Physics in the 20th Century
National Science Foundation
About the Lecture
It has become fashionable in some quarters to assert that "the end of physics" is in sight.
Indeed, a plausible argument can be made that the kinds of entities that physics is now poised to investigate are either so weird (axions, supersymmetric particles), so tenuous (quantum fluctuations, gravity waves, dark matter) or so small (superstrings) that it will be virtually impossible to continue research in this century at the pace or on the scale of the 1900s.
Fortunately, history provides ample reason for optimism. Scientists in the 20th century faced similarly pessimistic criticisms, and problems that seemed equally impossible. We will examine five apparently intractable cases from the past century, and how they were resolved. And then we'll take a look at five frontier research areas for the present century and the ways physicists hope to explore them.
About the Speaker
Curt Suplee is the Director of Legislative and Public Affairs for the National Science Foundation. Before coming to NSF, he spent 25 years at The Washington Post, serving as science editor and writer. He is the author of three books, including Physics in the 20th Century (1999) and has won numerous national prizes. These include the AAAS Science Writing Award, the American Chemical Society's Grady-Stack Award for Communicating Chemistry to the General Public, and the American Astronomical Society's Award for Popular Writing on Solar Physics. He has written for magazines as diverse as Harper's, Smithsonian and Vogue, and is a frequent contributor to National Geographic.
President McDiarmid called the 2135th meeting to order at 8:16 p.m. on October 26, 2001. The Recording Secretary read the minutes of the 2134th meeting and they were approved.
The speaker for the evening was Curt Suplee. The title of his presentation was “Physics in the 20th Century”.
The era of modern physics began 100 years ago when quantum and relativity theories were proposed. Physics advanced because powerful mathematical tools were available to make precise predictions that could be tested experimentally. While the costs of performing increasingly complex theoretical calculations fell, the costs and complexity of performing the necessary physical experiments increased more rapidly. This kind of physics now seems to have run its course. The sentiments expressed by some that “the end of physics” is in sight are very reminiscent of statements made at the end of the 19th Century. In his book The End of Physics, David Lindley argues, not that all the major discoveries have been made, but that it is the abstractness of mathematical constructs, seemingly unrelated to the real world, that is bringing on the death of experimental physics. This was expressed by Eugene Wigner in “The Unreasonable Effectiveness of Mathematics in the Natural Sciences” (Communications in Pure and Applied Mathematics, vol. 13, No. I, February 1960). Why does mathematics, a philosophical abstraction, seem to describe reality so well? It is argued that the entities physicists are seeking are either so weird (axions, supersymmetric particles), so tenuous (quantum fluctuations, gravity waves, dark matter) or so small (superstrings) that it may be impossible to continue research at the same pace or scale into the 21st century.
History, however, provides ample reason for optimism. Scientists in the last century faced similar pessimism and seemingly impossible research difficulties. Paul Dirac's prediction of antimatter in 1928 was confirmed with the discovery of the positron in 1932 by Carl Anderson. That led by the 1990's to Positron Emission Tomography (PET) for brain imaging. Similarly, Isidor Rabi discovered the magnetic resonance of atomic nuclei in 1938, and by the end of the century it was being used for Magnetic Resonance Imaging (MRI).
In the 1920's, it was noticed that b decay was unusual in that there was missing energy; the mass of the emitting particle was greater than the mass and kinetic energy of the observed emitted particles. To explain the deficit, Wolfgang Pauli in 1930 postulated that small neutral particles, which would be difficult to detect, were also emitted. In 1934, Enrico Fermi worked out a theory of a weak force to explain b decay with the small neutral particles that he named the neutrinos. They were finally detected in 1956 by Frederick Reines and Clyde Cowan. Now, we think there are three different, interconverting neutrinos. The Standard Model for 16 fundamental particles is the 20th century's “periodic table”.
u c t g
d s b g
ne nm nt Z
e m t W
The “top” quark was the last of the standard particles to be detected. The Higgs boson, predicted in a theory of how particles acquire mass, does not fit in this table and has not yet been detected.
Another difficult theoretical problem has been nonlinear behavior arising from deterministic equations. Richard Feynman said that turbulence was the most important unsolved problem in classical physics. Today, supercomputers are used to model plasma confinement and turbulence suppression for the control of fusion.
In astronomy, through the use of radio telescopes and other instruments it has been discovered that at least 80% of the universe is some sort of “dark matter” not accounted for in the Standard Model. This was conjectured from the observed spin dynamics of galaxies, and then from the observation of gravitational lensing. One leading candidate for the missing mass is the WIMP, Weakly Interacting Massive Particle. They are being looked for in a seasonal variation in the galactic wind. Faint variations in the cosmic microwave background radiation are being used to study the era of electromagnetic uncoupling approximately 300,000 years after the big bang. Recently, a new type 1A supernova was discovered with a standard luminosity that will enable us to extend the luminosity scale of distance measurements, just as Henrietta Leavitt in the early part of the last century used cepheid variables to calculate distances to galaxies.
Instead of abandoning a dying field, physicists are doing frontier research with new instruments and new materials. They are searching for gravity waves with 4 km Laser Interferometer Gravitational Wave Observatories in Hanford, WA, and Livingston, LA [see LIGO Website]. They are using large Cherenkov radiation detectors to investigate neutrino mutation and mass that would explain the solar neutrino deficit. They have made a long-predicted Bose-Einstein condensate and are beginning to investigate its weird behavior. Although superconductivity was discovered in 1911, new materials with higher transition temperatures continue to found almost every year.
These new explorations of physics bring to mind the story of Michael Faraday showing his laboratory to the Prime Minister who was impressed, but asked what the good of electricity was. Faraday is supposed to have replied, “I cannot say, but one day Her Majesty's government shall tax it.” [see Urban Legends Questionable Quotes]
Mr. Suplee kindly answered questions from the floor. President McDiarmid thanked Mr. Suplee for the society, and welcomed him to membership. The Recording Secretary announced that the minutes would be posted on the Philosophical Society web site after they are read. The President made the announcements about membership, the next meeting, parking, and refreshments, and adjourned the 2135th meeting to the social hour at 9:24 p.m.
Links: Find 'Curt Suplee' at amazon.com
John S. Garavelli