Does 'many worlds', imply worlds before the Big Bang?

[bland]

TL;DR Summary

I don't know how to (TL;DNR) this summary but I'm wondering basically if my reasoning is flawed to conclude that Many Worlds, appears to imply they happen on both sides of the creation event, otherwise known as the BB.

I'm at this point because a whole bunch of audio books I've been indulging in all seem to be converging on Many Worlds, and this has been given extra authority now because Sean Carroll appears to be a convert. I used to wonder if this was actual physics or metaphysics, and I've given up asking that question.

However... if I accept from reputable physicists that Many Worlds is indeed true, and if I am completely agnostic about whether it's 'testable' my current understanding appears to be that it must imply a genuine infinity of many worlds, for a similar reason that there are an infinite amount of real numbers between any two real numbers and there are an infinite amount of real numbers. I understand that there are different sizes of infinities but even then my reasoning says (if I have understood many worlds correctly) that every quantum event splits the universe.

And there must be countless trillions but perhaps a finite number of trillions of splittings going on at any instant. And every single one of them will be a split universe. My confusion about the multiverse (taking it to be the same as many worlds which some people do) is that some camps seem to qualify whether many worlds is infinite or just really big. But the biggest really big that I've come across so far is the number 10 to the power of 500. And while this is certainly enormously big, it's not even close to infinity.

The question that I want to get an answer to relies on there actually being and infinity of infinites, and not just a qualified infinity or a very big number. So I think it's fair to assume bearing in mind that each moment trillions upon trillions of many worlds are going on and that number is increasing exponentially, at least.

Where I'm going with this is it occurred to me that the further back we go in time as we near the creation event itself we come to a point where there aren't yet enough quantum events going on to be infinite. I know that the BB was not the creation event itself, because it had already begun otherwise there'd be nothing to bang. Long story short it appears to me that if there is an infinite number of infinities of many worlds that it must go back through the BB, which I suppose means that our universe is a quantum foam of various size multiverses, and I have just discovered that some physicists see these multiverses as the same thing as many worlds. Which I find confusing because I thought that the multiverse was a big number not an infinite number.

What is bothering me me most is all the above speculation sounds like someone in the 1970's just smoked some strong weed and spaced out, as it were. But we're in 2020, and on one hand we have respected physicists like Carroll, imploring us to accept that an infinite?! quantity of ourselves, providing that the laws of physics are not broken, is actually a real thing, and not metaphysical bs.

If I had one wish it would be to live in a time way off in the future when someone does to quantum physics what Einstein did to classical physics. i.e. that quantum physics is still used and is useful, but it is subsumed into some other theory where many worlds just disappears as the laughable naivety of the 21st Century.

I feel really let down by Sean Carroll as he seems too serious to write him off. Does anyone else feels that the lay public is being taken for a ride by some physicists who are sounding more like Professor Stoners? The only thing that tethers me to reality these days is the comfort that a cloud of hydrogen, has condensed into I and the world I live in which I accept to be true, and that in itself is so preposterous that I can't really dismiss anything.

I'm really feeling like 'shutTF up and calculate' is more to my liking. In other words, I'd much rather good explainers like Carroll would just concentrate on writing better physics books for the lay person than flying off into these confuddling grotesque abominations, and then expect me to take it seriously because 'it's just what the wave function says', as if that's some kind of a justification.

I suppose this post is going to go straight into the forum trash can, which I don't really think is warranted. I'll check back in a few days. I pine for the intellects of John Bell and Dick Feynman. If anyone can understand this, I'd really appreciate some serious grounding rather than mere repetition of more metaphysics.

Are any physicists here thinking to themselves that we might have to accept that we'll never understand the measurement problem, or do they have hope that we'll get there one day without the madness that we seem to be willingly heading towards.

 

[PeterDonis]

if I accept from reputable physicists that Many Worlds is indeed true

No reputable physicist should be telling you that the Many Worlds interpretation (MWI) is "true". They might say it's the interpretation they prefer, but no QM interpretation can be any more "true" than any other, since they all make the same predictions for all experimental results, and that's the only way we have of comparing hypotheses in science.

my current understanding appears to be that it must imply a genuine infinity of many worlds

Only if you understand what "worlds" means in this context. It does not mean that there are a genuine infinity of universes. There is only one universe in the MWI. The state of that universe is described by one wave function. That one wave function can have multiple terms in it that describe different states of quantum systems entangled with different states of observers like you and me. Each term in the wave function that describes such an entanglement is a "world" in MWI terminology.

If there are an infinite number of entangled terms in the one wave function, then there are an infinite number of "worlds" in MWI terminology. But there is no requirement in the MWI that that must be the case, or must always have been the case.

every quantum event splits the universe.

Not quite. According to the MWI, every interaction that entangles two quantum systems creates entangled terms in the wave function, and thus creates "worlds" in MWI terminology. But not all quantum events entangle quantum systems.

Where I'm going with this is it occurred to me that the further back we go in time as we near the creation event itself we come to a point where there aren't yet enough quantum events going on to be infinite.

With a correct understanding of what the MWI says (see above), this is not an issue.

Also, we don't know that there was a "creation event". The Big Bang itself, properly understood, is not one: it is just the hot, dense, rapidly expanding state that is the earliest state of the universe for which we have good evidence. In inflationary models, which are the current front runners, the Big Bang state occurs at the end of inflation. Some inflationary models have a beginning event at the start of inflation, but others (such as the "eternal inflation" models) do not.

You should rethink your understanding of what the MWI is saying and what implications it might have for cosmology in the light of the above.

some physicists see these multiverses as the same thing as many worlds

For one particular definition of "multiverse", yes. But that's not the only possible definition. For example, in eternal inflation models, there are infinitely many "universes" in a multiverse contained in an eternally inflating background; but this has nothing whatever to do with the MWI and is the case regardless of which interpretation of QM you adopt.

I thought that the multiverse was a big number not an infinite number.

The sense of "multiverse" you're probably thinking of here is the string theory "landscape", which is supposed to contain something like ##10^{500}## possible solutions of the equations of string theory. But that's not the same as the MWI; the "landscape" of string theory is the same regardless of which QM interpretation you adopt.

I'm really feeling like 'shutTF up and calculate' is more to my liking.

Plenty of physicists feel the same way. You are under no compulsion whatever to adopt a QM interpretation you don't like. As I said above, all QM interpretations make exactly the same predictions for all experimental results, so choosing between them is a matter of personal preference.

 

[bland]

OK, thanks for that considered response, Mr Donis. I'm beginning to feel like it's OK for me to say to my own private self that 'many worlds as even a serious conjecture is science fiction nonsense', and also while I'm at it, 'I have free will'.

If Sean Carroll did not say precisely 'many worlds is true' then he is definitely getting as close as it's possible to get to that without actually saying it, as per his recent book and also his recent YouTube interviews with very many different people. Sean Carroll is definitely going at this a lot stronger than many worlds is his preference, this is what has really got me a little het up lately. I was fine as long as people admitted it was metaphysics. You see when Carroll says something that 'these many worlds are simultaneously existing' rather than something more qualified it dances very close to saying they are real. I mean 'are existing', ARE, existing.

However even saying that many worlds is as good as any other explanation of the collapse of the wave function also sounds very suspect. I mean the collapse of the wave function is in effect the same thing as the entangled particles instantaneously doing the same thing, with regards to them both referring to non locality. And as far as I can tell, that is what Feynman meant when he said 'no one understands it'. And if that is the case then postulating these many worlds of infinite me's only limited by physical laws, is very very far from simply saying 'we don't understand the collapse of the wave function.

Would it be proper for me to ask you personally do you think that many worlds is nonsense metaphysics even though that's what the wave function says without any adornment, apparently. I mean it doesn't even sound like Everett took it seriously.

It's ironic that for years I've just thought Bohr was a bit of an arrogant ass with his private attack dogs like Rosen that he would unleash when required, but now I agree with him.

Is it perhaps possible that we'll never understand what this collapse is, without a complete new set of physics that engulfs quantum physics? Why can't this collapse that is leading to so much metaphysics just be compared to the anomalous error in the shift of mercury's perihelion? Like we don't understand it but we probably will eventually.

What seemed like an interesting bit of science based whimsy, has exploded into a 'many worlds' pandemic.

 

[PeterDonis]

If Sean Carroll did not say precisely 'many worlds is true' then he is definitely getting as close as it's possible to get to that without actually saying it

In pop science books, articles, and videos, perhaps. But you won't find him saying it in actual textbooks or peer-reviewed papers. This is why, if you want to actually learn science, you can't trust pop science sources, even from scientists; scientists will say all kinds of things in pop science sources that they know they would never get away with in a textbook or peer-reviewed paper.

many worlds is as good as any other explanation of the collapse of the wave function

Many worlds is not an "explanation of the collapse of the wave function". There is no collapse in the MWI; everything is unitary evolution all the time.

do you think that many worlds is nonsense metaphysics

As I've already said, all QM interpretations make the same predictions for all experimental results, so as far as science is concerned, they're all the same. At some point, some QM interpretation might lead someone to construct a different theory from standard QM--something that actually makes different predictions than standard QM about some experimental result--and then we can test to see which theory is right. Until then, I have no opinion about whether any of the interpretations are "nonsense"; it's a meaningless question in the absence of any way to test them against each other.

Is it perhaps possible that we'll never understand what this collapse is, without a complete new set of physics that engulfs quantum physics?

Sure, it's possible. Quite a few physicists think the same thing. But so far nothing along these lines has worked out.

 

[bland]

scientists will say all kinds of things in pop science sources that they know they would never get away with in a textbook or peer-reviewed paper.

That is useful, thanks.

Many worlds is not an "explanation of the collapse of the wave function". There is no collapse in the MWI; everything is unitary evolution all the time

Yes, my bad.

it's a meaningless question in the absence of any way to test them against each other.

Fair enough. I'm satisfied with your responses.