What's the current perspective on string theory and the existence of gravitons?

[touqra]

I read from this site: http://www.math.columbia.edu/~woit/blog/archives/2004_04.html

refering to the last blog dated 1 April 2004, that "Science Times" will run an article by NYT reporter James Glanz in which several leading string theorists say that they are giving up on the idea is rapidly spreading throughout the particle theory community.

Is this true or a joke?

 

[marcus]

I read from this site: http://www.math.columbia.edu/~woit/blog/archives/2004_04.html

refering to the last blog dated 1 April 2004, that "Science Times" will run an article by NYT reporter James Glanz in which several leading string theorists say that they are giving up on the idea is rapidly spreading throughout the particle theory community.

Is this true or a joke?

April 1 (so-called "April Fools Day") is a special day for
harmless jokes and hoaxes
newspapers and magazines sometimes have an April 1 issue devoted
to satire and pretended news stories

this is a custom in English-speaking places, I don't know if
other language-groups have it

 

[touqra]

I am currently doing an undergrad project on topological defects in quantum field in compactified dimension and I stumbled across that site for informations on string theory. I got a shocked and stop all my work to ask this question on this physics forum. Arrgh.
Anyway, I don't really agree much with strings cause there's too many new matter predicted yet been seen.

 

[marcus]

...I got a shocked and stop all my work to ask this question on this physics forum. Arrgh.
Anyway, I don't really agree much with strings cause there's too many new matter predicted yet been seen.

I am curious as to what culture does not have "April fools day"
If not too much trouble would you tell me your native language?

As English speaker i too easily assume everybody knows what to expect
at April 1. lots of silly jokes. this is not necessarily bad especially since it is only once a year.

 

[touqra]

April Fool is really an English medium Western stuff.

I'm from Malaysia. A Chinese. Though we speak English as a second language and know about April Fool but we don't really celebrate, not even hoaxes on papers or magazines. April 1 is as normal a day as any day else, besides mayb we get a couple of pranks from friends on dat day.

My native language is Mandarin.

I'm not use to having such a joke on a blog. It reminds me of 1900 when Max Planck reveals quantization and ppl began to lose trust on the classical.

 

[marcus]

...

My native language is Mandarin.

I'm not use to having such a joke on a blog. It reminds me of 1900 when Max Planck reveals quantization and ppl began to lose trust on the classical.

I understand how it could have been a shock to read that!
But now I hope you are again working hard on your undergraduate physics project. I wish you all possible success with it.

 

[Tom McCurdy]

Speaking of sparticles and such predicted particles from M-theory... has any of the predicted particles have been found...

what is the up to date status of string theory

and
Super Symmetry
Brane Theory
Sparticles
the the search for a gravton disapearing or not

 

[selfAdjoint]

Supersymmetry is currently being squeezed by the latest increase in the reported mass of the top quark. In the simplest supersymmetry theory, the lightest supersymmetrical particle's mass depends sensitively on the top mass, but is also constrained from above. And the window where its mass must lie just got very narrow, leading many physicists to fell uneasy about supersymmetry and several contrarians to do a war dance.

The search for large extra dimensions and possible evidence for gravitons has turned up nothing so far.

AFAIK that's the experimental situation on the questions you asked.

 

[marcus]

... And the window where its mass must lie just got very narrow, leading many physicists to fell uneasy about supersymmetry and several contrarians to do a war dance.

...

the natives are restless

 

[Mike2]

Hopefully this is not too off topic for this thread, "Strings".

But strings have waves of vibration that circulate on the string. How is it that the energy of a string that causes the vibration stays on the string and doesn't dissipate in all directions? The string is embedded in the rest of the dimensions, isn't it? So does the distortion on the string not in the other dimensions? Is it only in the direction of the string so that as you approach the string from a transverse dimension there is zero field until you get directly on the string and then there is a field strength? That would present a discontinuity when approaching the string from a transverse direction. What keeps the string being a string? Why doesn't it immediately dissipate in all directions?

 

[selfAdjoint]

The string vibrates transversely in the dimensions not along its length and not timelike. So that's in 24 dimensions for the bosonic string and 8 for superstrings. Why should the energy dissipate?

 

[Entropy]

Sparticles

Heheh... "Sparticles." Thats a funny word.

What?

 

[selfAdjoint]

You think that's funny, how about Wino, the fermionic supersymmetry partner of the W boson. Or stop, the bosonic partner of the top quark.

 

[Mike2]

The string vibrates transversely in the dimensions not along its length and not timelike. So that's in 24 dimensions for the bosonic string and 8 for superstrings. Why should the energy dissipate?

It's like the surface of a pond of water. The undistrubed water occupies the x-y plane, and waves are disturbances in the z directions. A string is a one dimensional object in many dimensions. So having a distrubance on a superstring only is like seeing a piece of string in a pond of water oscillating and saying that the surface itself is not oscillating. But if the whole surface were to oscillate due to a distrubance started by the string, then all the energy that originated with the string would dissipate across the entire surface. In this analogy, the surface of the water plays the part of the background spacetime. Does this make more sense? Thanks.

 

[selfAdjoint]

In this analogy, the surface of the water plays the part of the background spacetime. Does this make more sense?

But the water is material, and obeys all sorts of material laws, including thermodynamics, to take away the energy. There is nothing corresponding to that in the background spacetime of string theory.

 

[Mike2]

But the water is material, and obeys all sorts of material laws, including thermodynamics, to take away the energy. There is nothing corresponding to that in the background spacetime of string theory.

OK, so maybe that analogy broke down. Let me try this: (Correct me anywhere I'm wrong). The string undergoes transverse oscillations. This mean different portions of the string are moving faster then other portions at a given time. These different portions have a different mass/energy since there is a tension (force) on the string for the distance of that portions. Doesn't mass/energy warp and curve the background? Wouldn't this warping tend to propagate away from the string (in the form of gravity waves) as the portions change? Wouldn't this gravitational wave propagation dissipate any energy in the string?

 

[Mike2]

OK, so maybe that analogy broke down. Let me try this: (Correct me anywhere I'm wrong). The string undergoes transverse oscillations. This mean different portions of the string are moving faster then other portions at a given time. These different portions have a different mass/energy since there is a tension (force) on the string for the distance of that portions. Doesn't mass/energy warp and curve the background? Wouldn't this warping tend to propagate away from the string (in the form of gravity waves) as the portions change? Wouldn't this gravitational wave propagation dissipate any energy in the string?

You'd would have reason to believe a point particle would not dissipate since there is no mass changing velocity in the frame of the point particle itself so no gravity wave would develop to carry away energy. But when you talk about strings and higer order object then you do have mass (=energy of tension times distance of protions of the string) whose velocity changes with time giving rise to gravity wave (or graviton?) that would carry away the energy.

 

[selfAdjoint]

OK, so maybe that analogy broke down. Let me try this: (Correct me anywhere I'm wrong). The string undergoes transverse oscillations. This mean different portions of the string are moving faster then other portions at a given time. These different portions have a different mass/energy since there is a tension (force) on the string for the distance of that portions. Doesn't mass/energy warp and curve the background? Wouldn't this warping tend to propagate away from the string (in the form of gravity waves) as the portions change? Wouldn't this gravitational wave propagation dissipate any energy in the string?

The background spacetime in string theory is FLAT. That's what the LQG people keep complaining about. The spacetime doesn't get modified by the physics. So no, the mass/energy doesn't warp the background.

 

[Mike2]

The background spacetime in string theory is FLAT. That's what the LQG people keep complaining about. The spacetime doesn't get modified by the physics. So no, the mass/energy doesn't warp the background.

Which leaves us asking the question, "Where did the background spacetime come from?"

OK, so string theory poses gravitons in a flat spacetime. But gravitons are just the quantized version of the gravitational field - instead of waves, there are gravitons. Still when mass accellerates, instead of waves, gravitons are given off. So I suppose that when portions of a string accellerate, graviton would be given off, and the energy of the string would be dissipated by gravitons.

Maybe it is the case that if the fluctuation were large enough, then a gravition is given off. Is there a minimum energy of a graviton?

 

[selfAdjoint]

Is there a minimum energy of a graviton?

I wouldn't think so - like photons, there's no "mass gap" to keep them from going down to as low an energy as you like.

 

[Tom McCurdy]

What other theories besides strings require gravitons, and do these require the gravitons to "stay" in our dimensions before disapearing to higer dimensional space?

 

[sol2]

What other theories besides strings require gravitons, and do these require the gravitons to "stay" in our dimensions before disapearing to higer dimensional space?

Graviton permeate all dimensions.

 

[Tom McCurdy]

-

ty for the response but i was wondering which theories require or allow for gravitons besides M-theory

 

[Mike2]

Which leaves us asking the question, "Where did the background spacetime come from?"

OK, so string theory poses gravitons in a flat spacetime. But gravitons are just the quantized version of the gravitational field - instead of waves, there are gravitons. Still when mass accellerates, instead of waves, gravitons are given off. So I suppose that when portions of a string accellerate, graviton would be given off, and the energy of the string would be dissipated by gravitons.

The question would then be why does not the graviton then dissipate, and what dimension of object is a graviton.

It still bothers me how you could travel towards as string and there be no indication that it is there until all of a sudden to bump into it when you reach it, assuming you could bump into its length when it has no cross sectional area. What are the odds of that? This seems to suggest a discontinuity where something exits only along a line without cross section.