Is physics about to hit a dead end, or am I jumping to conclusions?

[eiyaz]

Based on the news coming out of every corner of the physics world it seems that String Theory is about to die and possibly SM if they don't find the higgs boson.

http://www.newscientist.com/article...easurements-reveal-shape-of-the-electron.html

First they discovered that the electron is almost a completely perfect sphere which contridicts SUSY. Am I correct in saying that even if SUSY is not discovered at the LHC range, it can still be disproved if we detect that the electron is spherical beyond 10^19?

Since string theory REQUIRES SUSY, not discovering SUSY should greatly hinder string theory.

Also dark matter is a no show:

http://www.sciencenews.org/view/generic/id/74592/title/News_in_Brief_Dark_Matter_meeting_

Since the electron is perfectly spherical SUSY cannot be used to explain why matter prevailed over antimatter.

Also ST predicts higher dimensions and missing energy due to the graviton both of which have not been discovered.

Assuming by the end of 2012, we still do not see anything, does this spell the end of string theory? And if we do not find the higgs boson does that mean the end of SM? If so, what is the next most promising theory is it the vanish dimensions hypothesis?

Why has still not been posted on the forum yet? Seems like this is huge!

 

[Kevin_Axion]

I'll be honest with you, New Scientist knows nothing and for that matter all science magazines are mostly misleading.

 

[marcus]

Based on the news coming out of every corner of the physics world it seems that String Theory is about ...
Why has still not been posted on the forum yet? Seems like this is huge!

Thanks for posting about this! We don't have to exaggerate the importance by shouting about all of physics hitting a deadend . What you have pointed us to is IMHO already very interesting!

I don't think from a broader historical perspective the String program is necessarily so important. SUSY could be abandoned, String could go out of fashion in theory circles, and still physics would be full of vitality and continue to make progress. No one single assumption or research program is essential. The past is littered with ideas that shone brilliantly in their day and then died. So let's not overdramatise.

I'd like to understand better what you pointed out to us:
http://www.nature.com/nature/journal/v473/n7348/full/nature10104.html

It is a Nature journal article about the shape of the electron.
=====quote Nature=====
Improved measurement of the shape of the electron

J. J. Hudson, D. M. Kara, I. J. Smallman, B. E. Sauer, M. R. Tarbutt & E. A. Hinds
Nature 473, 493–496 (26 May 2011)
Received 18 February 2011 Accepted 08 April 2011 Published online 25 May 2011

The electron is predicted to be slightly aspheric¹, with a distortion characterized by the electric dipole moment (EDM), d_e. No experiment has ever detected this deviation. The standard model of particle physics predicts that d_e is far too small to detect², being some eleven orders of magnitude smaller than the current experimental sensitivity. However, many extensions to the standard model naturally predict much larger values of d_e that should be detectable³. This makes the search for the electron EDM a powerful way to search for new physics and constrain the possible extensions. In particular, the popular idea that new supersymmetric particles may exist at masses of a few hundred GeV/c² (where c is the speed of light) is difficult to reconcile with the absence of an electron EDM at the present limit of sensitivity^2,4. The size of the EDM is also intimately related to the question of why the Universe has so little antimatter. If the reason is that some undiscovered particle interaction⁵ breaks the symmetry between matter and antimatter, this should result in a measurable EDM in most models of particle physics². Here we use cold polar molecules to measure the electron EDM at the highest level of precision reported so far, providing a constraint on any possible new interactions. We obtain d_e = (−2.4 ± 5.7stat ± 1.5syst) × 10⁻²⁸ ecm, where e is the charge on the electron, which sets a new upper limit of |d_e| < 10.5 × 10⁻²⁸ ecm with 90 per cent confidence. This result, consistent with zero, indicates that the electron is spherical at this improved level of precision. Our measurement of atto-electronvolt energy shifts in a molecule probes new physics at the tera-electronvolt energy scale².
==endquote==

Eiyaz, thanks again! IMHO this is potentially quite interesting. And any information, any advance, is good for physics. Anything unexpected or surprising that challenges theorists adds to the momentum of research. Negative results are great! I think we are in for some very exciting times over the next 10 years or so. No dead end at all!

I say that independently of anything about this paper. It is too early for me to say anything definite about this particular paper. Just that I want to understand better what their result implies. Nature is a good journal so it is probably solid research.

Here is an earlier paper by the same team:
http://arxiv.org/abs/1103.1566

 

[Kevin_Axion]

Another misleading article, it isn't the shape of the actual electron but its dipole moment.

 

[marcus]

Hmmm, how could the editors of Nature have missed that?

But actually they make crystal clear up front that they are talking about the dipole moment (that's what I assumed when I originally saw the title).

BTW in case anyone is interested, here is the teams March 2011 article which is kind of an "appetizer" for the one just published:

http://arxiv.org/abs/1103.1566
Prospects for the measurement of the electron electric dipole moment using YbF
B. E. Sauer, J. J. Hudson, D. M. Kara, I. J. Smallman, M. R. Tarbutt, E. A. Hinds
(Submitted on 8 Mar 2011)
We discuss an experiment underway at Imperial College London to measure the permanent electric dipole moment (EDM) of the electron using a molecular beam of YbF. We describe the measurement method, which uses a combination of laser and radiofrequency resonance techniques to detect the spin precession of the YbF molecule in a strong electric field. We pay particular attention to the analysis scheme and explore some of the possible systematic effects which might mimic the EDM signal. Finally, we describe technical improvements which should increase the sensitivity by more than an order of magnitude over the current experimental limit.
Comments: 6 pages, 2 figures

 

[GDogg]

I think theoretical physics has been more or less stuck at a dead for a long time, probably since the completion of the Standard Model in the 70s. And I'm not only referring to String Theory, but to most competing programs as well.

However, I also think that's a good thing. The same happened at the end of the 19th century and we got quantum mechanics and relativity out of it. As Lee Smolin puts it borrowing from Kuhn, we need revolutionary science for this period.

 

[suprised]

What a nonsense... as if theoretical particle physics woulnd't have been extremely prolific during the last decades! Full of important and groundbreaking ideas, like the holographic principle. There is absolutely no lack of revolutionary ideas, like anthropic principle and the landscape. But armchair critics are hard to satisfy.

 

[ordered_chaos]

Entropic theory, Category math, Relative Relativity, CERN, and new communication channel such as blogs, forums and whatever is on the interwebs. **** is just getting interesting imo.

 

[GDogg]

What a nonsense... as if theoretical particle physics woulnd't have been extremely prolific during the last decades! Full of important and groundbreaking ideas, like the holographic principle. There is absolutely no lack of revolutionary ideas, like anthropic principle and the landscape. But armchair critics are hard to satisfy.

Changing the definition of science and making unfalsifiable or tautological claims is not revolutionary. THAT is nonsense.

 

[Physics Monkey]

Physics is not nearing a dead end. This is trivially true given that physics and theoretical physics in particular is a lot more than just high energy theory. Just to name two of interest to me, quantum condensed matter physics and quantum computing are both booming areas of investigation with many fundamental theoretical and experimental problems wide open.

Of course, high energy physics is hardly dying either. Dying fields don't get 1-2 colloquium slots at major universities every semester just on the LHC alone. (As an example, old fashioned nuclear physics MIGHT be an area where you can argue for an actual decline.) Of course, there are also an enormous number of dark matter experiments. I would argue that contrary to the hypothesis of decline, high energy physics is roaring. One has for the first time in a long time an almost guaranteed look at physics beyond the standard model at the LHC. One has many cosmological puzzles on which we are poised to make non-trivial progress. On the theoretical side, one has highly non-trivial agreement between theory and experiment owing to the finely crafted nature of the LHC and the really sophisticated understanding of QCD, etc. that has been won by theorists. And of course, string theory continues to churn away ...

 

[suprised]

Changing the definition of science and making unfalsifiable or tautological claims is not revolutionary. THAT is nonsense.

THAT is research in progress and whether it will lead to anywhere or not will be seen. Would YOU propose to stop all research you don't understand? Better leave the judgement to professional scientists rather than to self-declared internet experts!

 

[Schreiberdk]

String theory not falisifiable? I don't think so. Check out https://www.physicsforums.com/showthread.php?t=502265

 

[Kevin_Axion]

In the words of Kierkegaard: "...[it's] a leap of faith."

 

[marcus]

String theory not falisifiable? I don't think so. Check out https://www.physicsforums.com/showthread.php?t=502265

For me, this version of the URL works better:

https://www.physicsforums.com/showthread.php?t=502265

Try removing the "www." in front of physicsforums.com and see if you experience any difference.

BTW Schreiber,
in your thread you point to this paper:
http://arxiv.org/abs/1105.5283
Does it really propose a way to falsify all possible string theories?
I didn't see where the authors actually said this. I will look back again. Maybe you could point us to the place where you saw them talk about falsifying string in general.

 

[Schreiberdk]

I don't really see the difference marcus, but I'll do it for future links to PF thread ;)

 

[atyy]

I guess the usual example is Dirac's lone monopole theory as an explanation of charge quantization.

Is that falsfiable?

Is that scientific?

Some have said the theory is not falsifiable even in principle, yet it clearly is scientific. Hence falsifiability has been falsified.

 

[marcus]

Schreiber, I went back and took a second look at the Durrer et al paper you pointed to.
http://arxiv.org/abs/1105.5283
I tend to respect Ruth Durrer FWIW. I'm no expert so my approval of her work does not necessarily mean much :-D

The paper says:
==quote Durrer et al==
Conclusions and Outlook We have shown that the gravitational wave background from inflation is strongly modified by an intermediate matter dominated era. If string theory leads to an intermediate matter dominated phase, as claimed in [2, 3], this will be observable in the gravitational wave background: on CMB scales one will detect the unmodified background from inflation, e.g., with the Planck satellite [23] or with a future CMB polarimeter [24]. However, on higher frequencies like milli-Hz or Hz probed by the gravitational wave detectors indicated in Fig. 2 no signal will be detected. In other words, if these experiments will detect the signal from the inflationary gravitational wave background as expected from the CMB, this will rule out string theory as the fundamental theory of Nature.

==endquote==

At first sight the test seems to depend on a claim made in references [2,3] and also on some advanced "gravitational wave detectors indicated in Fig. 2".

Footnote #19 mentions a few of the proposed gravitational wave detectors.
==quote==
[19] Future ground-based observatories are advLIGO [30], LCGT (Large Scale Cryogenic Gravitational wave Tele- scope) [31] and ET (Einstein Telescope) [32]. The limits shown in Fig. 2 assume two-detector correlations with an observation time tobs = 4 months. Proposed future satellite missions are LISA (Laser Interferometer Space Antenna) [33, 34], BBO (Big Bang Observatory) [36], DECIGO (DECI-hertz interferometer Gravitational wave Observatory) [35] and LISAIII [37]. For the satellite missions we assume t_obs = 10 y. IPTA [38] is the International Pulsar Timing Array project.
==endquote==

The key assumption was based on references [2,3] which are:

[2] G. Kane, Phys. Today 63N11, 39 (2010).
[3] B. S. Acharya, G. Kane and E. Kuflik, arXiv:1006.3272 .

Here is [3]:
http://arxiv.org/abs/1006.3272
String Theories with Moduli Stabilization Imply Non-Thermal Cosmological History, and Particular Dark Matter
Bobby Samir Acharya, Gordon Kane, Eric Kuflik
(Submitted on 16 Jun 2010)
In recent years it has been realized that pre-BBN decays of moduli can be a significant source of dark matter production, giving a 'non-thermal WIMP miracle' and substantially reduced fine-tuning in cosmological axion physics. We study moduli masses and sharpen the claim that moduli dominated the pre-BBN Universe. We conjecture that in any string theory with stabilized moduli there will be at least one modulus field whose mass is of order (or less than) the gravitino mass and we prove this for a large class of models based on Calabi-Yau extra dimensions. Cosmology then generically requires the gravitino mass not be less than about 30 TeV and the cosmological history of the Universe is non-thermal prior to BBN. Stable LSP's produced in these decays can account for the observed dark matter if they are 'wino-like,' which is consistent with the PAMELA data for positrons and antiprotons. With WIMP dark matter, there is an upper limit on the gravitino mass of order 250 TeV. We briefly consider implications for the LHC, rare decays, and dark matter direct detection and point out that these results could prove challenging for models attempting to realize gauge mediation in string theory.
Comments: 8 pages.

I suspect Durrer's claim of testability may not be as robust as it appeared at first sight. It seems based on an assumption for which the support seems a bit slender---more of a "special case" situation. I'd like to hear other people's opinions on this.

====================
About links to http:physicsforums.com
compared with those with the extra "www."
I think I may be the only person who experiences trouble with the latter. It may just be a problem with my system, not with anyone else's. So you should just do whatever is natural and most convenient for you. I will take care of it at my end---don't want to cause bother.

 

[GDogg]

THAT is research in progress and whether it will lead to anywhere or not will be seen. Would YOU propose to stop all research you don't understand? Better leave the judgement to professional scientists rather than to self-declared internet experts!

Oh I understand what the landscape and the anthropic principle are alright. That's why I call it nonsense.

I never said I propose to stop all research. I just propose presenting what I just mentioned as nothing more than wild speculation that changes the way we do science, especially to the general public.

And I'm not a self declared internet expert. Would you call Lee Smolin and David Gross Internet experts too?

 

[marcus]

String theory not falisifiable? I don't think so. Check out https://www.physicsforums.com/showthread.php?t=502265

To sum up what I said in the past several posts, I'm not sure that the claim of falsifiability made by Ruth Durrer will hold up. It seems to be based on some tentative speculation by Gordon Kane et al. Here is a sample excerpt from the Kane paper that Durrer cites:

==quote Kane et al. ==
CONCLUSIONS
We have argued that if our universe is described by a compactified string theory then the presence of stabilized moduli would likely imply that the cosmological history is non- thermal before BBN. In particular, dark matter can be produced from moduli decays and generically has to be wino-like in order to have a consistent abundance. The analysis that leads to these results sharpens the arguments that there is always a modulus with mass of order the gravitino mass or less in such theories. These plus cosmological considera- tions emphasise some difficulties in realizing gauge mediated supersymmetry breaking in string theory. We also described an upper limit on the gravitino mass of order several hundred TeV. The appendix contains a study of the known examples of string theory vacua with stabilized moduli and shows they agree with the results above.
==endquote==

It would be interesting to hear other people's views on this.

 

[atyy]

The broad idea of the anthropic principle is classic science - using data to constrain parameters. Some versions of it are fuzzy and constrain nothing, but there is nothing unscientific about the general idea.

 

[suprised]

Oh I understand what the landscape and the anthropic principle are alright. That's why I call it nonsense.

I never said I propose to stop all research. I just propose presenting what I just mentioned as nothing more than wild speculation that changes the way we do science, especially to the general public.

And I'm not a self declared internet expert. Would you call Lee Smolin and David Gross Internet experts too?

These are experts, but the ones who cry loudest aren't, they are often not even scientists.

Surely the landscape etc is a hotly debated controversial issue, but it's impossible to say whether it will prove fruitful in the future or not. It is is not at all clear whether this will stay untestable forever. There are ideas like, for example, that Hawking radiation emanating from the boundaries of our "bubble" could carry information from outside; so the existence of other phases may in principle be testable. These matters are certainly in need to be investigated by scientific methods, and are therefore part of science.

Anyway, just _because_ so many people outrightly dismiss this kind of ideas, which go so much against their gut feelings, makes these ideas potentially revolutionary, more or less per def!

So my point is that poeple should not complain that there won't be any revoluntionary ideas or no progress in particle physics. Maybe they are witnessing it without realizing it!

 

[smoit]

To sum up what I said in the past several posts, I'm not sure that the claim of falsifiability made by Ruth Durrer will hold up. It seems to be based on some tentative speculation by Gordon Kane et al. Here is a sample excerpt from the Kane paper that Durrer cites:

==quote Kane et al. ==
CONCLUSIONS
We have argued that if our universe is described by a compactified string theory then the presence of stabilized moduli would likely imply that the cosmological history is non- thermal before BBN. In particular, dark matter can be produced from moduli decays and generically has to be wino-like in order to have a consistent abundance. The analysis that leads to these results sharpens the arguments that there is always a modulus with mass of order the gravitino mass or less in such theories. These plus cosmological considera- tions emphasise some difficulties in realizing gauge mediated supersymmetry breaking in string theory. We also described an upper limit on the gravitino mass of order several hundred TeV. The appendix contains a study of the known examples of string theory vacua with stabilized moduli and shows they agree with the results above.
==endquote==

It would be interesting to hear other people's views on this.

The paper of Acharya, Kane et. al. basically summarizes and sharpens the argument for what had already been known, see http://arxiv.org/abs/hep-th/0602246" for example.
The conclusion about the non-thermal history is very generic and can be simply understood from the fact that in N=1 D=4 supergravity, which effectively describes many realistic string compactifications at low energies, the mass of the s-goldstino, aka the lightest modulus, is related to the mass of the gravitino. As a consequence, if SUSY were to stabilize the gauge hierarchy, the existence of light moduli is almost inevitable.
Of course, one may argue that the N=1 D=4 supergravity does not arise in all string compactifications or SUSY is broken at some very high scale and does not stabilize the gauge hierarchy either but then the point about the non-thermal history is moot.

As an afterthought, I just realized that there is a much easier way to rule out the conclusions of Acharya et.al. experimentally, namely if the LHC discovers a sparticle spectrum consistent with gauge mediation, where the LSP is generically the gravitino.

 

[eiyaz]

My title is a bit deceptive, what I am saying is in terms of string theory. Why is string theory considered unfalsifiable, when recent discoveries are definitely giving a blow to the theory. Will this be a deadly blow to the string theory, or can the it recover and how?

 

[smoit]

... when recent discoveries are definitely giving a blow to the theory. ...

Which recent discoveries do you have in mind? Could you give a reference?

 

[eiyaz]

Which recent discoveries do you have in mind? Could you give a reference?

The electron dipole moment being perfectly spherical, lack of SUSY, and higher dimensions. I know these haven't been completely verified but speaking hypothetically if they are ruled out, does this not discredit string theory since it requires SUSY?

 

[suprised]

The electron dipole moment being perfectly spherical, lack of SUSY, and higher dimensions. I know these haven't been completely verified but speaking hypothetically if they are ruled out, does this not discredit string theory since it requires SUSY?

For the n-th time: string theory does NOT logically require SUSY. The toy models people investigate are mostly supersymmetric (meant to be spontaneously broken), because otherwise the models are hardly tractable; but this does not imply strings must be supersymmetric.

 

[mitchell porter]

eiyaz, I've just looked into the literature regarding supersymmetry and a dipole moment for the electron, and so far I have no idea where New Scientist got its claim that "while the standard model suggests the electron is egg-shaped by only one part in 10^28, supersymmetry sets the range at between one part in 10^14 and one part in 10^19". They must be talking about a particular class of supersymmetric model, but I can't even tell which class.

The facts appear to be: 1) any source of CP violation might contribute to a dipole moment for charged elementary particles, 2) the standard model contains a form of CP violation which would make a very small contribution (around one part in 10^40), 3) supersymmetric theories contain many potential new sources of CP violation, but the strength of the effect always depends on a parameter, and that parameter can be zero, 4) in one class of models, those parameters are routinely assumed to be zero, 5) in another class of models, the effect must be nonzero, so you may get large dipole moments, 6) but even in that class of models, it's possible to have large CP violation but very small dipole moment.

 

[eiyaz]

@marcus, hey thanks for all the information :), I was wondering how this could damper string theory.

eiyaz, I've just looked into the literature regarding supersymmetry and a dipole moment for the electron, and so far I have no idea where New Scientist got its claim that "while the standard model suggests the electron is egg-shaped by only one part in 10^28, supersymmetry sets the range at between one part in 10^14 and one part in 10^19". They must be talking about a particular class of supersymmetric model, but I can't even tell which class.

The facts appear to be: 1) any source of CP violation might contribute to a dipole moment for charged elementary particles, 2) the standard model contains a form of CP violation which would make a very small contribution (around one part in 10^40), 3) supersymmetric theories contain many potential new sources of CP violation, but the strength of the effect always depends on a parameter, and that parameter can be zero, 4) in one class of models, those parameters are routinely assumed to be zero, 5) in another class of models, the effect must be nonzero, so you may get large dipole moments, 6) but even in that class of models, it's possible to have large CP violation but very small dipole moment.

It's more than just new scientist, in fact a great deal of sources suggest the same parameter of 10^14 to 10^19 for SUSY and 10^28 (some sources say 10^22 or higher for SM):

http://news.google.com/news/more?hl...sult&ct=more-results&resnum=1&ved=0CC0QqgIwAA

There are a lot of articles in the link above that establish those parameters. What are leading SUSY models suggesting? Are there promising models who range of detection are not yet reached?

According to this article:

http://www.dailymail.co.uk/sciencet...-world-How-electrons-perfectly-spherical.html

An increase in sensitivity of 4 fold can effectively rule out SUSY. Is this correct?

 

[mitchell porter]

See http://www3.imperial.ac.uk/ccm/research/edm/overview" from the researchers' website. As you can see, they want several extra orders of magnitude, not just a "four-fold" increase (perhaps the Daily Mail means four orders of magnitude) in order to falsify the models they describe as "Multi Higgs", "Left Right", "MSSM, phi ~ 1", and "MSSM, phi ~ alpha/pi", and the Standard Model prediction is somewhere below 10^-36 in units of "e.cm" (size of electron charge times centimeter). Unfortunately, despite examining several of their papers, I can't find a source for these figures. MSSM is minimal supersymmetric standard model, Left Right is probably the Pati-Salam model, but these models have many free parameters and hundreds of papers have been written about them.

Failure to detect an electron dipole moment will definitely not falsify supersymmetry. It probably doesn't even falsify the general idea that supersymmetry might be detectable at low energies. Presumably it would make trouble for a particular set of models, but so far I can't find the details.