What is the difference between dark matter and dark energy?
Dark matter behaves much like a collection of ordinary matter made of particles, except that it’s dark. In particular, dense regions of dark matter tend to become even more dense, as the mutual gravitational force of the matter pulls it together. For this reason, we suspect that the dark matter is some sort of new, massive particle, just one we haven’t yet discovered in the laboratory (yet). Dark energy, on the other hand, doesn’t act anything like particles: it doesn’t cluster together, nor does it dilute as the universe expands. Its density remains constant (so far as we can tell) throughout space and time. So whatever the dark energy is, it’s something different than dark matter.
