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Lorentz violating severely restricted: Mqg/Mplank > 1200

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#19
Aug16-09, 07:09 AM
P: 343
Quote Quote by lumidek View Post
This approach was really falsified in 1905, by Einstein's special relativity, and I think that 104 years of tests that speak such a clear language is a long enough time for the people who reject the very relativity to be called crackpots.
Oh so this is how science works. Some one writes down a theory and then we gather evidence for that supports that theory for an arbitary amount of time, say I dunno 104 years, then we conclude that the theory is correct and unquestionable.
ensabah6
#20
Aug16-09, 10:02 PM
P: 716
Quote Quote by lumidek View Post
I don't have any respect because they don't deserve it. The Academia and professional science has been literally flooded by low-quality people who justify their existence (and funding) by brainwashing, lies, victimism, and whining. Most of this stuff is paid for by the taxpayer. Science has lost much of the standards and is becoming unworthy of respect as a whole, and I just think it is a very bad evolution.

So what I want is the return to the standards. People predicting correct things must get advantages while people predicting wrong things - and people who are generally incompetent - should never be getting the same thing, regardless of the amount of demagogy and disgusting pathetic whining like yours. They must be eliminated, otherwise the science and mankind will face for a real trouble soon.

I was always interested in all the approaches, and I know all of them in more detail than most of those you call "specialists", but that doesn't mean that I think it is correct to fill science with zombies and it is wrong for science to be overwhelmed by theories and approaches that have already been falsified. This approach was really falsified in 1905, by Einstein's special relativity, and I think that 104 years of tests that speak such a clear language is a long enough time for the people who reject the very relativity to be called crackpots.

Although there's no doubt that this is the real situation, many people even on the "correct side" fail to say things that clearly because what they're really for in science is money, and it is useful for them to team up with the crackpots. Sorry, I find it immoral and I will never join such a behavior.

Lubos,
what about condense-matter analogue approaches like Volvovik and Wen?

Perhaps the "atoms" of spacetime are discrete, but they give rise via collective emergent properties into a superfluid spacetime that appears continuous and lorentz invariant to particles (in 4D, SUSY optional)
lumidek
#21
Aug17-09, 07:25 AM
P: 92
Quote Quote by ensabah6 View Post
Lubos,
what about condense-matter analogue approaches like Volvovik and Wen?

Perhaps the "atoms" of spacetime are discrete, but they give rise via collective emergent properties into a superfluid spacetime that appears continuous and lorentz invariant to particles (in 4D, SUSY optional)
Dear ensabah6,

I don't think that you're quite understanding the observation. The observation implies that the Lorentz symmetry not only "appears" to be there but it "is" actually there, up to 100 times the Planck scale. If the Lorentz symmetry were only an artifact of emergent or collective or blah blah features of many degrees of freedom, it would be violated at the Planck scale, but it is demonstrably not violated.

All these condensed matter-like theories of spacetime were obviously falsified, too. Sorry I didn't include them to the list but I thought it was obvious that they were dead, too.

Cheers
LM
ccdantas
#22
Aug17-09, 09:33 AM
P: 344
Lubos,

In the supporting material document to that paper (Fermi collab.), the authors mention on page 24:

"A specific model of particular interest that has been proposed is a space-time foam scenario inspired by string theory that predicts a small retardation of photon velocity to first order in Eph/MQG(...)"

and cite this paper:

SI39 - Ellis, J., Mavromatos, N. E., & Nanopoulos, D. V. “Derivation of a vacuum refractive index in a stringy space time foam model”, Phys. Lett. B 665, 412–417 (2008), and references therein.

Do you have any particular comments on that paper (Ellis et al 2008)?

Thanks.

Christine
lumidek
#23
Aug17-09, 10:31 AM
P: 92
Quote Quote by ccdantas View Post
Lubos,

In the supporting material document to that paper (Fermi collab.), the authors mention on page 24:

"A specific model of particular interest that has been proposed is a space-time foam scenario inspired by string theory that predicts a small retardation of photon velocity to first order in Eph/MQG(...)"

and cite this paper:

SI39 - Ellis, J., Mavromatos, N. E., & Nanopoulos, D. V. “Derivation of a vacuum refractive index in a stringy space time foam model”, Phys. Lett. B 665, 412–417 (2008), and references therein.

Do you have any particular comments on that paper (Ellis et al 2008)?

Thanks.

Christine
Dear Christine, the most important fact about the paper is that their predictions have been falsified as cleanly as the predictions of any other kind of fundamental Lorentz-violating theories on the market. What they call the "most conservative" scenario has been proved right and it is not relevant for anything they want to speculate about in the paper.

Not even the word "stringy" could have saved them.

I respect at least some of the co-authors of this paper but I have always found such models dumb. By the way, they may have called it "stringy" but the model has nothing to do with string theory. The closest feature of this model to "string theory" is that they cite a paper or two co-written by people who are otherwise "string theorists" (like Myers, coincidentally at the Perimeter Institute), but those papers don't build on string theory, and they usually don't even pretend so (unlike your particular paper): Myers et al. just write some effective field theories. And Ellis et al. here cite many "anti-stringy" people (Amelino-Camelia, Jacobson, Gambini, Pullin, Magueijo, Smolin etc.) and essentially call their work "stringy", even though it's demonstrably not stringy: they do this trick probably to order to increase the credibility of those authors who are the real background of the paper by Ellis et al.

String theory doesn't allow any kind of "foamy" violations of the Lorentz symmetry near the Planck scale. The latter is fundamentally incorporated into the theory, and it can only be broken by configurations (e.g. B-fields) of matter, and such breaking normally starts at low energies, while the violation is *smaller* at very high energies, much like in all other kinds of spontaneous symmetry breaking. Every well-known string theorist, and every grad student who is on her way to learn string theory from the textbooks, knows this much.

I don't really believe that e.g. Ellis doesn't know, but if he doesn't, he may be getting too old. But this question - stringy or not - is less important than the basic adjective about the paper: it is wrong. So while the superficial label could be perhaps compatible, because string theory predicts no lags here, none of the details is compatible with reality, so the paper's model is exactly on the same level of falsification as any model that deliberately wanted to start with a "non-stringy" vocabulary.

Best wishes
Lubos
MTd2
#24
Aug17-09, 10:42 AM
PF Gold
P: 1,960
Quote Quote by lumidek View Post
Dear Christine, the most important fact about the paper is that their predictions have been falsified as cleanly as the predictions of any other kind of fundamental Lorentz-violating theories on the market.
No, it wasn't. They predict a distribuition for a given photon energy over a range for values of delay. That one photon that arrived to early is just one lucky that wasn't significantely delayed by the quantum foam.
lumidek
#25
Aug17-09, 11:07 AM
P: 92
Quote Quote by MTd2 View Post
No, it wasn't. They predict a distribuition for a given photon energy over a range for values of delay. That one photon that arrived to early is just one lucky that wasn't significantely delayed by the quantum foam.
I have already explained that this may only be an interpretation of a downright crackpot.

The probability that a multi-hour hour would be erased by "chance" is effectively zero, because it is the value of the probability distribution 10 sigma away from the central value etc. The photon would have to be created long time after (or before) the actual burst, and it's just negligibly unlikely.

At any rate, your new, increasingly awkward hypothesis will be easily yet gradually falsified by further bursts in the future. When Fermi sees another burst of the same kind with a 30+ GeV photon, when do you think it will probably arrive? Together with others, like in the May 2009 case, or two hours or two weeks later? This is a test of basic intelligence and if you answer b), you should seek medical help.
atyy
#26
Aug17-09, 11:48 AM
Sci Advisor
P: 8,396
Quote Quote by ensabah6 View Post
Perhaps the "atoms" of spacetime are discrete, but they give rise via collective emergent properties into a superfluid spacetime that appears continuous and lorentz invariant to particles (in 4D, SUSY optional)
Quote Quote by lumidek View Post
I don't think that you're quite understanding the observation. The observation implies that the Lorentz symmetry not only "appears" to be there but it "is" actually there, up to 100 times the Planck scale. If the Lorentz symmetry were only an artifact of emergent or collective or blah blah features of many degrees of freedom, it would be violated at the Planck scale, but it is demonstrably not violated.

All these condensed matter-like theories of spacetime were obviously falsified, too. Sorry I didn't include them to the list but I thought it was obvious that they were dead, too.
Volovik actually envisages the Lorentz breaking scale far-above the Planck scale (Eqn 4.1, http://arxiv.org/abs/0801.0724).

I don't really understand why the latest observation change the likelihood of the various theories much, because the other theories had much bigger problems even before this - Volovik had a massive graviton, Xu and Wen got quadratic and cubic graviton dispersions respectively, Wen cannot (yet?) get chiral interactions, and Horava has an extra scalar mode. So they were all already dead (are they deader now?) - but I've always found them well-motivated and really like their playful style.

Similarly with LQG - I've not found it well-motivated, because, for example, Ashtekar kinda uses Asymptotic Safety to backup one of his points in his FAQ. But then why not just pursue Asymptotic Safety, which is a logical possibility and a well-defined programme?
MTd2
#27
Aug17-09, 11:51 AM
PF Gold
P: 1,960
Don't try to convince Lubos. You will waste your time.
jal
#28
Aug17-09, 12:15 PM
jal's Avatar
P: 640
All these condensed matter-like theories of spacetime were obviously falsified, too. Sorry I didn't include them to the list but I thought it was obvious that they were dead, too.
It appears that the discussion has hit the "wall".
Discrete, continuous and at what scale.
(Planck scale or some other minimum length.)

If you have a perfect liquid, do you have confinement?

What experimental approach (CERN?) will shed light on which theories to pursue?
jal
ccdantas
#29
Aug17-09, 12:20 PM
P: 344
Lubos,

Thanks for your response.

As far as I understand, the limits found in that paper are specially worrisome for the n=1 (linear) models. On what grounds do you claim that the whole programme of LQG has been falsified by the Fermi observations? See the question #6 by Ashtekar's FAQ paper arxiv:0705.2222: "Will Lorentz invariance be violated in the low energy limit of LQG dynamics?". Please, if possible, state your counter-arguments according to the exposition presented in that paper by Ashtekar.

Quote Quote by lumidek View Post
String theory doesn't allow any kind of "foamy" violations of the Lorentz symmetry near the Planck scale.
I would like to invert the question the other way around. Would it be correct to affirm that *if* Lorentz violations were observed, string theory would be promptly falsified?

Thanks.
Christine
lumidek
#30
Aug17-09, 12:46 PM
P: 92
Dear Christine,

the research program of LQG has been falsified because an observation showed that its basic prediction about the character of spacetime - Lorentz violation at the Planck scale - is incorrect. This procedure of "falsification" is the main part of the scientific method.

For the same reason, many other classes of theories have also been falsified, including causal dynamical triangulations, emergent condensed matter-like spacetimes, Horava-Lifgarbagez gravity, and many others.

To address your particular question and to see why LQG predicts that the Lorentz invariance can't exactly hold, see either my much more concise argument, or any of dozens of papers about this very question, e.g.

http://arxiv.org/abs/gr-qc/9809038
http://arxiv.org/abs/hep-th/0108061
http://arxiv.org/abs/gr-qc/0411101
http://arxiv.org/abs/gr-qc/0403053
http://arxiv.org/abs/hep-th/0603002
http://arxiv.org/abs/hep-th/0111176
http://arxiv.org/abs/hep-th/0208193
http://arxiv.org/abs/hep-th/0501116
http://arxiv.org/abs/gr-qc/0207030
http://arxiv.org/abs/gr-qc/0207031
http://arxiv.org/abs/gr-qc/0207085
http://arxiv.org/abs/hep-th/0501091
http://arxiv.org/abs/hep-th/0605052
http://arxiv.org/abs/gr-qc/0404113

Best wishes
Lubos
lumidek
#31
Aug17-09, 12:56 PM
P: 92
Quote Quote by ccdantas View Post
Lubos,

Thanks for your response.

As far as I understand, the limits found in that paper are specially worrisome for the n=1 (linear) models. On what grounds do you claim that the whole programme of LQG has been falsified by the Fermi observations? See the question #6 by Ashtekar's FAQ paper arxiv:0705.2222: "Will Lorentz invariance be violated in the low energy limit of LQG dynamics?". Please, if possible, state your counter-arguments according to the exposition presented in that paper by Ashtekar.

I would like to invert the question the other way around. Would it be correct to affirm that *if* Lorentz violations were observed, string theory would be promptly falsified?

Thanks.
Christine
Two sentences I didn't address. Yes, if the spacetime were found to deviate from Lorentz symmetry by order-one terms at the Planck scale, string theory - as understood by real string theorists and taught by Polchinski or GSW or Becker or other textbooks would be instantly falsified.

Second point. Ashtekar arguments that he would love to have Lorentz invariance in LQG are nothing else than a wishful thinking, and all his detailed statements - especially those in between the lines - are just plain wrong. It is not true that the split of dimensions to 3+1 is the only or main feature that makes LQG violate Lorentz symmetry. It is not enough to be able to define generators on a Hilbert space if one wants the dynamical laws to be symmetric - because the former condition is kinematic and knows nothing about the dynamics, while LI invariance is a dynamical question.

Also, it is not true that one can actually define proper generators on the spin network Hilbert space. Also, it is not true that discrete area spectrum may be compatible with the Lorentz symmetry. If there is any formula for the areas that is a manifestly a sum of real discrete numbers, the theory automatically violates the Lorentz invariance - for example because areas in Lorentz-invariant theories can be both real and imaginary (spacelike vs timelike).

So all his verbal proclamations seem to be wrong and there's no calculation. So what should I do with that? It's just rubbish. The other papers at least try to calculate something, and of course, they end up with the only possible answer they can: LQG much like any other theory with a naive mechanistic discrete picture of space at the Planck scale violates the Lorentz symmetry. I am sure that you know very well that Ashtekar's paragraph is pure babbling and there exists not a single paper that would make a single calculation supporting the wishful thinking in the paragraph.

Best
Lubos
atyy
#32
Aug17-09, 01:50 PM
Sci Advisor
P: 8,396
Quote Quote by lumidek View Post
For the same reason, many other classes of theories have also been falsified, including causal dynamical triangulations, emergent condensed matter-like spacetimes, Horava-Lifgarbagez gravity, and many others.
Maybe not CDT - I believe CDT is more like computational asymptotic safety - CDT itself is not a complete theory - and asymptotic safety, although it may have other problems, surely respects Lorentz invariance?
ccdantas
#33
Aug17-09, 02:25 PM
P: 344
Quote Quote by lumidek View Post
Ashtekar arguments that he would love to have Lorentz invariance in LQG(...)
Hmm, I'm not here in defense of anyone, but I do not find evidences for that claim in his paper, only that

"In full non-perturbative quantum gravity there is no background metric whence some
care is needed to speak of Lorentz invariance. The question can only refer either to asymp-
totic symmetries in the asymptotically flat context or effective low energy descriptions. I
would expect LQG will have the first type of Lorentz invariance generated by global charges
corresponding to asymptotic symmetries. But unfortunately so far global issues related to
asymptotic flatness have received very little attention." p. 13.

Quote Quote by lumidek View Post
Also, it is not true that one can actually define proper generators on the spin network Hilbert space.
Would you please elaborate on that?

Quote Quote by lumidek View Post
So all his verbal proclamations seem to be wrong and there's no calculation. So what should I do with that? It's just rubbish.
The paper is a summary for a general audience at the 11th Marcel Grossmann meeting, so there are no detailed calculations, as expected, but I suppose some can be found in the list of references that he provides (see also his footnote #8). I would have to check on that, though.
lumidek
#34
Aug17-09, 02:40 PM
P: 92
Quote Quote by atyy View Post
Maybe not CDT - I believe CDT is more like computational asymptotic safety - CDT itself is not a complete theory - and asymptotic safety, although it may have other problems, surely respects Lorentz invariance?
There is no asymptotically safe theory of gravity, because of technical RG reasons and because of wrong scaling for the entropy at high energies that should be dominated by black holes. And even if there were one, CDT couldn't be its approximation.
lumidek
#35
Aug17-09, 02:43 PM
P: 92
Quote Quote by ccdantas View Post
Hmm, I'm not here in defense of anyone, but I do not find evidences for that claim in his paper, only that

"In full non-perturbative quantum gravity there is no background metric whence some
care is needed to speak of Lorentz invariance. The question can only refer either to asymp-
totic symmetries in the asymptotically flat context or effective low energy descriptions. I
would expect LQG will have the first type of Lorentz invariance generated by global charges
corresponding to asymptotic symmetries. But unfortunately so far global issues related to
asymptotic flatness have received very little attention." p. 13.



Would you please elaborate on that?



The paper is a summary for a general audience at the 11th Marcel Grossmann meeting, so there are no detailed calculations, as expected, but I suppose some can be found in the list of references that he provides (see also his footnote #8). I would have to check on that, though.
Dear Christine, sure, I will happily elaborate on that. One link is enough. The most cited loop quantum gravity paper in 2005

http://arxiv.org/abs/hep-th/0501114

shows that the algebra of constraints, including the Hamiltonian, doesn't close in loop quantum gravity (besides dozens of other lethal problems). So this particular Ashtekar's statement has been shown incorrect.
atyy
#36
Aug17-09, 03:25 PM
Sci Advisor
P: 8,396
Quote Quote by lumidek View Post
There is no asymptotically safe theory of gravity, because of technical RG reasons and because of wrong scaling for the entropy at high energies that should be dominated by black holes. And even if there were one, CDT couldn't be its approximation.
I understand the plausibility of the first two statements - but why can't CDT be an approximation to an asymptotically safe gravity, if such a thing existed?


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