Dax discussions of Beyond SM theories/including newcomer questions

[Kevin_Axion]

Awesome! That's probably my dream job, something involving High Energy Physics.

 

[Lt_Dax]

Always follow your dreams, regardless of what other people tell you. And physics in 10 years will probably be fascinating, with less emphasis on this string argument. I remember a popular article a year back detailing some of the extremely smart new proposals for testable theories of quantum gravity, so string theory may reach the point where they stop making unwarranted claims about what it is, because its tools and methods will get sucked into the newer ideas (I think marcus made this point better than I could).

 

[Kevin_Axion]

Yea, I actually live pretty close to PI so I'm planning on going to the University of Waterloo and they have awesome courses like introduction to QFT (Feynman Path Integrals) and Particle Physics in fourth year courses. I can't wait and thanks for the support despite my arrogant attitude before.

 

[PAllen]

I skimmed a lot of this thread, could hardly read it all. I'm surprised I didn't see anyone noting the following positions which have been raised in other forum threads.

1) It is not clear that GR and QFT must be considered in conflict that must be resolved somehow. I've seen a growing number of papers arguing several related points:

a) The need for quantum gravity at all should be considered subject
experimental verification. Maybe some form of QFT in curved
space is a valid model.

b) Progress in quantizing GR as an effective field theory
least raises the question of whether the conflict is as deep or
needful of whole new frameworks.

2) Supersymmetry preceded string theory, if my recollection is right, and has been pursued independently of string theory.

3) Thus one could posit that a research program aiming to be more in touch with experiment would look for ways choose a preferred SUSY extension to SM that had appropriate dark matter candidates, and perhaps combined with effective quantized gravity explained dark energy.

In short, there are more minimalist approaches to make progress using current conundrums and unexplained results.

However, I have no problem with the idea that physicists should do what seems most promising to them. Dead ends will be be pruned eventually, no one knows them beforehand, outside officials certainly shouldn't be making these decisions.

And I see shifting emphasis happening naturally. 'Radical' approaches other than M theory and LQG are being done as well as a growing number of papers on more limited approaches, as above. Success will draw followers, stumbling blocks will push some people in new directions.

 

[Haelfix]

Thank you Pallen, that's an excellent post that is succint, logical and has some nonzero probability for interesting physics discussions that others here might get something out off. It is also points of view that I happened to share not so long ago.

It is precisely questions like this (or should I say, the 'probable' answers) that lead people to believe in string theory.

On the other hand, this thread is so devoid of any meaningful content, that it would be best served in its own thread.

 

[marcus]

Hi PAllen,
Its possible some of the "other forum threads" relating to minimalist proposals were ones I started. Are you familiar with what could be called "no-frills" proposals of the following two sets of authors?
Hermann Nicolai and Kris Meissner
Shaposhnikov and friends

Nicolai presented his idea at the July 2009 XXV Max Born conference. It was LHC testable, predicted no new energy scales between EW and the Planck scale, required just one new field. No low energy SUSY. No extra dimensions etc. Gravity was not included in the talk, as I recall, but they have described a way to include it elsewhere. The slides are here:
http://www.ift.uni.wroc.pl/~planckscale/lectures/1-Monday/3-Nicolai.pdf
The 40 minute video of Nicolai's talk is here:
http://www.ift.uni.wroc.pl/~planckscale/movie/
The first 5 minutes provides an "executive summary" so you can get the gist without going the whole 40 minutes.
He referred to Shaposhnikov's work, and Shaposhnikov has also cited the Nicolai Meissner papers. Some points of similarity.

I've reported on these minimalist initiatives in other threads. So I am curious if these are some of what you were thinking. I haven't paid much attention to Effective Field Theory (EFT) à la John F Donoghue and several others, because I've been interested especially in Nicolai Meissner ideas. There is something more to it---the attempt is to extend the Standard Model, with very little extra, all the way to Planck scale and get something moreover that the LHC could falsify.

Their first paper was written in 2006 and has been followed up by a handful of others, indeed they just posted a new one in October 2010.
Here's the 2006 paper:
http://arXiv.org/abs/hep-th/0612165

A good way to dig up minimalist papers might be to look down the list of the 40 papers that cited it:
http://www.slac.stanford.edu/spires/find/hep?c=PHLTA,B648,312

I've highlighted some bits of your post that interested me especially.

I skimmed a lot of this thread, could hardly read it all. I'm surprised I didn't see anyone noting the following positions which have been raised in other forum threads.
...
In short, there are more minimalist approaches to make progress using current conundrums and unexplained results...

And I see shifting emphasis happening naturally. 'Radical' approaches other than M theory and LQG are being done as well as a growing number of papers on more limited approaches, as above...

 

[Fra]

There are some quite deep aspects of these things, but this can easily be misinterpreted as it's a thin line between acknowledging the subjective nature of expectations and arbitrariness in particular for anyone that doesn't understand the difference.

Scientists believe in things, but they believe in things based on evidence (and they try to do this even in the fluffy early beginnings of a theory, otherwise there's no justification to call it a theory. Even hypotheses have experimental origin). Religious people believe in things based in faith.

To believe in something due to evidence is basically a rational expectation; this is different from stating that all evidence is unique, or that there is an objective "TRUE" or "correct" expectation.

Two scientist making different observations, will form two possible contradictory but still RATIONAL expectations of nature. What further happens is that these scientist "interact" in the scientific community in order to negotiate an objective consensus. Still this consensus is only objective relative to the local community.

The idea of rational expectation is completely disjoint from the idea of objective truth, because evidence is not objective. I don't think we should confuse "science" which to me is all about rational and justifiable expectations and actions, with illusions absolute truth.

Science isn't necessarily about unravelling eternal absolute truth or timeless laws - it is IMHO about rationally learning and forming expectations of nature, for basis of further rational action.

An expectation can be fully rational, and yet "wrong", since the measure of wrong is also merely a rational expectation which is observer dependent.

This association with "intelligent design" everything one discusses this seems to be an american phenomenon, I personally don't have any problem distinguishing this discussion from religion.

/Fredrik

 

[PAllen]

Hi PAllen,
Its possible some of the "other forum threads" relating to minimalist proposals were ones I started. Are you familiar with what could be called "no-frills" proposals of the following two sets of authors?
Hermann Nicolai and Kris Meissner
Shaposhnikov and friends

I've seen a couple of threads of yours here, not sure I've seen these specifically. I was using the work 'minimal' in a generic sense, interesting that it might have a more specific sense similar to what I was getting at.

Nicolai presented his idea at the July 2009 XXV Max Born conference. It was LHC testable, predicted no new energy scales between EW and the Planck scale, required just one new field. No low energy SUSY. No extra dimensions etc. Gravity was not included in the talk, as I recall, but they have described a way to include it elsewhere. The slides are here:
http://www.ift.uni.wroc.pl/~planckscale/lectures/1-Monday/3-Nicolai.pdf
The 40 minute video of Nicolai's talk is here:
http://www.ift.uni.wroc.pl/~planckscale/movie/
The first 5 minutes provides an "executive summary" so you can get the gist without going the whole 40 minutes.
He referred to Shaposhnikov's work, and Shaposhnikov has also cited the Nicolai Meissner papers. Some points of similarity.

That's really interesting, especially if they tackle gravity. Do they have dark matter candidate and any approach for dark energy? (I will look over these references, but can't right away; by look at, I mean understand what I can from the abstract and general logic; I can't follow details of such papers). I am particularly interested in the idea of explaining the major evidence beyond SM with a theory that may not be 'ultimate' but is less of a leap than M-theory. In effect, suppose something like M-theory is the ultimate theory at the Planck scale, yet given the enormous difficulties of completing its formulation let alone understanding how to use it, it could be really worthwhile to pursue more partial theories that make progress on currently known conundrums.

Besides dark matter, and dark energy, other things that might progress are reducing the number of free parameters in SM via some new explanations. I remember in high school (60s) raising the plethora of particle masses as a signficant thing to explain, and being told that 'well, no one knows how to use such information'. Then, over next 10 years we get SM that now does derive things like proton/neutron mass (and was theoretically expected to explain such things evern before the calculations could be carried out).

Of course, I know the landscape hypothesis suggests most of these parameters may be accidents, and I can't say 'I know this is wrong', but I hope it is. I remember clearly the initial excitement with string theory, including the expectation (more than just a hope) that virtually all of these parameters would be derived quantities in string theory.

I've become somewhat enthusiastic about SUSY without string theory as a practical approach because of the synergy between something originating with unification (GUTs, QG separate from string theory as well as within string theory) that also predicts the seeming best candidate for dark matter so far. The big difficulty here (my opinion) being how to pick some preferred SUSY extension and work out the details.

I've reported on these minimalist initiatives in other threads. So I am curious if these are some of what you were thinking. I haven't paid much attention to Effective Field Theory (EFT) à la John F Donoghue and several others, because I've been interested especially in Nicolai Meissner ideas. There is something more to it---the attempt is to extend the Standard Model, with very little extra, all the way to Planck scale and get something moreover that the LHC could falsify.
Their first paper was written in 2006 and has been followed up by a handful of others, indeed they just posted a new one in October 2010.
Here's the 2006 paper:
http://arXiv.org/abs/hep-th/0612165

A good way to dig up minimalist papers might be to look down the list of the 40 papers that cited it:
http://www.slac.stanford.edu/spires/find/hep?c=PHLTA,B648,312

I've highlighted some bits of your post that interested me especially.

Atyy has posted several papers on effective field theory approach to quantum gravity over on the relativity forum. From these I perceive recent progress. Yes, one of them was by John F. Donoghue. What I like here is the ability to actually do quantum gravity calculations right now. Unfortunately, they seem to suggest that deviations from GR may not be testable for a long time.

A separate line of thought is the 'is quantum gravity' necessary at all. I am thinking here about recent papers arguing that you can 'almost prove' that the graviton will never be detected, even if it exists. Given the key role of the photon's particle like properties in the development of QM, this makes me ask the question of necessity for the whole enterprise. For example:

http://arxiv.org/abs/gr-qc/0601043

Closely related are papers like the following, proposing that the need for unification itself should be subject to experiment and is not strictly required:

http://arxiv.org/abs/0803.3456
http://arxiv.org/abs/0802.1978
http://arxiv.org/abs/0809.4218

Hope this reply isn't too 'all over the place'. My main thrust is there is a lot that can be done while 'waiting for TOE', if we need it at all. However, I don't perceive any 'problem' in theoretical physics. I have seen your (Marcus) threads noting changes in emphasis in research, and that is the natural way such things sort themselves out.

 

[Lt_Dax]

@Pallen

a) The need for quantum gravity at all should be considered subject
experimental verification. Maybe some form of QFT in curved
space is a valid model.

This is the kind of thing I've been trying to say all along. When your premise is also your conclusion, it's circular reasoning.

@Haelfix

On the other hand, this thread is so devoid of any meaningful content, that it would be best served in its own thread.

You can't just keep repeating that the thread is meaningless to keep yourself satisfied. If it it so meaningless, why participate in it? The fact that you started the sentence with "on the other hand" shows that it was preceded by some point you made, so clearly you are lying that there is nothing to engage with.

I still find it hard to believe that a seasoned veteran of physics (a science advisor no less) can resort to a cheap dismissal of an important discussion. There is a teenager here who shames you in terms of maturity. Many different things have been discussed for such a meaningless thread. The fact that you're irritated is sign enough that something substantial has been said which bothers you.

 

[marcus]

Pallen,
I think what I share with you is an interest in approaches which are seen as conservative, minimalist, with prospects for testing with the means at hand.

I'm not convinced that TOE is a logical next step.
Both the conventional SM and classical GR have problems, it gets my attention when I see people address the problems without necessarily reaching for complete unification.

Nicolai Meissner's proposal is intriguing and LHC testable, but not primarily TOE. They have discussed some nebulous ideas of how to link up with gravity and have tried teaming their model up with a version of supergravity. In Nicolai's talk at the Planck scale conference he said he was going to try to be "agnostic" about what version of QG could go with their proposal. My paraphrase doesn't do justice, I fear.
=========================

Where our thoughts differ is also interesting. It may simply reflect where we are coming from--prior concerns. In my case the needs of observational cosmology seem central---it's a personal perspective that influences how I see things. I'm sympathetic to your point that a graviton may never be observed. Indeed the concept itself may be more at home on a flat, or at least fixed, geometric background than in what I would call a more realistic setting.

 

[Lt_Dax]

Einstein thought that a TOE was the logical next step, but he was missing many important pieces of the puzzle (including two forces!). I've always believed it to be extremely strange that we act as though the current situation is different. A person pursuing a TOE is effectively claiming that the essential features of nature are known, and we just need to develop the correct mathematical apparatus. Extremely suspicious, and unlikely.

 

[Fra]

A person pursuing a TOE is effectively claiming that the essential features of nature are known, and we just need to develop the correct mathematical apparatus

I don't agree with that conclusion, there are other ways to think about that.

The inference perspective to physics, suggest a natural unifying framework based not on what nature is or must be, but rather on what inferences any observer can make on nature, and that from such a perspective all inferences should be unified in a general inference framework, because to suggest that there exits information that isn't the result of inference is to resort to non-scientific notions.

So unificiation is not expected because nature has to be this or that way, but rather because whatever nature is, all information about it must be the result of a scientific process. So the learning process "unifies" all knowledge.

Anyone that like me, thinks that physical processes in nature, can be thought of as inter-system inferences, may choose to seek a TOE (=GUT +gravity) in terms of trying to understand generic communication between two systems, and that unification corresponds to the limit where the complexity of the communicating parties approach zero. Then try to understand how to pull the 4 forces out of that abstraction, to the extent possible.

So I think the feature that no observer CAN know everything, is even the key to unification. Unification by undecidability. Whenever diversity isn't distinguishable, there is unification, not by enlightment but by ignorance.

/Fredrik

 

[Lt_Dax]

So unificiation is not expected because nature has to be this or that way, but rather because whatever nature is, all information about it must be the result of a scientific process. So the learning process "unifies" all knowledge.

... So I think the feature that no observer CAN know everything, is even the key to unification. Unification by undecidability. Whenever diversity isn't distinguishable, there is unification, not by enlightment but by ignorance.

I think we agree more than you might think. You could argue that unification (the way you describe) is the operation of physics as a subject, but it is and always has been a piecewise process, not a one shot approach, and above all, an evidence based approach. That's why we don't even have a proper union of QCD and Electroweak yet in the Standard Model. The SM, Higgs notwithstanding, represents what we actually know about nature, and nothing more.

If the 'let's try to develop a complete TOE' approach was a worthy method, it would have worked for Einstein. He failed because he had incomplete knowledge. Who are we to claim that things are different now? I would unhesitatingly bet money that future historians of science will view current attempts at a TOE in the same light as we currently view Einstein's attempt. This is the precise reason why the piecewise, experimental approach is the time tested way of discovering new information about how the universe works.

 

[marcus]

I want to see how Pallen would separate some issues out. He suggests that QG might not be needed because gravitons might in effect have no universal or fundamental existence---might just be an artificial construct that is perhaps useful for some purposes.

I agree with downplaying the graviton's significance---it doesn't come up much in nonperturbative QG. But that does not remove the need for QG, as I see it. One still wants a quantum spacetime geometry--a concrete mathematical representation of dynamic geometry--in order to do early-universe cosmology.

I guess my bias is kind of gradualist/incrementalist. The spacetime geometry of classical GR fails in the early universe. I want to see some improvements on GR tested. A TOE seems like a red herring, an impractical distracting goal.

I'm afraid of boring you with my list of phenomenologists. I find it exciting that they have taken the bit in their teeth. I just saw that Tsujikawa is on board. He has a paper in prep that says Loop cosmology is falsifiable* by available means: as I understand it, by the next CMB mission after Planck. Planck is now taking data.
We are talking about a bunch of phenomenologists who are not Loop people, and CMB polarization missions with provisional names like "B-pol" and "CMBpol".
Having Shinji Tsujikawa's participation is important, as I see it. In case someone is unfamiliar with him here is his home page at U Tokyo:
http://www.rs.kagu.tus.ac.jp/shinji/Tsujikawae.html

Key people, in my view, are Aurelien Barrau, Julien Grain, Wen Zhao, and Shinji Tsujikawa---together with the people who have co-authored with them on this topic.

*Broadly, not just one particular model or version.

 

[marcus]

You may decide I am responding to the current situation in a naive way. It requires going out on a limb. I hope to convince you that working cosmologists will not be satisfied with a perturbative treatment of geometry.
They are used to a geometry which can expand quickly by over 20 orders of magnitude.
The typical benchmark factor given is e⁶⁰ or 10²⁶ but the precise number hardly matters.
And if you change something may expand much less, or not at all, or may even collapse again. That kind of geometry is not a perturbation around some fixed pre-destined one.

A nonperturbative treatment of geometry should also be quantum--a QG in other words. Given that matter is quantum and influences geometry anything else seems unrealistic and even logically impossible.

What we are looking for is a conservative, minimalist, modification of GR. It must retain the most basic features of GR, to be conservative: no fixed geometric background, not perturbative, and so forth. It has to have, to a relativist/cosmologist, the "look and feel" of GR. And be quantum.

The idea is to do only what is absolutely necessary to achieve the incremental goal of a nonperturbative backgroundless quantum geometry. In other words don't go haring off after a TOE

And be testable.

 

[friend]

The idea is to do only what is absolutely necessary to achieve the incremental goal of a nonperturbative backgroundless quantum geometry. In other words don't go haring off after a TOE

I would have to disagree with you here. Geometry is very basic and fundamental. And you seem to be talking about finding fundamental reasons for the geometery we observe, even reasons why this geometry changes and even comes about in the first place in the big bang. I suspect you will not find those answers without explaining everything else in the process. I think it will take a TOE to explain QG. For if you explain where spacetime comes from to begin with, then you'll probably discover where particles come from that move in that spacetime.

I have more to say about a TOE in post 58 of this thread.

 

[Lt_Dax]

What if it takes 5,000 years to develop this TOE? It still wouldn't prevent us from discovering things, but it renders the concept of a TOE somewhat meaningless. Why do people have the feeling that to discover fundamental things about the geometry of space time we need to explain "everything"? How can you explain everything until you know what everything is? As I've said, Einstein thought "everything" was GR + EM. I don't feel this theory of everything language has ever been justified. Letting go of it will not cripple our ability to make genuine progress. Some people have said, well, surely the language used in unimportant, but I think it is - because the belief that you can create an all-explaining, all-knowing "framework" is probably highly misleading and is not a meaningful goal for a physicist to work towards, in my view.

 

[marcus]

... I suspect you will not find those answers without explaining everything else in the process. I think it will take a TOE to explain QG. For if you explain where spacetime comes from to begin with, then you'll probably discover where particles come from that move in that spacetime.
...

Friend! You sound as if the game, for you, is to find ultimate answers to the most basic questions!
Ultimately you might well be right that to finally understand the intimate dialogue between matter and geometry one will have to express them as both rooted in a common mathematical ground. As different aspects of the same thing.

But we don't always aim directly at what we think we want. In the current situation cosmologists have the opportunity to make a little incremental progress in studying the early universe. There are massive amounts of data coming in. This data has to be organized and compared with mathematical models, even if they are not exactly the right ones.

Our models never are exactly the right ones. :rofl:

Take a more pragmatic view and agree with me that cosmologists are allowed to use LQG (as many now seem to want to) as conservative modification of GR (retaining essential GR features) applicable to the early universe.

Indeed in the process they may falsify the existing Loop cosmology framework, depending on what ripples the next spacecraft see in the CMB.

 

[friend]

Friend! You sound as if the game, for you, is to find ultimate answers to the most basic questions!
Ultimately you might well be right that to finally understand the intimate dialogue between matter and geometry one will have to express them as both rooted in a common mathematical ground. As different aspects of the same thing.

Ever since issues of incompatibility arose between GR and QFT, there has been talk about having to make corrections to one or the other or both. This is because we don't have any logical justification for the absolute necessity of either. All we've accomplished is to find curves and equations that fit the data. Some are even asking what observations require us to apply the principles of QM to GR. So it seems we need to answer the questions of what make QM so logically necessay, and why should it be applied to GR? Something as funamental as why QM applied to something as fundamental as spacetime seems like a TOE to me. For I don't think you're going to find out why QM/QFT is necessary by finding higher energy particles. Those are just another reason to use it, not where it came from to begin with.

I suppose we can continue to grope in the dark and fit pieces together by chance. But I'm beginning to see light at the end of the tunnel.

 

[PAllen]

I want to see how Pallen would separate some issues out. He suggests that QG might not be needed because gravitons might in effect have no universal or fundamental existence---might just be an artificial construct that is perhaps useful for some purposes.

I agree with downplaying the graviton's significance---it doesn't come up much in nonperturbative QG. But that does not remove the need for QG, as I see it. One still wants a quantum spacetime geometry--a concrete mathematical representation of dynamic geometry--in order to do early-universe cosmology.

I guess my bias is kind of gradualist/incrementalist. The spacetime geometry of classical GR fails in the early universe. I want to see some improvements on GR tested. A TOE seems like a red herring, an impractical distracting goal.

I'm afraid of boring you with my list of phenomenologists. I find it exciting that they have taken the bit in their teeth. I just saw that Tsujikawa is on board. He has a paper in prep that says Loop cosmology is falsifiable* by available means: as I understand it, by the next CMB mission after Planck. Planck is now taking data.
We are talking about a bunch of phenomenologists who are not Loop people, and CMB polarization missions with provisional names like "B-pol" and "CMBpol".
Having Shinji Tsujikawa's participation is important, as I see it. In case someone is unfamiliar with him here is his home page at U Tokyo:
http://www.rs.kagu.tus.ac.jp/shinji/Tsujikawae.html

Key people, in my view, are Aurelien Barrau, Julien Grain, Wen Zhao, and Shinji Tsujikawa---together with the people who have co-authored with them on this topic.

*Broadly, not just one particular model or version.

This will have to be my last post in a while due to outside constraints. I may check back real quickly.

I think Marcus has hit the nail on the head that we both are excited by theoretical progress that attempts to solve known issues by expeditious and testable means. (It would be different if there were no major loose ends to explain, just dissatisfaction with existing theories. I believe that is not the case, and has never really been the case).

However, it is really interesting how perception of what are big problems skews your preferences. For me, dark matter and dark energy are the elephants in the room (also, extending SM to work consistently higher energies, explaining at least some relationships of the fundamental parameters, are major things to focus on), while drawing strong conclusions about the first microseconds of the universe is risky business that is hard to firmly interpret. Marcus' information about testability of LQG is very interesting. Perhaps I should take early universe modeling as a theory testbed more seriously.

Be that as it may, my current thinking has been more along the following lines (it changes twice a year anyway):

First, I see the key ingredient of QG most likely will never be observed, distinguishing it from all other quantum theories. That is unfortunate, but not decisive by itself. Then, I see that it is not so clear QG is needed at all, instead you should try to test whether it is needed (see the 3 papers on this I posted in my other thread). Then, the effective field theory papers attempt to answer the testability question, and they come out mostly in the negative: no effects at accesible energies; look inside event horizons (and die happy) or the first moments of the universe. So, I wonder whether there is anything worth doing on this.

This underscores my bias toward dark matter and dark energy as the big things to focus on. For these, SUSY extensions to SM look very promising to me, as well as just directly trying to improve SM to extend to higher energies (thus Marcus' references are *very* exciting to me on this score). Look into new vacuum theories to address dark energy.

Now I guess if you must to address those early universe issues, you need something more than this. So for this I guess I would have similar leanings as Marcus, for creative yet conservative approaches are worthwhile. Is a near singular modification of GR itself possible? Can the efffective field theory approach be extended to provide something useful here? Some other direct attack on the problem besides LQG? Maybe QFT in very curved space leads to exotic stress energy tensors that violate the assumptions of the Hawking-Ellis-Penrose singularity theorems?

(On the other hand, I definitely think string theory is still worth pursuing in the mix. Getting 4 forces without assuming them is not boring to me, it remains one of the high points of my following physics. Then there is the toolbox string theory has and presumably will continue to develop)

That's all I have for now, just the opinions of a long time avid follower of physics, not a practitioner (once upon a time, long ago, seriously studied physics).

 

[Lt_Dax]

@PAllen

On the other hand, I definitely think string theory is still worth pursuing in the mix. Getting 4 forces without assuming them is not boring to me, it remains one of the high points of my following physics.

I know you don't have the time to respond, just wanted to say I found your post very interesting. I'd like to pick up on the above point if I may. It's a plausible sounding view and I totally agree that models are worth studying because we can learn useful mathematical things from them (AdS/CFT is particularly interesting), but to me the inherent problem is, again, the assumption that we know what the new TOE "needs to do". There could be 7 forces, not 4. Where does that leave us then?

Such a drastic alteration would probably call for an equally drastic revision of what the fundamentals of the model are in order to "predict" the new reality. I find it to be totally suspicious, because that process of revising our view of what we need to predict from first principles could go on forever. There is a better way (and in my view the only real way) to find out new physics; i.e. experiment. Cosmological observations are the way to go, I would think, in the near term future, unless someone figures out how to build an accelerator the size of the universe.

 

[PAllen]

@PAllen



I know you don't have the time to respond, just wanted to say I found your post very interesting. I'd like to pick up on the above point if I may. It's a plausible sounding view and I totally agree that models are worth studying because we can learn useful mathematical things from them (AdS/CFT is particularly interesting), but to me the inherent problem is, again, the assumption that we know what the new TOE "needs to do". There could be 7 forces, not 4. Where does that leave us then?

Such a drastic alteration would probably call for an equally drastic revision of what the fundamentals of the model are in order to "predict" the new reality. I find it to be totally suspicious, because that process of revising our view of what we need to predict from first principles could go on forever. There is a better way (and in my view the only real way) to find out new physics; i.e. experiment. Cosmological observations are the way to go, I would think, in the near term future, unless someone figures out how to build an accelerator the size of the universe.

Just a quick reply to this. Maybe we should eliminate the abbreviation TOE altogether. TOE is a very arrogant claim, that though no scientific theory has ever survive 500 years, ours will.
However, isn't a TOESF (theory of everything so far) of great interest? Maxwell's theory was a TOESF that was one of the great milestones of physics. If QM got delayed a bit, GR+EM (even without Einstein's attempt at 'further unification' ) would have been a coherent TOESF (I don't think unification per se, must be a feature of a TOESF). So why do I still find getting the 4 known forces without assuming them still exciting? Not so much for the unification per se, but the promise that the framework that does this can allow coherent computation of all of them together. If string theory had already achieved this, we wouldn't be having this discussion. So what if string theory is the right approach but it is like the Riemann Hypothesis in math? I like that analogy. It is a good candidate for being the most important open problem in math, but its great difficulty has led, over time to a balance - some people are always working on it, but not at the expense of other work.

 

[Fra]

I think we agree more than you might think.

Maybe.

but it is and always has been a piecewise process, not a one shot approach, and above all, an evidence based approach.

I fully agree - inference is evolving (~piecewise) - but if people have taken this seriously, then why doesn't our current theories reflect this inference structure? To me this is significative of lack of some deep insight. (that's not to say that people should have understood 100 years ago what we understand now, I'm just saying that MAYBE time is soon ripe for such insight, although it's still absent)

We do have some of this in history, for example statistical mechanics/thermodynamics, and to a limited extent quantum mechanics, but this is just scratching the surface as I see it.

If the 'let's try to develop a complete TOE' approach was a worthy method, it would have worked for Einstein. He failed because he had incomplete knowledge. Who are we to claim that things are different now?

Maybe we mean different things by TOE. I'm not talking about "a theory that answers every question" in the sci-fi sense, I'm talking about the nice but still more modest ambition to find a coherent understanding that includes the four konwn forces. Such a TOE would NOT mean we have absolute knowledge of anything, beucase such a "TOE" should SCALE with the observer, and with it the level of undecidability. What most realist would think of as TOE is the large compelxity limt of that scaling, which corresponds to a birds view - which I think is non-physical. So that limit is not interesting. What's more interesting is the scaling itself (not the limits), and how that encodes the forces.

All respect to Einstein but I find it unfair to compare Einstein with any new ideas. The inference perspective, and the idea of rational action and evolving law are IMO a complete new way of thinking that doesn't even compare to Einsteins old style, strongly realist type thinking, of TOEs Einsteins was looking for.

Edit: I don't mean it's complete new in absolute sense, there are some people in the past who has been into this direction (shannon, ET Jaynes, as well as current people), I just mean that relative to the dominating dogmas in physics so far, its' new.

/Fredrik

 

[marcus]

Dax, since new you may not know about the private message PM feature. Upper righthand corner of screen.

My question is along the lines of what's the best thing to do. Rest, assimiliate, have time for other things (like your research ) or put some more thought into this thread---clarify issues, try for conclusions, take a new direction, risk another spate of vehement controversy,...

At the moment I feel like quietly mulling, but I'm up for other people's suggestions and initiatives.

I was amused by the debating use of the term barm cake. It impressed me as a flat-out body slam after which you really have to let your opponent get up and dust himself off.

 

[Lt_Dax]

Yes I've "ruffled a few feathers" here and there as one fellow put it, which on most occasions is probably a good thing! Nevertheless not all opponents resorted to weak arguments, so I've learned some things too.

And yes! Since the thread died down I've made much more progress at work! Such is life, doesn't mean it wasn't worth it...

 

[atyy]

Just to be clear Donoghue's exposition of gravity as an effective theory is not UV c omplete. It is a good theory of quantum gravity at low energies, and agnostic about whether the UV completion should be Asymptotic Safety or something like string theory.

Nicolai and Meissner are assume a the UV completion of their theory will be something like string theory.

 

[marcus]

Something someone said in this thread reminded me of Urs Schreiber, one of the string theorists who has moved out of physics into the math department. By coincidence he recently commented on Woit's blog, just this afternoon (22 November). I mentiond Urs earlier in this thread:

...
You ask what would happen if String moved to the math department. That might be very interesting! Then it would be competing for jobs, for citations, for seminar attendance, for the hard to define "prestige" that math people confer on each other...

...Actually some string physicists have moved over into the Math Department ... Urs Schreiber ... Now he is in the Hamburg University math dept...

That was my offhand remark, not especially considered, it would be better to let Urs speak for himself. I respect his ability despite differing viewpoint.

What he means by "spectral geometry" is what Alain Connes calls Noncommutative Geometry (NCG).

==quote Urs at Peter's blog 22 November==
...I suppose you have followed Alain Connes’ construction (here is a survey and links) of the standard model by a Kaluza-Klein compactification in spectral geometry. It unifies all standard model gauge fields, gravity as well as the Higgs as components of a single spin connection. Connes finds a remarkably simple characterizaiton of the vector bundle over the compactification space such that its sections poduce precisely the standard model particle spectrum, three chiral generations and all.

Alain Connes had computed the Higgs mass in this model under the big-desert hypothesis to a value that was in a rather remarkable chain of events experimentall ruled out shortly afterwards by the Tevatron. But the big desert is a big assumption and people got over the shock and are making better assumptions now. We’ll see.

Apart from being a nice geometrical unification of gravity and the other forces (credits ought to go all the way back to Kaluza and Klein, but in spectral geometry their orginal idea works out better) Connes’ model has some other striking features:

the total dimension of the compactified spacetime in the model as seen by K-theory is and has to be, as they showed, to produce exactly the standard model spectrum plus gravity: D= 4+6.
...
...

I think there is some impressive progress here. It is not coming out of the physics departments, though, but out of the math departments. For some reason.
==endquote==
http://www.math.columbia.edu/~woit/wordpress/?p=3292&cpage=2#comment-69896

Urs recent papers have been posted under the main headings Algebraic Topology, Quantum Algebra, Category Theory---math.AT, math.QA, and math.CT. Collaborated quite a bit with John Baez (similar mix.)

It's an interesting point, I don't how many people would agree. Another person that comes to mind is Matilde Marcolli (in NCG). She is in the Math department at Caltech. She organized that recent workshop at Oberwolfach on Spin Foam and NCG.

Another person is John Barrett at Nottingham. He does both NCG and spin foam LQG. I think he is in Mathematical Physics, I'll check. Yes, my impression of him is that he's a mathematician but maybe the fact is he is amphibious, foot in both communities, connections-collaborations-workshops in both.

I must admit distinctions blur for me. I'm not sure what to think. But what Urs said about more progress being made in math departments rang a bell.

Later the same day Urs posted again, saying in part:

==quote Urs 22 November==
because the most impressive progress in fundamental physics these days does not quite percolate through the physics community.
==endquote==

I don't know if what he says is right but it gets my attention when a ex-string physicist (of first-rate ability) says that Alain Connes' realization of the Standard Model is "the most impressive progress" in fundamental physics. And that this is not getting through to the physicists.
Connes, I guess you would say, is 100% mathematician. Never been in a physics department in his life. Like his collaborators Matilde Marcoli and Ali Chamseddine.
It sounds like he's critical of the community, would say the community got on the wrong track, and some mathematicians are on the right track. Do we take what Urs says seriously? I'm a bit puzzled. Maybe someone else can give a clear picture.

 

[atyy]

http://en.wikipedia.org/wiki/Lucasian_Professor_of_Mathematics

 

[Lt_Dax]

http://en.wikipedia.org/wiki/Lucasian_Professor_of_Mathematics

Physicists in the centuries past have often needed to be mathematicians too - Newton didn't have the luxury of being able to select the mathematical tools required to explain the motion of physical objects (observations), so he had to invent calculus. So the Lucasian chair has real meaning to these fellows as a mathematical accolade, but it doesn't mean that physics and mathematics are the same subject. I think we all agree that the standard of "proof" in mathematics (formal theory) and physics (empirical/scientific theory) are different (the few who disagreed were using such poetic license with the meaning of meaningful words such as to render the discussion meaningless, if you'll pardon my poetry).

Physicists can even make proper contributions to mathematics (e.g. Witten with topological field theory). Sometimes a person's activity can be properly described as mathematics, sometimes as physical science. It matters in terms of assigning public funding to advance our knowledge of the universe, but it doesn't matter with regards to assigning public chairs and the like.

I also noticed an earlier point someone made (mostly unrelated to this) about a parallel between the Yang-Mills controversy and the String controversy. I believe this analogy is deeply flawed and misleading. Yang-Mills theory was well suited to explain the remaining features of the SM because it only introduced a minimum of exotic concepts. Yang-Mills is an example of brilliant abstract mathematical machinery, and there is plenty of historical evidence that this is perfectly ok (abstract maths often precedes its actual use in explaining experimental oddities). Not only does ST go far beyond both minimalism and mere abstraction, but the analogy with explaining the unexplained in highly unclear - the most fantastic explanatory power of ST proposed so far is to explain that which we already have a theory for (and a real scientific one at that), the SM, and even this claim is questionable, which is something new I learned in this thread - strengthening my view further, rather than weakening it.

 

[atyy]

Does pure mathematics exist?

 

[friend]

Does pure mathematics exist?

Do propositions "exist"? Any part of reality can be described with a proposition, no matter how small. And we can say that propositions that do describe reality have the truth-value of being true. Does this mean that the purely mathematical concept of a proposition can actually exist?

 

[marcus]

...the Lucasian chair has real meaning to these fellows as a mathematical accolade, but it doesn't mean that physics and mathematics are the same subject...

Dax, I think we may agree that they are different because they are practiced by different communities, in different departments, with different standards (as you point out.)

Ultimately there are these self-selecting (somewhat structured) communities that maintain and pass along traditions---of what is interesting, what you talk about, how you resolve disagreements, what you have to take seriously and what you don't, which journals are good to publish in...etc.

History is what historians do. No verbal formula exactly defines the discipline/activity.

Mathematics is what mathematicians do. It is separate from physics precisely to the extent that the communities are separate---which means the border is fuzzy, with shifting and irregular bits of overlap, but you can distinguish two communities.

A cluster analysis of journal citations and conference attendance would probably work for someone unable to see the difference.

And if long ago or far in future you didn't/don't see two different communities, then math and physics were/will be the same.

I think dictionary prescriptions don't work because a scholarly community is semi-autonomous--as long as it can get funding it will do what it wants. There is a lot of built-in inertia---tradition, mentorship, committees, seniority, institutional inertia--so it looks stable, but still no hard and fast dictionary definition.

So it could be a useless distraction to start trying to say in abstract terms what physics "is" and what separates it from mathematics.

==========================

What I had in mind was a more pragmatic and real-world community based issue that Urs raised.

He seems to criticize the realworld physics community for being impervious, for not letting significant progress in NCG particle model percolate through it.

His criticism may be wrong. It is not about an abstraction in any case but about behavior. He points to the behavior that, as he sees it, more progress in fundamental particle theory is being made in certain math departments than is occurring in physics departments.

When you think about it, that is a pretty radical statement. Sounds almost preposterous.

Back in 2004, when I became aware of Urs, he was one of the most promising young German string theorists. Much respected, exceedingly bright. An organizer too: one of the founders of the group blog "String Theory Cafe" and the USENET board called "sci.physics.string".

His criticism is basically directed at the theoretical physics community leaders---how they have managed their resources, directed research, assigned conference time, distributed theory grants, theory postdocs, promotions. He says "how did this happen?" Connes approach to Standard Model goes back 10 years or more (the big success being 2006). So why are there not already a lot of physics postdocs and junior faculty working on it? Why does this not "percolate" in the physics departments? What is wrong with the management?
Or is it the worldview?

And Urs could be wrong. Maybe someone here will want to dismiss him, or his criticsim, or say that is not really what he meant.

 

[atyy]

Atiyah constantly makes the point that mathematics must be in contact with physics, for the health of mathematics.

And does Penrose do maths or physics?

Yes, it is funny that Penrose accused Witten of being a mathematician

Go twistors!

 

[marcus]

I looked some more at what Urs is saying and he seems to have a good point. I or someone else here may want to start a separate thread about his ideas, so it doesn't get in the way of this one.
In the meanwhile, I'll collect some links and some more quotes.
http://ncatlab.org/nlab/show/FQFT
Functorial qft is a generalization of topological qft (TQFT). Atiyah's axioms.

http://www.math.columbia.edu/~woit/wordpress/?p=3292&cpage=2#comment-70046
The following is a reply to Prof. Thomas Schaefer (NC State Raleigh)

==quote Urs at Woit's blog 23 November==

The lack of response to Connes’ theory is indeed interesting. I think the problem is that nobody has been able to explain in a language that particle theorists can understand whether this is indeed a new idea (and if so, what the new idea is) or whether this is just a complicated way to formulate an old idea (GUT’s or maybe Gravi-GUT’s).
​

Yes. Generally my impression is that the number of theoretical physicists actively aware of or at least interested in the issues of what it means to find a conceptual or even axiomatic framework for fundamental physics is currently much lower than it used to be. It seems to me that in the early 90s or so the situation has been very different. In fact from that time date a few articles by string theorists who had read Connes, had understood what he is after and had tried to connect it to string theory.

Because the curious thing is: what Connes suggests is precisely the 1-dimensional version of the very idea of perturbative string theory (which is the 2d version of an even more general idea)...
==endquote==

You can see him striving to explain Connes NCG "in a language that particle theorists can understand"--which Thomas Schaefer says nobody yet has been able to do.
Maybe Urs will be the one to do that. And the community will become more permeable. And NCG or as he calls it "spectral geometry" will be able to percolate through it better.

In case anyone wants: the homepage of Prof. Schaefer.
http://wonka.physics.ncsu.edu/~tmschaef/

 

[atyy]

Yes, I would really like to know what Barrett means in this talk about NCG and spin foams (state sum models) when he queries "Other levels: strings, membranes??" http://hep.itp.tuwien.ac.at/~miw/bzell2010/Barrett-2010.pdf (slide 13)

I also want to know what the subtext of Baez and Huerta's http://arxiv.org/abs/1003.4485 is.