Cosmic Mysteries

John Mather is a Nobel Prize–winning astrophysicist for his work on the Cosmic Background Explorer (COBE) satellite and an Honorary Member of Sigma Pi Sigma. He is a senior astrophysicist at the NASA Goddard Space Flight Center and was senior project scientist for the James Webb Space Telescope (JWST) from 1995 to 2023.

Who are the researchers you look up to and find inspiring?

I’m very impressed with the people who built the James Webb telescope. We have four instrument teams, and they are located around the world. I’m so thrilled that the work that they started so many years ago turned out so beautifully. And then, of course, the team that built the telescope itself. It focuses so beautifully. It’s a combination of engineering and science to do all of that.

Do you have any advice on maintaining a healthy work–life balance while working in physics?

Well, it depends. Everybody has different things that they want to do, but if you don’t maintain your body health and your emotional health, after a while you peter out. You have to give yourself whatever it takes to keep you going. A little athletics is probably good. You can’t just stare at the dang computer all day long. You need emotional support from your friends. You can tolerate total concentration for a while, but you can’t do it forever.

How has widespread access to computational technologies affected theoretical physics?

Computers are so much faster than they were, and we’re using them to develop some artificial intelligence approaches. You can simulate the formation of galaxies with basic equations of motion, but it’s awfully expensive to do that. Instead you can use artificial intelligence to detect patterns, and machine learning. That means you don’t have to consider every single detail of every object all the time. We’re learning to use new tools even beyond straightforward algorithms. That’s cool.

What questions do you hope JWST will answer?

What’s the first thing that grew out of the big bang material? Was it black holes?

Did the galaxies form top-down with big structures and then subdivide, or did small things form that were pulled together to form the big galaxies? We’re already getting some surprises, in the sense that galaxies group quicker than we thought.

How are stars born? That happens inside beautiful clouds of glowing gas and dust, and the process is pretty well hidden from visible light, so we can’t see inside.

How about the planets? Are there any solar systems like ours? The Webb telescope isn’t specifically aimed at that―we can’t see planetary systems―but if somebody sees one, we can try to pick it up.

How did black holes form? Every galaxy seems to have a big black hole in the middle. How did that happen? Is it because the halo was formed as the various pieces merged? Did we have lots of little galaxies, each with its own black hole, that merged together, or is there something else going on?

What are your thoughts on data that some say suggest that the galaxy is older than 13 billion years? Could it potentially disprove the big bang?

The evidence is certainly too weak to do that. We do have to understand why the stars don’t look the right age. The expanding universe has been known since 1929―it’s the details we have to work on.

Could there be some errors in how we’ve measured the age?

Yes. A star doesn’t have a clock on it, so you start with a model for how it works. Then you have to measure everything in your observations very well. If the model and observations don’t match, you have to say, In what ways could this be wrong? A long time ago we really did have a problem because we didn’t know about the acceleration of the universe. It looked like the universe was quite a lot younger than it really is.

So does the big bang need to be revised?

We have to understand something called Hubble tension. We have multiple ways of measuring the rate of expansion and hence the age of the universe, and they’re not giving us the same answer at the level of several percent. That’s enough to be important these days. When we launched the Hubble telescope, there were two camps of thought and they were off by a factor of 2. It’s a much smaller percentage that we’re arguing about now. There’s something we’re missing about the cosmic dark energy.

A guest lecturer told us that celestial bodies are rapidly accelerating away from each other according to their redshift. How does this affect cosmology?

Let’s talk about the cosmic redshift. Edwin Hubble drew a chart of the redshift of galaxies versus their distance from us. Cosmic acceleration was discovered because the curves didn’t behave right. We’re still worrying about the right shape of the curve. In particular, is there just one term in the cosmic acceleration? Is it explained by Einstein’s constant? So far his constant fits really well, but is there anything else going on? Who says that’s the whole story?

This interview has been edited for length and clarity.