2 ms·

> but what the heck else are you expecting to pop up to explain redshift For example, some kind of phenomenon that happens to photons but only when they travel

> but what the heck else are you expecting to pop up to explain redshift For example, some kind of phenomenon that happens to photons but only when they travel great distances. Or that maybe the space(-time) is not uniform and we're in an area that has properties slightly different from the surrounding space. What happens if JWST sees galaxies that, according to their redshift, were formed before the supposed moment of the big bang?

ben_w 4y ago
> some kind of phenomenon that happens to photons but only when they travel great distances. Or that maybe the space(-time) is not uniform I think people have explored the photons thing with regard to “solving” dark matter, and found the evidence lacking. As for spacetime… trivially yes, but I don’t think this is what you meant? I mean, spacetime being non-uniformly curved just means there’s stuff in it, and that is literally one of the things we can directly observe, and we see that in e.g. the Bullet Cluster the dark matter kept moving when the visible matter collided and slowed down. > What happens if JWST sees galaxies that, according to their redshift, were formed before the supposed moment of the big bang? If, after careful work to exclude all other possibilities, then a party and a Nobel prize.
andrewflnr 4y ago
> some kind of phenomenon that happens to photons but only when they travel great distances Tried, found wanting. Repeatedly. https://en.wikipedia.org/wiki/Tired_light https://en.wikipedia.org/wiki/Tired_light Anisotropy of space is (a) again adding complications and (b) unlikely to produce such a spherically symmetric redshift. The CMB is infamous for how smooth it is. The different region of space would have to be perfectly spherical with us in the dead center. May as well revive geocentrism. Look, if we did find evidence like that from JWST or whatever, we'd re-evaluate what best meets Occam's razor for the totality of the evidence. But that doesn't change the fact that with our current evidence, that explanation is expansion of space. Other stuff is sci-fi at best. Fun to think about, but no reason to actually believe it. The story for dark matter is more complicated, but similar in broad outline. The more the alternative theories try to fit all the evidence, the closer they get to reinventing dark matter. You have something that walks like matter and quacks like matter, so the smart money says it's matter.

ben_w 4y ago

> some kind of phenomenon that happens to photons but only when they travel great distances. Or that maybe the space(-time) is not uniform I think people have explored the photons thing with regard to “solving” dark matter, and found the evidence lacking. As for spacetime… trivially yes, but I don’t think this is what you meant? I mean, spacetime being non-uniformly curved just means there’s stuff in it, and that is literally one of the things we can directly observe, and we see that in e.g. the Bullet Cluster the dark matter kept moving when the visible matter collided and slowed down. > What happens if JWST sees galaxies that, according to their redshift, were formed before the supposed moment of the big bang? If, after careful work to exclude all other possibilities, then a party and a Nobel prize.

andrewflnr 4y ago

> some kind of phenomenon that happens to photons but only when they travel great distances Tried, found wanting. Repeatedly. https://en.wikipedia.org/wiki/Tired_light https://en.wikipedia.org/wiki/Tired_light Anisotropy of space is (a) again adding complications and (b) unlikely to produce such a spherically symmetric redshift. The CMB is infamous for how smooth it is. The different region of space would have to be perfectly spherical with us in the dead center. May as well revive geocentrism. Look, if we did find evidence like that from JWST or whatever, we'd re-evaluate what best meets Occam's razor for the totality of the evidence. But that doesn't change the fact that with our current evidence, that explanation is expansion of space. Other stuff is sci-fi at best. Fun to think about, but no reason to actually believe it. The story for dark matter is more complicated, but similar in broad outline. The more the alternative theories try to fit all the evidence, the closer they get to reinventing dark matter. You have something that walks like matter and quacks like matter, so the smart money says it's matter.