George Smoot talks to the Bulletin

Antimatter, dark matter, dark energy, the nature of space and time… The Nobel Laureate George Smoot answers Paola Catapano’s questions about his career and the many issues about the Universe that are still open.


You started your scientific career as a particle physicist, but soon you moved to astrophysics and in particular the Big Bang theory and cosmology. What motivated your interest in the Big Bang theory?

After I graduated from MIT, I went to Berkeley to work with particle physicist Luis Alvarez. He knew I was interested in many areas and said, “tell me what you would like to do and we’ll try and work on that”. I saw astrophysics as a new field, with a lot of new and exciting opportunities. I started doing experiments looking for antimatter, which eventually led to the idea of ASTROMAG and later to AMS. Studying antimatter, we found that it was in less than one part in 10,000. I thought: “There’s no antimatter around us and in the nearby stars, so I should think about looking at other science to pursue. We know the Big Bang happened, and we know it was very energetic and related to particle physics. It should tell us much more about fundamental physics.”

From AMS you moved on to build extremely complex telescopes and detectors, from balloon-borne to spy-plane-borne detectors, located in extreme places, from space to the South Pole. Can you summarise the steps and discoveries that led to your Nobel Prize?

It all began by trying to find the best approach to look at the relic radiation from the big bang. We started by putting a prototype detector on a mountain. When that worked, we wanted to get it much higher up, in either an airplane or a balloon. I had done a bunch of experiments with balloons and knew that equipment could easily get damaged in them, so I wanted to use an airplane. We found that the U-2 spy plane was perfect for our experiment, as it flew very high and evenly. The only problem was that it was designed to look down, so we had to convince NASA and Lockheed to build a hatch that looked up. Once we’d done that, we developed the technology for the flight-high-quality radio receivers, good antennas and techniques of switching and interchanging - most of which was refined from previous concepts. The next step was to make a cooled version of it to get more sensitivity, and then make a refined version of that to fly on the COBE satellite, and an even further refined version for the WMAP satellite.

So, there was a whole sequence of developments that made the measurements better and better. I don’t see it as just one achievement. Once we’d succeeded in taking measurements, we learnt how to improve them for new projects. That’s one of the things that Alvarez taught us. He’d say, “Don’t just repeat the measurements unless you know how to improve them in a way that leads to new science; otherwise, see if there’s something else you should be doing”.

Now we’re starting the development of the next generation of detectors. Nowadays, just a few detectors are not enough. We want to make, say, a thousand detectors. And not only do we have to make them, but we also have to make them work in a focal plane.

Let’s go back to COBE. Since the start of your scientific ventures, you’ve been looking for “anisotropies”, that is, you were trying to prove that the Universe is not homogeneous. Can you explain why this is important?

Actually, we were looking for three things with the COBE satellite. We had come to the conclusion, from measurements from our balloon and ground-based experiments, that the fluctuations in the Universe were very small - too small for galaxies to form if the Universe was only made of ordinary matter. Dark matter hadn’t really taken off as a concept then, so the question was how could galaxies possibly have formed? That depended on whether or not Cosmic Background Radiation really was relic radiation from the Big Bang, and if the Big Bang was as simple as we thought it was. So the first COBE experiment studied this radiation, using a far-infrared spectrum photometer, designed for precise measurements. We discovered that the spectrum had the right shape to conclude that this was the first radiation – it was a relic of the big bang. This was the first COBE discovery.

We then undertook a second experiment, looking for fluctuations in the Microwave Background Radiation that would lead to the formation of galaxies. After improving our measurements, we found that the fluctuations make up only one part in 100,000 - a very tiny amount. The Universe is as smooth as a billiard ball and incredibly uniform, but those small variations are enough if you have dark matter. Dark matter does not interact electromagnetically with light, so it does not get blown apart by light pressure from radiation that dominated the early Universe.

Understanding the origin of these fluctuations was the goal of the third experiment, accomplished using WMAP and PLANCK. The fluctuations meant that we had to have some other kind of phenomenon making the fluctuations. A piece of new physics that made it possible for the Universe to be both big and flat, while also allowing the fluctuations to form galaxies. With these experiments, we gained further insight into the fluctuations and their spectrum we can tell how much dark matter there is, how much ordinary matter there is, and other processes.

But how does it all fit together? What do our results mean to high-energy physics? What do they tell use about the fundamental nature of space and time? That’s what I’m looking at now. My career has been one very exciting trip and it just keeps on going.

This text was adapted by Katarina Anthony for the Bulletin and is based on a longer interview that Paola Catapano conducted with George Smoot for RAI TV.

by CERN Bulletin