Are superstrings the only option? What about GR approaches?

[Chronos]

Finding the right ToE, would be a wonderful achievement, but for now, I would be content with a viable quantum theory of gravity. My nagging suspiscion is that gravity resists renormalization because renormalization is inherently unsound.

 

[marcus]

Hi vanesch,
in post #48 I was mostly joking (going to the moon is a technical goal----supporting theory is an honorable thing to do and should NOT be goal-oriented: humanity should support our brilliant creative theorists to develop the theory IN THE WAY THE THEORIST THINKS IT SHOULD GO and not according to some preconception planted in the minds of Congressional committee-members)

so I should not give the impression that going to moon and supporting theory are comparable REGARDLESS OF THE MERITS----it is two very different ballgames. Like soccerfootball versus GOLF or something.

AFAIK the "ToE Dream" of circa 1985 is probably not a good idea of what a real unification in physics should look like. Visionaries and their visions get old, like everything else. Last year's Grail can be wrong for today's Quest. It's just a truism.

You mention that for 20 or 25 years the theorists didnt come up with anything much. OK, my point is that "FOR THE HONOR OF THE HUMAN MIND" we pay them to do whatever they can and want to do and we can't complain if they happen to waste their time. And maybe it wasnt a waste, maybe something was found out. We can't say the money (which for theorists is just a little money compared with for moon) was wasted because "they didnt get there". That would be to suppose that there is a welldefined place they should have gotten.

I am skeptical that the circa 1985 goal of "ToE" is even welldefined. We can see the moon but we cannot see where human physics theory is supposed to go. We will only know what the place is when one of them finally finds it.

So I'm fine with the situation. Except I think funding should go less to a preconceived program and more to the individual creative mind with his or her track record. but that is a side issue. Basically I'm happy we support theory people and want that to be generous.

And no detailed preconception like "ToE" or "moon"

What do we really KNOW about a ToE now, that we didn't know in 1985, in the different viewpoints (except that the question was harder than anticipated) ? What results are more or less established, as compared what are still open questions ?

This is an honest question. It is my impression that *some* results have been achieved in each approach, only I don't really know what.

Ask John Baez, he just gave a talk about this at Luminy.
Or ask Carlo Rovelli, they both keep track of history and use it as a guide in their thinking.
Rovelli just wrote a historical perspective paper called "unfinished revolution"
Some people could find it FRUSTRATING to read, but IMO it does address exactly what you are asking about.

Hey vanesch! you are in France. Will you by any chance be in Paris on June 14?
Smolin is talking at the Ecole Poly. It will be a perspective talk that is partly historical in nature. the present situation of fundamental theory seen in historical light. (this is at the heart of your question)

 

[marcus]

Vanesch, I think you are "smoking me out" in a nice way.
I think you may want to know what I personally think!
OK. this is my own view and other people can have all different ones, this is just my private perspective----the unification we approach now is
the GenRel-ization[/color] of quantum physics.

To do it, theorists will have to find a new description of dynamical geometry that works better than the traditional, and that new model of space will incidentally give birth to the required particles and fields of matter. Indeed they will probably recognize that it is the right model of space exactly when they see it giving birth to the appropriate fields and particles!

 

[Careful]

**Vanesch, I think you are "smoking me out" in a nice way.
I think you may want to know what I personally think!
OK. this is my own view and other people can have all different ones, this is just my private perspective----the unification we approach now is
the GenRel-ization[/color] of quantum physics.

To do it, theorists will have to find a new description of dynamical geometry that works better than the traditional, and that new model of space will incidentally give birth to the required particles and fields of matter. Indeed they will probably recognize that it is the right model of space exactly when they see it giving birth to the appropriate fields and particles! **

Since the 1927 Solvay conference, there has been only one outstanding task for theorists, that is: ``formulate a single dynamics for individual particles'' and guess what : Bohmian mechanics does not solve it. Those who manage to find a real answer to that question do not only solve all conceptual problems of quantum mechanics but probably also quantum gravity. So marcus, the question of quantum gravity was well posed since 1927; therefore it seems that in 1985 this should have still been the case. To imagine that people will see particles in the future in any Planck scale theory is like the most silly thing I ever heard, elementary particles have diameters of the order of 10^15 Planck lenghts, which implies around 10^45 Planck scale degrees of freedom for - say - an electron. You might want to figure out that renormalization transformation first.

 

[f-h]

Let me wax philosophicaly for a moment:

Some questions get answered, some questions disappear. It is not clear to me that the question you are quoting, Careful belongs to the former or latter category, and if to the latter, what the question is we must answer to make the question you recall disappear.

 

[Careful]

Let me wax philosophicaly for a moment:

Some questions get answered, some questions disappear. It is not clear to me that the question you are quoting, Careful belongs to the former or latter category, and if to the latter, what the question is we must answer to make the question you recall disappear.

This question never dissapears and it certainly has never been properly answered, actually 't Hooft adresses *precisely* this issue in his deterministic Planck scale mechanics underlying QM ; it also forms the cornerstone of the reasoning by Penrose.
Bohmian mechanics was actually known since 1919 in an even more complex (and better?) version ``la theory de double ondes'' of Prince Louis de Broglie. Trying to avoid this question inevitably leads to trouble (and the one observer universe Carlo ``loves'' so much, or some non-local dragon) - stricly speaking, a time dependent probability density *such as in quantum mechanics* is even an unsound concept. This question is so basic to a deep understanding of the world that it cannot be avoided ; trying to tell that the task of 21 century physicists is to assimilate the wonders of the 20'th century is precisly doing the opposite : the true theoretical wonder simply never occured.

 

[vanesch]

Hi vanesch,
in post #48 I was mostly joking (going to the moon is a technical goal----supporting theory is an honorable thing to do and should NOT be goal-oriented: humanity should support our brilliant creative theorists to develop the theory IN THE WAY THE THEORIST THINKS IT SHOULD GO and not according to some preconception planted in the minds of Congressional committee-members)

Well, for sure I agree with this (is about what Smolin suggests, no, that it is the people, and not the program, that should get funding). I was certainly not suggesting that one should stop funding theoretical physics.

AFAIK the "ToE Dream" of circa 1985 is probably not a good idea of what a real unification in physics should look like. Visionaries and their visions get old, like everything else. Last year's Grail can be wrong for today's Quest. It's just a truism.

Yes, but there's a problem. You cannot continue to require funding for a programme for 20 years, with the motivation that it IS the Grail, so that it is worth funding, make a lot of fuzz about it, and then conclude after 20 years, well, that it isn't, after all, the Quest. That's being unfair towards taxpayers. I agree with Smolin's vision, that it is no waste to have paid brilliant people to pursue their own ideas and not much came out of it (kind of former Bell labs policy). After all, it's society's duty to occupy its brilliant people for otherwise they make havoc in serious places
But setting up a specific *programme* for years should be more project oriented, with "deadlines" and checks on results. Of course there can be unforseen difficulties and so on, but each time, these difficulties should
give rise to a re-evaluation of the programme, and eventually its abolishment.
You cannot ask for funding for going to the moon for 10 years, and say, that after all, with all the money, you didn't succeed to build a rocket, but after all, maybe making a rowing boat is also a nice idea, no ?
If you do such a thing as a project manager, you'll "never work in this town again"

You mention that for 20 or 25 years the theorists didnt come up with anything much.

It's my impression, but then I'm rather ignorant. So that was why my question was an honest one: what *are* the results (discussed in an open and objective way, which are not oversold, or broken down, depending on to which camp one belongs).
I'll check the things you quoted, thanks, Marcus.Again, there's a difference between "paying some theorists to fiddle around with the ideas they happen to have" (which is a good thing), and "funding an ambitious research programme at the expense of all others" (which is a project oriented approach, and should hence be treated as such).

The danger of having a project-oriented funding style, but without the requirement of achieved goals at deadlines, is that you both kill the brilliant individual, and fund the bad theorist, which is just happening to be on the right band wagon.

 

[vanesch]

trying to tell that the task of 21 century physicists is to assimilate the wonders of the 20'th century is precisly doing the opposite : the true theoretical wonder simply never occured.

I think nobody should try to tell what is the task of 21th century physicists, if it is not to set up a theory - any theory - that is fully consistent and totally in predictive agreement with what is experimentally established. There are no a prioris, what counts is the end result on which the work will be judged: does it allow, or not, to be in full predictive agreement with experiment. You cannot know beforehand what *ought* to be the basic principles on which this looked-for theory must rest - in the end, there's only one criterium: agreement with experiment (and there might be a sub-criterium, when several theories are experimentally equivalent, which is a more subjective one of elegance and soberness of concept).
AS LONG AS THIS POINT IS NOT REACHED, no judgement can be made over the validity or not of a certain approach.

In the 20th century, this programme brought about GR and quantum theory (up to the standard model) - so these should be "effective" theories coming out of all 21th century ponderings (at least, up to the point where GR and QM-SM have been experimentally verified). That's *the only requirement* (apart from logical consistency) for 21th century theorists as of now. Maybe in the near future, new empirical data will come in which will go beyond GR and QM-SM: this will then be a valuable source of inspiration for our beloved theorists. However, it will not take away the burden to establish the effective emergence of GR and QM-SM (at least within their domains of validity).

Any approach that has not reached at least that stage is still in the "twilight zone", and I think nobody can tell beforehand why a certain approach *should* work, as long as the result isn't on the table. Of course you can have your personal, intimate convictions, you can think of yourself much smarter than all the others (and the others think the same of course), but your guess is as good as anybody's guess. That's probably why the battles are so harsh, the words are so hard and the emotions run so high: we're not talking science, we're talking religion and faith.

If history is any guidance, without empirical inspiration, people never succeeded in "taking the next step", so I'm pretty pessimistic about it being different this time.
Newton had Kepler's results, Maxwell had Faraday's results,
Einstein had the MM results and the Mercury perihelion shift,
the QM founders had a lot of spectroscopy results, and for QFT, there were results like the Lamb shift, a lot of particle collision data,... The standard model is based upon gigabytes of collider data...

 

[Careful]

What I am saying is even much more basic : quantum mechanics is incomplete as a physical theory and is lacking a sound spacetime interpretation (it does not even make sense to speak about the quantum mechanics of the universe). That is no matter of personal taste or the desire to know better, this is a simple fact (and we better recognize it as such) of life. And as you probably know, the lamb shift, the g-factor of the electron and so forth have been accurately computed from an *exact, finite* firstly quantized theory; that is the Barut self field approach (and spectroscopy results never have been a good reason to abolish classical reasoning, people knew already about non linear dynamical systems with a discrete number of attractors in that time).

In science, it has never been a rewarding policy to put your head in the sand and it never shall be. Neither do I say that everyone needs to be occupied with this question, but it is a cynical fact of life that almost nobody even *acknowledges* it anymore. Even worse, there is a whole program to dessiminate this kind of B.S. The ``solutions'' proposed today for QG were in one form or another the emergency scenario's 30 years ago. The most amazing result so far (at least up till 10 months ago) IMO comes out of CDT, where it has been shown last year that on short scales the ``would be'' universe is on average two dimensional, thereby making a possible bridge with spin foam models (and this is not a rigorous result yet).

Cheers,

Careful

 

[vanesch]

What I am saying is even much more basic : quantum mechanics is incomplete as a physical theory and is lacking a sound spacetime interpretation (it does not even make sense to speak about the quantum mechanics of the universe). That is no matter of personal taste or the desire to know better, this is a simple fact (and we better recognize it as such) of life. And as you probably know, the lamb shift, the g-factor of the electron and so forth have been accurately computed from an *exact, finite* firstly quantized theory; that is the Barut self field approach (and spectroscopy results never have been a good reason to abolish classical reasoning, people knew already about non linear dynamical systems with a discrete number of attractors in that time).

You're misreading what I want to say. I'm not saying that some fundamental principles of quantum theory are everlasting (it might, it might not). What is an undeniable fact is that quantum theory, as it stands now, has a huge list of experimental confirmations (even though you could call this "quantum theory with the right mix of intuition", let's call it "practical quantum theory") that's no proof of the correctness of its basic postulates of course ; but any potential competitor must first show at least the same list of success before being taken seriously, no matter what are ITS fundamental principles - which might take over something, or nothing at all, from the fundamental principles of quantum theory. The ONLY way to do so in a practical way, is to *derive* the current practical quantum formalism as an approximation, no matter what are its foundations.

Science has ALWAYS worked that way: the "former successful theory" has always been a limiting case of the "new god in town".

You make from these isolated cases (Barut's self field theory), Santos' SED ..., some hints about discreteness arising from continuous nonlinear systems... what you want. If you want to read a deep message in it, be my guest, I'm not going against it. But understand that others might find this also intruiguing without necessarily seeing this as any kind of "proof of what ought to be the correct approach". That said, I can see the utility (up to some point) in trying to find more of these examples. Whether they will remain curiosa, or an important discovery, is an open question.

I repeat: as long as the new theory (with no matter what fundamental principles, based upon the superposition principle or not, return to classical or not, something completely new and unexpected or not) has not derived AT LEAST compatibility with the *practical and empirically confirmed* parts of currently existing theories (GR and "practical QM"), then all arguments about the correctness of its starting principles is all just faith, religion, intuition, gut feeling or whatever you like to call it. It is very difficult to argue over that - hence all the "religious wars" going on.
One cannot deny the empirical success of "practical quantum theory". That doesn't mean necessarily that in its foundations it is not totally misguided - it might be, as it might not be. Everybody is free to LOOK for other approaches, but this is, to a high degree, a totally personal matter.

In science, it has never been a rewarding policy to put your head in the sand and it never shall be. Neither do I say that everyone needs to be occupied with this question, but it is a cynical fact of life that almost nobody even *acknowledges* it anymore.

Well, it has also not been a very rewarding policy in science to neglect empirical success :-) Look at GR: Einstein knew that he needed to find Newton's gravity as a limiting case. In the same way, *practical* quantum theory restores classical results in many examples (the "practical part" being the judicious choice of how and when to apply Born's rule).
As such, the very first indication of the potential correctness of a new paradigm is the derivation (even if some handwaving is needed) of all these limiting cases. As long as that is not achieved, one can hardly speak of "results" and hence of an indication that the paradigm has a leg to stand on. Only your intuition and faith are your guiding principles until that point is reached. And what's your intuition and faith worth more, or less, than anyone else's.

It is like trying to argue over the right approach to find a proof of a newly postulated theorem or its contrary. As long as the proof is not written down explicitly, there's no real way of knowing which approach is finally going to work. One CAN however rather quickly establish which approaches are certainly NOT going to work, but until the final proof is written down, one cannot be sure that one or the other strategy is going to work.

 

[Careful]

**
I repeat: as long as the new theory (with no matter what fundamental principles, based upon the superposition principle or not, return to classical or not, something completely new and unexpected or not) has not derived AT LEAST compatibility with the *practical and empirically confirmed* parts of currently existing theories (GR and "practical QM"), then all arguments about the correctness of its starting principles is all just faith, religion, intuition, gut feeling or whatever you like to call it. **

I don't know why we speak about this all again, since I fully agree with you (apart from some small issues). Any dynamics one comes up, has to agree with undisputed experiment, period. Whether the underlying dynamics is a locally stochastic theory of a determinstic one with information loss, to what degree the Bell inequalities have to be violated, how the causal transmission of information has to be implemented are all open issues (to which I am open). Apart from Barut self field and Santos/Marshall SED, there is not so much done around this yet (and even these approaches are not known by most physicists !). There are very compelling reasons for the ZEP EM field and certainly there is a deeper content to that. Concerning Barut Self field, it appears to me very instructive to know of a nonperturbative rigorous theory (in that sense it is far superior to QED) which reproduces known effects. So, these are the first things to take into account when you want to adress the above question.


**Everybody is free to LOOK for other approaches, but this is, to a high degree, a totally personal matter. **

Not entirely (!), I said practical QM is incomplete; so the fact of looking is not personal. IN WHICH DIRECTION one looks is more open to that comment (and even not entirely).

**
Well, it has also not been a very rewarding policy in science to neglect empirical success :-) **

Cannot agree more...

** Look at GR: Einstein knew that he needed to find Newton's gravity as a limiting case. In the same way, *practical* quantum theory restores classical results in many examples (the "practical part" being the judicious choice of how and when to apply Born's rule). **

Well yes, hence QM is incomplete (GR does not have that problem), therefore what is the discussion about? I only said that whatever approach you try, you need to find an answer to that question (whether it be gravitationally induced or spontaneous collapse models or whatever). Moreover, there are clear, well known relations between SED/Barut self field and standard QFT.

So I say one has to *look* for this dynamics, how to do that is an entirely different matter to which I have no prejudices whatsoever.

Cheers,

Careful

 

[vanesch]

** Look at GR: Einstein knew that he needed to find Newton's gravity as a limiting case. In the same way, *practical* quantum theory restores classical results in many examples (the "practical part" being the judicious choice of how and when to apply Born's rule). **

Well yes, hence QM is incomplete (GR does not have that problem), therefore what is the discussion about?

I'm more careful than you here, I think. I'm not convinced that QM has to be considered incomplete as a "toy model". You (as many others) don't like MWI scenarios because 1) they sound so strange and 2) they DO need, IMO, indeed an extra postulate about such a volatile concept as "conscious observation". But when you are willing to accept that, I think that QM can be made as complete as any other theory. I will not deny that this is intuitively uncomfortable, but it is logically thinkable.

It's a different mindset to consider a theory a priori badly constructed (and hence, one should not pay much attention to its foundations) as you seem to think about QT, and to consider that a theory could be well constructed and hence its foundations might, or might not last, and nature (experiment) is the ultimate judge of that.
In the first (your) case, you will simply try to start "anew from scratch", while in the latter (my) case, you'd be more reluctant to let go *entirely* a scheme that worked well.

I think this is the main difference: you say, because QM is ill founded, its founding principles have no real value ; I'm not so sure about that.
If, in the end, it turns out that nothing remains of the principles of QM, then you are of course on a head start because others will still try to save some of its structure, in vain ; if however, some principles are supposed to remain for ever with us then you've cut yourself off the correct track.

 

[Careful]

** I'm more careful than you here, I think. I'm not convinced that QM has to be considered incomplete as a "toy model". **

You are not grasping my point yet. QM is fine as a toy theory for predicting statistics of *repeated*, ``indentical'' experiments, but is incomplete as a *spacetime* theory (even James Hartle does not adress this).

**You (as many others) don't like MWI scenarios because 1) they sound so strange and 2) they DO need, IMO, indeed an extra postulate about such a volatile concept as "conscious observation". But when you are willing to accept that, I think that QM can be made as complete as any other theory. I will not deny that this is intuitively uncomfortable, but it is logically thinkable. **

Well, two things : (a) you might guess what my grandmother says when I explain MWI to her (b) I excluded MWI as it stands now when I asked for a *dynamics* of single particles. And again, even the most perfect MWI theory possible does not make sense in a spatio temporal framework (you might want to think about that ! - there are very serious logical objections against it).

**
..
I think this is the main difference: you say, because QM is ill founded, its founding principles have no real value ; I'm not so sure about that.
If, in the end, it turns out that nothing remains of the principles of QM, then you are of course on a head start because others will still try to save some of its structure, in vain ; if however, some principles are supposed to remain for ever with us then you've cut yourself off the correct track. **

Wrong guess again , I do not say QM is ill founded, I say it incomplete in a crucial sense for QG. However, if you think about the dynamics for a single particle long enough, then you will understand that in order to regain *a large part* of the quantum statistics, one needs very different foundations. So, of course I am not saying one has to trow the child away with the bathtob (something many people like to think ) ! People did not dispose of thermodynamics either after it was explained through the means of statistical physics.

I ask you to read *carefully* my messages over again (no offense of course :-)), there is some specific point I highlight which you are missing ; that is : practical QM does not make sense in a *spatio-temporal* sense (for the universe). In your comments you are mixing up other ``realist issues'' with QM; QM has many different realist problems, it is important to keep them distinct. (anyway, I have to go now, we can perhaps continue this discussion in 2 weeks)

Cheers,

Careful