3 ms·

> A side effect of this is that the motions of objects would depend not just on their own mass, but all other masses in their neighborhood. As I understand gra

by ollysb 6y ago

> A side effect of this is that the motions of objects would depend not just on their own mass, but all other masses in their neighborhood. As I understand gravity warps spacetime which seems to imply that the masses of all objects in the neighbourhood would be taken into account because they all exert a warping effect on the same spacetime. Could somebody clarify what the difference is that they’re referring to? (or possibly the error in my understanding)

deleted 6y ago
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codethief 6y ago
MOND is a modification of Newtonian gravity and thus doesn't (yet?) take relativistic corrections into a account (see the last paragraph in [0]). So it's hard to predict what the fully relativistic picture is going to look like. I'm not a MOND theorist, though, so I might be wrong. (There are some relativistic generalizations[1] of MOND but it doesn't appear the MOND community has settled/agreed on one approach yet.) [0]: https://en.wikipedia.org/wiki/Modified_Newtonian_dynamics#Outstanding_problems_for_MOND https://en.wikipedia.org/wiki/Modified_Newtonian_dynamics#Ou... [1]: https://en.wikipedia.org/wiki/Modified_Newtonian_dynamics#Relativistic https://en.wikipedia.org/wiki/Modified_Newtonian_dynamics#Re...
- cygx 6y ago
  There's conformal gravity, which replaces the Einstein field equations with ones derived from a conformally invariant action. Like MOND, this allows you to fit rotation curves nicely without invoking dark matter, see eg [1][2]. [1] https://arxiv.org/abs/1211.0188 https://arxiv.org/abs/1211.0188 (2012) [2] https://arxiv.org/abs/1812.03152v3 https://arxiv.org/abs/1812.03152v3 (2018)
garmaine 6y ago
I think what it is saying is that the gravitational effect of a mass depends on the gravitational environment in which it exists. So a given sample of mass warps space more or less depending on whether it is near other masses or not. I’m not a MOND theorist though. That’s just my generous interpretation of that statement.

by ollysb 6y ago

deleted 6y ago

[deleted]

codethief 6y ago

MOND is a modification of Newtonian gravity and thus doesn't (yet?) take relativistic corrections into a account (see the last paragraph in [0]). So it's hard to predict what the fully relativistic picture is going to look like. I'm not a MOND theorist, though, so I might be wrong. (There are some relativistic generalizations[1] of MOND but it doesn't appear the MOND community has settled/agreed on one approach yet.) [0]: https://en.wikipedia.org/wiki/Modified_Newtonian_dynamics#Outstanding_problems_for_MOND https://en.wikipedia.org/wiki/Modified_Newtonian_dynamics#Ou... [1]: https://en.wikipedia.org/wiki/Modified_Newtonian_dynamics#Relativistic https://en.wikipedia.org/wiki/Modified_Newtonian_dynamics#Re...

cygx 6y ago
There's conformal gravity, which replaces the Einstein field equations with ones derived from a conformally invariant action. Like MOND, this allows you to fit rotation curves nicely without invoking dark matter, see eg [1][2]. [1] https://arxiv.org/abs/1211.0188 https://arxiv.org/abs/1211.0188 (2012) [2] https://arxiv.org/abs/1812.03152v3 https://arxiv.org/abs/1812.03152v3 (2018)

garmaine 6y ago

I think what it is saying is that the gravitational effect of a mass depends on the gravitational environment in which it exists. So a given sample of mass warps space more or less depending on whether it is near other masses or not. I’m not a MOND theorist though. That’s just my generous interpretation of that statement.