Blocking Gravity

[ellipsis]

I just had this random thought...

Since electric field can be blocked by a metal sphere in electrostatic equilibrium (when there is a charge outside the sphere and the sphere reaches equilibrium, it becomes an object of equal potential, so electric field lines can't penetrate the sphere), is it possible to block gravitational field?

[Kyrisch]

There are many differences between electricity and magnetism versus gravity. First, electric and magnetic fields can produce both attractive and repulsive forces while gravity is only attractive. Things that block electric fields like faraday's cages and such utilise these opposites to create a neutrally charged zone which cannot be done with the strictly attractive force of gravity.

[Reaper]

Correct, gravity only attracts, never repels, so I don't see a way you could possibly "cancel" the effects of gravity (unless, of course, antigravity is possible, but such a phenomenon has never been observed).

[DrP]

Maybe if we come up with the grand unification theory and unify the forces. But this is beyond us as of yet.

[Sisyphus]

Such a thing would almost certainly be impossible, for a number of reasons, which you may or may not find satisfying. First, as mentioned, it's a "one way" force, so you can't really neutralize it with some "opposite" force. (You can, of course, just put an equal mass an equal distance away in the opposite direction, but I don't think that's what you mean.) Second, it's not really a "force" at all, per se, so much as the "shape of space," hence there's nothing really to "block." And finally, it would totally invalidate a number of fundamental laws in really obvious and extreme ways. For example, you could easily make a perpetual motion machine by "blocking the gravity" to the upward swing of a wheel and not the downward. Simply put, if that were possible, it would be happening somewhere with such extreme and bizarre effects that we would have to notice it.

[Edtharan]

Maybe if we come up with the grand unification theory and unify the forces. But this is beyond us as of yet.

But what if that Grand Unified Theory said that it was impossible? Current attempts at a GUT don't allow for antigravity, so it appears that it might not be something that comes out of GUT.

[DrP]

But what if that Grand Unified Theory said that it was impossible? Current attempts at a GUT don't allow for antigravity, so it appears that it might not be something that comes out of GUT.

 

Your right - that's why I had hoped to cover my statement by beginging it with the word 'maybe' I was deliberately being a bit ambiguous because as you have pointed out we are nowhere near getting anything near it or even knowing if it is possible.

[timo]

Maybe if we come up with the grand unification theory and unify the forces. But this is beyond us as of yet.

- Grand unified theories are usually not understood as saying anything about gravity. The terminology usually refers to an encapsulation of the three gauge groups (the things that later lead to the observed interactions for elementary particles) of the Standard Model into a single gauge group.

- Coming up with a theory for something usually is not really a problem.

- The problem is that the theory should reflect nature. Taking the simplemost case of Newtonian Gravity, there is absolutely no problem to get gravity repulsive: Just use negative masses. The problem is that there does not seem to be negative masses in nature.

 

I think I understand what you meant, namely that having a good theory for something might help predicting and developing techniques and applications that were not thought of before. But since I have the feeling that theories are often way overranked in an inappropriate manner I at least wanted to point out that if you consider your statement from the other side you could as well completely dismiss it by (imho quite reasonably) assuming that nature cares nothing about man-made theories about nature.

 

EDIT: For completeness: The term "theory" in above refers to "theory of nature" of "physical theory". I certainly do not claim that every theory of any field of science has to relate to nature.

Edited June 6, 2008 by timo

[DrP]

I think I understand what you meant, namely that having a good theory for something might help predicting and developing techniques and applications that were not thought of before. .........I at least wanted to point out that if you consider your statement from the other side you could as well completely dismiss it by (imho quite reasonably) assuming that nature cares nothing about man-made theories about nature.

 

 

Fully accepted.

[ellipsis]

Wow... very interesting insights. Thank you!

[qlue]

If the space-time continuum is similar to the surface tension of a pool of water, and all matter/energy is riding on top of that surface tension, then breaking the surface tension would create an antigravity force with catastrophic effects. Whole regions of space would, almost instantly, be swept aside by the receding surface tension. Do we really want to dabble with that?

[Klaynos]

I think you're reading a bit too far into the analogy...