Samuel Ting shared the 1976 Nobel Prize in physics for the discovery of the J/psi meson, which consists of a charm quark and a charm antiquark.
More recently, he has led international collaborations in experimental physics onboard the Space Shuttle Discovery and the International Space Station, as well as at accelerators in the United States, Germany and Switzerland.
Ting is the Thomas Dudley Cabot Professor of Physics at the Massachusetts Institute of Technology. He attended the University of Michigan, earning a B.S.E. in mathematics and physics in 1959 and a doctorate in physics in 1962.
He delivered the Eugene P. Wigner Distinguished Lecture on June 17, 2021, sharing an update on the Alpha Magnetic Spectrometer Experiment, which is being conducted on the ISS.
1. What is the Alpha Magnetic Spectrometer, and what do we hope to discover from it?
The Alpha Magnetic Spectrometer is a physics spectrometer used in large accelerators, like in Fermilab or CERN, but this time using space. It measures the momentum, the energy and other properties of cosmic particles and nuclei.
In the past 100 years or so, we have studied cosmic rays, but those studies were done with balloons and small satellites. This is the first time a precision detector normally used in accelerators was put into space to understand the properties of all the cosmic rays.
It’s like if you look at an object with your eye or with the telescope, you'll see very different things. We have been in space for 10 years, collected about 180 billion cosmic rays, up to energies of trillions and trillions of electron volts. And so far, we have many, many results on the properties of the cosmic ray elements as well as electrons and their antiparticles — positrons — and protons and their antiparticle — antiprotons. And so, they have a distribution. The rate changes with energy. Because of the precision we have been able to collect the data, and the results have completely changed our understanding of the cosmos.
2. Why are you looking for antimatter specifically?
If you believe the universe came from a big bang, then you ask, at the very beginning, the universe is a vacuum. Right after the Big Bang, there must be equal amounts of matter and antimatter. Otherwise, it would not come from a vacuum. So, we now have cosmic rays. We have Oak Ridge lab, we have MIT, and we have you and me. Where is the other half? We know the other half — antimatter — exists in accelerators, because in accelerators you have neutrons, antineutrons, protons, antiprotons from large accelerator, nuclei and its antinuclei. That is not a question. The question is if indeed all these things came from a big bang, there must be heavy antimatter in space. In the past, people have not been able to look for antimatter, because antimatter has the opposite charge as matter. So, you need a magnet. If it’s positive, the magnet makes it bend one way. If it’s negative, it bends the opposite way. Putting a magnet in space is difficult, because just like a magnetic compass, it will always point to the north. We managed to solve this problem; the Alpha Magnetic Spectrometer magnet is permanent and very large — about 1 meter in diameter, 1 meter in length. It doesn't rotate in space. Actually, it’s a very simple trick, but people didn't find it until 40 years later.
3. What has the AMS revealed in its first decade?
It has revealed the flux — the rate — of electrons from very low energy to trillions of electron volts is different from positrons, and protons are different from antiprotons.
Also, all the cosmic ray nuclei in the periodic table have a behavior that is totally unexpected. Cosmic rays have two classes: primary cosmic rays and secondary cosmic rays. Primary cosmic rays like helium, carbon and oxygen come directly from nuclear fusion and are then accelerated by supernovas. The rigidity dependence of primary cosmic rays — rigidity means momentum divided by charge — is exactly the same. Secondary cosmic rays are primary cosmic rays hitting the interstellar medium, like lithium, beryllium and boron. Unexpectedly, their rigidity dependence is also exactly the same, but different from primary cosmic rays.
None of our results are predicted by any theory. You can adjust the parameters of the theory to fit one of the measurements, but the same parameter cannot fit the other measurements. We’re back to square one.
4. Why was it important for you to talk with the people at Oak Ridge National Laboratory?
When I graduated from the University of Michigan, the first thing I got was a notice from the draft board. Then I went to get a physical and classified as A-1, ready to be drafted.
That was 1959. At the same time, I saw at the University of Michigan Physics Department, there was an announcement from Oak Ridge on behalf of the Atomic Energy Commission. There was a national competition to select some students in a competitive way who were good at math and physics and biology. That’s because, in those days, they were competing with the Soviets, who had just launched Sputnik. They wanted to catch up and encourage people to enter the competition.
So, I went to the competition and was selected. Once you’re selected, you could go to any graduate school, and the Atomic Energy Commission, via Oak Ridge, would pay your tuition and $2,000 a year for support. Mind you, in 1959 that was more than enough to go to graduate school.
So, I wrote to Oak Ridge and said I wouldn’t be able to accept this AEC fellowship because I’d been drafted. I think someone in Oak Ridge got in touch with someone in Washington and said they should not draft me.
That’s why I didn’t go to Vietnam.
After I got my degree, the first offer I had was from Livermore. And I remember it was $30,000 a year — at that time a very high salary. But it had one condition: I could not publish my work. Then I got a second offer, from Columbia University as an instructor. It was $7,500 a year. That’s how I went to Columbia and later MIT.
