Sabine Hossenfelder's "Multi-Particle States in Deformed Special Relativity

[marcus]

By my judgment as a bystander watching from the sidelines, this is a fantastically high quality paper.
Unless someone finds an error---which I don't think they will.

It just came out.

http://arxiv.org/abs/hep-th/0702016
Multi-Particle States in Deformed Special Relativity
Sabine Hossenfelder

"We investigate the properties of multi-particle states in Deformed Special Relativity (DSR). Starting from the Lagrangian formalism with an energy dependent metric, the conserved Noether current is derived and is found to be additive in the usual way. This quantity had previously been discarded because it was correctly realized that it does no longer obey the DSR transformations. We identify the reason for this mismatch in the fact that DSR depends only on the extensive quantity of total four-momentum instead of the energy-momentum densities as would be appropriate for a field theory. We argue that the reason for the failure of DSR to reproduce the standard transformation behavior in the well established limits is due to the missing sensitivity to the volume inside which energy is accumulated. We show that the soccer-ball problem is absent if one formulates DSR instead for the field densities. As a consequence, estimates for predicted effects have to be corrected by many orders of magnitude. Further, we derive that the modified quantum field theory implies a locality bound."

We knew Bee (as "Hossi") even before she started her blog and moved from SantaBar to Perimeter and got married etc. She used to post here at PF, and seemed to like to argue a lot. We can rightly be proud of this.

The new paper shows you what Perimeter got away from KITP or UCSB, someone who can do actually useful research. This paper (if someone doesn't find an error) actually FURTHERS things. It advances the parade.

 

[marcus]

Maybe somebody reads this and wonders why I am so happy with this new paper of Bee's

superficially it looks like a setback because it says that Glast cannot really check for DSR, but that is not how it works.

The thing is the paper (if correct) resolves something more important than just getting quick falsifiability for QG.

The issue is that QG is looking for the fundamental degrees of freedom of space time and matter from which the macro illusion of continuous spacetime emerges.

And the 64,000 question that so many people forget to ask themselves is WHAT KIND OF CONTINUUM EMERGES as a largescale illusion?

Is this continuum going to be a vintage 1850 Riemann with FLAT TANGENT spaces? Like with Minkowski flats plastered all over it?

Or is the emergent continuum going to be vintage 1920 Cartan with CURVED tangent spaces? Like with DeSitters plastered all over to approximate it locally.

Minkowski flats don't expand, and real space expands, and even accelerates (which Minkowski never heard of.) So Minkowski bandaids don't stick, and vintage Riemann probably won't work. Maybe will maybe wont, in any case the Cartan idea is extremely interesting.

But the tip of the Cartan iceberg when it first appeared to us as DSR had a problem called the SOCCERBALL.

Bee Hossenfelder just cured the Soccerball.

 

[Chronos]

But it is a prediction, and a very important one. Hossi has stuck her neck out on this and I applaud her audacty. I think she might be right. It makes sense to me.

 

[f-h]

... cured the Soccerball and unfortunately also the potentially testable predictions.

 

[jal]

Minkowski flats don't expand, and real space expands, and even accelerates (which Minkowski never heard of.) So Minkowski bandaids don't stick, and vintage Riemann probably won't work. Maybe will maybe wont, in any case the Cartan idea is extremely interesting.

I've never been able to visualise an expanding units of space and still keep the speed of light a constant for 14 B. years.
It's pretty hard to visualise different rates of expansions at different rates (because of the gravitational effects) at different places.

The simplest way, to have an expanding space, would be to keep adding units of the same size.

Problem solved.
jal

 

[hossi]

thanx

... there went another comment and vanished in virtual nirwana... 2nd try...

Hi Marcus,

thanks for mentioning my paper. I am kind of sorry for not having been around here more often, but I've been pretty stressed out. Yes, for me the paper is definitely a step forward. What is funny is that now that it's out everybody I've talked to says it sound somewhat obvious.

Chronos: Hossi has stuck her neck out on this and I applaud her audacty.

Well, as you might have guessed, it doesn't make people round here exactly happy. But I should add though that while working on the paper I came (as always) across more and more questions, so there's more to come. Despite the fact that I say the made predictions will not be observed, I find it possible that there might be other observables. For sure, we'd all like to see some experimental facts for quantum gravity.

All the best,

B.

... I hope this reply doesn't get lost again... now here we go... 'submit'...

 

[Chronos]

As you are aware, there is a reason they call the frontiers of science 'the cutting edge'. It cuts you in or out of the mix. I think you are more right than wrong, but the scales of evidence fall upon your shoulders. Are you up to that task [pushing you a bit closer to the abyss].

 

[marcus]

As you are aware, there is a reason they call the frontiers of science 'the cutting edge'. It cuts you in or out of the mix. I think you are more right than wrong, but the scales of evidence fall upon your shoulders. Are you up to that task [pushing you a bit closer to the abyss].

That is a surprising interpretation, Chronos! I didn't read Bee's paper that way at all.
they way I see it, she just corrected other people's reasoning and math mistakes.

they did some imperfect analysis of QG models and concluded that the models predict GLAST will see dispersion (energy-dependence of photon speed)
so they declared those QG models to be at risk of falsification (if dispersion is not seen). But as it happens they were mistaken.

Bee does not offer any new QG model or make any falsifiable prediction She simply corrects their analysis and says that these same QG models do NOT actually predict dispersion. So she concludes analytically that these same models (which the others thought were at risk) are NOT at risk of being falsified if GLAST fails to see dispersion.

So she herself is not risking or undergoing empirical test. Doing analysis just CHANGES THE TERMS of how we interpret the experiments vis-a-vis the models. You can maybe find a mistake in somebody's analysis but you cannot falsify it empirically.

Now if Glast sees no dispersion it is no skin off anybody's back. But if Glast DOES see dispersion this does not contradict Bee! It is just tough for the predominant mostly loop-inspired QG models because Bee has shown that they don't predict it. So if it is seen, then those models should be ashamed of themselves for not predicting it!

So I do not see Bee as at the edge of any cliff, as you do. It is just solid helpful phenom. work the way phenomenologists are supposed to do. they let theoreticans make the theories and they let experimentalists make the observations and they mediate between and decide analytically how the experimental measurements impact the models.

Also I think Jerzy K-G must be content with Bee's paper because he is a major DSR guy who has been saying for several years that as he understands DSR it does NOT predict GLAST observing dispersion. In this way Bee's paper helps to create harmony among DSR people.

My new slogan is "DSR means De Sitter Relativity" :-)

 

[hossi]

where is my mind

As you are aware, there is a reason they call the frontiers of science 'the cutting edge'. It cuts you in or out of the mix. I think you are more right than wrong, but the scales of evidence fall upon your shoulders. Are you up to that task [pushing you a bit closer to the abyss].

No need to push, I'm not afraid to jump. Let's just wait two years and see the GLAST results, then I'm either disproven or people will come back to what I've said.

Never thought about 'cutting edge' this way though... I ought to think it's nature that decides who's right and who's wrong. But you have a point there. I don't mix well anyhow ;-)

 

[marcus]

Let's just wait two years and see the GLAST results, then I'm either disproven or people will come back to what I've said.
...

As I read it, you are not disproven either way GLAST comes out. what am I missing?

If GLAST sees no dispersion then you are not disproven because you say QG does not predict dispersion.

If on other hand GLAST sees dispersion then you are not disproven. It is the QG models, which didn't predict it, that are disproven and must either be abandoned or revised.

 

[marcus]

Well, as you might have guessed, it doesn't make people round here exactly happy...

Now that is the kind of audacity I understand:rofl:
Social audacity in plenty, even surplus.

I just don't see that your paper puts you at logical risk of your statements being disproven.
And as for people "coming back" to your paper in 2 years after GLAST results, well why should they be coming back if they are unable to forget it in the meantime. It is part of an unignorable coherent pulse of papers by K-G and by L.F. that say the same thing in different ways: no dispersion.

 

[f-h]

As i understand bee she doesn't say no dispersion in the K-G sense (I have only skimmed the paper, I'll give it a proper reading later), but that the effect might be orders of magnitude smaller then anticipated, depending on the energy density rather then the energy...

My own personal intuitive reaction: It makes perfect sense in about every way if you think about it from a GR position, but seems somewhat strange if you think of a QFT constructed in the usual fock way from one-particle Hilbertspaces... these don't really know anything about densities a-priori.

 

[Chronos]

I perceive bee has added a new twist to the definition of background independence. I can see how that is unsettling to the LQG crowd.

 

[hossi]

Dear Marcus,

Our comments above must have crossed, I hadn't read yours when I wrote mine. Some clarifications:

A) Yes I say DSR does not necessarily have a modified dispersion relation, but I've said that before (repeatedly, see e.g. http://arxiv.org/abs/hep-th/0510245 or http://arxiv.org/abs/hep-th/0603032) . That's also why I say one shouldn't start with the dispersion relation, but with the symmetry in momentum space. The dispersion relation is already a contraction and one has lost some information there.

B) The new paper says (as fh correctly mentions) even if there is a modified dispersion relation, the effects are far too small to be observable.

C) As I read it, you are not disproven either way GLAST comes out. what am I missing? If GLAST finds an energy dependent time of flight and it is possible to trace this back to one of the previously discussed DSR versions (that depend on total energy rather than density), then I am disproven.
(Please note: a breaking of Lorentz-invariance, alias a preferred frame would give rise to similar effects but this is a different issue).

D) I don't think this is going to happen for the reasons stated in the paper. I should add though that I personally find it very possible that we indeed might have a preferred frame on macroscopic scales.

E) The folks are unhappy because everybody wants to see some experimental data on QG. I'm not saying there is none, I'm just saying one first needs a QFT with DSR, and a self-consistent one, that reproduces the Standard Model and soccerballs. Then we can go talk about predictions. Okay, I admit, I kind of like handwavy arguments, but one can't stop there. The soccer-ball problem is a serious one and I can't trust a theory that isn't able to solve it.

F) Now if Glast sees no dispersion it is no skin off anybody's back. True. That's why I think people will come back to what I've said. But it's unpleasant because the community has made a point out of observability (as opposed to you-know-what) and falsifiability (as opposed to you-know-what). Of course I would love to come up with a test for QG, but I just don't think it's as easy as combining some kinematic equations.

Working at it...



B.