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Neptune hypothesis was successful, Vulcan wasn't [1] [1] https://en.wikipedia.org/wiki/Vulcan_(hypothetical_planet) https://en.wikipedia.org/wiki/Vulcan_(hypot

Neptune hypothesis was successful, Vulcan wasn't [1] [1] https://en.wikipedia.org/wiki/Vulcan_(hypothetical_planet) https://en.wikipedia.org/wiki/Vulcan_(hypothetical_planet) In both cases, the assumption about another planet was a reasonable thing to investigate. Dark matter is much worse, because we are not introducing single planet to explain another planet behaviour, but we are introducing new "stuff" that can be distributed in space largely arbitrarily and we have great amount of freedom to fit the observations. Add a little dark matter here, remove little dark matter there, now we can fit a bear.

Keysh 5y ago
In fact, assuming extra undetected mass to explain the anomalous motions of galaxies in clusters (as originally noted by Fritz Zwicky in the 1930s) was at least partly correct, because we now know that galaxy clusters contain rarified, extremely hot intergalactic gas (detectable only by its X-ray emission) in amounts equal to five or ten times the stellar mass of the galaxies. You still need even more mass in some as-yet-unidentified form (i.e., "dark matter") to fully explain cluster dynamics, but the basic hypothesis was at least partly successful. (The "undetected mass" hypothesis also turned out to be successful in the cases of binary stars, including things like Sirius B, where the companion turned out to be a bizarre type of star never before seen or theorized.) And, no, dark matter can't be distributed "arbitrarily": its distribution has to be consistent with gravity acting on an initially almost-uniform distribution with small cosmological perturbations (consistent with those seen in the cosmic microwave background).
- posix_me_less 5y ago
  > its distribution has to be consistent with gravity acting on an initially almost-uniform distribution with small cosmological perturbations That may be a restriction that some may operate with, but it is non-obvious why only models obeying this restriction are to be allowed. Some people do not care about cosmology and want to fit just rotation curves. And even if someone does care about cosmology, why would initial uniform distribution would be the only acceptable one?

Keysh 5y ago

In fact, assuming extra undetected mass to explain the anomalous motions of galaxies in clusters (as originally noted by Fritz Zwicky in the 1930s) was at least partly correct, because we now know that galaxy clusters contain rarified, extremely hot intergalactic gas (detectable only by its X-ray emission) in amounts equal to five or ten times the stellar mass of the galaxies. You still need even more mass in some as-yet-unidentified form (i.e., "dark matter") to fully explain cluster dynamics, but the basic hypothesis was at least partly successful. (The "undetected mass" hypothesis also turned out to be successful in the cases of binary stars, including things like Sirius B, where the companion turned out to be a bizarre type of star never before seen or theorized.) And, no, dark matter can't be distributed "arbitrarily": its distribution has to be consistent with gravity acting on an initially almost-uniform distribution with small cosmological perturbations (consistent with those seen in the cosmic microwave background).

posix_me_less 5y ago
> its distribution has to be consistent with gravity acting on an initially almost-uniform distribution with small cosmological perturbations That may be a restriction that some may operate with, but it is non-obvious why only models obeying this restriction are to be allowed. Some people do not care about cosmology and want to fit just rotation curves. And even if someone does care about cosmology, why would initial uniform distribution would be the only acceptable one?