At left, a lensing magnification curve is shown for a standard, boring, oversimplified, smooth dark matter profile. At right, three different profiles are shown if one replaces that assumption with various realizations of wave-like dark matter. But is the data good enough to support one picture over the other? (Credit: A. Amruth et al., Nature Astronomy, 2023)

True or false: Does gravitational lensing reveal dark matter’s nature?

The best evidence for dark matter is astrophysical and indirect. Do new lensing observations point to ultra-light, wave-like dark matter?

When it comes to the question of “what is the Universe made of,” modern science has revealed the answers like never before. The material that makes up the planets, stars, gas, and dust in our Universe is all normal matter: stuff made of protons, neutrons, and electrons. Protons and neutrons are further composed of quarks and gluons, and electrons are one of six species of leptons in the Universe. Along with the force-carrying particles, the bosons, these elementary particles represent a total of about 5% of the total energy in the Universe.

But the other 95%, while we know how to categorize it — 27% dark matter and 68% dark energy — remains elusive as far as its true nature goes. While astrophysics has revealed many of their properties, with dark energy behaving as a species of energy uniformly inherent to space itself and dark matter behaving as though it was made of slow-moving, cold, collision-free massive particles, we still have yet to directly uncover their true nature.