5 ms·

If gravity is simply the curving of space caused by matter, why must there be 'dark matter'? Why cant there be something else that bends space? Or who says spac

by bawana 6y ago

If gravity is simply the curving of space caused by matter, why must there be 'dark matter'? Why cant there be something else that bends space? Or who says space is homogeneous and flat-why cant there be 'bubbles' of positively and 'negatively' curved space? If the universe is expanding, why would it expand homogeneously in all directions? After all, isn't the cosmic microwave background anisotropic?

caymanjim 6y ago
> Why cant there be something else that bends space? That's literally what dark matter is. It's something else that bends space. It's called "dark" because no one knows what it is.
- magicalhippo 6y ago
  > It's called "dark" because no one knows what it is. It's called "dark" because we can't see it, except for the gravitational effects it has on visible matter. Neutrinos hardly interact at all with normal matter, as such it is a form of dark matter called hot dark matter[1]. However based on measurements we've ruled out[2] neutrinos as the main source of dark matter, hence we're looking for something else. Since the only clue we have so far is the gravitational effect, it is possible that the solution is to modify the theory of gravity instead of finding new particles. People are looking into this as well. And heck, maybe it's both. Time will tell! [1]: https://en.wikipedia.org/wiki/Hot_dark_matter https://en.wikipedia.org/wiki/Hot_dark_matter [2]: http://w.astro.berkeley.edu/~mwhite/darkmatter/hdm.html http://w.astro.berkeley.edu/~mwhite/darkmatter/hdm.html
  - mikhailfranco 6y ago
    Only conventional left-handed neutrinos are ruled out as significant HDM. It is rarely mentioned amongst all the Higgs back-slapping, that the Standard Model does not yet have a complete and verified theory of neutrino physics: masses? Majorana/Dirac? self-anti-particle? chiralities? ... There may be right-handed neutrinos that do not interact via the weak force (which is maximally parity-violating). They would only interact gravitationally and play a role dark matter: https://en.wikipedia.org/wiki/Sterile_neutrino https://en.wikipedia.org/wiki/Sterile_neutrino
laretluval 6y ago
“Dark matter” just means it’s something that behaves like matter wrt gravity.
andrewflnr 6y ago
I mean, it's conceivable that there could be some unknown thing that curves space in oddly specific ways that look just like matter, and also kind of moves in bulk like matter, but that would be drastically crazier than even dark matter is, so no one should expect it to be more likely.

by bawana 6y ago

caymanjim 6y ago

> Why cant there be something else that bends space? That's literally what dark matter is. It's something else that bends space. It's called "dark" because no one knows what it is.

magicalhippo 6y ago
> It's called "dark" because no one knows what it is. It's called "dark" because we can't see it, except for the gravitational effects it has on visible matter. Neutrinos hardly interact at all with normal matter, as such it is a form of dark matter called hot dark matter[1]. However based on measurements we've ruled out[2] neutrinos as the main source of dark matter, hence we're looking for something else. Since the only clue we have so far is the gravitational effect, it is possible that the solution is to modify the theory of gravity instead of finding new particles. People are looking into this as well. And heck, maybe it's both. Time will tell! [1]: https://en.wikipedia.org/wiki/Hot_dark_matter https://en.wikipedia.org/wiki/Hot_dark_matter [2]: http://w.astro.berkeley.edu/~mwhite/darkmatter/hdm.html http://w.astro.berkeley.edu/~mwhite/darkmatter/hdm.html
- mikhailfranco 6y ago
  Only conventional left-handed neutrinos are ruled out as significant HDM. It is rarely mentioned amongst all the Higgs back-slapping, that the Standard Model does not yet have a complete and verified theory of neutrino physics: masses? Majorana/Dirac? self-anti-particle? chiralities? ... There may be right-handed neutrinos that do not interact via the weak force (which is maximally parity-violating). They would only interact gravitationally and play a role dark matter: https://en.wikipedia.org/wiki/Sterile_neutrino https://en.wikipedia.org/wiki/Sterile_neutrino

laretluval 6y ago

“Dark matter” just means it’s something that behaves like matter wrt gravity.

andrewflnr 6y ago

I mean, it's conceivable that there could be some unknown thing that curves space in oddly specific ways that look just like matter, and also kind of moves in bulk like matter, but that would be drastically crazier than even dark matter is, so no one should expect it to be more likely.