does gravity always exist?

[ydoaPs]

if there was only one object in the universe, would gravity exist? gr says that gravity is the warping of space caused by matter. so, in gr, there would be gravity. but, in qm, gravity is caused by graviton exchange. so, in qm, there wouldn't. what's the deal?

[Ophiolite]

One object, composed of many fundamental particles, happily exchanging gravitons, n'est pas?

[5614]

If there's only one thing then there's nothing for gravity to act on.

 

There's no yourdadonapogos to wonder about this problem, it would have no effect on anything whatsoever until you add a second object, at which point QM and GR says gravity exist.

[ydoaPs]

i was thinking object as in one particle, say a neutrino.

 

edit:in gr, there would still be the warp.

[Kingpin1989]

The fact that there is only one object makes the discussion of whether or not gravity exists moot. Gravity is caused, simply, by mass. If there is mass, there is Gravity. There just isn't anything for it to effect!

[Johnny5]

I would answer this way.

 

Depends on the object.

 

Your question is conceptual.

 

Suppose the object was a particle, with no internal parts.

 

Then there is nothing which can exert a force upon this particle, so that it is a free particle.

 

Therefore, in any inertial reference frame, either this particle is at rest, or moving in a straight line at a constant speed.

 

So there would be no gravity, no gravitational force.

 

On the other hand, suppose that all the matter in the universe, which currently exists, wherever it is, used to be concentrated into a single body.

 

Gravity would make the shape spherical rather quickly (and I know this is true without needing a theory of gravity, I can see what it does to moons, planets, suns, etc. ).

 

And if it was already spherical, then all the parts would pull on all the other parts.

 

So I would say that in the case where the one object isn't a particle, that gravity would shape that object.

 

Regards

 

PS:

 

As for whether or not every single particle constantly gravitationally interacts with every other particle, I have to say I don't know. In fact, I am not even sure zero-dimensional particles exist.

[swansont]

if there was only one object in the universe, would gravity exist? gr says that gravity is the warping of space caused by matter. so, in gr, there would be gravity. but, in qm, gravity is caused by graviton exchange. so, in qm, there wouldn't. what's the deal?

 

AFAIK there is no finished, working quantum theory of gravity. Perhaps this is one of the reasons why.