The Perfect Theory (16 page)

Radio waves behave just like light waves, but their wavelengths are a billion times longer than those of visible light. The light we can actually see, which makes up the bulk of the sun's rays, has a wavelength that is less than a millionth of a meter. Radio waves have gigantic wavelengths, ranging from a millimeter all the way up to hundreds of meters. Jansky had found that the Milky Way was emitting an extraordinary amount of radio waves, day in and day out. Even though the sun was much brighter in the sky than the whole Milky Way put together, it didn't emit as many radio waves. In an article “Electrical Disturbances Apparently of Extraterrestrial Origin,” published in 1933, Jansky systematically took apart all possible sources of static and showed a map of where the radio waves were coming from. His methods revealed a different way of looking at the cosmos. Instead of using giant telescopes with lenses on mountaintops, this kind of observation could be done with chicken wire, steel, and dishes out in the open plains. Rather than looking at the faint light of distant objects, astronomers could pick up the radio waves coming from outer space.

Jansky's discovery was mostly ignored. When he proposed that Bell Labs build a new, improved antenna, he was refused. They weren't in the business of astronomy. And so Jansky moved on to other things. But his work wasn't completely forgotten. An idiosyncratic radio engineer and amateur astronomer from Wheaton, Illinois, by the name of Grote Reber read about Jansky's discovery in
Popular Astronomy
and set about building a bigger and better antenna in his backyard in Wheaton. Reber's antenna had a 9-meter dish, with metal scaffolding that extended out in front to capture the reflected waves. It was the first proper radio telescope, much like the ones we see today. With it, Reber set out to make a finer map of the radio emissions of the Milky Way and build a detailed map of the radio sky. He submitted his work to the
Astrophysical Journal
where Chandra, who was the editor at the time, was intrigued by Reber's results and bemused by his persistence—he accepted the paper for publication. And so in 1940, Reber's “Cosmic Static” was published with his very own maps.

Reber's new radio maps of the Milky Way were interesting, helping to map out in detail where all the mysterious waves were actually emanating from. But Reber's measurements also revealed something else: a few isolated points on the maps were beaming copious amounts of radio waves. While Reber was able to place each of the points near a constellation—Cygnus, Cassiopeia, and Taurus—they did not correspond to objects emanating visible light. Reber had discovered a new type of astronomical object that became known as a radio source or radio star.

“Cosmic Static” opened up a new window on the universe. Unfolding before a new generation was perfectly uncharted territory, and Martin Ryle was ready to explore. Along with Lovell's and Pawsey's groups, from the late 1940s onward, Ryle and his group at Cambridge began mapping the cosmos. Deploying the techniques that he had learned while working on radar, Ryle designed a new generation of radio telescopes that would transform Cambridge into one of the premier centers for
radio astronomy. But it also would bring him up against Hoyle and his collaborators.

 

Martin Ryle was more of a radio-ham amateur and an electrical engineer than a cosmologist, so it was surprising that he would get caught up in a fight with “theoreticians,” as he would disparagingly call Hoyle and his colleagues. But he had walked right into it. He had first tried to find more bright radio sources, like those Reber had observed, and pinpoint their locations, but unfortunately he made the wrong call. It seemed clear to him that all these objects were firmly embedded in the Milky Way. In a clearly argued paper in 1950 he made the case that the majority of radio sources should lie within our galaxy. There could be a few odd outliers, but on the whole they must be close by. What he said made sense and was entirely reasonable.

Ryle presented his results at a meeting of the Royal Astronomical Society in 1951. In the audience were his Cambridge colleagues Gold and Hoyle, who stood up and casually conjectured that the radio sources might actually be extragalactic. Ryle, who had carefully thought through his arguments, was annoyed and dismissed Gold and Hoyle, saying,
“I think the theoreticians have misunderstood the experimental data.”

It was a clash of cultures pitting the highbrow theoretical astronomers, versed in mathematics and physics with elegant yet odd theories that explained the whole universe, against the tinkerers, the radio operators who built kits and played with electronics. Ryle couldn't stand the perceived condescension of his colleagues. He felt he understood the data in a way that these people who worked solely with pencil and paper couldn't. Unfortunately for Ryle, Gold and Hoyle were eventually proved right as more and more radio sources came to be associated with objects outside the Milky Way. They were indeed extragalactic, and Ryle had to accept that the theorists
did
in fact understand the data.

But Ryle didn't accept defeat quietly. Given that these radio sources lay outside the galaxy, they could be used to say something about the universe. So Ryle turned to amassing more observations and using his data to go after Hoyle and Gold's baby, the steady-state theory. He did so by counting the number of radio sources as a function of their brightness and trying to relate this number to the underlying properties of the universe. The farther away a radio source is, the dimmer it will be, so the dimness of a source can be seen as an indicator of its distance. The universe is a big place and there is a lot of space out there, so one would expect to see more dim, distant sources than bright, close ones. It turns out that the ratio of the number of dim sources to bright ones is a good way of figuring out what type of universe we might live in. When we look at distant sources, their light has taken time to reach us, so we are looking at the universe when it was younger. If we live in Hoyle, Gold, and Bondi's steady-state universe, the density of sources remains constant over time, so the total number of sources within a certain volume should be directly proportional to that volume. In an evolving universe like the one Friedmann and Lemaître proposed, the universe was denser in the past than it is now, so there should more distant, dimmer sources than close, bright ones. By counting the number of dim sources relative to the bright sources, it should be possible to determine whether our universe adheres to the Big Bang or the steady-state model.

Ryle compiled a list of almost two thousand sources in what was called the 2C Catalogue (
C
stands for Cambridge). It built on a much smaller list of fifty sources (known as the 1C Catalogue) and seemed, to Ryle's satisfaction, to have far too many dim sources compared with bright sources for it to be consistent with the steady-state theory. Ryle saw this as the killer blow for Hoyle's theory and immediately set about advertising his results. In a prestigious lecture he was invited to give at Oxford in May 1955, he came out with a bold indictment of his rivals:
“If we accept the conclusion that most of the radio stars are external to the galaxy, and this conclusion seems hard to avoid, then there seems to be no way in which the observations can be explained in terms of a steady state theory.” Ryle had seemingly demolished Hoyle and Gold's model.

After Ryle's lecture at Oxford, Hoyle and his collaborators were on the defensive. Hoyle took the data seriously, but Gold was suspicious of the results, advising Hoyle, “Don't trust them, there might be lots of errors in this and it can't be taken seriously.” Gold was right. This time Ryle was thwarted by his own cohort, the same tinkerers who were building radio astronomy into a bona fide science. Two young Australian radio astronomers, Bernard Mills and Bruce Slee from Sydney, reanalyzed the 2C data and found a completely different result from Ryle's. Instead of trying to come up with a catalogue of thousands of sources to rival Ryle's, they opted to focus on a small subset of the whole survey, about three hundred sources, and measured them in exquisite detail. This small catalogue was picked so it overlapped with Ryle's catalogue and could be used to actually check Ryle's measurements.

Mills and Slee's published results completely destroyed the credibility of Ryle's survey. In their paper, they said that their “catalogue is compared in detail with a recent Cambridge catalogue . . . it is found that they are almost completely discordant.” Mills and Slee went on to suggest that “the Cambridge catalogue is affected by the low
resolution of their radio interferometer.” Ryle's results were simply not good enough—Mills and Slee were working with a better telescope that was more precise, and their results could not exclude the steady-state model as a possible model of the universe. A radio astronomer from the rival group in the UK named Jodrell Bank chimed in, saying, “Radio astronomers must make considerable progress before they can offer the cosmologists anything of value.” It seemed that the radio astronomers couldn't agree on their data, let alone use it to test cosmological models, so it was deemed best to ignore that data for now. Hoyle and his collaborators had a field day.

Ryle retreated to Cambridge to work on the next generation of his source catalogue. Singed by the debacle of his questionable results, Ryle and his team spent the next three years building a new catalogue, unimaginatively called the 3C Catalogue. The new results would decisively shoot down the nonsense that Hoyle and his team were peddling, or so Ryle thought. In 1958, when the 3C Catalogue was finally revealed to the world, Martin Ryle finally felt he had his
pièce de résistance:
a collection of radio sources that everyone agreed with. Yet it still wasn't good enough. Bondi was skeptical and pointed out that Ryle had a tendency to claim that his measurements were better than they actually were; Ryle often claimed to have ruled out the steady-state model when really he had just reached the limits of what could be said with his data. Whenever anyone went back and reanalyzed Ryle's data and found that the errors were larger than previously claimed, the steady-state model was ruled back in the game. Indeed, as Bondi said publicly, “this has happened more than once in the last ten years.”

In February 1961, Ryle presented his analysis of what was now the 4C Catalogue at the Royal Astronomical Society meeting. He argued that the results were simply incompatible with those of the steady-state model—there were far too few bright sources relative to the dim ones. The observations, he said,
“appear to provide conclusive evidence against the steady state theory.” The newspapers picked up on Ryle's announcement and came out with headlines claiming that “the Bible was right” about the existence of an initial moment of creation. As other teams in Australia and the United States reproduced Ryle's results, it seemed that Ryle had finally sorted it out.

Hoyle and his collaborators were worried but not convinced. As Bondi told the
New York Times,
shortly after Ryle announced his analysis, “I certainly don't consider this the death to continuous creation,” adding, “A similar statement has been made by Professor Ryle in 1955 but the observations on which it was based were later found to be incorrect.” There was something irrational about Ryle's personal quest to kill the steady-state theory, even though the data was improving year by year. To Hoyle, Bondi, and Gold, radio hadn't killed the steady-state theory, at least not yet.

 

The fight between Hoyle and Ryle, centered in Cambridge as it was, may seem like an unnecessary distraction from the inexorable progress of general relativity and cosmology. Few people outside the United Kingdom had any interest in Hoyle's model. To many, the debate seemed fickle, almost unscientific, driven by personalities and vendettas. Visitors to Cambridge would comment on the poisonous atmosphere between Ryle and Hoyle's group.

But their rivalry resulted in significant scientific progress. Fred Hoyle would go on to be lauded as one of the great astrophysicists of the second half of the twentieth century. With William Fowler and Geoffrey and Margaret Burbidge from the United States, he would end up developing a brilliant theory for the origin of the elements in stars. Some might point to his maverick nature and his insistence on supporting the steady-state model to explain why he was not included as one of the awardees of the 1983 Nobel Prize in Physics. In 1973 he left Cambridge to live in the Lake District and write novels.

Hermann Bondi would end up creating a vibrant general relativity group in King's College London, and Thomas Gold would end up setting up the world's largest radio telescope in Arecibo in Puerto Rico. Martin Ryle's group developed a reputation for secrecy and paranoia, yet they were behind some of the great discoveries in radio astronomy of the following two decades. Ryle won the Nobel Prize in 1974. The rise of radio astronomy and the elusive nature of radio sources would play a crucial role in the advancement of general relativity, which was about to enter a new phase.

Chapter 7

J
OHN ARCHIBALD WHEELER
personally discovered relativity by way of nuclear physics and quantum theory. In the spring of 1952, Wheeler found himself wondering what happened at the end of the lives of stars made of neutrons, the building blocks of nuclear physics that Wheeler had spent his life until then studying. He was puzzled by Robert Oppenheimer's prediction that the endpoint of the gravitational collapse of such a star could be a singularity, a point of infinite density and curvature at the star's center. To Wheeler, these singularities didn't sound right. They couldn't be truly physical, and there must be some way to avoid them. To understand this bizarre prediction, Wheeler would have to learn general relativity. He figured the best way to do that would be to teach it to the students at Princeton. And so, in 1952, in the home of Einstein, Gödel, and Oppenheimer, John Archibald Wheeler taught the first course on general relativity in the Princeton department of physics. Until then it had been considered an abstract subject more suitable for a mathematics department. It was a momentous departure, one Wheeler would recall years later as
“my first step into a territory that would grip my imagination and command my research attention for the rest of my life.”