5 ms·

What kind of detecting/trapping? We have to be specific. If we hypothesize a kind of matter that does not interact electromagnetically (only gravitationally), t

What kind of detecting/trapping? We have to be specific. If we hypothesize a kind of matter that does not interact electromagnetically (only gravitationally), then it's kind of nonsensical to say that only direct electromagnetic interactions with such matter will count to confirm its existence.

rpedela 7y ago
Well that is the crux isn't it? How do we directly detect gravitational particles?
- snowwrestler 7y ago
  Maybe we don't. The evidence for general relativity is all indirect--we can't directly detect space-time. But plenty of people seem to think it's a solid theory anyway.
  - deleted 7y ago
    [deleted]
  - simonh 7y ago
    There is a significant difference in that GR made numerous very testable claims about all sorts of phenomena, which would not be at all expected without GR to explain them. It also depends what is consider direct detection, which I accept is a matter of opinion. For example I'd consider comparing the times on atomic clocks inside and outside a gravity well to be direct measurement of time dilation.
simonh 7y ago
This is exactly why the hypothesis is weak. At the moment it postulates a particle that only ever manifests in such a way that it explains gravitational behaviour at a microscopic scale, in certain observations, and has no other detectable interactions or properties whatsoever. There’s no theory of how it forms, no theory of how it might be created or annihilated, no evidence for it in any particle physics experiments. We just have this one class of equations that produce unexpected results, so we put in an extra term and say were done. That’s just not good enough to say anything definitive about what it is. Physicists know that’s not good enough, and that it’s a major problem. I hope we do make progress, do come up with further experimental evidence or ideas for experiments we can test. For dark matter I think that’s actually likely, but I’m not so convinced about dark energy, there the evidence is a lot thinner.

rpedela 7y ago

Well that is the crux isn't it? How do we directly detect gravitational particles?

snowwrestler 7y ago
Maybe we don't. The evidence for general relativity is all indirect--we can't directly detect space-time. But plenty of people seem to think it's a solid theory anyway.
- deleted 7y ago
  [deleted]
- simonh 7y ago
  There is a significant difference in that GR made numerous very testable claims about all sorts of phenomena, which would not be at all expected without GR to explain them. It also depends what is consider direct detection, which I accept is a matter of opinion. For example I'd consider comparing the times on atomic clocks inside and outside a gravity well to be direct measurement of time dilation.

simonh 7y ago

This is exactly why the hypothesis is weak. At the moment it postulates a particle that only ever manifests in such a way that it explains gravitational behaviour at a microscopic scale, in certain observations, and has no other detectable interactions or properties whatsoever. There’s no theory of how it forms, no theory of how it might be created or annihilated, no evidence for it in any particle physics experiments. We just have this one class of equations that produce unexpected results, so we put in an extra term and say were done. That’s just not good enough to say anything definitive about what it is. Physicists know that’s not good enough, and that it’s a major problem. I hope we do make progress, do come up with further experimental evidence or ideas for experiments we can test. For dark matter I think that’s actually likely, but I’m not so convinced about dark energy, there the evidence is a lot thinner.