Lubos style critique of Strings

[Kea]

I'm not going to say anything about the anthropic principle (strong or weak form) because that's so clearly stupid that it speaks for itself. I'm also not going to say anything about the lack of observational evidence, because, let's be honest, we're all in the same boat on that one, probably until about 2008. The mathematics of Strings is complex and undeniably beautiful. This is a critique of the physical concepts underlying String theory.

Having looked through a few M-theory papers, I was absolutely flabbergasted to see that it's all still about taking something true and tried (path integrals), generalising it a little, and finding it might contain something like gravitons (which may not even exist). Wow! A theory of quantum gravity. Yeah, right.

When Einstein and Grossman were developing GR, did they focus their attention on classical field theory? No! The physical principles are everything. In fact, it was Einstein's difficulty in accepting general covariance on physical grounds that held him up for years. General relativity is a 'background independent' theory. Until String theory comes to terms with the importance of this 100 year old physics it cannot possibly hope to capture the essence of quantum gravity.

The fact that spin foam models are beginning to make contact with M-theory (see
John Baez & Urs Schreiber
Higher Gauge Theory: 2-Connections on 2-Bundles
http://www.arxiv.org/abs/hep-th/0412325 ) should start alarm bells ringing! And not just one of those 9V battery ceiling alarms, but a whole 1960's city of fallout shelter jobs.

After I pointed out that within category theory it was clear how to generalise twisted K-theory in a way relevant to physics, Urs Schreiber (the String theorist) replied that set theory has an answer, too. This statement can hardly be refuted, to the satisfaction of the majority, until real proof is available, along the lines of a derivation of the fine structure constant, or something like that. One can point out, over and over again, that a very ordinary category of sheaves is, axiomatically, outside the realm of set theory. But as such objects may be discussed within set theoretic mathematics, they will be by those who believe that Strings (for instance) have reached a level of abstraction sufficient for unification. It is as if people are mesmerised by the thought we've been trying for 30 years now, and this maths is pretty cool, so we must be close now. Nature, of course, really doesn't care very much about how much effort we've put in.

Quantum mechanics is about logic and axiomatics. So is sheaf theory. GR is about sheaf theory (twistors for instance). Quantum Gravity needs to get the logic right. Crazy? No! Bloody obvious!


:grumpy:

 

[marcus]

I'm not going to say anything about the anthropic principle (strong or weak form) because that's so clearly stupid that it speaks for itself...

I feel like applauding, not sure why. Maybe it is the element of mimicry which comes off well. Or the sentiments themselves, expressed with a fine curved upper lip. For some reason this got me laughing:

"This statement can hardly be refuted, to the satisfaction of the majority, until real proof is available, along the lines of a derivation of the fine structure constant, or something like that. One can point out, over and over again,..."

 

[marcus]

... I was absolutely flabbergasted to see that it's all still about taking something true and tried (path integrals), generalising it a little, and finding it might contain something like gravitons (which may not even exist). Wow! A theory of quantum gravity. Yeah, right.
...

It just occurred to me this morning that the correct adjective for Motl-like is Motly

this refreshingly outspoken post is a gem, Kea. Hope I did not offend by detecting a note of parody in the tone, at least at one point. But it reads OK straight as well.

Woit flagged an interesting article today
http://www.dailyfreepress.com/news/2005/01/25/Science/The-Thin.Line.Of.Theory-840583.shtml

reporter from a Boston U. newspaper called Daily Free Press
interviewed physicists at BU and Harvard, among whom were differences of opinion---a cat-fight ensued which goes on for 5 pages.

 

[marcus]

What Glashow and Ginsparg said in 1986

they had this short opinion piece in Physics Today, May 1986
http://www.arxiv.org/abs/physics/9403001
Incidentally isn't Ginsparg the guy who thought of having ARXIV.ORG and got it set up (please correct me if I am mistaken about this). Arxiv began around 1991 or 1992, so this little piece by him and Glashow only got posted retroactively.

they evoke an echo of Sixties political political slogans (Freedom Now! X Now! Y Now!) when they mention eagerness for "unification now".

the title of the piece recalls a popular film of the 1980s "Desperately Seeking Susie"

Here is an exerpt of Glashow and Ginsparg's "Desperately Seeking Superstrings"

"...How tempting is the top-down approach! How satisfying and economical to explain everything in one bold stroke of our aesthetic, mathematical or intuitive sensibilities, thus displaying the power of positive thinking without requiring tedious experimentation! But a priori arguments have deluded us from ancient Greece on. Without benefit of the experimental provocation that led to Maxwell’s equations and, inevitably, to the special theory of relativity, great philosophers pondering for millennia failed even to suspect the basic kinematical structure of space-time. Pure thought could not anticipate the quantum. And even had Albert Einstein succeeded in the quest that consumed the latter half of his life, somehow finding a framework for unifying electromagnetism and gravity, we would by now have discarded his theory in the light of experimental data to which he had no access. He had to fail, simply because he didn’t know enough physics. Today we can’t exclude the possibility that micro-unicorns might be thriving at a length scale of 10^?18 cm. Einstein’s path, the search for unification now, is likely to remain fruitless."

I sporadically revisit Kea's post and reflect on various things, like
"I'm also not going to say anything about the lack of observational evidence, because, let's be honest, we're all in the same boat on that one, probably until about 2008..."

and also this:
"General relativity is a 'background independent' theory. Until String theory comes to terms with the importance of this 100 year old physics it cannot possibly hope to capture the essence of quantum gravity.

Quantum mechanics is about logic and axiomatics...Quantum Gravity needs to get the logic right. Crazy? No! Bloody obvious!"

it seems to me that the message is:
The goal of formulating a general relativistic quantum physics
is not the same as the goal of "unification"

In fact the goal of unification may be inappropriate at present because not sufficiently provided with experimental data (notice theorists' apparent inability to risk predicting LHC results)

However the goal of reformulating Quantum Physics in a background independent way compatible with (100 year old physics of) General Relativity may be a timely and appropriate one. Even long overdue one might say. this can be called "getting the logic right"

So one has to make fine distinctions between different kinds of "top-down" goals. Developing top-down is not intrinsically unwise, but it has to be guided by a sense of what is ready to happen and what isnt.

just the view of a kibbitzer

 

[marcus]

maybe this is the key line in Kea's delphic post

"The fact that spin foam models are beginning to make contact with M-theory ... should start alarm bells ringing! And not just one of those 9V battery ceiling alarms,..."

I don't understand this utterance (delphic utterances are supposed to make one think, one doesn't necessarily understand them, wondering what they mean is part of the process of starting to think differently)

however this morning it occurred to me that what this statement by Kea might mean is that Grothendieck is the Riemann of today
because it has been about 50 years which is about the right time

what i mean is Riemann invented manifolds and curvature tensors and stuff around 1850 which Einstein and the others needed some 60 years later
to do a background independent theory of gravity and a new theory of spacetime
and there is a dimly emerging analogy here with Grothendieck in the 1950s or thereabouts.

Has anyone seen Zazie Dans Le Metro a wholesome family-style french movie in which Grothendieck has a cameo role---if cameo is the right word. It is about a little girl named Zazie and Grothendieck plays the bar-tender

 

[Kea]

... this morning it occurred to me that what this statement by Kea might mean is that Grothendieck is the Riemann of today
because it has been about 50 years which is about the right time.

Has anyone seen Zazie Dans Le Metro a wholesome family-style french movie in which Grothendieck has a cameo role---if cameo is the right word. It is about a little girl named Zazie and Grothendieck plays the bar-tender

Hi Marcus

I really enjoy chatting with you - I've just been very busy. I'm at yet another conference right now.

Grothendieck and Riemann - spot on! Not long ago I heard Ross Street introduce topos theory with a brief introduction to Geometry, spanning 2500 years. A topos really is a generalised idea of a space. Grothendieck's ideas are way ahead of his time.

I heard the following story about him. Apparently a respectable mathematician went to see him recently (he is notoriously difficult to contact). Grothendieck said he would be happy to talk if this person could answer one simple question:

What is a metre?

The great mathematician went away for a while, thought about it, and returned with an answer of some sort (huh!). Grothendieck slammed the door in her face.

I haven't seen the movie.
Kea

 

[marcus]

what a rude old curmudgeon
in the film (made in the early sixties) he is totally shiny bald
and what a terrible thing to happen to the respectable lady mathematician

slam if you feel inclined, I care not, a metre is the distance light travels in
1/299792458 of a second, in vacuo. for so it was declared in 1983 by an international body empowered by treaty to decide such matters

 

[marcus]

Miss Otis regrets (she's unable to LunHC today)

the final paragraph of Michael Dine et al new paper

"From all of this, it appears that it is difficult, in principle, to decide whether or not the landscape predicts supersymmetry. If one hypothesizes that it does, than one may be able to make predictions about the scale and nature of supersymmetry breaking. If it does not, it will be difficult to extract any real predictions; at best, one might give a rationale for the appearance of technicolor or warping in low energy physics – or their absence."

Dine, O'Neil, Sun Branches of the Landscape hep-th/0501214