What proof is there of the multiverse?

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

My God! There must be many worlds than just our one?

But more

There are moments in time where one path is taken and not another... but what if all paths are taken, somewhere?

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.

[H]ow does one look at atoms and say "My God! There must be many worlds than just our one?"

Electrons. You've seen the model of the atom, right? Cluster of balls in the middle (protons and neutrons) and the electrons are little balls that whizz around like little planets around a Sun?

That model is a simplification of the truth. It turns out that it is impossible to pin down where an electron is and also know what it is doing. And if you know what it's doing (you can see its effects), you'll have no idea where it is.

Where they are has to be measured by probability. "It's bound to this nucleus / taking part in a chemical bond so it's likely to be in this vicinity", is about as close as you can get.

There is literally nothing excluding that electron from temporarily being a billion miles away. That's astronomically unlikely, but it's not impossible.

And by some measurement methods, when you do try to pinpoint where the electron is, it can appear to be in multiple places at once.

This can be interpreted as bleed-through from nearby quantum realms, maybe even other universes, where the electron is in one place per nearby universe. One of those places is ours, but we cannot tell which. And by the time we've made any kind of determination, the electron has moved. They never stop.

Photons - particles of light - also do this. All subatomic particles do this.

The more subatomic particles you have in some combined state (as an atomic nucleus, or even a molecule), the lower the probability is that that bound state can be in multiple places at once, but again, it is not ruled out.

But it does mean that the more bound particles an object is made from, the more definite its position appears to be, which is what we're used to at our human-sized scale.

If you want to know why it's taken seriously:

https://m.youtube.com/watch?v=kTXTPe3wahc

Tl;dr: you need to actually understand the physics at play that lead to serious consideration of the many worlds theory. It's not the pop-sci it gets painted as. It's much more specific.

Multiverse and many worlds interpretation are two different things.

The idea of multiverse is that there are many other universes existing in parallel with ours. Either the universes are created through different big bangs, or maybe the universe is constantly splitting into many other universes. This is mostly science fiction.

MWI is one of many competing ideas to help coming to terms with the counterintuitive nature of quantum physics. A particle can be in many places at once when not observed. Once it’s observed, it chooses to stick in one place. MWI is one interpretation of why this is happening.

I admit that I might be dumb, but, how does one look at atoms and say "My God! There must be many worlds than just our one?"

Well, we looked at atoms and found out that the only meaningful way to describe them is with quantum mechanics. This is the most precise and possibly best tested physical theory ever developed. And it says that if an atom starts out in state A, it will then naturally evolve into a state A+B.

Now, A and B are mutually exclusive. So what does that mean? One reasonable way to view it is that it is indeed physically in both states A and B as the theory says. That's ultimately what leads to the many worlds interpretation. The atom is both in state A and state B, and the universe accepts both of the different trajectories of reality that leads to.

This view is equivalent to a number of other ways of view things, all of which lead to the same prediction of physical behaviour for now, so essentially you can just pick your favourite.

If you want to go into depth on this, I recommend you look up Sean Carrol talking about the subject - or read his book Something Deeply Hidden, if you're up for it - he's one of the best science communicators I've heard and a strong proponent of many worlds.

But to try to summarize it in very short: the "multiversal" behavior is already baked into quantum mechanics - a particle can be in two places at once, as in the double slit experiment - just at a very small scale. Traditional quantum physics postulates that there's some mechanism by which this behavior is cut off before it reaches the macroscopic scale (wave function collapse). Many Worlds just asks "Do we actually need this postulate? What would it look like if we didn't have it?" And the answer is, it would look like the universe we experience, just with a multiverse along side it.

Two points:

• The MWI/Everett interpetation is the simplest interpretation of quantum mechanics—other interpretations have to add additional assumptions to prevent it from happening.
• The most common version of the MWI is actually an interpretation of an interpretation (i.e., Bryce deWitt’s reinterpretation of Hugh Everett's 1957 thesis), but many of those who subscribe to deWitt’s interpretation (including deWitt himself) don’t seem to grasp how it differs from Everett’s. Everett’s thesis makes no explicit reference to multiple worlds—just a single wave function that can be measured in different bases to produce multiple versions of each observer, each of which perceives a different version of the universe. For Everett, the wave function was ontologically prior to the material world, so his universal wave function was a complete explanation as-is. But for deWitt (and for most people), the material world is ontologically prior, while the wave function is just a tool for describing its behavior. So by their reasoning, those multiple perceived worlds must all really exist as parts of the wave function in some sense.

https://arxiv.org/abs/1301.1069

Effectively there is no current consensus on the issue, though Many Worlds and String Theory are widely regarded outside their adherents as non-falsifiable and therefore not legitimate theories.

Essentially the proponents of the theory have created beautiful math that fit their view, but absolutely nothing in the real world that can show that it is a more valid theory than any of the other theories which have equally elegant math to back them.

None.

It is, however, actually simpler than other theories, in that if you just let quantum mechanics do it's thing without extra (unknown) parts to limit it, it produces many worlds. So, by Occam's razor...

None. There is absolutely no proof of many worlds or the multiverse. RE the god of the gaps. It's much more interesting to do physics rather than speculate about what falls outside the purview of the scientific method.

movies

I'm not sure that there is proof. But there are quantum effects like wave function collapse, what a wave or particle seems to exist in multiple ways until measured.

I had a though experience years ago on mushrooms, that our universe lives in a blackhole. Just think about it, when stars big enough implodes it creates a black hole in the fabric of space, where nothing can escape (not even light).

The beginning of our universe is somehow related to a condensed hot/light that explodes and creates the actual expansion we see right now... Kinda curious right?

Also there's somehow a limit how far we can see through our universe, that's also odd... It's impossible at the moment to see outside our own universe, because remember nothing can escape outside a blackhole, not even light !! Soo yeaah that's why I think we live in a multiverse.

Also on a final note, Rick&Morty said so 🤷‍♂️

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