Register to reply

Is String Theory really a theory?

by whydoyouwanttoknow
Tags: string, theory
Share this thread:
sol2
#19
Aug5-04, 11:45 AM
sol2's Avatar
P: 915
Quote Quote by notevenwrong
My interests and background are rather different than Smolin's. He has been doing quantum gravity from the beginning of his career more than 25 years ago (he and I
overlapped at Harvard where I was an undergraduate, he was a graduate student). He approaches quantum gravity often by trying to dig into the deep conceptual and philosophical problems that it raises. My background is in quantum field theory and mathematics, and to the extent that I think about quantum gravity it is from a particle physicist and mathematician's point of view, which is rather different than Smolin's. One thing he and I agree on though is that the current state of fundamental theoretical physics is quite disturbing, with a dangerous "group-think" about string theory. He and I have met and correspond every so often, but I correspond with a lot of people on these topics. The recent behavior of Susskind in response to Smolin's serious criticism of the unscientific nature of "anthropic" reasoning is an example of the all too common way in which some string theorists react to any criticism of what they are doing.

I'm not a proponent of LQG, although I find it a more promising idea about quantizing gravity than string theory. Unlike string theory it seems to me to be a healthy part of physics, with a reasonable number of people working on it and slowly making progress. Someday we'll know enough to see how well some of the LQG ideas work.
No one knows the right answer to the question of how to quantize gravity. Physics would be a lot healthier if there were many different research programs going on in this area, not just one huge dominant one with one small challenger.
Thanks Peter for being honest.

Did you see the importance of the question I asked in regards to a anomaly that exists in the colliders?

I am a outsider, looking in, and wondering what lead these thinkers to conclude these extra dimensions, and to demonstrate a philsophical position, is much more deeply considered, then being past off as, flights of fancy.

regards,
sol2
#20
Aug5-04, 11:53 AM
sol2's Avatar
P: 915
Quote Quote by Marcus
Two separate aims jeff mentions.
A. quantize gravity
B. integrate all fundamental interactions
The gravitational waves were already quantizied in the graviton.

I have concistently showed that the integral approach is being implored right now from a LQG perspective in Glast.

If you change the question around in terms of Gamma ray detection, you would ask, what is revealed in a photon interaction going through a gravitonic gathering?

But this could hurt Strings?

"If GLAST detects violations of lorentz invariance in the form of
energy-dependent photons velocity, in agreement with theoretical
calculations, such observations and such agreement would strongly
support LQG. It would also represent a severe problem for
string/m-theory, as string theory in its current formulation
presupposes lorentz invariance is an exact symmetry of nature, valid
at all scales.

http://en.wikipedia.org/wiki/Loop_quantum_gravity"
I must admit Urs wasn't to forth coming when I asked the question.


Quote Quote by sol
Can someone speak to the quoted paragraph?
We all know I have lots to learn
sol2
#21
Aug5-04, 12:01 PM
sol2's Avatar
P: 915
Quote Quote by whydoyouwanttoknow
So, um, the answer is that it's not a theory?
I think we are still debating your question?
Ontoplankton
#22
Aug5-04, 12:06 PM
P: 155
Quote Quote by marcus
I believe Susskind's influence is harmful to String research program---it distorts it, takes it in unscientific directions, and damages respect for it.

(...)

He has gone wacko and must be muzzled for his own good and the good of String research.
And muzzling people "for the good of String research" isn't unscientific?

Susskind's recently expressed opinions may or may not turn out to be true, but they seem quite sane to me, and I'm glad he's expressing them. If there's a fatal problem with the anthropic principle, please show this using careful reasoning (more careful than Smolin's) rather than calling it names like "unscientific" and "cop-out".
marcus
#23
Aug5-04, 12:31 PM
Astronomy
Sci Advisor
PF Gold
marcus's Avatar
P: 23,274
Quote Quote by Ontoplankton
And muzzling people "for the good of String research" isn't unscientific?
...
science is as science does
senior people are trying to get Susskind to shut up, I gather,
his own String colleagues are the ones who have to deal with the problem

I personally dont care. If I was narrowly "anti-String" then I would be enjoying every minute of the Susskind show and rejoicing in it. From the narrow standpoint of someone only interested in Loop Quantum Gravity and allied approaches to quantizing Gen Rel, I would be happy about everything that has happened in String since the Jan2003 Kachru paper, the 10100 stringy Vacuums, Susskind's attempted salvage by Anthropery and the Landscape. It has been horrible for String and is apparently causing an exodus of researchers. My personal point of view is not that one-sided. I assume other stringfolk are pressuring him to stop
and I wish them all success.

whoever at arXiv suppressed Susskind's first response to Smolin did Susskind a favor---which he wasted by sending the paper out to a big email list so it became semipublic anyway (I havent seen it)

arXiv is one of the central institutions of science---the "e-prints"---an organ of the new post-WWW science. arXiv did something unprecedented in muzzling Susskind in this case, and it is easily seen that it was done
in Susskind interest and in String interest. If you think that was "unscientific" then take it up with Ginsparg at arXiv (dont quarrel with me about it)----science has to be a self-regulating community and there are other considerations that must be balanced against free access to publication
CJames
#24
Aug5-04, 12:34 PM
CJames's Avatar
P: 355
I'm no physicist so this is a question not a statement. In "The Elegent Universe" Greene makes some mention of branes being used to explain black holes. They used the theory to build I five dimensional black hole, and then developed five dimensional relativity to see if the equations matched and they did. Is this the closest they have gotten to experimental prediction? They did, afteral, predict something before verifying it through conventional theory. If so, is this enough to start calling it a theory in progress rather than a well developed hypothesis or research project? Or would this even be enough to start calling it a theory?

Later.
jeff
#25
Aug5-04, 12:39 PM
Sci Advisor
P: 660
Look, the issue has never been whether we need to invoke the anthropic principle or whether it indicates some basic flaw in string theory. The issue is that people are wasting time trying to solve problems that string theory in it's current state of development isn't ready for. So when you read discussions about the poor state of the collective "mental health" of the string community, it's not about their refusal to admit that string theory is somehow pathological - it clearly isn't - but rather that they need to stop trying to make huge conceptual leaps and instead work towards making more incremental and hence surer progress.
marcus
#26
Aug5-04, 12:47 PM
Astronomy
Sci Advisor
PF Gold
marcus's Avatar
P: 23,274
Quote Quote by whydoyouwanttoknow
So, um, the answer is that it's not a theory?
Read jeff's post.
jeff is our unofficial string-spokesman here at PF
he says it is a "Research Program", as opposed to a theory
he indicates he believes, for various reasons, that it is a very promising program

String may in time become a well-developed scientific theory and
make unequivocal predictions of definite numbers that can be tested
In which case it will be possible to prove wrong.

the criterion of a scientific theory is that it bets its life on predicting
the outcome of future measurements
(if it can accomodate any future measurement it has no meaning as science----it is more of a daydream or a poem)

So when String becomes clear enough and definite enough that it could be shot down or refuted by some empirical observation it will be a scientific theory and it will be running the daily risk that this entails.

General Relativity was published in 1915 and by 1919 there was the first test, which could have invalidated it but didnt, and it continues to be testedeven today with things like Gravity Probe B satellite, and it could be found to be off by even a little----in the sixth decimal place, like----at any time but it hasnt yet. That is a theory.
marcus
#27
Aug5-04, 01:01 PM
Astronomy
Sci Advisor
PF Gold
marcus's Avatar
P: 23,274
Quote Quote by jeff
... that string theory is somehow pathological - it clearly isn't - but rather that they need to stop trying to make huge conceptual leaps and instead work towards making more incremental and hence surer progress.
Yes
there was a good, lengthier, post by Lubos Motl to this effect
He said that the "string cosmology" stuff was premature
He said young researchers in the field should be advised not to
work on the more optimistic speculative things (I think he meant
"colliding braneworlds" and stringy multiverses and such) but instead
to grapple with basic problems. the post contained warnings and
he used the word "premature" more than once. I will try to find it
unless someone else can come up with a link.

In that same post, Lubos mentioned the need for "background-universal"
string models. Sounds encouragingly like background independent

On hearsay, I believe also that Lubos is very strong in rejecting Anthropery.

If we could filter out the voices of silliness we could hear the reasonable voice of string more clearly.

[edit: this blog has a pointer to a relevant Lubos post, and I see Peter was agreeing with Lubos there]
http://www.math.columbia.edu/~woit/b...es/000028.html
sol2
#28
Aug5-04, 01:50 PM
sol2's Avatar
P: 915
Quote Quote by Sol2
What are your thoughts on probing dimenisons in context of what I have shown in regards to the graviton(energy in energy out-where has it gone if not equal?) in regards to the colliders? Do you have another explanation?
Peter gave a response and was honest. If Jeff is suppose to be the official spokesperson, then he obviously hasn't given much here in PF to consider in regards to strings.

As a laymen I like to understand the experimental approach as well. Given indications here, from what has so far been considered(dimensions), although labelled whacky by a large segment, has something it is deriving itself from?

No? Yes?

The original question is still being poised, from the start of this thread. Is there scientific validation being looked at in the colliders?
jeff
#29
Aug5-04, 03:07 PM
Sci Advisor
P: 660
Sol,

What's your first language?
Gza
#30
Aug5-04, 03:45 PM
Gza's Avatar
P: 525
I'm entering grad school within under two years, and still trying to figure out what I want to specialize in. I have been pretty fascinated by string theory and got a chance to take an undergrad class in it, which furthered my interest, but I am worried about what the state of it will be by the time I am a few years into research. If it hasn't given testable results in this many years, how many more years will people continue to hold onto it? Also, what fields are you guys currently specializing in?
marcus
#31
Aug5-04, 04:30 PM
Astronomy
Sci Advisor
PF Gold
marcus's Avatar
P: 23,274
Quote Quote by Gza
... Also, what fields are you guys currently specializing in?
I'm a physics watcher and my special area of interest currently is Quantum Gravity Phenomenology.
This combines recent invovations in theory (extensions of special relativity to more than one invariant scale) with developments in instrumentation and satellite observatories such as GLAST, and PLANCK gammaray burst astronomy, ultra-high-energy-cosmic-ray, UHECR, astronomy, and other.

The latest conference on this was WS-2004 in Poland February 4-14
on the subject "Quantum Gravity Phenomenology"
Talks by a dozen or more experts included several people doing observational work

http://ws2004.ift.uni.wroc.pl/html.html
click on "lectures"

Steve Carlip, Roger Penrose and Carlo Rovelli were on the program committee: choosing the lecturers and which topics to cover.
Lee Smolin and Jerzy Kowalski-Glikman were among the theorists giving talks.
Observationalists Piran and Lipari gave talks on UHECR and Gamma Ray Burst astronomy.
The talks by these and other observational astronomers were
plentiful and of special interest. In (Loop especially) Quantum Gravity the trend is now to get busy with predicting and testing.
One wants to find LQG signatures in the spikes of gammaray bursts, for instance.
GLAST, the first gammaray array sensitive enough to see such things is not scheduled to fly until 2007 but in the meantime the observationalists are sort of "warming up" by doing whatever they can do with the instruments they have.

So that is a central interest for me. Exciting things are happening in Quantum Gravity, including the beginnings of prediction and testing, and i like to keep track of that.

I also have an interest in (Loop especially) Quantum Cosmology---basically the consequences of removing the big bang and black hole singularities by quantizing the relevant GR models.
arivero
#32
Aug6-04, 04:21 AM
PF Gold
arivero's Avatar
P: 2,938
Quote Quote by marcus
I'm a physics watcher and my special area of interest currently is Quantum Gravity Phenomenology.
I keep wondering why you (and some other people which seems to have both the time and the interest) do not upgrade from "watcher" to "student" or something so.
arivero
#33
Aug6-04, 04:31 AM
PF Gold
arivero's Avatar
P: 2,938
Quote Quote by whydoyouwanttoknow
So, um, the answer is that it's not a theory?
Hmm it depends. There is a "naive string theory", or "promised string theory", which was to have some nice properties (background-free to name one) letting us to justify mathematically the properties of the smallest elements of Nature. Such entity is not a theory but a goal. In pursuing it, the string practicioners were able to build a theory of perturbation for kaluza klein space-times with a matter content fixed by the theory. They did it twenty years ago; since then, the scientific discussion is about the utility of such object.
marcus
#34
Aug6-04, 09:32 AM
Astronomy
Sci Advisor
PF Gold
marcus's Avatar
P: 23,274
Quote Quote by arivero
I keep wondering why you (and some other people which seems to have both the time and the interest) do not upgrade from "watcher" to "student" or something so.
a student may mature into a researcher and do original research in the chosen field

a watcher may aspire to gain historical perspective on the human quest for knowledge and perhaps to arrive at a journalistic account

it is a private-language distinction---I dont want to force it on anyone else and I am happy to be thought of as a student

Alejandro, have a good walking tour in the spanish country.

when you get back, here is a request

Could Meteor or you supply the original-language quote from Alfonso
(probably in 13th century Castilian)
"If I had been present at the creation, I would have given some useful hints on the ordering of the universe."

that guy was as smart as a cat, if he really said that,
and very right they called him Alfonso Sagio or whatever it was.
Nereid
#35
Aug6-04, 10:04 AM
Emeritus
Sci Advisor
PF Gold
P: 4,014
Quote Quote by marcus
String may in time become a well-developed scientific theory and make unequivocal predictions of definite numbers that can be tested In which case it will be possible to prove wrong.

the criterion of a scientific theory is that it bets its life on predicting the outcome of future measurements (if it can accomodate any future measurement it has no meaning as science----it is more of a daydream or a poem)

So when String becomes clear enough and definite enough that it could be shot down or refuted by some empirical observation it will be a scientific theory and it will be running the daily risk that this entails.

General Relativity was published in 1915 and by 1919 there was the first test, which could have invalidated it but didnt, and it continues to be testedeven today with things like Gravity Probe B satellite, and it could be found to be off by even a little----in the sixth decimal place, like----at any time but it hasnt yet. That is a theory.
[nitpick]A scientific theory *also* has to be consistent with all historical observations and experimental results (within its domain of applicability).[/nitpick]

This can be a truly awesome mountain to climb; many new theories do it by showing that they are consistent with well-established existing theories they hope to go beyond, to within the limits of experimental error, 'in the limit' of the domains of applicability (or best current tests) of those current theories.
Tom McCurdy
#36
Aug8-04, 12:23 PM
P: 1,113
As far as evidence goes for String theory-- there is some evidence for it just not as solid as we would like. For example as Ed Witten points out one of the biggest pieces of evidence for String Theory is gravity-- a postdiction that String theory requires. I am not talking about the graviton which would provide much more "proof" (especially if it were at the moment of disapearence into the extra dimensions) but there seems to be some evidence. Also as many people feel is the weakness is string theory but many people feel the evidence is in the beauty of the equations... they have to be right there just too elegant to be wrong.


Register to reply

Related Discussions
String theory ~ the theory of physical theory? Beyond the Standard Model 32
Applied mathematics of Game Theory overlooked as a representaiton in string theory? Beyond the Standard Model 0
Does String Theory Satisfy Einstein's Conditions for a Physical Theory? Beyond the Standard Model 44
Matrix string theory, contact terms, and superstring field theory Beyond the Standard Model 2
How does string field theory differ from string theory Beyond the Standard Model 17