Is String Theory A Waste Of Time?

[RandallB]

Randall it is soooooo simple.

Amazing how something so simple can generate so many comments. – But rather helpful ones, as I took your advise and thought this one over a bit.

The tune up in my thinking was where I’d though of Special and General Relativity both as being Classical 4D ideas. My problem was thinking Classical as 4 D. But as said here:

However, it is also possible to treat time as an independent variable. That is, one can treat time as separate from the geometry of space. --- a classical way of treating space and time. .

I.E. Classical is not 4 Dimensional but 3 D with time being separate from Euclidian space.

This classical way was fine for SR with the SR equations being more precise solutions to the ones Newton provided.

But the classical was unable to depict how gravity worked. So we have the first really significant application of Riemannian geometry (from mid 1800’s I think) in order to build General Relativity. As 4D thinking to create “Warped space-time” was needed. Thus I shouldn’t think of Time by itself as being a dimension independent of three spatial ones where all four would have a metric. But instead :

In Gen Rel you start with a 4D space-time manifold (without a metric) and some matter …. where you solve for the gravitational field, which is becomes the metric.

So on the main point - understanding GR as being non-classical, is because of the need for Riemannian, I think I’m very clear on that and how that works.

In the QM arena :
On the issue of “perturbative” (String & M Theory) and “non- perturbative” (CDT, Triangulations) Background Independence are both of these significantly different that the BI of Gen Rel?
Is QM by definition Background Independent? with perturbative just one way of recognizing that aspect of QM.
Or is there even such a thing a Background Dependent QM theory?

Thanks for the links, and comments from all.
RB

 

[Juan R.]

"inefficient"

CDT path integral has not given any signs of being an inefficient approach to quantum gravity, and to the extent that one can compare the two rather different approaches I would say that it is MORE background independent than canonical LQG.

Among tested, well-established theories, General Relativity is the most background independent model we have. When quantizing Gen Rel, it is obvious to try to preserve the B.I. feature if one can. The comparative success or failure of various attempts to do this is not relevant to the validity of the effort.

With both String and canonical Loop experiencing difficulties, one sees that it is actually the most background independent approach that is currently making the most progress.

I would remark that in post #99 i said (readers could think that i said other thing since you cited to me out of context)

Do not forget that LQG is claimed background independent whereas continue to be an “inefficient” approach to quantum gravity.

 

[marcus]

Juan, you are doing the right thing to re-focus the discussion on the main question. I will try to prevent any misunderstanding by also giving CONTEXT of quotation. It is a very good idea. Here is my post #96

1. it doesn't mean anything unless you say FOR WHOM it is a waste of time.

2. increasing numbers of people seem to be deciding that FOR THEM it is a waste of time, and so they are getting out of the field, or they are not writing so many research papers as they did. (However on arxiv I see a growing number of string papers by people at Beijing Normal and other large Chinese universities. These people do not think string is a waste of time for them and they are responsible for an increasing fraction of the research postings.)

3. your statement does not have a clear meaning unless you specify a waste of time AS WHAT. I think a lot of people would agree that string theory can lead to ideas and results that are interesting AS MATHEMATICS.

4. your statement would not apply to a mathematically gifted young person who goes into string and discovers something interesting and valuable AS MATHEMATICS. You cannot say that such a person is wasting their time!
What gives mathematics intrinsic WORTH is the interest it evokes from other mathematicians. It does not need to be a fundamental testable model of nature.

5. however your message, suitably qualified and restricted, is a very helpful one to have expressed---and voicing it actually DOES STRING THEORISTS A FAVOR by increasing the pressure on them to arrive at a nonperturbative background independent formulation that makes falsifiable predictions. This is the only way to be sure that string theorizing is not a waste of time AS PHYSICS.

You responded in a forceful and substantive way to ALL my points in your post #99, but right now I want to focus on your reply to point 5. You argued that it would NOT BE A MAGIC CURE for the troubles of string theory for researchers to concentrate their effort on finding a nonperturbative and background independent formulation, and you gave an example where background independence has, by itself, not led to complete success (as I would freely admit.)

Do not forget that LQG is claimed background independent whereas continue to be an “inefficient” approach to quantum gravity

And I will agree with you that there are no magic cures (this was your phrase in post #99) in other words no certain method to rescue string from the landscape quagmire and make it a predictive testable theory. But nevertheless, have a look at this chart that shows my perspective and will help you understand why I think that working on a nonperturbative version of string COULD help the field advance. the percentage change is output is over the 3 years 2002-2004:

[u]QG approach        % change in output            progress      [/u]
strings (least indep)      decline                bogged down in landscape
loops (indep)             increase    cosmology, Freidel TFT, uniqueness theorem
triangles (most indep)    rapid increase          dramatic advance

strings is the least indep, assuming a manifold WITH prior metric, and it has experienced a substantial decline in research output: number of papers per year. except in China, people seem to be leaving the field.

loops is more indep, assuming a manifold WITHOUT prior metric, and has had something like 50% increase in research output, people entering the field

CDT triangles is a small field, but it is the MOST indep, and its spacetime is not even a differentiable manifold (although piecewise flat manifs are used in an approximation method). So this is radical, taking independence to a new level, and this approach has made the most pronounced progress, with percentagewise more people entering the field

Juan, you can challenge any of this because this is largely my personal perspective. Progress is hard to measure objectively and one must use individual judgement. But I am giving you this comparison chart so you will better understand my point of view.

You have argued that it would NOT help string become more predictive (that is: falsifiable) to develop a version that DOES NOT ASSUME A PRIOR METRIC. This would be the first kind of independence to ask for---a version that you can CALCULATE from without depending on a prior metric on the manifold.

My guess is that, on the contrary, it WOULD help theorists arrive at a falsifiable theory, if they would focus effort on making it nonperturbative.
Nonperturbative theories are harder to construct, and the difficulty narrows down the range of options. By denying themselves the convenience of a prior-chosen metric, the researchers might very well arrive at a theory that could be falsified through inconsistency or by experiment. This is how scientific theories are supposed to be and would constitute a kind of long-delayed success. And so i see it as a hopeful possibility---but I certainly confess that it is not a certainty!

 

[Juan R.]

Juan, you are doing the right thing to re-focus the discussion on the main question. I will try to prevent any misunderstanding by also giving CONTEXT of quotation. It is a very good idea. Here is my post #96



You responded in a forceful and substantive way to ALL my points in your post #99, but right now I want to focus on your reply to point 5. You argued that it would NOT BE A MAGIC CURE for the troubles of string theory for researchers to concentrate their effort on finding a nonperturbative and background independent formulation, and you gave an example where background independence has, by itself, not led to complete success (as I would freely admit.)



And I will agree with you that there are no magic cures (this was your phrase in post #99) in other words no certain method to rescue string from the landscape quagmire and make it a predictive testable theory. But nevertheless, have a look at this chart that shows my perspective and will help you understand why I think that working on a nonperturbative version of string COULD help the field advance. the percentage change is output is over the 3 years 2002-2004:

[u]QG approach        % change in output            progress      [/u]
strings (least indep)      decline                bogged down in landscape
loops (indep)             increase    cosmology, Freidel TFT, uniqueness theorem
triangles (most indep)    rapid increase          dramatic advance

strings is the least indep, assuming a manifold WITH prior metric, and it has experienced a substantial decline in research output: number of papers per year. except in China, people seem to be leaving the field.

loops is more indep, assuming a manifold WITHOUT prior metric, and has had something like 50% increase in research output, people entering the field

CDT triangles is a small field, but it is the MOST indep, and its spacetime is not even a differentiable manifold (although piecewise flat manifs are used in an approximation method). So this is radical, taking independence to a new level, and this approach has made the most pronounced progress, with percentagewise more people entering the field

Juan, you can challenge any of this because this is largely my personal perspective. Progress is hard to measure objectively and one must use individual judgement. But I am giving you this comparison chart so you will better understand my point of view.

You have argued that it would NOT help string become more predictive (that is: falsifiable) to develop a version that DOES NOT ASSUME A PRIOR METRIC. This would be the first kind of independence to ask for---a version that you can CALCULATE from without depending on a prior metric on the manifold.

My guess is that, on the contrary, it WOULD help theorists arrive at a falsifiable theory, if they would focus effort on making it nonperturbative.
Nonperturbative theories are harder to construct, and the difficulty narrows down the range of options. By denying themselves the convenience of a prior-chosen metric, the researchers might very well arrive at a theory that could be falsified through inconsistency or by experiment. This is how scientific theories are supposed to be and would constitute a kind of long-delayed success. And so i see it as a hopeful possibility---but I certainly confess that it is not a certainty!

In short, string theory fails because is NOT a theory about our universe. This validation of the theory is rather broad and is not based in specific issues like BI.

Our universe is TODAY 4D and non supersymmetric, therefore we may develop a quantum theory for 4D and nonsupersimmetriy. Perhaps tomorrow new experiments discover hidden dimensions or super partners of currently known particles, but FIRST one may develop a theory for the universe that we know TODAY.

The problem of 40 year of impressive failure of ST is in the violation of scientific method. String theorists followed an initial "beatiful" idea and develop a theory for 26, 10 or 11D with supersimmetry and other stuff according to mathematical incosistency of the beatiful initial idea. How there is no posibility for developing a consistent theory for 4D without supersymmetry, there is possibility for computing nothing of this world from ST. Precisely this is the history of the field on last 30 years. Nothing computed or when computed with wrong behavior (nuclear force), wrong models (spliting of metric violating GR) or discrepancies of 50 orders of magnitude between theory and data.

And all of that even ignoring recent advanced stuff that is developed in other fields of theoretical science and ignored by super masterminds string theorists (of course some are respectful and hones but others are not). Stuff known in chemistry during 30 years (see Nobel lecture by Prigogine) is being introduced these days by string theorists in a new revolution.

That is, that was known 20 or 30 years ago in other fields is the last fad for ignorant (but very arrogant) people like Witten, Vafa, Greene, Schwartz, Motl, etc.

already explained that even with 2 or 3 new revolutions, string theory continue to be a joke (irrelevant) for people working in serious stuff.

Finalize saying that the idea of nondifferentiable spacetimes is also one of my ideas, but string and M theorists (yes those that claim for the Final theory the theory most sophisticated of the world, etc, etc.) continue working with "old" differentiable manifolds (e.g. famous CY of string theory or the new G2 of M-theory).

The arrogance of many string theorists permit to me writte this hard words (that i newer wrote for other honest researchers, including trinagulation ones)

I would say that there is posibility for reduction of dimensionality on my work and contacted with the author of paper you cite time ago. We discussed the rumour that a decrease on Newton force has been measured. If finally true this is another hard knock for ST which always has claimed that Newton force may be stronger on small distances.

F = (1/r^(2+D))

with D additional dimensions. Curiously doing D = -2, that is, reduction of dimensionality, one obtains less force (if confirmed experimentally) and absence of divergences for r = 0.

This argument is not riguroius but offer an idea of the surprising things that one can learn from alternative points of view.

 

[Juan R.]

According to

https://www.physicsforums.com/showthread.php?t=85971

there is not violations of Newtonian force known.

 

[marcus]

According to

https://www.physicsforums.com/showthread.php?t=85971

there is not violations of Newtonian force known.

Hello Juan, I liked your most recent long post. We still should provide some documentation---I should supply some data for the percentage changes in research output over the 3 years 2002-2004 and so forth.
But I couldn't think of anything more to say right now.

Yes, about the short range Newton law measurments. I know. Ohwilleke noted this in a thread in this section also. If you want to post on Ohwilleke's thread you might get some discussion. I don't connect this immediately to string theory because I don't find string theory very interesting and in the long run it might not be all that important. but verifying Newton law of gravity at short range does seem interesting. maybe Ohwilleke or somebody will expand on this subject

GRAVITY NORMAL AT SMALL SCALES
https://www.physicsforums.com/showthread.php?t=85989

check it out. Haelfix and Chronos have already replied on that thread.

--------------------------

by the way, something different. Do you know the story (arivero told me) of the two men discussing whether a white-ish block of material soap or cheese
one says it is soap, the other says it is cheese, and to prove it he cuts a sample and starts chewing it up----he will show it is cheese by eating some.
After a while he begins to foam and bubble at the mouth, and he stops chewing and says:

"Sabe a jabon, pero es queso."

We might translate this as
IT TASTES LIKE EPICYCLES, BUT IT'S REALLY A THEORY OF EVERYTHING.

 

[CarlB]

But the classical was unable to depict how gravity worked. So we have the first really significant application of Riemannian geometry (from mid 1800’s I think) in order to build General Relativity. As 4D thinking to create “Warped space-time” was needed.

This is outside my area, but there are a few physicists who are convinced that gravity can be done on a Euclidean basis. I think the best explanation is that of David Hestenes:

Lasenby, Doran and Gull have recently created a powerful coordinate-free reformulation, re¯nement, and extension of general relativity [1,2]. It is a gauge theory on °at spacetime, but it retains the attractive geometric structure of Einstein's theory.
...
Indeed, the method amounts to a new approach to differential geometry which could fairly be called gauge geometry.
...
Part II develops gauge covariant Riemannian geometry on flat spacetime. The main objective is to clarify the fundamental ideas and provide a systematic account of the definitions, theorems, proofs, and computational techniques needed to apply the spacetime calculus efficiently to any physical problem. Specific physical applications are not addressedhere; excellent examples, which amply demonstrate the computational power of the calculus, have been worked out in [1,2] and [9-13].
...

http://modelingnts.la.asu.edu/pdf/NEW_GRAVITY.pdf

Unfortunately, understanding the above paper requires a certain amount of understanding of "geometric algebra", which is a type of Clifford algebra where the basis vectors are associated with the tangent vectors at a given point of the manifold of space-time.

Carl

 

[Juan R.]

This is outside my area, but there are a few physicists who are convinced that gravity can be done on a Euclidean basis.

Carl

Well, the popular understanding of GR is that gravity is spacetime curvature, but this is rather difficult to believe by several motives.

1) Nobody has measured spacetime curvature directly.

2) Spacetime curvature does not imply curved space. Usual popular image of curved space around Sun is pictorial only.

3) The curved spacetime view is not exclusive. E.g. torsion formulations, Cartan-Ehelers reformulation, etc.

4) The curved spacetime view is problematic on the Newtonian limit. Far from common understanding, nobody has derived the Newtonian limit from GR. This is easy to understand. In the limit c -> infinite the curvature of spacetime may be zero like correspond to the Newtonian approach but then, if gravity is curvature, gravity may be zero. Textbook’s derivation of Newton second law is a derivation valid only when c is finite and the approximation is non linear. c finite contradicts Newtonian theory. Ehlers reformulation of GR does not obtain the Newtonian limit (even if Ehlers claims the contrary). His formulation on flat spacetime has problems: I) the splitting of curved derivatives is not unique and additional equations does not contained in GR are needed, ii) the compatibility with Newtonian limit is done invoking “asymptotic flatness”, which is experimentally unsustainable.

5) The geometric approach breaks the unification with rest of forces.

6) Far from standard claims the geometric approach of GR does not explain the misterium of gravity. This is easy to understand. In Newtonian theory, one has an equation for computing the force, but none explaining of underlying mechanism of it. In Einstein (really Hilbert-Einstein-Grossmann) theory, one has equations for computing spacetime curvature, but none explaining of underlying mechanism of it. GR substitutes the question "How does Earth know that force that Sun does" by "How does Earth know the curvature that Sun does". Far from common statements in GR literature, GR does not explain gravity.

The solution is not a geometric approach to quantum gravity. The solution is a force-like approach to GR that can be quantized more a demonstration of that GR is, strictly speaking, wrong.

Regarding your link, not only the choosing of Minkoskian spacetime metric is not correct (related to imposibility for obtaining correct Newtonian limit, that was the source for the search of alternatives like NCG and similar), moreover, i see fundamental difficulties with the "gauge" line element (7.7) that appears to be the basis of all the "gauge" approach.

 

[Mike2]

At best String Theory can only be an effective theory, not a TOE. This is because there seems to be nothing in String/M-theory itself that explains where the strings or membranes came from to begin with. What process creates these membranes/strings from the background? I suppose that there was a background without strings when the universe was very, very small, and then at some later time some process gave rise to strings and/or other membranes. How did that happen?

I suspect that if we knew the process by which strings/membranes come into existence, then this might give us constraints on which strings/branes can exist and allow a choice from the landscape.

 

[RandallB]

there are a few physicists who are convinced that gravity can be done on a Euclidean basis. I think the best explanation is that of David Hestenes:
http://modelingnts.la.asu.edu/pdf/NEW_GRAVITY.pdf

If you know of one, I’d love to see where someone makes a serious attempt at a Euclidean explanation, I’ve never seen one.

I have to disagree on David Hestenes. He cannot be talking about a Euclidean basis while using GR and Riemannian geometry. That is 4D and Euclidean is 3D where time is just a variable. GR/Riemannian is also “Background Independent” as I understand it, and Euclidean would be Background Dependent.
While the successful current theories GR and QM are not.
At least I think QM is background independent.

The ideas that wish to replace or correct GR and/or QM, all seem to get more complex in both their concept and mathematics. Maybe that’s because reality is complex.

I still feel that String theory has been successful in showing that 11 dimensions “appear” to be required. Therefore, in my opinion any proposed new theory needs to explain why that appeared to be true. That includes variations on Strings, canonical science, and even Euclidean explanations.

RB

 

[Juan R.]

At best String Theory can only be an effective theory, not a TOE. This is because there seems to be nothing in String/M-theory itself that explains where the strings or membranes came from to begin with. What process creates these membranes/strings from the background? I suppose that there was a background without strings when the universe was very, very small, and then at some later time some process gave rise to strings and/or other membranes. How did that happen?

I suspect that if we knew the process by which strings/membranes come into existence, then this might give us constraints on which strings/branes can exist and allow a choice from the landscape.

An effective theory for that? From ST one can compute absolutely nothing and nothing can be explained on a sound basis. ST is mathematical gulash with no link with nothing of this world.

The strings of string M theory -really one would talk of the p-branes- are really inmortal on the formulation proposed. In fact some brane inspired cosmology models claim that the big bang was (of course is just a especulation) the outcome of a collision of two 5D branes.

 

[Juan R.]

If you know of one, I’d love to see where someone makes a serious attempt at a Euclidean explanation, I’ve never seen one.

I have to disagree on David Hestenes. He cannot be talking about a Euclidean basis while using GR and Riemannian geometry. That is 4D and Euclidean is 3D where time is just a variable. GR/Riemannian is also “Background Independent” as I understand it, and Euclidean would be Background Dependent.
While the successful current theories GR and QM are not.
At least I think QM is background independent.

RB

I will say nothing on your claim that QM is BI.

Regarding above link you would read it first before disagree . Already in the abstract you can see that are talking of a flat spacetime not a flat space. See also my post #131.

The ideas that wish to replace or correct GR and/or QM, all seem to get more complex in both their concept and mathematics. Maybe that’s because reality is complex.
RB

One may simply explain world. Often this is done by the use of more complex formulations and novel mathematical tools. All attempt to quantize gravity rely on new math and concepts do not included on GR + QM.

But whereas many of others approaches focus on physical insight, ST is just a mathematical goulash around an initially "beatiful" idea that was discarded in accelerator experiments many decades ago.

I still feel that String theory has been successful in showing that 11 dimensions “appear” to be required. Therefore, in my opinion any proposed new theory needs to explain why that appeared to be true. That includes variations on Strings, canonical science, and even Euclidean explanations.

RB

Required for what? for fulfilling ArXiv with dozens of ineffective preprints? After of more than 30 years, string theory is even poor that when began.

Things are much more simple: any proposed new theory needs to explain the world like it appears to us. Today we know that the world is 4D and non supersymmetric, therefore the first quantum theory of gravity may be a formulation for 4D and without supersimmetry. Precisely this is the point of LQG and other approaches.

If at 2007, supersimmetry is experimentally observed. No problem! your theory will continue to be correct (as Newtonian mechanics is in Formula 1), simply you will need generalize to supersimmetry.

The problem of ST and M theory is that 11D and supersymmetry, and the rest of mathematical gulash, are just a mathematical gulash added to the theory because was internally inconsistent or violated experimental data. For example supersymmetry was added ad hoc in the 80s because string theory without it predicted tachions which were newer observed

The aim of physics is to explain universe as it is, is not to develop a theory of "like world would be for me".

All on string theory is about things that are not about our universe. Nothing of standard model or of GR is obtained from ST. At the best, one obtains certain models (after of tricks and ad hoc asumptions) that look like but are not equivalent.

Almost any young student knows the myth that ST predicts gravity or that GR is recovered in the low energy limit but both of those claims are not true.

In fact, causality in ST is defined in a flat metric whereas causality in GR is not. Then what? In the past they say like ST is not 100% compatible with GR and ST is mathematically "beatiful" then the problem may be with GR.

In fact, you appears to ignore that only some years ago string theorists claimed that one would do not take GR "too seriously" . Even today some guys claim that one would ignore experimental data of GR in favor of string theory!

All of this is a nonsense, ST is outside of physics.

Those "details" are do that ST was a waste of time or in the words of P.W. Anderson

a futile exercise like physics

 

[marcus]

...

I still feel that String theory has been successful in showing that 11 dimensions “appear” to be required. Therefore, in my opinion any proposed new theory needs to explain why that appeared to be true. That includes variations on Strings, canonical science, and even Euclidean explanations.

strange thought, Randall

to the ancient alchemists, it appeared that all matter could be explained by combining 4 elements

shall we require of all future theories of matter that they explain why that appeared true to the alchemists?

 

[Juan R.]

strange thought, Randall

to the ancient alchemists, it appeared that all matter could be explained by combiniing 4 elements

shall we require of all future theories of matter that they explain why that appeared true to the alchemists?

Nice reply!

You explained better and shorter (= two time better) than my

 

[marcus]

Nice reply!

You explained better and shorter (= two time better) than my

I owe this entirely to your inspiring example, Juan
thank you kindly


however on another matter, I feel a deep attachment to the geometric explanation of gravity and, although I am disinclined to argue with you, I wish you would not so often castigate it with your disapproval

but if you must, by your very nature as Juan, then I guess you must

 

[CarlB]

If you know of one, I’d love to see where someone makes a serious attempt at a Euclidean explanation, I’ve never seen one. I have to disagree on David Hestenes. He cannot be talking about a Euclidean basis while using GR and Riemannian geometry. That is 4D and Euclidean is 3D where time is just a variable.

Look at chapter IV of this link, which is from Foundations of Physics, 35: 1-67 (2005):
http://modelingnts.la.asu.edu/pdf/GTG.w.GC.FP.pdf
http://modelingnts.la.asu.edu/html/GCgravity.html

I think the above link is a better article in its explanation of the theory than the one I originally posted.

GR/Riemannian is also “Background Independent” as I understand it, and Euclidean would be Background Dependent. While the successful current theories GR and QM are not. At least I think QM is background independent.

I believe that the standard model of QM is background dependent. Or more precisely, that it can be cast in a background dependent interpretation. Here's an arxiv article on the subject that explains it pretty much the way I see it, except that I think that background dependence is a good thing, not something to be gotten rid of:
http://arxiv.org/PS_cache/hep-th/pdf/0409/0409048.pdf

A typical QFT textbook will deal with the background dependence of the theory by showing that while the calculations do assume a background (in the form of a particular metric), the results of the calculations are compatible with Lorentz / Poincare symmetry. That is, if you assume a different reference frame, your calculation will be different but the final result will be the same. The fact that they have to show this is an indication that the theory is not in itself inherently background independent. From my point of view, this is evidence that the universe does have a "background". It's just that since we're a part of the universe, we have great difficulty figuring out exactly what that background is.

The ideas that wish to replace or correct GR and/or QM, all seem to get more complex in both their concept and mathematics. Maybe that’s because reality is complex.

Even simple equations can have very complex solutions. If one were to look at the table of the elements, one might conclude that Schroedinger's wave equation, which pretty much explains the thing, must also be complex. My guess is that simplicity should be at the core.

I still feel that String theory has been successful in showing that 11 dimensions “appear” to be required. Therefore, in my opinion any proposed new theory needs to explain why that appeared to be true. That includes variations on Strings, canonical science, and even Euclidean explanations.

I only bought one string theory textbook. Different chapters in the book purport to prove why N dimensions are necessary for a consistent theory. The only problem is that N is not a constant but changes from chapter to chapter.

My guess is that quarks and leptons are the results of a two stage condensation. The second stage is the combination of left and right handed massless chiral particles to form fermions. This is almost a part of the standard model, the difference being that the standard model requires a Higgs particle to be absorbed (or emitted) at the vertices where left and right handed chiral fermions convert to each other. The first stage of the condensation is one that produces the massless chiral fermions and is beyond the scope of this discussion. But this sort of concept does get back to string theory, or at least to the concept of hidden dimensions, by the fact that if one ignores a condensation of subparticles, (that is, if one only looks at the interactions of the combined system), one will end up with unexplained degrees of freedom. These extra degrees of freedom can be naturally explained through the notion of hidden dimensions.

As an example, if two subparticles combine to form a tightly bound composite particle, we will use center of mass coordinates for the composite particle. But there will still be a set of relative coordinates for the two subparticles. Since it is a bound state, the relative coordinates will be compact and therefore will look (mathematically) like a space of compactified dimensions. This gives some hope of determining the topology of string theory from the mechanics of the subparticles.

Carl

 

[RandallB]

strange thought, Randall

to the ancient alchemists, it appeared that all matter could be explained by combiniing 4 elements

shall we require of all future theories of matter that they explain why that appeared true to the alchemists?

Excellent point and
YES WE SHOULD
BUT - “ancient alchemists” ideas have been explained as wrong, based on current science. And we do understand how their old view of reality; lead them to think they way they did.
So that job has been done.
I also understand need for a New Theory to show the old wrong theories to be wrong to make way for a new one.
However, loudly proclaiming that GR and QM are wrong is far short of showing them to be wrong.

True enough not every idea that falls off the truck should qualifies to set yet another standard that must be disproved of proved by any future new theory. That will always be an individual judgment call. But where rigorous scientific interpretation of observations and rigorous math has been applied to build a view of a theory - some explanation as to why the theory was constructed incorrectly should be proved by a replacing better theory. Just as has been done with Alchemists Theories. If it cannot do so what makes the new theory better?
In the worst case view of both GR and QM they have certainly met that standard.
But, for all those that have better answers than GR or QM, I've never seen a reasoned explanation as to why GR and QM work so well and are yet wrong.

Now I’m no String or M theory expert, in fact I don’t see how they could be correct. But based the quality of the people and the work they have done, I trust and I believe the ideas were rigorously formed. And for me the idea of 10 or 11 dimensions was reasonable reached in this case. So for me I feel they have met the standard. Even though I do not believe in extra dimensions myself I feel it’s only responsible to accept the higher standard. Therefore if I want to show strings to be wrong, and there is something better, I must understand how they made the mistake of assuming the extra dimensions. If I can’t take the responsibility to do that, then why should anyone take a new idea seriously?

I just find this a more reasoned and logic approach to the issue rather than just cobbling a bunch of ideas together with no proofs, and no explanations of how the others made the wrong conclusions.

Is that easy to do – of course not it's harder, nobody promised easy.

RB

 

[selfAdjoint]

I have to disagree on David Hestenes. He cannot be talking about a Euclidean basis while using GR and Riemannian geometry. That is 4D and Euclidean is 3D where time is just a variable. GR/Riemannian is also “Background Independent” as I understand it, and Euclidean would be Background Dependent.

"Euclidean" in this context refers to any geometry where the line element ds^2 = g_{ab}dx^adx^b is positive definite. So you can have Riemannian geometry that is Euclidean. The line element of GR is not positive definite, because the "time" term is a different sign from the "space" terms.

And "background independent" is a property of the physics together with the geometry, not the kind of geometry alone. If the physics acts on the geometry, and the geometry determines the physics, so there is self-interaction, then you have background indpendence.

 

[marcus]

...And "background independent" is a property of the physics together with the geometry, not the kind of geometry alone. If the physics acts on the geometry, and the geometry determines the physics, so there is self-interaction, then you have background independence.

nice way to put it. points up a positive quality instead of the negative quality of not being dependent on something like a prior fixed choice of background metric. different ways of saying the same thing but more intuitive/evocative to say it in this positive way

 

[Juan R.]

however on another matter, I feel a deep attachment to the geometric explanation of gravity and, although I am disinclined to argue with you, I wish you would not so often castigate it with your disapproval

At the best, i think that you would only find difficulty with point 4) of post #131, since rest is standard or almost standard. And, of course, with my own solution to the problem.

I think that once the paper was published you could study it carefully and write a public comment if you consider that GR is still a good approach after of reading my work.

If i am wrong you will help to me to understand correctly gravitation .

If i am not wrong then I will help to you to understand correctly gravitation.

 

[Juan R.]

I only bought one string theory textbook. Different chapters in the book purport to prove why N dimensions are necessary for a consistent theory. The only problem is that N is not a constant but changes from chapter to chapter.

Carl

Very good point!

In fact the history of dimensions is

4D, 5D, 26D, 10D, 11D, ...

According to B. Greene some string theorists are now working in the posibility of more than one time dimension whereas others claim that the fail of compactification may indicate that there are still unknown 4D-versions of "string" theory.

Also the size of strings changes from "chapter to chapter" from "infinitely" small (Planck) to mm range to again "infinitely" small to infinitely large. There is a version that says that compactified dimension are the usual 4D ones, etc.

The rest of "theory" is also chapter-dependant and even book-dependant or author-dependant!

 

[Juan R.]

Now I’m no String or M theory expert, in fact I don’t see how they could be correct. But based the quality of the people and the work they have done, I trust and I believe the ideas were rigorously formed. And for me the idea of 10 or 11 dimensions was reasonable reached in this case. So for me I feel they have met the standard. Even though I do not believe in extra dimensions myself I feel it’s only responsible to accept the higher standard. Therefore if I want to show strings to be wrong, and there is something better, I must understand how they made the mistake of assuming the extra dimensions. If I can’t take the responsibility to do that, then why should anyone take a new idea seriously?

I just find this a more reasoned and logic approach to the issue rather than just cobbling a bunch of ideas together with no proofs, and no explanations of how the others made the wrong conclusions.

Is that easy to do – of course not it's harder, nobody promised easy.

RB

This sounds like the main argument for studying string theory that some string theorists use: "Because Witten believes on it".

That is not a scientific argument.

The "quality" of people is a subjective concept and, moreover, is not guarantee of a good work. Look for example the history of QFT, almost all great guys Schrödinger, Dirac, etc. did the wrong work and a new generation of young people did QFT. In fact, this argument against string theory has been recently used by Dyson.

Regarding the "quality" of the work they have done, i could say that the quality is very low, with lot of wrong details that are corrected after of decades. Material known in other fields is introduced decades after in string theory. In concrete points, I can assure that the quality of Seiberg's work on NC geomstry is low, the quality of Schwartz's work on unitarity is low, the quality of Witten's work on QM foundations is low, the quality of Nanopoulos' work on the arrow of time problem is low, etc.

So for me I feel they have met the standard.

Curiosly the standard in quantum gravity research is not that.

Therefore if I want to show strings to be wrong, and there is something better, I must understand how they made the mistake of assuming the extra dimensions.

Curiously science does not work on that way. Are string theorists who may show that universe is 11D! Curiously string theorists have shown nothing and none of their initial promises has been done after of more than 30 years!

It is time for exploring other alternatives.

 

[RandallB]

It is time for exploring other alternatives.

Well at least that's one point we completely agree on.
I just hope and even expect that a good alternative will prove strings wrong by show how/why it appeared to them there should be multi D's. I'd even expect proving so can be helpful.
RB

 

[RandallB]

"Euclidean" in this context refers to any geometry where the line element ds^2 = g_{ab}dx^adx^b is positive definite. So you can have Riemannian geometry that is Euclidean. The line element of GR is not positive definite, because the "time" term is a different sign from the "space" terms.

And "background independent" is a property of the physics together with the geometry, not the kind of geometry alone. If the physics acts on the geometry, and the geometry determines the physics, so there is self-interaction, then you have background indpendence.

So is GR consided background indpendent ??
Does "The line element of GR is not positive definite" address this issue?

The Lee Smolin link (Thanks for finding Marcus)
http://arxiv.org/abs/hep-th/0507235
Provides a firm argument the GR is “relational” or background independent.
At least where “warping” is concerned.
Is this generally accepted as the case or is this a “debated point” ?

 

[CarlB]

In fact the history of dimensions is
4D, 5D, 26D, 10D, 11D,

If you attribute the hidden dimensions in string theory to internal degrees of freedom between constituents of the supposedly fundamental particles, then the varying number of hidden dimensions is an obvious indication that the number of constituents varies between the particles.

If spin-1 bosons have more internal constituents than spin-1/2 fermions, (as one might expect if all these particles were condensed from fermionic subparticles) it is quite natural that in string theory, the fundamental bosons would have a larger number of hidden dimensions than the fundamental fermions.

The quarks and leptons seem to require 10 or 11 dimensions in total, while the various gauge bosons require 26. (I'm reading Polchinski.) These numbers are about right for the spin-1/2 fermions to be composed of three fundamental subparticles, while the spin-1 bosons are composed of six. That is, three subparticle fermions would have a total of something around 12 degrees of freedom, while six subparticles would have about 24.

Various authors have proposed that the quarks and leptons are condensed states and the number of subparticles is frequently given as three. My own proposal is along this line, but is somewhat radical:
http://brannenworks.com/PHENO2005.pdf

Carl

 

[Juan R.]

If you attribute the hidden dimensions in string theory to internal degrees of freedom between constituents of the supposedly fundamental particles, then the varying number of hidden dimensions is an obvious indication that the number of constituents varies between the particles.

If spin-1 bosons have more internal constituents than spin-1/2 fermions, (as one might expect if all these particles were condensed from fermionic subparticles) it is quite natural that in string theory, the fundamental bosons would have a larger number of hidden dimensions than the fundamental fermions.

The quarks and leptons seem to require 10 or 11 dimensions in total, while the various gauge bosons require 26. (I'm reading Polchinski.) These numbers are about right for the spin-1/2 fermions to be composed of three fundamental subparticles, while the spin-1 bosons are composed of six. That is, three subparticle fermions would have a total of something around 12 degrees of freedom, while six subparticles would have about 24.

Various authors have proposed that the quarks and leptons are condensed states and the number of subparticles is frequently given as three. My own proposal is along this line, but is somewhat radical:
http://brannenworks.com/PHENO2005.pdf

Carl

However, in string theory, the hidden dimensions are not related to internal degrees of freedom on a 4D universe.

"then the varying number of hidden dimensions is an obvious indication that the number of constituents varies between the particles."

I do not understand to you here. The varying number of hidden dimensions is just historical one. In superstring theory, the number of dimensions is 10 and 11 in the new M theory, but is not 10D for some particles and 26D for others. Superstring theory is a priori valid for both bosons and fermions. Only the old bosonic string theory is for 26D.

I do not know if fermions are elementary or composed objects. Nobody know that, still let me highlight that in superstring, brane and M theory fermions are elementary objects, of course are vibrational states of the p-brane but are not composed of collection of branes. They are the brane itself.

 

[CarlB]

However, in string theory, the hidden dimensions are not related to internal degrees of freedom on a 4D universe. ... I do not understand you here. The varying number of hidden dimensions is just historical one. In superstring theory, the number of dimensions is 10 and 11 in the new M theory, but is not 10D for some particles and 26D for others. Superstring theory is a priori valid for both bosons and fermions. Only the old bosonic string theory is for 26D.

I don't mean to argue that string theory is correct, but instead to point out that the dimensional regularization that leads to various assumptions of dimensions in string theory is an argument that can also be applied to the hidden dimensions arising from multi particle bound states.

Since string theory, like Kaluza-Klein, only deals with the lowest modes, there will inevitably be many different physical arrangements that will give those same modes. In other words, by ignoring all but the lowest energy modes, the mathematics problem of defining the physical situation from the spectrum is severely under constrained. What I'm suggesting is that the modes that correspond to the standard model can be written as the lowest modes resulting from composite particles. I think that this can be done in a manner compelling in its simplicity. But when you're done with this, there may be a way to solve the string theory vacua problem, at least on a particle type by particle type basis.

Carl

 

[Juan R.]

I don't mean to argue that string theory is correct, but instead to point out that the dimensional regularization that leads to various assumptions of dimensions in string theory is an argument that can also be applied to the hidden dimensions arising from multi particle bound states.

Since string theory, like Kaluza-Klein, only deals with the lowest modes, there will inevitably be many different physical arrangements that will give those same modes. In other words, by ignoring all but the lowest energy modes, the mathematics problem of defining the physical situation from the spectrum is severely under constrained. What I'm suggesting is that the modes that correspond to the standard model can be written as the lowest modes resulting from composite particles. I think that this can be done in a manner compelling in its simplicity. But when you're done with this, there may be a way to solve the string theory vacua problem, at least on a particle type by particle type basis.

Carl

Aha!

Well, unfortunately i cannot help to you here. I am a bit confused on the question of unification and i do not know which could be the best (promising!) way.

- Perhaps composite particles.
- Perhaps pure geometric arguments on 4D on style of Connes program.
- Etc.

Unfortunately, i cannot valuate your proposal now. I am just focusing in quantization of pure gravity and spacetime.

 

[sssddd]

i would really like to know the background of the guy who says string theory is a waste of time.

 

[RandallB]

i would really like to know the background of the guy who says string theory is a waste of time.

He has promoted links to canonical science in earlier posts here that might help. I could never make heads or tails of it though. Maybe you’ll have more luck.