# Anti-gravity

What would be the effects of a device that could shield itself from gravity? Would it fly off into space? Would it just float around in the air?

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It’d fly away. The air which is affected by gravity would try to take its place and push it upwards.

yeah, I am very much antigravity myself. Where do I sign?

Remember, gravity’s not just a good idea …
it’s the law!

Arjuna34

I think the only “anti-gravity” possible wouldn’t be true anti-gravity but would be more of a passive repulsion system, maybe like an electro-magnetic field that pushes away from earth. Something like that could be regulated in intensity, and the user should be able to control if they are a meter off the ground or a mile.

I don’t think it would be possible to have something that is completely unresponsive to gravity, because that would apparently violate General Relativity. G.R. views gravity as the result of the curvature of spacetime, rather than a force; the path of a freely falling object is simply the shortest geodesic in the local spacetime.

I think something that would be the functional equivalent of antigravity would have to somehow be “pushing” against the mass of the Earth.

Is gravity real or does earth just suck?

Hmm, a way of shielding a device from gravity… how about if you get rid of or “hide” the mass of an object? Would that be considered a way of evading gravity?

Oh this is easy. You could easily build an anti-gravity field, if you just had a way to manipulate enough matter and energy.

The only way to experience no local gravity standing on earth would be to be halfway between earth and a mass equal to earth. Think about an Apollo space capsule going to the moon. Most of the time they are in the Earth’s gravity pull, later on as they get closer to the moon, the moon’s gravity will pull them forward. But at the exact midpoint of these gravity fields, the pull is equal, gravity is essentially cancelled. If you dropped a satellite there with no motion towards or away from the moon, it would just stay in position as if gravity was not acting on it. I think they call this the L3 point or the L5 point or something.

So anyway, the L3 point here is close to the moon because the moon isn’t as massive as the earth. If the moon’s mass equalled the Earth’s mass, the L3 point would be exactly halfway inbetween.
So let’s hypothesize that you could harness enough matter, like 1 earth mass, and compress it to maybe the size of a marble. Suspend it maybe 10 feet off the surface of the earth. There would be a field under it where gravity would be cancelled. Now of course, I’m talking about stellar quantities of energy to compress some matter into something like neutron star matter, and an equally stellar amount of energy to keep it in position. And it would throw the earth out of orbit. But if you could just harness enough energy, it could be done.

Chas, your idea would cancel out gravity on a macro level (that is, to a point where the naked eye can’t discern the gravitational differences). However, in order to truly, completely cancel out gravity, you have to find a means to nullify ALL sources of gravity in the universe.

To get back to the OP (being not about IF antigrav is possible, but what would happen if it WERE possible), if someone built, say, a sphere with an antigrav mechanism inside, which generated a field, say, ten centimeters out from its surface, that nullified 100% of the gravity fields affecting everything inside said field…

…I’d imagine that it’d just kind of float in midair. See, this object, inside the gravity field, would essentially weigh nothing. A single atom flying around would cause it to start moving, but inside the atmosphere, it’d have a (roughly) equal amount of atoms pummeling it on each side. However, if you were to push it in a certain direction, it’d keep going that way until something else stops it.

As Lumpy said, the universe essentially IS gravity. There is no escaping it.

I doubt that it’s possible to shield an object from gravity, but you might be able to build a device that would counteract the effects of gravity by reverse warping space-time. The problem is that if you did this to null the Earth’s gravity then the Moon’s gravity would start pulling on you… and Mars… and Jupiter… and the Sun… You would also have to contend with large objects, like mountains and buildings. These all exert gravitational forces on us every day. As, has been pointed out - gravity is all around us. We just don’t notice because the Earth makes a much bigger dent in local space-time.

If you could build a device that was capable of sensing gravity from all sources simultaneously and compensating by reverse warping space-time, then it would just float about freely - similar to objects in space (objects in space still experience gravity, the effects are just less pronounced). If your device merely nulls the center of gravity of the Earth, then it would hover and would tend to drift towards more massive objects, unless acted on by other forces. Of course, in our atmosphere, wind currents would tend to be much stronger than the gravitational attraction of large masses, so usually the device would just get blown around…

What do you mean IF you can built an antigravity machine? I have one right here, it’s called an elevator!

Wouldn’t it be the opposite, that WE would fly off into space relative to the object? If it were truly anti-gravity, wouldn’t its motion relative to us change, and just kinda “stay where it is” while we continue moving on?

I am, of course, totally out of my league on this question, but I can’t help trying to sound smart. (emphasize trying)

I have no clue how one might actually create a “null-gravity” device of some sort, but it’s quite likely that if it were possible, such a device would also eliminate all effects of inertia. In other words, there is no way to predict what such a device would end up doing. It could accelerate in any direction at any rate with any or no stimulation from outside forces. To be on the safe side, we’d better assume a device that reduces gravitational and inertial effects almost, but not quite, to zero, in which case a very small force in any given direction would cause a large acceleration in that direction.

True antigravity, as opposed to null-gravity (would repell ordinary matter, instead of attracting it) is, conceptually, at least, much simpler: You just need something with negative mass. Don’t ask me where you get negative masses from; I think that they need to be special-ordered from that store that sells frictionless pulleys and massless, unbreakable string.

Aren’t elevators based on counterweights?

There is a classic H.G.Wells novel called “The First Men in the Moon”, in which a scientist invents an alloy that is opaque to gravity. He makes a system of shutters around a glass sphere, so he can allow gravity in on only one side if he wants. He and his partner get in, screw on the lid, and close the shutters. The air above them no longer ‘feels’ the earth below it, and is pushed out to space. The ship is likewise thrown off the planet. Once in space, they open a shutter to allow the moon’s gravity to affect them, and they fall toward the moon.

But it seems the OP is talking more about null-gravity, not blocking gravity. Still, it seemed appropos.

It does seem that gravitation and inertia are linked effects of having mass. So to have null-g, you’d either have to unlink the three properties (gravity, inertia, mass), or eliminate them all. If you actually got them to zero, you’d have macroscopic photon, essentially. Such things just don’t stand still, so I think it would take off in a hurry, probably at c.

If you could find a way to leave the mass and inertia in place while cutting off gravitation, you would need to anchor it somehow to keep it on the planet. There’d be no reason for it to stick around, unless something blocked it. It would fly off at a tangent to the earth’s orbit, since it would no longer orbit with the planet.

not only would the air push it away, it would no longer be held in an orbit which would let it “hover” near Eath. since it is already moving at the Earth’s orbital velocity, it would quickly shoot away from the planet as it continued to move in a straight line at that speed. (The Earth would continue to follow its orbit)

Sofis is right as to what a null-gravity object would do (presuming the device in question only cancels gravity, and not inertia somehow). The object would become weightless and would be displaced by heavier objects (air) which would be attracted to the nearest gravitational source (Earth). Thus it would rise to the edge of the atmosphere (and probably beyond, but only due to the inertia it gained from the trip up; once it reached the end of the atmosphere, bouyancy would no longer provide an upwards force).

As to whether this is possible…
…the degree of difficulty in part depends on what gravity is (and nobody knows for sure).
If gravity is just the curvature of spacetime in the presence of matter/energy (General Relativity), then it would seem to be unlikely that anything with positive mass could be immune (an orbit is actually the shortest path in non-Euclidian spacetime in the presence of a massive object). You would most likely have to resort to balancing the forces of gravity with other counterforces (helicopters and airplanes do it all the time).

If gravity is carried by an exchange particle graviton (Quantum Field Theory), then it might be theoretically possible to block/divert the gravitons in some way that shields you from gravity. It is known that if gravitons exist, they must have neutral charge (otherwise we’d observe gravitational fluxuations in the presence of an electromagnetic field), but if you could somehow get a charge, or a magnetic moment, induced on the gravitons, you could then manipulate them with an electric or magnetic field.

Bottom line: I wouldn’t sell my shares of Boeing or Weight Watchers just yet…

I won’t get into the theory about creating such a device but as for what would happen if you stopped gravity from affecting an object it is easy.

The Earth is spinning really fast we need some force to suppy the centriptal force to hold us to the earth. Gravity supplys this force. If you made a device that was sheilded from all gravity it would fly off in a path tangential to the rotation of the rotating earth. It is like if you whirl a ball on a string around your head and suddenly let go.