Does string theory predict additional long range forces gravity EM

[ensabah6]

Does string theory predict additional long range forces gravity EM?

One of the most touted features of String theory is that it correct predicts and even requires 2 infinite long range forces, gravity and E&M.

I've heard that string theory though also predicts additional non-observed long range forces which are not observed, and allowing gravity and E&M to exist in string theory while suppressing the non-observed long range forces requires a lot of fine-tuning. Another way to hide these long-range forces is to associate them with dark energy.

Is this correct? if gravity is a triumph of string theory then what about unseen forces that are equally an implication of string theory?

 

[javierR]

The various string theories do generally have additional long range forces. Anytime you have extra U(1) gauge interactions e.g. (One thing to note with supersymmetry is that if there are gauge fields with scalar superpartners, these scalars also couple to charged fields like their vector-field partners, so you have to worry about those guys as well). As you mentioned, all these types of interactions may be suppressed, but not just through fine tuning; there are other situations like intersecting branes and domain walls in which these interactions can more naturally be suppressed.
Some scalars, though, may indeed be useful phenomenologically for the strong-CP problem or Dark Energy if they are very weakly interacting, e.g., so that we would have missed them in experiments to date. I wouldn't say this is "hiding" them, but using them.
Also, I wouldn't say that string theory makes specific predictions much more than quantum field theories do with regard to what kind of interactions to expect. String theory has a great flexibility in what kinds of low energy effective theories you can get from it. So to address your last question, yes string theory predicts gravitons and many other particles and interactions, but we see the first as a triumph and the latter as a challenge due to the fact that we haven't seen evidence for those new interactions in nature, so you have to push them out of the way according to experimental bounds. Another challenge is that there are expected to be numerous string scenarios that would be consistent with experiments to date and yet predict different beyond-the-standard-model interactions and particles. If you can't make tests to distinguish them, where do you go from there?

 

[Entropia]

It is true that string theory predicts the existence of both gravity and electromagnetism as long range forces. This is one of the major successes of the theory, as it is able to provide a unified framework for understanding these two fundamental forces in physics.

However, string theory also predicts the existence of other long range forces that have not yet been observed. These forces are often referred to as "hidden" or "extra" forces and are typically associated with extra dimensions in the theory.

The existence of these additional long range forces is a consequence of the mathematical structure of string theory, but they have not been observed in experiments. This has led to the need for fine-tuning in order to suppress these forces and allow for the observed long range forces of gravity and electromagnetism to dominate.

Another possibility is that these extra forces could be associated with dark energy, which is a mysterious force that is believed to be responsible for the observed acceleration of the expansion of the universe. However, this is still an area of active research and there is no consensus on the connection between dark energy and the extra forces predicted by string theory.

In summary, while string theory does predict the existence of additional long range forces, they have not been observed and their existence requires further investigation and fine-tuning in order to reconcile with the observed forces of gravity and electromagnetism.