The 2,105th Meeting of the Society

April 23, 1999

The Problem of Mass

Jonathan A. Bagger

Johns Hopkins University

About the Lecture

Particle physicists have probed deeper and deeper into the heart of matter. During the past fifty years, they have moved from atoms and nuclei to protons and neutrons to quarks and leptons. In the process, they have discovered what are believed to be the fundamental building blocks of the Universe. At the close of the twentieth century, physicists have a quantitative understanding of the structure of matter to about 10-16 cm. This is a remarkable achievement, likely to be regarded among the most important advances of the past hundred years. This success does not represent an end, but rather a new beginning. It points the way to an even deeper understanding of our Universe, to the origin of mass itself. Indeed, the present theory breaks down when particles are collided at energies ten times higher than can be reached today. These energies will be achieved at CERN's Large Hadron Collider, scheduled to begin operation in 2005. This simple fact means that the CERN LHC is certain to discover new physics, beyond anything known today. What it will be, we do not know. All we know for sure is that we are on the verge of uncovering the microphysical origin of mass.

About the Speaker

Jonathan Bagger is Professor of Physics and Mathematics at the Johns Hopkins University. He received his doctorate in 1983 from Princeton. Since then he has held appointments at Stanford, Harvard, and the Institute for Advanced Study. He has served as a consultant on particle physics to the National Science Foundation and the Department of Energy. He is presently a member of the Fermilab Board of Overseers, as well as an editor of the Physical Review, Physics Reports and the Journal of High Energy Physics. Bagger's research interests lie in the area of particle physics at the interface between theory and experiment. He has authored four books and approximately 100 articles, including the monograph Supersymmetry and Supergravity.

Minutes

President Garavelli called the 2105th meeting to order at 8:15 p.m. on April 23, 1999. The Recording Secretary read the minutes of the 2104th meeting and they were approved.

The speaker for the 2105th meeting was Jonathan A. Bagger of the John Hopkins University. The title of his presentation was, “The Problem of Mass.”

Of late, particle physicists have probed ever deeper into the heart of matter. During the past fifty years, they have moved from atoms and nuclei, down to protons and neutrons, and then on down to quarks and leptons. In the process, these particle physicists discovered what are believed to be the fundamental building blocks of the Universe. Now, at the close of the twentieth century, particle physicists have a quantitative understanding of the structure of matter down to 10-16 cm. To provide us with a visual sense of this measure, 10-16 cm is the same distance looking in as it is to looking out to the nearest star. This is a remarkable achievement and is likely to be regarded among the most important advances of the past hundred years. However, this success does not represent an end, but rather a beginning. It points the way to an even deeper understanding of our Universe and to the very origin of mass itself.

We have seen the Standard Model of Matter as an effective theory at present day energy levels. However, problems in the theory have appeared on the horizon.

According to the speaker, the Heisenburg principle says we can never know exactly where anything is. It also says we can violate the rules of motion over short periods of time and over small distances. In other words, the laws of the conservation of energy and momentum can be violated over short times and distances. The time span we're talking about is less than 10-26 sec and the distances are less than 10-16 cm. Thus, we can enter a domain where the standard rules of science don't work. Consequently, new physics will surely happen and the associated new rules will have to be discovered.

It turns out that the present theory breaks down when particles are conceptually collided at energies only ten times higher than can be reached today. Further, results of current experiments are beginning to push into the region where new models and theories of matter such as supersymmetry, must come into play.

The needed energies for this new frontier are only slightly beyond our present day capabilities and will surely be achieved at CERN's Large Hadron Collider, scheduled to begin operation in 2005. This means that the CERN collider is certain to discover new physics. What this new physics will be, we do not know. However, we do know we are on the verge of uncovering a deeper understanding of the microphysical origin of mass.


Mr. Bagger then closed his presentation and kindly answered questions from the floor. President Garavelli thereupon thanked Mr. Bagger for the society, announced the next meeting and made the usual parking announcement. He then adjourned the 2105th meeting to the Social Hour at 9:35 p.m.

Attendance: 42
Temperature: 13.1°C
Weather: clear

Respectfully submitted,

Bill Spargo
Recording Secretary