Though, the outlook of getting an answer to "is there really a multiverse out there or is the multiverse just a sequence of simulation runs on some future teenagers quantum computer simulator trying to find the best set of meta-parameters" is probably bleak...

A theory involving a multiverse can make observable predictions even if the other regions are not accessible.

I should have said evidence rather than proof, my mistake.

>theory involving a multiverse can make observable predictions even if the other regions are not accessible

All those predictions would serve as evidence for the same theory without involving a multiverse.

The prediction that objects continue to exist when we're not looking at them is not testable in the same sense (you could even say it's unfalsifiable and therefore not scientific); nevertheless most of us tend to believe in it.

We have experimental evidence that certain light patterns have been observed. For any theory that has Jupiter in it, you could make the same theory without involving Jupiter. I don't see any fundamental difference between the evidence for Jupiter and the evidence for the multiverse.

Another universe, basically by definition, has no observable characteristics. We can seemingly only observe our universe, and have no way of knowing if something unobservable is impacting our universe.

Sure, but isn't it the same for multiverse theories? Obviously we don't observe the multiverse directly, but we observe data for which the best explanation also implies a multiverse, just as the best explanation for various observations implies the planet Jupiter.

> Another universe, basically by definition, has no observable characteristics. We can seemingly only observe our universe, and have no way of knowing if something unobservable is impacting our universe.

There's a lot we can't observe or interact with directly; we can't interact with the past, we can't observe the future, we have to real way of interacting with distant galaxies, we can't actually observe inflation at all... a good multiverse theory (of which I'm not sure there are any, but I think they're possible in principle) would be in much the same category as inflation AFAICS: we can't observe the thing itself but we can observe things that seem most likely to be consequences of it.

No, we don't have observational data supporting a theory of a multiverse. With Jupiter, if there were a planet there we would expect x to happen due to our understanding of planetary physics. We then observe, and x happens.

We can't repeat this with a multiverse, as all of our observational data ever provides no insight into how another universe works.

Two people keep saying this, it is easy to prove me wrong here.

>There's a lot we can't observe or interact with directly;

None of which are science. We have past observations, and we can make predictions of the future, but that's basically the extent of their place in science. We do observe distant galaxies, and that's where are understanding of them comes from.

As for inflation, like of space? As we do have experimental data for that, something about how long light takes to reach us. If you're talking economics, very little of it is science.

No we don't - I assume you're thinking of dark energy, which is a separate and (as far as we know) unrelated phenomenon. The evidence for inflation is basically "the cosmic microwave background looks like it was produced by the universe behaving in such-and-such a way"; it had no effects except for very shortly after the big bang, so we can't use it make predictions about the future and observe whether they happen or not. (We can, and have, made "predictions" about things that haven't yet been measured, e.g. inflation was used to predict what the CMB polarisation would be before we launched Planck to measure it - but what we're measuring is something that happened in the very early universe).

So I don't see a lot of difference between that and e.g. a theory that says (with evidence) that our universe is the result of a symmetry-breaking process that would naturally have produced an ensemble of similar universes.

I was talking about the expansion of the universe that is still ongoing.

Inflation has observational data already, the radiation you mention, and much of the work done with particle accelerators is to recreate the conditions of these kinds of events. This is enough to make it science, even if completely wrong.

I thought of perhaps a simpler way to put this. The realm of science is the observable universe. We can use that to develop theories of events in our universe we can't observe, as there are still remnants in the observable universe. We can't develop theories of things that never happened in the observable universe though.

Maybe someday someone will develop some method to observe effects that would show evidence of a multiverse. It hasn't happened, and personally it seems unlikely.

"For some reason" is not a theory and it makes no testable predictions.

One with the same evidence as "god did it."

> is not a theory and it makes no testable predictions.

This is true of the multiverse too. It is an attempt to explain why things are like they are rather than a testable theory.

Okay, this is just going in circles. Up above you accepted that multiverse theories did make testable predictions. And they do, which is what makes them science.

edit let's use a concrete example. This thread is about the cosmological constant. I could easily say that concept is causes by multiverse influence on this universe, just as rightly I could say it's god's finger on the scales. Neither now have experimental data because I can say that.

further edit sorry, this is a bit stuck in my head. Look here

https://en.wikipedia.org/wiki/Multiverse

Notice that it is labeled a hypothesis, and the theories that involve evidence predict a multiverse may be possible with these conditions.

I don't understand this criticism. It's my understanding, the double slit experiment shows interference between universes. What is the alternative? decoherence?, but how do you develop an experiment that result in evidence that decoherence is real?

From a experimental point of view, multiverse have the same evidence that the alternative. From an epistemological point of view, multiverse is a more simple theory. Ergo, until we have more data, we have to prefer the multiverse theory.

Yes, the alternative is that classical mechanics is incomplete and quantum mechanics is necessary. And there has been plenty of experiments supporting this conclusion.