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What proof is there of the multiverse?
(sh.itjust.works)
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this post was submitted on 03 Aug 2025
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There isn't any "proof"; in fact, Many Worlds is what's called "unfalsifiable", which means we don't have a way through the scientific method to show Many Worlds to be false.
Also, it's not really
But more
It's not meant to be a valid theory, it's just a possible outcome of having a spacetime continuum; because it's not falsifiable though, it's not worth pursuing right now, only worth keeping in mind in case we come across new evidence to evaluate.
Thank you for making the point so cleanly. I was about to piss a lot of people off
That's not actually true
For one thing, any experiment which demonstrated objective collapse (which aren't just possible in theory, they've actually been performed) would falsify MW.
I'm aware of the double slit experiment and its variations, but I probably do misunderstand Many Worlds to at least some degree; how does wave collapse prove Many Worlds to be false?
Well, under Many Worlds, wave function collapse isn't a real "thing"; it's just an illusion caused by the observer becoming entangled with the wave function. Objective Collapse theories, however, propose a real physical mechanism of wave function collapse. If that's true, and there was found to be a real mechanism of collapse, then MW would be impossible, because the wave function would collapse before any "branching" could happen.
And what is there to stop the collapse from being the branch point? In one world, it collapses one way; in another, another. There doesn't seem to be any inconsistency there.
Well, because under Many Worlds, the wave-function not collapsing is the reason there are multiple branches; the wave function is the multiverse. So if the wave function has collapsed into a single, definitive state, then there is only a single, definitive universe.
Sorry, that doesn't prove that there's not actually Many Worlds out there. The whole point is that there would be a single, definitive universe state for every possible valid configuration after wave-function collapse. The reason it's unfalsifiable is that it cannot be proven currently whether or not it's a literal plurality of alternate worlds. I would also argue that if there's but one "definitive universe" state then it's not really a Many Worlds theory at all, but just a different theory of the Universe.
I'm not saying you're wrong, or that this interpretation of Many Worlds is wrong - I'm just saying we've not yet developed a way to prove it one way or another. And if we did develop that technology to prove it one way or another, that would in itself unlock a whole new world of questions to answer. Thinking about what those questions might be is worthwhile science, in my view.
I think you misunderstand me. I'm talking specifically about the Many Worlds interpretation of Quantum physics specifically, the one originally formulated by Hugh Everett. I'm not talking about just some general notion that "there might be other universes".
It's just an indisputable fact that the MWI requires their to be no wave function collapse, and if you don't understand why, you really have not learned enough about it to be in a position to declare it "unfalsifiable".
Well, I did allow for that earlier. I'm not a physicist. However, I wouldn't be so sure I don't understand why. Reading back over the thread as a whole, you're right - I did misunderstand you. Let me put it in my own words for you:
But you said above:
and
Could you link the experiments which have definitively shown objective collapse and not just an entanglement illusion? Fair warning, I may need to ask for a layman's explanation of how they proved the collapse was objective and not just the aforementioned illusion.
Essentially, yes. I think the important point is that MWI is only concerned with the multiverse that an uncollapsed wave function represents, not any other kind of multiverse that might exist in science or philosophy.
Here's a reasonably good article about them.. But to try and give a short explanation, the experiments were for a class of objective collapse theories were individual particles collapse spontaneously with a certain probability, and take any particles they're entangled with with them. The probability of any one particle collapsing at any given time is extremely low, but a macroscopic collection will collapse almost instantly, in the same way a uranium atom will take millions of years to decay on average, but a chunk of uranium sitting on a table will make your gieger counter sound like it's full of bees.
The important part though, is that - for reasons that are quite technical - the collapse of the particle actually emits a small but measurable amount of radiation, which is what the experiments were looking for.
To be clear, they didn't find it, which is bad for these theories. But if they had found it, it would have falsified Many Worlds.
Funnily enough, I found that article while reading up on MWI and was keeping it in my back pocket to compare with whatever you ended up linking.
So here's where I think we're getting tripped up. You're talking as though detecting this radiation would have falsified Many Worlds; I still think it would not. It would have created an explanatory burden on proponents of MWI, to explain where this radiation is coming from if not wave function collapse. These experiments wouldn't have been able to prove that the collapse was causing any kind of radiation emission; only that radiation emission was concurrent with it. We could conclude the collapse was the source only if all other sources were ruled out as possibilities.
Here's why: Each "world" would observe its own collapse of the wave function. The parameters of the emitted radiation - particle or wave type, energy level, charge, spin, colour, direction of travel, everything - would be different for every collapse, because every collapse is a branch point for a new world that can observe that specific collapse.
The trouble here is that you're taking the "objective" in "objective collapse" at face value. No experiment has been performed that has detected this radiation being emitted, but if it had, it still wouldn't have falsified MWI. I'm quite sure there's no experiment that can be performed that can't also be explained away with branching paths. Certainly not an experiment possible with current technology or theories.
The problem is, as I said, one of perspective:
Both frameworks ultimately make identical (observable) predictions from within each world, which is what makes MWI unfalsifiable. If you had a way to definitively show from within this world that MWI's other worlds don't actually exist, then it'd be falsifiable. The ontological claims of a theory are not what make it unfalsifiable.
Ok, well now you've basically argued that falsification in general is impossible, for anything. Just like geocentrists could always add more epicycles to explain the motion of the stars, any theory can add more post-hoc explanations for any observations. This isn't a standard you would apply to anything else, so I don't know why you're applying to MWI.
No they wouldn't, the laws of physics still apply
And why shouldn't I?
Yes, but by your standard, nothing can ever be falsified.
You asserting it doesn't make it true.
Except there is no radiation emission unless the wave-function objectively collapses. That's the point.
No, they don't. One predicts spontaneous radiation release, and one doesn't.
literally asking to prove a negative.
English comprehension fail, no I didn't. I said you can't prove other worlds exist or not if you can't access anything other than this universe's information, which is true. Because if you can't access anything other than this universe's information there's no experiment to run on information about other worlds. This stems from not being able to observe those worlds by which to gather information about them, which is quite important to the scientific method.
You think "the laws of physics" state there's only one outcome for every trait of a radio wave or excited particle? Because that's what your statement here means, since you're disagreeing with me. We're talking about how everything is a cloud of possibilities and you want to tell me now that every trait and path is predestined? That's just wrong.
Because reality is not objective, duh. Quite literally what we've been talking about this whole time.
Still as wrong when you said it here as at the start.
I was being polite. Show me the experiment, and this time don't just link any old shit in the hope I won't read or understand it. Despite my words, I know what I know, and you don't get to condescend to me without proving me wrong. Which you haven't done yet, due to the aforementioned failures in your English comprehension.
There's no radiation emission at all that we've observed, but even if there were, you can't just demonstrate something happening around the same time and call it causality. You have to the show the radiation didn't come from another source, and anyone who disagrees with your conclusions has to show it did, and then we all get together and pick it all apart in peer review until we've decided whose argument is the best-supported.
Which is like now, but you're not showing any evidence of these "objective experiments" we've been running that supposedly prove anything about or have access to information from outside our universe.
Explain how you plan to show that the spontaneous radiation release was not a result of being entangled with the thing you're observing. Your whole argument rests on information from this world, I'm blown away you don't see the fault in it.
Yeah you're right, let me rephrase: if you had a way to definitively show from within this world that MWI’s other worlds DO actually exist, then it’d be falsifiable.
There. Now go ahead and prove that other worlds exist.
You spent a lot of words to say you don't understand that we don't live in an objective universe, or what falsifiability really is. I'm just willing to allow that I might be wrong even when I'm not, and you aren't because you're so certain you're right you can't see what you're actually saying.
I'm done with this conversation now; I hope you go do some reading on the scientific method to address these shortcomings, because I am positive you're not going to do the one thing you need to (which, again, is just to show the objective experiments you're talking about, rather than condescending to and insulting me).
I want a paper that analyses information observed from other worlds, which yours DID NOT. Try taking your own advice to that other person in this topic, and read what I wrote.
Okay, apparently I need to take you to school before I go to work. I didn't realise it was my turn with you this week. Just to catch you up: https://www.nobelprize.org/prizes/physics/2022/advanced-information/
(That bit, by the way, is why I'm right and you're wrong. Not experimentally testable? Not falsifiable. Period.) And
Now I'll be blocking you. Happy reading.
I think you missed the part where I said I'm done.
Seems like it's splitting hairs and saying the "many worlds" part of MWI doesn't count, as that is only a prediction not postulated.
No? I'm not sure how you got that from my comment
I'm taking about the linked page.
I mean, to be fair that is what the linkes page says, but people are misunderstanding the hypothesis everyone calls many worlds (also what the page says) as Many worlds is just a follow up of the theory not the theory itself.
Like Einsteins Relativity didn't say in the theory that we would be able to predict Mercury's orbit, but it comes from it.
By the linked argument, introducing any sort of nondeterminism into classical physics would predict many universes.
If I flip a coin, a classical statistical model would predict I have a 50/50 chance of getting a heads or a tails. I can predict different things will happen as things react to the heads/tails result, and describe different “universes” where each of those outcomes happen.
Do those “other universes” really exist? Or are they simply a figment of my statistical analysis of the situation? That’s the part that’s unfalsifiable.
Not necessarily, objective collapse theories can be non-deterministic without predicting many universes. The extra universes only appear if the wave function never collapses, and stochastic collapses are entirely possible.
Yes, but critically - under classical mechanics - this is only because you have imperfect knowledge of the system. From the perspective of Laplace's Demon, the result of the flip is 100% deterministic and the chance of it landing the other way is 0. But this is not the case in quantum physics unless a hidden variable theory turns out to be true (and thus any experiment which discovered hidden variables would also falsify MWI)
Well, no. Because you're talking about classical mechanics, where probability is just about imperfect information and isn't part of the underlying ontology. So no, those universes don't really exist. That's completely different from quantum physics, where the wave function actually exists - it's not that the electron only goes through one slit and we just don't know which one: it really does go through both slits.
All it takes to produce the many worlds is the assumption of true nondeterminism that isn’t simply “imperfect information”.
Conversely, if you interpret quantum mechanics as a rethinking of statistics rather than some additional physics for the universe, you can make sense of the world without the need for a multiverse.
Incorrect. As I said, objective collapse theories can be non-deterministic without predicting many universes. The extra universes only appear if the wave function never collapses, and stochastic collapses are entirely possible.
But you can't. Quantum physics cannot be explained by classical mechanics alone. If it could, we never would have formulated quantum physics to start with.
Yea, the difference between a classical statistical theory with and without many worlds is whether or not you maintain a state that includes all possible outcomes as you continue your analysis, or restrict the state you are analyzing to one possible outcome from one of your statistical events. The same is true of quantum mechanics.
I’m arguing that quantum mechanics is a rethinking of statistics more so than a rethinking of physics. The world cannot be explained without it.
I think that even if I must consider a state that includes all possible outcomes while doing my analysis of the situation, that doesn’t mean those “alternate worlds” necessarily physically exist in any meaningful way.
Yes, but, again, this is only because you have imperfect information about the underlying physical system. The array of possibilities presented by classical statistics are strictly epistemic; the actual real state of the system you're analyzing is always definitive and determinate.
And very, very importantly, this is not that case in quantum physics. The indeterminacy of state in a super position is not just the result of imperfect information; it is a fundamental part of the underlying system. It is not the case that, in the double slit experiment, the electron only travels through one slit, and we just don't know which one. It really really does travel through both. This is fundamentally different from classical mechanics.
Look, if you want to try and argue that quantum physics isn't physics, I won't stop you, but you'd better have an extraordinary argument, because this is an extraordinary claim. One that rejects the last century of scientific consensus. If you can demonstrate that quantum mechanics is just a different statistical model of classical physics, it would be a revolution in science.
That's correct, and MWI doesn't argue otherwise. The important part isn't just that these states are possible, it's that they have real physical existence.
You are glossing over my point. I’ll try to put it as concretely as I can think of:
Assume for the sake of argument that there is a process in an otherwise classical physical system that is truly nondeterministic, meaning there is randomness that isn’t due to any hidden variable or otherwise incomplete knowledge of the state of the system.
When describing such a system, you will run into the same dilemma of either needing a “wavefunction collapse” or “many worlds” interpretation of your statistics.
And yet this model is not quantum. It is a classical nondeterministic model.
My point being, it’s the existence of true nondeterminism that leads to the “many worlds” idea, not the other strange properties of quantum mechanics.
I really, genuinely, think this is not a controversial take. The idea that quantum mechanics is more of a rethinking of statistics than physics comes from my own personal experience studying quantum physics. Most of the time, you take the classical Newtonian mechanics equations (sometimes including “corrections” for relativity), and treat them with the “quantum mechanics” version of statistics, and out pops all the important things you’d like to model, like how electrons arrange into orbitals in an atom. The results of slit/entanglement/bell experiments depend on having an object that obeys quantum statistics, but it can be a wide variety of objects with vastly different physical properties and behaviors (e.g. slit experiments have been done with both photons and electrons).
I don’t think there is any reason to believe the “other worlds” needed to analyze quantum systems “physically exist” to any meaningful extent. It’s the same as considering all possible outcomes of a classical truly random event (if you assume there exists true nondeterminism, not simply a lack of complete information).
I promise I'm not doing it deliberately.
Yes, I would agree with that if we're using "wave function collapse" to refer to any truly probabilistic mechanism in a general sense (as, strictly speaking you could have a non-deterministic mechanics without wave functions at all).
But I note the important fact that you don't need both.
Well no, it's the existence of true non-determinism without any form of wave function collapse.
Well if that's the case, with all due respect, I think you need to study quantum physics more. Because trying to overturn a century of scientific consensus is definitely controversial, at best.
How, specifically, are you modeling the double slit experiment using only Newtonian Mechanics? How about quantum tunneling?
Are claiming that super positions don't actually exist at all? Because, again, you'd better have a solid argument for such a radical claim.
Is it? Hard to say when we're talking about something that doesn't actually exist.
I don’t think what I’m suggesting is “trying to overturn a century of scientific consensus”. It’s a mildly different interpretation of the same math, that doesn’t require many physical worlds. It’s also not that uncommon. The “many worlds” idea is not scientific consensus. Go read about interpretations of quantum mechanics from sources other than Sean Carroll.
Both the double slit experiments and quantum tunneling emerge when you apply quantum statistics to any point particle following Newtonian mechanics.
Superpositions are a mathematical tool for describing the statistics of potential measurements.
Here’s an interesting example:
The Bell test about entanglement is one of the best-known proofs that quantum mechanics can’t be explained using classical statistics.
The Bell test is an analysis of the correlation between two entangled particles.
However, that correlation is only notable because we are analyzing the evolution of both particles.
If we analyze one particle, alone, we wouldn’t be able to determine if it is entangled with any other particles (and we wouldn’t be able to model it without the need for quantum mechanics).
In other words, you only need the “other worlds” when you are analyzing a system and trying to predict its behavior. You can completely ignore all information or “other worlds” external to the system you are studying.
That seems to demonstrate the opposite of your argument though, because the other particle does still exist even if you don't consider it.
Great answer, but it unfortunately is taken seriously. The reason is because it is an "end of the road" hypothesis. It tells you all the weirdness is fundamental and no further thought is required. Just like good old Copenhagen. The unfalsifiability is a virtue here, it's a complete explanatin without the messy testing. Now stop thinking, shut up, and calculate.
To be clear, the reason Many Worlds hypothesis exists in the first place is because it's a possible solution to the calculations. It's not that someone just came up with an idea to get out of doing real work. It's just unfortunate when the universe puts multiple possible solutions out of reach of experimentation. But hey, there was a long time of history where virtually any belief about the composition of the moon was considered unfalsifiable.
The "solutions" are not out of reach. Just do the experiment more than once, like any statistical theory.
The moon thing: yes because it was hard to get to, not impossible in principle. If the moon was in a parallel universe your analogy wouldn't be irrelevant.
Why is that unfortunate? It's an extremely well justified theory.
I'm not sure why you say this? If anything, that's a description of Copenhagen, which MWI is a response to.
You can probabilistically prove the many worlds exist, because it implies quantum immortality. Just connect a short-half-life Schrödinger mechanism to a nuclear bomb, and some of you will survive for a statistically impossible number of half lives. That version of you will have proven the many worlds to be true.
Right, and you can find out what it looks like beyond the event horizon of a black hole by just throwing a probe in that can survive the approach. Mind you, you're not getting any information back out of the black hole, but it'll be there in the probe's databanks regardless. I suppose you can have it back over the span of the rest of the black hole's life; though, you'll need to record everything else coming out of it and somehow cohere all that information back together in the right order.
Which is only about as difficult to get anything scientifically useful from as your probabilistic proof machine. Both involve lots of radiation though, so they're basically the same thing! (👉ﾟヮﾟ)👉
Except you might be the version who survives!
Except you might be the person who survives!
Except you might be the person who survives!
I don't think it proves many worlds any more than it proves you have a fairy godmother manipulating quantum states for you. All you've done is shown an unlikely occurrence happened, not what caused it.
That's all science is. Collect data, and show how it's unlilely unless your hypothesis is true. Five sigma later, and you've made a discovery.
The quantum immortality experiment doesn't do that, though. The outcome, by definition, always occurs within the realm of random chance. Your environment needs to create an outcome that is extremely unlikely to occur by random chance. The experiment is not repeatable. It makes no predictions about what's going to happen if you try again. It doesn't do anything useful to bolster the many worlds theory.
If you survive 32 half lives, I'd call that extremely unlikely! Give a try.
The experiment, as defined, only leads to your survival by random chance. The experiment does not create any outcome except by random chance so it cannot be used to prove anything.
Every half life you survive is an experiment.
The chance you'll survive a half life is exactly the same whether MWI is real or not. It doesn't give you any useful information. You have no way of distinguishing between being just that lucky or MWI being true.
That's not the case with other experiments. If you assume your hypothesis is correct, the chance of the experiment being successful is higher than the chance of it happening by random chance if your hypothesis is not. That's a key difference.
You're right, of course. But it feels like science.