Hypothesizing that a planet might be over there is a testable hypothesis.
Have we found a way to verify the presence of dark matter yet? Or is it still an untestable hypothesis sprinkled around distant galaxies so their acceleration curves look right?
That's not quite true. General relativity predicts gravitational lensing, not dark matter. Lensing has been used as an experimental probe for the presence of dark matter.
MOND is an alternative theory of gravity competing with GR. People usually forget that while MOND started to present a different explanation for Dark Matter, it is a theory of gravity. Dark Matter is not a theory of gravity and is compatible with GR.
Well of course. What I clearly meant was that DM predicts lensing effects in a magnitude that cannot be explained with ordinary matter. See bullet cluster or weak lensing observations.
I’m particularly amused by the hypothesis that spacetime can be bent without the presence of matter. We can’t detect dark matter because there’s no such thing, it’s just a brute topological fact.
