The First 35 Years of the Aspen Center for Physics

by Jeremy Bernstein



Chapter VI Ad Astra

Physics is Not Static

I want to use cosmology as an example of how rapidly a scientific field can change and how agile a place like the Center has to be to keep up. There are many other examples in other fields of physics but cosmology is of general interest and the issues can be explained even to people without a professional background.

I would like to begin with a story that the Columbia University astronomer Ed Spiegel told me one summer at the Center. You will have to bear with me because this story needs a little scientific background. Until the events of 1964, which I will shortly describe, cosmology, the study of the origin and destiny of the universe, was as much science fiction as science. There were, broadly speaking, two opposing theories. One was the invention of Hermann Bondi, Thomas Gold and Fred Hoyle. This was known as the “steady state” theory and favored the “perfect cosmological principle” according to which in the large, nothing much happened in the universe. There was no beginning and no end. To preserve this steady state, despite the fact that the universe was expanding, small amounts of matter were continuously being created out of nothing. A completely opposite theory was being promoted by George Gamow, a wonderful, outsized, extremely imaginative Russian–born physicist.

Gamow favored a cosmology in which the universe began with a cosmic explosion. As a joke Hoyle referred to this derisively as the “big bang.” The name stuck and the joke was on Hoyle. Gamow had a gifted student named Ralph Alpher. He and Gamow set about to see how you could build up the known elements from the neutrons and protons and the other particles that were created in the bang. This became Alpher's thesis and he and Gamow wanted to publish a paper. But to Gamow's fertile imagination, the situation was too good. If only he could bring Bethe on as a collaborator then the authors would read, Alpher, Bethe and Gamow. Bethe was contacted and agreed after he had checked the paper and offered some suggestions. Alpher was not too thrilled since he was just starting his scientific career and did not need another co–author. The αβγ paper entitled “The Origin of Chemical Elements” was published in the Physical Review in 1948. They could not explain the origin of the heavy elements, which gave Hoyle more ammunition. Now you have enough information to understand Spiegel's story.

There was an astronomy conference at which Gamow was a speaker and Spiegel was in attendance. He and some other “young Turk” astronomers spotted Gamow in the hotel bar having his habitual afternoon quaff. They bribed a cocktail waitress to go over to him and say, “There is a telephone call for you Professor Hoyle.” Without skipping a beat Gamow replied, “Don't throw Hoyle on troubled waters.”

The events that began in 1964 are a perfect counter example to Pasteur's dictum that in the process of scientific discovery, chance favors the prepared mind. In this instance chance favored the totally unprepared minds of Arno Penzias and Robert Wilson, two physicists who had come to Bell Labs, then part of AT&T, to work on a newly built horn reflector radio telescope that had been installed in Crawford Hills, New Jersey. The telephone company was interested because satellite communication was just emerging. Penzias, who had come to Bell Labs a year before Wilson, had earned his degree at Columbia where he had constructed a maser – a device that amplified microwave signals – to be used for detecting signals from hydrogen in galaxies. Penzias asked the head of the Crawford Hill Laboratory, Rudolf Kompfner, if he could have a temporary job to use a recently constructed Bell Labs maser with the radio telescope to redo his thesis which he did not think was very good. Kompfner told him he should take a permanent job, or at least as permanent a job as Bell Labs offered. Wilson took his degree from Caltech and did a thesis that involved radio astronomy. Along the way he had taken a course with Hoyle and had decided that the steady state cosmology might well be right. During a postdoctoral year at Caltech, a Bell Labs recruiter told him about the possibilities of doing radio astronomy at Crawford Hill and in the spring of 1963 he joined Penzias.

When they hooked things up so that they could detect radiation something was terribly wrong. There was noise – static – and it simply would not go away. They tried everything including the removal of a pair of nesting pigeons and seeing if nearby New York City might be the source. It wasn't and the noise persisted night and day for about a year with no explanation. What finally broke the impasse was explained to me by the MIT radio astronomer Bernard Burke on one of his visits to the Center. Another radio astronomer named Ken Turner had heard a talk at Johns Hopkins given by a young Princeton theoretical astrophysicist named P.J.E. Peebles who discussed what remnants from the Big Bang might look like. Over the thirteen–odd billions of years since the explosion, the universe has been expanding and the radiation cooling. Now the radiation should be in the microwave regime, the wave lengths at which radars operate. This is something that Gamow also understood but he never actually suggested an experiment. I think also that his flamboyant character and the nature of the subject prevented people from taking him entirely seriously. In any event, Turner told Burke about the possibility of the cosmic radiation and Burke told Penzias whom he knew.

At Princeton a very imaginative physicist named Robert Dicke had been thinking about cosmology. He favored an “oscillating” universe which had cycles of expansion which had been preceded by a cosmic explosion followed by a cycle in which the universe would collapse, followed by another explosion. We were now in an expanding phase so he reasoned there should be remnants in the form of microwave radiation, which should be observable. Dicke had forgotten that in 1946 he had done such an experiment but had not been able to detect anything. Dicke gave Peebles the task of estimating the temperature that such radiation would have now. The reason that it has a temperature is that this radiation is what is known as “black body” or “cavity” radiation, terms that date from the 19th century.

If you take a container the interior forms a cavity. Now you heat the walls of the container. This excites the electrons of the atoms out of which the walls are made and they radiate. This radiation bounces around in the container and an equilibrium situation is produced. At this equilibrium the radiation assumes a spectral form – distribution of the relative intensity of the radiation at different wavelengths – that does not depend on any properties of the container such as its shape. The only thing the form of the spectrum depends on is the temperature. But the universe is a container and if at some point an equilibrium had been achieved between photons and electrons this would have produced a black–body spectrum for the photons. Peebles estimated that the temperature should be about 10 degrees above absolute zero, whereas the present experiments show it to be 2.725 degrees.

Dicke had two young associates, P.G. Roll and D.T. Wilkinson. He suggested that they build a small, low–noise, radio antenna on top of Palmer Laboratory at Princeton, which incidentally, was some forty miles from Crawford Hill. This antenna was to be used to measure the cosmic background radiation, which Dicke was sure would be present. Before they could get up and running Dicke received a call from Penzias. The Princeton physicists then made a trip to Crawford Hill. Penzias and Wilson told them about their observations and they told Penzias and Wilson about the cosmological interpretation. Neither of them was entirely persuaded. As Wilson once told me, “Although we were pleased to have some sort of answer, both of us at first felt a little distant from the cosmology. I had taken my cosmology from Hoyle at Caltech, and I very much liked the steady–state universe. Philosophically. I still sort of like it. I think that Arno and I both felt that it was nice to have one explanation, but that there may well have been others.”

In addition to philosophical reservations there was a good physics reason to be cautious. What the theory predicts is a black–body curve with a plot that covers all wavelengths. But what Penzias and Wilson had observed was the effect at one–wave length. From that, one could not conclude anything about a curve. Hence they could not be sure that there was a black–body curve. Penzias and Wilson wrote an understated article in which the cosmology was barely mentioned and the Princeton people wrote an accompanying article, which discussed the cosmological interpretation. Nowhere was the work of Gamow and his collaborators, Ralph Alpher and Robert Herman, mentioned. (Spiegel informs me that Gamow tried unsuccessfully to persuade Herman to change his name to “Delta.”) The physicists in the Bell Labs and Princeton groups had never read the work of Gamow and his collaborators. Sadly Gamow died in 1968 so he did not live long enough to see the full effect of the revolution in cosmology. The Princeton and Bell Labs groups measured the radiation in different wavelengths and within a few years the entire black–body curve had been filled in. Even Wilson conceded that the steady–state theory was dead.

The effect of this discovery was profound. Cosmology became a branch of science and this was reflected in the composition of university departments and in the Center. Cosmology was a “hot” subject and people like Peebles began organizing working groups of cosmologists from all over the world at the Center. This was a somewhat different modus operandi than Stranahan's original vision. When Stranahan founded the Center his vision was that it should in no way imitate university physics departments. There would be no specialties and there would be no students. Professors were not even allowed to bring with them their PhD candidates. There would be few if any seminars. Recall that in the original plans for the first building there was not even a room to hold a seminar. There would be no “faculty” meetings. People would stay in their offices and work. The Center would be run by a few employees including, over the course of things, a part–time librarian.

People Are Not Static

The Center developed a very fine library of technical books and journals. Some of the physicists would, on a voluntary basis, act as trustees and officers of various kinds. To the average participant this would all be invisible. As the place grew, there was need for an outside accountant and a lawyer. For a number of years the latter was J. Nicholas “Nick” McGrath. McGrath had come to Aspen during its hippie period and indeed sported a pigtail. One could have won bets in the local bars by betting if McGrath had ever clerked for a Supreme Court Justice. He had – Thurgood Marshall. McGrath liked people who were extremely smart and slightly off–center. The physicists were an excellent fit. He believed sometimes that they were very bright children in need of guidance. He made sure that the Center had bylaws that made it a legitimate Colorado non–profit corporation and he helped guide its land acquisition. For a while there was a myth that the Center had a lease from the Institute granting its use of its land in perpetuity. No one could find such a lease and McGrath pointed out that “in perpetuity” is not a legally defensible time interval. When he died unexpectedly in 2002 at the age of 62 there was a feeling of personal loss. He had become part of the Center family.

Stranahan's utopian vision did not last long. Physics is such a complex subject that it inevitably divides itself up into sub–specialties. It is said that the last person who had a grasp of the entire field of physics was Enrico Fermi. He contributed to the theoretical physics of every branch and won his Nobel Prize for experimental work in nuclear physics. Most physicists work in one specialty and have a hard enough time to keep up with that. At some point early in the Center's history the notion of the “workshop” came into being. This would consist of a smaller sub–group of physicists who came to Aspen to work on some specific branch. Their modus operandi was to have frequent seminars in which new work could be presented. Since two or three of these workshops went on at the same time the notion of a weekly colloquium was introduced. In this a representative of one of the workshops would explain its work to the rest of the group, which included some people who were not affiliated with any workshop. The subject matter of these workshops reflected the state of the field. I give the list for the summer of 2010. Note the division of fields. There are some such as “Strong Dynamics Beyond the Standard Model” that deal with the physics of elementary particles. There are some that are pure astrophysics and some that deal with condensed matter. There is even one on biophysics and there are two on cosmology. Before the events that began in 1964 the notion of having workshops on cosmology would not have aroused much interest. The list:

Critical Behavior of Lattice Models in Condensed Matter and Particle Physics–May 23 to June 13

Strong Dynamics Beyond the Standard Model–May 23 to June 13

Forefront QCD and LHC Discoveries–May 23 to June 20

GeV and TeV Sources in the Milky Way–June 13 to June 27

Astrophysics and Cosmology with the 21–cm Background– June 13 to July 4

From Colliders to the Dark Sector: Understanding Dark Matter at Particle Colliders and Beyond–June 20 to July 18

New Mathematical Methods in Quantum Gauge Theories– June 27 to July 25

Low Dimensional Topological Matter–July 18 to Aug 8

Quantum Many–Body Physics in One Dimension–July 25 to Aug 22

Taking Supernova Cosmology into the Next Decade–Aug 8 to Aug 22

Star Formation in Galaxies: From Recipes to Real Physics– Aug 22 to Sept 12

New Perspectives in Strongly Correlated Electrostatics in Soft Matter–Aug 22 to Sept 12

Patterns in Thin Sheets: From Stressed Inanimate Materials to Biomembranes and Growing Tissues–Aug 22 to Sept 12

By the 1980's cosmology played an important role in the workshops. I attended one that was presided over by Peebles. The subject was the geometry of the universe in the large. A school of thought at the time claimed that it was the geometry of Euclid – in short that space was “flat.” Another school said that it was not and that the geometry was non–Euclidian like the surface of a sphere. It all hinged on whether a certain parameter Ω was or was not one. The empirical evidence was not as yet decisive. Faced with this, Peebles said that it should be decided by a vote. We all voted and Ω=1 – flat space – won. It turned out that this was right.

Chapter VII