The Hidden Universe

man smiling in front of a stone building

As a physics doctoral candidate, Matt Carney ’14 is helping shed light on the dark energy of the cosmos


For astronomers working to unravel the secrets of the universe, the launch of the James Webb Space Telescope on December 25 came as last year’s ultimate Christmas present. Decades in the making, JWST is the most powerful observational tool ever sent into space. As it orbits the sun at a distance of nearly a million miles from earth, it will enable scientists to see objects far older and fainter than anything we’ve previously known. To put it all in perspective, we talked to Matt Carney ’14, a Ph.D. student in physics at Washington University in St. Louis who specializes in theoretical cosmology.

What is theoretical cosmology?

That’s the big question. Hopefully by the end of my Ph.D., I’ll know! Cosmology, roughly speaking, is the study of the origins of the universe. A big part of it is looking at what’s known as the expansion history of the universe. Our universe is expanding, and expansion means the universe is a dynamic entity. It’s evolving, which in turn affects the dynamics of galaxies and planets and stars and clusters of galaxies. I work on something called large-scale structure in the universe. And when I say large scale, I mean bigger than galaxies, bigger than clusters of galaxies, bigger than superclusters of galaxies. How do we get stuff in the universe?

What makes the James Webb  Space Telescope so exciting?

In cosmology there’s this principle that the farther you look out into the universe, the farther back in time you’re seeing. You’re looking at a snapshot of the far distant past, simply because light can’t reach you instantaneously. It takes time to travel. We measure this in terms of something called redshift. The wavelength of a photon gets redder the more it is stretched, and it gets bluer the more it is squeezed. So, you can actually tell if something is moving toward you or away from you based on if it’s shifted red or shifted blue. It looks blue coming toward you and red going away. The James Webb Space Telescope can see out to about redshift 10, which is insanely far. We will get to see potentially the birth of some of the first galaxies in the universe.

Are there particular issues in cosmology this radical new sensitivity can help resolve?

For me, the dream would be dark matter. The origin and nature of dark matter is, in my opinion, the most pressing unanswered question in physics. The constituents of the universe are somewhat shocking if you haven’t heard them before. About 67 percent of the universe’s content is in something called dark energy. Then another 25 percent is dark matter. And the little bit that remains is all the things that we think of as the universe, the stuff that makes up your desk, flesh and blood, puppies.

We know that dark energy exists primarily from a cosmological standpoint. For the expansion history of the universe to match up with what we observe, there needs to be a very large constant force that is causing the expansion. This is what we call dark energy. Similarly, there has to be matter that we’re not accounting for. You can tally up all the missing matter in the universe based on galaxy measurements and try to match it to the missing matter in expansion history, and you get fairly good agreement. We know dark matter exists and we know it is responsible for the vast majority of matter in the universe, but beyond that we have frighteningly little knowledge of it. Part of what’s hopeful with the James Webb is that the farther out you can get, the closer you can bridge the gap between early, early universe measurements and local ones.

What are the practical applications to life as we live it here on earth?

A fair question! I think there are two answers, and some people will find one more satisfying than the other. The most direct answer is that theoretical investigations have a way of leading to valuable technological breakthroughs that no one ever anticipated. Research in nuclear physics, for instance, is responsible for MRI machines. And we didn’t start out by saying, “let’s look for some way we can image things using magnetic resonance.” The other answer is more philosophical. To me, exploring the universe and our place within it is one of the most important things we can do. Thinking about things bigger than ourselves is entirely self-justifying.