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.

This was mentioned (not fully, but enough to get some of the ideas) recently in an episode of PBS Space Time

As far as MWI itself, my understanding is that it comes from simply taking the same math that works for atoms (as you say) and applying it to everything - the observers of a quantum system, the earth, the whole universe. I think it really comes down to the question: If Everything is a wave function, what would it look like from the inside? And MWI pops out of trying to answer that.

And the other interpretations of quantum mechanics don't even seem better to me, requiring arbitrary conditions for a state to collapse to a single value for example. That feels to me like an entity of the type Occam meant.

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.

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.

https://youtu.be/XjsgoXvnStY

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.

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 on multiple bases that 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.

An analogy, if you're into programming, is that when the universe splits it will not duplicate the code of the universe but rather branch the state out.

Still though the universe would need some endless amount of memory to handle all the different deltas.

https://interestingengineering.com/science/the-first-ever-evidence-of-the-multiverse

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.

You're asking a couple different questions at once...

But basically assume that there are multiple (maybe infinite) big bangs, and each time that happens, the resulting universe has its own laws of physics. We wouldn't see slight changes, things would be drastically different, but since they keep popping up. Eventually we'll see every permeation happen. Including identical everything to ours, but just one random difference that created the TV version of alternate realities.

You might think entropy prevents that, but "entropy can't be reversed" is less a fact and more "the simplified version laypeople are told in science class".

And a different option would be that rather than one straight line of time, any possible choice can branch and create its own timeline that can then branch, etc.

And that might seem like we're "stuck" but nothing in physics even requires one way direction of time. The only reason we need to perceive it in only that way, is without linear time consciousness couldn't happen. Without cause and effect, consciousness can't exist

Great question. That’s all I have. Gonna be trusting folks that have worked in this field and have an extensive an incredibly qualified viewpoint from vast sources around the planet. That and there is an applicable physics understanding that honestly has no known bias. Sure, there are some varied hypothesis and theories within the scientific community. Ultimately, the actual science just is. It don’t care about your feelings. I do because I’m a human being. I hope you are having a wonderful day. But if for a moment you are peddling pseudo science, I want to make one thing clear, keep up the bullshit & Ima take you to the edge of the planet and throw yo’ ass of the edge. Try me. I will work on crowdfunding this project. I’m taking your dumb ass up in a big fucking jet & we are gonna fly the goddamn planet until we reach our point of origin from the opposite direction.