Questions About String Theory: Get Answers Here

[ZapperZ]

In my opinion Woit knows he is saying.
The relevant part is not if in string theory one can construct models or not. The relevant part is
Adjusting different parameters ad hoc one can construct models where deviations from Newtonian physics are observed at mm-range or beyond. That is not a prediction
In fact note that your "So yes, a possible detection has been proposed, but it has failed miserably so far." has not stopped string theory. string theorists invoke a new change of scale or a new scalr field or some extra dimension etc each time that a predictions from string theory is invalidated.
Some time ago, string theory WAS the explaining of dark matter and energy, now after the revolutionary paper suggesting that GR does not need dark matter or dark energy, string theorists do not claim that were wrong in the recent past.
I cannot wait honesty from a man who claimed that evident absence of aliens in the universe was a proof of string theory was correct. The "argument" was that aliens were very advanced and using string theory developed a engine for travel via hidden dimension to a parallel universe.

I do not want to get into this with you, because in my personal opinon, you have a rather unhealthy obsession with this thing. I am NOT a fan of String Theory, and I know many prominent physicists who aren't either. But they don't go out of their way and have the compulsion to intrude into string theory discussions.

My point was that there WERE attempts at trying to come with some measureable effects. It's only fair to point this out, even when it has failed. This is what experimentalists like me would want to test, and they have.

Done!

Zz.

 

[Juan R.]

Noises now coming out of Washington indicate that they may have found something. See Runner up at
http://www.symmetrymagazine.org/cms/?pid=1000189"
Very tentative.
Regards,
George

Do you refer to the Eöt-Wash group?

If yes, let me say that measured deviation (if it is correct) from Newtonian behavior goes AGAINST string theory.

Basically, string theory 'predicts' an increase of Newtonian force due to extradimensions

F = 1/r^(2+D)

with D the number of additional dimensions D= 6, 7 in string M-theory. However the experiment -that is being repeated- measured a decreasing of the force strengh.

Curiously a decreasing of Newtonian force could be compatible with other models of quantum gravity. For example, in triangulations, recent simulations suggest that at small scales dimensionality reduces from 4 to 2. See also Baez comments on this in sci.physics.research

Formally, we can take the number of extradimension to be -2 in the triangulation model discussed by Baez

then

F = 1/r^(2-2)

One finds both decreasing of force and elimination of divergences at r=0.

Of course, this is not rigorous, but it offers an idea of "not all is string theory". There are very revolutionary and interesting views outside of string theory dogma.

 

[selfAdjoint]

Curiously a decreasing of Newtonian force could be compatible with other models of quantum gravity. For example, in triangulations, recent simulations suggest that at small scales dimensionality reduces from 4 to 2. See also Baez comments on this in sci.physics.research

This thought had also occurred to me, but I lack the background to follow it up. Would a low dimension at small scales (=high energy) imply a weaker gravity? In the Randall-Sundrum model the weakness of gravity relative to the other three forces is explained by allowing it to propagate in more dimensions. Plus, in a two dimensional world, the force would only fall off as the inverse first power, so it would be stronger, not so?

 

[Juan R.]

I do not want to get into this with you, because in my personal opinon, you have a rather unhealthy obsession with this thing. I am NOT a fan of String Theory, and I know many prominent physicists who aren't either. But they don't go out of their way and have the compulsion to intrude into string theory discussions.
My point was that there WERE attempts at trying to come with some measureable effects. It's only fair to point this out, even when it has failed. This is what experimentalists like me would want to test, and they have.
Done!
Zz.

I did not say you was a FAN nor nothing of the rest.

i simply explained that Woit's comment was correct, because string theory predicts nothing. Only that!

I do not doubt that one can construct 'models' on string theory, but string theory predicts nothing since models are constructed ad hoc. What supersimetry is not detected where suggested by string theorists no problem! one change the scale until a new acellerator again proves that superimmetry was not wher was 'predicted'.

The same holds about the rest of 'predictions' of string theorists, including deviations from Newtonian law.

 

[maverick280857]

This question, which is perhaps trivial for the forum (and may not be germane to the present discussion, in which case please accept my apologies), is from an enthusiast's point of view who is interested in learning more about string theory: What are the prequisites for studying and understanding string theory and quantum field theory? At what stage does one become eligible (formally, or on paper) to delve into string theory?

 

[Juan R.]

This thought had also occurred to me, but I lack the background to follow it up. Would a low dimension at small scales (=high energy) imply a weaker gravity? In the Randall-Sundrum model the weakness of gravity relative to the other three forces is explained by allowing it to propagate in more dimensions. Plus, in a two dimensional world, the force would only fall off as the inverse first power, so it would be stronger, not so?

Basically, if gravity 'dilutes' between other dimensions doing that at macroscopic scales we can only detect the 3D-part then at small scales it may be stronger. This is said by string theory.

See http://www.aip.org/pt/vol-53/iss-9/p22.html

for the force, the dependence is 2+D instead of (D+1). D is the number of extradimensions. If you reduce from 4 to 2 the spacetime, then the number of extradimensions is, formally, D = -2 and therefore the force is more weak at small scales -whereas string theory 'predicts' the contrary-.

when r --> 0

1/r^2 >> 1/ r^1 >> 1/r^0

what 1/r^0 to small scales appears to eliminate 'divergences' of quantum gravity has been also pointed by J. Baez.