The vast majority of the matter in the Universe appears to be entirely invisible to us. This mysterious substance, dubbed dark matter, has mass and a gravitational pull, but doesn’t seem to interact in any significant way via any of the other forces. We don’t yet know what dark matter is made of, but there’s a lot of very good evidence that it is real and is out there (and possibly passing through us right now!).
I study a lot of different aspects of dark matter, including finding new ways to rule out or confirm various ideas about what it might be. In some of my most recent work, I study models of dark matter in which it has some very rare interactions with itself or with other kinds of matter, and could even annihilate with itself when enough is collected together. These interactions could have had an impact on the growth of the first stars and galaxies in the Universe.
You can read more about dark matter here.
With the discovery of the Higgs boson, particle physicists found out something disconcerting about our Universe: it might not be entirely stable. The basic idea is that the mathematical structure that determines the laws of physics — what we call the “vacuum state” — might not be the one that the Universe, in some sense, “prefers.” If this is true, then there’s a chance that someday our Universe will suddenly transition to the preferred state, destroying everything in the Universe. The chances of this happening any time soon are astronomically low, but it’s a dramatic enough possibility that physicists are taking it seriously and trying to understand if it’s actually possible, or if it is, instead, giving us a hint about some new physics that could change the picture entirely.
Cosmic Dawn and reionization
In the beginning, there was the Hot Big Bang. This is a term cosmologists use to talk about the time when the cosmos was hotter, denser, and in some sense, smaller than it is today. We see evidence of this hot dense state by looking at the cosmic microwave background — the afterglow of the Big Bang. But once the primordial plasma cooled, the Universe was mostly rapidly diffusing neutral hydrogen, with the denser pockets slowly being pulled together by dark matter to form the first stars and galaxies. During these “cosmic dark ages,” before the stars, the cosmos was dark and opaque to visible light. The era when stars first ignited is known as the “cosmic dawn,” and when there were enough of them burning to cut through the haze of the neutral gas and ionize everything, the Universe underwent a process called “reionization.”
Understanding reionization would give us insights into the very first structures in the Universe, and could even help us answer some of the most challenging questions about dark matter and the evolution of the cosmos.
To read more about reionization and why it matters, see my blog post here.