The latest issue of Scientific American is devoted to articles about Einstein and his legacy. One article in the magazine doesn’t really have much to do with Einstein and I believe would make him gag if he were still around. The article, entitled “The String Theory Landscape” is by Raphael Bousso and Joe Polchinski. In it they claim credit for the pseudo-scientific idea of “explaining” the value of the cosmological constant by the existence of the “landscape” and the anthropic principle. It’s sad to see this nonsense being purveyed by the most respected and well-known popular science publication in the US.
For something more sensible about the anthropic principle, see a recent column from Nature.
Not at all. It’s precisely the opposite IMO – they’ve been so poisoned by Bourbakian formalism that they’ve lost their esthetic judgment and are willing to “settle for less”.
My own “feeling” about this is – why should we expect our little efforts to somehow be vastly different from past efforts? That is, whatever works will almost certainly fit nicely into the existing pattern of development, going right back to Air Earth Fire and Water.
To be more precise – a good theory needs a unique context. Every theory to date has provided its own unique context. This even goes for phenomenological theories that work (e.g. BCS – Cooper pairs – WGS – Higgs mechanism etc.)
The thing that gives GR a unique context is background independence.
Well, OK, but then what is it that you are looking for? Interesting mathematics or physics? It seems that fundamental physics has reached its present impasse exactly because people have been – to use Newton’s image – too busy picking up and examining pretty mathematical seashells rather than trying to build a fully consistent understanding of the physical world.
I would not consider it to be gravity, period. There is already a formulation like this for classical GR, which also is not gravity.
Change of space element as in the Pluecker line geoemtry – say, building spacetime and matter from twistors anf getting some sort of quantification from that – might barely make it under the wire.
-drl
If someone came up with a QG model where gravity was just another field on a Minkowski background, which was such that the classical limit gave one Newtonian gravity with light bending, etc. would people just dismiss it as too boring? I ask this question seriously. The main approaches to QG at the moment (Loops and Strings – NB: in alphabetical rather than slice-of-science-budget order) were inspired by, rather than derived from known physics, and in neither case has it been demonstrated that GR emerges as a classical limit. And with regard to Danny’s requirement of background independence, given that SR is one of best verified theories yet, is this requirement not more to do with a feeling of mathematical “rightness” rather than any physics?
In short – anything that claims to extend or sharpen GR will certainly be background-free – that is the unique context that GR introduces. (Every real theory introduces a new physical context.)
-drl
Danny,
What would be the dire consequences of a quantum gravity NOT being background free?
I never quite understood the arguments in favor of background independence in quantum gravity. On the surface they so far seem like hand waving arguments, which extrapolate classical general relativity notions and impose them by “decree” in the quantum regime.
The essential thing about gravity, quantum or not, is background-freeness. Clearly you’re never going anywhere without that as the central idea. That’s what makes GR what it is. All this obessive “quantum gravity” kvetsching is just misguided. That will probably take care of itself in it the long run, and probably fix field theory as a side effect. The absolutely key thing is background-free field theory.
Of course, this is a danger for all research in quantum gravity. I find myself thinking that we need a radically simpler and deeper insight into the problem very soon, or we need to let the field lie fallow for a while. Perhaps a shock will come from outside that brings this about.
When all contrieved ideas have failed, maybe people will have to turn to the obvious ones. Like the quantum representation theory of the diffeomorphism group might be useful for understanding diff-invariant quantum theories.
There is of course no guarantee that this is the right thing to do. But it seems to me that good new ideas are in short supply indeed. When the old ideas have failed to describe the physics of our universe (and why else do string theory leaders focus on other universes?), what’s the alternative?
Back to the Landscape — I just came across this remark supposedly made by Bill Clinton in another context:
“When ideologues find themselves in a hole, they dig harder.”
The manifestation of this in string theory is that its adherents seem to be convincing themselves that they making headway with every interesting new mathematical result, and the mathematical territory they have opened up seems to offer an unlimited supply of them, enough of which offer hints of real physics to continue reinforcing the ideology.
Of course, this is a danger for all research in quantum gravity. I find myself thinking that we need a radically simpler and deeper insight into the problem very soon, or we need to let the field lie fallow for a while. Perhaps a shock will come from outside that brings this about.
Matt:
QED is obviously part of a bigger theory, and, who knows, maybe it is a limiting case of some as-yet-undiscovered Planck-scale dynamics. In the absence of any observational data about quantum gravity, the imagination can run free. AFAIC people can construct whatever theories they like about QG, provided that they have the right classical limit and do not contradict QM. My personal preference is toward simpler rather than more complicated ones, but that is just me.
One must, however, make a distinction between approximation and inconsistency. Non-relativistic mechanics works fine when motion is not relativistic. Classical electrodynamics works well when the number of photons is large. Naïve QED, OTOH fails at all energy scales, and can only be rescued by mathematics that would get you an “F” if you were to do it in an exam.
Steve:
Would you agree that the natural ultraviolet regulator in QFT is provided by spacetime foam with a lower bound l_{b} acting as a natural cutoff ?
Under no circumstances! A posteriori tampering with a theory that has failed to give the correct, or even a finite answer can never be acceptable.
All the problems in field theory and qft (and yes string theory) no doubt arise from having a static deterministic classical background manifold which is an ok approximation at large scales/low energies. Thus the bag of mathematical tricks needed to make qft theory work.
You are asking me to abandon Minkowski space just because an approach to QFT that I would not have expected to work, does not work. I refuse to do it.
Chris et al.
Would you agree that the natural ultraviolet regulator in QFT is provided by spacetime foam with a lower bound l_{b} acting as a natural cutoff ?(Where this would be the Planck scale typically). This is not a new idea and was considered decades ago by Salam I believe. Not much subsequent work on the idea really (an old paper by Smolin, and some others, and a paper by L H Ford).
One might try and formulate QFT or classical field theory on a fluctuating/stochastic classical geometry rather than a smooth deterministic manifold. Hard vertices in Feynman diagrams should then get smeared out. Of course this was one of the motivations behind perturbative string theory but the idea can exist outside of string theory when one tries to accomodate the presumabley discrete or foamy micro-structure of spacetime. Delta function singularities associated with propagators in qft should be regulated in a natural way.
As for classical electrodynamics and the problem of point charges, the introduction of a lower bound l_{b} in spacetime or 3-geometry corrects it quite easily. Delta functions simply get smeared out into very narrow highly peaked Gaussians of width l_{b}. If G(x-y) is a simple Green’s function for an electrostatic potential \phi(x)where
nabla^{2}G(x-y)=-delta^{3}(x-y)
then this simply becomes a nonlocal Laplace field equation, smearing out the delta fn. into a very narrow Gaussian of width l_{b}:
nabla^{2}G(x-y)=-Aexp(-(x-y)^{2}/l_{b}^{2})
A point charge then gets smeared out into a ring or a “string”. The corresponding classical self energy is also finite and becomes infinite only as l_{b}–>0. There is an old paper by a guy called Namsrai that considers this and the subsequent theory of QED that follows (might be in the archive as a scanned pre-latex entry). Such nonlocal electrostatic equations are used for real in computational chemistry in order to accomodate the finite size of ions, large charged molecules or charged polymers in solutions, which can be modelled as charged strings.
All the problems in field theory and qft (and yes string theory) no doubt arise from having a static deterministic classical background manifold which is an ok approximation at large scales/low energies. Thus the bag of mathematical tricks needed to make qft theory work.
Chris —
If you’ll accept that classical electrodynamics need only be a limiting case of QED (one might even say, suggestively, an effective theory), why do you think that QED needs to be “fixed” rather than only exist as a limiting case of some fundamental theory of quantum gravity?
Matt
… fixing QEM means first fixing CEM
What you are saying is pretty much the received wisdom on the matter, and I do not agree with it. Classical Electrodynamics only needs to exist as a limiting case of Quantum Electrodynamics. In any case, Classical Electrodynamics only breaks down in situations where QED would be expected to take over, i.e. point charges. Fix QED and you automatically fix CED.
Chris –
Dirac was none too happy with classical EM, which is also horribly broken. He tried on three different occasions spanning 50 years to fix it.
As Einstein said, “the electron is a stranger in electrodynamics”. IMO nothing short of the full background-free Monty will ever fix it, and that fixing QEM means first fixing CEM.
Still, the forms of EM persist – so the structure of the theory is (almost) right.
-drl
Thomas,
I don’t want to go on about this too much as we are getting off topic, but clearly Feynman, Schwinger and Tomonoga were not proud of the infinite subtractions they had to do and were looking for a future development to correct this. The future, or at least 57 years of it, has just said, “well it was good enough for Feynman, et al, so it’s good enough for us”. My point is just that, in fact, it was not good enough for them, and they were looking for something better.
Chris,
There is certainly room for improvement of the standard model; e.g., I believe that understanding the group of gauge transformation may cast light on things like confinement and renormalization. However, an improvement would not make the standard model wrong, like special relativity didn’t render Newtonian mechanics wrong. Incomplete, yes, but wrong, no.
A website dedicated to slaying the standard model would rightly be laughed at.
Read the Nobel prize speeches of Feynman, Schwinger and Tomonoga and decide for yourself whether or not they saw room for improvement in QED.
Thomas, I heartily concur – in fact Peter has brought back my enthusiasm for discussing physics, starting with his courageous posts to SPR.
I have access to some excellent forum software that runs (flawlessly) on Linux. I’m sure if we put it up, and created some topics, the boards would be jammed with conversations.
If you want to see it in action go to z spot iwethey spot org.
-drl
In general, the important question is how to deal with the fact that the academic power structure in particle theory is now completely dominated by an entrenched cadre of people devoted to a failed dogma. Trying to set up a new, alternative power structure looks near to impossible, but the current one is based on such a shaky foundation that its collapse sooner or later seems inevitable. The question is how to help that process along so it happens before we’re all dead and gone.
Peter, I think you underestimate your own power. You, and this forum, are undoubtedly starting to wield non-neglible power, for the simple reason that you are right and people know it. Of course, pointing out that the emperor is naked will only be taken seriously if he really lacks clothes. A website dedicated to slaying the standard model would rightly be laughed at.
ROFL!
I’m not convinced by Vafa’s argument. When Dorothy entered a parallel universe, the first thing she found was a wicked witch.
OTOH the aliens, good and bad alike, may have left our universe because they found it too boring (“What, the Earth-bars don’t serve Ammonia? The Earthlings can’t levitate? Nobody smokes Magnesium? … Let’s get out of here!”)
OMFG! The “Over the Rainbow” Hypothesis!
Das RegenbogensÜberführungshypothese!
From a footnote in physics/0308078:
“Cumrun Vafa thinks that the fact that we do not see aliens around could be the first proof of the existence of brane worlds: all advanced aliens would have emigrated to better parallel universes (our Universe has zero measure).”
Read it and weep…
Hi Chris,
A conference devoted to alternative to string theory would in principle be a good idea, but someone with funding and credibility has to be willing to organize it.
Conferences tend to fulfill two separate kinds of functions.
1. Allowing people working on the same topic to get together, talk and find out what each other are doing.
2. An important social function of determining power and status within the community. This is determined by who gets invited, who gets invited to speak, who hangs out with whom, etc.
One problem with an alternatives to string theory conference would be that mostly people not doing string theory are doing very different things, with very different philosophies, and it’s unclear how much they really could communicate usefully with each other. The loop quantum gravity community is one of the few that has enough people to do this usefully, and they have their own conferences.
If a conference were organized by people or an institution with little or no status in the particle theory community, it couldn’t fulfill the social function. It would be completely ignored by mainstream physicists, no one would care who was invited or who spoke. Networking at the conference wouldn’t be very helpful as you would be meeting people who have as little power as oneself. Keeping the crackpots from dominating the thing would be no easy task either.
In general, the important question is how to deal with the fact that the academic power structure in particle theory is now completely dominated by an entrenched cadre of people devoted to a failed dogma. Trying to set up a new, alternative power structure looks near to impossible, but the current one is based on such a shaky foundation that its collapse sooner or later seems inevitable. The question is how to help that process along so it happens before we’re all dead and gone.
Peter,
It seems to me that it might not be a bad idea to organise an “Alternatives to Superstrings” conference/workshop. What do you think?
On the “Science Channel” tonight (formerly “Discovery Science”) Hawking is repeating the party line, CC, canceling to 120 places not enough, accelerating, string theory takes us close, nothing left to discover, etc. etc. etc.
Is it possible to just have a science show that DOESN’T have an obsession about “it all”?
Hawking, Galileo, and Einstein are described as “daring revolutionaries, scorned tradition, brilliant radicals” etc. etc. More BS. Einstein scorned tradition? Which one? The guy in Manhattan who owns the bagel shop?
I’m certainly no expert either, but my impression was that the answer to this question is that these solutions are not static, but metastable. Sooner or later they tunnel to zero energy.
In concede I am no expert in these matters and my knowledge is probably out of date by now, but how can one use “The String Theory Landscape” to justify a cosmos with a tiny positive lambda (ours)?
A clear-cut no-go theorem (e.g as discussed by Maldacena and others) states that you cannot compactify 10-dimensional superstring effective actions (or supergravity) on static internal compact geometries, down to 4 dimensions and then get an induced positive potential or CC in the dimensionally reduced effective string action (leading to accerating cosmological solutions or deSitter space). Even Witten says he doesn’t know how to get deSitter space or a CC out of even classical string compactifications.(“Quantum Gravity In de Sitter Space” preprint.)
Also, a small cosmological constant or potential term in a dimensionally reduced effective string action will manifestly break S-duality (at least for toroidal compactifications). In some ways that might be good since very small numbers in physics (e.g. non-zero particle masses for example) seem to be associated with broken symmetries. One can compactify string actions on time-dependant internal hyperbolic spaces for example (relaxing the constraints of the no-go theorem) and try to get accelerating cosmological solutions that way, but I just don’t get all this “Landscape” reasoning to “explain” a small CC.
I heard a bit about the Stanford stuff and flux compactications but it seems very artificial. A whole anthropic dogma seems to be emerging based on this “Landscape” though. Even with a vast landscape of solutions/vacuua for 4-dimensional string theory, based on known compactication technology, surely none of them should have a small CC? I admit I have lost the plot now with string cosmology, not having followed any literature for quite a bit, although I don’t think the subject is developed enough to really deal with such cosmological issues with any real confidence anyway. Maybe Urs or someone can enlighten/update me here or point me to some useful preprints? (which I would welcome).
I still believe the CC (or dark energy if you prefer) is a hard number that has to be (somehow) rigorously calculated or explained and not “anthropicised” away.
The funny thing is – I wrote this paper which shows that in order for Riemannian geometry to be a proper limit of Weyl geometry, lambda=0 – and this was already known by Pauli in the 4d context long, long ago.
Never was so much effort spent by so many on something so zero. The CC is nothing but an artifact of an assumed global symmetry, and somehow it got promoted to God in the Machine.
A scientifically honest person must spend his days filled with Sartrian nausea at such a spectacle.
Maybe, but religious fanatics will always be with us and can generally be easily ignored. More serious is the abandonment by leading physicists of the scientific method for understanding the world in favor of a dogma which explains nothing and for which there is no evidence. And it’s not even a very attractive or satisfying dogma.
Any bets the anti-science religious fanatics will use articles like this to justify their religions and/or ideologies, or as a way to discount “science” as irrelevant?
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