# The Rovelli Point of Wrong Turn

## Where the "Wrong Turn" was made?

5 vote(s)
31.3%

2 vote(s)
12.5%

7 vote(s)
43.8%
4. ### There is no Wrong Turn

2 vote(s)
12.5%
1. Jun 30, 2006

### Gebar

The "Rovelli Point of Wrong Turn"

In 2003 Carlo Rovelli wrote a paper entitled "A dialog on quantum gravity" (Int.J.Mod.Phys. D12 (2003) 1509-1528, http://www.arxiv.org/abs/hep-th/0310077). There, in the form of a dialog between professor Simp, a high energy physicist, and Sal, a graduate student who has decided to study loop gravity, Rovelli gives a "State of the Union" (read Unification) account of theoretical physics.

The paper gives a picture of the theory as well as a comment on the sociological effects of the String Wars, but it also makes a point that I think is very important and may lead to a very useful question. It concerns the historical course of theoretical physics through the maze of possible theoretical formulations in its effort to arrive at the one that will describe satisfactorily physical reality.

And I quote:
...
Simp – It is not the fault of the theoretical physicist if the path of the natural evolution of the research has lead to a theory which is very complicated.

Sal – And if it was the fault of the theoretical physicist? I suppose when you say “the path of the natural evolution of the research” you mean the line that goes along Fermi theory, QED, SU(2)×U(1), QCD, the standard model, and then grand unified theories, the revival of Kaluza-Klein, supersymmetry, supergravity, . . . strings. . .

Simp – Yes.

Sal – But what if this “path of natural evolution” has taken a wrong turn at some point. Seems to me there is precise break along this path.

Simp – What do you mean?

Sal – Dirac predicted the positron, and it was found. Feynman and friends developed a calculation method for photon-electron interactions, and it works to devastating precision. Weinberg Glashow and Salam predicted the neutral currents and they were found, and the W and Z particles and Carlo Rubbia found them, precisely where predicted, just to name some . . .

Simp – So?

Sal – And then?

Simp – Then what?

Sal – Then the Veneziano formula predicted a very soft high energy behavior of the amplitudes, and nature was not like that. The grand unified theories predicted proton decay at some precise scale, and proton decay was not found where expected. Kaluza-Klein theory, revived, predicted the existence of a scalar field that was searched by Dicke, and not found. Supersymmetry predicted the supersymmetric particles and these were not found where repeatedly annunciated. Extra dimensions did not show up where recently suggested by string theory. . .

Simp – But the proton may take a bit longer to decay, the masses of the supersymmetric partners may be higher . . .

Sal – Of course, they “might”. Everything is possible. But the cut between the previous fantastic sequence of successful predictions right on the mark, and, on the other hand, the later series of unsuccesses is striking. Before, experimental particle physicists were always smiling and walking like heroes: looked like God was reading Phys Rev D and implementing all suggestions of the theorists. Nowadays, thanks god they are still busy figuring out aspects of the standard model, because all the new physics that theoreticians have suggested wasn’t there . . .

Simp – Theory has always made wrong predictions.

Sal – Yes, but also right predictions, and those are missing, after the standard model.

Simp – It is because energies of new predicted physics are too high.

Sal – Not at all. There have been plenty of predictions that were well within reach. They just were wrong.

Simp – So, what do you make of this?

Sal – That perhaps Nature is telling us that our path of theoretical research has taken a wrong turn, at some point . . .

Simp – This is not a proof.

Sal – Of course. The fact is that we do not know. ...

...​

(Boy, that bit about God and Phys Rev D was too much.) :rofl:

And so, I would like to pose exactly this question here. Where do you think this wrong turn was made? At which point after (or within) the Standard Model?

Or, you may think there is no wrong turn anywhere; that the historical course of theoretical physics is the best possible. (This should probably include an explanation of the cause of the "precise break along the path" that will not involve energy levels.)

Or, finally, you may take the completely heretical view that the wrong turn was made even before the Standard Model. This seems like crackpot country, but you never know.

So, place your bets, ladies and gentlemen! (This may seem inappropriate, but at the current state of affairs what one believes on this point does seem like a gamble.)

2. Jun 30, 2006

Staff Emeritus
I wou;d say it was when Fadeev and Popov quantized nonabelian gauge therory and found their ghosts (foreseen by Feynmann) as necessary to preserve unitarity within gauge freedom. Once physicsts had gulped and swallowed that, they would gulp and swallow anything.

3. Jun 30, 2006

### Careful

**
Or, finally, you may take the completely heretical view that the wrong turn was made even before the Standard Model. This seems like crackpot country, but you never know.

So, place your bets, ladies and gentlemen! (This may seem inappropriate, but at the current state of affairs what one believes on this point does seem like a gamble.) **

I think your way of presenting it is far too simplistic as is usually the case for people making polls. Clearly, the standard model, QM and all this are good approximations to nature; the far more difficult question being on what scales one has to take these theories seriously. For example, no serious local realist (which you probably would consider a heretic) would doubt the accuracy of the standard model in high energy experiments, however he/she could say that the one particle interpretation of QM is incorrect (which is actually consistent with the statistical interpretation of QM). Strictly speaking, it is rather easy to construct local hidden variable models which reproduce the QFT correlation functions. Given the fact that in QFT only correlation functions are computed, there is even no contradiction at this level ! So, the game is much more subtle and the possibilities you offer are irrelevant; local realism was disposed of socially'' prior to the birth of the standard model, but nothing really went wrong in the standard model provided you interpret it correctly.

What could very well have gone wrong, is the possibility that the question of quantum gravity is meaningless or posed way too early to say the least.

Careful

4. Jun 30, 2006

### Gebar

Careful:

The question was very specific (if you care to address it, of course; I can perfectly well accept your answer as it is): how do you explain this "precise break along the path" of theory development in terms of the successful predictions made up to a point and the unsuccessful ones made from that point onwards.

5. Jun 30, 2006

### Careful

You misread me: the question is fine, the *options* you offer in your poll are not (that is what I said literally) - they do not reflect the subtlety in foundational issues we are confronted with today. I mean for all practical purposes, we have incompatible theories which give very accurate predictions in different domains of length (energy) scales - so there is no lack of prediction, there is only lack of a unified concept. In this matter, I fear that some frameworks were pulled out of context, and extrapolated to domains where they don't belong. More on that later.

Careful

Last edited: Jun 30, 2006
6. Jul 2, 2006

### arivero

Of course there is a wrong turn very early: to assume that the angular momentum can happen [and, particularly, that it can change,] in quantities as small as one wants. But it happenned too many time ago. Two close friends of the author of this assumption convinced him to retain publication until the argument were closely examined, and this delay went into a priority dispute. It is the only "before standard model" thing I can imagine.

7. Jul 2, 2006

### marcus

this whets my curiosity. would you please give a little more detail?

8. Jul 2, 2006

### arivero

a old history. The first excuse of Newton in the Dispute was that two very close friends of him have suggested him to do not publish because of some doubts they raised. He does not tell us which the doubts were, but historians have read and reread the notebooks and early manuscripts of the Principia and it seems that the heaviest edited "proposition" is the one of the angular momentum under central forces. I have been a bit sloopy in the previous remark, because it not exactly the variation of angular momentum which is at stake (after all, it does not change), but the need of taking smooth paths during the process of proof, and the adequate conditions for convergency. In fact the drawing of the proof of this theorem closely remembers Feynman's path.

This wrong turn was, in principle, corrected by Nature, when She told us that the angular momentum in 3D was to be token always as integer multiple of a quantity, and then She hinted Pauli that this was to be interpreted as discrete derivatives. Pauli gave the hint to Heisenberg, and Heisenberg to Born and Jordan.

But Meanwhile, the XIXth century saw the development of Lagrangian Mechanics, Hamilton Mechanics, and Classical Field Theory. The history of the second half of the XXth century is to try to correct the misunderstanding also in these newer mechanics.

Last edited: Jul 2, 2006
9. Jul 2, 2006

### Careful

***
This wrong turn was, in principle, corrected by Nature, when She told us that the angular momentum in 3D was to be token always as integer multiple of a quantity, and then She hinted Pauli that this was to be interpreted as discrete derivatives. Pauli gave the hint to Heisenberg, and Heisenberg to Born and Jordan.

But Meanwhile, the XIXth century saw the development of Lagrangian Mechanics, Hamilton Mechanics, and Classical Field Theory. The history of the second half of the XXth century is to try to correct the misunderstanding also in these newer mechanics.**

Euh, correlation functions and operators in quantum mechanics and QFT are usually smoother (often analytic) than the classical paths in Lagrangian and Hamiltonian mechanics are (and the number of smoothness/continuity notions in QM are at least four times more numerous than in ordinary CM). You refer to the fact that the non-smooth paths dominate the path integral sum of the free particle kernel, so what, that does not mean anything. You can figure out similar models for classical field theory : cfr. cellular automaton models for the Maxwell field. Moreover, nature did not tell us at all that angular momentum *is* quantized ; a continuum theory can cover very well for the appearant discreteness in the measurement outcome.

Careful

Last edited: Jul 2, 2006
10. Jul 2, 2006

### arivero

Indeed I am telling that quantum mechanics is a better tool than classical mechanics.

My last parragraph aimed to state that while the 1st third of the XXth century was about quantisation of classical almost newtonian things, the second half was after quantisation of field theories and other more dreadful beasts emanating from the XIXth century mechanics.

Last edited: Jul 2, 2006
11. Jul 2, 2006

### arivero

Now that was the "old wrong turn". To me, the modern wrong turn is the interpretation mismatch between Wilson-Kogut-Etal renormalisation group and perturbative renormalisation group. We have started to discuss about it in another thread.

Last edited: Jul 2, 2006
12. Jul 3, 2006

### Careful

**Indeed I am telling that quantum mechanics is a better tool than classical mechanics. **

Funny enough, I don't even disagree that it is a better TOOL. The founding fathers just saw something which defied what they knew about classical mechanics and developped mathematical equations designed to match the observed statistical predicition - so that is a huge shortcut in our understanding'' .

**
My last parragraph aimed to state that while the 1st third of the XXth century was about quantisation of classical almost newtonian things, the second half was after quantisation of field theories and other more dreadful beasts emanating from the XIXth century mechanics. **

Euh, dreadful beasts ??! I have been repeatedly mentioning that experiment cannot even distinguish between these beautiful classical field theories and undefined quantum whatsoevers (they are not even theories yet). And I guess you are going to tell now that spin is not a continuous quantized variable ?

13. Jul 3, 2006

### vanesch

Staff Emeritus
My personal feeling is that the "wrong turn" was made when theorists stopped looking at experimental data, and tried to go far beyond what was experimentally hinted at.
It never happened before that theories "came out of the blue" with no experimental hints.
Newton was based upon Kepler's observations. Maxwell was based upon countless empirical laws. Special relativity was based upon a re-interpretation of the symmetry group of the Maxwell equations (the Lorentz transformations) which had already some empirical success.
The closest hit to "a theory out of the blue" was general relativity, but apart from the mathematical difficulty, there was a basic guiding principle and it was "sufficient" to work this out. And even there, there WAS some empirical suggestion (the perihelion shift of Mercury).
Quantum theory was "shoved down the throat" of theorists from spectroscopy (Balmer series and all that). QFT had a difficult emerging, and was essentially guided by some empirical data like the Lamb shift. The entire standard model was a theoretical fit on a huge amount of experimental data, where concepts were introduced in order to explain phenomenologically observed regularities.

And then, theorists left off, and went for a "beauty contest". They invented unified groups (because U(1) x SU(2) x SU(3) was "ugly"), they invented supersymmetry, they invented strings...

It is exactly at the point where theorists didn't try anymore to model experimental data, but where they entered in beauty contests independent of experiment, that wrong predictions came out as indicated here before.

14. Jul 3, 2006

Staff Emeritus
"Why sometimes I've believed six impossible things before breakfast", said the White Queen in Through the Looking Glass. It's before MY breakfast this morning so let me see if I can find six impossible things that physicists still believe in.

1. The big wave function; it spreads to the end of the universe, but when somebody in Podunk does a measurement it all collapses. Pop! Goes the wave function.
2. Path Integrals. Feyman's examples in NRQM are so pretty and he is by every account a mighty genius, and all those java applets of toy situations are so impressive, but Wick rotation? Can't we admit it's an unbeautiful kludge that nobody would take seriously if it weren't essential to save us from seeing that the great man's celebrated method... doesn't work.
3. Virtual particles. You knew they would be in here but "off the mass shell?" I ask you, Energy squared less than zero, and what do we know about squares less than zero?
4. Fadeev-Popov ghosts. The ghosts are your friend! They are essential to preserving unitarity among all those gauge transformations. Fermions with boson behavior; goodbye spin-statistics. Oh wait ! They're "off the mass shell" again like virtual particles. Should count as TWO impossible things but I'll stand ya a twofer.
5. Invisible extra dimensions. Curled up in weeny little balls they are; but in an earlier day any physicist whose theory told him the dimension of spacetime is 26 or 10 or whatever, would have abondoned it as a bad job.
6. And lastly and very much leastly, the landscape. I don't think there is anything I could say about this abortion that some famous physicist hasn't said already.

When was the wrong turn? When people started taking Niels Bohr seriously!

15. Jul 3, 2006

### Gebar

Ah, the infamous Wrong Turn at Copenhagen! I'll buy that.

16. Jul 3, 2006

### marcus

so it could be that Bohr did not make the wrong turn himself.

Maybe he escaped that self-delusion, and it was left to other people later to "re-ify" or "ontologize" the wavefunction framework for handling information that he offered them.
("re-ify" = thing-ify = mistakenly imagine that it is a real thing)

But perhaps you cannot so easily locate the wrong turn geographically, or pin the blame on Bohr.

Personally i do not know much of the history but I think Bohr said something like QM is not about what is in nature, it is about what we can SAY about nature----that is, it is about information: what correct statements an observer can make based on what he or she has observed.

This leaves all the room in the world open for people to construct ontologies, if they want to construct them and they are not satisfied with the traditional intuitive idea of what is real.

But those who tried to promote Bohr's information theoretical QM to an idea of fundamental existence----so as to enshrine the big wave function as existing like some real object----these people may have been deluding themselves. I would like to absolve Bohr and say he did not tell them to do it

17. Jul 3, 2006

Staff Emeritus
Before there was QM there was the "Old Quantum Theory". It was entirely the work of Bohr, and it was frankly magic; the electrons in their shells did not obey the known laws of physics, but no explanation or even description was given as to how that should be so. Once physicsts had got used to that (It was successful in accounting for gross features of the spectrum of Hydrogen, but failed at every other task) the Heisenberg-Schroedinger QM came as a breath of common sense!

18. Jul 3, 2006

### marcus

I see what you mean. In that sense the mistake you refer to was when people started taking Niels Bohr original idea seriously. (but I think maybe you are joking )

I am hopeful about something Baez said roughly like this:
in its basic outlines QM resembles a theory of spacetime, and some things that seem counterintuitive or paradoxical about QM are very intuitive when you look at the counterpart in spacetime geometry (nCob)

so one can hope that there is something more fundamental than QM which will make better sense.

and it will be a theory of spacetime (and material as well) that will among other things explain why QM works so well as a theory of asking questions and getting answers

and since i am engaging in hopeful or wishful thinking I will go all the way and say something else:

I think that to construct an ontology on the basis of QM, and to imagine that the wavefunction is really there
(and that it has occasional fits of epilepsy and collapses foaming at the mouth when someone in Podunk does something) is simply a case of PREMATURE REIFICATION.

I liked your Podunk example.

I think that people get into this "premature ontology" business when they imagine that QM must be the final theory, so, they ask, WELL if you do not make an ontology with one or more wavefunctions, then what is the matter with you? don't you have any ontology? don't you believe in ontology? what are you, some kind of solipsist?

and I say that no I am not a solipsist or anything, i believe it is possible to have a good ontology SOMEDAY, but I think it is premature to try to get it by bronzing Schroedinger's 1927 babyshoes. One should be patient and live with a traditional commonsense ontology a little more. QM is not so close to a final theory that one can make therefrom a likeness of nature.

Last edited: Jul 3, 2006
19. Jul 3, 2006

### marcus

This strikes me as a really good list, I would just like to see Bohr absolved of any wrong-doing.
If I had to guess as to where a misstep occurred in the last century, it would be a sin of omission---in NOT taking Gen Rel seriously.

Probably they should have put more effort into devising a General Relativistic Quantum Physics.
(kind of thing you see Baez friends doing, linking nCob to Hilb, the former being a general relativity animal and the latter a quantum animal.)

Perhaps late 20th physicsists were seduced by GEOMETROLOGY, which is an addictive practice analogous to ASTRology and NUMERology.
As when people get hooked on inventing formulas that calculate the right numbers----because of the richness of numerical formulas it seems possible to get formulas that produce any result you want. So likewise they can get hooked the same way on differential geometry and all the beautiful machinery of manifolds. Somewhere i heard the phrase "accursed fecundity of differential geometry" applied to late 20th century theorizing.

And maybe the Geometrology hocus pocus distracted them from confronting the job of taking Einstein seriously and devising a general relativistic quantum physics.

20. Jul 3, 2006

### Gebar

Well, I'll second that. GR showed that gravity's "spooky action at a distance" is curved spacetime. The next step would be to see how this could also hold true for EM forces. Kaluza did this, but he was ignored, AFAIK because nobody could see the fifth dimension. And so the compactification thing started with Klein. What I haven't understood is why we flatlanders should be able to see the fifth dimension --which could also provide perhaps non-local hidden variables. But instead people went the other way, and instead of turning EM into spacetime geometry like GR the turned GR into EM with virtual gravity particles.