

[CoolMint]

Wavefunctions are mathematical entities. How would they 'interact' in the first place?

 

[PeroK]

Wavefunctions are mathematical entities. How would they 'interact' in the first place?

In MWI, there is only the one universal wavefunction. It has branches that represent the different worlds. The branches do interfere but always destructively, so that hybrid branches have vanishing probabilites.

 

[PeterDonis]

It doesn't make sense to say that you are only one of those versions of yourself when the world splits, unless all along there were multiple yous and multiple worlds and they only become separate by having different events in them, rather than literally splitting from one single reality.

The part that I bolded in the quote above is actually the case if the MWI is true. The terms in the wave function that correspond to "different worlds" are already there before the "splitting" (which, as I think I've already pointed out in this thread, is a misleading term in this context). All that happens when "the world splits" is that you (the quantum system that is your body and brain) interact with something (some other quantum system) whose state is not an eigenstate of the "you making an observation" observable. This interaction entangles the "you" quantum system with the other quantum system. But it doesn't change what degrees of freedom are in either system; it doesn't make "copies" of either system. It just entangles them. As I pointed out in an earlier post, time evolution in the MWI is always unitary, and unitary evolution can't create or destroy anything.

in the Many Worlds Interpretation, what causes the many worlds not to interact with each other?

The fact that they are decohered.

 

[CoolMint]

How does the fact that probability amplitudes lose coherence lead to the suggestion that they land in... other unobservable universes?

 

[PeroK]

How does the fact that probability amplitudes lose coherence lead to the suggestion that they land in... other unobservable universes?

That question has lost coherence!

Seriously, you need to read up a bit on the MWI, rather than react with astonishment or consternation at every turn this thread takes!