Is a New Principle Necessary to Resolve Quantum Gravity and Unify Interactions?

[tom.stoer]

how can you know what I know?

I mean, I am open enough to ASK, so it should be rather clear what I don't know.

 

[Careful]

how can you know what I know?

I mean, I am open enough to ASK, so it should be rather clear what I don't know.

Therefore my conclusion
But asking is good.

 

[arivero]

Ok, you do suzy in the ''reverse'', I added 1/2 spin, you substract 1/2 spin. Just a tiny question: won't these scalar particles cause lot's of trouble?

Well, my point -which does not follow from the maths, but it is only my personal oppinion- is that these scalar particles actually exist, because they are just the classification of Regge trajectories of the hadronic strings. If you wish, call them diquarks and mesons. The only problem of the group theoretical "constuct" comes with the scalars uu, uc and cc (the extant three pairs from the 15 of 5x5=15+10, which I did not mention in the previous discussion), which fail to have a elementary partner. Only recently I have retaken this issue and I think I am close to an answer.

Of course, it could also be said that all these pairings are pieces of the fundamental string, and then yet to be discovered particles. In such view, our SU(5) would be a kind of tree level version of SO(2^5); this relationship was exposed time ago by the people looking at Chan-Paton charges in open string theory. I find this interpretation more weak, as it is agains Occam razor. But at least, it still would predict three generations.

 

[tom.stoer]

The main argument is negative, Sorkin's approach is the only one which respects Poincare symmetry (which is a very nontrivial statement). There are some positive arguments too, but they are not too compelling in my view.

In which sense do other approaches violate Poincare symmetry? And why should (linear) Poincare symmetry be a good symmetry of nature at all scales?

 

[Careful]

In which sense do other approaches violate Poincare symmetry? And why should (linear) Poincare symmetry be a good symmetry of nature at all scales?

Global Poincare symmetry should be to a very high precision a property of the universal vacuum state. None of the other approaches can achieve that although they have something like local Lorentz invariance. Why should linear Poincare symmetry be a good symmetry? See http://www.physics.princeton.edu/~mcdonald/examples/mechanics/levy-leblond_ajp_44_271_76.pdf Obviously, I, II, III and IV have to hold for vacuum. Recently, local Lorentz invariance has been tested for gamma ray bursts to an extraordinary precision, hence naturalness dictates that Lorentz symmetry must be a symmetry of nature.

Careful

 

[unusualname]

The main argument is negative, Sorkin's approach is the only one which respects Poincare symmetry (which is a very nontrivial statement). There are some positive arguments too, but they are not too compelling in my view.Obviously, I mean fundamental discreteness, everybody does so.

You're obsessed with Poincare Symmetry. If nature is discrete and maybe even has discrete time evolution then it has discrete symmetries, and anything continuous is wrong human thinking.

It's ironic that, at about the same time Planck discovered nature was discrete, Poincare discovered that (non-linear) continuous differentiable models of nature give us irresolvable problems with chaotic solutions that can't be solved analytically. Kinda two big hints to us at the same time.

there are people working on discrete models you know
http://www.phy.syr.edu/research/fundamental_theory/computation.html

 

[Careful]

You're obsessed with Poincare Symmetry.

For GOOD reasons !

 

[arivero]

It's ironic that, at about the same time Planck discovered nature was discrete, (...)

there are people working on discrete models you know
http://www.phy.syr.edu/research/fundamental_theory/computation.html

The point if discretization and continuous limit is well known by mathematicians, and this is still the kind of research of the people working on discrete models.

What Plank discovered was that _angular momentum_ is discrete. Or even more precisely, variations of angular momentum. This is relevant because the infinitesimal area swept by a particle around a central point is proportional (via the mass and an infinitesimal of time) to angular momentum. A problem already noticed by the founding fathers, and obvious during two hundred years to anybody willing to do Fourier transform (having an exponential of the product of xp, it needs to add a constant to make the whole term adimensional).
In some sense Planck constant was similar to Einstein cosmological constant: it was there, but it was ignored or taken negligible until measurement show that it had a definite, finite value.

 

[tom.stoer]

Global Poincare symmetry should be to a very high precision a property of the universal vacuum state. None of the other approaches can achieve that although they have something like local Lorentz invariance.

Why?

If you look at spin or angular momentum you can achieve a "symmetry" w.r.t. to an algebra w/o exponentiating it. That's sufficient for all observables in QM. A continuous symmetry is only required if you start with continuous spacetime for quantization. But if you forget about quantization at all but start with a discrete structure there is no reason for a continuous symmery at all.

If you accept H~0 i.e. "timeless QG" not even time evolution needs to be continuous.

[all you need is a low-energy effective theory that looks like a continuous manifold]

 

[MTd2]

Arivero, I still don`t get what you want to accomplish. You say that quarks do not have a substructure, but it seems that the leptons of the SM have a substructure when you make such construction. Is that it?

 

[arivero]

Ok, now I see what you try, let me see your original post again and redo your arguments for myself.

While you are on it, let me to try to rephrase it now in terms of SU(5). First, this SU(5) is justified either theoretically, as the unique solution to the bose/fermi pairing (post #41 above) , or empirically via the naturalness principle, which tell us that some symmetry must protect the u,d,s,c,b quarks. Perhaps also as the 5 of SO(2^5) in open superstrings.

Our pairings are the 15 of 5x5=15+10, the 24 of 5x5=24+1 and the 15 of 5x5=15+10.

If we wish, we can interpret these charges by using U={u,c} and D={d,s,b} to build SU(2) and SU(3) subgroups of SU(5). But it is more intuitive at this level to keep using the U,D and quark labels. Anyway:

The 24 is colour neutral, and we see that it contains the states for the partners of three generations of Dirac electrons and neutrinos.

15+ 15 contains the partners of three generations of Dirac quarks up and down, plus the six partners of three chiral particles.

Colour is a vector interaction. So Dirac quarks see it, and their partner states of the previous multiplet can hold colour charge. Then we have three "12+12". Adding them to the ones of the 24, we have built 96 states.

Up to here, we have built the Standard Model scalar-fermions.

The chiral particles are colour blind, and so their partners must be. So our extant problem is to explain the role of these six "3+3" states related to uu, cc, cu and their antiparticles. Such "colour blind diquarks" are a strange beast. They are also "electricity blind" in some aspect, they could see hypercharge and weak isospin, but they can not see B-L for instance. (EDIT: The point is that if we assume some U(1)_vector related to B, we can use it to get rid of some thirds and sixths, and the objects can be more manageable. Still, we need a pair of them -cc,uu?- to have charge +1 and other one -cu?-to have zero charge. The point is complicated -to me- because in the electroweak model the W+ and W- particles can be managed separately, while in the Susy electroweak model there is a fermion having two degrees of freedom in the W+ and other two in the W-. And the Z has another of it, massive but chiral)

What is peculiar, and I had not noticed until some weeks ago, is that the mass mechanism for the supersymmetrical electroweak bosons needs to eat not one scalar but two. This is because in SUSY a massless vector supermultiplet gets mass by eating a massless chiral supermultiplet. One of the bosons becomes the spin zero projection of the massive boson, and the other stays as a scalar. So our spureus degrees of freedom seem to be the number we need to break the electroweak symmetry. Then, is electroweak symmetry break also a prediction of the dual "gluon/pion"-quark model? Could be.

Note also that on this count, where the chiral partners do not see colour, the total count of bosons is 96 of the standard sfermions plus six "exotics" plus 24 gauge group, equal 126. It is very tempting to include the graviton in the "gauge group" side, to round off to 128.

 

[arivero]

Arivero, I still don`t get what you want to accomplish. You say that quarks do not have a substructure, but it seems that the leptons of the SM have a substructure when you make such construction. Is that it?

No, neither the quarks or the leptons have substructure as far as I know. I have built substructure for the scalar partners of quarks and leptons, while I kept agnostic about the substructure of quarks and leptons themselves. Furthermore, I show that this substructure has the same form that a flavour group built from the five mass-protected quarks u,d,s,c,b. And I show that the general case with any number of quarks and any number of Dirac generations only solves for three Dirac generations and five substructure quarks.

You can be confused by the word "sfermion" or "scalar-fermion" It is standard jargon to refer to the scalar partner of a fermion.

While it is not used in the maths, the main piece of the construction was to apply the naturalness principle to the masses of quarks and leptons, effectively separating the five quarks which are not in the range of the electroweak scale, and looking for a symmetry for them.

Also, is is only conjectural, not proven, that 1) the substructure is actually a superstring theory, proving that at the end (or for the very start), string theory was right. 1.5) That, incidentally, Chew was right too. 2) That the construction implies the breaking of electroweak symmetry by using the six extra bosons and 3) that the whole thing fits in a 128 dim supergravity multiplet.

 

[Careful]

Why?

If you look at spin or angular momentum you can achieve a "symmetry" w.r.t. to an algebra w/o exponentiating it. That's sufficient for all observables in QM. A continuous symmetry is only required if you start with continuous spacetime for quantization. But if you forget about quantization at all but start with a discrete structure there is no reason for a continuous symmery at all.

You can say what you want and try to cook up whatever it is you want but simple fact is that nature satisfies these laws amazingly well. For any conceivable experiment I do in near empty space, almost any boosted experiment will give me the same outcome. Now, you may try to philosophize and say that there is nothing if space is truly empty and so on and so forth (thus not obeying the standard Fock picture) and that you will be clever enough to find a theory of creation out of platonic nothing. The thing is that once you start creating it and you let your universe grow, Lorentz invariance must be pretty well satisfied on large energy scales. Let me also remind you that nobody has even managed to make sense of these discrete singular geometries in the quantum world. Even in the classical world, this is a hell of a job, see eg. the Sorkin-Rideout dynamics.

[all you need is a low-energy effective theory that looks like a continuous manifold]

Low energy? The continuum description must certainly hold up till scales of 10^{-23} meters and probably still way beyond that. Nobody has a control over the geometry at these distance scales, I would welcome the first paper after 25 years which did

Careful

 

[Careful]

While you are on it,

I will do these calculations tonight, busy now

 

[tom.stoer]

Careful, classical geometry and Poincare invariance is not and will never be tested at the Planck scale. There is no experimental guideline.

 

[Careful]

Careful, classical geometry and Poincare invariance is not and will never be tested at the Planck scale. There is no experimental guideline.

Sure, likewise we do not know whether little angles are not pushing the planets so that they follow their orbits Why don't you go and devise a theory of that ? :zzz:
Seriously, let me give an elementary course in what are good ideas in physics and what are bad ideas:
(a) a good idea always gives instantaneous pay-back. You give something up which makes life a bit more complicated, but you get rewarded by piles of gold. Giving up the continuum does not satisfy this criterion and for sure does not giving up Lorentz invariance.
(b) a bad idea is physically unmotivated, but merely stems from mathematical masturbation excercises such as : (i) help QFT has infinities, we have to cut these out! (ii) let us apply the Heisenberg uncertainty principle where we shouldn't ''we will apply it to space-time coordinates! (which have no operational meaning)'' or (iii) euh the vacuum energy diverges, we can correct this if we modify the dispersion relations (unguidedly), let's do that and proclaim that we magically turned infinity into a finite number (not that it would solve any phyiscal problem).
(i) applies to causal sets, all of them apply to the rest (and I can easily figure out some more of them).

Careful

 

[MTd2]

Arivero,

so, you have a supertring theory, but the symmetry is SU(5). The anomaly cancellation happens in d=10, and the group of symmetries is E8XE8 or SO(32). So, this is a kind of non critical string, is that it?

 

[arivero]

Arivero,

so, you have a supertring theory, but the symmetry is SU(5). The anomaly cancellation happens in d=10, and the group of symmetries is E8XE8 or SO(32). So, this is a kind of non critical string, is that it?

Yes and perhaps no exactly. http://www.slac.stanford.edu/spires/find/hep/www?j=PHLTA,B188,58 did an argument where the SO(32) group appears after world sheet quantization of five quarks. And they conjectured, in other work, that this number was coming from the dimensionality of space time.

And the construction does not use the dimensionality of space time, so it is general. If it is connected to Marcus-Sagnotti, then it is more a kind of low-energy or un-quantified aspect of the critical string.

EDIT: More important, if we accept the interpretation of bosons as QCD strings straightly -it is not needed for the math, but it is the most obvious interpretation- then we answer to the main criticism of susy, because we know what all the bosons in the sfermion sector have been already found The only BSM particles should be the partners of the gauge bosons.

 

[qsa]

Somehow I lost track.

Did we manage to identify some new principles or indications what they could be?

I guess the last papers Careful mentioned should provide some guideline; especially Sorkin is far from mainstream and could perhaps have some reasonable ideas - besides his causal sets.

My problem is that most answers seem to be in the nagative; there are indications how things will NOT work (or only to a certain approximation). But I am afraid that we here cannot be smarter than excellent thinkers out there ...

It is happening again, the thread started beautifully, but side issues took over. I have a question:do you think holography is inconsistent with the virtual particle-antiparticle picture of forces or graviton. and if that is true, shouldn't that be the most important conflict to be worked on to understand QG.

 

[arivero]

It is happening again, the thread started beautifully, but side issues took over. I have a question:do you think holography is inconsistent with the virtual particle-antiparticle picture of forces or graviton. and if that is true, shouldn't that be the most important conflict to be worked on to understand QG.

I disagree. The thread started badly, going straight againts its own tittle, menacing to focus in gravity, and avoiding any mention of the problems of BSM. After that, we got to do some post on principles; I myself invoked naturalness, and some other were mentioned. And we did also some calculations. Fine enough for a PF thread.

I will ask again: Why the heck do all of you identify BSM="lets speak of gravity"? Is it an idea of your own, or does it come from some TV series? It should be pretty obvious: if it does not contain the SM in some limit, it is not BSM.

 

[qsa]

One more Question: the ultimate background independent theory is a theory were space and time are emergent, causal set, arkani-hamed's theory and torstens theories come to mind. shouldn't somebody study the connection.

 

[qsa]

I disagree. The thread started badly, going straight againts its own tittle, menacing to focus in gravity, and avoiding any mention of the problems of BSM. After that, we got to do some post on principles; I myself invoked naturalness, and some other were mentioned. And we did also some calculations. Fine enough for a PF thread.

I will ask again: Why the heck do all of you identify BSM="lets speak of gravity"? Is it an idea of your own, or does it come from some TV series? It should be pretty obvious: if it does not contain the SM in some limit, it is not BSM.

QG stands for quantum gravity after all, but I did not imply that SM should not be considered. but only to have some themes to consolidate to reach some insight.

 

[PAllen]

I disagree. The thread started badly, going straight againts its own tittle, menacing to focus in gravity, and avoiding any mention of the problems of BSM. After that, we got to do some post on principles; I myself invoked naturalness, and some other were mentioned. And we did also some calculations. Fine enough for a PF thread.

I will ask again: Why the heck do all of you identify BSM="lets speak of gravity"? Is it an idea of your own, or does it come from some TV series? It should be pretty obvious: if it does not contain the SM in some limit, it is not BSM.

Well these forums seem to define this subject category as anything beyond GR+SM. It might be clearer to have separate subject areas (quantum gravity, BSM), with string ideas appearing in both, depending on the emphasis.

 

[atyy]

Sure, likewise we do not know whether little angles are not pushing the planets so that they follow their orbits Why don't you go and devise a theory of that ? :zzz:
Seriously, let me give an elementary course in what are good ideas in physics and what are bad ideas:
(a) a good idea always gives instantaneous pay-back. You give something up which makes life a bit more complicated, but you get rewarded by piles of gold. Giving up the continuum does not satisfy this criterion and for sure does not giving up Lorentz invariance.
(b) a bad idea is physically unmotivated, but merely stems from mathematical masturbation excercises such as : (i) help QFT has infinities, we have to cut these out! (ii) let us apply the Heisenberg uncertainty principle where we shouldn't ''we will apply it to space-time coordinates! (which have no operational meaning)'' or (iii) euh the vacuum energy diverges, we can correct this if we modify the dispersion relations (unguidedly), let's do that and proclaim that we magically turned infinity into a finite number (not that it would solve any phyiscal problem).
(i) applies to causal sets, all of them apply to the rest (and I can easily figure out some more of them).

Careful

Does the Poisson sprinkling in causal sets not bother you?

 

[tom.stoer]

do you think holography is inconsistent with the virtual particle-antiparticle picture of forces or graviton.

Holography today is - in my opinion - like scratching at the surface hiding a fundamental principle still to be fully understood; like Mach's principle was a guideline for Einstein which did not made to a fundamental principle in GR (... he must so to speak throw away the ladder, after he has climbed up on it ...); nevertheless holography is certainly some aspect of reality b/c it shows up in so different approaches so that it's hard to deny that there is something fundamental behind it.

Gravitons (including virtual particles of the gravitational field) on the other hand are mathematical artefacts of perturbation theory; of course some strong-weak dualities allow us to express certain amplitudes in certain regimes using perturbation theory but that doesn't mean that the graviton itself is a fundamental concept; there are too many scenarios where the graviton concept fails completely or is too restricted (just like the virtual gluon concept fails in non-perturbative QCD).

So for me holography is a concept or a guideline pointing towards a fundamental principle, whereas gravitons are a rather limit calculational tool valid only in a rather limited regime.

 

[MTd2]

Arivero, let me try to think now qualitatively. Each string is a mix of heterotic and Type I strings, that is, open and closed strings but there are bosonic fields on this story, formed by bound fermions. And also, fermion fields are superpartners of boson fermions. Is that it?

 

[tom.stoer]

Why the heck do all of you identify BSM="lets speak of gravity"?

BSM is of course not QG exclusively but something like SM+QG = ? So in order to talk about ? One should talk about QG as well.

Of course there may be some intermediate steps beyond SM - like SUSY (w/o QG; just like e.g. LQG is QG omitting the SM).

 

[arivero]

Well these forums seem to define this subject category as anything beyond GR+SM. It might be clearer to have separate subject areas (quantum gravity, BSM), with string ideas appearing in both, depending on the emphasis.

Indeed. And the subject of the topic should indicate the emphasis. Perhaps it was a mistake of the OP poster, but I understood that the topic of the thread was about new principles and ideas for particle theory beyond the standard model. QG and String theory are valid in this topic if they are used to construct models whose limit in some aspect is the standard model.

It is OK for me if people wants to speak of "beyond standard quantum gravity". Just create a thread with such title. But do not come to rant that a thread about Standard Model has gone offtopic because it is not addressing quantum gravity.

BSM is of course not QG exclusively but something like SM+QG = ? So in order to talk about ? One should talk about QG as well.

No! BSM is something as SM + XXX = YYY. The either the XXX or the YYY could be QG, but they could be any other thing, and we should be on topic. But if SM is not in the equation, we are off-topic.

(w/o QG; just like e.g. LQG is QG omitting the SM).

My point, indeed.

 

[atyy]

SM does include gravity!

So to say it cannot be BSM without including SM would rule out all BSM that does not "solve" QG.

 

[arivero]

Arivero, let me try to think now qualitatively. Each string is a mix of heterotic and Type I strings, that is, open and closed strings but there are bosonic fields on this story, formed by bound fermions. And also, fermion fields are superpartners of boson fermions. Is that it?

I am not sure if I parse adequately your description. Your first phrase seems an attempt to describe the different kinds of critical strings, and indeed you can have gauge and gravity multiplets, but it needs more detail.

As for superpartnering, a fermion of spin 1/2 is usually partner of two "sfermions", the s standing for "scalar". Never heard of "bfermions", but it is a good idea if you are not sure if they are spin 0, spin 1 or spin 2

 

[Careful]

What I build was different: I built 18 (=3x(3x2)) particles of charge +2/3, 18 of charge -2/3, 18 of charge -1/3 and 18 of charge +1/3 by putting quarks at the extremes of the QCD string. Again, sorry the confusion.

Let's do this step by step (I never build such stringy models so I am not going to rush here). You say you build 18 spinless bosons of charge + 1/3, this implies that you consider oriented strings (since the only way to sum up the spin degrees of freedom is by up down - down up), do QCD strings enjoy that property and so yes how does it reflect on the physics? Second question for now is, why are 9 spinless bosons of charge 4/3 forbidden?

 

[arivero]

SM does include gravity!

Sorry? Say again.

 

[atyy]

Sorry? Say again.

All SM fields are just effective. So we just add the EH term, and we are all right at all energies experimentally accessible thus far. I think electroweak and Higgs will fail way before the EH term does.

Then the question is, do you want to fix all the problems together, or hope some separate out?

 

[Careful]

Does the Poisson sprinkling in causal sets not bother you?

It is mathematically rigorously defined. If you ask me whether I think the Poisson sprinkling will have anything to do with the final theory, the answer is no. The way I think about it is as a guideline to construct realistic theories.

Careful

 

[atyy]

It is mathematically rigorously defined. If you ask me whether I think the Poisson sprinkling will have anything to do with the final theory, the answer is no. The way I think about it is as a guideline to construct realistic theories.

Careful

Well, mathematically rigourous but I feel conceptually klugey (that's subjective, of course). But how can the Poisson sprinkling not be in the final version if Lorentz invariance is to be maintained? I prefer LLI not be maintained, but I think LLI was one of causal sets motivations?