The Multiverse.

[peter]

If I'm correct there are versions of the multiverse theory [is it a theory?] that posit an infinite number of Universes [are there versions that do not?].

Lets think about that. Does that mean that any variation on the Universe I can care to concoct in my fevered brain must exist [lets say the one where I wake up tomorrow and find that rather than being a human I'm a tardigan that had a particularly bad night's dreaming, or indeed the one where the toothsome shop assistant from...... develops an irresistable urge to tear off all her clothes and ravage me] or are some possibilities going to be 'instantiated' [is that the right word - I mean going to actually exist] and others not?

If the former is the case - ie that all possibilities will exist somewhere in an infinite number of Universes - then the concept is trully staggering; I will [in some Universe] wake up to be a figment in the mind of every entity that has ever, or will ever exist [who knows - I might be that figment right now!] and there will be a further infinite number in which I do not exist at all - and each and every molecule that exists will have it's own infinite number of universes where it occupies every different spot and role that existance has to offer. The degree of extension required to contemplate such a situation is truly beyond the human mind as it stands.

If alternatively, some possible Universes exist, and some do not.......how is the decision made as to which will and which will not be instantiated. This [to me] makes no sense.

The truth is that there is something offensive to logic in both situations and at the end of the day we have at some point to trust our 'gut-feelings' as to whether our science is going in the right direction or not. But then - when you think about it, is it any more ofensive to logic that the 'infinite multiverse' should exist that that just the one we have should, so really it all depends on the sums. In the mean time I'll keep going to the shop in the hope that this Universe turns out to be the one where............ [ ]

[Hashi Lebwohl]

There are multiple dimensions, many of which we will never "see" from any experimental point of view other than on a chalkboard, but only one universe.

I have a regular 6-sided die in my laptop case (don't ask why--I just have it). If I roll it right now, it won't land on a number and also simultaneously split off into 5 parallel realities in which every number came up; instead, the probability function will collapse as the die runs out of inertia and no external forces act on it, resulting in it coming to a state of rest and one result occurs. Of course, in reality there is no probability function because that is a mathematical convenience we have for describing the potential outcomes of the die roll.

Comic books and movies which rely on "alternate realities" as a plot device are simply interesting "what if" scenarios but they have no basis in scientific fact.

[Vraith]

If I'm correct there are versions of the multiverse theory [is it a theory?]

that posit an infinite number of Universes [are there versions that do not?].

I don't think it quite qualifies as a proper theory yet. There isn't, AFAIK, any direct evidence---and may never, even in principle be the possibility of direct evidence.
I also don't think there is any indirect evidence yet---but the last decade at least, it's becoming more likely that indirect evidence will be within our reach.
It's more than just speculation/metaphysics, because if it is true it solves some real/practical/scientific problems/questions---but less than a true theory.

I think the multiverse frame has to result in infinite universes, and that all possible ones must be instantiated.

A fun thing---many [if not all] of the multiverse things you mention [and probably many more] that stagger and/or boggle the mind are still/also real, and so continue to stagger/boggle, if there is only one infinite universe.

[peter]

Yes, I remember that from Deutsch V. - but I'm sure that given a bit of thought it'd be possible to come up with logical paradoxes, say of the different infinity set types or whatever, in the infinite number of universes idea. But anyways, if I read Hashi correctly, the multi verses will not exist anyway. One single but infinite universe, while it might have all the variations on a theme I mention above, would not allow for their fungibility in the same way as a multiverse would it?

[Vraith]

One single but infinite universe, while it might have all the variations on a theme I mention above, would not allow for their fungibility in the same way as a multiverse would it?

I don't know---I'd have to think---but instant reaction is that that's completely backwards.

It's the infinite-but-single universe that is, in some ways, fungible.
In a single one, there is at least some theoretical/in principle possibility that "you" and the other "yous" are equivalent/could be swapped/traded, and probably lots of other things. And you could communicate knowledge/info/stuff easily [relatively easily].

All the 'verses in the multiverse are exactly, precisely not swappable. Each one is unique---in fact, the proposition/theory of multi arises [among other things] BECAUSE of uniqueness/differences/uncertainty.

First impression, anyway.

[wayfriend]

I thought the multiverse theory was based on the idea that every choice that could be made results in different universes, each where a different result happened.

If so, then the only universes that exist are the ones that could have resulted from outcomes of choices. Just *any* universe would not exist, just ones that follow a chain of outcomes from a given point. A universe exists where you went to a different college, maybe, but not a universe where you are a tardigan.

Which, incidentally, is an interesting way to discuss contingent truths vs necessary truths, now that I think about it.

[Vraith]

Just *any* universe would not exist, just ones that follow a chain of outcomes from a given point.

Yea..but every possible outcome from every possible choice is a universe that must exist.
Could a chain/universe exist where peter is a tardigan, because things from what we think is a show are real there, and we aren't, we are the show?
[[isn't there some story/novel that proposes that all of the fiction we create is seepage, that it all is real someplace?]]

[Hashi Lebwohl]

No, what I mean is that there are no variations on the theme. There is no alternate universe where I have black hair or brown eyes or where I chose to go to College A rather than College B. This is the only universe and as far as anyone can tell it consists of 11 dimensions, most of which we cannot currently measure or detect outside equations on a chalkboard.

The "multiverse", for lack of a better word, contains the individual membranes which gave rise to what we know as "the universe". Don't fall into the trap of thinking "what is outside the multiverse, though?" because the concept of "outside" doesn't exist outside this universe--spatial dimensions have no meaning there.

I mentioned rolling a die earlier. If I roll it, that roll doesn't create 5 alternate realities in addition to the result I see. Only one result happens and that is the universe which exists. It might be neat to think about what would have happened if the result came out 3 instead of 5 but if the result is 5 the other results never happened. At the quantum level it may be possible to jump backwards and choose a different path, resulting in a universe different than the one which previously existed, but we don't live at the quantum level.

[Zarathustra]

Comic books and movies which rely on "alternate realities" as a plot device are simply interesting "what if" scenarios but they have no basis in scientific fact.

Deutsch's book might change your mind. He claims that of all the interpretations of quantum physics, the many worlds interpretation (i.e. multiverse model) is the only one that has any experimental basis in fact. All the other interpretations are only tenable by not taking seriously the very theory in question (which isn't really in question, since it's the most experimentally proven theory in history), and then coming up with ways to deny what the theory itself implies, usually in ways that deny our ability to gain knowledge in those areas--for example, an alternate universe which we merely assume we can't possibly know. But Deutsch claims it's not only possible to gain knowledge of these other universes, but quantum computers (which he has pioneered) are only possible due to taking advantage of the other universes in the multiverse.

Infinite universes don't mean that every imaginable possibility exists. Most of them are identical copies (or very nearly so) of each other.

[Vraith]

Infinite universes don't mean that every imaginable possibility exists.

Most of them are identical copies (or very nearly so) of each other.

Hmmm...I'm not sure.
It's possible to imagine impossible possibilities, and those of course don't exist in his argument. So I agree if that's basically what you mean.
But if you can imagine it and it is an actual possibility, within the rules, then existence follows from that. I think. But I'd have to go back and re-read a lot [maybe the whole thing] to be sure...

The second---it seems to me his discussion of infinity makes that not so.
How'd he say it? Something like when dealing with infinities, you are always extraordinarily close to the beginning. So, with infinite universes, an enormous number would be nearly identical to "your own." But an infinitely greater enormity [so most] would be significantly different.

I'm reasonably confident of that...maybe 70 or 80%.
[[though it might make some difference depending on what ones definition of "nearly identical" is. If "nearly identical" means "shares the same physical constants and laws"---well, that's a lot of universes that would be nearly identical and very, very different at the same time.

[Hashi Lebwohl]

Deutsch's book might change your mind. He claims that of all the interpretations of quantum physics, the many worlds interpretation (i.e. multiverse model) is the only one that has any experimental basis in fact. All the other interpretations are only tenable by not taking seriously the very theory in question (which isn't really in question, since it's the most experimentally proven theory in history), and then coming up with ways to deny what the theory itself implies, usually in ways that deny our ability to gain knowledge in those areas--for example, an alternate universe which we merely assume we can't possibly know. But Deutsch claims it's not only possible to gain knowledge of these other universes, but quantum computers (which he has pioneered) are only possible due to taking advantage of the other universes in the multiverse.

Infinite universes don't mean that every imaginable possibility exists. Most of them are identical copies (or very nearly so) of each other.

I really need to get that book. I keep telling myself that and so far I keep failing to get it done.

Taken at face value, though, I would argue that there is no way to experimentally measure an alternate universe--we can't sense it, detect it, or interact with it in any way so there is no way to verify that it exists or that it doesn't exist. We might as well be talking about angels at that point.

Quantum computers are not taking advantage of alternate universes; that is simply ridiculous. He is saying that only so that he can sell people on ideas he is pioneering. His argument here boils down to "appeal to authority" citing himself as the authority....but to be fair to him I should really read the book for myself.

[Avatar]

Everett Wheeler Graham Multiple Universe Interpretation

Instead of the waveform collapsing into a single actuality, every possibility splits off to its own actuality.

--A

[Mighara Sovmadhi]

Well actually there's a striking theory being propounded a lot in modern cosmology circles (or so it seems to me) that if the Big Bang was symmetrical, as it is supposed to have been, more than less, then our cluster of galaxy clusters, the observable universe, is actually mirrored by some enormous number of other galaxy-cluster clusters, containing various mirrors or duplicates of individual objects therein, hence various analogs, mirrors, or duplicates of ourselves.

Now I know that this symmetry thing is the main motivation for the idea, or I think it is at least, but other than that, there doesn't seem to be an argument for it that I've heard of.

[peter]

Would that be within our own universe - just the non-observable part: I remember something I Deutsch's book where he said that an infinite universe functioned pretty much the same as a multiverse in terms of its capacity to contain alternative versions of the 'same' things and events.

And what about 'handedness': didn't I read somewhere that the universe is left-handed in terms of (insert the correct term here): would that tie up with this mirror image idea in that the duplicate would be handed in the opposite direction?

[Mighara Sovmadhi]

(insert correct term here) = chirality??

As for the mirroring thing, I was just jumping on a word similar to "analog" and "duplicate," not a geometrical description. But even so the element of symmetry in this circumstance, does point to your question I think in this very important way: would it be possible to "test for" the alternative states' existence, by showing whether or not their presence would violate chirality somehow (or something)? IDK...

Also re: an infinite universe being the functional equivalent of a multiverse, that does follow on the above picture of a "multiverse," but consider this:

The working definition of a universe, in modern physics, seems to be based on contiguity. That is, an object is not in a universe if it is not contiguous under any rotation in any dimension, with any space in that universe. Thus each realm is causally closed (this fits the QM multiverse and the philosophers' "modal realist" demesne) or some such thing. Then again, we might refer to 4+1 spacetime sets of continguity as the universes, allowing for dimensional-rotational access between universes in the higher spaces (think the string-theory landscape/M-theory's possibly colliding branes).

So for all that, this one philosopher/physicist, Max Tegmark, has posited "the Ultimate Ensemble."

[Vraith]

Some interesting things I've run across lately.
The first one I almost put in your fine-tuning thread, peter.
Apparently there are a few papers coming out this year that show fine-tuning isn't so necessary after all...that the force constants can vary by plus/minus 100 times the strengths we have and still form universes capable of sustaining stars, galaxies, and life. I'll come back with those if they're accessible when published, since what I saw is just blurb/advertising.

And there's this guy Woit, [[who seems to have other folk in his camp, and a decent reputation]] has a site "Not Even Wrong." He doesn't like String Theory, M-theory, Multiverses. In re the Multiverse, he quotes someone else on it---[[notice he agrees with Deutsche on what should be, but disagrees on the 'verses.]]

n order to explain the one simple universe we can see, the inflationary multiverse and accidental universe hypotheses posit an infinite variety of universes with arbitrary amounts of complexity that we cannot see. Variations on the accidental universe, such as those employing the anthropic principle, do nothing to help the situation.

Scientific ideas should be simple, explanatory, predictive. The inflationary multiverse as currently understood appears to have none of those properties.

Also, especially for Z, who I know is even more fan than me, Penrose somehow has a new book out that I hadn't heard about even though it's a few months old "Fashion, Faith, and Fantasy"---according to the blurb, he is taking some pretty big shots at String, Quantum, and Cosmology.

[peter]

I'll look forward to seeing them V. I read a Penrose book yonks ago that while a bit 'mathy' for me, was still highly entertaining stuff. If anyone is qualified to question the big theories of physics it's him!

[Ur Dead]

Wow.. Multi-dimensions within multi-universes..
I wonder if they would exist after you die?
(As per another thread here)

Would it be possible for a "flatland" universe
(that would be one extra large size piece of paper )
or a single dimension universe?
(Would "Black Holes" in our universe constitute a single
dimension universe within our universe?)

[Fist and Faith]

At the quantum level it may be possible to jump backwards and choose a different path, resulting in a universe different than the one which previously existed, but we don't live at the quantum level.

To get in WAY over my head, and perhaps ramble more than anything else...

The die would not come up a different number than it did without something else changing first. One of the factors that helped determine the outcome would have to change. And that something would have to be the person who rolled it. The breeze is already blowing as it is, and can't change. The surface is composed of the material it is composed of, has the imperfections it has, etc., and can't change. Same with the die. Once the die is released, there is only one possible outcome. If we were good enough, we could measure every variable at the time of release, and calculate (never realized "calculate" looks so much like "chocolate" before) the result. We'd never have to see it stop to know the result.

For the result to change, the person rolling it has to hold it at a different angle; or let go of it at a different time; or let go of it a little faster; or... The only way to change the outcome is to choose to do it a little different. We cannot calculate the result until it's released.

But why would my choice change? Why did I make the choice I did in the first place? Why did I throw it with the force I did, at the angle I did? It doesn't seem that I did it exactly as I did for specific reasons. Yet, opening my hand when I did is surely a conscious action. I had to think about opening my hand, or I wouldn't have, and I'd still be holding the die. How much of it was blind chance? Is this consciousness at the quantum level? For NO reason, uncaused, I choose X instead of Y?

[Vraith]

If we were good enough, we could measure every variable at the time of release, and calculate (never realized "calculate" looks so much like "chocolate" before) the result. We'd never have to see it stop to know the result.

As a matter of fact, that is not known to be true.
Many think it is so. But many don't.
On top of that, as things are, it is not possible even in principle to EVER be able to measure every variable...we couldn't know the result for certain, even if it WAS completely determined.

Also, there is a paper I'm waiting for publication of that demonstrates [supposedly] that in every given space that contains anything, there are objects and events that that are INDEPENDENT of, not contingent on, past/causes. And the number of those is not small. I hope it's right and published soon, and the blurb wasn't misleading/clickbait.