Yet, how do we know that dark matter is a particle? Despite multiple experiments designed to detect this particle, no co

[answerhappygod]

Yet, how do we know that dark matter is a particle? Despite
multiple experiments designed to detect this particle, no
convincing evidence of detection has been observed. Since dark
matter must interact only weakly, this is not too surprising—but,
we cannot claim to understand this phenomenon without having
clearly directly detected such a particle. We must keep an open
mind and consider many other potential solutions. For example,
several decades ago astronomers proposed that these gravitational
effects might be coming from neutrinos. As we’ve learned, these are
small particles that mostly pass straight through solid objects
like the Earth; they also do not form atoms, since they do not
interact by the strong nuclear force, and so they seem like a
promising candidate. Further, they have been directly observed,
and, although they do interact with light, they interact only
weakly. Unfortunately, neutrinos are too light and not numerous
enough to explain these observations. Astronomers have also
proposed that this missing mass might be black holes, as described
in the above-linked video.
Instead of hypothesizing missing matter, some astronomers
propose that these effects are instead due to a breakdown of
Newton’s laws. This is referred to as modified Newtonian dynamics
(MOND). MOND can explain galactic rotation curves quite well, but
has trouble fitting all of the other data. We know that Newton’s
laws work well on cosmological and Solar System scales, and this
places stringent limitations on MOND models; these models then end
up adding in some dark matter. Nonetheless, this is an active area
of research.
Please watch the linked video about the possibility that dark
matter consists of black holes. In a paragraph or two, briefly list
two questions you have about dark matter. We will discuss these
during the WP session this week.