Stephen Hawking's Final Paper Cuts the Multiverse Down to Size

https://www.livescience.com/62459-hawking-final-paper-physics.html

by jonbaer • 8 years ago

89 80 8 years ago

everdev• 8 years ago

this proposal implied something strange: that the multiverse is infinite, with endless, uncountable parallel universes existing alongside our own

My biggest skepticism of the multiverse or even an infinite universe is the amount of energy required. Here on Earth energy is finite and cannot be recreated without using more energy in the process.

For an infinite universe or multiverse with infinite mass, you'd need infinite energy, right?

Infinity seems more like a concept than a physical property. It's easy to imagine an infinite number line, but harder to think about an infinite number of intelligent beings (which I suppose would be possible in an infinite universe).

netzone• 8 years ago

What if we only get precisely the amount of energy we require? Each universe won't need infinite energy.

BlackFly2• 8 years ago

For an infinite universe or multiverse with infinite mass, you'd need infinite energy, right?

Given that the current best guess for the geometry of the universe is (conformally) flat, this universe already contains infinite energy. From what I recall, the normal definitions of total energy of a spacetime are not possible to formulate for non-asymptotically flat spacetimes. So it is a bit nonsensical to talk about the total mass/energy.

The easiest skeptical take on multiverses is simply that there are no measurables defined by multiverse theories yet. I usually lump them in with anthropic theories, which a lot of GR theorists seem to love.

evanpw• 8 years ago

Talking about asymptotics already assumes that the universe is infinite. Any smooth, finite spacetime will have finite energy. The interesting thing about asymptotically flat spacetimes is that they can be infinite in volume but have finite energy.

ouid• 8 years ago

The "anthropic theories" aren't really something you can be skeptical about in the normal sense of skepticism, unless I'm misunderstanding your point.

YCode• 8 years ago

"Some have posited that there are an infinite number of molecules outside of the one we call home. They vary in size and shape, according to multimolecule theory. In some of them it is said the hydrogen galaxy is in the outer section, some the exact center, and some have no hydrogen galaxy at all!"

"My biggest skepticism of this theory is that it has been proven here in our molecule we cannot create or destroy atoms. Insofar as we know no atom has ever been added or removed from our molecule in the millions of plancks we have observed the known molecule for and none ever will."

"And for there to be an infinite number of molecules beyond the confines of our own - each with their own strange and exotic configuration expanding and changing off into eternity - you would need an infinite amount of atoms and electron fields to properly bind the vast regions of atoms. And as it's been well proven, atoms in this molecule are finite and unchanging."

consumer451• 8 years ago

If the zero-energy hypothesis[0] is correct, wouldn't the energy cost of infinite universes still be zero?

[0] https://en.wikipedia.org/wiki/Zero-energy_universe

darkmighty5• 8 years ago

Multiverse theories aside, as far as we know our current universe could, or should (depending on who you ask), be infinite. There is no evidence that its topology is closed (from estimates of curvature), so infinitely large is indeed the default assumption.

liberte82• 8 years ago

Is the theory that space-time is infinitely large, or also that there is an infinite amount of matter/energy within it?

kazinator7• 8 years ago

Energy is just a concept in our particular universe. The idea behind the multiverse hypothesis is that everything is just "math all the way down". Other universes do not all have the pieces of math which underlie "conservation of energy", and so on. The equations of each universe determine whether or not it has any phenomenon resembling our energy.

CuriouslyC• 8 years ago

The idea that the multiverse can continue to expand at the incredible rate that would be required based on the idea as stated always made it seem implausible to me. Furthermore, it bothers me that the idea discards the notion of probability inherent in quantum mechanics, since everything that can happen, does.

A more sane model for me is to imagine the state of the universe as a quantized distribution over a set of set of states with finite measure. This is sort of like the multiverse in that the wavefunction doesn't "collapse" but instead reality "branches." Unlike the multiverse, branches are constantly being created and dying off, since the information content of the universe is conserved. This also preserves the probability derived from the wavefunction - states are kept or discard based on their probability.

mikeash2• 8 years ago

I personally find the idea of finiteness much harder to accept.

Infinity makes sense to me. It just means there’s no limit to stuff. Why should reality have a limit?

A finite reality is just plain weird because it implies there’s a single actual number describing how much stuff there is. The universe contains X godzillion kilograms, or is Y billion light years across. Where did those numbers come from? What determined them? Why isn’t there more stuff, or less?

klodolph• 8 years ago

This reminds me of the kind of magical thinking that people like Aristotle used. Why should the universe be easy or hard for you to accept? Why is it important that these numbers "come from somewhere" or be determined by something?

Why doesn't the same thing apply to e.g. energy density? Fine structure constant? Gravitational constant? Why isn't the gravitational constant higher or lower?

Tyr422• 8 years ago

I mean, it makes some sense if there was a big bang X years ago, that everything ends up withing X lightyears of each other.

I find it easy enough to think of there being a beginning, since we know that stars age, and use up energy, so they can't have been running forever.

Since we think the big bang was 13.7 billion years ago, we can put Y at about 2*13.7 billion light years across as a first guess. Though there's something funkey with the spacetime stretching or whatever. So maybe more.

sandworm101• 8 years ago

> For an infinite universe or multiverse with infinite mass, you'd need infinite energy, right?

Except that under some theories the net energy in our universe is actually zero. Antimatter+matter = nothing. So the concept of unlimited energy can be acceptable under the rubric that energy in one area is mirrored by anti-energy in another.

dragonwriter• 8 years ago

Antimatter+matter = nothing.

Matter and antimatter both are forms in which energy (and not “anti-energy”) is bound up; matter + antimatter = energy, as is observable in particle / anti-particle interactions.

spiralx2• 8 years ago

Except that under some theories the net energy in our universe is actually zero. Antimatter+matter = nothing. So the concept of unlimited energy can be acceptable under the rubric that energy in one area is mirrored by anti-energy in another.

No, anti-matter still has positive energy. It's the gravitational potential energy that balances out all of the other energy to leave a total of zero - every particle's energy is cancelled by its negative potential energy of its gravitational field.

assblaster4• 8 years ago

Who/what created the multiverse?

Do matter and energy simply exist without creation?

Is proving the existence of the multiverse possible?

jerf3• 8 years ago

"Is proving the existence of the multiverse possible?"

It's proving it's nonexistence that is quite a challenge. Proving their existence could be demonstrated by, for instance, traveling to them. I personally see no reason to believe that is possible, but if somebody traveled to one and thereby disproved me, that would be that.

That said, it might just about take that to prove one. Even if one produces theories that say a multiverse might be possible, I expect there will always be a simple transform for which the equations still work but there is only the one universe. For instance, taking well-established existing equations, while the QM field equations may imply that a quantum multiverse is possible, no matter how mathematically distasteful some people may find it the Copenhagen interpretation is still possibly the truth, and I'm not sure what possible experiment could disprove that. (The Universe may do as it damn well pleases.) I'm unsure what evidence we could collect other than concrete proof of existence that would somehow prove multiverses.

maxfurman• 8 years ago

if somebody traveled to one and thereby disproved me

That person would have to travel back as well, thereby making this proof doubly hard :-)

assblaster4• 8 years ago

Proving nonexistence is impossible because there is an infinite number of possible explanations for how the multiverse can exist without being able to be proven, and that these explanations can themselves require proof of nonexistence.

The premise of proving nonexistence is the wrong way to assess credence of a theory.

Likewise, proving existence of multiverse is as impossible as proving nonexistence for the reason that the multiverse is postulated as existing independently in an infinite number of permutations that can not interact with each other. If multiverse permutations can exist in the same time and space as another permutation, then matter and energy are supposed to exist in infinite number of states simultaneously, and would be impossible to measure.

mietek2• 8 years ago

In his 1985 paper, “Quantum theory as a universal physical theory”, Deutsch writes:

I have pointed out several times in the preceding sections that the C.I. and the Everett “interpretations” are really different formalisms for quantum theory—in effect, different physical theories. It is usually claimed that although their assertions as to the nature of objective facts are radically different, the two “interpretations” agree about all subjective experiences of observers, and cannot therefore be distinguished experimentally. That this claim is false is shown by equations (40) and (42) which summarize the different predictions of the two “interpretations” concerning further measurements on subsystems one of which has completed a measurement on the other.

https://pdfs.semanticscholar.org/c948/44bc9128e77077abdf36a6...

kazinator7• 8 years ago

Any place you can travel to is by definition part of this universe. According to the multiverse hypothesis, any mathematical structure is a universe. For instance, "the locus of points equidistant from a given point" is one of the universes. You cannot travel there; that universe has no way to accomodate a representation of you, let alone a representation which could record the experiences of being in that universe and then travel back to tell about it.

kazinator7• 8 years ago

Who/what created the multiverse?

The multiverse hypothesis (in the style of Tegmark, et al) is partially motivated to render this sort question invalid. You're asking, effectively, "what are the hidden variables behind the multiverse", whereas the idea specifically asserts that there aren't any.

The idea is that what underlies each possible universe is just math, "all the way down".

So the question you're asking is exactly like, who created the sinusoid curve, pi, or prime numbers.

Proving the idea may be impossible. That doesn't make it wrong. If some aspect of reality is not provable, then that can't be helped.

The fascinating thing is that the hypothesis cannot be disproven either. The hypothesis that there is only one universe also isn't provable; the fact that other universes haven't been discovered/accessed doesn't prove it, since lack of evidence of existence isn't a proof of nonexistence.

The hypothesis that there are multiple universes is simpler than the hypothesis that there is just the one. It's more believable, and explains more. For instance, all remarkable coincidences in the structure of our universe are explained via the anthropic principle, which is greatly boosted by the multiple universe hypothesis.

TheOtherHobbes• 8 years ago

What created math?

I don't see how the essentially magical appearance of an incredibly complex set of axioms from nothing at all is a plausible answer to the 'Why something instead of nothing?" question.

To be clear, I have absolutely no idea how to answer that question. I'm certainly not a closet theist. My best guess is that a useful answer is currently some way beyond our pay grade as a species.

So I don't find "Because math" to be any more convincing as an answer than suggesting god did it.

darkmighty5• 8 years ago

I also find Tegmark's (and to an extent Schmidhuber's) multiverse theories attractive, I'm quite leaning towards believing they must be true.

But, if I'm not mistaken, the multiverse hypothesized by Hawkin, and the usual multiverse from String theory is not this mathematical multiverse. In String theory multiverses, not every possible universe is allowed to exist, only universes satisfying string theory conditions. That's not to say those hypothesis are inconsistent -- the String thoery multiverse may exist within the "Mathematical multiverse". Once we accept that falsifiability isn't the only motivation to create theories (say by subscribing to MUH), then we need to accept that maybe our universe is also part of a larger non-observable universe, if and only if this provides a particularly "simple" explanation to our existence.

fallingfrog• 8 years ago

The laws of physics seem to point towards some form of multiverse. Do some research on schrodinger's cat and quantum superpositions to understand that. As far as "creation" is concerned, you are making unwarranted assumptions about the nature of time when you talk about the universe itself having been "created". These are very difficult questions and no simple answer will be the right one.

darkmighty5• 8 years ago

Those questions are irrelevant to multiverse hypothesis because they apply to any theory. That is, if there is no multiverse, you can still ask "Who/what created the universe? Do matter and energy simply exist without creation?", etc.

Do matter and energy simply exist without creation?

It depends on your definition of "creator" but indeed it is almost a logical necessity for something to exist without a creator. Since if you assume a creator is necessary, you'd still need someone to create the creator, and so on going infinitely. And then there's the question of creation of this infinite chain itself, etc -- the recursion never ends. It seems much more simple to assume some system must simply exist without necessity of creation.

kazinator7• 8 years ago

Do elliptic curves, pi, Catalan numbers, spaces Euclidean and otherwise, ... exist without creation?

justhelpingout• 8 years ago

It seems much more simple to assume some system must simply exist without necessity of creation.

You are spot on. This system must exist in-itself. That is, it must be so simple that its existence cannot be separated from its nature (to use Aristotelean terms). In other words, I AM WHO AM.

MadcapJake• 8 years ago

Is proving the existence of the multiverse possible?

I remember reading somewhere an argument that universes could interact in a fashion not unlike bubbles in foam and perhaps we can measure the amount by which our particular universe is being "squished" by the surrounding universes.

But on another note, I would like to call Kant to the debate. Kant argued that humanity will never arrive at any useful understanding of universal origin (or even microscopic/macroscopic limits) because it is beyond our mental tools of comprehension. Science does attempt to bridge that gap, however how much can it help if our initial assertions require using subjective reason?

https://en.wikipedia.org/wiki/Kant%27s_antinomies

perpetualcrayon• 8 years ago

It still boggles my mind, but I honestly believe that there is something beyond our own universe. The other thing that trips me up but I can conceptualize is the idea that there may be things that had no beginning and will have no end. The human mind is very much suited to understand things to have beginnings and ends. Our own universe very clearly had a beginning and will certainly have an end. But that which exists beyond our own universe. Is it necessary that whatever is there did not exist at some point? I think it's entirely possible that whatever exists beyond our own universe may have been there always and will continue to be there forever. No beginning and no end.

snissn• 8 years ago

Pascal's mugging is a really cool thought experiment. Similarly is the thought that what if instead of the entire universe being the size of the viewable universe it's 10^N power, so just another exponential leap in size. Then our little corner of the multi-verse becomes such a tiny speck.

Retric• 8 years ago

Pascal's mugging is simple failure to recognize probabilities can be and grow arbitrarily small. If a mugger paying you 4,000 dollars is less than half as likely as them paying you 2,000 dollars and you repeat that as the numbers grow then there is no inflection point.

deciplex5• 8 years ago

Multiverse and universe-outside-the-visible-universe are not the same thing.

neolefty3• 8 years ago

Well explained! And I wonder: Does the existence of our universe require that something else "exist" outside of time?

People claim it as a proof of "God" or a creator, and I used to be skeptical of that logic (albeit I am a theist, for other reasons) but the way you put it I find pretty convincing.

neolefty3• 8 years ago

According to Hawking's "no-boundary proposal," before the Big Bang, when the entire universe was compressed into a single, infinitely small point, there was no directional time as we experience it. Time was a closed, boundary-free thing, like a sphere without edges. ...
Scientists later determined that this proposal implied something strange: that the multiverse is infinite, with endless, uncountable parallel universes existing alongside our own....

This is the first time I'd heard of that proposal. It rings true to me (I know—naturalness is another word for the truthiness fallacy) in the sense that the outer reality needs to transcend time and therefore—if our universe is time-bound—contain infinite time-bound sub-universes whose origination and final fate are not externally bound by time. Or perhaps the "no-boundary proposal" is just a succinct way of saying that!

That wild situation presented a number of problems for science, most significantly that it rendered most basic scientific ideas about the multiverse impossible to test. ...
"Hawking was not satisfied with this state of affairs," Hertog told Live Science in March. "'Let's try to tame the multiverse,' he told me a year ago. So, we set out to develop a method to transform the idea of a multiverse into a coherent, testable scientific framework."

This reminds me of Einstein's discomfort with true unpredictability—"God does not play dice"—how he helped lay the foundations for quantum mechanics but never fully accepted it himself because it was too weird (as I understand it—I'm a rather poor historian).

Hawking's final paper suggests a framework for understanding the universe that would render the multiverse finite, countable and subject to meaningfully engagement via the tools of science.

smallnamespace• 8 years ago

The human mind is very much suited to understand things to have beginnings and ends. Our own universe very clearly had a beginning and will certainly have an end.

I think you might be overstating your case a bit. Non-Western cultures don't have as much an emphasis on things having a clear beginning, middle, and end, the cosmological claim that the universe clearly must be temporally bounded is not even the dominant stance for modern day inflation theorists. There are other alternates (eternal inflation [1], 'big bounce' [2], etc.)

I think part of the confusion stems also from language. A multiverse where other 'universes' are physically accessible to us in principle (if we're willing to wait long enough or go far enough), should that really be considered another universe? On the other hand, there are even parts of our current space-time that are so remote that we will never see them—so are they other 'universes'?

As a counterpoint, Chinese culture certainly focuses more on the inherent cyclicality of things—even beginnings and ends are embedded in a larger cycle that may not have bounds. “话说天下大势，分久必合，合久必分” It is said that in the great scheme of the world, that which is long divided, must unite, and long united, must divide

[1] https://en.wikipedia.org/wiki/Eternal_inflation

[2] https://en.wikipedia.org/wiki/Big_Bounce

toxicFork• 8 years ago

We can only comprehend matter that affects only the five senses that we use to perceive "the universe".

What if there's a kind of matter that cannot be perceived by the five senses that we use, and does not interact in any way with the matter that can be sensed?

Could we consider each of these kinds of matter to belong to another universe?

SonOfLilit• 8 years ago

Affects directly or indirectly.

But indeed, anything that does not affect anything that affects anything [..] that could be perceived, can not be considered in any meaningful way to belong to our universe.

Isn't that the meaning of "universe"? The set of all things closed under all possible physical interactions?

harshulpandav• 8 years ago

Agreed. Definition of matter should be relative. A radio wave doesn't see a wall like how we do. Also, Time seems to be one the biggest discovery of Humans even when we don't see it, feel it, smell it, hear it, taste it. Possibly there are other such things like time yet to be discovered in this universe.

arbitrage• 8 years ago

There are more than five senses.

http://www.bbc.com/future/story/20141118-how-many-senses-do-...

zamalek• 8 years ago

Keep in mind that only some multiverse hypotheses are extradimensional. Many would prohibit viewing other universes because they don't occupy the same "space" as us. For example, one hypothesis suggests that black holes are the creators of universes (where a star collapsing in our universe occurs simultaneously with a big bang within the singularity). We'd never be able to reach that universe and so could not perceive it, regardless of exotic senses.

wuliwong2• 8 years ago

"like a sphere without edges"

That's a strange analogy. I would think of an infinite cube but then I guess I'm thinking in cartesian space. :)

dmayle2• 8 years ago

I don't know... something that always bothered me about multiverse theory is that multiverses are supposed to be the explanation for why a lot of our quantum math works out so beautifully.

Matter is continuous into other dimensions, and this is why things like the photon/wave duality can work, interaction with other realities.

In our reality, however, our universe is so sparse as to be almost non-existent (density of the universe is something like 1 hydrogen atom for every 5k cubic meters). This has been measured, and means that our universe is flat (Euclidean).

In my mind, in order to connect the density of the universe with the continuity of quantam behavior, than every reality must have the same density, and flow continuously from ours, which would mean that every reality is Euclidean.

This is where it gets fuzzy for me, because it's my understanding that the multiverse is not Euclidean....

deciplex5• 8 years ago

Isn't this post conflating multiverse hypotheses with the relative-state formulation of quantum mechanics?

dmayle2• 8 years ago

To be fair, isn't Everett's relative-state formulation the basis/beginning of all multiverse hypotheses?

AndrewKemendo• 8 years ago

What is more mind boggling to me than this is the fact that Professor Hawking could accurately and properly collaborate on such complex topics with other researchers at this level given the limits to his communication.

I had the privilege of attending a live speech Professor Hawking give back in 2002 or so, and the most impactful thing about it was that it wasn't pre-recorded. He would "speak" a sentence and then there would be between 10-45 seconds of silence and then another sentence. This continued for about an hour and a half and nobody lost interest.

I have to assume that the typing, formatting etc... of this paper was handled by someone else, however even just communicating greek characters, algorithms and diagrams must have been a feat.

Stephen Hawking's Final Paper Cuts the Multiverse Down to Size

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