Tuesday, August 10, 2010

An update on the status of DSR

Some months back, I summarized for you a paper that I wrote last year about a model called "Deformed Special Relativity" (DSR) with an energy-dependent yet observer-independent speed of light. In my paper, I essentially constructed a scenario that allows one to conclude these models are in conflict with observations to very high precision. Since then, several of you have been asking what happened after that, so here's a brief update.

A short version of my paper was published in PRL, and was mentioned in Science. As you can guess, this made some people quite unhappy. After all, the version of DSR I argued to be ruled out to high precision due to incompatibility with well-confirmed physics of the standard model is the one that's been claimed for a decade to allow a first glimpse on quantum gravitational effects. Frankly, I'm not even happy myself the model doesn't work because I'd very much prefer would we be able to observe something and connect our research to experiment.

Since my paper was published, Giovanni Amelio-Camelia and Lee Smolin, who have both worked on DSR, put out a few papers attempting to find a flaw in my argument. You find these papers here, here and here. My replies to these papers are also on the arxiv, you find them here, here and, the most recent one from today, here. In a nutshell, Amelino-Camelia et al's argument is just wrong due to a mistake in the re-calculation of the constraint. Smolin's two papers are more interesting in that he's doing the smart thing: trying to find an assumption I've made that can be replaced or shown to be not fulfilled to find a way DSR might work. One has to give it to him, he is actually amazingly creative. So far however, neither of his arguments has worked, though they gave me something to think about I hadn't considered in my original paper. Note also that Smolin has meanwhile updated his paper from April, while I haven't come around to update my reply yet, so don't get confused.

In any case, I'm afraid this won't be the end of the story. I'm admittedly quite tired of the whole issue since I have nothing really to win here. I'm either wrong, then I'm wrong, or I'm right, then I'm wasting my time arguing about a model that's wrong. Anyway, if you have any questions about this discussion, that's the place to ask.

30 comments:

Steven Colyer said...

My basic question is how civilly did the 3 of you get along at the recent ESQG workshop? We know that you and Lee get along well which is not surprising given lee's desire to promote an entire generation's worth of young seers such as yourself, and Lee is involved in tons of fledgling theories. I was thinking more of A-C's position, as he seems to be the primary developer (Father?) of the field.

Mostly, I hope you come back that all concerned acted like grown-ups, and no egos were deflated in the process (that would be my guess). There seems to me to be a notable lack of maturity in so many parts of Theory of late (does everyone think they're Pauli?), which OK depends on the individuals concerned, yes, but which also seems to be mostly absent in other fields, at least in Mathematics where co-operation and respect seem to trump competitiveness and self-love.

And yup, I'm kind of sad too if it turns out that DSR is not true. I've also followed it and found it quite intriguing. Your honest thoughts on same are refreshingly honest (but then you always are eh Bee?) and appreciated.

Uncle Al said...

Contemporary physical theory is the politics of continued funding. Description, prediction, and attempted empirical falsification are not in the business plan. Next in line must surely be "extensions" whose implications are devastating and protected from criticism by complexity.

The LHC Higgs search will be strung out until Enviro-whiners compassionately end European power generation. The greatest obstacle to understanding reality is not ignorance but the illusion of knowledge. Reality is not a peer vote. Reality is what it is.

Bee said...

Hi Steven,

I can report we all got along very civilly despite our disagreements. Neither Giovanni nor Lee seem to take my criticism personally, which I'm very relieved about.

Well, in the long run only the truth will lead to progress. I hope that something constructive will come out of this, maybe a new and better model that doesn't have the problems of the previous one, but presently I can't see it. Time will tell. Best,

B.

Jeremy said...

You do all realize that Lorentz invariance violating theories have been studied to death? Starting in the 1800s with trying to fix E&M, in the 1900s trying to see if SR's Lorentz invariance was approximate, in the 1910s-20s to see what GR had to say about it, in the mid 1900s with group theory and group extensions to understand how the Galleli group sits inside the Lorentz group, and if it could sit inside something else, in the 1950s-60s to understand interactions in matter which aren't Lorentz invariant, in the 1960s-70s-80s to see what symmetry breaking has to say about it and if what modern EFTs have to say about it, etc, etc...

The question of if DSR--or, generally, any other enlargement/extension/perturbation/deformation/whatever of the Lorentz group is allowable has been pretty well understood for a very long time (spoiler: the answer is no, it's never okay, as basically a mathematical theorem).

As a hint for why: the problem is that the Lorentz group acts differently than internal symmetry groups, which are allowed to be approximate/explicitly broken.

But you don't have to tell him he's wrong, everyone competent else already understands why he's wrong... and have for decades...

Steven Colyer said...

Jeremy, have you made the classic mistake of just because a mathematical solution predicts a certain thing, that it may not necessarily be true.

That's for Physicists to decide, not Mathematicians, no? Or yes?

One VERY important thing I have learned in my mere newbie 23-mo slow (so careful) return to the math phys I loved a as child, is:

Mathematicians LOVE "Infinity". Zero too, but let's talk about Infinity.

Talk to ANY Engineer or Experimentalist, dude, and they will blatantly tell you, based on experience, that "Infinity" is a mathematical concept that in our "real" world, doesn't really exist.

I mean, it's a nice concept and all. It sure makes the equations sing.

But reality says otherwise.

Max Planck knew what I'm talking about, even if nobody else does.

Uncle Al said...

Lorentz invariance contains a loophole as large as Hallandsåstunneln, and as poisonous.

Quantum field theories (QFT) with hermitian hamiltonians are invariant under the Poincaré group containing spatial reflections. Parity is a spatial reflection but is not a QFT symmetry. Covariance with respect to reflection in space and time is not required by the Poincaré group of Special Relativity or the Einstein group of General Relativity (GR). Noether's theorems require continuous symmetries or their approximation by a Taylor series. Physics is blind to metaphoric opposite shoes.

Excise and compare corresponding millimeter square patches from opposite shoes. There is no apparent difference. Repeat until the shoes are piles of dust. Nothing. The difference between opposite shoes is emergent - it is a property of the whole. A left foot cannot be detected by a a pair of socks or a left shoe. A left foot is detected by a right shoe.

Selective Lorentz invariance violation in the massed sector (photons are inert) is empirically accessible in existing apparatus by detecting a chiral vacuum background. Selective anisotropic vacuum demands selective violation of conservation of angular momentum. Bee is already in Sweden, saving December travel expenses.

http://www.mazepath.com/uncleal/erotor1.jpg
The worst it can do is succeed.

As Euclid fell to his Parallel postulate and Green's theorem (forced achiral!) does not appear in GR, so physics could be apparently seamless yet terribly wrong given an exquisitely selective footnote falsifying its illusion of knowledge. Somebody should look.

Zephir said...

/* deformations .. they generically result in a modified dispersion relation and an energy-dependent speed of light In the low energy limit, this energy dependent speed of light coincides with the speed that we have measured..*/

This perfectly follows AWT model, in which photon is density fluctuation travelling through another ones, represented with cosmic microwave background noise. The more wavelength of photon differs from wavelength of CMB, the more it will be slowed down by this noise. This correspond well with fact, microwaves aren't bend/attracted in gravity field of massive objects, neither they exhibit various red shift related effects..

Actually your case was wasted for me at the moment, when Lubos Motl has started to support it. Because Mr. Motl is sort of W. Pauli regarding his ability to predict things in realistic way. So, if Lubos supports some idea, one could be perfectly sure, this idea is just plain wrong.

With compare to Lubos, who never failed in such case.

Zephir said...

/*...It is thus puzzling how an energy-dependent speed of light that takes different values can also be observer-independent..*/

Because (photons forming the) observers are behaving in the same way, like the photon observed and they're getting heavier with increasing speed in the same way, like the photon observed. So from observer's reference frame nothing change with energy-speed dependence of photon observed. Right?

Zephir said...

Actually, from AWT follows, every dispersion relation will become violated less or more later because of emergent character of vacuum fluctuations - so that every formal theory will become wrong in sufficiently distant perspective.

So that DSR will fail at cosmological distances (for example the Doppler anisotropy of CMB is a good example of violation of dispersion equation symmetry) - but at shorter ones it can still bring a valuable correction of SR.

Zephir said...

The speed dependency of photon will lead to few fundamental predictions, in which such idea can be tested independently: the tachyonic character of radiowave photons and blue shift/gravitational collapse of Universe observed in radiowave spectrum. Actually some of these effects were observed already, they just were explained in less transparent way. For example distant radiowave sources were observed brighter with respect to their distance, then the objects shinning in visible light.

http://www.physorg.com/news190476830.html

Peter Shor said...

Are there different DSR models which can survive your criticism, or are all DSR models dead at this point?

Bee said...

Jeremy:

DSR does *not* break Lorentz Invariance, that's the whole point. For that reason it evades all the constraints you're talking about. (At least that's how the argument goes. It's actually hard to say exactly how that works, given that there is no consistent model.) Best,

B.

Bee said...

Hi Peter,

There are models of DSR that do not have an energy-dependent speed of light. They still have modifications of interactions and/or multi-particle states. I've worked on a model of that sort for a while. These are not affected by the bound I've derived because they have no issue with macroscopic locality. However, they also don't have observable effects. At least not that I know of. Same problem as always: It's not that there are no modifications, they are just too tiny to be measurable. (They do have measurable effects if working in a scenario with a lowered Planck scale.)

The story is that in the first paper I wrote on the topic, I assumed the speed of light has to remain constant because I couldn't make sense of the model otherwise. Not that I thought about it very much at that point. I learned later that what I'd been working on is closely related to DSR, just that the models that seemed to be favored there had an energy-dependent speed of light which leads to much more interesting predictions. Naturally, that got me thinking about whether one can or can't have an energy-dependent speed of light while preserving observer-independence. Best,

B.

Zephir said...

/* .. It's actually hard to say exactly how that works, given that there is no consistent model. ..*/

If the speed of photon depends on its energy, it means for example, the distant gamma rays burst are slowed down. But when all photons are slowed down in the same way, we cannot perceive it, because we have no reference particles for comparison.

Actually this effect is just a consequence of the fact, gamma ray photons ehhibit their own gravity field, so they're held together in burst even et the moment, when they're differ quite a lot in their energies (they're forming dense cluster, where lightweight photons encircling these heavier, slower ones).

The terresterial observer would see all photons ariving in the same moment - so he can get (wrong) illusion, the Lorentz symmetry wasn't violated and the dispersion dependency to energy doesn't work. In this way the light spreading fooled both proponents of Lorentz symmetry, both proponents of Lorentz asymmetry...

Phil Warnell said...
This comment has been removed by the author.
Phil Warnell said...

Hi Bee,

Thanks for the update in regards to the state of the ongoing discussion in respect to DSR and your box problem . It’s unfortunate you’ve grown somewhat tired by it all as it’s important to know whether the theories are sound or not irrespective of how much anyone would like them. Good science is as much to figure out which way it should be looking and part of it is to indentify which way is not the right one or what else is required to have things work and thus what you have done is a vital part of that process.

Best,

Phil

Lee Smolin said...

Dear Peter, Sabine and all



First, to answer Peter's query, there are forms of DSR without an energy dependent speed of light. Those are not subject to Sabine's analysis although as I show in my papers some of these, connected with non-commutative geometry, still have issues with apparent non-locality or coordinate ambiguity very far from the origin of an inertial frame's coordinates.

 But, I argue that these are coordinate ambiguities, arising from a breakdown in the procedure to extend inertial coordinates to distant events, and not physical non-localities.

Second, yes, the discussions involving a number of experts in DSR has been respectful and professional. Even if I think that Sabine's claim to have derived an experimental bound on a parameter in a theory is mistaken, I believe that her paper puts a focus on a key issue involving the interplay of lorentz invariance and non-locality in DSR theories that needs to be better understood. Some very interesting work has been done which has deepened our understanding of the proposal of DSR and its physical interpretation.


I would suggest that interested readers read the papers before making up their minds which is correct or whether more work must be done to resolve the issues. I can mention that the second of my papers on this subject, arXiv:1007.0718, was updated yesterday with a stronger argument for the main claim and a note added to address Sabine's critique posted yesterday. The appendix of that paper also gives a summary of the state of the argument as I understand it.


Thanks,

Lee

Bee said...

Dear Lee,

Thanks for your comment. As I mentioned, I'll address your update in an update of my reply. Best,

B.

Aaron Sheldon said...

Personally, I've stopped bothering with ideas that I think are wrong. It is more personally productive to ignore them, and let them die on the vine by attrition. The worst that can happen is that a few fortunate researchers get some extra funding because they are following the latest fad and bulking up their CV.

Honestly, 99% of all peer reviewed literature is forgotten within 5 years anyways; especially the results that cannot be, or are never, independently confirmed. There are just not that many ideas or experiments that make a lasting impact over generations.

Aaron Sheldon said...

Sorry one more thing, this reminds me of the old sharp phrase: "article xyz fills a necessary gap in the literature"

Phil Warnell said...

Hi Bee,

After my initial reading of both papers all I have been able to conclude thus far is the type of invariance Smolin is referring to is as you pointed out as being of the type constructed as to be explained by Albert Einstein. However despite this agreement the consequences are taken as entirely different. This is reminiscent of a dispute that J.S. Bell had with a researcher at Cern about a situation where two accelerating space ships, exactly matching each other’s accelations and having a thread between the two. This researcher and the majority of his colleagues insisted the thread would not break as a result of SR and Bell said would citing the same.. Needless to say Bell was able to demonstrate he was right and the researcher(s) wrong as the string would eventually be stressed (by Fitzgerald’s contractive effect) to breakage accordingly. This was the event that inspired J.S. Bell to write his paper “How to Teach Special Relativity”. I’m not suggesting this is the same situation here yet suspect it rests with some misunderstanding about the true nature of accepted theories in respect to their application in this context.

”Basically, Smolin is saying that we can only consider the DSR-transformation to be a local transformation. But then what is the global transformation? Well, the only global transformation that has no nonlocality neither at the detector nor at the source is one that has a fixed point both at the detector and the source, and is thus just the usual special relativistic transformation. This necessitates together with the low-energy limit of the speed of light that we are dealing with an energy-independent speed of light in ordinary special relativity6.

- Sabine Hossenfeder-Comment on arXiv:1007.0718 by Lee Smolin (Aig, 07, 2010)

”With regard to the discussion of the assumptions of this paper, it is simplest just to say that I am proposing to apply to DSR theories exactly the same operational procedure for the construction of the coordinates of an inertial observer that Einstein used in his original papers on relativity.”

-Lee Smolin-On limitations of the extent of inertial frames in non-commutative relativistic spacetimes (revised Aug, 11, 2010)

Best,

Phil

Phil Warnell said...

Hi Bee,

I meant to finish my last comment with this quote of J.S. Bell’s yet couldn’t because of space allotment limitations.

“The approach of Einstein differs from that of Lorentz in two major ways. There is a difference of philosophy , and a difference of style.The difference of philosophy is this. Since it is experimentally impossible to say which of the two uniformly moving system is really at rest, Einstein declares the notions ‘really resting’ and ‘really moving’ as meaningless. For him only the relative motion of two or more uniformly moving objects is real . Lorentz, on the other hand, preferred the view that there is indeed a state of rest, defined by the ‘aether’, even though the laws of physics conspire to prevent us from identifying it experimentally. The facts of physics do not oblige us to accept one philosophy rather then the other. And we need not accept Lorentz’s philosophy to accept a Lorentzian pedagory. Its special merit is to drive home the lesson that the laws of physics in any one reference frame account for all physical phenomena, including the observations of moving observers. And it is often simpler to work in a single frame rather than hurry after each moving object in turn.

The difference of style is that instead of inferring the experience of moving observers from known and conjectural laws of physics, Einstein starts from the hypothesis that the laws will look the same for all observers in uniform motion. This permits a very concise and elegant formulation of the theory, as so often happens when one big assumption can be made to cover several less big ones. There is no intention here to make any reservation whatsoever about the power and precision of Einstein’s approach. But in my opinion there is something to be said for taking students along the road made by Fitzgerald, Lamour, Lorentz and Poincare. The longer road sometimes gives more familiarity with the country.” .”



-J.S. Bell “How to teach special relativity”-Progress in Scientific Culture, Vol. 1, No. 2, summer 1976


Best,


Phil

Zephir said...

/*...no proposal has been yet made for how to construct a global mathematical framework that patches together the limited local non-commutative inertial frames...*/

I presume, universe could be described with trivial wave equation, just in sufficiently high number of dimensions. With increasing number of dimensions local models (low dimensional slices of the global solution) will become poorly conditioned - but they should converge mutually. This framework actually corresponds the multiverse concept of string theorists.

Anonymous Snowboarder said...

B: A very interesting discussion and while I can understand your prespective on the back and forth, I do wonder if being the one who kills a theory is not ultimately better for establishing your own bona fides than coming up with a unique new theory which may not stand or be sufficiently complete? Or at least I would think any new ideas you put out would now be taken more seriously.

Now I must get back to my work on the physics of potholes and frost heaves.. snow will be here soon!

Bee said...

Aaron,

Well, DSR was not forgotten after 5 years. Makes one wonder, doesn't it, if not that was the case because people didn't bother...

Best,

B.

Bee said...

Hi Snowboarder,

Sometimes I'm wondering how much the "being taken seriously" really has to do with the content of ones papers, or if not it's more a matter of having-been-around, like, see I have gray hairs and an office to myself now ;-) Best,

B.

Steven Colyer said...

Hi Lee,

You wrote:
Second, yes, the discussions involving a number of experts in DSR has been respectful and professional.

Phew. Glad to hear it. I hoped & suspected as much, but wasn't sure until you and Bee weighed in. I guess I'm guilty of reading The Refernotnice Frame (by Big Oil's VP of Climate Change Denial Spin, European Division) too much (it's on my feed, sorry), which I've noted can lead to depression. :( It's always nice to get away from that, and be reminded that some professionals actually act ... professionally. There may be hope for our species yet.

Now, if Giovanni would care to weigh in, we'll have a trifecta!

By the way Lee, when will your book on Time come out? Just visited Amazon and I didn't see even a pre-order. We're looking forward to it and thanks for writing.

Phil Warnell said...

Hi Steven,

I wonder how many Generals over the last few centuries would have reported the conduct of the battles they were engaged in similarly as being respectful and professional. I’m just kidding of course as Bee for instance has explained this debate has regardless of anyone’s feelings placed her in a no win situation, which sounds more like modern warfare:-)

Best,

Phil

Steven Colyer said...
This comment has been removed by the author.
Steven Colyer said...

I've studied modern warfare, Phil, as well as zero-sum (W-L) game theory by the 98% right great Hungarian-American Mathematician John von Neumann. (In the hope of course to moving on to their dual, Win-Win scenarios. This is why I switched to Business at age 23, Phil.)

This is not modern warfare, Phil. It's Professional differences of opinion. However, because it is Science, it is a logic-based careful "discussion" that will require additional time to work itself out. Last chapter ain't been written yet, my friend.

I suppose military analogies could be brought into play, but I prefer to think of military as taking advantage of Science, as opposed to being a part of it other than imposing many bureaucratic impediments toward its progress other than the Leslie Groves approach: Just let Oppenheimer call the shots, we have a serious job to do, and who the hell as been breaking into my safe?