We can’t find any trace of cosmic dark matter perhaps because our models of the early universe are missing a crucial piece, says astrophysicist Dan Hooper
13 November 2019
WE SEE its effects in how stars move within galaxies, and how galaxies move within galaxy clusters. Without it, we can’t explain how such large collections of matter came to exist, and certainly not how they hang together today. But what it is, we don’t know.
Welcome to one of the biggest mysteries in the universe: what makes up most of it. Our best measurements indicate that some 85 per cent of all matter in our universe consists of “dark matter” made of something that isn’t atoms. Huge underground experiments built to catch glimpses of dark matter particles as they pass through Earth have seen nothing. Particle-smashing experiments at the Large Hadron Collider, which we hoped would create dark matter, haven’t at least as far as we can tell. The hunt for dark matter was never supposed to be easy. But we didn’t expect it to be this hard.
Dark matter’s no-show means that many possible explanations for it that people like me favoured just a decade ago have now been ruled out. That is forcing us to radically revisit assumptions not only about the nature of dark matter, but also about the early history of our universe. This is the latest twist in a long-running saga: our failure to detect the particles that make up dark matter suggests that the beginning of the universe may have been very different from what we imagined.
Let’s start with what we do know about this substance or perhaps substances. Dark matter isn’t familiar atomic matter, or any of the exotic forms of matter created at the …