So, dark matter’s effects are real. We just don’t know what it is. Dark matter seems not to interact through the strong nuclear force, so it cannot make nuclei. It hasn’t been found to interact through the weak nuclear force, something even elusive neutrinos do. It doesn’t seem to interact with the electromagnetic force, so it doesn’t make molecules and concentrate into dense balls of dark matter. Nor does it absorb or emit or reflect or scatter light. As we’ve known from the beginning, dark matter does, indeed, exert gravity, to which ordinary matter responds. But that’s it. After all these years, we haven’t discovered it doing anything else.

So, dark matter’s effects are real. We just don’t know what it is. Dark matter
seems not to interact through the strong nuclear force, so it cannot make nuclei. It
hasn’t been found to interact through the weak nuclear force, something even
elusive neutrinos do. It doesn’t seem to interact with the electromagnetic force, so
it doesn’t make molecules and concentrate into dense balls of dark matter. Nor
does it absorb or emit or reflect or scatter light. As we’ve known from the
beginning, dark matter does, indeed, exert gravity, to which ordinary matter
responds. But that’s it. After all these years, we haven’t discovered it doing
anything else.