Dark matter: should we be so sure it exists? Here's how philosophy can help

Newtonian laws may work slightly differently when there’s extremely small acceleration involved, such as at the edge of galaxies. This tweak was perfectly compatible with the observed galactic rotation. Nevertheless, physicists today overwhelmingly favour the dark matter hypothesis incorporated in the so-called ΛCDM model (Lambda Cold Dark Matter).

 If the two competing theories of dark matter and modified gravity can equally explain galactic rotation and other anomalies, one might wonder whether we have good reasons to prefer one over another.

Philosophy cannot ultimately tell us whether astronomers are right or wrong about the existence of dark matter. But it can tell us whether astronomers do indeed have good reasons to believe in it, what these reasons are, and what it would take for modified gravity to become as popular as dark matter.

We still don’t know the exact answers to these questions, but we are working on them. More research in philosophy of science will give us a better verdict.