The formation of cosmic structure, on both large scales and small scales, is highly dependent on how dark matter and normal matter interact. Despite the indirect evidence for dark matter, we’d love to be able to detect it directly, which is something that can only happen if there’s a non-zero cross-section between normal matter and dark matter. The structures that arise, however, including galaxy clusters and larger-scale filaments, are undisputed. (ILLUSTRIS COLLABORATION / ILLUSTRIS SIMULATION)

No Amount Of ‘Normal Matter’ Can Eliminate The Need For Dark Matter

Whatever’s lurking out there, it isn’t all, or even mostly, normal matter.

When it comes to the Universe, it’s only natural to wonder what, exactly, it is that makes everything up. While some of it is matter like us — things assembled out of atoms, which in turn themselves are made of subatomic particles like protons, neutrons, and electrons — there’s overwhelming evidence that the majority of material that’s out there is fundamentally different from what it is that we’re made out of. In fact, when we sum up every type of known fundamental quantum, everything that’s made out of particles of the Standard Model, we come up tremendously short.

Not only is the Universe not made out of the same stuff we are, but it’s not made out of anything that we’ve ever directly detected. In fact, to an incredible degree of both precision and certainty, we know precisely how much of the Universe, in terms of total energy, is made up of everything whose properties are definitively known: just 5%. The rest of the Universe must be some form of energy that has, thus far, evaded direct detection, with 68% being dark energy and 27% dark matter.

On the surface, it seems reasonable to wonder whether what we’re calling dark matter might not be real, but…