# I Fundamental forces

1. Nov 16, 2016

### Chan Pok Fung

As far as I know, we regard the electromagnetic force, gravity, strong and weak interactions as the four fundamental forces.

We know that Newton's law of gravitation does not perform as well as Einstein's general relativity. Scientists are now using energy-stress tensor to describe gravitational fields. Here comes my question: How do we interpret the other three forces? I am more familiar with the EM interaction. Let me focus on it.

When I first learn the Columb Force, my teacher told us that it behaves just like gravitation - both decay inverse squarely. Now, we have a new theory explaining gravity. Do we have a new theory for Columb force? I read some articles saying that string theory is trying to do this. My main concern is: do we find any inconsistency between experiments and our Columb Force theory, just like the case of Mercury's precession?

2. Nov 16, 2016

### DennisN

Yes.
Hmm, yes and no , it's not a new theory. It is called Quantum Electrodynamics (QED). And it is not like general relativity.

and, if you are interested
Please note that there are no experimental evidence (yet) for string theory .

3. Nov 16, 2016

### Simon Bridge

The comparison of the Coulomb force and gravity is for teaching purposes only - it's a handy analogy for givig students a loose feel for electrostatic forces. The two are not considered anything alike IRL.
At some point in those lessons, the analogy should break.

We understand the "other three" forces in terms of quantum mechanics and, specifically, field theory... in this picture, the forces are the result of interactions with fundamental particles whose behaviour is described using probability and statistics. The particles themselves appear as small fluctuations in the overall field.
We understand gravity as a pseudoforce arising from the geometry of space-time.

However - there are fundamental disagreements between quantum mechanics and general relativity which remain unsolved.
String theory is a work in progress that attempts to do this, or, at least, tries to find out what such a solution may look like.
You will also see references to "quantum gravity" which attempts to treat gravity like a quantum mechanics force.

4. Nov 16, 2016

### Chan Pok Fung

Wow, your comments are awesome! Can I say gravitation is somehow different from the other three forces?

5. Nov 16, 2016

### Simon Bridge

At current state of knowledge it is fair to say that gravity is understood in a quite different way to the other forces.