Studying string theory

  • #1
bigplanet401
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Hey, I wanted to ask you guys a few questions about string theory. It seems like a really neat area, but is over my head. These questions are based on stuff I've gleaned from reading the "beginner" section popular websites:

(0) Why study string theory?
-----

(1) Is string theory (still) an active area in physics? Have there been any major advances in the field since the "revolutions" of 1984 and 1995 (dualities)?

(2) Is string theory at the mercy of results from the Large Hadron Collider experiment?

(3) How hard is it to get a job as a professor in string theory?

(4) How many string theorists are there in the U.S? World?

Thanks for any help!
 

Answers and Replies

  • #2
Kalimaa23
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Al very good questions. I ought to be able to answer them, since I'm starting my Masters thesis on String Theory this very year.

0) It depends. There are different viewpoints, ranging from people fervently believing that it is the one and true road to unifying all the fundemantel forces, to people who believe that even it does not lead to realistic physics it is still a usefull tool, who's results could have a lot of influence in other domains of mathematics and physics, especially as a dual description of supersymmetric field theories. I tend to fall in the later category.

1) Incredibly active. In fact, there have been complaints (like from Smolin), that it is too dominant at the moment, and that it is difficult for a high energy theorist that is not working on ST to get hired.

2) Not really. The theory does not as of now give any low energy predictions. A downer would be if no SUSY would be discovered, but even then the masses of the sparticles could be higher than the 14 TeV scale of the LHC, so it wouldn't be conclusive. Expect parties all round if SUSY would be discovered though.

3) As easy as it can be in high energy theory. So not so very easy, but it's worse for other fields.

4) A few tens of thousands would be my guess. I aspire to be one soon :biggrin:
 
  • #3
Juan R.
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bigplanet401 said:
Hey, I wanted to ask you guys a few questions about string theory. It seems like a really neat area, but is over my head. These questions are based on stuff I've gleaned from reading the "beginner" section popular websites:

(0) Why study string theory?
-----

(1) Is string theory (still) an active area in physics? Have there been any major advances in the field since the "revolutions" of 1984 and 1995 (dualities)?

(2) Is string theory at the mercy of results from the Large Hadron Collider experiment?

(3) How hard is it to get a job as a professor in string theory?

(4) How many string theorists are there in the U.S? World?

Thanks for any help!


My hot reply is as follow

(0) If you want waste your time... (this is not my personal opinion. It is based in people who began a PhD in string theory and after of some years abandoned the field. A woman even abandoned physics and said to me string theory is a waste of time).
-----

(1) Yes it is still an active area in physics. Also the study of epicicles was a active area of study in the époque...

The number of physicists working on ST is each day more low and continue to low. No, there are not advances. In fact, this 2005 is the year of "no-go" therorems. Basically theorems that prove that string theory newer will be predictive and therefore physics. There is an increasing rumour that Witten will abandon the field this year

(2) Many people (including Nobel laureate Laughing) believe that LHC will be the end of string theory. I wait see that before 2007!

(3) It would be very hard in next years since in some few years the topic will be practically abandoned (except by radical followers). Moreover, the money is little and...

(4) US 100-800? Rest of civilizated world ST is not very popular. In Europe ST is not very popular.
 
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  • #4
marcus
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Big,

your question (1) concerns research activity.
One measure of that is number of research papers published per year. I may be able to get some information about that if you are interested.

Another way to measure is to use citations as a measure of quality. the number of times other papers cite a given one is a rough indicator of how influential and interesting other professionals consider it. (the measure is imperfect, but it is still used by departments to rate people considered for jobs and tenure---it's good to write papers that get a lot of citations)

so one can measure trends in citations, as an alternative to raw output, to gauge the research activity in a field

we looked at that, as regards string, in a PF thread, check it out if you want:
https://www.physicsforums.com/showthread.php?t=81739
 
  • #5
marcus
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Big,

one way to respond to your question (0) would be to list the Pros and Cons of string theory----what's good about it, making it appealing as an area of research, and what's bad, making the prospects less than rosy.

Every year at Stanford/SLAC they have an elite summer workshop (for graduate students, postdocs, working physicists etc.) and this year a string theorist named Joe Lykken taught a course that was originally publicized as "String Theory for Dummies" (that's what the original poster on the web says) and later renamed "String Theory for Physicists".

I don't think the content changed, just the course title.

and to start off the course he listed and discussed STRING THEORY GOODS AND BADS

remember he is a string theorist and was chosen to present an introductory course to string for people who already have some training in physics. his view is apt to be upbeat. but at least he mentioned some "bads"---he was not just a booster. I think he listed 7 goods and 7 bads.

We talked about this a bit in a PF thread:
https://www.physicsforums.com/showthread.php?t=81739

If you read the list, in that thread, and have any questions, you might post them on that thread and maybe someone who understands Lykken's points will explain or clarify----not certain but some chance of it anyway.
 
  • #6
marcus
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bigplanet401 said:
...

(0) Why study string theory?

(1) Is string theory (still) an active area in physics? Have there been any major advances in the field since the "revolutions" of 1984 and 1995 (dualities)?
...

Probably the most useful document to look at in connection with these two questions is the 2 hour Video of the June 2005 Toronto Panel discussion.

We have a PF thread about that here:

https://www.physicsforums.com/showthread.php?t=84585

If you download the video so you can watch it, you can scroll to different places-----points along the timeline.

the overall topic is the future of string theory-----spiffy title: "the next string theory revolution" but no agreement emerged about when or what that might be

the question "why do string theory?" came up, and was responded to, primarily at two points in the video

1:23:28 and following (question by someone with a Russian accent, I think Sergei Ketov, but could be George Minic, he says he used to have obvious confident answers as to why, now he has a harder time justifying it to himself and other physicists, so he asks what do you say? some people respond in various ways)

1:26:20 great short speech by Andy Strominger, young Harvard faculty. forthright and courageous. my favorite part of the video. he is addressing this very issue---why should researchers do it? why should agencies fund it? what do you tell prospective students? colleagues in other branches of physics?

the first hour of the video is a series of 7 or 8 minute presentations prepared by the panel members----it is not so interesting, I recommend skipping to the start of the second hour

the second hour is a lively discussion where the audience participated and the panelmembers and moderator responded to questions. except for some three minutes taken up by a (...) person who should not have been there, the whole second hour is worth listening to, in my opinion.

However if you do not have time to listen to the whole discussion, at least scroll to Andy's two minute speech
 
  • #7
marcus
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  • #8
benjamincarson
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Juan R. said:
There is an increasing rumour that Witten will abandon the field this year
Can you cite a reference please, I've heard nothing of this.

Bigplanet401: Don't let Juan's attitude toward string theory affect your own. While it may not turn out to be the "theory of everything", a lot of good can come out of it, as Dimitri has already illustrated.

I guess Juan would rather recruit you into his "canonical science" project...an even greater waste of time.
 
  • #9
Juan R.
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marcus said:
Another way to measure is to use citations as a measure of quality. the number of times other papers cite a given one is a rough indicator of how influential and interesting other professionals consider it. (the measure is imperfect, but it is still used by departments to rate people considered for jobs and tenure---it's good to write papers that get a lot of citations)

marcus, citations is in general a good index but

i) it is only valid for standard communities with relative weak internal bonds. It would be distorted in a small community like string theory with rigid bonds due to external 'attacks' from other communities. In that case self-citation and citation of friends is an usual practice.

ii) LQG community is, in general, less arrogant people, and doing general surveys in quantum gravity (e.g. Smolin papers) they CITE work done by several communities: strings, loops, triangulation, Euclidean sector, etc.

In their papers, string theorist claim that string theory is the only quantum gravity approach and do not cite relevant works of others communities outside string theory doing irrealistic the citation index to relevant papers.

I remember the term used by certain guy (navigate a little by personal Peter Woit webpage): mafia.
 
  • #10
Juan R.
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benjamincarson said:
Can you cite a reference please, I've heard nothing of this.

Journal of TOEs, 2005, issue 666, page "infinite - infinite"

:rofl: :rofl:

benjamincarson said:
Bigplanet401: Don't let Juan's attitude toward string theory affect your own.

Cannot i state my opinion? Cannot i say to Bigplanet401 what my opinion is also maintained by lot of serious physicists including several great Nobel laureates for physics: Anderson, Laughlin, Dyson, Glashow, etc.

Robert Laughlin makes the point that string theorists are trying to camouflage the theory’s increasingly obvious flaws by comparing the theory to

a 50-year-old woman wearing way too much lipstick.

and adds

I think string theory is textbook ‘post-modernism’ (and) fueled by irresponsible expenditures of money.

cannot i to say that great men like Penrose or Hawking think of string theory? Hawking has said that string theory has been oversold.

The name "waste of time" is not my invention is based in reality of the 40 years failure of string research, and is used by many people in several forms and sinonyms. For example, Anderson uses the term "futile exercise" when refer to string theory. Great cosmologist Krauss named "complete failure", etc.

There are two books in the topic that Bigplanet401 would read before taking a final decision

"Not even wrong" by Peter Woit, one of more active critics of the theory for recent years. It was discussed in PF thanks to marcus. The book is recomended by Penrose, also active critic of the theory.

If you want know a bit the history of that book (subtitled the failure of string theory) and how members of the string theory community did several atemtps for the book was NEWER published, you can see

http://www.math.columbia.edu/~woit/wordpress/?p=245

Other interesting book is

Hiding in the Mirror : The Mysterious Allure of Extra Dimensions, from Plato to String Theory and Beyond by Lawrence M. Krauss. As said, he has recently characterized string theory like a complete failure. In fact previous attempt for explaining dark matter, inflation, etc from string theory all failed. The discrepancy in cosmology wetbeen string theory and experiment is in some models of order of 10^120!

The popularized brane model of universe was totally demolished in a series of interesting papers by great specialist A. Lindé, etc. Standard string theory was brilliantly showed incomplete by decades of effort of the Brushels School, etc.

both books are available on amazon

benjamincarson said:
alot of good can come out of it

Yes, this is the 40 years result of string theory "can", "could" "would" "we hope", etc.

benjamincarson said:
I guess Juan would rather recruit you into his "canonical science" project...an even greater waste of time.

I said nothing about that. Read my post #3.

But you remember to me that i also wrote about why string theory is a waste of time. Thanks :!)

http://www.canonicalscience.com/stringcriticism.pdf

And it would be a good thing read it (read the quotes to that people think about string theory even like string theorist Lubos Motl critize the way of string theory research of last years) before to take a final option about future career...

Regarding your last words. It is really curious that people -who has read papers, articles, and even is revising a book- claim. Even people like S. Weinberg who has read a paper on the topic of canonical science applied to particle physics do not claim that was a "waste of time".

People like renowned Nobel winner Ilya Prigogine was interested before his passed away and we collaborate in thermodynamics of small bodies, etc.

Interesting!

Let me add the last reply received from a mathematician working in relativity theory.

It is nice to see that, indeed, you belong to those "rara avis" of deeply
thinking physicists. And what you write about Special Relativity seems
indeed quite puzzling ...

Consequently, I am reading with much interest your paper.

Also our recent research in history of relativity (which is not related to canonical theory of course but is an "index" of our reasearch posibilities) has been aknowledged for a number of people in sci.physics.research and in private communications. Names will appear in the final version of the document

http://canonicalscience.blogspot.com/2005/08/what-is-history-of-relativity-theory.html


P.S: About Witten i am sure that i read in Woit blog but i cannot say where. If you are interested you would search there
 
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  • #11
misogynisticfeminist
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bigplanet401 said:
(2) Is string theory at the mercy of results from the Large Hadron Collider experiment?

anything which is not at the mercy of any experiment cannot be called physics at all.
 
  • #12
marcus
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Juan R. said:
Cannot i state my opinion? Cannot i say to Bigplanet401 what my opinion is also maintained by lot of serious physicists including several great Nobel laureates for physics: Anderson, Laughlin, Dyson, Glashow, etc.

Robert Laughlin makes the point that string theorists are trying to camouflage the theory’s increasingly obvious flaws by comparing the theory to

"a 50-year-old woman wearing way too much lipstick,"

...
...

cannot i to say that great men like Penrose or Hawking think of string theory? Hawking has said that string theory has been oversold.

The name "waste of time" is not my invention is based in reality of the 40 years failure of string research, and is used by many people in several forms and synonyms. For example, Anderson uses the term "futile exercise" when refer to string theory. Great cosmologist Krauss named "complete failure", etc.

In your compendium of distinguished chuckles at superstring you forgot to mention Nobelist Gerard 't Hooft. He teaches a string course at Utrecht but is skeptical of calling it a theory. Here is a quote from his popular book In Search of the Ultimate Building Blocks:

Actually, I would not even be prepared to call string theory a “theory” rather a “model” or not even that: just a hunch. After all, a theory should come together with instructions on how to deal with it to identify the things one wishes to describe, in our case the elementary particles, and one should, at least in principle, be able to formulate the rules for calculating the properties of these particles, and how to make new predictions for them. Imagine that I give you a chair, while explaining that the legs are still missing, and that the seat, back and armrest will perhaps be delivered soon; whatever I did give you, can I still call it a chair?

quote courtesy Woit http://www.math.columbia.edu/~woit/wordpress/?p=258#comments

Your quote from Laughlin occurred in this piece San Francisco Chronicle
http://sfgate.com/cgi-bin/article.cgi?f=/c/a/2005/03/14/MNGRMBOURE1.DTL

the same newspaper article has relevant quotes from Lawrence Krauss and others


misogynisticfeminist said:
anything which is not at the mercy of any experiment cannot be called physics at all.

I disagree. A theoretical development still under construction may be considered part of the enterprise of physics even though it is NOT YET ready to make an unambiguous prediction.

I would agree with you that a mature theory, to be considered science, must be potentially falsifiable in the sense that it makes some new prediction by which it can be tested. If there is no performable experiment that could refute the theory, by having the "wrong" outcome, then it's not part of what's usually thought of as science.

String theorizing has still not given us a mature theory able to put its life on the line----to bet its life on the outcome of a possible experiment where it unambiguously predicts something not already predicted by predecessors.

So this just means, I think, that it is not mature yet.

To the extent that people express certainty that string has something to do with nature and eventually will provide satisfactory predictions and explanations, I think they are not being scientific. It has become a matter of faith or superstition for them.

But not all people who work in string believe in it in this quasi-religious way. I think some of them probably just want to develop the theory further to help get it to the point of making predictions so it can be tested (along with competing alternative theories). So they work in a properly skeptical rational frame of mind.

So why should we judge this theory-in-development to be unscientific? It may have taken a little bit too long to come to maturity and be still in the development stage----this is admittedly a problem.
 
  • #13
selfAdjoint
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I have a belief, it's only a belief, that something of the string theory enterprise will prove to have been the path, or one of the main maths, to the next stage, the nonperturbative unification of the three presently quantized forces with gravity. There may well be other paths involved too - triangulations, spin foams, phoenix program, whatever, but somewhere among the mathematical-physical researches in the greater string theory program will be an important key not available in other traditions.

Studying string theory is important if only for the tools it puts in your tool kit.
 
  • #14
marcus
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For me, this post of selfAdjoint chimes with the two-minute statement by Strominger starting at time 1:26:20 in the Toronto video,
http://www.fields.utoronto.ca/programs/scientific/04-05/string-theory/strings2005/panel.html

and also with Strominger 8 minute presentation starting at 52:00 near the end of the first hour

I mentioned it earlier in post #6 of this thread
Probably the most useful document to look at in connection with these two questions is the 2 hour Video of the June 2005 Toronto Panel discussion.

We have a PF thread about that here:

https://www.physicsforums.com/showthread.php?t=84585

If you download the video so you can watch it, you can scroll to different...points along the timeline...

in the 8 minute talk, Strominger expressed the belief that string theory has SOMETHING, maybe only a little bit, to do with nature. I was impressed by the conservatism and modesty of what he claimed, and by the overall reasonableness. Since he was the last panel member to speak, everybody applauded. I would encourage everyone interested in the status and future prospects of string to listen to what starts at minute 52:00 of the video.
 
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  • #15
Ratzinger
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Plus it's funny to watch how he is struggling with the microphone at the start.
 
  • #16
bigplanet401
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DT et al.

Thanks for your quick replies; your posts have taken some of the indirection out of such an abstract subject. It seems that there is no clear-cut opinion, though. And after watching the latter half of the STRINGS 2005 panelists' discussion, I am more confused.

DT responds optimisically:

1) Incredibly active. In fact, there have been complaints (like from Smolin), that it is too dominant at the moment, and that it is difficult for a high energy theorist that is not working on ST to get hired.

So are there more high-energy theorists who are string theorists than not?
Have there been any major advances since 1995? J R.'s faith in the field seems less-than-fervent:

(1) Yes it is still an active area in physics. Also the study of epicicles was a active area of study in the époque...

The number of physicists working on ST is each day more low and continue to low. No, there are not advances. In fact, this 2005 is the year of "no-go" therorems. Basically theorems that prove that string theory newer will be predictive and therefore physics. There is an increasing rumour that Witten will abandon the field this year

So is the criticism here that ST is not really physics, but mathematical machinery and formalism? I would also like to know where the rumor of EW's departure came from. J R., DT claims participation on the order of 10^4, though...your estimate is lower by a factor of ten.

4) A few tens of thousands would be my guess. I aspire to be one soon

Who can act as the arbiter here?

---

s-A, you say:

I.

I have a belief, it's only a belief, that something of the string theory enterprise will prove to have been the path, or one of the main maths
, ...

What is the timescale for your belief? Do you think that ST ideas now will be applicable in 1 year? 10 years? 1000 years (whimsical comment made in the video), if they have any merit at all?

II.

This attitude has always been a source of repose for me:

Studying string theory is important if only for the tools it puts in your tool kit.

Is this the reason for some Ph.D's leaving physics to pursue a career in business (and the dollar-signs that go with such a career?)

And marcus, thank you for the link to STRINGS `05 video. Here is what I picked up from it:

i. The last two revolutions were separated by about ten years. Moderator was concerned that ST was overdue for another one, but that ST papers on the "archive" were being ignored.

ii. Moderator was "bothered" by the idea of quantum gravity being described by ANY quantum system (especially the "antidesitter, conformal field theory" correspondence -- do I have that right?)

iii. "Young people" will lead the next Revolution.

iv. ST is the only consistent theory of quantum gravity that exists.

v. There was a joke about the Bush administration's willingness to fund ST...

vi. (from a member on the panel): Told the audience to not argue the ST case, but rather explain it to people, and let them decide whether to enter the field. Called for optimism on audience's part.

vii. An audience member who asked about a possible interface between ST and astronomy and cosmology was "canned" by the moderator.

viii. (panel) The LHC will not address quantum gravity, but should tell scientists something about supersymmetry.

I appreciate this very much. Thank you!
 
  • #17
marcus
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bigplanet401 said:
...

iv. ST is the only consistent theory of quantum gravity that exists.

moderator Steve Shenker said that when an audience member asked "why do string theory?" and none of the panelists offered to reply so Steve, as moderator, had to say something and move on.

I would advise taking it with a grain of salt. It is debatable.

You mentioned people getting out of string----there has been a fairly steady decline in the number of stringy papers per year since 2001. People who slow down or stop doing string research don't necessarily all go to work for Wall Street. Some just move into other physics areas. I have not heard any indication that stringy math is better preparation for Wall Street than, say, statistical physics. My guess would be that it's less helpful than some lines of physics which involve more numerical modeling of complex systems.

Here is a graphic picture of the growth areas in physics:
http://arxiv.org/Stats/
The fourth chart, at the bottom, is the clearest:

You can see green and red have caught up with blue. Blue leveled off a few years ago. Green may pass it this year.

A fair number of people leaving string seem to go into astrophysics, including a new field called astro-particle physics, which has been growing.
Also condensed matter physics has been growing. Both astro and condensed have a theoretical sector---problems theorists can tackle. I don't have statistics on where people go, only individual cases I have noticed. This kind of shifting is not so unusual, people who are able to move from a slow field to a hotter one sometimes do make transitions within physics.

for a sense of what the currently attractive areas of research are in physics, look at successive years of MIKE PESKIN'S REVIEW here at the Stanford/SLAC website
http://www.slac.stanford.edu/library/topcites/
he does an annual report on "What's hot in high energy physics?"
Note the change over the years 2001, 2002, and 2003.

It is about time for Peskin to post his review for what was hot in 2004. He takes a while to write and post the review. I've been expecting it this month.

If you just want raw numbers then what I find using keywords {M-theory OR brane OR AdS/CFT} is a 20 percent decline over a 4 year period from 2001 to present, of papers published per year. That is roughly 5 percent decline per year. Could actually be 20 percent decline over 3 years---6 percent annually. Part of this is just the decline in high energy versus other areas.
 
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  • #18
Chronos
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When you promise the moon, green cheese will not suffice. After a ~40 year 'renaissance', string has failed to deliver the goods. That does not mean string is the 'wrong' road: just that it might need a course correction. Perhaps Loops or CDT will get it back on track. That is the peril of doing science... sometimes you eat the steak, sometimes you get the stake.
 
  • #19
Juan R.
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marcus said:
In your compendium of distinguished chuckles at superstring you forgot to mention Nobelist Gerard 't Hooft.

Thanks!

Also i read in some part that Feynman was also skeptic and do not believed in string theory. Is this right?
 
  • #20
Juan R.
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bigplanet401 said:
J R.'s faith in the field seems less-than-fervent

J.R. and many many other people. In one of his last 'This Week’s Finds in Mathematical Physics' (available here in PF), John Baez’s has expressed similar view to mine ones regarding string theory.
 
  • #21
marcus
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Juan R. said:
Thanks!

Also i read in some part that Feynman was also skeptic and do not believed in string theory. Is this right?

Feynman did not like string theorizing and he expressed his skepticism in colorful ways. Sometimes not in print, so one only has second-hand sources----the "oral tradition", as one says. What I will quote to you is according to Lawrence Krauss.

As you know, a notable embarrassment of string is its not making predictions by which it can be tested, and this is explained in various ways by string apologists (like, the energy is too high, or we don't need experimental confirmation to know that string is right, or whatever).

But Feynman thought that any theory worth spending time on should make predictions, so, when this topic came up, he said

"String theorists don't make predictions, they make excuses."
 
  • #22
Juan R.
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marcus said:
"String theorists don't make predictions, they make excuses."

Thanks by the quote :!) i think that reflects exactly the current status of string theory.

I had heard that Feynman also said some thing about a cat, emphasizing that he thought that string theory was not correct. But unfortunatelyi cannot obtain the quote.
 
  • #23
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marcus said:
In your compendium of distinguished chuckles at superstring you forgot to mention Nobelist Gerard 't Hooft... Here is a quote from his popular book In Search of the Ultimate Building Blocks:

Imagine that I give you a chair, while explaining that the legs are still missing, and that the seat, back and armrest will perhaps be delivered soon; whatever I did give you, can I still call it a chair?
...

this is my favorite. It is not, so to say, sharp and cutting like the Feynman quote. Instead it is more cheerful and friendly. It is nice that it does not mention string directly---so that the listener must GUESS what it is about and thus becomes an accomplice to the laughter.

I already have a "sig" ---- a "sig" is like a tattoo that is so fashionable with young Americans I see, something that always appears on one's posts at the bottom line.

But you don't. I suggest we have a contest, where everyone can suggest a sig for you. then you can be the judge and decide if you like any of them enough to use them. My entry in the contest shall be this quote from 't Hooft. With no mention of string theory (and after all the mockery applies to other incomplete theories as well!)
 
  • #24
marcus
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Juan R. said:
Also i read in some part that Feynman was also skeptic and do not believed in string theory. Is this right?

Juan R. if you are collecting quotes---as your post #19 suggests---you might get a few out of these comments on Woit's blog:
http://www.math.columbia.edu/~woit/wordpress/?p=272#comments

This segment starts about halfway down the comments.
----quote----

Tony Smith Says:
October 5th, 2005 at 7:22 am
NIgel said: “… My information for Feynman being critical of strings is the book Davies & Brown, ‘Superstrings’ 1988. I haven’t read it since 1988 so cannot quote it …”.

Here are some excerpts from Feynman’s statements in that book, at pages 194-195:
"… I do feel strongly that this is nonsense! … I think all this superstring stuff is crazy and is in the wrong direction. … I don’t like it that they’re not calculating anything. … why are the masses of the various particles such as quarks what they are? All these numbers … have no explanations in these string theories - absolutely none! … ".
---end quote---

the comments continue on from there, a few posts later:

---quote---
scott Says:
October 5th, 2005 at 3:04 pm
Just to corroborate Feynman’s distaste for string theory. In the book Feynman's Rainbow, by some dude who postdoced at tech, it was mentioned that string theory upset him so much that his doctor encouraged him not to discuss it...
---endquote---

here's something about the book Feynman’s Rainbow by Leonard Mlodinow


here's something about Superstrings, a Theory of Everything? by Davies and Brown.
 
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  • #25
Haelfix
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To be perfectly fair, String theory developed a lot since Feynman's death. They are able to write down models that can predict masses and so forth.

The problem is they have way too many models, very few have clean profiles without exotics (and then there are usually residual problems), and they haven't been able to constrain phenomonology like it was once hoped for from first principles in the theory, there are just too many possible scenarios.

Again, a lot of people are hoping for the LHC to shed some light on certain major aspects. If supersymmetry is found at LHC energies, that's huge, eliminating a huge class of stringy models and giving a glimpse into potential GUT scale effects. If the axion is found or Kaluza Klein modes, again huge.

In general, the more exotics we see at the LHC, the better off we are. More particles = much tighter model constraints and input, and it should give string theory phenomonologists a much needed breather (they have a horrendous job sorting through a gigantic mess of possibilities, as only one amongst millions of possibilities having anything remotely to do with the real world).

Now, its not just string theory that has this problem, field theory in general is a mess at the moment. There are literally thousands of models that nature could plausibly pick out, and its a hard task classifying the various ideas, much less distinguishing them experimentally or finding a mathematical flaw. Thats why they call it the LHC lottery game.

Personally I am getting rather pessimistic at this whole game. It just seems like nature has many different haphazardous scales where new physics perpetually enter the picture, and that's fine conceptually speaking. It would even be interesting, were we not stuck with bigger and better particle accelerators quickly fading from the realm of human possibility.

I mean look at the history of this. Everytime we've probed deeper in energy atoms --> nuclei --> quarks ... electroweak symmetry breaking scale --> SUSY breaking scales --> GUT scales, at each step people always thought that was it, they nearly ahd the whole shebang done. Yet time after time, more structure was discovered, some of it experimentally and rather recently mathematical argumentation. I remain skeptical that more won't invariably show up to ruin our 'nearly finished' mindset.
 
  • #26
marcus
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Haelfix said:
...
The problem is they have way too many models, very few have clean profiles without exotics (and then there are usually residual problems), and they haven't been able to constrain phenomonology like it was once hoped for from first principles in the theory, there are just too many possible scenarios.
...
Personally I am getting rather pessimistic at this whole game. It just seems like nature has many different haphazardous scales where new physics perpetually enter the picture, and that's fine conceptually speaking. It would even be interesting, were we not stuck with bigger and better particle accelerators quickly fading from the realm of human possibility...

Haelfix some of your post evokes a "russian doll" picture where there is a never ending search for what is fundamental. But inside one thing is always found another...
You sound discouraged by this, but it may just be a sign that a nonperturbative QG approach is needed.

So I can see this as a reason to be hopeful: the lines of investigation you discuss (QFT and related) all build on a GIVEN FIXED SPACETIME.
They investigate particles and fields on some assumed spacetime. That could be what is wrong.

they do not include the microscopic dynamics of spacetime itself in the search.
for example look at John Baez notes for his talk tomorrow at Potsdam.
He is talking about progress towards a quantum spacetime dynamics.
Once one has a better idea of what spacetime itself is, then I suspect there will appear DIFFERENT WAYS TO REPRESENT fields and particles, as, so to speak, organic parts of spacetime.

So the sterility which you depict in your post is essentially the sterility of CONTINUING A PERTURBATIVE line of investigation, where you keep the underlying continuum fixed and it does not participate. But that sterility which you identify does not affect NONPERTURBATIVE approaches.

Including matter is the topic of a number of papers at the current Loops 05 conference (not only LQG but a number of converging approaches to non-perturbative/background independent quantum gravity)

Anyway, cheers. I think some progress is being made, just in a different area.
 
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  • #27
Pyro
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Here are some excerpts from Feynman’s statements in that book, at pages 194-195:
"… I do feel strongly that this is nonsense! … I think all this superstring stuff is crazy and is in the wrong direction. … I don’t like it that they’re not calculating anything. … why are the masses of the various particles such as quarks what they are? All these numbers … have no explanations in these string theories - absolutely none! … ".
Is Feynman really asking a "why" question? In order to be a good, respectable physicists, aren't you suppose to abandon the "why" questions?

It's seems that physicists only ask "why" when they don't like a theory.
 
  • #28
marcus
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Pyro said:
Is Feynman really asking a "why" question? In order to be a good, respectable physicists, aren't you suppose to abandon the "why" questions?...

read Haelfix post---he says in string's defense that some versions can calculate some mass ratios.

ever since Kepler the game has been to see patterns in the salient numbers so that you can explain why THOSE numbers, using a SMALLER SET of numbers.

Kepler had, besides the earth, 5 planets. He had TEN numbers which were 5 distances from the sun (in multiples of earth-sun distance) and 5 orbital periods (in fractions or multiples of the Earth year).

He found a way to say WHY the period was whatever it was, based on what the distance from sun was, whatever it was. So he BOILED IT DOWN TO FEWER NUMBERS that you had to explain.
 
  • #29
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marcus said:
He found a way to say WHY the period was whatever it was, based on what the distance from sun was, whatever it was. So he BOILED IT DOWN TO FEWER NUMBERS that you had to explain.
The question was not, can string theory or physics answer the "why" question, but rather do physicists such as
Feynman have a double standard as to when you can invoke the "why" question. Most physicists will tell you physics cannot answer "why" because it is a philisophical question. Well.. Feynman is asking why. I guess he isn't a respectable physicist.
 
  • #30
marcus
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IgorSnor said:
.. Most physicists will tell you physics cannot answer "why" because it is a philisophical question...

What is your source. Please give an online authority for this.

My experience of physicists is that they often use the word "why" and they often ask "why?" questions WHICH ARE NOT PHILOSOPHICAL.

typically a why question, like "why is the sky blue", is shorthand way of asking for a derivation of some quantitative thing (like a frequency or wavelength) FROM SOME MORE FUNDAMENTAL DATA

as I said, typically the game is to derive a larger set of numbers from a smaller set.

this is what the standard model of particle physics does---one inputs a couple of dozen numbers (coupling constants and mass ratios) and it calculates many other energies and masses etc for you.

if one ever goes beyond the standard model to find a SUCCESSFUL replacement, it will be able to derive the same quantities from FEWER inputs.

In other words a better standard model will be able to SAY WHY THE MASSES OF PARTICLES ARE WHAT THEY ARE based on fewer input data.

this use of word "why" in my experience is

1. NOT philosophical (basically it is talking about the number of independent and dependent variables in some math formulas)

2. very much how physicists talk, at least informally among themselves.

==================

So I tend to think that you, Igor and Pyro, may be inexperienced or deluded. If you want to convince me otherwise, please give some authoritative online source that shows that

A. a why question is always Philosophical, never about physics.

B. physicists really never ask why when they talk among themselves.
 
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  • #31
JesseM
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IgorSnor said:
The question was not, can string theory or physics answer the "why" question, but rather do physicists such as
Feynman have a double standard as to when you can invoke the "why" question. Most physicists will tell you physics cannot answer "why" because it is a philisophical question. Well.. Feynman is asking why. I guess he isn't a respectable physicist.
Wrong, Feynman understood perfectly well that physics is not about ultimate "why" questions, although of course phenomena on one level can have explanations in terms of more fundamental laws. Here is a long quote from chapter 2 of "The Character of Physical Law", titled "The Relation of Mathematics to Physics", which I typed out a while ago in another discussion, I'll repost it here:
On the other hand, take Newton's law for gravitation, which has the aspects I discussed last time. I gave you the equation:

F=Gmm'/r^2

just to impress you with the speed with which mathematical symbols can convey information. I said that the force was proportional to the product of the masses of two objects, and inversely as the square of the distance between them, and also that bodies react to forces by changing their speeds, or changing their motions, in the direction of the force by amounts proportional to the force and inversely proportional to their masses. Those are words all right, and I did not necessarily have to write the equation. Nevertheless it is kind of mathematical, and we wonder how this can be a fundamental law. What does the planet do? Does it look at the sun, see how far away it is, and decide to calculate on its internal adding machine the inverse of the square of the distance, which tells it how much to move? This is certainly no explanation of the machinery of gravitation! You might want to look further, and various people have tried to look further. Newton was originally asked about his theory--'But it doesn't mean anything--it doesn't tell us anything'. He said, 'It tells you how it moves. That should be enough. I have told you how it moves, not why.' But people are often unsatisfied without a mechanism, and I would like to describe one theory which has been invented, among others, of the type you migh want. This theory suggests that this effect is the result of large numbers of actions, which would explain why it is mathematical.

Suppose that in the world everywhere there are a lot of particles, flying through us at very high speed. They come equally in all directions--just shooting by--and once in a while they hit us in a bombardment. We, and the sun, are practically transparent for them, practically but not completely, and some of them hit. ... If the sun were not there, particles would be bombarding the Earth from all sides, giving little impuleses by the rattle, bang, bang of the few that hit. This will not shake the Earth in any particular direction, because there are as many coming from one side as from the other, from top as from bottom. However, when the sun is there the particles which are coming from that direction are partially absorbed by the sun, because some of them hit the sun and do not go through. Therefore the number coming from the sun's direction towards the Earth is less than the number coming from the other sides, because they meet an obstacle, the sun. It is easy to see that the farther the sun is away, of all the possible directions in which particles can come, a smaller proportion of the particles are being taken out. The sun will appear smaller--in fact inversely as the square of the distance. Therefore there will be an impulse on the Earth towards the sun that varies inversely as the square of the distance. And this will be the result of a large number of very simple operations, just hits, one after the other, from all directions. Therefore the strangeness of the mathematical relation will be very much reduced, because the fundamental operation is much simpler than calculating the inverse of the square of the distance. This design, with the particles bouncing, does the calculation.

The only trouble with this scheme is that it does not work, for other reasons. Every theory that you make up has to be analysed against all possible consequences, to see if it predicts anything else. And this does predict something else. If the Earth is moving, more particles will hit it from in front than from behind. (If you are running in the rain, more rain hits you in the front of the face than in the back of the head, because you are running into the rain.) So, if the Earth is moving it is running into the particles coming towards it and away from the ones that are chasing it from behind. So more particles will hit it from the front than from the back, and there will be a force opposing any motion. This force would slow the Earth up in its orbit, and it certainly would not have lasted the three of four billion years (at least) that it has been going around the sun. So that is the end of that theory. 'Well,' you say, 'it was a good one, and I got rid of the mathematics for a while. Maybe I could invent a better one.' Maybe you can, because nobody knows the ultimate. But up to today, from the time of Newton, no one has invented another theoretical description of the mathematical machinery behind this law which does not either say the same thing over again, or make the mathematics harder, or predict some wrong phenomena. So there is no model of the theory of gravity today, other than the mathematical form.

If this were the only law of this character it would be interesting and rather annoying. But what turns out to be true is that the more we investigate, the more laws we find, and the deeper we penetrate nature, the more this disease persists. Every one of our laws is a purely mathematical statement in rather complex and abstruse mathematics.

...[A] question is whether, when trying to guess new laws, we should use seat-of-the-pants feelings and philosophical principles--'I don't like the minimum principle', or 'I do like the minimum principle', 'I don't like action at a distance', or 'I do like action at a distance'. To what extent do models help? It is interesting that very often models do help, and most physics teachers try to teach how to use models and to get a good physical feel for how things are going to work out. But it always turns out that the greatest discoveries abstract away from the model and the model never does any good. Maxwell's discovery of electrodynamics was made with a lot of imaginary wheels and idlers in space. But when you get rid of all the idlers and things in space the thing is O.K. Dirac discovered the correct laws for relativity quantum mechanics simply by guessing the equation. The method of guessing the equation seems to be a pretty effective way of guessing new laws. This shows again that mathematics is a deep way of expressing nature, and any attempt to express nature in philosophical principles, or in seat-of-the-pants mechanical feelings, is not an efficient way.

It always bothers me that, according to the laws as we understand them today, it takes a computing machine an infinite number of logical operations to figure out what goes on in no matter how tiny a region of space, and no matter how tiny a region of time. How can all that be going on in that tiny space? Why should it take an infinite amount of logic to figure out what one tiny piece of space/time is going to do? So I have often made the hypothesis that ultimately physics will not require a mathematical statement, that in the end the machinery will be revealed, and the laws will turn out to be simple, like the chequer board with all its apparent complexities. But this speculation is of the same nature as those other people make--'I like it', 'I don't like it',--and it is not good to be too prejudiced about these things.
 
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  • #32
marcus
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Pyro said:
Here are some excerpts from Feynman’s statements in that book, at pages 194-195:
"… I do feel strongly that this is nonsense! … I think all this superstring stuff is crazy and is in the wrong direction. … I don’t like it that they’re not calculating anything. … why are the masses of the various particles such as quarks what they are? All these numbers … have no explanations in these string theories - absolutely none! … ".

Is Feynman really asking a "why" question? In order to be a good, respectable physicists, aren't you suppose to abandon the "why" questions?
It's seems that physicists only ask "why" when they don't like a theory.

Hi Pyro, I can see how you might misunderstand this and think a double standard was being applied, if you think that it isn't normal for physicists to ask "why". But in the sense of Feynman's question it is normal. The Standard Model (SM) is considered a great success because it explains why many numbers are what they are, given only a couple dozen inputs.

John Baez has a nice introductory discussion of the SM at his website you might like to read, or at least about the inputs it requires
http://math.ucr.edu/home/baez/constants.html

Early on, with string, there were high hopes that it would explain those two dozen numbers, why they are what they are, from FEWER. Maybe, the hope was, string could just have ONE input and from that you could derive all two dozen inputs to the SM----the quark masses and so on., the fine structure constant 1/137 and so on. It was a great hope. but that was 20 some years ago.

So what you hear from these older physicists is not unfairness but rather impatience. Impatience for string to do what earlier models have done when they were successful. The SM allowed you to derive the masses of almost everything, with a few exceptions like neutrinos, with just some 26 or so inputs---when are we going to see the next step? And the SM gave meaning to the expensive and elaborate accelerator experiments because it could predict things that, if you didnt observe them, would show the SM was wrong. It was something you could really test---that unequivocally bet its life on observable outcomes. So they are understandably impatient for this generation of theorists to offer something that can measure up to the SM of the 1970s.

have to go, back later. trying to explain. hope this isn't too wordy.

BTW here is a Sheldon Glashow interview that has the same impatience. notice the why questions.
http://www.pbs.org/wgbh/nova/elegant/view-glashow.html
 
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  • #33
marcus
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Yeah here is an exerpt from that Glashow interview:
---quote---
OVA: What would string theory need to do to make a believer out of you?

Glashow: Well, you must understand that I don't understand string theory, so I can't describe its inner nature to any extent. But I could imagine that string theory would succeed in encompassing the standard model. It might then answer any number of outstanding questions. Why is the muon, some dumb particle, 200 times heavier than the electron? Why is the proton about 2,000 times heavier than the electron? Why is the electric charge of the electron what it is? Why are there six quarks in nature? Why not seven or eleven or five? There are many, many "why" questions. Also a number of 'how' questions. What is the mechanism that causes the weak interactions to be weak and the electromagnetic interactions not weak?

All kinds of questions remain. Many have to do with cosmology. How did the universe originate? How did the galaxies become distributed in space like the suds in the kitchen sink, as one of my colleagues has described it? Why is the cosmological constant apparently very tiny but non-zero and has a peculiar value that leads the universe to expand more rapidly?
---endquote---

Here's the link:
http://www.pbs.org/wgbh/nova/elegant/view-glashow.html

He's not holding string to a different standard, although it may have sounded like that to you. these why questions are modern versions of the kind of question that earlier models succeeded in answering. that is how the basic list of fundamental constants got narrowed down to 26 or however many. He is calling for today's theorists to carry on the work that he and others were involved in, and take the process further.

It's interesting that Glashow and Feynman (not to mention other critics like Philip Anderson and Robert Laughlin) won their Nobels for work back in the 1970s and earlier. since 1985 particle theory has kind of shrunk into its own shell and its connection with experiment has cooled. the critics feel that is somehow wrong---they expect a close relationship

maybe all or some of this is well-known to you
 
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  • #34
Juan R.
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Haelfix said:
To be perfectly fair, String theory developed a lot since Feynman's death. They are able to write down models that can predict masses and so forth.

If Feynman was live today his criticism would be still more important. It is false that string theorists developed models that predict masses. String theory only deals with hypotetical supersimmetric states in unobserved 10-11D for light hypotetical particles like gravitons. There is not posibility for obtainining heavy particles in some of vibration models of strings (branes) unless you were forcing the model because you know a priori the result.

String theory fails to provide any mechanism to generate the very small nonzero masses that are observed in nature, or to remove the exact spacetime supersymmetry, which is not observed in nature TODAY.

The same criticism about the 'prediction' of gravity claimed by Witten during decades.

String theory predicts nothing and all models are previous adaptations ad hoc of the theory to previously known data.

In fact, this year is the year on which many authors agree that string theory is not predictive and has failed due to publication of many papers with 'no-go' theorems. As suggested by recent strings 05, half top string community (anti-landscape) still believes that a new revolution will break the barrier of compactification (that is just a hope). The other half (pro-landscape) already understand that string theory is not predictive and newer will be. All one can do is to adjust by hand parameters of the theory (> 10000) in the hope of obtaining some concordancy with outcomes of experiments which result may be previously known.

Some celebrated string theorists as Susskind begin to accept that the theory cannot explain anything and this has caused some recent trouble. Susskind (pro-landscape) adds:

More and more as time goes on, the opponents of the idea admit that they are simply in a state of depression and desperation.

The famous 'cyber-string' theorist Luboš Motl (anti-landscape) has recently wrote:

Some people really seem to be excited by the very fact that they can embed a relatively convincing framework into string theory whose conclusion is that we can't predict anything [...]

Independently of if you are a 'pro' or an 'anti', actually string theory predicts nothing and members of 'anti' simply believe that any new future version (still to be developed) of string-M theory can change status.

And do not forget that M-theory is the name choosed for a theory that nobody has formulated still (in fact nobody even know if M-theory exists).
 
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  • #35
marcus
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JesseM said:
Here is a long quote from chapter 2 of "The Character of Physical Law", titled "The Relation of Mathematics to Physics", which I typed out a while ago in another discussion, I'll repost it here:

Jesse, thanks for sharing that quote. Even if you are a good typist, it must have be a fair amount of work to type it in. It's helpful to have an extended quote rather than merely paraphrase and short exerpts taken out of context---I think you get more out of it.
 

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