Does the gravitational force actually exist?

[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...

 

[Nenad]

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

 

[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)...

 

[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.

 

[lvlastermind]

To be more exact, does gravitation have a force similar to the other basic forces: electromagnetic, strong and weak force?

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.

 

[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...

 

[pmb_phy]

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...

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 referred to as an inertial force which means it has an existence 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 existence 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

 

[DW]

That's why the gravitational force is referred to as an inertial force which means it has an existence which depends on the frame of reference. But its as real as any other force.

You just contradicted yourself.

 

[Chronos]

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

 

[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

Can gravitation and inertia be identical? This question leads directly to the General Theory of Relativity. Is it not possible for me to regard the Earth as free from rotation, if I conceive of the centrifugal force, which acts on all bodies at rest relatively to the earth, as being a "real" gravitational field of gravitation, or part of such a field? If this idea can be carried out, then we shall have proved in very truth the identity of gravitation and inertia. For the same property which is regarded as inertia from the point of view of a system not taking part of the rotation can be interpreted as gravitation when considered with respect to a system that shares this rotation. According to Newton, this interpretation is impossible, because in Newton's theory there is no "real" field of the "Coriolis-field" type. But perhaps Newton's law of field could be replaced by another that fits in with the field which holds with respect to a "rotating" system of co-ordiantes? My conviction of the identity of inertial and gravitational mass aroused within me the feeling of absolute confidence in the correctness of this interpretation.

 

[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.