Are superstrings the only option? What about GR approaches?

[Careful]

**
No, I said it was a spin foam model. You can see causal dynamical triangulations as a funny kind of spin foam model if you like, but this is not that. It's the Ponzano-Regge model of 3d gravity, the grand-daddy of all spin foam models. **

Right, it was only in the title of the paper (which I missed), but if you would have had a quick look at my post 29, then you would have seen that I had a 2 minut glance at the paper (and mentioned the above myself); and I am very aware of how Pozano-Regge works, so no need to explain that. You know very well (I hope) that my other questions were asked in the context of a CDT like model.

**No embedding in Minkowski spacetime.**

So, how do you justify the choice of background state ?

**
Sorry to be negative-sounding. Try looking at the paper - I gave a link so people could easily check it out. There's no need to guess what's going on. **


Fine, and some people claim to have read it, so I guess it is my good right to ask questions. Your comments remind me of the attitude ``model ueber alles !''. The point is that I can imagine how to retrieve similar results from a simplified CDT model with a cutoff, so the specific toy model at hand is of no importance to this discussion whatsoever (and in that specific sense, I am not guessing at all). Look, if I would carefully read any paper people suggest here, then (a) 80 percent of the cases this would be a total waste of time (b) I would have detailed objections which nobody cares to answer (c) I have something better to do. So, all I am interested in is having answers to some specific questions; in contrast to you I do not fancy whether the specific model employed is variant 29 in category 5, or whether it is the trefoil or figure eight knot people are suddenly keen upon (without deep motivation).


Moreover, the original discussion went about the nonrenormalizability of gravity (a) this paper has nothing to do with it (b) the action in this paper is clearly Einstein Hilbert (so there is life beyond the Fock state). AFAIK, neither ST, nor LQG have adressed this issue yet (and are nowhere near that goal).

 

[Careful]

**I'd be lying low too if I posted a simple question and got back a load of quasi-political posturing. You and John Baez gave straight answers within your rescript, but it seems to me that everyone else, and I do not exclude myself, was in a pi**ing contest. **

If there was quasi-political posturing at all, then the two gentlemen you mentioned are certainly not innocent. Josh1 is simply doing what you and marcus are doing *all the time* for LQG ; I guess I do not need to quote all posts where frantic reactions towards ST were made by the two of you. This website is like the most DANGEROUS one for ``students'' to learn about anything at all, facts are twisted, pulled out of context and moreover, people who barely know what a tensor density is are doing nothing but quoting brainless, irritating one liners and attacking anyone who offers a more down to Earth perspective (when it doesn't fit the goals).

 

[marcus]

...
If there was quasi-political posturing at all, then the two gentlemen you mentioned are certainly not innocent. Josh1 is simply doing what you and marcus are doing *all the time* for LQG ; I guess I do not need to quote all posts where frantic reactions towards ST were made by the two of you. This website is like the most DANGEROUS one for "students'' to learn about anything at all, facts are twisted, pulled out of context and moreover, people who barely know what a tensor density is are doing nothing but quoting brainless, irritating one liners and attacking anyone who offers a more down to Earth perspective (when it doesn't fit the goals).

We don't make visible just one favorite QG approach. Right here at this forum we have a thread about your papers (Johan Noldus thread) and we also have a thread (Quantum Graffiti) about the Renate Loll group where you were postdoc.
I like to initiate discussion of any unconventional QG approach I find, if the others have any interest in talking of it.
We have had not just you here, but obviously Sabine and Kea as well, and also Mattej Pavsic, Garrett Lisi, Carl Brannan, Rafael Porto (of the Gambini group), and Alejandro Rivero and Hans de Vries too ...It is an incredible mix. There is no "official house-brand" QG or approach to unified physics.

What gets discussed at PF is mostly what people find interesting and want to discuss. Anyone can start a thread. I start a lot, to see what takes off and what doesnt. If the topic is right, the thread will take off and fly, if not is is just informational and eventually goes away.

I'm proud of our group. We have several grad students in QG and related, and we benefit a lot from having their instincts about what is interesting and what is not. Basically my role is like short-order cook at the diner (or librarian). I can flip the burgers but they decide what they like to eat.

If you think that there is some "house-brand" QG that I personally favor, you may be confusing several quite different approaches ALL of which interest me a great deal because I see a lot of action in those research lines. As a watcher/reporter what gets my attention is where people are publishing new papers and appear to make progress.

The trouble with personal attacks, like you just did, is that it DISTRACTS FROM THE THREAD. Robert100 the O.P. asked this question. That is the issue. personalities, and what different people contribute to the forum, are not the issue we should be discussing.

If you want to vituperate or express grievances, Dr. Noldus, then you can start a thread specifically for this. It might be fun and interesting! who knows? If you want to discuss Noldus papers, we already have a thread and you are welcome to start another---I feel sure the mods won't mind a little duplication! It is a great educational opportunity to have authors come and talk about their work.

Thanks to all for good contributions to this Robert100 thread!
Even when the tone gets a little testy we get lots of informative stuff out on this table. Kudos to Robert100 for starting lively discussion---hope to eventually see him back with a reaction.

 

[Careful]

**We don't make visible just one favorite QG approach. Right here at this forum we have a thread about your papers (Johan Noldus thread) and we also have a thread (Quantum Graffiti) about the Renate Loll group where you were postdoc. **

:rofl: :rofl: Haha, your tactics are so transparant, I was making a bet two hours ago with a friend of mine, how many words it would take you to say ``Noldus''.

**
I like to initiate discussion of any unconventional QG approach I find, if the others have any interest in talking of it. We have had not just you here, but obviously Sabine and Kea as well, and also Mattej Pavsic, Garrett Lisi, Carl Brannan, Rafael Porto (of the Gambini group), and Alejandro Rivero and Hans de Vries too ...It is an incredible mix. There is no "official house-brand" QG or approach to unified physics. **

Euh, where did I involve these other people ? :grumpy:

**
What gets discussed at PF is mostly what people find interesting and want to discuss. Anyone can start a thread. I start a lot, to see what takes off and what doesnt. If the topic is right, the thread will take off and fly, if not is is just informational and eventually goes away. **

It hasn't anything to do with the ``right'' topic.

**
I'm proud of our group. We have several grad students in QG and related, and we benefit a lot from having their instincts about what is interesting and what is not. **

Please, do not present yourself as the pater familias...

** Basically my role is like short-order cook at the diner (or librarian). I can flip the burgers but they decide what they like to eat. **

Oh no, you do much more than that (as anyone can see).

**
If you think that there is some "house-brand" QG that I personally favor, you may be confusing several quite different approaches ALL of which interest me a great deal because I see a lot of action in those research lines. **

Hahaha :rofl: :rofl: that is soo typical : (a) I never said that you confine yourself to one approach but merely you seem to eat the whole QG spaghetti and nothing else (b) you never go deeper into the content - but as a reporter - you manipulate public opinion by overwhelming almost every thread with QG spaghetti and your comments how fantastic and underapreciated it all is.

** As a watcher/reporter what gets my attention is where people are publishing new papers and appear to make progress. **

Well, why did I not see anything about Brian Greene then ? He is like the most public figure in ST and good looking too :rofl:, should be attractive for a reporter.

**
The trouble with personal attacks, like you just did, is that it DISTRACTS FROM THE THREAD. **

Oh no, who was making attacks ad hominem before !? Who does systematically play the card of the person when he deems necessary? Who are you mr. Marcus ?

** Robert100 the O.P. asked this question. That is the issue. personalities, and what different people contribute to the forum, are not the issue we should be discussing. **

Glad you tell that : you are already two times in contradiction in one post containing this message ! (not to speak about the cult you organized around miss antigravity !)

**
If you want to vituperate or express grievances, Dr. Noldus, then you can start a thread specifically for this. It might be fun and interesting! who knows? If you want to discuss Noldus papers, we already have a thread and you are welcome to start another---I feel sure the mods won't mind a little duplication! It is a great educational opportunity to have authors come and talk about their work.**

:rofl: :rofl: I have honestly given my opinon about this and I am afraid there is not more to tell yet. Please refrain yourself from guessing ``emotions'' of people (I thought you did not want this ??) you have never met, since I can affirm you are very wrong in this case.

Having said that, can we talk science ?

 

[f-h]

...dangerous to students...

That would be me then, hu?
Students are not idiots. Nor mere unreflective consumers of presented information. Marcus is frequently spreading a very excited mood about several results in QG (in my very personal opinion often overly so, without many of the necessary caveats which invariably get added in the discussion though), and unfortunately String Theory isn't very well represented in this forum, but then, there are plenty of places on the net where it is, so it's certainly not likely that a student who has found this forum doesn't know about half a dozen places where he can learn about the state of the art in String Theory.

As for how deep we can go, I'm a beginner (and I can't say much on the reference state they are using, it's gaussian as far as I know, crucially with the extrinsic curvature as phase), in many threads we have nobody who is an expert on the subject, so by neccesity the discussion remains cursory in many cases. Where it could go deeper we seem to often have a severe language problem. I don't speak effective field theory very well for example, but in my understanding eft is not a very good language to phrase the LQG/propagator results into begin with.

It's just an Internet Forum where people interested in this stuff meet, not a closed expert community, though such a community would undoubtably be nice.

Edit: I should make clear that with this I mean it's more usefull if you/I/we simply point out the over-enthusiasm where we see it rather then asking people to be less enthusiastic. With this contribution I don't see how this forum could be misleading to any moderately intelligent student.

 

[wolram]

If anyone of you would get down to the nitty grtty of some testable theory
maybe this topic would not be so boring, (to a numbskull) you are talking to
a very limited audience all ready, soon you will be talking to yourselfs.

 

[Careful]

**That would be me then, hu? **

Not at all. You are lucky to be in a good place, I was aiming at those who come from the small universities (or not from universities at all) where one rarely has the occasion to talk to someone who has different opinions. And despite of the ``rough'' start, I have noticed you have a calm intelligent view on some issues which I appreciate.

**
Students are not idiots. Nor mere unreflective consumers of presented information. **

I know, but there is too much (des)information around for a young intelligent student to make a ``deliberate'' choice. That is why IMO an unpartial, not too lengthy, deep paper about the *problem* of QG ; its proposed solutions and the ``ungone'' paths is probably the biggest gap in the literature (actually, 't Hooft has written a paper about the problem with perturbative quantum gravity precisely for that purpose I guess).

** Marcus is frequently spreading a very excited mood about several results in QG (in my very personal opinion often overly so, without many of the necessary caveats which invariably get added in the discussion though), and unfortunately String Theory isn't very well represented in this forum, but then, there are plenty of places on the net where it is, so it's certainly not likely that a student who has found this forum doesn't know about half a dozen places where he can learn about the state of the art in String Theory. **

Well, perhaps, but that does not imply that a fair assesment is not a benefit for everyone. The problem is that marcus has sometimes the tendency to become personal (and disrespectful) to people who are not so cheerful about LQG.

**As for how deep we can go, I'm a beginner (and I can't say much on the reference state they are using, it's gaussian as far as I know, crucially with the extrinsic curvature as phase), in many threads we have nobody who is an expert on the subject, so by neccesity the discussion remains cursory in many cases. Where it could go deeper we seem to often have a severe language problem. I don't speak effective field theory very well for example, but in my understanding eft is not a very good language to phrase the LQG/propagator results into begin with. **

Fine, language is difficult - especially when you speak to someone with a different background. That is why I sometimes take the effort to explain calmly what I mean precisely, it is something which you have to practice constantly and one can only hope it gets better when age increases. When you will finish your PhD you will notice that in order to appreciate a paper - you only need the answer to a few specific questions.

**
It's just an Internet Forum where people interested in this stuff meet, not a closed expert community, though such a community would undoubtably be nice. **

I very much agree. Most of the forums I have briefly visited are either about complaining and insulting by some specialists, or either about overspeculative science fiction by sometimes smart but not down to Earth people. An open expert community where people would calmly explain at a fairly technical level what the exact state of the field is, what the shortcomings are, the strong points and so on, would form a major contribution to the speculative part of theoretical physics.

**Edit: I should make clear that with this I mean it's more usefull if you/I/we simply point out the over-enthusiasm where we see it rather then asking people to be less enthusiastic. With this contribution I don't see how this forum could be misleading to any moderately intelligent student. **

Sure, I still get excited plenty of times when I discover by myself or in some paper a nice aspect of physics I did not realize yet but I am ``old'' enough to calm down before I start telling this to anyone.

 

[f-h]

And despite of the ``rough'' start...

Yes our start was rather unfortunate, I believe to a degree due to my language deficits (I'm glad to see that it didn't leave an overly lasting impression...).
I'd hope to revisit that topic again at some point, since it does concern precisely the stuff I have worked on so far...

 

[Careful]

Yes our start was rather unfortunate, I believe to a degree due to my language deficits (I'm glad to see that it didn't leave an overly lasting impression...).
I'd hope to revisit that topic again at some point, since it does concern precisely the stuff I have worked on so far...

Ah, let's not talk about that Sure I am willing to think about what you were busy with ... however I will be off from may 31 - june 16, so perhaps postpone it a bit.

Cheers,

Careful

 

[f-h]

Oh I won't be talking about anything until I have finished writing things up in a month or two, I was thinking later, too. ;)

 

[Robert100]

I am excited to see so many responses to my question, and I'm glad to hear that so many people are open to various pathways to a ToE, and not just string theory.

Marcus, I couldn't respond to this discussion thread sooner because of time constraints from work, and spending time with family and friends the last few days, but I sincerely am reading each reply, and appreciate the time taken to address this issue.

Warning - philosophizing mode on:

Einstein almost had it easy, compared to those working today on a potential theory of everything (ToE). In 1905 we already had James Maxwell's equations, and the damning, direct observational evidence concerning the speed of light: No one had ever seen light moving slower than c, even light from distant galaxies. Further, no one could detect an ether, even with experiments that went well beyond the Michelson-Morley experiment. Thus, with all the evidence in place , it was (by ToE standards) almost easy for Einstein to describe reality (first with special relativity, then with general relativity.)

As for the standard model, we have made firm progress because of a plethora (*) of results from ever more powerful particle accelerators. But what next? Although I am curious about finding a ToE, it seems thar many physicists were just letting their mouths run from the 1960s up until recently. Even Hawking seemed pretty certain for a while there that a ToE was just around the corner. Do we really have any evidence that this is so? As far as I can tell, we have no idea how difficult it will be to formulate a ToE. Such a level of understanding, of course, may well be within our reach in the next decade...but it also may be out of our reach for the next century. (Or if one is more pessimistic than me, out of our reach forever.)

We simply don't have enough experimental evidence on which to peg a Theory of Everything at the moment. For goodness sakes, we aren't even certain where mass comes from, and the Higgs boson isn't yet discovered.

As such, I can't imagine taking bets for or against any version of loop quantum gravity, superstrings, or anything else that makes it through peer review. Its a good idea for physicists to divide into groups, pick different favorite approaches, and critically analyze each other's views. Let's go for it. Its all an argument for the sake of heaven (to use a classical rabbinic Jewish allusion.)

More thoughts to come soon,

Robert


(*) Digression coutesy of "The Three Amigos"
Jefe: We have stuffed many pinatas for your birthday celebration!

El Guapo: How many pinatas?

Jefe: Many pinatas, many!

El Guapo: Jefe, would you say I have a plethora of pinatas?

Jefe: Yes, El Guapo. You have a plethora.

El Guapo: Jefe, what is a plethora?

Jefe: [pausing, clearly uncertain what the word "plethora" means] Do think perhaps El Guapo it is you 40th birthday today and you are just taking it out on me?

 

[Robert100]

What I think we should get out of this discussion

Marcus writes:
"Wikipedia is not such a good place to start. Wiki's articles relating to quantum gravity have parts which have been repeatedly tug-of-war edited and re-edited so as to in some cases down-play the interest and importance of non-string approaches. IMO Wikipedia is not as authoritative or reliably unbiased in that department as it is in many other areas---some passages may give quite a wrong impression. In the case of several Wikipedia articles, I've found it interesting to click on "history" which gives the history of the article, how it was written, who changed what, who then changed it back---and so on. A kind of "scrimmage". "


Marcus, that's my impression as well! Wikipedia has a tremendous number of excellent articles, but it suffers from a number of its own self-created flaws. The results of its flaws (which I won't go into here) are that (a) fine articles go into edit wars like you describe, (b) articles with correct information are sometimes written by grad students, for grad students, and become incomprehensible to the lay public, even those with a B.S in physics, and (c) articles sometimes include pseudoscientific crap, just to appease someone's peculiar notion of "Neutral Point of View", Wikipedia's guiding principle, and sometimes worst enemy.

I started this thread because I am hoping that some of us (i.e. people way smarter than me) will be motivated to come up with a list of proposed Theories of Everything. For the general reader on this forum, and for inclusion in a Wikipedia article, it might a be a good idea to describe:

* the current approaches to Theories of Everything (ToEs).

* for each approach discuss the basic idea, and discuss the ideas perceived strengths and weaknesses.

* mention the current experimental evidence (if any) that this idea may be correct (or incorrect.)

* mention the experimental tests that are being proposed, which may help distinguish which ideas are correct.

* mention who their advocates and critics are

* Give some seminal and recent papers on the topic, both technical and general reviews.


By the way, when I asked people to limit their discussion to mainstream ideas, I didn't mean to limit the discussion to widely accepted ideas. Even ideas held among a tiny minority of physicists should be included in this list, as long as articles on said approach are by practicing physicists and have passed some form of meaningful peer review.

I have a strong bias against ideas that cannot make it through peer review. If someone presents theirs ideas clearly, their math is good, then eventually people will say "Oh, I get it. Maybe this is a path worth exploring, and maybe its worth publishing these ideas." Ok, it might take ten years for people to be open minded, but in the long run truth really does make it through scientific peer review, while quackery doesn't.

Thoughts?

Robert

 

[marcus]

Its all an argument for the sake of heaven (to use a classical rabbinic Jewish allusion.)
...

my stock phrase that I got from a French blogger (Lucien Besnard) is that it is "for the honor of the human mind".

In either case there is a little problem with justifying tax dollars
but it is sure better than going to the moon IMHOGlad to see you back!

does it mean a "fullness" or an "excess" El Guapo?
=================

my personal feeling about the quest for the holy toe is that if I were a professional researcher------not just a spectator amateur librarian, a kind of sportsfan----I would want to keep my mind very free of PRECONCEPTIONS ABOUT WHAT THE TOE WILL LOOK LIKE so that I could hopefully be very open to surprises and to noticing what I wasnt expecting

in this way RIVALRY AND ARGUING could actually be counterproductive---because it makes people grip their own preconceptions more tightly. But certainly there are other ways in which peaceful rivalry is good and stimulating---helps keep people on OH NO! I AM ABOUT TO SAY IT! *toes*

 

[marcus]

Robert, I just saw your post #47. When I replied earlier I was responding to your #46 with the El Guapo birthday dialog.
this last post raises interesting questions. I will hold off answering and give the others a shot.

the basic background question is, I think.
1. What is the present historical situation in physics?
2. What is the next big theoretical breakthrough or revolution that one should be anticipating?
3. How would one recognize it, if one bumped into it?

In other words, what actually IS a "toe"? It may not be quite the same as what we have been taught to visualize and expect, but if "toe" is the next big step due in physics theory, then what is one likely to look like?

Maybe, so as not to gum up your thread, i will start a thread about this---ask these basic background questions and see what people think.
Not sure i want to. But it would be better than risk distracting the conversation here (any more than normal human nature does already)

 

[vanesch]

my stock phrase that I got from a French blogger (Lucien Besnard) is that it is "for the honor of the human mind".

In either case there is a little problem with justifying tax dollars
but it is sure better than going to the moon IMHO

Well, I don't have to be convinced of the relatively low scientific value of going to the moon, but I'm not so sure about your last statement!
It seems that, at this point, we got more out of going to the moon than of 20-30 years looking for a ToE as economical return, no ?
(ok, I didn't check, probably the amounts of money aren't comparable either)

Now, I don't follow much of this ToE research, and maybe I'm totally wrong. As such, I'm also interested in Robert's question, in fact. However, I'd like to leave out speculation. Instead of looking in the hopeful near and unknown future, where of course each approach sees marvelous things happening, can it not be summarized what has been *achieved as of today* in the different approaches ? What are the tangible results that are here, that weren't around 20 years ago, and that have been the fruit of this labor over 20 years, instead of guessing what will come out of it, hopefully "next year" ?

I'm of course aware that no approach has reached the "finish" but let's take out time traveling machine and go back to say, 1985, and the same question is asked, and now you're allowed to "speculate on the results in the coming 20 years" with some hindsight. What are the important breakthroughs in each approach, by themselves ? What are the results that are with us NOW, and weren't with us 20 years ago ?
If Robert (or a student hesitating on which band wagon to jump in 1985) would have asked the question in 1985, with the idea of spending 20 years on it, what are the highlights that he will meet in this career that will eventually make him pick one or other way, as a function of the highlights that will remain with us and his personal tastes ?

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.

 

[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 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 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 :rofl: (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 :grumpy: ) ! 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