You think there's a multiverse? Get real

[Garth]

I really appreciated the article in this week's New Scientist You think there's a multiverse? Get real based on Lee Smolin's new book "The Singular Universe and the Reality of Time", which is co-authored with Roberto Mangabeira Unger.

Lee has changed his tune from the days of his Cosmological Natural Selection hypothesis in which every BH spawns a new universe and a natural selection process fine tunes the physical constants to maximise the number of BHs a particular universe produces, incidentally also fine tuning the universe to be propitious for life, so there is a multitude upon multitude of universes.

Now he, with the philosopher Unger, embraces scientific realism and as he writes in the article:

Thus the multiverse theory has difficulty making any firm predictions and threatens to take us out of the realm of science. These other universes are unobservable and because chance dictates the random distribution of properties across universes, positing the existence of a multiverse does not let us deduce anything about our universe beyond what we already know. As attractive as the idea may seem, it is basically a sleight of hand, which converts an explanatory failure into an apparent explanatory success.

Smolin, rejecting the multiverse as having no predictive power, suggests we need to reject some of the principles (excess baggage) standard cosmology is built on, the scaling up of physical laws from the laboratory or solar system up to the entire universe and the 'Newtonian paradigm' (the predictions of future states from initial conditions under a set of laws).

Once we accept that we need a new paradigm to do science at the level of the universe as a whole, the next question to ask is what principle that new paradigm should be founded on...

The first is that there is just one universe. The second is that time is real and the laws of nature are not timeless but evolve. The third is that mathematics is not a description of some separate timeless, Platonic reality, but is a description of the properties of one universe.

I agree with the first and second - laws can evolve in alternative theories such as a suggested variation of G - however I find it hard not to accept the 'eternal' truths of Mathematics - Platonist as I am! I like to think 1+ 1 = 2 whether there is anybody around to think so or not.

Personally I ask the question, "Whenever we talk about a quantity, Mass, Length, Time etc., both defined here in the laboratory or applied to the distant universe, we have to also ask 'How is that quantity measured and compared with its standard unit.'h

Garth

 

[Stephen Tashi]

Is there any way to decide whether a physical quantity (in a given system of units) must always be a rational number? I don't see that assuming physical quantities can be any real number (as opposed to only a rational number or only from some other dense subset of the real numbers) has any predictive power. However, convenience and mathematical aesthetics lead to using the model of the real numbers (and the complex numbers) in physics. By analogy to that situation, the fact that a multiverse theory is not predictive doesn't rule out the fact that it might be turn out to be a good theory if the mathematics of it can be shown to be convenient.

 

[Chalnoth]

These are just the standard, baseless objections that have been answered many times before.

He seems to be defining the multiverse out of existence by saying, "There's one universe, with changing physical laws," while neglecting to notice that this guarantees that there will be different regions with different physical laws, which in turn is one kind of multiverse that many people discuss.

 

[Garth]

These are just the standard, baseless objections that have been answered many times before.

He seems to be defining the multiverse out of existence by saying, "There's one universe, with changing physical laws," while neglecting to notice that this guarantees that there will be different regions with different physical laws, which in turn is one kind of multiverse that many people discuss.

The difference being that we might be able to observe these regions with evolved physical laws and 'constants'.

Garth

 

[Chalnoth]

The difference being that we might be able to observe these regions with evolved physical laws and 'constants'.

Garth

Uhh, no. There is precisely zero difference.

To within current measurement errors, physical laws have not changed within the observable universe. And many ways that the laws can change would result in changes being phase transitions that happen suddenly rather than gradually, such that you'd never detect a change by looking at tiny variations of the laws within the observable universe.

The way you detect such different physical laws is basically identical to the multiverse theories: you don't look for the changes themselves, but for other consequences of the theory that predicts the changes that are measurable.

 

[Chronos]

I am admittedly sympathetic with Carlos Rovelli's view on multiverse theories from a 2012 interview as reported in Scientific American - re: http://blogs.scientificamerican.com...losophical-superficiality-has-harmed-physics/ :

Horgan: Do multiverse theories and quantum gravity theories deserve to be taken seriously if they cannot be falsified?

Rovelli: No.

 

[Garth]

I am admittedly sympathetic with Carlos Rovelli's view on multiverse theories from a 2012 interview as reported in Scientific American - re: http://blogs.scientificamerican.com...losophical-superficiality-has-harmed-physics/ :

Horgan: Do multiverse theories and quantum gravity theories deserve to be taken seriously if they cannot be falsified?

Rovelli: No.

I agree Chronos, and as Smolin's NS article says after talking about the unusual initial conditions of the original GR BB model:

The challenge that cosmologists face is to make sense of this specialness. One approach to this question is inflation – the hypothesis that the early universe went through a phase of exponentially fast expansion. At first, inflation seemed to do the trick. A simple version of the idea gave correct predictions for the spectrum of fluctuations in the cosmic microwave background.

But a closer look shows that we have just moved the problem further back in time. To make inflation happen at all requires us to fine-tune the initial conditions of the universe. And unless inflation is highly tuned and constrained, it leads to a runaway process of universe creation. As a result, some cosmologists suggest that there is not one universe, but an infinite number, with a huge variety of properties: the multiverse. There are an infinite number of universes in the collection that are like our universe and an infinite number that are not. But the ratio of infinity to infinity is undefined, and can be made into anything the theorist wants. Thus the multiverse theory has difficulty making any firm predictions and threatens to take us out of the realm of science.

Until observations demonstrate that such other universes do exist with high statistical significance (95% at least) then for one I am convinced that multiverse theories have taken us out of the realm of science.

Garth

 

[Chalnoth]

I agree Chronos, and as Smolin's NS article says after talking about the unusual initial conditions of the original GR BB model:

Until observations demonstrate that such other universes do exist with high statistical significance (95% at least) then for one I am convinced that multiverse theories have taken us out of the realm of science.

Garth

Would you reject any theory, then, which happens to include a multiverse as one of its predictions?

 

[marcus]

Would you reject any theory, then, which happens to include a multiverse as one of its predictions?

that's not a well-defined question. It's verbal and people fudge around with what they mean by "multiverse".
Some people are in love with the word "multiverse" and will apply it to any model of the UNIverse where some physical quantity (which might otherwise be taken to be constant) varies.
The model is what I would call a universe, operating under a set of natural laws, and predictable enough to be tested. But they point to some little "sub-law" that varies and say "look! there are different REGIONS in the universe! Therefore it is a MUUULLLTTEEEVERSE!

I would go along to a large extent with the essay in NATURE by two of the world's most prominent and respected cosmologists: Joe Silk and George Ellis. They are definite about what they mean should be regarded as outside the bounds of science. They define their terms and give their reasons.
As I recall the essay was titled something like
Defend the Integrity of Physics
Yes, here is a link:
http://www.nature.com/news/scientific-method-defend-the-integrity-of-physics-1.16535
Here are some excerpts:
==quote==
Scientific method: Defend the integrity of physics

• George Ellis
• & Joe Silk

16 December 2014
Attempts to exempt speculative theories of the Universe from experimental verification undermine science, argue George Ellis and Joe Silk.

This year, debates in physics circles took a worrying turn. Faced with difficulties in applying fundamental theories to the observed Universe, some researchers called for a change in how theoretical physics is done. They began to argue — explicitly — that if a theory is sufficiently elegant and explanatory, it need not be tested experimentally, breaking with centuries of philosophical tradition of defining scientific knowledge as empirical. We disagree. As the philosopher of science Karl Popper argued: a theory must be falsifiable to be scientific.
Chief among the 'elegance will suffice' advocates are some string theorists. Because string theory is supposedly the 'only game in town' capable of unifying the four fundamental forces, they believe that it must contain a grain of truth even though it relies on extra dimensions that we can never observe. Some cosmologists, too, are seeking to abandon experimental verification of grand hypotheses that invoke imperceptible domains ...

These unprovable hypotheses are quite different from those that relate directly to the real world and that are testable through observations — such as the standard model of particle physics and the existence of dark matter and dark energy. As we see it, theoretical physics risks becoming a no-man's-land between mathematics, physics and philosophy that does not truly meet the requirements of any.

The issue of testability has been lurking for a decade. String theory and multiverse theory have been criticized in popular books1, 2, 3 and articles, including some by one of us (G.E.)4. In March, theorist Paul Steinhardt wrote5 in this journal that the theory of inflationary cosmology is no longer scientific because it is so flexible that it can accommodate any observational result. Theorist and philosopher Richard Dawid6 and cosmologist Sean Carroll7 have countered those criticisms with a philosophical case to weaken the testability requirement for fundamental physics.
...
...

MANY MULTIVERSES
The multiverse is motivated by a puzzle: why fundamental constants of nature, such as the finestructure constant that characterizes the strength of electromagnetic interactions between particles and the cosmological constant associated with the acceleration of the expansion of the Universe, have values that lie in the small range that allows life to exist. Multiverse theory claims that there are billions of unobservable sister universes out there in which all possible values of these constants can occur. So somewhere there will be a biofriendly universe like ours, however improbable that is.

Some physicists consider that the multiverse has no challenger as an explanation of many otherwise bizarre coincidences. The low value of the cosmological constant — known to be 120 factors of 10 smaller than the value predicted by quantum field theory — is difficult to explain, for instance.
...
...
[Sean Carroll] argues that inaccessible domains can have a “dramatic effect” in our cosmic back yard, explaining why the cosmological constant is so small in the part we see. But in multiverse theory, that explanation could be given no matter what astronomers observe. All possible combinations of cosmological parameters would exist somewhere, and the theory has many variables that can be tweaked. Other theories, such as unimodular gravity, a modified version of Einstein’s general theory of relativity, can also explain why the cosmological constant is not huge7.

Some people have devised forms of multiverse theory that are susceptible to tests: physicist Leonard Susskind’s version can be falsified if negative spatial curvature of the Universe is ever demonstrated. But such a finding would prove nothing about the many other versions. Fundamentally, the multiverse explanation relies on string theory, which is as yet unverified, and on speculative mechanisms for realizing different physics in different sister universes. It is not, in our opinion, robust, let alone testable.

The manyworlds theory of quantum reality posed by physicist Hugh Everett is the ultimate quantum multiverse, where quantum probabilities affect the macroscopic. According to Everett, each of Schrödinger’s famous cats, the dead and the live, poisoned or not in its closed box by random radioactive decays, is real in its own universe. Each time you make a choice, even one as mundane as whether to go left or right, an alternative universe pops out of the quantum vacuum to accommodate the other action.

Billions of universes — and of galaxies and copies of each of us — accumulate with no possibility of communication between them or of testing their reality. But if a duplicate self exists in every multiverse domain and there are infinitely many, which is the real ‘me’ that I experience now? Is any version of oneself preferred over any other? How could ‘I’ ever know what the ‘true’ nature of real ity is if one self favours the multiverse and another does not?

In our view, cosmologists should heed mathematician David Hilbert’s warning: although infinity is needed to complete mathematics, it occurs nowhere in the physical Universe.
...
...
The consequences of overclaiming the significance of certain theories are profound — the scientific method is at stake (see go.nature.com/hh7mm6). To state that a theory is so good that its existence supplants the need for data and testing in our opinion risks misleading students and the public as to how science should be done and could open the door for pseudoscientists to claim that their ideas meet similar requirements.

What to do about it? Physicists, philosophers and other scientists should hammer out a new narrative for the scientific method that can deal with the scope of modern physics. In our view, the issue boils down to clarifying one question: what potential observational or experimental evidence is there that would persuade you that the theory is wrong and lead you to abandoning it? If there is none, it is not a scientific theory.

Such a case must be made in formal philosophical terms. A conference should be convened next year to take the first steps. People from both sides of the testability debate must be involved.

In the meantime, journal editors and publishers could assign speculative work to other research categories — such as mathematical rather than physical cosmology — according to its potential testability. And the domination of some physics departments and institutes by such activities could be rethought1,2.

The imprimatur of science should be awarded only to a theory that is testable. Only then can we defend science from attack. ■
_______________________________________
George Ellis is professor emeritus of applied mathematics at the University of Cape Town, South Africa. Joe Silk is professor of physics at the Paris Institute of Astrophysics, France, and at Johns Hopkins University in Baltimore, Maryland, USA.
e-mails: george.ellis@uct.ac.za; silk@iap.fr
==endquote==
http://en.wikipedia.org/wiki/George_F._R._Ellis

 

[Chalnoth]

It is beyond foolish to disregard an entire class of theories as being "untestable" without any consideration of whether or not they are, in fact, testable.

 

[Garth]

To within current measurement errors, physical laws have not changed within the observable universe. And many ways that the laws can change would result in changes being phase transitions that happen suddenly rather than gradually, such that you'd never detect a change by looking at tiny variations of the laws within the observable universe.

The way you detect such different physical laws is basically identical to the multiverse theories: you don't look for the changes themselves, but for other consequences of the theory that predicts the changes that are measurable.

That's the point - By saying "To within current measurement errors, physical laws have not changed within the observable universe" you are showing the idea that laws change is testable, and by your assessment falsifiable.

Now what observations "to within current measurement errors" have demonstrated the existence of other universes or more to the point could possibly falsify the existence of such a universe?

Would you reject any theory, then, which happens to include a multiverse as one of its predictions?

Of course not - I would just classify and reject that particular prediction as being "outside the bounds of science". (Thank you Marcus)

It is beyond foolish to disregard an entire class of theories as being "untestable" without any consideration of whether or not they are, in fact, testable.

I absolutely agree - therefore what are the falsifiable tests for a multiverse?

Garth

 

[Chalnoth]

Now what observations "to within current measurement errors" have demonstrated the existence of other universes or more to the point could possibly falsify the existence of such a universe?

The existence of spontaneous symmetry breaking that impacts low-energy physical laws is evidence of other "universes".

Spontaneous symmetry breaking is at the heart of the standard model of particle physics, and one of the results of said symmetry breaking is the Higgs boson, which was recently detected.

I absolutely agree - therefore what are the falsifiable tests for a multiverse?

Popperian falsifiability has not been a significant restriction of science for a very long time. More recent notions recognize that it is entirely possible for a theory to be unfalsifiable in the strict Popperian sense, while it still being possible for evidence to support the theory.

This frequently occurs, for example, with theories that have free parameters. To take a simple example, imagine a theory with a parameter that varies from 1-1000. If this parameter is between 1-5, then current experiments can detect it. If, on the other hand, the parameter is between 6-1000, then it cannot be detected. If the parameter is between 500-1000, then there is no possible way to detect evidence for the theory, even in principle. Such a theory is not falsifiable in the strict sense, but it is still possible to collect evidence that supports the theory if this parameter happens to be within the detectable range.

This is the sort of thing that people deal with with regard to a "multiverse". That the evidence is generally going to be indirect should bother nobody (our physics theories have become so abstract that evidence for them has been quite indirect for a long time now).

 

[Garth]

The existence of spontaneous symmetry breaking that impacts low-energy physical laws is evidence of other "universes".

Spontaneous symmetry breaking is at the heart of the standard model of particle physics, and one of the results of said symmetry breaking is the Higgs boson, which was recently detected.

You are confusing yourself.

If there is an ensemble of different universes in which spontaneous symmetry breaking occurs bestowing different values to physical constants and laws (resulting in the present asymmetric system in this universe) then you can explain particular (anthropic) values of those constants and laws as a selection effect. We are in this universe because we can be in no other.

So if you are saying, "spontaneous symmetry breaking ... is evidence of other "universes," then the multiverse is an a priori assumption, not a prediction, of the theory.

If you stand a box worth of pencils on their tips and let go one will end up pointing (more or less) north.

However, on the other hand, you don't need a box worth, a single pencil thus let go might end up pointing north by chance.

This universe might be a 'fluke' - how could we tell otherwise with a statistical sample of one?

Spontaneous symmetry breaking does not require a multiverse let alone provide evidence of one.

We have not yet developed a quantum gravity theory, there could be some "Beyond the standard theory" model out there that includes an explicit symmetry breaking, one that does not respect the symmetry of the equations that define why the laws and constants of physics are as they are.
(Stand a single pencil on its point and then blow on it)

therefore what are the falsifiable tests for a multiverse?

Popperian falsifiability has not been a significant restriction of science for a very long time.

Let me rephrase then, "what are the tests for a multiverse?"

Garth

 

[John_QPublic]

In the movie "The Principle" (www.ThePrincipleMovie.com), George Ellis makes the point that the multiverse has way too much explanatory power, yet is undetectable and unverifiable/unfalsifiable. Martin Selbrede states that basically cosmology is at the point where it is either God or the multiverse. If you are in southern California or Spokane, you should go see the movie.

 

[Nugatory]

In the movie "The Principle" (www.ThePrincipleMovie.com), George Ellis makes the point that the multiverse has way too much explanatory power, yet is undetectable and unverifiable/unfalsifiable. Martin Selbrede states that basically cosmology is at the point where it is either God or the multiverse. If you are in southern California or Spokane, you should go see the movie.

This might be a good note upon which to close the thread.

 

[Garth]

In the movie "The Principle" (www.ThePrincipleMovie.com), George Ellis makes the point that the multiverse has way too much explanatory power, yet is undetectable and unverifiable/unfalsifiable. Martin Selbrede states that basically cosmology is at the point where it is either God or the multiverse. If you are in southern California or Spokane, you should go see the movie.

Hi John,

I remember a 1970's paper (in Nature if I recall) by Fred Hoyle in which, after conceding the end of his infinite and eternal Steady State Theory, he is arguing the universe had to be closed ($\Omega$ > 1) so you can have an eternal oscillating universe thus giving enough time for the immensely improbable life to form. To close the universe he needed a lot of unknown mass, which before the Cold DM days, he thought could be in the form of massive neutrinos - as there was so many of them. The only alternative he could think of was 'God did it'. (Note Fred Hoyle was the 1950's and 60's equivalent of Richard Dawkins - known more by the general public for his atheism than for his science.) I remember a conclusion of his paper that said, "Either the neutrino has mass or there is a God", which I thought at least intellectually honest (possibly admitting defeat) if a little unorthodox.However as far as the multiverse or God dilemma is concerned Smolin and Unger suggest a third way and propose a 'new paradigm'. (Don't you just love it when people use that word.;))Garth

 

[Chalnoth]

You are confusing yourself.

If there is an ensemble of different universes in which spontaneous symmetry breaking occurs bestowing different values to physical constants and laws (resulting in the present asymmetric system in this universe) then you can explain particular (anthropic) values of those constants and laws as a selection effect. We are in this universe because we can be in no other.

You don't need an ensemble. All you need is a big universe. In such a universe, the symmetry breaking will take on different values in different locations.

So if you are saying, "spontaneous symmetry breaking ... is evidence of other "universes," then the multiverse is an a priori assumption, not a prediction, of the theory.

False. The extra "universes" in this case arise from the simplest possible assumptions you can possibly make about the theory. It is necessary to add additional assumptions to get rid of the multiverse.

 

[marcus]

==quote Garth==
Smolin and Unger suggest a third way and propose a 'new paradigm'. (Don't you just love it when people use that word.;))
==endquote
Thanks Garth, for this nimble wide-ranging and entertaining discussion! Indeed there must be several "third ways". I mean lines of investigation that don't "give up" but continue to attempt to empirically explain why cosmology is the way it is---how the world comes to be this way. I wonder if Silk and Ellis will get the international community-wide conference they call for!

I quoted from the Silk Ellis call to "defend the integrity of physics" in post #9. I think "outside the bounds of science" was one of the phrases they used for what they consider dangerous trends:
disguised failure of explanation--pretended explanation on imaginary grand scale
retreat to mythology--with the elegance and patness that traditionally accompanies mythology
relaxing the rules of evidence to include elegant ways of giving up

Silk and Ellis call for a conference this year! It could be interesting if they get one started organizing, even if it doesn't actually convene in 2015. I think of it as a
"taking out the rubbish" conference.
Deciding collectively what the criteria are for empirical/testable. They are suggesting such standards be reflected in the editorial policy of physics journals and in departmental faculty makeup. It's a pleasure to hear senior people so outspoken :w

========================
Anyway there must surely be "third ways" in the making. Smolin et al "evolving laws" idea is impressive but the first order of business seems to me to be a combined quantum theory of geometry and matter (like the recent proposal of Chamseddine Connes & Mukhanov to see if GR and StdMdl can grow from a single algebraic root)
It makes sense to me that one first gets the laws (for quantum mechanics, geometry, matter) and THEN one begins to conjecture about how they might have evolved. We don't seem to have a fully unified set of laws yet. But maybe it is good what Smolin Cortes and Unger are doing. Wolfgang Wieland, a QG postdoc whose research I like very much, may have started working with Cortes and Smolin. Sorry if this post is a bit vague, basically just wanted to express appreciation.

 

[ShayanJ]

Let's look more closely to the idea of multiverse. Is it testable? Is it falsifiable? Is it useful? Is it physics? Is it about "our world"?
I don't know that much about this theory to talk about it technically and with mathematical rigour and physical precision. But I think I see some issues about it which I want to share.
Before starting, I want to quote an amusing thing from one of my professors which I think may be of use in my explanations. I had classical mechanics with him and, as you know, there's usually a discussion about motion in accelerated frames in such a course. Now when he wanted talk about the fictitious forces in such a frame, he explained it like this:
Imagine someone who has lived all of his life in a wagon and knows nothing about the outside world. Any time the wagon accelerates, he sees that all stuff moves toward one of the walls with non-zero acceleration. So he may think that "wow man, interesting, looks like there is a special kind of force, which I give it the name wagon-wall force, that from time to time accelerates these objects toward that particular wall." He then may extend his theory to answer the questions "when the force appears?" or "why only that particular wall exerts this force on objects?" And so he'll probably be OK with his own "physics" because he can explain things.
Now we're actually in such a condition. We're inside something we can't get out of. All we say is about inside this "wagon". Let's see what's the difference between an "inside-wagon" theory and an "outside-wagon" one.
All laws of physics we have now(I mean the well established ones of course), are "inside-wagon" theories. They only refer to things inside the wagon and just couldn't care less about what's outside or even whether there is anything outside or not. The important thing about such theories is that...(Not sure how to say it!)...is that we can think about them from different perspectives and study them in different experiments. I mean, we can look at them anyway we want and we can be sure there is something in nature telling us whether that perspective makes sense or not. So we understand these theories very well. And we want all our incomplete theories be like this.
But what about the "outside-wagon" theories like the multiverse? Let's just take it for granted that there can be(or even there already is) evidence for multiverse. But what kind of evidence is it? Surely it can in no way be like the evidence we have for e.g. QED. Because QED is an "inside-wagon" theory. We know from a great number of experimental and theoretical evidences we have that this should be correct. But all other universes, by definition of the multiverse, are just very much disconnected from us so the theory itself is telling us that even if it has any evidence, it should be too little. And now like that guy inside the wagon who can build his own physics without referring to outside, we always can have "inside-wagon" theories that have much more evidence and also include that little evidence of multiverse. So it seems to me any physical "inside-wagon" theory is by definition superior to multiverse.
Now this argument may seem too hand-wavy to dismiss a whole theory based on it but it actually is not that hand-wavy. I know people may say that "yeah, but that doesn't prove multiverse is wrong!". Yeah I know, but even if actually multiverse is right(which has no meaning for me), how does it make a difference to physics? Let me rephrase the question, how is it different from saying that god created the universe? Its really naive to think that only because a physicist knowing lots of fancy math is saying that, then it is physics. Because there can always be people saying that "yeah guys, we know how this universe is created, its the multiverse, and you guys don't know!...blah blah blah" and all other physicists just ignoring them because they know there should be an "inside-wagon" theory giving the solution and it doesn't matter for how long they they wait for that theory to show up, they just keep working on it because they think it should be an "inside-wagon" theory. Now doesn't this remind you anything? Let me tell you what is it. Its the same gap between people who say god created the universe and no more and people who think science can explain everything and doesn't need god.
My point is, science tries to talk about this world and "this world" is defined(inescapably) by what we can observe. So I guess we can say science is a fuzzy set. For any statement, there is an evaluation function which tells us how much this statement is part of science. And that function is the amount we can observe things about that statement. Now god is something unobservable by definition and so our function gives zero for it. This means the word "god" should appear in no statement which is intended to be called scientific. This also means science is unable to talk about god. And multiverse, our functions doesn't give zero for this but it seems to it gives a very small value. As I said, by definition, multiverse is much less observable than other theories and so its much less inside physics than other theories. So I would say, the multiverse explanation is just a little more related to science, than is the explanation "god created it".

 

[Garth]

f there is an ensemble of different universes in which spontaneous symmetry breaking occurs bestowing different values to physical constants and laws (resulting in the present asymmetric system in this universe) then you can explain particular (anthropic) values of those constants and laws as a selection effect. We are in this universe because we can be in no other.

You don't need an ensemble. All you need is a big universe. In such a universe, the symmetry breaking will take on different values at different times.

Are we taking here about "different regions with different physical laws" in the one universe (Your #3)? The words "Other universes" was yours (#12), but alright let me rephrase:- If there is an ensemble of different regions with different physical laws in which spontaneous symmetry breaking occurs... (the rest follows..)

So if you are saying, "spontaneous symmetry breaking ... is evidence of other "universes," then the multiverse is an a priori assumption, not a prediction, of the theory.

False. The extra "universes" in this case arise from the simplest possible assumptions you can possibly make about the theory. It is necessary to add additional assumptions to get rid of the multiverse.

But only if the symmetry breaking is "spontaneous" i.e. stochastic. That itself is an a priori assumption.
Explicit symmetry breaking under some constraint in a Theory of Everything may "get rid of the multiverse".
Now I haven't (yet) got a testable TOE but then neither have you.

I had an extended internet debate on the origin of the universe with someone who argued that in the BB the universe sprang out of nothing.
As there really had been no-thing, no matter, energy or physical laws in existence then there had been no conservation laws to say it couldn't happen.
A very convincing argument.
However my response was that my problem wasn't that his argument explained nothing but that it explained everything and anything and therefore it explained nothing.

I read a similar objection to the multiverse by Paul Steinhardt in an Edge article 'Theories of Anything'.

A pervasive idea in fundamental physics and cosmology that should be retired: the notion that we live in a multiverse in which the laws of physics and the properties of the cosmos vary randomly from one patch of space to another...
Among these patches, in the words of Alan Guth, "anything that can happen will happen—and it will happen infinitely many times". Hence, I refer to this concept as a Theory of Anything...
I think a priority for theorists today is to determine if inflation and string theory can be saved from devolving into a Theory of Anything and, if not, seek new ideas to replace them. Because an unfalsifiable Theory of Anything creates unfair competition for real scientific theories, leaders in the field can play an important role by speaking out—making it clear that Anything is not acceptable—to encourage talented young scientists to rise up and meet the challenge. The sooner we can retire the Theory of Anything, the sooner this important science can progress.

I cannot agree more.
Garth

 

[Chalnoth]

It absolutely disgusts me that so many people make the a priori assumption that there can be no multiverse, and then try to berate people who suggest it as a possibility.

 

[marcus]

I don't see anybody here (certainly not Silk and Ellis in the article I quoted) who rejects "multiverse" models a priori. So it is misleading and disingenuous to pretend people are doing that and fulminate against it. Silk and Ellis even mention an instance of a TESTABLE "multiverse". What they are fighting is the trend to erode empircism, relax requirements of testability.
These are world-class senior cosmologists and I took the trouble to quote some excerpts. I'd appreciate if people would have a look because I think it is an important development. Silk and Ellis want a physics/cosmology conference with people from different sides of the testability debate, to settle what the criteria are for testability and what is not testable and therefore outside science. they even call for a conference to be held this year (which might be sooner than it can be organized, I can't tell). they hope conclusions from such a conference influence journal editorial policy and departmental hiring trends.
The point is to examine, hear different sides, discuss, and hammer out appropriate standards for the community.
I will quote what I said about this in my previous post:
==quote my earlier post==
I would go along to a large extent with the essay in NATURE by two of the world's most prominent and respected cosmologists: Joe Silk and George Ellis. They are definite about what they mean should be regarded as outside the bounds of science. They define their terms and give their reasons.
As I recall the essay was titled something like
Defend the Integrity of Physics
Yes, here is a link:
http://www.nature.com/news/scientific-method-defend-the-integrity-of-physics-1.16535
Here are some excerpts:
==quote Silk Ellis essay in Nature==
Scientific method: Defend the integrity of physics
16 December 2014
Attempts to exempt speculative theories of the Universe from experimental verification undermine science, argue George Ellis and Joe Silk.

This year, debates in physics circles took a worrying turn. Faced with difficulties in applying fundamental theories to the observed Universe, some researchers called for a change in how theoretical physics is done. They began to argue — explicitly — that if a theory is sufficiently elegant and explanatory, it need not be tested experimentally, breaking with centuries of philosophical tradition of defining scientific knowledge as empirical. We disagree. As the philosopher of science Karl Popper argued: a theory must be falsifiable to be scientific.
Chief among the 'elegance will suffice' advocates are some string theorists. Because string theory is supposedly the 'only game in town' capable of unifying the four fundamental forces, they believe that it must contain a grain of truth even though it relies on extra dimensions that we can never observe. Some cosmologists, too, are seeking to abandon experimental verification of grand hypotheses that invoke imperceptible domains ...

These unprovable hypotheses are quite different from those that relate directly to the real world and that are testable through observations — such as the standard model of particle physics and the existence of dark matter and dark energy. As we see it, theoretical physics risks becoming a no-man's-land between mathematics, physics and philosophy that does not truly meet the requirements of any.

The issue of testability has been lurking for a decade. String theory and multiverse theory have been criticized in popular books1, 2, 3 and articles, including some by one of us (G.E.)4. In March, theorist Paul Steinhardt wrote5 in this journal that the theory of inflationary cosmology is no longer scientific because it is so flexible that it can accommodate any observational result. Theorist and philosopher Richard Dawid6 and cosmologist Sean Carroll7 have countered those criticisms with a philosophical case to weaken the testability requirement for fundamental physics.
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MANY MULTIVERSES
The multiverse is motivated by a puzzle: why fundamental constants of nature, such as the finestructure constant that characterizes the strength of electromagnetic interactions between particles and the cosmological constant associated with the acceleration of the expansion of the Universe, have values that lie in the small range that allows life to exist. Multiverse theory claims that there are billions of unobservable sister universes out there in which all possible values of these constants can occur. So somewhere there will be a biofriendly universe like ours, however improbable that is.

Some physicists consider that the multiverse has no challenger as an explanation of many otherwise bizarre coincidences. The low value of the cosmological constant — known to be 120 factors of 10 smaller than the value predicted by quantum field theory — is difficult to explain, for instance.
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[Sean Carroll] argues that inaccessible domains can have a “dramatic effect” in our cosmic back yard, explaining why the cosmological constant is so small in the part we see. But in multiverse theory, that explanation could be given no matter what astronomers observe. All possible combinations of cosmological parameters would exist somewhere, and the theory has many variables that can be tweaked. Other theories, such as unimodular gravity, a modified version of Einstein’s general theory of relativity, can also explain why the cosmological constant is not huge7.

Some people have devised forms of multiverse theory that are susceptible to tests: physicist Leonard Susskind’s version can be falsified if negative spatial curvature of the Universe is ever demonstrated. But such a finding would prove nothing about the many other versions. Fundamentally, the multiverse explanation relies on string theory, which is as yet unverified, and on speculative mechanisms for realizing different physics in different sister universes. It is not, in our opinion, robust, let alone testable.

The manyworlds theory of quantum reality posed by physicist Hugh Everett is the ultimate quantum multiverse, where quantum probabilities affect the macroscopic. According to Everett, each of Schrödinger’s famous cats, the dead and the live, poisoned or not in its closed box by random radioactive decays, is real in its own universe. Each time you make a choice, even one as mundane as whether to go left or right, an alternative universe pops out of the quantum vacuum to accommodate the other action.

Billions of universes — and of galaxies and copies of each of us — accumulate with no possibility of communication between them or of testing their reality. But if a duplicate self exists in every multiverse domain and there are infinitely many, which is the real ‘me’ that I experience now? Is any version of oneself preferred over any other? How could ‘I’ ever know what the ‘true’ nature of real ity is if one self favours the multiverse and another does not?

In our view, cosmologists should heed mathematician David Hilbert’s warning: although infinity is needed to complete mathematics, it occurs nowhere in the physical Universe.
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The consequences of overclaiming the significance of certain theories are profound — the scientific method is at stake (see go.nature.com/hh7mm6). To state that a theory is so good that its existence supplants the need for data and testing in our opinion risks misleading students and the public as to how science should be done and could open the door for pseudoscientists to claim that their ideas meet similar requirements.

What to do about it? Physicists, philosophers and other scientists should hammer out a new narrative for the scientific method that can deal with the scope of modern physics. In our view, the issue boils down to clarifying one question: what potential observational or experimental evidence is there that would persuade you that the theory is wrong and lead you to abandoning it? If there is none, it is not a scientific theory.

Such a case must be made in formal philosophical terms. A conference should be convened next year to take the first steps. People from both sides of the testability debate must be involved.

In the meantime, journal editors and publishers could assign speculative work to other research categories — such as mathematical rather than physical cosmology — according to its potential testability. And the domination of some physics departments and institutes by such activities could be rethought1,2.

The imprimatur of science should be awarded only to a theory that is testable. Only then can we defend science from attack. ■
_______________________________________
George Ellis is professor emeritus of applied mathematics at the University of Cape Town, South Africa. Joe Silk is professor of physics at the Paris Institute of Astrophysics, France, and at Johns Hopkins University in Baltimore, Maryland, USA.
e-mails: george.ellis@uct.ac.za; silk@iap.fr
==endquote from Nature==
http://en.wikipedia.org/wiki/George_F._R._Ellis
==endquote from my earlier post==

 

[Chronos]

An unfalsifiable theory is not science. It might be philosophy, even theosophy, but, not science. Science is empirical. That is arguably a weakness, I think it is an imperative.

 

[Chalnoth]

When you effectively tell people that they can't even *speculate* about multiverse ideas, yes, you are saying that you aren't willing to consider any theory which contains a multiverse. It's disgusting.

 

[ShayanJ]

When you effectively tell people that they can't even *speculate* about multiverse ideas, yes, you are saying that you aren't willing to consider any theory which contains a multiverse. It's disgusting.

Of course anyone is free to speculate about anything s\he wants. Otherwise we all would hate pure mathematicians, right?
The point is, as I said in my last post, it makes no difference to accept or not to accept multiverse. Its like QM's shut up and calculate. People say "yeah, we shut up and calculate but we also sometimes don't shut up!", now Bohr and Heisenberg may say "no guys, you should shut up" and the answer is just "yeah, you're right, its OK, we shut up but not always!". What I want to say is, people are free to speculate about multiverse and think it is the right theory, but it makes no difference that others accept it or not, anyway they'll continue to find other theories and , as I explained, any such theory will have more evidence than multiverse and this is inescapable.
You see, I'm only telling there is a big difference between multiverse and e.g. the standard model. People can forever resist accepting multiverse with no harm, but anyone reluctant to accept the SM, will be abandoned academically.
And this somehow defines how science should progress. Any theory should be somehow that the majority of the experts agree on it so that we have a mainstream path. Otherwise it becomes like philosophy that anyone is allowed to say anything and anyone can accept or reject anything. So the very fact that so many experts can simply ignore multiverse, is a philosophical problem for it which rules it out from physics to philosophy. I mean it can be correct, but not in a physical sense, but only in a philosophical sense. So if multiverse is going to remain in physics, it should change that. If it does, then its OK. Otherwise it will be philosophy, not physics.

 

[Chalnoth]

Then why are you hating on speculative models?

 

[Haelfix]

These threads always degenerate into a bunch of philosophy blah blah blah. There are also frequently very puzzling positions that I believe muddies the water considerably.

Look, cosmologists are intelligent people. The reason why many believe in multiverse theories, is that they were LED to that conclusion by the preponderance of the evidence and the available theoretical models. Indeed there is a rather intricate chain of reasoning involving the evidence for the existence of inflation (CMB data, etc), the space of theories within the inflationary framework, the physics of spontaneous symmetry breaking in the presence of gravity (the Coleman-DeLucca analysis), the metastability of the electroweak vacuum and the smallness of the cosmological constant. If someone doesn't understand what or why these assorted experimental facts mean for the case for multiverse, then they haven't thought about this properly and they ought to think about it harder.

In particular, the notion that the status quo will remain forever is just completely wrong. It will be decided by data as per usual. For instance, the case for a multiverse is drastically modified (I would say put in the hospital), if the following data sets (prior to this week) turn out to converge: Planck, WMAP, BAO and BICEP. The four of them together implied a value of the spectral tilt and r, that was simply inconsistent with inflation. Therefore a lot of the chain of reasoning necessary for the multiverse would collapse and scientists will have to come up with something else. However, (and this has been happening for 30 years now) if the data continues to favor inflationary scenarios that involves chaotic or eternal inflation, then people will continue to favor multiverse models. My question to the naysayers is, how could this be any other way?

 

[Garth]

It absolutely disgusts me that so many people make the a priori assumption that there can be no multiverse, and then try to berate people who suggest it as a possibility.

Then why are you hating on speculative models?

I am not making the a priori assumption that there can be no multiverse - there may be as many other universes as you want - the point is we cannot see them. (Unless somebody travels through a BH into one and returns to tell, then the hypothesis will enter the realm of observed science.)

I don't hate speculative models - I have spent a lifetime trying to develop one, however I have also tried to see whether it can be tested and falsified. (In its last incarnation it was!)

Think of the Intelligent Design argument:

Q. Why is the gravitational constant 'just right'? Why is the Cosmological constant so little? etc. etc. -

A. God did it She made it 'just right'!

The problem with this answer is twofold - it is bad science - once you think you have the answer you stop looking for the real one. Also it is bad theology - as soon as somebody else finds the answer then your god, the god-of-the-gaps disappears a little more.

Now Q. Why is the gravitational constant 'just right'? Why is the Cosmological constant so little? etc. etc. -

A. The multiverse did it! With an a priori assumption that the symmetry breaking process is stochastic and therefore there are a large/infinite number (ensemble) of other regions/patches/universes where the values of these constants are different then we must be in this universe (or this part of the universe) where they are 'just right'.

What's the difference between the two answers?

Actually I might go further and say that as 'One unobservable God' is a simpler answer than a 'large/infinite number of other unobservable regions/patches/universes' then by Occam's razor it is the better answer and more scientific! ;)Perhaps looking for a 'third way' is not so "disgusting"?

Garth

 

[Larry Pendarvis]

It is beyond foolish to disregard an entire class of theories as being "untestable" without any consideration of whether or not they are, in fact, testable.

So the theory that a class of theories is untestable... is that theory testable?

 

[Larry Pendarvis]

"... They began to argue — explicitly — that if a theory is sufficiently elegant and explanatory, it need not be tested experimentally, breaking with centuries of philosophical tradition of defining scientific knowledge as empirical.We disagree."

It seems to me that the difference between an explanatory theory and a predictive theory is just history. In a low-density region of a galaxy where scientists have not yet observed gravity, string theory would predict gravity and that could be subsequently confirmed by experiment.

 

[stevendaryl]

I don't read Smolin as saying that multiverses are impossible. I just read him as saying that there isn't much we can learn from thinking about multiverses. He's really just saying that we should focus on the one universe that we can observe. So it seems to me more like his statement about what's worth spending our intellectual resources and time on.

 

[Garth]

I don't read Smolin as saying that multiverses are impossible. I just read him as saying that there isn't much we can learn from thinking about multiverses. He's really just saying that we should focus on the one universe that we can observe. So it seems to me more like his statement about what's worth spending our intellectual resources and time on.

Absolutley right.

Garth

 

[marcus]

I don't read Smolin as saying that multiverses are impossible. I just read him as saying that there isn't much we can learn from thinking about multiverses. He's really just saying that we should focus on the one universe that we can observe. So it seems to me more like his statement about what's worth spending our intellectual resources and time on.

Yes! The aim is to empirically explain and anticipate THIS nature and this cosmos that we live in, and experience, and are a part of.

 

[marcus]

Steven, thanks for the clear statement! This may be obvious and not need saying, but I think there is a special issue about the past, because we don't live in it and experiment with it or directly experience it. Some models of the past CAN be tested by what they tell us we may anticipate from future observations. IOW to fall within the bounds of science a model of the past must make unambiguous predictions about what we can observe by looking more closely at the present.

We had an example of this recently with the BICEP vs Planck controversy over possible polarization swirls in the CMB. Different early universe models (versions of inflation and no-inflation bounce starts) predict different amounts of swirl---different "tensor-to-scalar" ratios. Saying, in effect, if you look more closely at the CMB and measure polarization as well as temperature fluctuations you will see such-and-such.

A model of the past can't be too flexible as to what it leads us to anticipate, otherwise it's mythology, not science. This is the key to Paul Steinhardt's critique of cosmic inflation. He was one of a panel four cosmologists chosen to discuss the state of inflation scenarios at the December 2014 Paris conference on the Planck mission results.
He gave a really interesting talk (archived on video) which was then followed by the panel discussion. Here are links to conference videos:
Steinhardt's critical review:
http://webcast.in2p3.fr/videos-introduction-_critical_review_of_inflation
The panel debate ( Steinhardt, Mukhanov, Linde, Brandenberger) that followed:
http://webcast.in2p3.fr/videos-debate_theoretical_problems_way_forward

A bit of discussion here at PF:
https://www.physicsforums.com/threa...on-inflation-alts-and-spirited-debate.788685/

 

[Garth]

Of course the support for the multiverse hypothesis gets worse as there is now a problem with the evidence supporting inflation.

The first prediction of the inflation hypothesis, which was the universe should be approximately flat, seems to have been borne out by the CMB, although other models may also give a flat universe, even the old and discarded Steady State Model.

The second piece of evidence was the prediction of B Mode polarisation in the CMB due to gravity waves from inflation and apparently found in the BICEP2 polarisation data, loudly proclaimed in March last year. However it had now been shown by Plank that what they actually found was dust - more than they had expected
Constraint on the primordial gravitational waves from the joint analysis of BICEP2 and Planck HFI 353 GHz dust polarization data

We make a joint analysis of BICEP2 and recently released Planck HFI 353 GHz dust polarization data, and find that there is no evidence for the primordial gravitational waves

I was at a lecture back in November by http://www-astro.physics.ox.ac.uk/~Dunkley/Home.html of Oxford University who is working on the problem. As I said in this thread Was the announcement that BICEP2 has detected Inflation Gravity Waves premature? She is now working on a balloon experiment to be launched in two years time to see if there is an Inflation Gravity Wave signal hidden behind the dust signal detected by BICEP2.
Planck intermediate results. XXX. The angular power spectrum of polarized dust emission at intermediate and high Galactic latitudes

Finally, we investigate the level of dust polarization in the BICEP2 experiment field. Extrapolation of the Planck 353GHz data to 150GHz gives a dust power ℓ(ℓ+1)C^BB_ℓ/(2π) of 1.32×10⁻²μK²CMB over the 40<ℓ<120 range; the statistical uncertainty is ±0.29 and there is an additional uncertainty (+0.28,-0.24) from the extrapolation, both in the same units. This is the same magnitude as reported by BICEP2 over this ℓ range, which highlights the need for assessment of the polarized dust signal even in the cleanest windows of the sky.

Garth