String theory questions

[Sarevok]

1. Does string theory make any predictions that can be tested ?

2. Are there any practical applications of string theory that does not require almost fantastic science like negative energy ?

[mr friendly guy]

First let me say that I am definitely NOT an expert.. .. but

According to one of string theory's proponents, ?Witten or something like that he argues that string theory predicts gravity. Unfortunately it seems hollow since we already knew of the existence of gravity before hand, but at least this is something.

The other thing I know of its supposed to predict the existence of certain particles which have some relationship to existing particles. These new particles are known as Sparticles (S + particles) for some reason. This can be apparently tested if you have a big enough particle accelerator, like CERN.

Other than that I expect Kuroneko to come and explain it great details making a mere mortal like me look like a Philistine.

[Kuroneko]

1. Does string theory make any predictions that can be tested ?

Yes. For example, it incorporates exact Lorentz invariance, equivalence principle, and standard QFT at low energies. So the real question becomes: does it make predictions other than the theories it's designed to emulate that can be tested? That depends on how the "can be tested" is interpreted. In principle, sure--it constrains physics a great deal at high energies. In practical terms, not so much, since most of them involves rather energetic phenomena. However, ST predicts supersymmetric partners of normal particles (mentioned above), so if they're not found at increasingly higher energies, that would strongly undermine its prospects as a description of the universe.

2. Are there any practical applications of string theory that does not require almost fantastic science like negative energy ?

Yes. The AdS/CFT correspondence between string theory in anti-de-Sitter space and conformal field theory has applications in condensed matter physics*. Conformal invariance means insensitivity to scale, which is a very curious kind of thing that even approximately only happens in very special cases; fortunately, that includes superconductivity. Various CFT systems have a 'gravitational dual' in terms of string theory, which is useful in making them be more tractable. That's completely independent of whether string theory is a good description of nature in general.

* Theoretically, this is where the 'holographic principle' originally comes from, which is hoped to apply in more general cases. A more well-known related phenomenon is Hawking radiation of black holes (specifically, entropy of the event horizon).

[Korto]

These new particles are known as Sparticles (S + particles) for some reason.

Anyone else imagining a bunch of electrons, protons, neutrons and what have you all stepping forward and saying "NO! I AM SPARTICLE!"