I Is the multiverse fake physics?

[kodama]

Peter Woit considers everything based on string theory to be fake physics.

Judging by a combination of empirical success and empirical predictiveness, I'd say holographic QCD is the best thing to come out of string theory, then conventional string phenomenology, with multiverse reasoning in third place. Holographic QCD seems to be on a par with many other approaches to approximating QCD. Conventional string phenomenology has great potential, but too many things still can't be calculated. And multiverse reasoning is like evolutionary psychology, it really can make predictions (if the Higgs mass had been 141 GeV, Hall and Nomura 2009 would be famous), but only at the price of numerous "what if" hypotheses about the structure of the string landscape and the implications of the anthropic principle.

since the paper
A Finely-Predicted Higgs Boson Mass from A Finely-Tuned Weak Scale
Lawrence J. Hall, Yasunori Nomura

is falsified by LHC finding 126 gev, does this mean hypothesis of string landscape and multiverse is also falsified?

so string theory multiverse is fake physics in the sense it makes a prediction that has been falsified by the LHC

 

[Orodruin]

At the end of the day there is more to science than simply testability. There are also aesthetic and logical criteria as well. For that reason when people test inflationary models, simpler models are typically analyzed first

Simpler models are tested first because they are simpler to test. Beauty is not a viable scientific criterion. We may hope that Nature is kind enough to provide us with something beautiful - but you are never going to pick a beautiful theory that makes false predictions over an uglier one that makes correct ones. If in doubt - U(1)xSU(2)xSU(3) is not particularly beautiful.

but obviously if people discovered evidence that favored those classes of models the simplest one would be preffered

This is Occam's razor, which is essentially saying you should not overcomplicate things. Not that you should go out on a wild goose chase for something you find beautiful but can never test.

Anyway, there are many very good physicists who take this material (in its multiple incarnations) seriously, so its surely not junk science.

I do not think you can make this inference. By doing so you are essentially saying goid physicists cannot have any interests but physics. Of course they can! And a rather common one is the philosophy behind physics. Do not get me wrong, there is a point in thinking about such things and using them to pique people's interest.

 

[mitchell porter]

so string theory multiverse is fake physics in the sense it makes a prediction that has been falsified by the LHC

"Fake physics" is not physics that makes a wrong prediction, it's physics that makes no prediction at all, and is therefore not science. Woit doesn't say string theory has been falsified, he says it has "failed" because it predicts everything and nothing - everything because it has googols of possible vacua, nothing because you can't get numerical predictions from any of them. That would be his critique of conventional string phenomenology, anyway - the part of string theory that tries to guess the exact recipe of branes and dimensions that will give us the real world. The anthropic stuff (he would say) is even worse, since it doesn't even try to do that, it's mostly about producing dubious anthropic justifications for things already known.

But one goes too far by denying the status of science to string phenomenology and string multiverse reasoning. There are string phenomenology models and string multiverse hypotheses that do make predictions. It's just that those models and hypotheses are not as deductively clean as one would wish.

I can illustrate what I mean with another theory that you like, asymptotic safety of quantum gravity. Asymptotic safety is not a theory in the way that general relativity or supergravity is a theory. You can write an equation for them. Asymptotic safety is a property of a theory - it says that the theory has an interacting fixed point in the ultraviolet. The way it's supposed to work, you would write down the equation for quantized general relativity, and then you would simply deduce whether or not it has that infrared fixed point.

The problem is that no-one is able to do that. It's taken something like twenty years of work, just to show that the truncation of quantized general relativity to the first few terms of an infinite series expansion, has the property of asymptotic safety. What Shaposhnikov and Wetterich did, was to say, let's assume that quantum gravity is asymptotically safe, and let's assume a few other things (no new physics between the electroweak scale and the quantum gravity scale, and some technical assumptions about the gravitational contributions to the running of the Higgs couplings). From that they did deduce the Higgs mass. But note, they assumed asymptotic safety, they didn't prove that it's actually a property of quantized general relativity. And in fact they left it open as to whether some other theory of gravity, like conformal gravity or unimodular gravity, should be used instead.

Similarly, extra assumptions which ideally it would not be necessary to assume, are a commonplace in stringy models or hypotheses that actually makes testable predictions. The main exception to this might be when there is a qualitative prediction of something very exotic, like cosmic strings or particles with weird fractional charges - where you don't need to calculate much, and it's just obvious that the model contains such objects. But no such objects have been seen in the real world. So string phenomenologists are left with the task of picking a class of models that looks roughly like reality, and then working hard to identify the most promising members of that class, and to increase their quantitative understanding of how these models work.

It would be simpler if some string cosmologist could write a wavefunction for the universe, get a unique ground state, and then calculate the predicted particle spectrum. But it's not that simple. There's an enormous landscape of possible string vacua, there's no agreement about cosmology, and calculations range from difficult to impossible. So everyone just works on what they can and on what they think is promising.

 

[Dr_Zinj]

For something to be "scientific" it has to be testable to either confirm, or deny its existence. Since AFAIK the multiverse hypothesis isn't testable at this time, it doesn't qualify as science.

 

[mfb]

There is no single "multiverse hypothesis". There are models that lead to multiple universes, like eternal inflation, that lead to testable predictions about the early universe, for example.
See the example of galaxies beyond the edge of observable universe: We cannot see them. But we are sure they are there, based on a deeper model that predicts their existence. A universe that suddenly ends everywhere just behind the edge of the observable universe would be really unnatural.

 

[TeethWhitener]

Right but I mean if that's the criteria you use, then stars and galaxies beyond the cosmic horizon are also unscientific as well.

Aren't they? We can't say anything meaningful about them. Our assumption that they exist is based on the Copernican principle, but that's no proof in itself.

At the end of the day there is more to science than simply testability.

There may be more to science than testability, but there's certainly not less. In other words, testability may not be sufficient (that itself is debatable) for science, but it's certainly necessary.

 

[JorisL]

Judging by a combination of empirical success and empirical predictiveness, I'd say holographic QCD is the best thing to come out of string theory,

If I'm not mistaken the empirical success has become less significant when reaching higher energies e.g. for the case of a quark-gluon plasma.

 

[astrobassist]

To call string theory and the multiverse "fake" physics degrades the meaning of the term fake. People like to claim that the idea of the multiverse is inherently untestable, but that just represents a lack of imagination, a lack of understanding of the current state of the field, and a lack of a sense of how fields change over time, sometimes yielding tests down the line.

The multiverse may well have observational, even falsifiable implications. For instance, Garriga, Vilenkin, and Zhang have recently derived a distribution of black hole masses that would confirm/disconfirm the existence of some common multiverse models based on astronomical observations.

People thought Einstein's attempts to unify forces to be "fake" physics at the time, but now unification has yielded new "real" physics with confirmed predictions etc.

Real physics is a balance of theory and experiment. This balance is dynamic over time, and hard to assess at any particular time.

 

[Chronos]

I consider logical paradoxes a red flag in any theory. Since paradoxes are not known to occur in nature, theories that predict them deserve serious prejudice. This has nothing to do with mathematical 'elegance' or 'beauty'. Fortunately, nature has no evident interest in conforming to such anthropic concepts. In ancient times, science was fixated on symmetry. Everything under the heavens consisted of four irreducible elements in various combinations - earth, fire, wind and water. We've come a long way since then, even though we still have not entirely shaken the symmetry malaise. My predilection is to lump things like multiverse and MWI into that primordial symmetry bin - an extension of our innate desire for a higher 'purpose' in the natural order of things that suits our personal preferences. In that universe truth is unbounded, it's just a question of selecting the proper stage to set your play. We are better served by understanding how things really work than any ideas, however lovely, of how we think they should work.

 

[David Neves]

Without the multiverse, how would you explain the following?

In the second and third generation of fermions, the quark with 2/3 charge is heavier than the quark with -1/3 charge. If that were also true in the first generation, which you would logically expect to be the case since that's the pattern, the up quark would be heavier than the down quark, so the proton (uud) would be heavier than the neutron (udd), so then the proton could decay into a neutron, and the proton would be unstable outside the nucleus, so in the early Universe, all protons would quickly decay, and there would be no atoms at all. The most likely explanation is that that indeed is what happens in the vast majority of universes that have a particle spectrum resembling the Standard Model, but those universes have no physicists. We are in a rare exceptional universe in which the pattern is broken, enabling us to be here.

How could else could you possibly explain this without the multiverse?

 

[nikkkom]

How could else could you possibly explain this without the multiverse?

Take eternal inflation model. It may be so that there may be no "multi"verses: every newly created bubble of real vacuum (a "new Universe") has the same physical laws - ones we observe. IOW: the true vacuum state may be unique. All "Universes" are similar.

 

[mfb]

How could else could you possibly explain this without the multiverse?

It could be random.
There could be some deeper reason for the particle masses that we don't know yet.

If all up-type quarks would be lighter than their corresponding down-type quarks, we would get a universe similar to our own as well. So why don't we reverse the question: Why is m(charm)>m(strange) and m(top)>m(bottom)? How can you possibly explain this?

Aren't they? We can't say anything meaningful about them. Our assumption that they exist is based on the Copernican principle, but that's no proof in itself.

Consider galaxies that are currently 20 billion light years away from us. We can observe how they formed billions of years ago. Do they still exist? We cannot see them as they are today and we will never be able to do so at any point in the future. But it would be ridiculous to assume that they don't exist. We know the initial state, we know the laws that lead to galaxy formation. Even though we cannot have direct evidence of their existence today, we conclude that they exist (probably).

 

[TeethWhitener]

@mfb My point was that (other than via the Copernican principle) there is no way for us to assert the existence of stars and galaxies beyond the cosmic horizon. But I had a couple of other questions about your post.

Consider galaxies that are currently 20 billion light years away from us. We can observe how they formed billions of years ago. Do they still exist?

You'll have to bear with me, since this is not my area of expertise. It's unclear what you mean by "still exist" since this implies some sort of simultaneity, and events happening "now" at your far away galaxy are spacelike separated from us.

we will never be able to do so at any point in the future.

If we can observe the galaxy as it was in the past, aren't we inside its future lightcone? Why would we be outside of it at some point in the future?

But it would be ridiculous to assume that they don't exist.

I don't know if it's that ridiculous. What if all the Population III stars have gone supernova by now? (I use "now" to mean that observers at our position in 20 billion years would not observe your far away galaxy).

 

[mfb]

If we can observe the galaxy as it was in the past, aren't we inside its future lightcone? Why would we be outside of it at some point in the future?

We are not in the future lightcone of the galaxy now. Where "now" means the galaxy 13.8 billion years after the big bang, measured in the frame of this galaxy.
We are in the future lightcone of the galaxy when it was younger.

Why: Accelerated expansion of the universe. The amount of matter still in causal contact to us (with the same definition of "now" as above) is decreasing. In other words, matter constantly leaves the volume of the universe we can observe in the future. The rate is something like a galaxy per day, give or take 2 orders of magnitude.
I don't think anyone expects those galaxies to suddenly disappear just because their distance to Earth gets larger than some value. But they (or, more precisely, recent events there) become unobservable.

 

[David Neves]

It could be random.
There could be some deeper reason for the particle masses that we don't know yet.

What? You just happened coincidentally to have the value they needed to have for us to be here?

There are also many other free parameters where if their value had been even slightly different then life would not be possible in the universe. If the fine structure constant had a different value, we wouldn't be here. If gravity had been stronger, life would not be possible. If gravity had been weaker, late scale structure would not have formed, and again, life would not be possible. Are you are claiming that all of that is just a huge stupendous coincidence, and we are all just stupendously lucky?

If all up-type quarks would be lighter than their corresponding down-type quarks, we would get a universe similar to our own as well. So why don't we reverse the question: Why is m(charm)>m(strange) and m(top)>m(bottom)? How can you possibly explain this?

Well I would conclude from the pattern of the second and third generation that the progressing masses are the "natural state" of the universe, which holds true in the vast majority of universes, and some random statistical fluctuation put our universe in a rare aberrant state that broke the pattern, enabling biological life to be possible.

Consider galaxies that are currently 20 billion light years away from us. We can observe how they formed billions of years ago. Do they still exist? We cannot see them as they are today and we will never be able to do so at any point in the future. But it would be ridiculous to assume that they don't exist. We know the initial state, we know the laws that lead to galaxy formation. Even though we cannot have direct evidence of their existence today, we conclude that they exist (probably).

Are you trying to argue in favor of the multiverse? If that's your point, then I agree. Just because we can't see the other universes, does not mean they don't exist. We can infer the existence of other universes, even if we can't directly see them, the same as we can infer the existence of other galaxies, even if we can't directly see them.

 

[mfb]

There are also many other free parameters where if their value had been even slightly different then life would not be possible in the universe.

Or life would look differently.
Is the desert fine-tuned for the cactus?

As an example, it has been argued that we could get a universe similar to our own with much simpler rules - you can have a universe completely without the weak interaction and with just 4 fermions (up, down, strange, electron) (reference).

We don't know how large and how frequent regions that allow life are in the parameter space.

Well I would conclude from the pattern of the second and third generation that the progressing masses are the "natural state" of the universe, which holds true in the vast majority of universes, and some random statistical fluctuation put our universe in a rare aberrant state that broke the pattern, enabling biological life to be possible.

We have 1 generation where up-quarks are lighter and 2 generations where up-quarks are heavier. Based on that, you claim that heavier up-quarks are the "natural state" and our first generation is the big outlier?
If I throw a coin 3 times and get 1 "heads" and 2 "tails", should I conclude that the coin usually gives "tails" and "heads" was a big outlier?

We can infer the existence of other universes

In some theories. I'm arguing that we should consider the existence of other universe if (a) we have a theory that performs well within our universe and (b) this theory necessarily generates other universes.

 

[PAllen]

But this is the other way around! You can do away with the aether in LET and just be left with SR because there is no need to assume the aether of LET. In the same way, there is no need to assume an eternal inflation to explain what is going on in the observable universe.

Of course you can try to extrapolate a theory, but doing so you must be aware of that this is what you are doing - just as we know that we are extrapolating GR to a domain that by definition of the theory itself is untestable when we try to describe the interior of a black hole. If the theory is true in that regime - then you can never know that it is.

On the latter point, sure you can. You just can't tell anyone about it. (There are even stable orbits inside the outer horizon of a Kerr BH, so your life need not be short) The multiverse is fundamentally less accessible than this.

 

[Orodruin]

On the latter point, sure you can. You just can't tell anyone about it. (There are even stable orbits inside the outer horizon of a Kerr BH, so your life need not be short) The multiverse is fundamentally less accessible than this.

Agreed, I made the implicit assumption that the experimenter was not suicidal...

 

[Victor Ray Rutledge]

I find all of this to be a tempest in a teacup. http://www.math.columbia.edu/~woit/wordpress/?p=5907 is a discussion of current articles, and fails to point in any defined direction. Look at this piece of rampant speculation, to see what I'm discussing. http://www.livescience.com/17796-science-fiction-imaginary-worlds-countdown.html If we can't agree on what is even possible, then how can we expect to research what is probable?

 

[Urs Schreiber]

Even without inflation, there is no specific reason to assume that the observable universe is but a tiny speck in something much larger.

If people had been careful to always say "observable universe" instead of just "universe", then "universe" would simply refer to all that exists, and there'd be no particular reason to assume that what meets our eyes (via telescopes) is but a tiny speck of all that exists. But somehow people had been careless and started to say "universe" (or worse "bubble universe") instead of just "observable universe" and so then a new word was needed for everything that might be beyond, and that word is now causing unnecessary confusion.

The assumption that "all that exists" is enormously more and larger than what meets the eye is at least as plausible as the opposite assumption, if not more so. This is not fake anything, that's just the obvious state of the matter, as was clear to people like Giordano Bruno way back. The ignorants burned him for saying the obvious.

Similarly, that one needs to beware not to search for patterns where there is randomness. Poor Kepler would have saved himself some trouble with trying to fit the orbits in the solar system to the Platonic solids had he had some sense of how non-unique our solar system is.

The assumption that some facets of nature are random has always been at least as plausible as the opposite assumption. In fact the opposite assumption is rather weird, if you think about it. Even Hegel left room for randomness in his attempted deduction of the ...verse from first principles.

It is absolutely possible that some aspects of fundamental physics are random, subject to some constraints, and this has always been so.

The real question is whether it's particularly fruitful to fill research articles with this obvious possibility. The problem is not that it's fake, but that it's mostly premature: besides stating the possibility, there is just not much to be deduced at the moment.

 

[mitchell porter]

Judging by a combination of empirical success and empirical predictiveness, I'd say holographic QCD is the best thing to come out of string theory,

If I'm not mistaken the empirical success has become less significant when reaching higher energies e.g. for the case of a quark-gluon plasma.

I meant the part of holographic QCD that models hadron masses and couplings, e.g. this recent paper claims success in modeling rho and omega meson decays, and makes glueball predictions. The work on QGP seems to me less grounded and more qualitative, more about learning to model holographically the complicated phase diagrams of QCD-like theories. btw there was a new twist on QGP holography released today.

In the second and third generation of fermions, the quark with 2/3 charge is heavier than the quark with -1/3 charge. If that were also true in the first generation, which you would logically expect to be the case since that's the pattern,

In some models, it's not what you expect. For example, suppose that the quark-Higgs yukawa interactions (that generate the quark masses once the Higgs field develops a nonzero energy density) are all the same size in some basis - this is called "democratic" and it has been a common hypothesis, inspired among other things by how the BCS model for superconductivity works. A democratic matrix has one very large eigenvalue and two very small eigenvalues, so this implies one heavy quark and two light quarks. Then you need to suppose that there is an extra, "radiative" contribution to the light quark masses, from heavy particles in virtual loops. According to this 1992 study (see the very end), in some models this is enough to explain why down is heavier than up - because of how the radiative corrections work out.

In evolution they talk about proximate and ultimate causes. The proximate cause of a plant growing towards the light might be enzymes (auxins and expansins). The ultimate cause if that if it doesn't, it will die. So natural selection produced an organism with a mechanism capable of implementing that imperative. The relation between a model like the democratic radiative theory of quark mass, and anthropic reasoning, might be the same.

 

[bob012345]

woit over at his blog not even wrong considers string theory based multiverse to be fake physics. he cites sean carroll as others on his blog as examples of fake physics.

is string theory based multiverse fake physics?

Can you state your definition of what constitutes fake physics vs. merely disputed or wrong physics?

 

[Dr. Courtney]

As you have guessed, I strongly disagree with this. If there are no testable differences, I see no scientific point in debating the issue. Just pick whichever interpretation you fancy (if you must) and nobody can disagree with you. To me this violates the very core of empirical science.

The absence of testable predictions renders any theory meaningless and unscientific. It becomes a kind of speculation that may be interesting to some scientists, but it is not science.

At the end of the day there is more to science than simply testability.

Testability may not be sufficient, but it is absolutely necessary.

Anyway, there are many very good physicists who take this material (in its multiple incarnations) seriously, so its surely not junk science.

How many times in the past would have addressing the demarcation problem regarding what is and is not junk science by an opinion poll of physicists led to an unreliable result?

If enough good physicists support creation science, does that make it OK?

 

[AlexCaledin]

Probably the only way to think clearly about physics is to think like an engineer :

1. Real things have their physical interface and interact according to the universal physical protocol;

2. The physical science is the search for the mathematics constituting that protocol;

3 Multiverse (as well as electron, molecule etc) is no more than a mathematical object found in that search.

 

[stevendaryl]

Here's what annoys me---people moralizing about what physics other people should be doing.

 

[stevendaryl]

Here's what annoys me---people moralizing about what physics other people should be doing.

I also think that arguing about what is and is not physics is itself not physics. It's philosophy. That isn't to say that it isn't worth doing (unless you're one of those who say that philosophy is a waste of time, since it isn't physics...)

 

[Dr. Courtney]

Here's what annoys me---people moralizing about what physics other people should be doing.

You are absolutely right. We should not be concerned at all unless we are helping pay for it - like through tax supported grants or other public funding mechanisms.

If the scientific community does not monitor and police when other members of the community are wasting public money, then who will?

 

[stevendaryl]

You are absolutely right. We should not be concerned at all unless we are helping pay for it - like through tax supported grants or other public funding mechanisms.

If the scientific community does not monitor and police when other members of the community are wasting public money, then who will?

Well, what counts as a "waste"? From some people's point of view, funding science is a waste unless practical applications result from it. The relationship between cutting-edge physics and engineering that applied that physics stayed tight for a long period of time, but in my opinion, at some point, possibly in the 60s, experimental and theoretical physics began probing extremes of physical conditions that were unlikely to ever occur in practical applications. I suppose it happened even earlier with General Relativity: weak-field approximations have practical applications (accurate GPS, for instance), but extremes such as the early universe and black holes and cosmology have pretty close to zero practical value. That isn't to say that there is no point in funding it, but it's not a matter of getting return on research investment dollars (I guess there is the beneficial side-effects, which is that studying fundamental physics can spur progress in the engineering, computing and mathematics).

Anyway, I don't think that practical applications should be the criterion for whether research funding is "wasted", but if not that, what? Personally, I think that research is valuable if it connects to other research, and is a dead-end if it has no impact outside itself.

 

[stevendaryl]

Anyway, I don't think that practical applications should be the criterion for whether research funding is "wasted", but if not that, what? Personally, I think that research is valuable if it connects to other research, and is a dead-end if it has no impact outside itself.

Just speaking personally, I have no idea how much taxpayer dollars Sean Carroll receives, but I consider every penny to be worth it. He's the only physicist that I read on an almost daily basis (because he writes so much and does videos and so forth). So this taxpayer is happy with what he does. I think that young people are a lot more likely to enter physics because they are inspired by Sean Carroll.

 

[Dr. Courtney]

Well, what counts as a "waste"?

If a scientist is spending taxpayers' money, then what counts as waste is a public policy issue that gets decided by the taxpayers based on open discourse (remember the first amendment?)

Here's what annoys me---people moralizing about what physics other people should be doing.

Are you really saying those who pay for the physics should not have a say in which programs are worthy or unworthy of funding? It's a free country. Do whatever physics you want, as long as you don't want me to help pay for it.

But if you are asking for public funding, you need to be prepared for an open and honest discussion where people like me share our opinions that untestable aspects of string theory and speculations about "multiverses" are not real physics and certainly not worth the amount of public funding they have enjoyed.

When colleagues and I have science we want to do but are not willing to jump through all the hoops waiting for funding, we fund it out of our own pockets, subsidizing it with funds earned from more profitable science ventures. We don't stomp our feet, accuse detractors or moralizing, and whine about the disasters if the taxpayer isn't willing to pay for it.

See:
https://www.physicsforums.com/insights/science-love-money/