Multiverse Mania makes the big time this week, with a cover story Welcome to the Multiverse by Brian Greene in Newsweek. While the title indicates that the Multiverse is here and part of our scientific world-view, the subtitle is a bit cagier: “The latest developments in cosmology point toward the possibility that our universe is merely one of billions.”
The article is pretty uniformly a promotional piece for multiverse mania, although buried fairly deep in the piece is something a bit more skeptical:
because the proposal is unquestionably tentative, we must approach it with healthy skepticism and invoke its explanatory framework judiciously.
Imagine that when the apple fell on Newton’s head, he wasn’t inspired to develop the law of gravity, but instead reasoned that some apples fall down, others fall up, and we observe the downward variety simply because the upward ones have long since departed for outer space. The example is facetious but the point serious: used indiscriminately, the multiverse can be a cop-out that diverts scientists from seeking deeper explanations. On the other hand, failure to consider the multiverse can place scientists on a Keplerian treadmill in which they furiously chase answers to unanswerable questions.
Which is all just to say that the multiverse falls squarely in the domain of high-risk science. There are numerous developments that could weaken the motivation for considering it, from scientists finally calculating the correct dark-energy value, or confirming a version of inflationary cosmology that only yields a single universe, or discovering that string theory no longer supports a cornucopia of possible universes. And so on.
I don’t see how we’re anywhere near finding such a version of inflation or getting rid of the string theory landscape, so the only hope of getting any evidence against the multiverse seems to be to calculate the cosmological constant. The multiverse thus looks to be pretty much impregnable and immune to any conceivable scientific challenge. A few years ago, pieces like this would hold out hope that the LHC would discover something encouraging for the multiverse, but now the LHC isn’t even mentioned. The only possible positive evidence suggested is seeing remnants of bubble collisions in the CMB, but the very likely eventuality of not seeing such a thing doesn’t count as evidence against the multiverse idea.
So, I fear Brian is right: Welcome to the Multiverse, physics is going to be stuck with it for a very long time…
On the other hand, failure to consider the multiverse can place scientists on a Keplerian treadmill in which they furiously chase answers to unanswerable questions.
Kepler to Vincenzo Bianchi, 17 February 1619: ‘Don’t sentence me completely to the treadmill of mathematical calculations,…leave me time for philosophical speculations, my sole delight”. (from “Music and Science in the Age of Galileo, by Victor Coelho).
The book then goes on to describe Kepler’s attempt to relate musical scales to the fastest and slowest speeds of planetary motions.
So that is the Keplerian treadmill! I fail to see how the multiverse rescues scientists from the Keplerian treadmill. The multiverse sounds to me more like the music of the spheres…
The only purpose of the multiverse seems again to sell books and make headlines. I never went to a conference where I saw a speaker talking seriously about it. It does not explain anything and is completely shielded from experiment. Brian Greene used to promote string theory, but with no advances, no chances of telling if the theory is write or wrong, and the cherry on top: no signs of SUSY, the multiverse is what is left. The only thing I am amazed is how long are these guys going to repeat the same story again and again and still find suckers that are “fascinated” with it.
According to Kleban and Schillo and Guth and Nomura, observation of positive spatial curvature at \Omega_k < -10^{-4} would falsify the eternally inflating multiverse.
Moreover, if we live inside a bubble, we would not in general expect to be exactly at the centre of the bubble, so there would be a cosmically preferred direction pointing towards the centre of the bubble. Thus searches of this type can also favor or disfavor the multiverse.
I wonder if in any of the other universes their scientists realize how ridiculous this whole multiverse thing is?
Chris,
Somehow, I suspect that if spatial curvature of that magnitude and sign is found, some version of eternal inflation can be found to deal with the problem.
As for whether searches of the type you point to can “favor or disfavor” the multiverse, I gather they’ve already been done, with negative results, so the multiverse is already disfavored, no?
I think Brian Greene has reached the apogee of bad science popularization. His recent TED talk with the gratuitous use of multimedia makes him look less like a scientist and more like the pastor of a mega-church pitching the most fashionable current faith-based doctrine with slick animation and rock-star gimmicks but little to no substance.
Aspirin,
To be fair to Brian, I don’t know about TED, but my experience at TEDx was that “gratuitous use of multimedia” was part of the whole concept of the thing, and strongly encouraged. Personally I don’t have anything against him or others using gimmicks, multimedia or otherwise, to get people’s attention, but I do think it would be better to stick to topics with more solid content.
There really is a difficult question about what can be explained according to a broad covering law (e.g. Kepler’s phenomenological laws of planetary orbits being derived from Newtonian gravitation) and what is “accidental” (or “environmental” or “path dependent”), such as the particular spacing of planetary orbits in the solar system. Up until very recently, we had no ability to observe other star systems and detect their planets, yet scientists were still convinced that the particular size distribution and spacing of the planets in our system was an accident of history. Hence Kepler’s attempt to derive these spacings using Platonic solids was perceived to be wrong-headed. (Although everyone hasn’t given up: http://arxiv.org/abs/0903.1732)
I haven’t seen anyone trumpeting observations of extra-solar planets as verifying this conviction–it’s long been taken as an article of faith or common sense rather than a point of controversy that the particular configuration of our solar system is a unique combination of historical circumstance. It isn’t clear why a similar type of judgment could not be applied to, say, the masses of the fundamental particles, similarly without needing justification by empirical observation of other universes.
Solar systems are taken to be individuals rather than what philosophers call “natural kinds.” In biology, there was a significant change when Michael Ghiselin argued that species are best thought of as individuals rather than natural kinds–his argument has made considerable headway there. A minimal multiverse “theory” would simply claim that some physical constants, based on internal logical and observational grounds, don’t look to be derivable from more-fundamental laws but are brute facts that “could have been different.” That’s not obviously crazy, although it may be massively premature.
srp,
The problem with current string/multiverse “theory”(i.e. we’re in some random “string vacuum”, no way to figure out how we got there) is that it’s not a theory at all, just an excuse. In particular, it doesn’t tell you which things “could have been different” and which “couldn’t have been different”.
Peter:
I could really use clarification on what you believe is the methodological difference between a) the string theory “excuse” for not having a unique solution to our universe and b) the conviction that you can’t explain the solar system’s configuration without reference to historical accidents. I suspect I am not alone in this lack of clear understanding, at least among your lay readers.
It may well be premature surrender to say that, for example, we can’t derive the relative masses of the various particles from general principles just because string theory looks like it can’t do it. There might well be alternatives that could do the job. But someone who doesn’t care about string theory at all might still agree with the intuition that particle masses, say, are “arbitrary” parameters, and that people working on trying to derive them from higher symmetry principles are as misguided as Kepler was in trying to fit planetary distances to the Platonic solids.
Not sure if I’m missing your point or just communicating my point badly.
As an outsider looking in, I’m simply astounded that something as unscientific as this, is being taken seriously. If we had even a shred of evidence to think this way, that would be one thing, but as far as I can tell we don’t.
I hope the data from the LHC will return physics to a more reality-based science, because it’s going to be hard to fund something like that again, if the public thinks the money is going to nonsense.
srp: Dont know about Peter, but for us two accept the “anthropic” explanation for solar system dynamics two things had to happen:
a) A clear understanding of the theory of gravity. In particular, that it really has a continuum of solutions and no fundamental way of choosing between them
b) An quantitative experimental validation of the theory of gravity, both for problems independent of the planetary one and for the “phenomenology” of planets (deriving Kepler’s laws and such).
Once (a) and (b) were satisfied, we could confortably accept an anthropic explanation for planetary motion, and this explanation became fully scientific.
Any chance of anything remotely comparable happening with the multiverse, both w.r.t. (a) and (b)?
srp,
It’s possible some of particle masses, mixing angles, coupling constants, theta-angles, gauge groups, gauge group representations are “environmental”, but to have evidence for this you need (as lun points out in the analogy) a well-defined theory which comes with a testable explanation of which ones are “environmental” and which ones aren’t. String theory doesn’t have that, it basically is being used to “explain” that everything we don’t understand can’t be understood, and this “explanation” can’t be tested.
To make the Keplerian analogy, it’s as if Kepler was being told there was no point to investigating planetary motion at all, since whatever laws governed it were “enviromental”, and different everywhere. No point in trying to relate Jupiter’s behavior to Saturn’s since they were operating under mysteriously different physical principles, due to the unknown different ways they came into being.
The problem with the string theory multiverse is circularity, string theory predicts the multiverse and the multiverse predicts that string theory can’t predict anything you can test. What’s being put together here is not a scientific theory, but a bunch of excuses for failure, carefully constructed to be untestable and immune to challenge.
lun:
Thanks for your response. Here’s my problem:
Could we not say the SM gives us a good understanding of all the observable interactions and so all the remaining parameters are plausibly environmental? My point is not that I believe this (I’m not qualified to have much of an opinion, for one thing), but that these things are judgment calls. In the solar system case, there are people playing around with the Bode-Titius law for example, but most people seem not to take this very seriously. Is the community giving up too quickly? Or are the enthusiasts on a wild goose chase?
Peter,
I totally get your complaint about using the concept of a string theory multiverse to “explain” the purportedly environmental nature of all the stuff that’s still not derivable from more basic principles. It smacks of special pleading. But my question is more basic and would hold even if there were no string/multiverse idea to swat at:
Kepler practically killed himself teasing out his three kinematic laws from Brahe’s data, but it worked. He also tried very hard to deduce mathematical principles for the spacing of the orbits, which most people now think was a wild goose chase. What was the a priori difference? If you could go back in time, could you advise Kepler, based on principles of theoretical methodology (NOT on the basis of knowing by hindsight how the science later developed), which of these two endeavors would be fruitful? And if so, is the argument you would make to Kepler also applicable to today’s high-energy particle theorists?
My guess is that that kind of question cannot be systematically answered. In the end, judgment or guessing is required and there is not way to be sure about who is right. But perhaps I’m missing some canon of method that can distinguish these cases.
srp,
I don’t think there’s any way to know in advance what will be fruitful things to look at because they have a simple, fundamental explanation, and which things will turn out to have a complicated, possibly “environmental” explanation. We have no idea what sort of explanation is needed to understand what determines particle masses. But whatever explanation one suggests, one has to come up with some way to test it, some way to show it’s not just something one cooked up to make the problem go away.
First: I recall hearing a math lecture where the speaker gave a very convincing dynamical argument for the spacing of asteroid belts; sorry I don’t have the reference, but basically if the rocks are in the wrong place resonances cause them to eventually be ejected from the solar system. So
sometimes weird numerical “coincidences” do have an explanation.
Second: If I understand part of srp’s point, it is that just because there is a valid stochastic model for something (for instance evolution of the species) it doesn’t mean that worlds actually exist where all the other paths were taken. On the face of it, that is ridiculous. Nevertheless, there is a stupid anthropomorphic argument that
I am here because I happen to be here. The only reason I am writing these lines is because my parents’ DNA happened to have met up in just that way. Similarly,
any small change way back when and the humans might have been wiped out, leaving only Neanderthals left to attempt to have this discussion. But so what?
We are lucky to be here. That could increase our sense of marvel. But the universe could care less, and will wipe us out in the near or distant future anyway. What makes us think we are so important? Only the fact that we are we, the ants don’t care either, unless we leave crumbs for them to eat.
But this evolution conversation happens within a given, fixed system (ours) and what seems ridiculous on the face of it is to postulate that: (1) changing the basic laws or constants can be treated in the same way; (2) we can then jump to saying that all sample paths actually “occur”.
Even an “anthropic” origin of the solar system should be able to explain some facts: why do all the planets orbit the sun in the same direction, and roughly in the same plane?
Similarly, there are some facts about the Standard Model that any good “anthropic” theory should explain: why are there several different generations of particles, that are identical except for their masses? If we had a truly random theory of physics, it seems very unlikely that the fermions would be organized into three generations the way they are. How does the multiverse theory explain that?
I really wish you would stay away from these depressing topics and stick to things that are interesting. Write something about K-theory. You should change the direction of this blog away from the war you’ve already won, and just ignore these idiotic articles. Even lay people I talk to now with interest in science have realized that all this nonsense is passe’.
-drl
I have to concur with DRL – in the sinking Titanic of theoretical physics, the Multiversers are the third-class passengers.
<aside>I notice that your book has appeared in Czech but not, for example, German or Spanish. Indirectly, you probably have Lubos to thank for that. I hope that you are sharing some of the royalties.</aside>
There’s what, 19 parameters in the Standard Model? What’s wrong with that number, and why would 5 be better than 19 and 1 better than 5? In the absence of any other compelling motivation, this seems to come down to some sort of numerological argument. Is this really the present case, or am I being unfair?
Same thing with the actual values of those parameters – given that they exist, why are people so uncomfortable with those particular values? After all, they have to be some particular number; indeed, given the range of numbers available, one could just as well express bemusement at how close they are to each other – within a factor of 10^50!
Finally, is there some sort of test or principle that would tell you where the regression stops? E8 has been a contender for the algebraic structure that ties everything together. Assume for the sake of argument that this is true and a complete theory of everything emerges which gives predictions in accord with reality down to the limits of testability. Wouldn’t you then have to ask why E8 and not, say F4 or G2? Or would you be able to supply compelling reasons for why these sorts of questions need not be pursued any further?
why do all the planets orbit the sun in the same direction, and roughly in the same plane?
Ignoring all the complexities of the models dealing with solar system formation, this can basically be explained via the angular momentum conservation. Think like this: the whole solar system started out as a big lump of gas, which gradually collapsed under its own weight to become coarser and eventually create the Sun and the planets. The initial lump had some nonzero total angular momentum, and since it is a conserved quantity, the solar system as we know it today still has it. This angular momentum determines both the plane and the direction of the rotation of planets.
In fact, it would be very weird if one of the planets were rotating in the opposite direction or in a different plane. I’m not even sure that this could be a stable configuration in the long term, given the attractive gravitational force among the planets themselves.
HTH, 🙂
There’s what, 19 parameters in the Standard Model? What’s wrong with that number, and why would 5 be better than 19 and 1 better than 5? In the absence of any other compelling motivation, this seems to come down to some sort of numerological argument. Is this really the present case, or am I being unfair?
Having 19 or so parameters is considered too complicated. By your argument, one could have stopped at the periodic table of elements and be content that there are cca 110 (or so) “elementary atoms”, without ever asking if they have any structure or not. Today, we have cca 100 “elementary particles” which can be arranged into a similar “periodic table”, so it stands to reason to ask about some deeper explanation for that as well.
The number of experimental parameters in a given physical theory is just a measure of our theoretical ignorance about the physics in question. The less experimental parameters, the better the theory, and thus the greater the understanding.
The multiverse idea is a premise that denies us the ability to ask this sort of question. And furthermore, that premise is even untestable. By some definitions, such a framework can be called a religion, rather than science.
The anthropic explanation of the Michelson-Morley experiment: a non-zero ether wind is incompatible with human life.
Having 19 or so parameters is considered too complicated. By your argument, one could have stopped at the periodic table of elements and be content that there are cca 110 (or so) “elementary atoms”, without ever asking if they have any structure or not.
By my argument? Well, no, I’m perfectly happy with having 19 parameters if that’s what it takes to have the explanatory power of the Standard Model. Less than 19 doesn’t give enough freedom to satisfactorily explain observable phenomena and more than 19 is unnecessary.
Contrariwise, the motivation for finding a deeper structure to atoms wasn’t because there were “too many” of them; it was because the theory of indivisible atoms did not accord with observable reality (iirc, J. J. Thomson’s discovery of the electron.)
By all means, speculate on why there are three spacial dimensions instead of four or four hundred, or why we live in a world based on the L2-norm instead of the L1-norm. But istm that if your only reason for doing so is that three and two are unsatisfactory numbers then your motivation seems to be more numerology than science.
ScentofViolets,
Actually, 19 is just the number if all neutrinos were massless, so you need a few more for neutrino masses and mixing angles.
One can happily decide to just accept the SM as is, and have no interest in attempts to improve it. But, it’s a structure that sure looks like something we don’t completely understand, so (some) people are motivated to try and do better. Such a better understanding may lead to the possibility of computing some of these parameters, or just to knowing why one can’t.
The multiverse idea is a premise that denies us the ability to ask this sort of question. And furthermore, that premise is even untestable. By some definitions, such a framework can be called a religion, rather than science.
In that case, why stop at the multiverse? Why not extend the scope to include a class of universes whose basic structure is an infinite-dimensional Hilbert space, for example? One could even populate it with hypothetical beings who use anthropic arguments to reason that of course since life needs an infinite number of dimensions to exist, that must be why the universe is observed to have an infinite number of dimensions.
Iow, the Landscape idea seems to be little more Tegmark’s notion that all mathematical structures are realized “somewhere” and throwing in a few restrictions to make it less ridiculous as a scientific theory.
Funny to mention Brian Greene. As a layperson I read his “The Fabric of the Cosmos” and I still remember vividly how my feelings about the book changed at the break between part 3 and 4:
Part 1: Reality’s Arena
Part 2: Time and Experience
Part 3: Spacetime and Cosmology
========= break =======
Part 4: Origins and Unification
Part 5: Reality and Imagination
Before the break it was an inspiring description of exciting (thought and real) experiments and weird surprising outcomes. It taught me a lot about modern physics.
After the break the whole atmosphere changed and somehow I found the whole thing depressing.
Much later I realized that it was the lack of “feet on the ground” in parts 4 and 5 that made this part of the book so unappealing.
Actually, 19 is just the number if all neutrinos were massless, so you need a few more for neutrino masses and mixing angles.
One can happily decide to just accept the SM as is, and have no interest in attempts to improve it.
But isn’t this just how science proceeds? Up to the point where neutrinos were found to have mass, 19 was enough. It is the updating of the facts that changes the number from 19 to whatever, not that 19 is an unsatisfactory number, therefore there must be something like a nonzero mass for the neutrino. imho.
But now I’m repeating myself.
I share Peter’s worry about the strength of the Multiverse attractiveness. Feynman noted in the The Character of Physical Laws “you cannot prove a vague theory wrong”. He preferred imagination “in a terrible strait-jacket” to derive new laws.
But in the final section of the book he goes very bleak: “some of my colleagues say that this fundamental aspect of our science will go on: but I think there will certainly not be perpetual novelty for a thousand years. This thing cannot keep going on so that we are always going to discover more and more new laws.”
Ultimately he foresaw ” the philosophers who are always on the outside making stupid remarks will be able to close in”
If we run out of testable new laws the stupid remarks may win.
Very precise carbon energy levels may suggest billions of other universes, or sheer luck in the only one that exists that creates self-aware neurons.
But I think Peter’s blog continues to raise a key point – fundamental physics has entered a strange phase of dual impenetrability – String Theory’s increasing esoteric nonsense, and the Multiverse’s low science but 1960s-sci-fi appeal.
The latter will be ascendant for a while. Feynman’s outlook doesn’t give too much optimism it will be usurped soon. New testable laws required.
This is not a joke. It is a disaster.
And its NOT about discrediting science.with the public. Horrid as that is.
Its about science destroying itself.
With nothing to show for 40 years, the big names like Greene have just left physics behind. So when the top guys spout fantasy, and the mainstream press promotes it, how do you stop this train wreck. Who has the prestige to stop them before they ruin the whole scientific endeavor?
No, not nothing to show for 40 years – I disagree – we have a whole set of approaches that had to be tried in order to be ruled out, there was no a priori way of knowing that these ideas would not work (I’m assuming of course that the current trend of these ideas not working continues.) It is on the shoulders of the unsung giants who cleared away all the unworkable underbrush that the future Newton might stand.
Please accept my applogy.
I didn’t mean to imply that physicists have not been working or learning for 40 years.
But it is my understanding that that the results of their work is negative. In other words they have shown what wont work rather than what does. If I’m wrong on this I’d be grateful to be told.
I have the highest respect for science. CP Snow said that science must be ruthless in surpressing those who state a aflsehood, even innocently. Otherwise the public has no rational basis to trust what it cant understand. This multiverse fantasy stikes me as far worse than what Snow feared. And it appears there is no will, either among individuals or institutions, to condemn those who advance it.
If so, this wont have a happy ending
srp,
The specific masses of the planets in the solar can’t be predicted from theory, but you can predict probability distributions for these planets, derive them from reasonable rigorous theories (eventually), and compare these to planetary distributions in other star systems, and even to unbound planets in free space.
For example, note that the Jupiter mass is a characteristic mass for masses of the largest planets around stars with planets… the largest planet is typically 0.5-2.0 jupiter masses. Thus, while the exact value can’t be derived from any specific model, good models of the probability distribution can be derived from gas and accretion physics, and are testable with real-world observations.
The less inherent quality a product has, the more important the advertising campaign. I think theoretical physics tolerates the Brian Greene’s of the world to help perpetuate funding in times when the cupboard is plainly bare.
Tammie, the standard model – the 40-year-old theory which explains almost everything we know about – has a lot of properties which in turn demand to be explained. Physicists have accumulated numerous ideas about how to explain them – e.g. grand unification to explain the patterns of fermions, and weak-scale supersymmetry to explain the “hierarchy problem”. Model-building in physics draws on these ideas but isn’t defined by them. It’s the difference between saying “Let’s have a simple symmetry group that incorporates all the separate symmetries” and “Let’s use SO(10) symmetry with the following superfields in the specified representations”. The true advance beyond the standard model will come when someone hits upon exactly the right combination – or when the LHC or some other experiment forces decisive new data upon us. Until then it’s trial and error, and we *are* learning, both by the accumulation of ideas and by the accumulation of models that are still consistent with the data, as well as by the falsification of those models which do become incompatible with experiment. Anthropic multiverse reasoning is a *very* small part of what goes on. Try the PDF at http://arxiv.org/abs/hep-ph/0207124 for a glimpse of what has actually been happening. It’s a technical account, but hopefully you will at least see that it still looks like science.
I’m perfectly happy with having 19 parameters if that’s what it takes to have the explanatory power of the Standard Model. Less than 19 doesn’t give enough freedom to satisfactorily explain observable phenomena and more than 19 is unnecessary.
How can you be sure that 19 is the minimal number of parameters that one needs in order to build the Standard Model? Maybe the same SM can be worked out as an effective model of some other theory containing only 2 or 3 parameters. In that case, 19 would be totally unnecessary. And in addition, this theory would provide us with deeper understanding of the mathematical structure of particles and interactions we observe in experiments. If all coupling constants and particle masses could be calculated out of some first principles and a couple of experimental parameters, it would be a massive gain in terms of “describe more by using less”.
That is the idea behind the program of unification of interactions. Of course, you are welcome to be content with the SM as it is today and its 19 parameters, and free to not look for a more profound theory. But claiming that people who do look for it are numerologists is a bit too much. Seeking out a more powerful model with less parameters is IMO a perfectly valid scientific question.
The fact that so far we have no experiments to force us into looking for a stronger theory is no excuse to claim that there isn’t one. Maybe the experimental data is just inaccessible for our current technological level. Imagine that Thompson did not find the electron (for example, if all subatomic particles were in principle harder to find experimentally). Would you be content with the periodic table of atoms as basic structures in Nature, given no experimental evidence to the contrary? The very fact that the periodic table is actually periodic is a hint that there is some simpler underlying structure. People who are (and were) looking for this strucure are certainly not numerologists.
Patterns do not emerge randomly. If your experimental data shows a pattern, it is quite reasonable and scientific to look for a rule that explains the pattern.
HTH, 🙂
I love Chris Oakley’s view, “in the sinking Titanic of theoretical physics, the Multiversers are the third-class passengers.” Very timely.
vmarko says: “The multiverse idea is a premise that denies us the ability to ask this sort of question. And furthermore, that premise is even untestable. By some definitions, such a framework can be called a religion, rather than science.” Hebrews 11:1 says: “Now faith is being sure of what we hope for and certain of what we do not see.” (NIV) Multiverse theory falls pretty neatly into that categorisation.
vmarko wrote: The fact that so far we have no experiments to force us into looking for a stronger theory is no excuse to claim that there isn’t one. Maybe the experimental data is just inaccessible for our current technological level.
Lets take this argument to its logical conclusion. Just like any pattern that we see in the Standard Model requires an explanation by a deeper theory, it is “obvious” that any event requires the will of an intelligent agent (or agents) as a cause. The Big Bang is an event, so lets call the agents that caused it, say, Magical Pixies. Of course, having no experimental evidence that forces us to posit the existence of these Pixies is no excuse for not doing so. After all, their existence explains so much and the needed evidence could be just around the corner, say when the LHC pumps up its energy!
Both these arguments rest on a faulty premise. In one case that is more obvious than in the other.
Would you be content with the periodic table of atoms as basic structures in Nature, given no experimental evidence to the contrary?
Contentment can be learned, while the universe is the way it is whether wer are content or not. It’s also worth remembering that identifying and documenting patterns in physical phenomena is useful in itself. This activity is not required to be a stepping stone to any more fundamental theory. Consider for instance the number of ways the periodic table has been rearranged. Each rearrangement, arguably useful for whatever is the intended practical purpose, is attempted despite that fact that we already know the underlying fundamental theory of electron shells.
Mitchell Porter,
The Witten article that you quote does an excellent job of explaining the case for SUSY/GUTs/strings. However, note that it is ten years old, and mostly about ideas that were nearly 20 years old when it was written, which haven’t received experimental confirmation. Quite the opposite actually, there’s:
“Supersymmetric particles should be in reach of the LHC – and maybe of Fermilab – since the supersymmetric approach to the hierarchy problem does not make sense if they are too heavy.”
The SUSY/GUTs/strings paradigm has so far been a failure, and it is this failure that has led to multiverse mania on the cover of Newsweek. Trying to claim this situation is not a problem for the field is not a good idea it seems to me…
Well judging by the title of his public lecture in Strings 2012 apparently Witten still believes in the Universe.
http://wwwth.mpp.mpg.de/members/strings/strings2012/strings_files/public/public.html
My feeling though is that again he will wash his hands like another Pontius Pilate.
But anyway let’s wait to hear what the big man has to say about this Multiverse controversy…
Thanks Giotis,
Very interesting, of course I’m curious what he’ll have to say. Funny that the title, which a few years ago would have seemed unremarkable, now sounds kind of polemical…
Beelzebud,
I agree that the hype is pointless outside selling books, and, were I a physicist, the multiverse would be right at the bottom of my list of research topics. But do you really think that the multiverse is unscientific? There’s nothing inherently unscientific about raising a hypothesis. It only goes beyond science when someone makes claims about the truth or falsity of the hypothesis in the absence of evidence, and I don’t think Greene has done that here.
More to the point is what difference does it make whether there is a multiverse? String theory’s central problem is finding at least one string vacuum that reproduces relativity and the standard model in the low energy limit, not explaining why it can’t find one. Would knowing that there is a multiverse bring us any closer to finding a useful string theoretic model?
I wonder if Greene has milked the last drop out of his writings. I wonder about what he could possibly write again that would have the same PR potential as his existing books. I have a post on my blog lamenting the sad state of the popular physics literature partly brought about by writers like Greene.
David Nataf:
Thanks for the update on solar system modeling and theory. It makes sense that not just anything can happen when a star system forms, or at least that certain things are not very probable.
But note that the sole empirical test of these theories comes from extrasolar planetary observations. My point was that long before these observations were available, many hypothetical “laws” of the solar system were considered to be mere accidental patterns found in contingent events. The non-lawful nature of the solar planets themselves, with their weird, wonderful, and largely unpredicted features lends extra force to the notion that much of what we observe came from historical “accidents.”
But maybe we are giving up too soon, and it will turn out that there is a class of star systems with inner, rocky planets, a couple of gas giants around Jupiter scale, and then some smaller gas giants, some of which have peculiar inclinations of their rotational axes relative to the ecliptic. We will learn this from empirical data if it is true, though, not from first principles of mathematical symmetry.
Peter, I agree with Danny and Chris. No one is paying attention to multiverse.
Maybe you could talk about conformal universe conference at PI
http://www.pirsa.org/C12027
which had talks by thooft
Shantanu,
Glad to hear that no one is paying attention. The conformal universe conference talks look interesting. A good reason for me not to talk about them though is that I know hardly anything about that subject…
Thanks for the heads-up, I almost missed the fact that Strings 2012 takes place in Munich, Germany (it is not widely advertised, for reasons unkown, at least not in Munich itself 🙂 Although I’m sure that Peter intends to cover it, right?
I will see to it that I make it to that public lecture.
Which is all just to say that the multiverse falls squarely in the domain of high-risk science.
High-risk science: is it the politicaly correct way of saying “pseudo-science”?
I thank Dr Porter and Dr Woit for their responses.
Regarding Dr Porter’s recommendation , I agree that I should read that article by Dr Witten. At best however, it would be a huge amount of work to understand it. For that reason I’m secretly hoping that string theory falls, letting me off the hook.
I especially thank Dr Jogalekar for reminding me that most of physics is a quiet and serious endeavor. Its a fact that people care most about advancing their religion (or their lack of it). So things like string theory and the multiverse will always, and justifiably, grab the most attention. By contrast, chaos, turbulence, superconductors, and adaptive systems don’t say much about our existence, but as sciences they are truly beautifu, and are making great progress.
Finally, I find the phrase “high-risk science” to be disgustingly false. Dr Green would do well to disown it. Whatever one can say about string theory, tenured professors working away in their specialty is not “high risk”. What would be high risk would be trying something new. Take the military. It needs diligent people of many talents. But it is ridiculous when a procurement officer poses as a war hero.
Please note, this has nothing to do with the merits of Dr Greene’s string theory, and whether he is right in persuing his specialty instead of abandoning it. But he should spare us the silliness.
Multiverse ‘studies’ may indeed have hit the big time, as Peter suggests, in popular culture terms. But the thing to watch for is just how much of an impact they (will) have in academic physics, and I think the right metric here is not how many news releases or conference presentations by Susskind, Greene et al. we see over the next few years, but how many doctoral dissertations are written and defended, in major departments, which take the multiverse as the central topic, or even a crucial component. Speculation is free, but if I were betting I’d put (a LOT of) my money on that number being on the rather low side…