Is String Theory A Waste Of Time?


by Juan R.
Tags: string, theory, time, waste
marcus
marcus is online now
#91
Aug17-05, 10:18 AM
Astronomy
Sci Advisor
PF Gold
marcus's Avatar
P: 22,809
Quote Quote by Telos
Juan, I do not think it is a waste of time to show that something is false.

Interesting book, though!
I see the book Juan mentioned (that amazon says is due out in October) is by the same physicist/cosmologist/popular author who wrote "The Physics of Star Trek" and "Fear of Phyics: a Guide to the Perplexed".

Telos, you are definitely on to something about time spent drawing testable conclusions from a theory so that it may be shown false.
marcus
marcus is online now
#92
Aug17-05, 11:11 AM
Astronomy
Sci Advisor
PF Gold
marcus's Avatar
P: 22,809
Quote Quote by Juan R.

You can be sceptic of my evaluation of the theory (that is not a problem for me). But my evaluation is, exactly, that string theory is a waste of time (and money). I could search other words for you but the message would be the same.
...
I am skeptical of the broad way the evaluation is stated. There are several things to say. One is that your opinion is shared (in a qualified way) by a growing number of physicists, for reasons that were mentioned in this earlier PF thread:
http://www.physicsforums.com/showthread.php?t=80760

In this thread, which Ratzinger started in June 2005, some knowledgeable PF people like Haelfix, selfAdjoint, Ohwilleke, concisely reported some reasons why there has been a decline, over the past 3 years or so, in interest and popularity of string research.

Increasing worry and pessimism among string researchers was reflected in the Toronto discussion video.
http://www.physicsforums.com/showthread.php?t=84585
One encounters expressions of disillusion among graduate students---some of whom are changing fields---and symptomatic efforts being made by string-loyal bloggers (such as Motl and Distler) to shore up morale among the graduate students.

We also see some statistical indications of the decline in string interest, popularity, optimism. One can always argue about how to interpret the various statistical measures, however.

I must say that observing this string "downsizing" going on has increased my respect for the honesty and courage of certain researchers such as Andy Strominger. He made an excellent two minute statement in the Toronto discussion at time 1:28:20
It put me in mind of a story in the Bible where a general tells his soldiers that anyone who wants to can go home, and about half of them leave (this is called "downsizing"), then the remaining ones go on to win the battle.

Anyway Juan, I will try to say what I think about your message that string theory is a waste of time.
marcus
marcus is online now
#93
Aug17-05, 11:30 AM
Astronomy
Sci Advisor
PF Gold
marcus's Avatar
P: 22,809
Quote Quote by marcus
...Anyway Juan, I will try to say what I think about your message that string theory is a waste of time.
1. it doesnt 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.
Telos
Telos is offline
#94
Aug17-05, 01:01 PM
P: 147
Quote Quote by marcus
Telos, you are definitely on to something about time spent drawing testable conclusions from a theory so that it may be shown false.
Wish I could say I thought of it myself!
marcus
marcus is online now
#95
Aug17-05, 01:46 PM
Astronomy
Sci Advisor
PF Gold
marcus's Avatar
P: 22,809
Quote Quote by Telos
Wish I could say I thought of it myself!
the important ideas are like that. you only pass them along, instead of originating them
Juan R.
Juan R. is offline
#96
Aug20-05, 08:49 AM
P: 416
As said, I do not think that the decline of string research program is just temporary one. In the past, there were difficulties but now people is seeing that each year original objectives of string theory are far, and far, and farther. String theory history looks like a divergent asymptotic series.

Quote Quote by Marcus
I must say that observing this string "downsizing" going on has increased my respect for the honesty and courage of certain researchers such as Andy Strominger.
Said I the contrary? I am against half-true that many string physicists popularized as the new standard in scientific communication. I am also against arrogance typical of many string theorists (of course not all).

Now, let me reply your very interesting comments.

Quote Quote by Marcus
1. it doesnt mean anything unless you say FOR WHOM it is a waste of time.
I disagree; I provided abundant data in all aspects of the theory (geometry, hidden dimensions pointlike behavior, spectral decomposition, relativity, arrow of time, reductionism, etc.) and already explained that I was talking of string theory like a TOE on post #5.

As said by Nobel laureate P. Anderson this year, string theory is a futile exercise as physics. I substituted “futile exercise” by “waste of time” but my evaluation of string theory continues being correct.

I would state that string theorists provide none serious argument why we would believe on string theory, only bold statements like "it is the most promising way" or wrong claims like "is the only was to quantum gravity". I see an injustice here with people that are not string believers.

Quote Quote by Marcus
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.)
I am sorry to say this Marcus but this kind of argument is childish. A theory (or hypothesis) is not a “futile exercise as physics” on function of the number of papers or researchers working in it. Or would I remember to you the number of papers in early investigation of perturbative quantum gravity until was shown that QGR was nonrenormalizable on independence of parameter of expansion taken. All previous work in dozens of attempts to quantize GR directly were a waste of time.


Quote Quote by Marcus
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.
The premise is obvious when one know why was formulated string theory. String theory is a “theory” of physics. Its main objectives are unification of forces quantizing gravity, systematization of the standard model, and possibly the explanation of some cosmological mysterious.

Has string theory been interesting on mathematical topics? Of course, but that does not justify the hype around it and its study on physics dept. Moreover, let me say that the impact of string theory in the whole of mathematics is not so huge, at least, it is not more important (by orders of magnitude) that impact of some field theoretical techniques. For example, contrary to popular belief, Fields Medal awarded to Witten was not by the application of pure string theory methods to math, most of mathematical work of Witten was from field theory. Atiyah, who is many times more smart and versed that i in these topics, affirms that string theory has had an impact on mathematics which has been really quite extraordinary. Well, he said that in a popular interview. However, far from popular claims, I see not radical advances on mathematics as provided by the own Atiyah on "index theorems" (theory of quantum operators in quantum field theory).

Quote Quote by Marcus
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.
Already replied. That young mathematician, if interested in string “theory”, would focus on the mathematical branches below string physical theory, including non-commutative geometry, G2 manifolds, K theory, topology, and news branches of analyses and algebra, etc. Of course, with an eye in the “physical” stuff.

Quote Quote by Marcus
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.
This is a very, very astonishing simplification of the problem. Background independence is not the magical cure to all problems of string theory. Even if one day a background independent version of string theory is achieved (I doubt), string theory will continue to be a waste of time like a TOE. Moreover, it will continue to be as non-predictive like is now.

Do not forget that LQG is claimed background independent whereas continue to be an “inefficient” approach to quantum gravity. In fact, there is no possibility for obtaining a consistent classical limit converging to GR after of 40 years from Hamiltonina gravity: geometrodynamics, Astherkar QGR, LQG, etc.

Smolin, as others loop theoreticians, assumes that relationism is correct, but it is not as already said. The idea of that causality becomes a fuzzy notion because of fluctuation of light cones is completely wrong.
lightcone
lightcone is offline
#97
Aug20-05, 12:36 PM
P: 4
i am sure strings are going to disappear and first sign of this is the idea os landscape of vacuua. it is such a comic trash that during seminar you feel like quiting physics because such are the things promoted as future directions.

but stringers cannot fool th world much long and more so because some of them are serious researchers with a conscience still alive.

plase read freeman dyson: disturbing the universe and you will know hy string theory qualifies as a failure.

The problem of delay in this being branded a failure is obvious, INERTIA. there are too many researchers persuing it who are trained as stringers unlike the masters who were all high energy physicists. S now we have this young generation of ignorant people who doesnt even know where to find mistake to stop doing it since they simply do not know physics. It is just poor quality mathematics.
marcus
marcus is online now
#98
Aug20-05, 01:04 PM
Astronomy
Sci Advisor
PF Gold
marcus's Avatar
P: 22,809
Quote Quote by lightcone
i am sure strings are going to disappear and first sign of this is the idea os landscape of vacuua. it is such a comic trash that during seminar you feel like quiting physics because such are the things promoted as future directions.

but stringers cannot fool th world much long and more so because some of them are serious researchers with a conscience still alive.
...
I agree with the respect you show for serious and principled researchers
"...serious researchers with a conscience..."

Public support for physics ultimately depends on the trust that nonspecialists have in the self-critical, "self-policing" ability of theorists to remain engaged with empirical reality. So your perception that there are some who are not indulging in a mathematical escapade is very important.
marcus
marcus is online now
#99
Aug20-05, 01:15 PM
Astronomy
Sci Advisor
PF Gold
marcus's Avatar
P: 22,809
Quote Quote by Juan
"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.
RandallB
RandallB is offline
#100
Aug20-05, 02:48 PM
P: 1,545
Marcus
On Strings I feel it’s future may well becoming a waste land. But I believe it has been very valuable in identifying the 11 dimensions issue. Lack of progress indicates that this idea is likely just wrong. But ANY future theory that proves 11 D as wrong, should also be able to explain why the 11 D issue appeared to be viable at all. Just this additional ‘test’ of future theories, I think that can be worth quite a bit.

Also, You mentioned something else I could use a little help on “how I think”
Quote Quote by marcus
Among tested, well-established theories, General Relativity is the most background independent model we have.
Having never really put it into words before, but I’d though of GM as background dependent. That is with the “warping” of space time was still a manipulation of a background dependent interpretation of space and time.

Your comment tells me I need to Fine Tune my thinking a bit. Does the following make sense:

SR Special Relativity - background dependent
Works on a ‘dependant’ background of space and time in a classical manner. Just the Newton formulas were inadequate and the measures of space or distance over time need to be understood by the better formulas provided by relativity.

GR General Relativity - background independent
The use of a warping of time and space into “space/time’ to understand gravity, releases us from a background dependent measure. That is the physics we see, relativity included, is not dependent on any background traceable measure in either distance. But rather only dependent on the “relationships” between physics events that cannot be tied down to a measurable background reference of space and time.

A fine point but seems an important one I’d not fully recognized.

In a similar fashion :

Quantum Theory - background dependent
Quantized the minimum amount of energy to be found in light “packets” now photons. And set minimum size of change in measure we could expect to ever make in both time and distance (space). Natural limitations associated with this made near impossible to make significant progress until.

Quantum Mechanics - background independent
Instead of “warping” the relationship of time and space, used the uncertainty principal to allow measure and predictions at the quantum level to become understandable.
Thus one way to explain the inability of combining the physics of QM and GR even though they are both “background independent” is that they arrived at their independence in dramatically different forms (warping vs., probabilities) that we so far have been unable to interrelate.
(I'd previously considered not being able to combine the two as a dependent vs. independent issue)

Is this a reasonable tune up to my thinking?
Let me know if I’ve gone off track on the “background” issue as it is a bit new to me.

Also are there any other “well-established theories” that arrive at their background independence though some other manner than GR or QM? I’m assuming that most all, like M-Strings, have their foundation in QM.

Thanks
RB
marcus
marcus is online now
#101
Aug20-05, 03:27 PM
Astronomy
Sci Advisor
PF Gold
marcus's Avatar
P: 22,809
Quote Quote by RandallB
Marcus
On Strings I feel it’s future may well becoming a waste land. But I believe it has been very valuable in identifying the 11 dimensions issue. Lack of progress indicates that this idea is likely just wrong. But ANY future theory that proves 11 D as wrong, should also be able to explain why the 11 D issue appeared to be viable at all. Just this additional ‘test’ of future theories, I think that can be worth quite a bit.

Also, You mentioned something else I could use a little help on “how I think”

Among tested, well-established theories, General Relativity is the most background independent model we have.
Having never really put it into words before, but I’d though of GM as background dependent. That is with the “warping” of space time was still a manipulation of a background dependent interpretation of space and time.

Your comment tells me I need to Fine Tune my thinking a bit...
this is a sign we need a link to basic Differential Geometry primer where the idea of a "differentiable manifold" (often a "smooth manifold") is defined

does anyone have an Intro to D.G. or Intro to Manifolds link?

Randall there are two abstr. math. ideas you need that are actually very simple and easy to get-----Manifold and Metric-on-the-manifold.

For 150 years the fundamental paradigm for a continuum that everyone uses is a Manifold (defined by Riemann around 1850).

the most common meaning of B.I. is you start with a Manifold without a metric.

in a B.D. theory you start with a manifold and give yourself a metric on it to start with as well

have to go back later
marcus
marcus is online now
#102
Aug20-05, 04:03 PM
Astronomy
Sci Advisor
PF Gold
marcus's Avatar
P: 22,809
Randall it is soooooo simple. I wish you would take a moment and think it over and come back and say honestly that you understand perfectly clear as day.

the reason we accumulate math concepts over the decades is ultimately MENTAL ECONOMY. they make thinking more efficient. and this is a case

the fundamental object in D.G. is the manifold which corresponds to the idea of a continuum without geometry. it is a blob that has coordinate functions defined on it
(local charts that are smooth and compat where they overlap)
but does not have any dingus or appliance that can tell you the distance between two points

because it has coordinates, at any point on the manifold you can explore all the possible directions in which you can take the derivative!!!!!!
All the possible DEE-EXES, and when you think calmly and patiently about this for a while you realize that this collection of all possible dee-exes IS the tangent space. it captures the essence of what we want the tangentspace at any give point to do for us. and it is intrinsic (defined without reference to anything surrounding the manifold)

this is a fundamental Idea of Western Civilization, like the freedom of the individual and the rule of law etc. this is the Idea of the Continuum which has been standard for 150 years

It is INTRINSIC. it doesnt have to be embedded in any larger space for you to know its tangent space at each point and be able to do calculus etc, and it STILL HAS NO IDEA OF GEOMETRY built in.

to do geometry you introduce a "metric" gizmo which is a bi-linear dingus defined on the tangent space at every point blah blah
and once you have a metric g(m) defined at every point m of the manifold then you can compute distances, angles, areas, volumes etc.

The most common meaning of B.I. is that you start with a manifold without a metric.

In Gen Rel you start with a 4D spacetime manifold and some matter and you set up this equation and Presto! you PULL THE METRIC OUT OF THE HAT! (EDIT: selfAdjoint objects to the wording. I mean that you solve for the gravitational field, which is the metric. more discussion of details of this in later posts...)

the metric, or geometry, can be totally freeform and it is determined dynamically by interaction with matter through the equation of the model.

This is VERY DIFFERENT FROM perturbative STRING THEORY where they start with a manifold that already has a prior-chosen metric defined on it.
Having a prior chosen metric lets you define the twangy equation by which the little thangs be vibratin'. Without that prior metric you got nothing to start with, stringywise.
selfAdjoint
selfAdjoint is offline
#103
Aug20-05, 04:23 PM
Emeritus
PF Gold
P: 8,147
Quote Quote by Marcus
In Gen Rel you start with a 4D spacetime manifold and some matter and you set up this equation and Presto! you PULL THE METRIC OUT OF THE HAT!
That's not quite right. You don't need the matter, it's strictly geometry. You don't pull the metric out of a hat, you introduce it as a general symmetric quadratic form, the coefficients of which turn out to form form a symmetric rank two tensor. This is just a generalization of Pythagoras's (or Lorentz's) rule. You can then express the very special connection (Levi-Civita) in terms of derivatives of the metric tensor, and from the connection coefficients you define the curvature tensor (Riemann-Christoffel tensor). In Riemannian geometry the metric comes before everything else.
marcus
marcus is online now
#104
Aug20-05, 04:33 PM
Astronomy
Sci Advisor
PF Gold
marcus's Avatar
P: 22,809
the fundamental string stumbling block is that in over 20 years nobody has succeeded in doing string without prior-choosing a metric

but to truly do Gen Rel you cannot choose the metric because geometry is a dynamic thing that comes out of the model----the geometry of the manifold is gravity and you do not stipulate it in advance

in standard vintage Gen Rel the gravitational field IS the metric g(m)
and it is what you solve for
it is the unknown distance function that the Einstein equation is about.

this is the basic obstacle that string research has always been up against

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

an amusing behavior of string theorists, which you can see recently over at the Coffee Table blog, is that whenever anybody reminds them of this major roadblock they immediately start talking defensively.

they dont stop, take a breath, and say "Yes that is right, we really need to put some effort into a nonperturbative, background independent formulation!"

Instead, they start making excuses and talking about the INADEQUACIES OF LOOP which is really irrelevant. They get into this complicated distracting discussion about how String "really" doesnt need to be B.I. and how it "really" is B.I. (if you define B.I. right) and how Loop is not "really" B.I. (if you define B.I. a certain way), and sometimes they start complaining that it isnt NICE of anyone to point out this defect because it might give non-experts the idea there was something wrong.

We just had an example of this at a couple of stringy blogs this month when folks were reacting to Smolin's paper "The Case for Background Independence". That paper was friendly advice, and the reaction was defensive, as if it were an attack. Check this out:

http://golem.ph.utexas.edu/string/archives/000621.html

I am waiting for someone like Andy Stromiger (who I suspect has guts) to come out with a clear statement on this and say "yes we need a B.I. formulation that we can really calculate with, and we ought to give his high priority and work on it, and we can do it"
marcus
marcus is online now
#105
Aug20-05, 04:43 PM
Astronomy
Sci Advisor
PF Gold
marcus's Avatar
P: 22,809
Quote Quote by selfAdjoint
... In Riemannian geometry the metric comes before everything else.
I agree totally. what I mean by pulling the metric out of a hat is that you SOLVE for the metric.

all the terms in the equation are defined based on the metric, so the metric comes before all that other stuff---curvature tensor like you say.

the idea I am trying to get across is somewhat simpler and more basic:

the gravitational field IS the metric
you don't start off knowing the metric
you SOLVE for it


exactly as you say, part of solving for the metric is going through stuff like the Riemann-Christophel tensor whose definition is based on the metric

thanks for adding some clarification, selfAdjoint.
would be great to have some standard links to basic D.G.
and a standard exposition of what B.I. is about
I appreciate your help
marcus
marcus is online now
#106
Aug20-05, 04:54 PM
Astronomy
Sci Advisor
PF Gold
marcus's Avatar
P: 22,809
my idea of a really background independent nonperturbative approach to QG is Loll triangulations path integral. I will get some links

http://arxiv.org/hep-th/0404156

Emergence of a 4D World from Causal Quantum Gravity

http://arxiv.org/hep-th/0505154

Reconstructing the Universe

http://arxiv.org/hep-th/0505113

Spectral Dimension of the Universe

http://arxiv.org/hep-th/0411152

Semiclassical Universe from First Principles

more here
http://arxiv.org/find/grp_physics/1/.../0/1/0/all/0/1

Eventually I hope to see some string theorists implement a version of string theory on the Loll CDT spacetime as a foundation. (rather than on their usual kind of manifold)

The original work in Dynamical Triangulations in early 1990s (which led to Loll CDT path integral in 1998) was actually an attempt by Ambjorn to find a NONPERTURBATIVE FORMULATION OF STRING---he thought he was doing matrix theory and he ended up with the CDT path integral.

One of Smolin's points is that a head-on effort to make string non-perturbative, or background independent, is likely to be fruitful (as it has been in the past) whether or not one finds a passage to the original goal

Another is that by throwing out assumptions one makes a theory more predictive---the less you assume the harder it is to build and the more restrictive it is---so the more falsifiable. So he proposes making the theory less dependent on comfortable background assumptions as a way out of the landscape confusion.
Hurkyl
Hurkyl is offline
#107
Aug20-05, 04:57 PM
Emeritus
Sci Advisor
PF Gold
Hurkyl's Avatar
P: 16,101
because it has coordinates, at any point on the manifold you can explore all the possible directions in which you can take the derivative!!!!!! ...
I feel the need to make a slight correction: you need a differentiable manifold to do this extra stuff!


Some manifolds are just so miserable that there is no way to equip them with a differentiable structure. Thus, no derivatives for you!

Some other manifolds are too accomodating: there are many fundamentally different ways to equip them with a differentiable structure! So you have to select which one you like before using derivatives!
marcus
marcus is online now
#108
Aug20-05, 05:15 PM
Astronomy
Sci Advisor
PF Gold
marcus's Avatar
P: 22,809
Quote Quote by Hurkyl
I feel the need to make a slight correction: you need a differentiable manifold to do this extra stuff!


Some manifolds are just so miserable that there is no way to equip them with a differentiable structure. Thus, no derivatives for you!

Some other manifolds are too accomodating: there are many fundamentally different ways to equip them with a differentiable structure! So you have to select which one you like before using derivatives!
You are absolutely right. I mean a differentiable manifold every time I say manifold. It just gets tiresome to type it after I have said it once.

Personally I like C-infinity, but at least C-one!


Register to reply

Related Discussions
Time in String Theory Beyond the Standard Model 5
Space-time in string theory Beyond the Standard Model 4
String Theory: peace in our time? Beyond the Standard Model 47