Have cosmologists lost their minds in the multiverse?

May 13, 2014 by Luke Barnes, The Conversation
If there’s a multiverse out there can we see it? Credit: Flickr/Maciek Bielec, CC BY-NC-SA

The recent BICEP2 observations – of swirls in the polarisation of the cosmic microwave background – have been proclaimed as many things, from evidence of the Big Bang and gravitational waves to something strange called the multiverse.

The multiverse theory is that our is but one of a vast, variegated ensemble of other universes. We don't know how many pieces there are to the multiverse but estimates suggest there many be squillions of them.

But (if they exist) there has not been enough time since our cosmic beginning for light from these other universes to reach us. They are beyond our cosmic horizon and thus in principle unobservable.

How, then, can cosmologists say they have seen evidence of them?

Seeing the unobservable

Unobservable entities aren't necessarily out-of-bounds for science. For example, protons and neutrons are made of called quarks. While they cannot be observed directly, their existence and properties are inferred from the way particles behave when smashed together.

But there is no such luxury with the multiverse. No signals from from other universes have or will ever bother our telescopes.

While there is some debate about what actually makes a scientific theory, we should at least ask if the multiverse theory is testable? Does it make predictions that we can test in a laboratory or with our telescopes?

The answer is yes, but perhaps not as you'd expect. And the exploration of the multiverse theory involves some very complex, and very controversial, ideas.

The mark of the generator

If your multiverse theory generates its universes via some physical process, then that process may leave its fingerprints on this universe. This is what BICEP2 might have seen.

Cosmologists think that in its earliest stages, the universe underwent an extraordinarily rapid expansion, known as inflation. In many versions of , leave an imprint in fossil radiation, recently observed as characteristic swirls in this ancient light; a successful prediction of inflation.

In some versions of inflation, the process that causes our universe to inflate is expected to produce huge numbers of other universes. Evidence for inflation isn't exactly direct evidence for the multiverse, but it's a start.

A LC-130 aircraft passing the NSF South Pole station Dark Sector which houses the BICEP2 telescope (centre). Credit: Steffen Richter, Harvard University, CC BY

A known generator

We cannot see the creation of other universes, but if we have evidence for the physics that powers the universe generator then we have another piece of the puzzle.

In particular, a multiverse theory that requires only well-tested physics such as gravity and quantum fields is preferable to one that requires new physics, or requires extrapolating known physics to situations where we expect them to break down.

Inflation's scorecard is mixed: some of the underlying physics is known, some is hypothetical, and some worry that it skirts close to (or perhaps into) the quantum gravity regime, where all tested physical theories break down.

Observing our universe in the ensemble

Let's think about prediction with a simple example. Alice predicts that a certain factory makes 99% red widgets, 1% blue. Bob predicts the opposite: 99% blue and 1% red.

A packet arrives from the factory and they open it to find a red widget – whose theory is correct? Neither theory is certainly false, but the evidence clearly favours Alice.

A multiverse theory will (by definition) predict the statistical properties of its universes. We can then ask whether our universe is the kind of universe one would expect to observe.

The more unusual our universe is, the more likely it is that a different multiverse theory would better explain our universe. And if our universe is just too weird for the vast majority of multiverse theories, then the whole idea of a multiverse comes under question.

It is thus relevant to ask: how typical is our universe of the set of possible universes?

There is one way in which our universe is highly unusual: it contains life. If our laws of nature were only slightly different then our universe would look and behave quite differently: atoms would fall apart, or the universe would have expanded so fast that stars and galaxies could not form.

Most cosmological scenarios would have left our universe stone-cold dead, devoid of life (as explained in the video below).

The multiverse can handle this. The probability of observing a particular type of universe depends on that universe first creating observers. We are not just passive observers, setting up our equipment and taking measurements of the universe at our leisure. We are products of this universe.

This video is not supported by your browser at this time.

While universes with observers may be highly unusual in the entire multiverse, they will obviously be the norm for observed universes. And so, the life-permitting nature of our universe can be counted as a successful prediction of the multiverse. (Prediction in the logical, rather than chronological sense.)

Revenge of the Boltzmann Brains

Or can it? We've assumed that the most likely way for a universe to make observers is via suitable laws and biological evolution, as in our universe. Such a universe is probably extremely unusual in the multiverse. But what if just any old universe could get lucky and fluke a few observers?

Quantum mechanics, the same physics that predicts the inflationary fluctuations in the , seen by BICEP2, also predicts that there is an extremely tiny probability of a fully-formed brain spontaneously popping out of "empty" space. Given enough time and space this vanishingly improbable event will occur.

While such freak observers, known as Boltzmann Brains, would be massively outnumbered by biological observers in our universe, they could be common in the almost unending time and space of the entire multiverse.

In that case, the fact that we are not that kind of observer is like seeing the red widget – it is evidence against a multiverse that says we should expect to be freaky observers. The multiverse is not just testable; it might even fail.

Ifs and buts

At the moment, there are too many ifs and maybes in this story.

Observations do not uniquely favour inflation though the BICEP2 results are an impressive step in this direction. It is a matter of some debate whether inflation naturally generates a multiverse.

Further, many multiverse theories struggle to predict anything, so clearly there is much much more to be done.

But positing the multiverse is not, as claimed by some, the end of science. It may be the start of the biggest scientific adventure of all.

Explore further: Pair of noted physicists contemplate future of cosmology after detection of primordial gravitational waves

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User comments : 28

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cantdrive85
2.1 / 5 (15) May 13, 2014
Have cosmologists lost their minds in the multiverse?

Yep, they've gone absolutely loony toons.
OdinsAcolyte
3.9 / 5 (7) May 13, 2014
Our universe is but a leaf on a branch and we do not know where the branch sits on the tree. Everything is possible. Cool.
El_Nose
3.3 / 5 (4) May 13, 2014
squillions does not belong in a scientific article
Uncle Ira
2 / 5 (4) May 13, 2014
I think I understand most of that article me. Basically it say on the really complicated theorying we got more work to do. And there is somethings even the really smart Science-Skippys don't have the handle on yet, That is right? What I don't understand too much is how somebody like the Ira-Skippy can tell when the Science-Skippys are going from what they really know to what they really not sure about yet but just maybe.
Uncle Ira
4.2 / 5 (5) May 13, 2014
squillions does not belong in a scientific article


I think what he mean by that is a whole lot of them and so many that any ol number will do as long as it is the BIG number.
antialias_physorg
5 / 5 (10) May 13, 2014
There is one way in which our universe is highly unusual: it contains life.

I don't know if this is so highly unusual. Any self-replicating mechanism is conductive to creating something like 'life' eventually.
And self replication can be a achieved with very simple means as long as some large reservoir of energy is available.

So I'm not sure that one can definitely already claim that life in a multiverse is somehow rare (or even unique).

The singular exampke of 'life is observed here, therefore it is a püredictor of a multiverse' seems as flawed as the Alice/Bob example.
One event does not make any prediction more true or false than any other - since you cannot base a prediction (read: a statistic) on one data point. At that level ofobservation the theory of "it's all totally random and there is NO law" is as valid as any other theory.
Writela
4 / 5 (1) May 13, 2014
The multiverse is not just testable; it might even fail.
This is not possible: until it's not testable, it simply cannot fail. It's not even wrong. And the multiverse model is not testable, until we define/constrain the properties of multiverses at least a bit. The unpleasant property of multiverse concept is, it's not only testable by itself, but it even harms the falsifiability of existing theories. In this moment it just represents a politically correct synonym of failure of existing theories: if we would observe the violation of some theory, we could always attribute it to manifestation of another universe instead of violation of existing theory. It's sorta analogy the God and creator concept in theology: you can explain literally everything, what you want with it. For example the violation of relativity with quantum mechanics could be interpreted like the mutual interaction of two multiverses, each of which fulfills its own model perfectly.
Returners
3 / 5 (6) May 13, 2014
But (if they exist) there has not been enough time since our cosmic beginning for light from these other universes to reach us. They are beyond our cosmic horizon and thus in principle unobservable.


This isn't even a proper use of the term "universe".

Being beyond the Light Horizon does not make something in "another universe", not even hypothetically.
dedereu
5 / 5 (3) May 13, 2014
Moreover, in quantum mechanics, following the quantum equations summing on all the possible histories, the universe is continuously splitting with multiverses where all the possible histories happen endless every microscopic times !!
Uncle Ira
not rated yet May 13, 2014
This isn't even a proper use of the term "universe".

Being beyond the Light Horizon does not make something in "another universe", not even hypothetically.


Truce Returnering-Skippy?

I looked on the google about that because you got me to thinking on it. Now I'll tell you right from the start this not the thing ol Ira knows a lot about.

But I think what read if it didn't read it wrong is this multiverse word they use is because that they is dealing with somethings that they had no ideas about being there so it doesn't have an already name. I think that's right but maybe no.

From what I read on the one place I looked. Long time ago they thought that the entire whole universe was just the here Milky Way, and they didn't know not to call that the universe. Then they started calling that a galaxy and made the universe for all the different galaxys. So maybe they are just not figured a good word for the new things they are finding or thinking up.Maybe but I might be wrong.
Mimath224
5 / 5 (1) May 13, 2014
@antialias_physorg, quite right! The other point is there is still debate about whether life exists elsewhere in OUR known universe let alone talking about whether or not it's rare in 'other universes'.
Other quantum universes/dimensions via compactification in SST, what, if anything, lies beyond our expanding universe? Extra macro dimensions, 'multiverses'. Ha, the 'mad hatter' and unicorns must be there somehere.
11791
5 / 5 (1) May 13, 2014
universe means a collection of everything there is, everywhere. the universes that comprise the theoretical multiverse should be termed, SUBUNIVERSES that are parts of the Big Universe that encompasses everything.
scuzzmonster
5 / 5 (4) May 14, 2014
squillions does not belong in a scientific article


I think what he mean by that is a whole lot of them and so many that any ol number will do as long as it is the BIG number.


Yes, but it's such an inelegant word. 'Shitload' would have been far more succinct.
AmritSorli
1 / 5 (5) May 14, 2014
GW are pure theoretical imagnation and are non existent in physical world.
Gravity has origin in variable density of quantum vacuum.
http://article.sc...3.11.pdf
antialias_physorg
5 / 5 (2) May 14, 2014
universe means a collection of everything there is, everywhere.

The current notion of what a universe is seesm to be the following:
a universe is:
a) a connected region (i.e. information is preserved)
and
b) has a certain set of physical laws that are 'universal' to it.

So you can have multiple universes with the same laws (e.g. if parts of this universe drift so far apart due to expansion that they move accross each others causality horizon)...or you can have universes that are fundamentally different but still able to influence one another (as in brane theory)

I was going to write "Having the same number of dimensions", but that gets iffy in the case of black holes where the whole dimensions concept gets put through the wringer.
Mimath224
not rated yet May 14, 2014
@11791
universe means a collection of everything there is, everywhere. the universes that comprise the theoretical multiverse should be termed, SUBUNIVERSES that are parts of the Big Universe that encompasses everything.

Not sure about that. We often talk of or expect physical laws to be the same elsewhere in the universe. If there other unverses where our physical laws were not valid then surely that would qualify them as being 'different univereses'?
Writela
1 / 5 (1) May 14, 2014
The multiverse stuff overlaps with concept of macroscopic extradimensions. The string theorists already assume, there are microscopic extra-dimensions, but when we assume these macroscopic ones, then their projection into our 3D universe would appear like the multiverse. Some string theorists therefore do share opinion, that the multiverse is equivalent to many words interpretation of quantum mechanics, developed with Everett at the end of 50's. The mirror existence of microscopic extradimensions at macroscopic scale follows from AdS/CFT correspondence. The water surface analogy illustrates it as usually: if we would observe the 2D water surface with its 2D waves only, then at small distance scale our perspective will be blurred with presence of Brownian noise in third dimension. But the same blurring we would observe at the large scale, where the waves get scattered with underwater too.
Writela
not rated yet May 14, 2014
The above interpretation of multiverse is solely private one, but if we don't attribute the multiverse some tangible properties, mathematical if possible, then the whole idea will remain untestable, unfalsifiable and as such non-scientific. Of course it's not the only definition of multiverse concept possible. For example, this page by Max Tegmark picks the four(!) different levels of multiverse. The Multiverse: is there evidence for it? See also Frank Wilzcek: Multiversality.
Iourii Gribov
1 / 5 (1) May 14, 2014
The described ideas about Multiverse assume physically disconnected hyper-inflectional 3D-bubbles in 4D-hyperspace (see picture in the article), they are totally contra productive – cannot say nothing, especially about the so monstrous nature of Dark Energy (DE) and Dark Matter (DM). But it is so natural to suppose that namely DE and DM are caused by a some kind of MULTIVERSAL 4D-spatial surrounding (3D-adjacent everywhere to our Universe 3D-slice).
Indeed, I. Gribov (1999-2013) recently proposed and developed the corresponding Periodic Waveguided Multiverse (PWM) concept: "From the waveguided gravity to the periodic waveguided multiverse as united solution of Dark Energy & Dark Matter & SUSY – mysteries". http://vixra.org/...35v1.pdf
All periodic 3D-Subuniverses are intrinsically physically equal to our Universe; few the nearest to us adjacent Subuniverses create invisible 95% of that we see on the sky (DE-antigravitational accelerative expansion, flatness, DM, bubble larg
Iourii Gribov
1 / 5 (1) May 14, 2014
All periodic 3D-Subuniverses (see my comments above) are intrinsically physically equal to our Universe; few the nearest to us adjacent Subuniverses create invisible 95% of that we see on the sky (DE-antigravitational accelerative expansion, flatness, DM, bubble large scale structure). All physically equal adjacent waveguides-Sub-Universes Un /Un+1 mutually behave as Universe and Antiuniverse – disclosing the nature of matter and antimatter particles, with emergent CPT-like symmetry between them, but now expanded to the gravity "charge" symmetry and this predicts antigravity – repulsion between matter and antimatter, where both spices EQUALLY are survived after Big Bang. The PWM explains our Universe flatness (gravity chargeless on the large scale), linear Hubble-expansion, Jeans instability, etc in the homogeneous gravity-antigravity system. // I. Gribov, S.A. Trigger. 2014. Jeans instability and anti-screening in gravitational-antigravitational model of universe http://arxiv.org/...7122.pdf
Whydening Gyre
5 / 5 (2) May 14, 2014
Moreover, in quantum mechanics, following the quantum equations summing on all the possible histories, the universe is continuously splitting with multiverses where all the possible histories happen endless every microscopic times !!

We humans LOVE to complicate and imagine.
However the simplest answer is this - It's all one big field of differing energy particles that relate to each other by a PHI ordered pattern rule.
ART rules!
antialias_physorg
5 / 5 (1) May 14, 2014
if we don't attribute the multiverse some tangible properties, mathematical if possible, then the whole idea will remain untestable, unfalsifiable and as such non-scientific. ...

Which is the point of the article: To see what kind of tangible evidence a multiverse would have and then go look if its there or not. That's scientific.

The complicated thing about science is not the invention of a theory. Any drunk at a bar (or poster in an internet comment section) has a theory. The real work is making up a theory AND THEN finding out what it would tangibly mean if that concept were true as opposed to if it were not (and then, preferrably, go out and test it).
antialias_physorg
not rated yet May 14, 2014
if we don't attribute the multiverse some tangible properties, mathematical if possible, then the whole idea will remain untestable, unfalsifiable and as such non-scientific. ...

Which is the point of the article: To see what kind of tangible evidence a multiverse would have and then go look if its there or not. That's scientific.

The complicated thing about science is not inventing a theory (anyone can say "multiverses - cool!").
Any drunk at a bar (or poster in an internet comment section) has a theory. The real work is making up a theory AND THEN finding out what it would tangibly mean if that concept were true as opposed to if it were not (and then, preferrably, go out and test it).
Pejico
May 14, 2014
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Pejico
May 14, 2014
This comment has been removed by a moderator.
Pejico
May 14, 2014
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cantdrive85
1 / 5 (2) May 15, 2014
I'm not here for fight with mainstream physics, but for its explanation.

I'm here in favor of the former.
Pejico
May 15, 2014
This comment has been removed by a moderator.
antialias_physorg
5 / 5 (4) May 15, 2014
It can be interpreted like multiverse effect too.

Lacking reading comprehension? Fitting observation to data is not science. That's 'doctrine of signatures'.

Make a PREDICTION that is not supported by mainstream theories and then go out and test it. Then you may have something (and while you're at it: show that your theory is at least as good or better at describing EVERYTHING that the old theory does...otherwise you still have only a crappy niche explanation)

Oh...and don't forget to do it with math. Otherwise it's just bunk.
Anda
5 / 5 (1) May 17, 2014
Very simple article. A much simplified synthesis of a question that can fill many physic theories books, so anyone can comment about subjects they don't know?
Level is really dropping in "phys", articles were more "serious" a way back...
orti
not rated yet May 18, 2014
phys.kuk – in the farthest multiverse to the left.
blueplanetjournal
not rated yet May 18, 2014
Nice read! I do remember reading in ancient Indian text mentioned that there are universes upon universes. We recently published an article which attempts to satisfy the curiosity that if we are living in a multiverse then how far can be our closest neighbors?

http://www.bluepl...rse.html