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Can gravity be absent? Not weightlessness as an astronaut experiences it because the astronaut's body still has gravity which will probably manifest in the presence of another smaller/larger body. For instance, given the mass of the moon it is subject to Earth's gravity holding it in orbit. I mean, total absence of gravity; can it happen?

I think this question will need to be edited; reading it seems even more muddled than the thought ... I can't express it. Feel free to vote to close/delete

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This is the question of whether there is a gravitational Higgs mechanism. The answer is probably no, but t'Hooft and Kakushadze gave ghosty realizations of this, the ghosts are probably unavoidable. If gravity is made massive, at long distance scales, there would be no gravity. – Ron Maimon Jul 30 '12 at 21:05
@RonMaimon: Could you please elaborate the Higgs mechanism, or recommend a link that may be read by a layman? I didn't comprehend the last bit - don't you mean if gravity is minute then at long distance scales there would be no gravity? – Everyone Jul 31 '12 at 17:29
@Everyone, if you are familiar with the weak (or electroweak) force, you might know that it is short ranged because of the Higgs mechanism; the weak force "photons" are massive instead of massless like the photon. What I believe Ron is getting at is to consider an analogous situation with gravitons, the "photons" of the gravitational field. If the graviton were massive via some kind of Higgs mechanism, gravity would be short ranged like the weak force and thus there would be no long range (macroscopic) gravity. – Alfred Centauri Aug 1 '12 at 14:15

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Yes, it could be possible to have a system without gravity. You've probably heard of the phenomenon called Dark Energy. This describes the accelerating expansion of the universe. There are theories that believe that this acceleration is not limited by the universal speed of light. The transfer of gravitational information is however thought to be limited by the speed of light. This means that if the space between the masses is spreading out faster than the information can be transferred, the masses will not interact with each other. In this senario it would be possible for there to be an absence of outside gravity. If you're interested in this concept you should look into the theories of Dark Energy and the Big Rip.

Hope this helped, and hope I got most of it right!

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Heard the term Dark Matter, but not Dark energy. What you describe feels similar to the thought I was trying to express. In the scenario in the answer the bodies still possess gravity; it's only that it can not be realized ... albeit if something were to exist without interaction with it's universe - it could probably be said to not exist at all, i think – Everyone Jul 31 '12 at 17:37
A bit misleading, Dark Energy is not thought to be related to Dark Matter, but is thought to comprise something like 72% of the universe. Basically this expansion of space is speeding up exponentially, to the point where our known universe will take on a "minimalist" appearance. Eventually we might only be able to interact with our local galaxy cluster, then eventually just our own galaxy, solar system, planet, etc, until matter itself is ripped apart. Hence the "Big Rip". – An0r4k Jul 31 '12 at 17:46
That isn't so much to say it doesn't exist though. There is a similar senario with a faraday cage that gives its interior electric shielding from the surroundings of the cage. This prevents the inside of the cage from getting any information on the electric field outside the cage. The sheilding however only works in one direction, as the shell (if spherical and ideal) will take on a universal charge equal to the net charge on its inside. In this setting information can travel in a single direction, even though the inside cannot be effected by the outside's electric fields. – An0r4k Jul 31 '12 at 19:35
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Since every object creates a gravitational field, the only way that there can be space with no gravity whatsoever is if you have no objects whatsoever. Even light will create a (generally very small) gravitational field.

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What about the middle point between two identical objects? There would be no net gravity field there, and I am wondering if that situation (no net gravity) can be physically distinguished from the situation where there is no gravity at all. – MSalters Jul 31 '12 at 12:41
Depends on what you're looking for. The gravitational potential at that point is nonzero, as are all derivatives of the field. A better example would be if you are inside a cavity in a spherically symmetric mass distribution. But the magic there would be broken the moment you looked outside the cavity. Are you talking globally or locally? – Jerry Schirmer Jul 31 '12 at 13:44
If you look globally, any universe with mass will have non-zero gravity somewhere. Locally, the question is indeed more interesting. Within that cavity, for example, is there anything you can tell about the gravity outside the cavity from the (lack of a) field inside? – MSalters Jul 31 '12 at 14:21
No. the field is zero and the potential is constant until you leave the cavity. – Jerry Schirmer Jul 31 '12 at 16:12
Isn't that the same as an electric charge on a container? It's apparently nil, and uniform within ... i remember reading – Everyone Jul 31 '12 at 18:19
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Absolute absence of a gravitational field in a region of space is plainly impossible, since in the universe there's at least one particle with mass which generates an infinite-reaching field (and in fact, there's obviously a lot of stuff out there, from planets to stars to galactic filaments). The gravitational force is the weakest of the fundamental interactions of Nature, and as the electromagnetic force, it has an infinite range; but unlike the latter, there's no "negative mass" equivalent which can "neutralize" the field far away from the interacting bodies.

That's why, among other things, that there's no macroscopic manifestation of the astronomically strong electric field that would be generated if all the elementary charges of electrons and protons, which compose every atom in any everyday object, were turned apart and separated. On the other hand, the gravitational force shapes the entire universe at the cosmological scale, and the electromagnetic interaction has no significant effect on large (neutral) objects like planets and stars.

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I don't understand. Surely every particle has an infinite field ... albeit it may be infinitesimal at infinite distance. – Everyone Jul 31 '12 at 18:30

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