Woit explains convincingly that even string theorists know that string theory has no foreseeable observational basis, and that the theoretical arguments currently being advanced are wanting as well.

what would happen if you compare the string results with lqg in 10d sugra

Towards Loop Quantum Supergravity (LQSG) Norbert Bodendorfer, Thomas Thiemann, Andreas Thurn

Should nature be supersymmetric, then it will be described by Quantum Supergravity at least in some energy regimes. The currently most advanced description of Quantum Supergravity and beyond is Superstring Theory/M-Theory in 10/11 dimensions. String Theory is a top-to-bottom approach to Quantum Supergravity in that it postulates a new object, the string, from which classical Supergravity emerges as a low energy limit. On the other hand, one may try more traditional bottom-to-top routes and apply the techniques of Quantum Field Theory. Loop Quantum Gravity (LQG) is a manifestly background independent and non-perturbative approach to the quantisation of classical General Relativity, however, so far mostly without supersymmetry. The main obstacle to the extension of the techniques of LQG to the quantisation of higher dimensional Supergravity is that LQG rests on a specific connection formulation of General Relativity which exists only in D+1 = 4 dimensions. In this Letter we introduce a new connection formulation of General Relativity which exists in all space-time dimensions. We show that all LQG techniques developed in D+1 = 4 can be transferred to the new variables in all dimensions and describe how they can be generalised to the new types of fields that appear in Supergravity theories as compared to standard matter, specifically Rarita-Schwinger and p-form gauge fields.

Problem #1: "Should nature be supersymmetric" which is almost surely isn't.

Problem #2: There is absolutely no evidence to suggest that reality has more than 4 dimensions.

Problem #3: String theory has all the problems it has always had, among the most dramatic being, that it is under constrained with countless vacua, not of which clearly correspond to the real world.

Today Quanta magazine has more of this sort of thing, with an article whose title shows up on the web as A Correction to Einstein Hints At Evidence for String Theory. The sub-headline tells us that

In a quest to map out a quantum theory of gravity, researchers have used logical rules to calculate how much Einstein’s theory must change. The result matches string theory perfectly.

which sounds pretty impressive. The article starts off with quotes such as:

The hope is that you could prove the inevitability of string theory using these [bootstrap] methods,” said David Simmons-Duffin, a theoretical physicist at the California Institute of Technology. “And I think this is a great first step towards that.

and

Irene Valenzuela, a theoretical physicist at the Institute for Theoretical Physics at the Autonomous University of Madrid, agreed. “One of the questions is if string theory is the unique theory of quantum gravity or not,” she said. “This goes along the lines that string theory is unique.”

The paper at issue is this one which appeared on the arXiv nearly a year ago. It’s not about string theory or about conventional quantum gravity in four space-time dimensions. The topic is graviton scattering in maximally supersymmetric theories in ten flat space-time dimensions, and the argument is that the basic principles of supersymmetry, Lorentz invariance, analyticity and unitarity imply a bound on the coefficient of the lowest order correction term. The only relation to string theory is that a string theory calculation of this correction coefficient satisfies the bound (as expected, since string theory is supposed to satisfy the assumed basic principles). Much is made of the fact that in string theory one can get any value of the coefficient consistent with the bound. This is taken as evidence for the “inevitability” of string theory, but I don’t see this at all.

how do this result compare with loop quantum of 11D: the maximal SUGRA

Lubos Motl, while he has some narrow technical brilliance, is also a crackpot and an asshole. He tilts at windmills like denying climate change and irrational opposition to COVID-19 measures. He leaps on dubious bumps that aren't globally significant while ignoring the forest of experimental confirmation of the Standard Model. He favors far right, verging on neo-Nazi political parties.

Motl is far from an even handed judge of the merits of string theory and supersymmetry.

Woit is discussing, among other things, the Quanta article and specifically discusses the shortcomings of those claims.

so I heard. Well he did grow up in a communist nation so he seems to rebel against far left.

Lubos points out that string/M-theory is mainstream among top physics departments.

Witten said that M-theory low energy limit is 11 dimensional supergravity.

11 dimensional supergravity can be loop quantized, as Ahsketer's original 4D treatment has been generalized to higher dimensions and with super symmetry

So how does the results in the Quanta article compare with loop quantized 11 dimensional supergravity since they were testing it using 10D string theory.

To say that string/M-theory is regularly taught (and honestly, that is pretty much exclusively at the graduate level), is not to say that it is taught as an accurate description of the world. It is taught as a hypothesis that has received significant academic attention and no experimental confirmation.

The results in the Quanta article are trivial because they don't rule out myriad other theories that also do not deviate from classical GR by more than the stated amount, and because there is no positive evidence that our universe really is 10 or 11 dimensional.

Still, it's worth pointing out the top physicists minds at Princeton, Harvard, Stanford, MIT etc, all work on string / M-theory to graduate students. QG for them is synonymous with string theory. AFAIK there aren't any non-string QG theorists at these elite physics departments.

re: Quanta article,

Quanta article which was done in 10 flat dimensions and SUSY

what do you speculate, and I've asked Lubos this on his blog, is the relationship between string/M-theory in 10/11 D and

loop quantization of 10/11D SUGRA.

since M-theory low energy limit is supposed to be 11 D SUGRA, does loop quantization, which has been generalized to higher dimensions, have any thing to say

is loop quantization of 11D Sugra a type of string theory?

lubos response awhile back is that string theory doesn't need LQG.

"Ashtekar's original 4D treatment has been generalized to higher dimensions and with super symmetry"

Not in any way that allows calculation, as far as I know. The usual LQG procedures depend on special properties of SU(2) etc; these generalizations modify the first steps of loop quantization, so that other groups can be used; but that's still just the first step. The resulting quantum theory is still undeveloped, with no proof it exists, no solutions worked out (except perhaps in minisuperspace?), and no reason to think it would resemble geometric space.

"Not in any way that allows calculation, as far as I know. The usual LQG procedures depend on special properties of SU(2) etc; these generalizations modify the first steps of loop quantization, so that other groups can be used; but that's still just the first step. The resulting quantum theory is still undeveloped, with no proof it exists, no solutions worked out (except perhaps in minisuperspace?), and no reason to think it would resemble geometric space. "

the paper I mention before by

Towards Loop Quantum Supergravity (LQSG) Norbert Bodendorfer, Thomas Thiemann, Andreas Thurn

Does the sedenion algebra offer a grand unification theory?

As with the numerological propositions, the algebrological propositions would only be physically meaningful if they were part of a dynamical theory. At least Stephane Bronoff understands this, he wants his algebrology to follow from the opaque category-theoretic metaphysics that he describes in his earlier paper. But he certainly doesn't exhibit this deduction.

In the end you ask, "is this paper to be taken seriously?" Obviously not as a completed theory of everything. The odds are also massively against an individual work of algebrology being THE ONE which has chanced upon the right way to motivate the symmetry group of the standard model, for the same reason that almost all numerological formulas must be red herrings.

This paper belongs to the major subgenre of algebrology which tries to obtain the standard model gauge groups from hypercomplex numbers.

## 11 comments:

10D with maximal susy could also be loop quantize

what would happen if you compare the string results with lqg in 10d sugra

Towards Loop Quantum Supergravity (LQSG)

Norbert Bodendorfer, Thomas Thiemann, Andreas Thurn

Should nature be supersymmetric, then it will be described by Quantum Supergravity at least in some energy regimes. The currently most advanced description of Quantum Supergravity and beyond is Superstring Theory/M-Theory in 10/11 dimensions. String Theory is a top-to-bottom approach to Quantum Supergravity in that it postulates a new object, the string, from which classical Supergravity emerges as a low energy limit. On the other hand, one may try more traditional bottom-to-top routes and apply the techniques of Quantum Field Theory. Loop Quantum Gravity (LQG) is a manifestly background independent and non-perturbative approach to the quantisation of classical General Relativity, however, so far mostly without supersymmetry. The main obstacle to the extension of the techniques of LQG to the quantisation of higher dimensional Supergravity is that LQG rests on a specific connection formulation of General Relativity which exists only in D+1 = 4 dimensions. In this Letter we introduce a new connection formulation of General Relativity which exists in all space-time dimensions. We show that all LQG techniques developed in D+1 = 4 can be transferred to the new variables in all dimensions and describe how they can be generalised to the new types of fields that appear in Supergravity theories as compared to standard matter, specifically Rarita-Schwinger and p-form gauge fields.

Problem #1: "Should nature be supersymmetric" which is almost surely isn't.

Problem #2: There is absolutely no evidence to suggest that reality has more than 4 dimensions.

Problem #3: String theory has all the problems it has always had, among the most dramatic being, that it is under constrained with countless vacua, not of which clearly correspond to the real world.

lubos motl would disagree

regarding the topic

Today Quanta magazine has more of this sort of thing, with an article whose title shows up on the web as A Correction to Einstein Hints At Evidence for String Theory. The sub-headline tells us that

In a quest to map out a quantum theory of gravity, researchers have used logical rules to calculate how much Einstein’s theory must change. The result matches string theory perfectly.

which sounds pretty impressive. The article starts off with quotes such as:

The hope is that you could prove the inevitability of string theory using these [bootstrap] methods,” said David Simmons-Duffin, a theoretical physicist at the California Institute of Technology. “And I think this is a great first step towards that.

and

Irene Valenzuela, a theoretical physicist at the Institute for Theoretical Physics at the Autonomous University of Madrid, agreed. “One of the questions is if string theory is the unique theory of quantum gravity or not,” she said. “This goes along the lines that string theory is unique.”

The paper at issue is this one which appeared on the arXiv nearly a year ago. It’s not about string theory or about conventional quantum gravity in four space-time dimensions. The topic is graviton scattering in maximally supersymmetric theories in ten flat space-time dimensions, and the argument is that the basic principles of supersymmetry, Lorentz invariance, analyticity and unitarity imply a bound on the coefficient of the lowest order correction term. The only relation to string theory is that a string theory calculation of this correction coefficient satisfies the bound (as expected, since string theory is supposed to satisfy the assumed basic principles). Much is made of the fact that in string theory one can get any value of the coefficient consistent with the bound. This is taken as evidence for the “inevitability” of string theory, but I don’t see this at all.

how do this result compare with loop quantum of 11D: the maximal SUGRA

Lubos Motl, while he has some narrow technical brilliance, is also a crackpot and an asshole. He tilts at windmills like denying climate change and irrational opposition to COVID-19 measures. He leaps on dubious bumps that aren't globally significant while ignoring the forest of experimental confirmation of the Standard Model. He favors far right, verging on neo-Nazi political parties.

Motl is far from an even handed judge of the merits of string theory and supersymmetry.

Woit is discussing, among other things, the Quanta article and specifically discusses the shortcomings of those claims.

so I heard. Well he did grow up in a communist nation so he seems to rebel against far left.

Lubos points out that string/M-theory is mainstream among top physics departments.

Witten said that M-theory low energy limit is 11 dimensional supergravity.

11 dimensional supergravity can be loop quantized, as Ahsketer's original 4D treatment has been generalized to higher dimensions and with super symmetry

So how does the results in the Quanta article compare with loop quantized

11 dimensional supergravity since they were testing it using 10D string theory.

To say that string/M-theory is regularly taught (and honestly, that is pretty much exclusively at the graduate level), is not to say that it is taught as an accurate description of the world. It is taught as a hypothesis that has received significant academic attention and no experimental confirmation.

The results in the Quanta article are trivial because they don't rule out myriad other theories that also do not deviate from classical GR by more than the stated amount, and because there is no positive evidence that our universe really is 10 or 11 dimensional.

Oh i understand this.

Still, it's worth pointing out the top physicists minds at Princeton, Harvard, Stanford, MIT etc, all work on string / M-theory to graduate students. QG for them is synonymous with string theory. AFAIK there aren't any non-string QG theorists at these elite physics departments.

re: Quanta article,

Quanta article which was done in 10 flat dimensions and SUSY

what do you speculate, and I've asked Lubos this on his blog, is the relationship between string/M-theory in 10/11 D and

loop quantization of 10/11D SUGRA.

since M-theory low energy limit is supposed to be 11 D SUGRA, does loop quantization, which has been generalized to higher dimensions, have any thing to say

is loop quantization of 11D Sugra a type of string theory?

lubos response awhile back is that string theory doesn't need LQG.

"Ashtekar's original 4D treatment has been generalized to higher dimensions and with super symmetry"

Not in any way that allows calculation, as far as I know. The usual LQG procedures depend on special properties of SU(2) etc; these generalizations modify the first steps of loop quantization, so that other groups can be used; but that's still just the first step. The resulting quantum theory is still undeveloped, with no proof it exists, no solutions worked out (except perhaps in minisuperspace?), and no reason to think it would resemble geometric space.

@mitchell

"Not in any way that allows calculation, as far as I know. The usual LQG procedures depend on special properties of SU(2) etc; these generalizations modify the first steps of loop quantization, so that other groups can be used; but that's still just the first step. The resulting quantum theory is still undeveloped, with no proof it exists, no solutions worked out (except perhaps in minisuperspace?), and no reason to think it would resemble geometric space. "

the paper I mention before by

Towards Loop Quantum Supergravity (LQSG)

Norbert Bodendorfer, Thomas Thiemann, Andreas Thurn

is the only LQ-SUGRA paper I could find.

these lecture slides

http://conf.itp.phys.ethz.ch/qg11/talks/bodendorfer.pdf

makes me wonder

since Witten said that M-theory low energy limit is 11D SUGRA,

if you could nonpertubatively quantize 11D SUGRA in analogy to LQG in 4D, what would be the relationship between such a theory and 10D string theory?

Ask Bodendorfer

@mitchell

Ask Bodendorfer

btw i saw this

Does the sedenion algebra offer a grand unification theory?

As with the numerological propositions, the algebrological propositions would only be physically meaningful if they were part of a dynamical theory. At least Stephane Bronoff understands this, he wants his algebrology to follow from the opaque category-theoretic metaphysics that he describes in his earlier paper. But he certainly doesn't exhibit this deduction.

In the end you ask, "is this paper to be taken seriously?" Obviously not as a completed theory of everything. The odds are also massively against an individual work of algebrology being THE ONE which has chanced upon the right way to motivate the symmetry group of the standard model, for the same reason that almost all numerological formulas must be red herrings.

This paper belongs to the major subgenre of algebrology which tries to obtain the standard model gauge groups from hypercomplex numbers.

https://physics.stackexchange.com/questions/413906/does-the-sedenion-algebra-offer-a-grand-unification-theory

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