You make it sound like physicists haven't tried looking for alternative explanations.
Faced with our many, varied observations there are two choices: either general relativity is wrong at larger scales, or there's some stuff out there that doesn't interact with light or much of anything else.
Maybe it's a combination of both, but to begin with it's usually a good idea assume the simpler alternative that it's just one of them.
Some physicists are looking at changing general relativity. MOND[1] is just a modification of Newton's law, so while it does reproduce the galaxy rotation curve observations it doesn't really explain anything in the same way GR does, and it's also non-relativistic which is pretty much a showstopper. There are efforts to make a relativistic MOND-like theory, such as TeVeS[2], but so far nothing has stood up. Some have considered that maybe quantum gravitational effects[3] reproduce the dark matter observations, but that approach also seem to have problems.
Your example implies a modification of GR. It appears to be very difficult to modify GR at large scales while conforming to all the observations which validate plain GR. So a good alternative guess is that there's something matter-like out there we can't see. Doing so, physicists have considered MACHOs[4], and they're currently searching for WIMPs[5], sterile neutrinos[6] and axions[7] to name a few candidate particles.
If some new theory comes along which supersedes GR, explains all the things plain GR can while also explaining the dark matter observations, then it would be welcomed and embraced by the physics community. Until then, physicists are looking in the direction they feel is the most promising one.
Faced with our many, varied observations there are two choices: either general relativity is wrong at larger scales, or there's some stuff out there that doesn't interact with light or much of anything else.
Maybe it's a combination of both, but to begin with it's usually a good idea assume the simpler alternative that it's just one of them.
Some physicists are looking at changing general relativity. MOND[1] is just a modification of Newton's law, so while it does reproduce the galaxy rotation curve observations it doesn't really explain anything in the same way GR does, and it's also non-relativistic which is pretty much a showstopper. There are efforts to make a relativistic MOND-like theory, such as TeVeS[2], but so far nothing has stood up. Some have considered that maybe quantum gravitational effects[3] reproduce the dark matter observations, but that approach also seem to have problems.
Your example implies a modification of GR. It appears to be very difficult to modify GR at large scales while conforming to all the observations which validate plain GR. So a good alternative guess is that there's something matter-like out there we can't see. Doing so, physicists have considered MACHOs[4], and they're currently searching for WIMPs[5], sterile neutrinos[6] and axions[7] to name a few candidate particles.
If some new theory comes along which supersedes GR, explains all the things plain GR can while also explaining the dark matter observations, then it would be welcomed and embraced by the physics community. Until then, physicists are looking in the direction they feel is the most promising one.
[1]: https://en.wikipedia.org/wiki/Modified_Newtonian_dynamics [2]: https://en.wikipedia.org/wiki/Tensor%E2%80%93vector%E2%80%93... [3]: https://en.wikipedia.org/wiki/Entropic_gravity [4]: https://en.wikipedia.org/wiki/Massive_compact_halo_object [5]: https://en.wikipedia.org/wiki/Weakly_interacting_massive_par... [6]: https://en.wikipedia.org/wiki/Sterile_neutrino [7]: https://en.wikipedia.org/wiki/Axion