Does the gravitational force actually exist?

1. Jul 4, 2004

Arawn

To be more exact, does gravitation have a force similar to the other basic forces: electromagnetic, strong and weak force? These other three are explained by the exchange of certain particles, but gravitation is explained by curving the spacetime. It doesn't look quite same to me...

2. Jul 4, 2004

a force is a force. No one said it has to come in one certain way.

3. Jul 4, 2004

Arawn

Yes, that's a good point... The mechanism how the gravitational force acts is just so different. With other forces, you have objects A and B changing particles... there's straight interaction between A and B. With gravitation, however, you have A and B sitting in the spacetime, and the curving of the mentioned spacetime makes them move closer each other. They don't interact with each other as much as they interact with the space itself.

But, as you said, a force is a force (is a force)...

4. Jul 4, 2004

Janitor

The desire to make all forces fit the same general quantum framework is why a lot of physicists expect that there is an exchange particle of a certain sort that they call the "graviton." I would be curious to hear anybody's thoughts on what it would take to experimentally confirm the graviton--and I don't just mean to experimentally confirm gravitational waves, something by the way that might well be done in my lifetime. For that matter, some would point to observations of close binary star systems that show they are losing gravitational energy, which in and of itself is good evidence that they are giving off gravitational waves, which carry energy away and allow the two stars to gradually get closer to one another, thereby changing their period of revolution.

5. Jul 6, 2004

lvlastermind

This is one of the questions that string theory is trying to answer. The relationship between EM, Strong, Weak, and Gravity. Some studies are now showing that gravity might actually be as strong if not stronger than the other forces. We cannont feel the full force of gravity or the graviton because it is not bound to our 3d universe like Em, Strong, and Weak are.

6. Jul 6, 2004

Arawn

What I've heard, the problem with the gravitons is that they only appear from the linear approximation of the general relativity, and cannot be reproduced from the exact solutions. In other words the concept of a graviton is just an approximation. That's why it seems to me that the gravitation is not like other three basic forces.

Might be that string theories can show us otherwise, one can always hope...

7. Jul 6, 2004

pmb_phy

It exists as soon as you define it. Force is defined as that time rate of change of momentum, i.e. as F = dp/dt. It has a different character as a force like the magnetic force or the electric force (i.e. the Lorentz force). That's why the gravitational force is refered to as an inertial force which means it has an existance which depends on the frame of reference. But its as real as any other force.

Spacetime curvature has very little to do with gravitational forces since its existance does not rely on it. I.e. you can have a non-vanishing gravitational force in a flat spacetime. The only relationship between spacetime curvature and gravitational forces is that when the spacetime is curved the gravitational force cannot be transformed away in a finite region.

Steven Weinberg has a nice section on gravitational force in his GR/Cosmology text. It's well worth the read. I can scan and e-mail that section to those who would like to see it.

Pete

Last edited: Jul 6, 2004
8. Jul 6, 2004

9. Jul 6, 2004

Chronos

Be nice, DW. Most of these guys are just asking well intended questions, not advocating crackpot new theories.

10. Jul 7, 2004

pmb_phy

{-edit-}

Nothing I've said is anything that can't be found in such texts as Basic Relativity, Richard A. Mould, Springer Verlag, (1994) or in Weinberg, Moller, Lanczos, or in The Meaning of Relativity, Albert Einstein

Consider also the article Einstein wrote which appeared in the February 17, 1921 issue of Nature

Last edited by a moderator: Jul 21, 2004
11. Jul 7, 2004

yogi

Much of modern physics is based upon particle interactions - but there is little to substantiate that these methods represent reality. Einstein spent the last half of his life contemplating how the geometric notions that were so effective in GR could be extended to explain electrical forces - interestingly, his views considered space as static rather than dynamic - but others such as Dirac were of the view that space could be defined by equations of motion -- one of the theories presently being knocked around is the in-flow theory that regards mass as an attractive center for inflowing spatial convergence - the predictions are in accord with GR.