# Why is gravity a problem?

1. Feb 5, 2014

### bobie

We have two main forces: gravity and electricity both acting at distance through vacuum.

This is a natural riddle, but while the electrostatic force causes no big trouble, they had to fancy relativity, spacetime curvature and recently strings to explain gravity.
I can see no difference:
I am surely missing something, can you tell me what?
Thanks

2. Feb 5, 2014

### Staff: Mentor

Don't forget the weak and strong interaction. They just have a shorter range where they are relevant.

Quantum electrodynamics (QED) is fancy as well. Actually, it is so fancy that general relativity was developed several decades before QED. I don't see a fundamental difference here.

Gravity is hard to integrate into a quantum-mechanical theory as it is not linear, and quantum field theory on a curved spacetime is problematic.

3. Feb 5, 2014

4. Feb 5, 2014

### bobie

Thanks,
could you tell me if is there any difference in (conceptual) questions the two forces raise?
I read in an academic paper re Compton scattering that the oncoming photon makes the electron oscillate in resonation and gives it KE, can we consider electrostatic force in the same way? Can we conclude that also any charge oscillates and makes another charge oscillate?

Is string theory in the same line, regarding mass?
What is the concrete evidence behind string theory?

Last edited: Feb 5, 2014
5. Feb 5, 2014

### Staff: Mentor

No, electromagnetic effects are not the same as electrostatic effects. Electrostatic effects are a small subset of electromagnetic effects - if nothing moves (by definition!).

String theory is a very speculative idea how to implement gravity in quantum field theory. It is completely different from other theories, and it is not even a proper theory (yet?) - just an idea how a theory could look like.
There is no evidence for string theory.

6. Feb 6, 2014

### bobie

Thanks,
gravity is explained by the curvature of spacetime, is it possible to say in simple words how QED explains electrostatic force?

7. Feb 7, 2014

### Staff: Mentor

If you find a simple way, let me know ;).