Is String Theory A Waste Of Time?

CarlB

But it's not starting from a point of "NO PRIOR METRIC". Instead they're talking about starting without a coordinate system. For example, from your very useful link:

http://www.arxiv.org/PS_cache/hep-th...12/0212340.pdf

In fact, each of the simplices that these guys are adding up does possess a metric structure. That's what gives the squared lengths of their edges. For that matter, if one knows the squared lengths of the edges, it's easy enough to define a coordinate system and metric for the simplice (which is assumed to be flat in the above link).

This concept of getting space back from just the edge lengths of simplices smells to me of pure mathematics. It's just not amazing to me except that so many people would work so hard on it. It's like a chapter from Bourbaki. What's more, it appears to provide no explanation for any physical phenomena such as masses or coupling constants or anything else not already covered by the standard model.

Carl

Also see:
So the metric nature of the simplices is quite explicit.

It seems to me that the whole difficulty in this endeavor comes from the requirement that the result be Lorentz symmetric. But there is also an apparent assumption of the existence of a global time: The underlying problem here is not with QM or gravity, it is in the unification. The above seems to me to suggest that the real problem is the assumption of Lorentz symmetry.

By the way, Hestenes believes that there is a method of putting gravitation onto a flat copy of his space time algebra (STA). Thus the underlying manifold would be flat. The method was found by Lasenby, Doran and Gull. If this is the case, wouldn't it make the whole problem of having to sum over bizarre geometries trivial? Here's a link to his article, please comment (as I know little about gravitation):
http://modelingnts.la.asu.edu/pdf/NEW_GRAVITY.pdf

Carl

RandallB

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: 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 :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.

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)

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

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:

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.

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 uinverse 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

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

there is not violations of Newtonian force known.

marcus

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 couldnt 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 dont connect this immediately to string theory because I dont 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
http://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

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:

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.

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

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.

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.

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.

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.

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

marcus

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.

Nice reply!!!

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

marcus

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

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.

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.

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 only bought one string theory text book. 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