# Gravity force: Isn't it just the shape of space?

Isn't the force of gravity just a result of the shape of space as it is affected by masses within it? Why is it believed that it is a force associated with theoretical force particles "gravitons"? I can understand that the electric or magnetic force is a product of particles with fundamental interactions, but isn't gravity different? I always imagined gravitational force being more a geometric result of masses bending the shape of space. I am only in Physics 2, undergraduate level, but this is a question I have been thinking about for months now. Should I be thinking about this in a different paradigm?

ChrisVer
Gold Member
Yes the gravity has to do with the geometry of spacetime. However QFT doesn't work like that, and so that's why you need to ask for a graviton to exist. And in the standard model you don't only have force mediator for the EM interactions (photon), you do have for the weak and strong interactions too (W's, Z and gluons).
Also there are people trying to connect the spacetime geometry to the gauge symmetries ones. For an example one could have a look at Kaluza Klein theories, trying to get a 5D spacetime and compactify the 5th dimension to a perfect circle- the result is to get gravity to the 4D and electromagnetism from the compactification (together with an extra scalar field).

pervect
Staff Emeritus
Isn't the force of gravity just a result of the shape of space as it is affected by masses within it?

If you replace space with space-time, the above is the classical view of general relativity. It's a good place to start learning GR.

Why is it believed that it is a force associated with theoretical force particles "gravitons"?

That comes from a non-classical view of quantum gravity. What we need to ask here is "are the experimental predictions of this theory any different" from the former theory. I'm afraid I don't know the answer for sure.

I can understand that the electric or magnetic force is a product of particles with fundamental interactions, but isn't gravity different? I always imagined gravitational force being more a geometric result of masses bending the shape of space. I am only in Physics 2, undergraduate level, but this is a question I have been thinking about for months now. Should I be thinking about this in a different paradigm?

I would suggest sticking with your current belief as representing the prevailing picture of gravity in the textbooks and literature at the current time, but keep in mind the fundamental principle that it should be observation that ultimately decides the issue, and that no theory, however elegant, can stand unless it's confirmed by experiment.

To make a decision between the two theories, it becomes necessary to understand what the two theories (the geometric theory and the spin 2 theory) actually predict. I'm reasonably familiar with what the curved space-time theory predicts, but not so familiar as to what the spin-2 theories predict.

Two widely respected papers with somewhat different views on the topic of whether the spin-2 theory has equivalent predictions to GR:

http://arxiv.org/abs/astro-ph/0006423
http://xxx.lanl.gov/abs/gr-qc/0409089

The bottom line - I would personally recommend that you keep on as you have been, but try to keep an open mind and not get totally "locked into" one viewpoint as much as you can.