BeGroMaS: gravity was renormalizable after all, so why all the fuss?

[atyy]

No, my complaint was basically about your misleading, overblown title.

 

[Careful]

The question remains: suppose that gravity has a UV fixed point and finite dimensional critical surface---in other words is nonperturabively renormalizable---what are the consequences and why does this seem to excite a reaction?

Ok, could you tell us the newspapers and conferences where this has attrackted lots of interest from a BROAD scientific community ??

Weinberg starting around minute 52 of his 6 July 2009 CERN talk (ask if you want the video link) put it this way, in words to this effect:
===approx quote===
I wouldn't urge anyone to stop doing string theory, but it might not be needed. String theory might not be how the world is. Instead it might just be gravity and good old quantum field theory.
==endquote==

Hahaha, I hope you are intelligent enough to distinguish some teasing from a serious message, are you? He just feels this program might have a slight chance and encourages some diversity, that's all. Nothing more to it.

Also, did anyone find anything wrong with the paper of Saueressig, Machado, Groh, Benedetti?
I have been reporting Asymptotic Safety talks and papers since about 2005 (when Reuter gave an invited talk about it at Loops 2005 conference) and this paper is, in a sense, just one in a series of noteworthy AS papers. Another one I would consider a landmark paper was by Percacci Codello Rahmede around 2007-2008.
No point quibbling about relative degrees of importance. The current paper is important. Shall we discuss why?

We made the entire discussion and everyone agreed it might be a small encouraging step forward if you happen to believe in this kind of stuff. That was the conclusion of almost everyone (including the stringy guys) who brought technical arguments forwards, except you. By the way, are you such a specialist that you can judge the merit of this paper by yourself on a technical level ?

Careful

 

[marcus]

No, my complaint was basically about your misleading, overblown title.

I'm curious, what was misleading?

I thought this much was funny: "gravity renormalizable after all, so why all the fuss?"

Why all the fuss is a question. The title is jocular and meant to start a discussion.

Do you object to saying "renormalizable"? Experts in the field, like Percacci and Reuter use it to mean what I said. I have heard the phrase "nonperturb. renorm'ble" I don't know how many times! It is hard to think of you finding fault with using accepted terminology.

And I had somehow to get across that there was a new paper. BeGroMaS is a clumsy abbreviation---meant as a pointer to the other title where all four names were listed in full.


Anyway Atyy, headlines are headlines---have to compress---you should read the item before you say "misleading". I think anyway.

 

[Careful]

Why all the fuss is a question. The title is jocular and meant to start a discussion.

We had a good discussion and it is over because everything has been said.

Experts in the field, like Percacci and Reuter use it to mean what I said. I have heard the phrase "nonperturb. renorm'ble" I don't know how many times! It is hard to think of you finding fault with using accepted terminology.

Actually, scientists almost never use the word expert within the QG community because it is very pejoritive, it implies that someone who is not working on your approach is no expert and therefore his opinion is less valuable. It doesn't work like that at all.

Anyway Atyy, headlines are headlines---have to compress---you should read the item before you say "misleading". I think anyway.

We all read them and all found it to be misleading.

 

[atyy]

I object to the "was".

 

[marcus]

Gravity is renormalizable after all, so why all the fuss?

I object to the "was".

Thanks for reply, Atyy! It's hard to know sometimes if you are teasing or merely speaking with cryptic brevity

I will assume this was your real objection (not kidding) and think about it.

Maybe it would have been better to say

"Gravity is renormalizable after all, so why all the fuss?"

Hmmm. It seems minor but maybe that WOULD have been better. You might be right.

I will try that out. Elaborate on the nuances you sense, if you feel so inclined.

 

[MTd2]

"Anyone want to attain fame and fortune by performing the first nontrivial test of the gravitational asymptotic safety hypothesis?"

Jacques Distler about the Goroff and Sagnotti term.

http://golem.ph.utexas.edu/~distler/blog/archives/001585.html

 

[atyy]

I object to "is" too.

Basically, the thread title says that BGMS claim that gravity has a non-Gaussian UV fixed point. They don't.

Why do so many people hate string theory? Because of overblown claims in the early days by a some practitioners that it is the TOE.

Are you trying to do the same for AS?

 

[MTd2]

Why do so many people hate string theory? Because of overblown claims in the early days by a some practitioners that it is the TOE

Not just that. It`s the great number of out of reach experimental texts. With AS Gravity, people would just have to sit down and keep confirm that nothing goes wrong or change... A pretty dull situation.

 

[atyy]

Not just that. It`s the great number of out of reach experimental texts. With AS Gravity, people would just have to sit down and keep confirm that nothing goes wrong or change... A pretty dull situation.

AS naively is also out of reach, as it would predict a very particular running of the coupling constants. But we would only see these at energies at which we could also test string theory. But one could be lucky, as AS people hope for some low energy manifestation of "universality", just like string theorists hope for some low energy stuff like large extra dimensions.

 

[MTd2]

AS naively is also out of reach, as it would predict a very particular running of the coupling constants.

And that`s all...

 

[marcus]

Gravity was renormalizable after all, so why all the fuss?

I object to "is" too.
...

Well I would like you to be happy with the title of the thread! So it looks like the problem is really with mentioning the authors of the new paper. I'd be glad to drop the "BeGroMaS:"
It always seemed like a blemish to me, better off without it.

So now we have the title
Gravity is/was renormalizable after all, so why all the fuss?

Does that meet with approval?

 

[MTd2]

How about gravity is almost persuasively renormalizable?

The pure gravity 1st divergence is nearly tractable now. See the conclusions.

 

[marcus]

Gravity is renormalizable after all, so why the big fuss?

I'm waiting to see if Atyy likes this one:

Gravity is renormalizable after all, so why the big fuss?

"almost persuasively" makes it too long. A headline has to be brief. It almost necessarily oversiumplifies but then you can look at the article itself to get the nuances and qualifications etc. etc.

 

[S.Daedalus]

I can't speak for atyy, of course, but my problem with the title (not that anyone need or should care) is that nobody's shown (or even claimed to have shown) that gravity is nonperturbatively renormalizable, and hence, the title contains a very misleading claim.

Other than that, the highlighted paper is certainly very interesting, as is the AS approach in general; but as of now, it's just as speculative as any other QG approach, and care should be taken (IMO) not to imply otherwise.

 

[humanino]

You probably know that I keep interest in all those different approaches. To answer

Gravity is renormalizable after all, so why the big fuss?

Independently of whether nature is stringy at a fundamental level, string theory methods proved invaluable to perform effective calculations of strongly bound systems. These methods apply broadly, from condensed matter to the very birth of strings, namely hadronic systems.

On top of that, you probably also know how twistor and string methods have uncovered new symmetries, dubbed Yangian, in Yang-Mills theories in general. Witten's 2003 paper was his most cited since it was posted, last time I checked. This approach covers from on one side very practical QCD background to LHC signals which were previously thought to be impossible to calculate to on the other side "gravity as the square of Yang-Mills" which Zee has added as a new chapter to the second edition of his Nutshell.

Progress is made by everybody on every side. I remain firmly convinced that no-one is entitled to dismiss the possibility that all those insights will eventually lead to different ingredients for a final theory of QG.

 

[Careful]

Progress is made by everybody on every side. I remain firmly convinced that no-one is entitled to dismiss the possibility that all those insights will eventually lead to different ingredients for a final theory of QG.

You see, that is not how it works. One will only recognize which idea comes back (either as fundamental principle or emergent property) after one has found the correct physical principles. What you say is in a certain sense trivially true, the probability for none of the current ideas to have some resemblance to a better theory is almost as good as zero, but where you get wrong is by suggesting that by considering each of these separate ideas one is somehow going to clear up the picture. That is very wrong indeed, one needs NEW ideas, this was already know to Feynman in the 80 ties and that's why one needs to be dismissive of ''partial'' ''solutions''.

 

[tom.stoer]

one needs NEW ideas, ... and that's why one needs to be dismissive of ''partial'' ''solutions''.

Yes ... No

New idas are indeed needed, but ongoing research must not be halted. The problem is that partially there are too many speculative ideas; that's not healthy for science. We can never be sure to capture entire new physical principles when we are not able to constrain these new ideas via experiments - which is currently the most pressing problem in fidning a theory of QG or unification! Therefore we need everything from rather conservative approaches like AS (no new physics, everything is rather boring up to the Planck scale) and LQG (a rather modest change in the quantization but no new physical principle), strings (indicating that there are new physical principles, but up to now being able to identify them clearly) and perhaps approaches like twistors, causal sets, NCG etc.

There is nobody out there who can safely say that one of these approaches is definately wrong!

 

[Careful]

Yes ... No

New idas are indeed needed, but ongoing research must not be halted. The problem is that partially there are too many speculative ideas; that's not healthy for science. We can never be sure to capture entire new physical principles when we are not able to constrain these new ideas via experiments - which is currently the most pressing problem in fidning a theory of QG or unification!

No it is not! Logical consistency is the most important guideline for quantum gravity. But yeah, you are simply not willing to make that excercise because then you feel dumb. You don't know then what to believe or to think anymore; it is much more safe to stick to a purely technical language even if it doesn't mean anything.

Therefore we need everything from rather conservative approaches like AS (no new physics, everything is rather boring up to the Planck scale) and LQG (a rather modest change in the quantization but no new physical principle), strings (indicating that there are new physical principles, but up to now being able to identify them clearly) and perhaps approaches like twistors, causal sets, NCG etc.

There is nobody out there who can safely say that one of these approaches is definately wrong!

Sure, we can, just investigate inner consistency. Can these approaches start defining thing like observer, observation in a dynamical way ? Do these ''theories'' allow for realistic measurements inside universe ? Are they based on logic grounds ?

Of course, almost no one is willing to make these excercises (except people in causal set approach and thinkers like Isham and Penrose)... You are all discussing about theories who are already dead in that sense from the beginning and then you hold up your little finger and say to someone like me I can only argue by technical means. I do that and reduce the probability of such program to less than 10 % (in my metric), then you see it becomes hopeless and ask me for no go theorems. Again, this is not science, I have better things to do.

Careful

 

[qsa]

Yes ... No

New idas are indeed needed, but ongoing research must not be halted. The problem is that partially there are too many speculative ideas; that's not healthy for science. We can never be sure to capture entire new physical principles when we are not able to constrain these new ideas via experiments - which is currently the most pressing problem in fidning a theory of QG or unification! Therefore we need everything from rather conservative approaches like AS (no new physics, everything is rather boring up to the Planck scale) and LQG (a rather modest change in the quantization but no new physical principle), strings (indicating that there are new physical principles, but up to now being able to identify them clearly) and perhaps approaches like twistors, causal sets, NCG etc.

There is nobody out there who can safely say that one of these approaches is definately wrong!

All these approaches are correct in one sense or another. Each approach carry some fundamental aspect of a final "fundamental model of reality". Some ingredients are not very well cooked, very few still missing. You need a guy with a clear head-maybe you tom- to tie all the particular fundamental together. It is very hard for paid researchers(who are very smart ,but tied to publish or perish i.e tied to specific issues). cool head. maybe a month or two in the mountains, with a stack of the most fundamental papers.

 

[qsa]

No it is not! Logical consistency is the most important guideline for quantum gravity. But yeah, you are simply not willing to make that excercise because then you feel dumb. You don't know then what to believe or to think anymore; it is much more safe to stick to a purely technical language even if it doesn't mean anything.

Sure, we can, just investigate inner consistency. Can these approaches start defining thing like observer, observation in a dynamical way ? Do these ''theories'' allow for realistic measurements inside universe ? Are they based on logic grounds ?

Of course, almost no one is willing to make these excercises (except people in causal set approach and thinkers like Isham and Penrose)... You are all discussing about theories who are already dead in that sense from the beginning and then you hold up your little finger and say to someone like me I can only argue by technical means. I do that and reduce the probability of such program to less than 10 % (in my metric), then you see it becomes hopeless and ask me for no go theorems. Again, this is not science, I have better things to do.

Careful

I agree that a quantum jump type thinking is also needed. But and I mean BUT, if the approach does not yield anything in a reasonable amount of time I think it should be looked upon as a nice exercise and move to another. I have seen so many researches with these nice wacky ideas(typically smaller universities) which they have worked on for year to no avail.just like your friends. But I guess there could always be an exception however unlikely.

 

[Careful]

.I have seen so many researches with these nice wacky ideas(typically smaller universities) which they have worked on for year to no avail.just like your friends. But I guess there could always be an exception however unlikely.

One you do not know my friends, many of them come from big universities. Second, you should not mean this in a pejorative sense since many breakthroughs in science did not come from a big american/european university. Many of them come from more modest places which has it's advantages and disadvantages. Third, you pretend like you can just make quantum gravity without such considerations (and believe me, the jump-process is just a tiny thing), well you cannot. So all you said is that people at big universities typically work on something which cannot work since they do not want to give the appearance that they work on something in which they might fail personally. Better to fail collectively, then nobody will notice; it is an expensive scam to the taxpayer though.

In my opinion, it is better to work on something which has an a priori chance of larger than 20% to work out, than on something which is known to be dead by all reasonable criteria.

 

[marcus]

This is an excellent statement, Humanino!

...Independently of whether nature is stringy at a fundamental level, string theory methods proved invaluable to perform effective calculations of strongly bound systems. These methods apply broadly, from condensed matter to the very birth of strings, namely hadronic systems.

Quite true. Useful as mathematics. Even returning to historical origins: studying hadrons.

This approach covers from on one side very practical QCD background to LHC signals which were previously thought to be impossible to calculate to on the other side "gravity as the square of Yang-Mills" which Zee has added as a new chapter to the second edition of his Nutshell.

Interesting. We should have a thread about "gravity as the square of Yang-Mills" if we haven't had one already. I can sign onto the next statement you make with some slight [additions]:

Progress is [or can be] made by everybody on every side. I remain firmly convinced that no-one is entitled to dismiss the possibility that [any or] all those insights will eventually lead to different ingredients for a final theory of QG.

I heartily agree, including Causal Dynamical Triangulations, Asymptotic Safe gravity, Spectral Geometry (Connes-NCG), Spinfoams and Group Field Theory (EPRL-GFT) and Loop Quantum Cosmology.

No one is entitled to dismiss the possibility that any of these will eventually be seen to have contributed to understanding the smallscale/highenergy geometry of the universe.

Indeed although I respect string theory as a body of mathematical discoveries/methods I learned back in 2003 to be critical of the way the program is managed and suspicious of string apologists precisely because of their vehement (often ill-informed) dismissal of such alternatives.

One can like the math, but not like the statements and behavior of individuals.

This includes the habit of defending (or trying to defend) String by badmouthing Loop. For example:

Loop is just as untestable.
Loop will encounter an "even worse" landscape dilemma.
Loop necessarily breaks Lorentz (implied earlier in this very thread!)
Loop must be wrong for these and these ten reasons.
(The ha-ha contempt defense) Loop researchers are stupid because they don't realize etc.

This kind of talk is symptomatic of insecurity. And why Loop in particular? Perhaps Loop serves here as symbol of a rising tide of alternatives. Or perhaps it actually is especially threatening--I don't know for sure. In any case badmouthing rivals is a poor way to win respect for string.

 

[Careful]

I agree that a quantum jump type thinking is also needed. But and I mean BUT, if the approach does not yield anything in a reasonable amount of time I think it should be looked upon as a nice exercise and move to another. I have seen so many researches with these nice wacky ideas(typically smaller universities) which they have worked on for year to no avail.just like your friends. But I guess there could always be an exception however unlikely.

Just for your information, from all nobelprize winners from 1901 - 1911, only one came from a big university (and no american is in the list of prizewinners); it is lord Rayleigh from Cambridge university. All the rest comes from less reknown places. So, I think your statistics is very wrong.

Careful

 

[Careful]

This includes the habit of defending (or trying to defend) String by badmouthing Loop. For example:

Loop is just as untestable.

It is !

Loop will encounter an "even worse" landscape dilemma.

I have never heard that, but loop certainly will face a landscape dilemma, every approach does.

Loop necessarily breaks Lorentz (implied earlier in this very thread!)

The point is that nobody knows what loop is. Loop is double faced, you have smolin with his ideas about kappa-Minkowki which does violate Lorentz invariance, then you have Rovelli LQG in which Lorentz invariance might be broken at the quantum level (not at the classical one) and then you have Alexandrov construction which is manifestly Lorentz covariant. So you know, it is easy to claim A and NOT A and argue that nobody can say something about A.

Loop must be wrong for these and these ten reasons.

But it is and is proven to be so several times.

But what is symptomatic for loopies is that they offer no reasons PRO loop; they only have a magical word ''background independence''.

 

[marcus]

I like the four sector characterization of the research scene, from "convervative approaches like AS" to "perhaps approaches like twistors, causal sets, NCG etc". I edited the quote to bring out the four-part list aspect:

...New idas are indeed needed, but ongoing research must not be halted. The problem is that partially there are too many speculative ideas; that's not healthy for science. We can never be sure to capture entire new physical principles when we are not able to constrain these new ideas via experiments - which is currently the most pressing problem in finding a theory of QG or unification! Therefore we need everything

from rather conservative approaches like AS (no new physics, everything is rather boring up to the Planck scale)

and LQG (a rather modest change in the quantization but no new physical principle),

strings (indicating that there are new physical principles, but up to now being able to identify them clearly)

[to] perhaps approaches like twistors, causal sets, NCG etc.

There is nobody out there who can safely say that one of these approaches is definately wrong!

All these approaches are correct in one sense or another. Each approach carry some fundamental aspect of a final "fundamental model of reality". Some ingredients are not very well cooked, very few still missing. You need a guy with a clear head-maybe you tom- to tie all the particular fundamental together. It is very hard for paid researchers(who are very smart, but tied to publish or perish i.e tied to specific issues). cool head. maybe a month or two in the mountains, with a stack of the most fundamental papers.

I also like Qsa's response although I don't completely agree. It doesn't have to be amateurs. Paid researchers (like Steve Carlip at Davis) can constructively step back, take a fresh look at the whole picture, and form a new synthesis. It won't be the "final" synthesis necessarily but may contain useful fresh insight. But that's a quibble---the professional/amateur issue doesn't seem so important as long as there is active variety within institutions. Europe may be doing a better job than the USA at present, in that respect.

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

Tom, your point about TESTING and the need for constraining the new theories (lest they become hopelessly lost in speculation):

1. AS. Right now it can probably be constrained by CALCULATION to map out the critical surface. I think calculation can be a game-changer in this line of research. And eventually precise measurement of parameters---there seem to be 3---to check that gravity as found in nature actually lies on the critical surface. Weinberg raised this issue in his AS talk to Strings 2010. He diplomatically insisted he was not there to "sell" AS but quietly pointed out a way it can be tested, mentioned among the "problems" with the theory. His mildness delivers the message while disarming resistance.

2. LQG. It consistently predicts a bounce. And several papers recently indicate that it makes adequate inflation natural/generic---removing much of the need for fine tuning. This has led a bunch of people to start working on ways to test LQG, by what it says about the early universe.

3. Can't say about string.

4. Among the "perhaps" approaches, NCG makes a lot of LHC testable predictions
https://www.physicsforums.com/showthread.php?p=3042880#post3042880

The LQG bid to become less speculative and more empirical is based on the fact that it has a model of the early universe's geometry. And there is a flood of data coming in on that. If you model early universe geometry you get to enjoy that flood of data. And you also risk being ruled out by it. In any case some constraint is in the works there.

 

[tom.stoer]

marcus,

of course I should think about minor corrections regarding my statements and regarding the entire list (there is a typo, regarding strings it should read "but up to now NOT being able to identify them clearly"). Of course discussion is needed.

The situation regarding testability may not be totally hopeless; there are indeed hints regarding big bounce CMB spectra etc. such that some experimental tests may become possible. But the power of these constraints compared to standard experiments e.g. for QM and QED is poor!

Careful,

you are too negative regarding well-established research progrems; they do not only survive because of money, influence and connections ... Look at the first three decades of the last century; nobody (Planck, Einstein, Bohr, ...) was willing to kill the rstablished theories; they all started rather conservative; they always tried hard to "save" the old approaches. They hesitated to start a revolution. I think the situation is rather comparable, except for the major difference that we today have more researches and more candidate theories. They should be investigated carefully.

There was I time when I was thinking that strings are dead b/c they are not testable. Unfortunately most theories of QG are nearly untestable. So killing one theory due to such a reason means killing them all (the same applies to reasons like internal consistency; it is by no means clear whether any of these theories is consistent or not; look t QM: it was definately inconsistent over decades; then - with Heisenberg et al. - there was a breakthrough; a few years later Dirac discoverd his equation -and run into new inconsistencies; another few years later QED ...)

 

[atyy]

I'm waiting to see if Atyy likes this one:

Gravity is renormalizable after all, so why the big fuss?

"almost persuasively" makes it too long. A headline has to be brief. It almost necessarily oversiumplifies but then you can look at the article itself to get the nuances and qualifications etc. etc.

No I don't like it either.

Both parts are misleading.

The first part of the suggested thread title is misleading because this article does nothing to make AS more persuasive than before. It is a computer algorithm. Yes, I like the paper, and I like AS, and I find all the previous hints intriguing. The thread title is misleading because it gives too much credit to the present work, and does not give sufficient credit to previous work which suggests AS is worth investigating.

The second part of the suggested thread title is also misleading because it makes it seem that people were unaware that AS is a well-motivated possibility (at least from the Wilsonian framework, which is shared between AS, strings, and Rivsseaueque GFT). In fact, it is stated as the alternative hypothesis in chapter 1 of Polchinski's standard textbook on strings. AS is just difficult to investigate because although Wilson indicates that non-perturbative fixed points must be ruled out before declaring a theory unrenormalizable, it is mathematically very difficult to find non-Gaussian fixed points (and perhaps even more difficult to prove their non-existence). Furthermore, even if AS is true, by virtue of strings as a consistent theory of quantum gravity, we will have to find out how the two fit together. For example, could we be off the critical surface, so that at lowish high energies, we will see the fixed point, but at even higher energies we will see strings? This is close to what Percacci says, except that he doesn't want to bet on the proper UV completion if we are off the critical surface (and neither do I, except that strings is the only example I have at the moment).

If there's any group of QG investigators who have not taken AS seriously enough, it is Rovellian LQG (Smolin clearly investigated it early, and got stuck because of the same difficulties that remain).

 

[MTd2]

Why are you so sure string theory is a consistent QG theory? Why are you sure it is the only one consistent? Why cannot have other consistent theories?

AS gravity with other stuff can render string theory useless as a fundamental theory and it does not need string theory to be consistent, if proven correct.

 

[humanino]

You see, that is not how it works. [...] suggesting that by considering each of these separate ideas one is somehow going to clear up the picture.

This is not what I suggested. I suggest to be "careful" and respectful of other's work. If the maths is right, it might somehow prove useful in the future. You know Polyakov's quote from "gauge fields and strings"

The garbage of the past often becomes the treasure of the present (and vice-versa)

I think I have argued enough with you whether the glass is half-full or half-empty. I believe we do not really disagree, we just approach the role of this forum quite differently. Bashing other's people work caused Motl to loose his academic position. I do not care for such behavior.