> I don't see how relabelling "collapse" to "separation" and adding more or less infinitely proliferating universes solves the problem.

MWI isn't just renaming the collapse. Copenhagen is fundamentally different in that exactly one outcome is somehow chosen / selected and all others cease to exist. In other words Copenhagen has to add / invent some information: Which world to pick and when to do so. MWI simply avoids having to pick by continuing every branch simultaneously and recursively.

Meaning that MWI is actually a simpler theory and shows that the selection is unnecessary and all problems that come with it can be avoided. In that sense, the burden of proof lies with Copenhagen IMO and it just gives handwavy answers that the selection process somehow involves a conscious observer, whatever that is ...

> MWI also contradicts itself. Supposedly the universes are independent, but if their influence doesn't define the wave equation they do nothing to help explain it.

In MWI the wave function IS the integral of all possible outcomes / worlds / branches. In that sense they don't just influence it, they define it. Not sure how that is contradictory.

Btw, the same goes for Copenhagen in the state of super position as well. So, they are identical up to the point where Copenhagen selects one (collapses) and MWI simply carries on.

> Copenhagen is fundamentally different in that exactly one outcome is somehow chosen / selected and all others cease to exist.

In MWI exactly one outcome / branch is somehow what we see and all others cease to exist to us. MWI just gives handwavy answers about how it is so.

It follows by contradiction of the opposite statement: Lets say that all "you"s across all branches perceive all the other branches as well. That means that they do influence each other. In other words they are not separated and never where different outcomes to begin with.

But, all the interpretations of quantum mechanics start with the axiomatic assumption that the universe is modal and that there are different possibilities / outcomes. They only differ in if they chose to turn hypothetical outcomes into real outcomes or simply let everything be equally real from the get-go.

And yes, even superdeterminism has to deal with / model hypothetical outcomes. It just says that some of them cancel out each other early on as they would lead to inconsistencies in the future otherwise.

We are seeing all the other outcomes and branches too, we just aren't aware of it since those are separate universes.

I don't believe "feeling" has anything to do with the MWI interpretation. At least I've never heard it described that way.

Given the equations that describe quantum mechanics (ie Schrodinger equation) MWI is essentially the "null hypothesis". No equations that describe collapse have ever passed the rigor of experiment and all collapse theories require modifications to the mathematics of QM. The burden of proof here is on theorists that support collapse theories not proponents of MWI.

> MWI is essentially the "null hypothesis"

Null hypothesis in the sense of not producing any predicition? /joking

I agree with the grand-parent that substituting a "collapse" that we cannot understand with a "separation" that we cannot understand doesn't seem a big step forward.

MWI doesn't posit that the universes are separated. Different classical states of a single quantum computer are technically in different "universes", but are still interacting with each other.

Separation that you are talking about boils down to different parts of wave function being uncorrelated with each other. If this is the case, then events in one "universe" can't have causal connection with another because that would imply correlation.

It's not just a relabelling. In collapse theories, the wavefunction stops obeying the Schrodinger equation for a moment and discontinuously jumps to a new state. The times when it performs a discontinuous jump are called "measurements", though this doesn't necessarily mean there's a scientist sitting there with a ruler, it just means that the system has interacted with its environment sufficiently. In the many worlds theory on the other hand, the wavefunction continues to obey the Schrodinger equation for all time, and the natural result of this is that the wavefunction becomes very complicated and entangled, so that the motion of atoms here on Earth is very entangled with photons heading away from us at the speed of light out into deep space, along with pretty much everything else. But there's no mention of "separation" or "worlds" in the basic description of the theory; the one sentence description of many worlds is "the wavefunction obeys the Schrodinger equation all the time with no exceptions".

Where the worlds come in is that it's impossible to do calculations on the wavefunction of the entire universe, so we need to come up with a way of dividing it up into manageable pieces. Not because the theory requires that it be divided into pieces, but because otherwise we couldn't handle the math. The worlds are one of the ways we do that: We break the wavefunction of the universe into approximately perpendicular components that don't interfere with each other very much and don't have too much entanglement making them hard to understand, and we call those worlds. We can further simplify things by just looking at a subsystem of the universe rather than the entire universe, which involves taking a partial trace (this tends to introduce randomness). As time goes on and entropy increases, the entanglement and complexity even within a "world" will continue to increase and at a certain point we may notice, "hey, this component is really complicated now, and it can itself be divided into subcomponents that are approximately orthogonal and don't really interact with each other much, I can simplify my calculations by treating those as separate worlds now". This is what we mean when we say that worlds tend to split apart, but since the worlds are only approximately orthogonal and independent, when you define splitting is really a matter of how much error you're willing to allow in your calculations. (Also, the process of splitting is driven by increasing entropy, so when (if?) the universe reaches a point of total heat death and entropy stops increasing, this will also imply that the worlds have stopped splitting.)

So I'm not sure what you mean by "strong and exceptional". It's just math, and can be compared with experiment just like any other piece of physics. Take the experiments done in the original article. If any kind of collapse had been observed, then that would have straight-up falsified the many worlds theory. Many worlds says that physical systems can become entangled with their environments, but their wavefunctions can never just collapse, and these two cases are distinguishable in a careful experiment. Since collapse wasn't observed when these tests were done, that provides a little bit of evidence in favour of many worlds.

Falsifiability is a little more complicated for collapse theories. People don't agree on the exact definition of a "measurement", and what level of interaction with the environment is required to trigger a collapse, but in order to have a falsifiable theory, it's important that we have a precise, mathematical definition of when a collapse should happen (this definition does not have to be deterministic, it could just give us a probability distribution). So various people have put forward different definitions, and it sounds like these experiments have ruled out a bunch of them, but obviously they haven't ruled out every collapse theory put forwards by every physicist ever. It's a bit like when the LCH failed to find any supersymmetry particles, and some physicists were like, "okay, but in my version of supersymmetry, the particles are heavier than the energies reachable by the LHC so of course we wouldn't expect to have seen them".