I know there is no solid proof of a multiverse. For the scientists in the room, what are your personal thoughts? Do you personally believe a multiverse exists?
Not a scientist, just an educated bloke with opinions…
I fell in love with the Expansionary Phase enhancement of the Big Bang Theory the instant I saw it. It can, perhaps, provide for one kind of “alternate universes,” specifically, regions of space, contiguous with our own, but so distant as to be causally isolated. It is possible that such regions have slight differences in the values of the basic physical forces. Maybe gravity is a bit stronger over there, etc.
The other commonplace alternate universe idea is the many worlds interpretation of quantum physics. Instead of the cat being alive/dead until the wave function collapses, the cat is both alive (here) and dead (in some other world.) It elegantly disposes of the various “observer” problems in QM. Now, we don’t need an observer: the experiment simply bifurcates the cosmos.
(It doesn’t have to lead to multi-zillions of universes all cluttering up the place. There doesn’t have to be, like, a world where Hitler was a bandicoot. There could be localized re-unification of universes. Alternate worlds could be “virtual” as in virtual particle pairs.)
I recommend Michio Kaku’s book “Parallel Worlds.” He deals with these, and several other varieties of multiverses, and at a level that the typical scientifically interested American can comprehend. Not too much math!
Michio Kaku, the Al Sharpton of physics.
Yes and no. Non-duality, so infinity everywhere really.
I have no idea and don’t really have an opinion on it.
But I do like the idea of a multiverse where every possibility happens since it eliminates the idea of free will. Which I don’t really believe exists and it would be good to get everybody on my side.
Um… Okay… Could you please expand on that a little? That’s one hell of a drive-by!
The physicist Brian Greene recently wrote a book titled “The Hidden Reality” about the different ways in which physic may allow for a multiverse. His explanation of the many-worlds interepretation of quantum physics makes a lot more sense to me than any other I’ve read in a popular-science book or magazine.
While I’m a proponent of the “many worlds” interpretation (MWI) of quantum mechanics, I should point out that there is an important distinction between it and a ‘multiverse’. The MWI is an interpretation of quantum mechanics involving multiple branches of the same universe; multiverse theories hypothesize the existence of other universes to which quantum mechanics (presumably) applies, but which may have different physical constants, or even different laws of physics.
My opinion is that a multiverse is very likely. There are a couple of reasons for this. One is fine-tuning: apart from anthropic considerations this one universe appears fairly arbitrary, and there doesn’t appear to be any good reason why it should be so special as to exist alone. A related reason is philosophical: modal realism or alternatively the mathematical universe hypothesis are frameworks that, while not very predictive (although there is the potential for them to be a lot more predictive than is currently advertised), at least provide an explanation for why we might find ourselves in a seemingly random universe, and furthermore provide an explanation for reality itself with a minimum of arbitrary assumptions. A third reason I suppose is also philosophical: it is obvious once you remove certain biases :). I know this might not sound like a very compelling argument, but for some reason a lot of otherwise smart people cringe at the idea of multiverses out of some fallacious bias vaguely grounded in Occam’s razor. First of all, the lack of a unifying explanatory framework makes the assumption that a “single universe is the simplest explanation” wrong for the simple fact that it is not an explanation. Second of all, there is absolutely no reason why the extent of the physical universe should coincide with that of the visible universe. For all we know, the universe is one million orders of magnitude larger than the visible universe, and the laws of physical vary from place to place. This brings me to a fourth reason, which is that string theory predicts the multiverse. It predicts that the visible universe is just a “pocket” in a much larger fabric with all kinds of pockets and varying laws of physics. To me this seems perfectly natural, but again it butts up against some peoples’ rather dumb biases (as does other aspects of string theory, like extra dimensions, as though somehow 4 dimensions is less arbitrary than any other number). And not only that, but string theory also predicts “hidden sectors” in our own region of the universe, which can be thought of as universes overlapping with ours, but perhaps only interacting with ours gravitationally (there is no reason why there can’t be other particles surrounding us but with charges that don’t interact with ours). This is a possible explanation for dark matter.
Anyways, for a variety of reasons, only some of which I have listed above, I strongly believe in a/the multiverse. Doesn’t seem weird or surprising to me, but rather expected.
They tell me it makes some of the maths work out right, but it’s way over my pay grade. For myself, no, I don’t. Since definitionally, we can never actually know that a multiverse exists, I choose to ignore it. It adds nothing to my conception of the Universe.
Michio Kaku likes to be in front of television cameras. I don’t blame him. He certainly knows more physics than I do. You can’t ignore the sensationalism in everything he says though.
Is this more than just a microevolution/macroevolution distinction? If enough little distinctions add up, doesn’t it amount, in the end, to very large divergences?
Certainly, whether or not I had eggs this morning – or whether or not this particular Uranium atom decayed at 12:00:00:01 or 12:00:00:02 – won’t add up to anything gigantic for a very, very long time… But the universe has had a very, very long time…
Ah! Being a camera-seeker is one thing; I thought the accusation implied that what he says is somehow biased or factually incorrect.
In “Parallel Universes,” Kaku is careful to explain that, yes, he has personal preferences and vested interests in some branches of research – but I considered that to be a good thing. He openly admitted that he isn’t perfectly objective.
Isaac Asimov was perhaps the God-King of all time in science explanation – and he was also hugely biased! He just never made any pretense otherwise.
No, it’s very different. In the Many Worlds Interpretation all those different worlds are different versions/branches of our own. That’s not the same as a universe that never had any connection to ours, has never been in the same spacetime as ours, and may well have major differences right down to the laws of physics. In fact, you could have both at once; different universes that all run according to the MWI model.
Ah! Gotcha. Sort of like the “family tree” idea, where every singularity pinches off an entirely new cosmos with its own Big Bang and (perhaps) its own entirely new set of physical laws.
Then there’s the in-between case, where the expansionary phase of our own Big Bang led to lots of causally isolated regions, which might have variations in the physical laws. They’re just so darn far away, the force of gravity might be a bit weaker over yonder.
Anyway, Kaku described something like eleven different cases, although some of them were a bit “woo.” For instance, he mentioned the “Sim” universe idea – we might all be living in someone’s holodeck – as a kind of alternate universe. Philosophically, it’s worth examining. In terms of practical physics, it doesn’t lead much of anywhere.
Explanation of my comment about Michio Kaku.
The man will take the most sensational view of anything in order to get put in front of a camera. I’ve never learned anything from him. He will talk about “quantum teleportation” or “invisibility cloaks” as if they really are what you’d think from their names. He is happy to misrepresent physics if it will get him more airtime. He will talk about subjects he knows little to nothing about as if he is an expert on the subject.
This is in stark contrast to people like Neil de Grasse Tyson, who can teach real science and make it accessible to non-experts in a very engaging way. I have great respect for people like that.
It depends a lot on what you mean by ‘multiverse’. First of all, I don’t think that even the universe is an objective, singular kind of ‘thing’: there exist many different, equally valid points of view about it. The most trivial example are literal points of view: you and me don’t share the same universe in the sense that there might exist, for instance, a galaxy from which light has had no time to reach me, but has already reached you (and will of course reach me in a fraction of a second). We’re kinda living in different ‘bubbles’ of observation.
More concretely, each of us has a distinct set of events that are causally related to us, i.e. that could have influenced us in any way – that we could observe, have heard of, base our decisions on, etc. These are the events within our past light cones, and they differ for every observer. It isn’t unreasonable to consider these events to constitute each observer’s universe, as nothing exists beyond them with which the observer could have interacted, and thus, have knowledge of. Then a ‘multiverse’ would be given by just the fact that there exist different observers (of course, for all practical purposes, ‘local groupings’ of observers would live in very similar universes, whose distinctions can be practically ignored). But I prefer this as meaning that the concept of universe isn’t quite sharply defined, and neither, by extension, is the concept of multiverse.
One could extend this view by considering different ways to draw the boundaries between observer and observed – one might imagine a universe, as a collection of events, facts, or whatever, being sliced in two, with one part constituting an observer, and the other his observed universe. Similar observers are produced by similar slicings, but one might imagine radically different cuts, yielding a completely different notion of what the observed universe looks like, that needs not have much in common with what we call ‘the universe’.
In fact, this pertains to the so-called ‘preferred basis problem’ in the many worlds interpretation: a quantum state can be decomposed in many equivalent ways, each of which can be considered a ‘set of worlds’ in the MWI sense. For instance, a quantum bit can take on any state consisting of a linear superposition of basis states |0> and |1>, such as the equal superposition 1/√2*(|0> + |1>). In the MWI, one would say that an observer, measuring this state, splits the universe into two worlds, one in which he obtains the outcome 0, and one in which he obtains 1. But the same state can be written in another basis, such as the |+>, |-> basis, in which it is merely the non-superposed |+>! An observer measuring in this basis would consequently not split the universe, but obtain the outcome + deterministically. Of course, in this case, the measuring equipment chooses the basis (say, by simply being spatially rotated), but the ultimate buck-stops-here measuring device is the observer himself – what chooses the basis he measures in? If one entertains the possibility that this is just arbitrary, then one can imagine observers of a fundamentally different kind, experiencing the universe in terms of a different basis, of different concepts and facts.
This is the same universe in one sense, from the ‘outside’ viewpoint, just as 1/√2*(|0> + |1>) and |+> are the same quantum states; but experience from inside the universe will be very different – thus, from the point of view of its inhabitants, one should perhaps rather speak of a multiverse.
So I think that in part, this whole universe/multiverse discussion misses the point: there’s no well-defined, unique notion of a universe, so there’s no good way to talk about a ‘collection of universes’, i.e. a multiverse. It’s just an artifact of our thinking: we like to consider only sharply delineated concepts, but reality is often much fuzzier. It’s often the case that something can’t be definitely A or B. Are you tall, or short? For some people, it’s obvious; but there are intermediate cases, where such an assignment is not unambiguously possible. Or take the grouping of animals into distinct taxa: it leads to ‘origin fallacies’ such as – the mother of every chicken is a chicken, so either there must have been a first, special chicken, or the succession of chickens stretches infinitely far back into the past (a lot of proofs for the existence of god are ultimately of this kind). But the solution is simply that ‘chickenness’ is not a sharp concept: while the mother of every chicken is a chicken, contemporary chickens have ancestors that are not chickens. That’s why the idea of evolution is so powerful: it provides perhaps the first explicit means to transcend such a ‘sharp categories’ kind of thinking.
So ultimately, I think that the notion of ‘universe’ is of a similarly unsharp character. Do you and me live in the same universe? Yes, in a sense; no, in another. Does the multiverse exist? Yes, in a sense; no, in another.
I’ve never seen him televised, only read his books; thank you for the amplification!
Is there even any solid evidence to consider?
The best “evidence” is negative: a reductio ad absurdam involving the “collapse of the wave function,” Schroedinger’s Cat, the observer effect, etc. The standard (is it standard any more?) notion that the wave function collapses “when observed” led to some unanswered (?) questions. The MWI avoids those paradoxes, anyway.
Not quite the same thing, too, but some of the many-dimensional string theory ideas suggest experiments that could offer evidence, if they were performed and if the results went in a particular way. This, if so, would be the first time that string theory was any more than a clever idea.
What he said.
Not really. The “evidence” that Trinopus cited merely allows for the possiblity of a multiverse. That’s not the same as actual evidence of its existence.
Personally, I think that the whole notion is ontologically bloated. That doesn’t make it impossible; however, from a philosophical viewpoint, I think that this notion is rather extravagant.