Thursday, March 04, 2010

The Box-Problem in Deformed Special Relativity

As you know, I'm presently visiting Perimeter Institute. I was asked to speak in today's Quantum Gravity group meeting about one of my recent papers:
Since it's not a technically very demanding argument, I thought writing up my thoughts in form of a blogpost has a double-benefit: It will help me organize what I'm about to say, and you'll get a summary of the paper. I will leave out some subtleties here, for details please look at the paper. This paper was the result of an argument I had about the usefulness or uselessness of thought-experiments which triggered this earlier post. In the following I will explain why combining an energy-dependent speed of light with observer-independence is inconsistent with experimentally well established theories to precision much higher than previously thought.

Deformed Special Relativity

An energy-dependent speed of light without the introduction of a preferred frame is a feature of what's become known as "Deformed Special Relativity" (DSR). If the energy-dependence is first oder in the photon's energy over the Planck energy, then it would become observable in the travel-time of highly energetic photons from distant gamma ray bursts. This prediction has received a considerable amount of attention. We previously discussed it here, here, here, here and most recently here. The reason that a tiny Planck scale effect grows to observable magnitude is that it adds up over the long distance the photons travel.

The amazing thing about this prediction is that there is actually no (agreed upon) DSR model in position space. DSR, pioneered by Giovanni Amelino-Camelia and later Kowalski-Glikman, Lee Smolin and João Magueijo, is a theory that is formulated in momentum space. It is motivated by the desire to modify the usual Lorentz-transformations such that the Planck energy is an invariant of the transformation, and it would appear the same for all observers. This works very well in momentum space. One obtains in these models a modified dispersion relation from which there follows the energy-dependence of the speed of light.

It is indeed interesting that it is possible to do that in an observer-independent way. The new transformations assure that the dispersion relation in its new form is the same for all observers. The one important equation to take from this is that also the energy-dependence of the speed of light is invariant when changing reference frames. Since the energy changes this means it's the functional relation that all observers agree on: if I change from one inertial frame to the other and the energy of a photon changes (by use of the new transformation) from E to E', then the speed of the photon changes to c'(E') which is the same as c(E'). That's what it means for the speed to be observer-independent. You cannot achieve this invariance of different speeds with ordinary Lorentz-transformations but the "deformed" ones do the trick.

But that's all in momentum space. So how was the prediction made for the photons propagating from the gamma ray burst towards Earth, arguably in position space? Well, one just used the c(E) that one obtains from the momentum space treatment. Now there's several technical arguments one can raise for why this is not a good idea (see eg this paper and references therein), but it later occurred to me there's a simpler way to see why this doesn't work. For this, let's just assume that one can indeed have c'(E') = c(E), and I'll tell you what a mess you get.

The Box Problem

Here's a very simple thought experiment. It is an extreme case but exemplifies the problem that is also present in less extreme situations. Consider you have a photon with Planck energy and a speed of light that decreases with increasing energy. Since the function c(E) should be monotonic and we don't want to introduce another scale, it's plausible that it drops to zero. So a photon with Planck energy, which is now the maximal possible energy, has zero speed, it doesn't move. I take that photon and put it inside a box. The box represents a classical, macroscopic system, one for which we know there's no funny things going on. It also takes into account that there's a finite precision to our measurements (the size of the box).

Now I change into a different reference frame, one in which the box moves relative to me. The photon's energy is by construction invariant under the transformation. If its speed is also invariant, it means the photon is in rest also in the other frame. This means however it can't remain inside the box. This is sketched in the space-time diagram below, the grey shaded area is the box, the red dashed line is the funny photon:


This peculiar transformation behavior was clear to Giovanni Amelino-Camelia already since the early days of DSR. In a 2002 paper he wrote:
"It is unclear which type of spacetime picture is required by the DSR framework. We should be prepared for a significant “revolution” in the description of spacetime ... In typical DSR theories ... one observer could see two particles ... moving at the same speed and following the same trajectory (for [this observer the particles] are “near” at all times), but the same two particles would have different velocities according to a second observer so they could be “near” only for a limited amount of time."

So far, so good. Then he writes
"For the particles we are able to study/observe, whose energies are much smaller than the Planck scale, and for the type of (relatively small) boosts we are able to investigate experimentally, this effect can be safely neglected."

And this unfortunately is not true for the following reason.

In the above figure you might not be too worried about the lines diverging. After all, it's hard to get two worldlines to be and stay perfectly parallel anyway, and it could take a very long time for them to diverge. But let's bring a third particle into the game. You can think of it as an electron that interacts with the photon inside the box which could be a detector. For simplicity think of that particle as being low energetic, such that additional DSR effects are irrelevant (that's not a crucial point). Then look at the same system from a different restframe (the green line is the electron):

What happens is that what was one space-time event (the black circle) in one restframe splits up into three different events. This generically happens if you have three lines. It is a very special case if they meet in one point. You make a small change one line (a different transformation behavior than the other lines), they'll fail to meet in one point and instead pairwise meet in three points. What this means is that not only is there no clear definition of "rest" or what it means for two particles to be "near." It's far worse: the notion of an event itself is ill-defined; it becomes an observer-dependent notion. Note that with the finite size of the box I've acknowledge that there's some fundamentally finite precision with which we can decide what's an event. But the DSR non-locality is well above that limit. The non-locality is in fact macroscopically large.

Consequences

And that's bad. That's really bad because it totally messes up particle physics in regimes where we've tested it to very high accuracy. Whether two particles did or didn't interact inside a detector better not be observer-dependent, because that interaction could have real-world consequence. You can't talk it away. In my paper the particle interaction in the box triggers a bomb. It blows up the lab in one frame and not the other.

The later sections of my paper study a more realistic setting of the same problem with actually achievable particle energies and relative velocities. It turns out that, if DSR had a first-order modification in the speed of light that was indeed observable in the measurements from gamma-ray-bursts, then the mismatch in the location of the events would be of the order of a km. Not exactly what I'd call safely negligible. The irony is that what makes this mismatch so large is what makes the time-delay for the gamma ray burst's photons observable in the first place: the long distance traveled.

The setup of the experiment in my paper might seem rather complicated, but that's because I've been very careful to chose a situation in which there's no loophole. So far nobody has found one. It follows from my considerations that DSR with an energy-dependent speed of light that has modifications to first order in the energy over Planck mass are ruled out.

It should be emphasized that the here outlined problem does not occur in theories with a modified dispersion relation that actually break Lorentz-invariance and introduce a preferred frame. But then there are tight constraints on Lorentz-invariance violations already. There are also versions of DSR where the speed of light is not energy-dependent. These form a subclass of the general case and also do not suffer from the here discussed problem. This subclass is what I've been working on for some while. Needless to say I still think it's the only case that makes sense :-)

I'm curious to hear what arguments will be raised in the discussion this afternoon.

51 comments:

muon said...

Hi,

This is very interesting. But I don't understand the need to make Mpl invariant - I thought it already was a Lorentz scalar through virtue of being an invariant mass. I imagine a two-particle interaction with a center-of-mass energy of Mpl - this is the same for all observers, at least in Special Relativity. I must be missing the point. :(

That aside, what impact does your argument make on the ultimate goal of making Mpl an invariant? You rule out a c(E) to a certain level, and thereby constrain DSR. Are there other ways of making Mpl an invariant?

regards,
Michael

Bee said...

Michael,

That's an excellent question. In fact, that's exactly what I've pointed out in this paper, and also mention in the last section of the paper I've been discussing here: To make the Planck mass an invariant on which all observers agree it doesn't have to be an invariant of the Lorentz-transformation. That's simply because the result of a Lorentz-transformation doesn't itself constitute an observable. You actually have to measure it somehow, ie you need some sort of interaction.

The com energy is of course by construction an invariant which I believe is what you're saying. But what one would like to have in addition if you believe that the Planck length is something like a fundamentally minimal length is that you can't resolve any structures to higher precision that that. For this you need some version of DSR, but not one with an energy-dependent speed of light. Best,

B.

Bee said...

Sorry, a correction: You don't need DSR to do that. You need DSR to do it if you want to stay within a QFT-particle physics framework. If you go beyond that and change the framework, you could achieve a finite resolution without modifying special relativity. You could thus say that the DSR modification does incorporate such behavior into the usual QFT framework. (In fact my motivation to look into such models came from string theory papers of Gross & Mende in the 80s.) Best,

B.

eric gisse said...

Why can't the speed of light be fungible and still preserve Lorentz invariance?

I'm thinking of the covariant (Lorentz invariance!) Proca (fungible speed of light) formalism as an example here.

Bee said...

Hi Eric,

Sorry, I don't know what you mean with "fungible." Would you explain? Best,

B.

Georg said...

"fungible" means prone to infection
by fungi, does'nt it? :=)
Seriosly, its a word from money-business
and des not apply her.

Bee said...

Hi Georg:

I see we were thinking among the same fungi-lines :-) Then I googled the word and found the following Wikipedia-entry: "Fungibility is the property of a good or a commodity whose individual units are capable of mutual substitution." Maybe I lack imagination, but while with some phantasy I can imagine a relation to mushrooms, I can't figure out what it should have to do with the speed of light. I've never heard the word before in a physics context. In any case, I think Eric had something specific in mind, so maybe he'll clarify. Best,

B.

lunogled said...

Hey bee... this, like the "soccer ball problem", looks more like a technical issue than a fundamental one.

First of all, by DSR, a photon can not have Plank energy, just like in SR a massive particle can not move at the speed of light.

The most you can have is a photon with "nearly" the Plank energy being "nearly" at rest. In this case, the size of the box also matters: If you really want to "imprison" the photon, youd also need a box of about a Planck length in size (for both good-old fashioned quantum mechanics reasons, and DSR ones). And then you can not anymore regard the box as a macroscopic object, you also need to Doubly Lorentz (DL) transform its size.

Point being... A "good" set of DL transformations can not be defined just in position space or in momentum space, they should be defined on both, in such a way that any "dimensionful microscopic" measure of the system can not reach Planck measure.

So, soccer balls are OK, because their Planck momentum gets distributed over a macroscopic size. Nearly Planck measure photons are also OK, because they would need Planck length boxes to imprison them.

You can say that such a comprehensive version of DL transformations has not been found, but I dont see any fundamental reason as to why this is impossible.
All that these Gedankenexperiments prove, is that such a formulation is necessary.

Best, Giorgio

Arun said...

Can QM mitigate some of the DSR paradox? In the case of Unruh radiation and perhaps in the case of a blackhole - infalling observer versus observer at infinity - certain "discrepancy" in the description is tolerable (sort of).

Neil B said...

This is the sort of thing I would expect to go wrong in any system that didn't follow strict, conventional SRT. I expect issues with conservation of energy (momentum too it seems.) Let's have a near-Planckian photon g1, with energy U1 in frame K. It can either hit a big resting block (momentum sink that won't move appreciably after that), or wait to be measured by another observer K' moving towards g1 and block.

Well, if p1 hits the block it imparts U1 into the block. The "story" behind how U1 got there is now lost, it is just more "energy" in a block. Then to K', this U1 is transformed to gamma*U1. But if the photon had missed, its energy is presumably not transformed to gamma*U1, but stays near U1. (Well, that's the whole point of DSR isn't it?) Similar issue for momentum p1 and gamma*p1. (I suppose the same relation p = U/c still holds in DSR in a given frame.)

BTW Bee, the Wikipedia article on DSR remains unupdated last I looked. I have an account. LMK if and what you want said, or reference, about your paper - unless someone beats me to the punch.

Neil B said...

Also, following on lunogled: REM that photons have a "coherence length" and some spread, and p,x trade-off depending on harmonic composition. It's easy to imagine generic "photons", but they aren't! It can even be detected by interferometry (that holds one path back by n periods to check for.) Some relevance I'm sure.

Bee said...

Giorgio:

I strongly recommend you read my paper before you make more off-target comments:

1) The example with the Planck-energy photon is, as I pointed out explicity, an extreme case to illustrate the basic problem (it's blog suitable). If you put in the numbers, you have a huge problem already with a GeV photon, where "huge" means of order 1km.

2) I never said anything about "imprisoning" the photon. I say if it's in rest and the box is in rest it will stay in the box, that's all.

3) The photon wouldn't have an extension of Planck length. Please see paper.

4) There's limits to where and how you can twist, modify or deform Lorentz-transformations. We have tested them pretty well for all sorts of "boxes" (planes, detectors, atoms, etc etc) and there's no deviation to be found from special relativity whatsoever.

5) This is not a technical issue. How much do I have to dumb it down that people see this so-called "theory" is sick? In my paper I have very clearly stated all my assumptions and the problem is that once you assume that c(E) does actually describe a speed in position space (as in \Delta x/Delta t) AND you want that to be observer-independent you have a problem. You don't need to know anything besides that. I have very carefully constructed the setup such that any other "DSR" effects are orders of magnitude too small to save the day.

If you want to circumvent my conclusion, you have to try harder.

Finally, let me mention that there is something really odd about me having to show that you cannot use an equation that has never been derived without running into big trouble (my argument is basically: let's assume this is true => bullshit), rather than those who used the equation having to show why it's appropriate to use it in the first place. Best,

B.

Uncle Al said...

Empiricists seek observation to falsify theory. Theorists never piss in other theorists' rice bowls because they are all wrong.

"Fungible" means "trivially equivalently replaced." Circuit boards are fungible - replace don't repair. Soldiers are trained and wear uniforms specifically to be fungible. Junior faculty are fungible.

Never make a testable prediction. SUSY proton decay was embarassed by Super-Kamiokande. Theory demands banning Gedankenexperiments and unfunding observation. The One True Church cherished Aristotle in just that way.

Neil B said...

Al, as many know (perhaps only too well ;-) I just love Gedankenexperiments! I thought that's just what theorists loved, in lieu of real experiments. But neither? BTW remember the wag (who, I forget) who said: ~ "An observation shouldn't be trusted until verified by a good theory"?

Bee said...

Dear Arun:

That's an excellent question. The short answer is: no. The long answer is in the paper: it's what I called Version 2.1 of the Box-Problem. I didn't write about it here, because this post is too long already and few people would have appreciated the full argument.

There's two quantum-effects that can come in here. One is that there's an additional contribution to the maximally possible localization of the particle at emission from a modification of the uncertainty principle which generically happens in DSR. For a GeV photon, this factor is entirely negligible (if you took it into account it would be a second-order effect). This does however solve the Box-problem in the simple version that I've discussed here, basically since there are DSR versions in which the Planck energy photon had infinite position uncertainty and wouldn't be inside the box in any sensible way in any frame.

The other contribution comes from the spread of the wave-packet during propagation. This does indeed save the day if you ask whether the people in the satellite see any nonlocal effects. But if you do moderate boosts up to \gamma=20, the problem creeps back to you.

It is actually very easy to see where the problem comes from and why you can't get rid of it: I've constructed a particular event in two ways: once by intersection of two worldlines of low-energy and/or macroscopic objects for which, if there was a DSR modification, it can be neglected for several reasons: it would be in conflict with observation (for the macroscopic bodies), the energy of the particle is too small and/or it hasn't travelled a long distance. The other way to construct the point is intersecting one "normal" worldline with the funny photon's worldline which, in order to allow c(E) to indeed be observer-independent has to transform differently. Now you have a mismatch, and you need to "hide" that mismatch in all reference frames. Or at least in those where it's observationally accessible. Now whenever you managed to hide it in one frame, you can boost into another and the problem comes back to you. That's simply a consequence of the different transformation behavior. You actually don't have to try very hard to see that it's really a large problem (large as in: it's not a Planck scale effect). Best,

B.

Bee said...

Neil: Thanks for the kind offer :-) I'll leave it up to you to decide whether it's worth mentioning in the wikipedia entry. Needless to say I think it should have been there years ago. Best,

B.

Arun said...

Dear Bee,
Thanks! Great work!
-Arun

Kay zum Felde said...

Hi Bee,

I don't understand, why the non-locality is macroscopically large ?

Best Kay

Bee said...

Hi Kay,

Roughly the effect is macroscopically large for the following reason: there's a very long distance to the gamma ray burst. It's about 4 Gpc. If you think in terms of space-time diagrams, when going from one reference frame to the other you change the slope of the worldline. Now usually the Lorentz transformations ensure that you change all slopes appropriately such that 3 lines that met in one frame in one point also meet in all the other frames. What happens here instead is that you have one line (the funny photon) that changes differently. Now you have a tiny change in slope (relative to what it would normally be), still the same emission point (the gamma ray burst), and at 4Gpc distance that tiny change has added up to macroscopically large distance.

Why is that a km for the example I've been using which is exactly the scenario for which the predictions where made: You have to note that the total delay that was predicted is about 1 sec. But in that one second the photon travels 300000km (the small contribution from the energy-dependence doesn't matter much for that distance). If you go to another reference frame (I chose a satellite in Earth orbit which moves at approx 10km/s which is about 10^-5 times (the usual) c), the mismatch comes out to be approx the total delay times the relative velocity, which is about 10^-5 seconds. (And then there's some factors that I omitted here, for details see paper.) You put in the numbers and find that the point where the particles meet in the satellite frame is about 1km outside the detector, whereas in the detector's restframe they meet inside the detector. Best,

B.

Neil B said...

Bee - tx for more about the positional paradox. Was I right about the energy problem, per 10:22 AM, March 05 ?

Bee said...

Neil:

It is very hard to say whether you're right or wrong because there's no (agreed upon) description of particle interactions in DSR either. In any case, energy and momentum conservation in DSR is non-trivial due to the non-linearity of the Lorentz-transformations. It's not just the sum of two (four) momenta that is conserved but some modified addition law (it follows from the Lorentz-transformations). That this funny addition law has to somehow vanish for macroscopic bodies and give back the usual one is what's known as the "soccer ball problem." That there's no decent theory of DSR interactions is why I haven't tried to argue along the lines you suggest, it would have been to easy for the proponents of the model to wave hands and say "All is different." (Besides this, the energy of a photon after a boost with \gamma isn't E*\gamma, but it's red/blue-shifted, relativistic Doppler.) Best,

B.

Neil B said...

Right, Bee, sorry I was careless & tx for answer. The Doppler blue shift gives gamma*(1 + v/c) times more energy to a photon approaching, not just gamma. In ordinary SRT that is consistent with the extra energy and momentum imparted to a block. (I forgot, the block's extra dv increment makes a difference in energy at block velocity.)

But it still has to be consistent. Indeed, I can't see how it could be consistent if the photon does not get more energy from blue shift - but now I know what to call the issue. All the subtleties clearly make a mess of appreciating the problem.

Kay zum Felde said...

Hi Bee,

actually I've red and I read about toposes, which might be helping and should be a solution to observer-dependent QM. As far as I've understood yet, the theory simply incorporates the observer. However it is relatively new. Chris Isham and later also Andreas Döring have done a lot in the past.

Best Kay

muon said...

I posted the following comment earlier, but somehow it seems to have gotten lost, so let me try again...

I read the paper by Mageijo and Smolin, and while it clarified many things for me, still I don't understand things too well. I hope you don't mind if I pose this question, nonetheless:

The light cone separates defines a boundary between a region of space time which is causally connected to a particle, and the region of space time which is not. The speed of light plays an essential role in calculating this boundary (the light cone).

If two observers in two different inertial frames view the same particle, they will assign a different energy to that particle, in general. The speed of light they use for calculating the light cone will be different, and so they will draw a different boundary between the causal and the non-causal regions of space time. Hence, there will be regions of space-time near their light cones for which they will not agree about having a causal link to that particle, which is nonsense I believe.

What am I missing here? (Probably lots of things!)

thanks,
Michael

Bee said...

Hi Michael,

I hadn't received your comment before so it indeed must have gotten lost. It's correct what you're saying. (Nonlocality easily also creates problems with causality.) I have no solution to your puzzle. As you can see, I also fail to make sense of the picture of space-time that these models force upon you. Best,

B.

Phil Warnell said...

Hi Bee,

Just to say thanks for taking the time to give explanation of your paper. Also to let you know as it being a paradox of sorts that I find it challenging , not just as to the implications it holds for DSR, yet rather more generally in respect to the ambitions of many to find a way to modify the impact of being left in holding to a strict adherence to invariance as a fundamental aspect of nature. I recognize that although at first paradox presents as being a barrier to progress, that ultimately often it being indicative solution may be nearer, or at least give hint to a path by which one might be found. I would wonder if this will have more to stop considering what could be wrong with invariance to rather consider what it means with having it be right. So you’ve thrown down the gauntlet so to speak and I will ne curious to see who will pick it up:-)

Best,

Phil

muon said...

Hi, how did your presentation go? Was your demonstration well received? Any insightful questions? Where will you go from here?

regards,
Michael

Bee said...

Depends on what you mean with "well received." Several people in the audience looked quite unhappy. Insightful questions: one, and that came from Lee. Where will I go from here: back to Stockholm presumably. More seriously: I've said what I wanted to say. I think it's about time people who have made big claims bother to either clarify their so-called model or correct their so-called predictions. In any case, the ball is in their court now. Best,

B.

Arun said...

In any case, the ball is in their court now.

Nah, I think you served an ace, and they are busy finding the ball wherever it is flown to, far off the court.

:)

Aaron Sheldon said...

You have my sympathies. No one likes a bubble popping nay sayer.

Despite the fact that I work in Medical Research I have nearly stopped reading the literature because much of it is so poorly thought out and so unsupported by evidence that it sends me into paroxysms of anger.

What sealed the deal for me was realizing how idiotic the vast majority of my own ideas are. Once I accepted that I myself am an idiot, I realized everyone else isn't any better off.

But what can you do? Waste your life pointing out the idiocies of others, or hold on to the distant hope of one day hitting the intellectual jackpot and having a somewhat decent idea of your own? I don't know which option is more disheartening.

Arun said...

But what can you do? Waste your life pointing out the idiocies of others, or hold on to the distant hope of one day hitting the intellectual jackpot and having a somewhat decent idea of your own? I don't know which option is more disheartening.

Practice clear thinking; enjoy your research; and whatever happens, happens, accept it.

Phil Warnell said...

Hi Bee,

I would be interested to know if your PI presentation of the Box Problem was recorded for PIRSA? Also just perhaps as a silly question, in scenarios where we have an energy dependant speed of light wouldn’t this have the consequence for photons with near zero energy (what ever that means) to be travelling at speeds much faster as to have zero energy as the limit where their speed to be infinite or instantaneous ( and with it the distance travelled) respective of other observed reference frames?

That is I guess what I’m saying if you feel that this contradiction to be in some way supportive of there being required an observer independent minimum length at the Plank energy, this seems to imply that there is a cut off in respect to a maximum length or distance which would correspond to a minimal (non zero) energy. That’s to ask what does it mean to have a minimum length tied to a maximum energy without requiring it also to be necessary in having a maximum length (distance) at a minimal energy? That is in analogy what does it mean to find that last Russian doll inside of another without their being a first one from which to begin the opening.


Best,

Phil

Bee said...

Hi Phil,

No, the group discussions are not recorded. At small energies the speed of light approaches a constant which is the usual speed of light that we've measured. If the new speed of light is a function of energy c(E), then it's in the low energy approximation c(E) \approx c(1+ \alpha (E/m_p) ), where \alpha is a constant (should be of order 1), m_p is the Planck mass and c is the usual speed of light. For small E (put in E=0), you recover the usual speed of light, thus no effect to be found there. That's not a coincidence, the model is constructed such that there's no deviation at small energies. Best,

B.

Neil B said...

Bee, I suppose you're trying to emulate LATEX formatting - but in comments of course, it just shows as the raw text. I'm not sure what your formula is here. Taking backslash as format for symbol, just written out plain we'd have:
c(E) = ~ c(1+ alpha*(E/m_p)). ["c" means the standard value.]
That implies that c gets bigger with higher energies. Doesn't that allow causality and time-order paradoxes with any signal speed above c? Did you mean, c/(1+ alpha*(E/m_p))? I would have worked more off the Wikipedia article but it isn't IMHO clear as the exposition I want to see.

Bee said...

Neil: I'm not trying to emulate anything, I know that blogger doesn't do Latex. Yes, the backslash just says I was too lazy to type α, the underscore indicates a subscript, the / is a fraction, etc. The equations are all nicely typesetted in my paper, so don't know why bother with blogger. Best,

B.

Steven Colyer said...

Neil, stop being a weenie please in this case; Bee is right.

Frankly, Neil, your "weenieness" is one of the things about you I like the most, but there's a time and a place for it and this is neither.

I left a comment at you blog btw Neil, when was the last time you checked it.

In any event, at least you have an idea that can be tested and confirmed or refuted, which is way better than many papers out there. Except you haven't written a paper on it yet, have you Neil? Why not?

Bee said...

Neil: \alpha can be larger or smaller than 0. There's nothing in the DSR setup that tells you one way or the other. Basically, the \alpha is what you'd have to measure experimentally. I already said above that yes, once you have nonlocality on a macroscopic level you've opened Pandorra's box and there's likely also problems with causality, etc. That just wasn't the point I commented on in the paper, it's bad enough already if you're throwing 50+ years of particle physics out of the window. Best,

B.

Phil Warnell said...

Hi Bee,

Thanks for the clarification as it makes a little more sense with maintaining c as the extreme limit. Still though it’s all counter intuitive with more energy resulting in less speed. It’s too bad that the group discussions are not recorded as it would have been interesting to be the fly on the wall in this instance as to hear the comments and gauge the reaction, especially in respect to a comment Smolin made which you alluded to. Then again I suppose there has to be times when everyone has a chance to not have their half baked thoughts and errors become a matter of public record:-)

I’m reminded of the stories in respect to the Fifth Solvay Conference where the discussion heated up at each breakfast with Bohr feverishly defending QM against Einstein’s thought experiments raised at each beforehand meeting at dinner. That’s to say it would be interesting to see how the attendees responded in real time when in such situations, although really not quite the same as everyone would have had plenty of time to prepare if they had read your paper. Sounds to me as Arun suggested that all they were left with was more time to practice their hand waving:-)

Best,

Phil

Bee said...

Hi Phil,

As much as I can sympathize with your wish to sneak in and hear what's going on (especially now that I'm not working at PI any more), I think it's good that there are meetings that respect some need for privacy and room to breathe. If every word you say is recorded and will appear online, it changes the atmosphere. (Some people will simply forget, but some won't). If there's any outcomes of this discussion you'll find it on the arxiv or on this blog sooner or later :-) Best,

B.

Phil Warnell said...

Hi Bee,

I agree that everyone needs times when they can simply let their hair down as media pressure would have to inhibit. Then again there are some that seem to thrive on the attention or even compete for it, with Susskind coming to mind. To tell you the truth it was this type of posture he took in his latest book that still has me finding trouble in finishing it. That’s not to say I eventually won’t, yet only to admit what I find more palatable and enjoy more are those that make evident their passion and fascination for science. rather then with themselves; ie. Randal , Greene and A.Zee. Now that I think of it I should have placed this comment in your one asking the value of books:-)

Best,

Phil

Bee said...

Aaron, Arun,

Regarding your above comments on idiocies of others.

First, I don't think it's fair to call things one doesn't believe make sense idiocies. This is science, so one has to argue with more than believe. Sometimes I thought maybe there is a way to make sense of DSR with an energy-dependent speed of light after all, but whatever I tried failed. Thus, I finally ended up showing that it has to fail. It wasn't actually so easy to pin it down as it might seem from this post.

Second, criticism is an essential part of scientific progress. There's nothing wrong with that, and I see it of part of my job to read and comment on other people's work (most of which doesn't go through this blog though). What causes problems is if too many people are ignorant of what's going on basically right next to their own research area (and justify their ignorance with tolerance), plus if people can blissfully ignore criticism on their research and happily continue to write and publish papers even though there have been fundamental flaws (or at the very least serious problems) pointed out about the topic they're working on.

You have to face that: DSR was proposed more than ten years ago. Dozens of papers have been written about it. A keyword search on the arxiv brings up more than 100, and that's not including a lot of the kappa Poincare stuff which doesn't always explicitly refer to DSR. The topic has been written about in Nature and NewScientist and so on. Repeatedly.

And that's despite the fact that it didn't take long for first problems to arise. Most notably there's the multi-particle issue and then there's the formulation in position space. You can see e.g. in Giovanni's paper that I mentioned above that it's not that these problems weren't know. What happened is that they were acknowledged and then raised to the level of "known problems," and where henceforth ignored. Look for example at the above comment from "lunogled" (who signed with Giorgio). I don't know who that is, but that's a *very* typical comment that I've heard very often: Oh, it's a technical issue. As if that would make it better.

What seems to have happened after the first years is that there began to evolve a disconnect between the mathematical physics section and the phenomenology section (with only a few people, like Lee and Giovanni in the middle). With that, the "technical issue" of making physical sense of the maths was increasingly put aside. (The one side didn't care about the physical sense, the other side didn't care about the technical issues.)

I should add that I hadn't actually worked on/followed any of that till 2006 or so (you can see it from my publication list), so I came late to the game. I couldn't make sense out of the literature, and ended up writing some papers that addressed the open problems. After that I sometimes got sent DSR papers for review and more often than not I actually had to tell the authors to at least mention and reference the still-unsolved problems of that so-called theory.

If there's one message that one should take out of my paper it's that when you're still working on DSR with an energy-dependent speed of light you're totally wasting your time unless you can come up with a very good reason how to solve the problem I've pointed out.

In any case, let me add that I can very well see the appeal of what DSR is trying to achieve. I would actually wish that it did work. It's a very straightforward extension of special relativity. I like the idea. It's simple, it's pretty. If it did work, it would mean that faster-than-(low energetic)-light travel was possible without spoiling special relativity. Unfortunately, I can't seem to find a way to reconcile it with the rest of known physics. In any case, I hope that my paper will stir up things a little and that this issue will eventually be sorted out one way or the other.

Best,

B.

Aaron Sheldon said...

I wasn't writing about the beliefs, in trenched or not.

What I was writing about was the best use of ones time. I've found, in agreement with Arun, that the best use of my time is to ignore all the things that are provably wrong, or observationally unfounded, and to concentrate on understanding the well reasoned, well proven work.

For me personally that has been studying Strong Laws of Numbers, Infinite Exchange-ability, and nearly anything in probability theory and measure theory by Kolmogorov. Fortunately, or unfortunately that tends to limit me to the more classically mature work. Which is a complete 360 from 15 years ago when I was fresh faced and wanted nothing more than to have my own latest and greatest ideas. Now I just want to understand the deep beauty in a lot of the classic material that was developed before my time.

I have found that my filter for speculation and fads in any field of science and academics has become increasingly intolerant.

I guess that makes me more of an art critic than an artist.

Bee said...

Hi Aaron,

Well, I guess I'm just more optimistic that some of the not-so-well proven, not-so-well reasoned work might turn out to be possible to prove and lead to observable consequences. Thus, I'm inclined to spend some time on other people's proposals even if they're not the most solid ones ever seen. Besides that, whether or not something is well reasoned is to some extend a subjective factor. Best,

B.

Steven Colyer said...

Woit mentions you here, Bee.

Please don't forget us small fry once you start golfing at The Masters. :-)

Bee said...

Hi Steven,

Thanks. I played golf exactly once and the only result were a lot of new holes in the green. So don't worry, it's not for me ;-) Best,

B.

Phil Warnell said...

Hi Bee,

Thought Experiment Torpedoes Variable Speed of Light Theories

-Science

Yes add my congratulations with all the others. I have one question though, after reading the headline I went through you paper again and couldn’t find where you used a torpedo in you experiment :-)

Oh yes they’re not called holes there called divots and all your suppose to do is replace the grass, no harm, no foul; unless of course you do it to the green with your putter rather than the ball, then advice you walk away quickly:-)

Beat,

Phil

P.S. This is one article I would have liked to be able to read beyond the abstract.

Bee said...

Psst. Don't tell anybody, but I'm not even sure I know what it means to "torpedo" something. I looked it up in a dictionary but it doesn't make sense. A back-forth translation came out with "to spike so.'s guns." I probably shouldn't have used the example with the bomb, too much warfare for me ;-)

Phil Warnell said...

Hi Bee,

Yes probably not the best choice of words considering your nationality, with films like Das Boot popularizing phrases like “torpedo los”. In more plain language it means you sunk the theory. Don’t worry about it though as Schrodinger is constantly criticized for his treatment of cats. Then again they shouldn’t have issue with either him or you yet take up their objections with Mother Nature as she decides outcome. There’s a expression for that as well which is “don’t shoot the messenger” :-)

Best,

Phil

Bee said...

*lol* I could have added a disclaimer to my paper that I read yesterday in Sean Carroll's book: "No animals will be harmed in our thought experiment." Besides that however, I haven't sunk anything. It's more like I'm saying better leave the boat...

Phil Warnell said...

Hi Bee,

I know it’s more in your nature to provide warning rather then threats. Perhaps in your next paper you can find still a way to have DSR work without the need to contradict invariance. Then Science’s next headline could read “ Thought Experiment Throws Physicists a Life Jacket ” :-)

Best,

Phil

stefan said...

Aha:

http://prl.aps.org/abstract/PRL/v104/i14/e140402


Cheers, Stefan