3 ms·

I just had four physicists in my Uber last weekend and we got into this a bit. The one guy said the biggest problem with gravity is we’ve never figured outs its

I just had four physicists in my Uber last weekend and we got into this a bit. The one guy said the biggest problem with gravity is we’ve never figured outs its opposite or if there even is an opposite. He mentioned something about negative mass, which is maybe the handwavium equivalent of anti-matter in science fiction? Gravity only attracts. It never pushes away. Yeah I’m way in over my head but it’s fun to poke around in things we don’t understand.

codethief 3y ago
> He mentioned something about negative mass, which is maybe the handwavium equivalent of anti-matter in science fiction? Well, anti-matter actually exists but its mass is positive. Also, the anti-particle of the (hypothetical) graviton is the graviton itself[0], so all in all nothing fancy happening there. > Gravity only attracts. It never pushes away. Cosmic expansion would like to have a word. (Though, admittedly, expansion doesn't happen in gravitationally bound systems, so from this point of view your statement is of course correct.) > The one guy said the biggest problem with gravity is we’ve never figured outs its opposite or if there even is an opposite. Interesting. Do you know whether he was an active researcher in the field of relativity? I can think of a lot of "big problems" in relativity but this wouldn't be one of them. I mean, don't get me wrong, it would be nice to have something to cancel out gravity since this would inspire lots of applications that we so far deem science fiction. But we already have a pretty good idea of the limits of what's possible[1]. [0]: https://physics.stackexchange.com/questions/273918/is-there-a-possibility-for-discovery-of-anti-graviton-i-e-the-graviton-antipar https://physics.stackexchange.com/questions/273918/is-there-... [1]: https://arxiv.org/abs/1611.01808 https://arxiv.org/abs/1611.01808 + the rigidity case of the https://en.wikipedia.org/wiki/Positive_energy_theorem https://en.wikipedia.org/wiki/Positive_energy_theorem suggest that one could theoretically "shield" / cancel out gravity to some degree but not everywhere (in all directions).

codethief 3y ago

> He mentioned something about negative mass, which is maybe the handwavium equivalent of anti-matter in science fiction? Well, anti-matter actually exists but its mass is positive. Also, the anti-particle of the (hypothetical) graviton is the graviton itself[0], so all in all nothing fancy happening there. > Gravity only attracts. It never pushes away. Cosmic expansion would like to have a word. (Though, admittedly, expansion doesn't happen in gravitationally bound systems, so from this point of view your statement is of course correct.) > The one guy said the biggest problem with gravity is we’ve never figured outs its opposite or if there even is an opposite. Interesting. Do you know whether he was an active researcher in the field of relativity? I can think of a lot of "big problems" in relativity but this wouldn't be one of them. I mean, don't get me wrong, it would be nice to have something to cancel out gravity since this would inspire lots of applications that we so far deem science fiction. But we already have a pretty good idea of the limits of what's possible[1]. [0]: https://physics.stackexchange.com/questions/273918/is-there-a-possibility-for-discovery-of-anti-graviton-i-e-the-graviton-antipar https://physics.stackexchange.com/questions/273918/is-there-... [1]: https://arxiv.org/abs/1611.01808 https://arxiv.org/abs/1611.01808 + the rigidity case of the https://en.wikipedia.org/wiki/Positive_energy_theorem https://en.wikipedia.org/wiki/Positive_energy_theorem suggest that one could theoretically "shield" / cancel out gravity to some degree but not everywhere (in all directions).