27 September 2010

The Nobel Prize That Got Away

Sometimes a great scientific idea needs time to take root. Sometimes the world simply isn’t ready. Continental drift comes to mind as an example, as well as germ theory. Continents moving around, microscopic bugs? Each of these propositions seemed too bizarre to accept right off. In such situations, scientists have to be convinced that a new concept is worth looking into.

Astronomy is no exception. A famous case is a cosmic prediction that first appeared in a 1948 scientific paper almost as an afterthought. Soon forgotten, it took years before the conjecture turned into cosmology’s greatest tool.

At the time scientists were grappling with a tough question: how did the universe come to manufacture its vast array of elements? Previous to this, everyone just assumed that matter always was and would always be, but revelations coming out of atomic physics laboratories—from radioactivity to nuclear transformations—in the first half of the 20th century completely altered that notion. The elements obviously came from somewhere. The most plausible factory was inside a star, but no physicist in that era could get stellar models to build an atom heavier than helium. Anything more weighty quickly disintegrated within their theoretical computations.

George Gamow
What to do? The Russian-American physicist George Gamow in 1942 simply looked around for another locale for cooking up the elements, and he found one in the “primordial atom,” the relatively new idea that the universe had emerged and expanded from an initial, hot plasma. (The term Big Bang didn’t arrive until 1949.)

Ralph Alpher
As Gamow’s graduate student at George Washington University in the mid-1940s, Ralph Alpher took on the challenge for his doctoral thesis and theoretically demonstrated how it could be done. Like some skilled astrophysical chef, he started with a highly compressed stew of neutrons that he dubbed ylem, after an ancient Greek word for the basic substance out of which all matter was derived. As the temperature of the cosmos began to plunge, some of these particles decayed into protons, which promptly began to stick to remaining neutrons. Step by step, each element was built up from the one before it—from helium to lithium, lithium to beryllium, beryllium to boron, and so on down the periodic table. In less than half an hour, when the last of the free neutrons decayed away, the cosmic meal was complete, with Alpher and Gamow concocting the full complement of universal “flavors,” all the way up to uranium.

Their first report on this finding, a one-page synopsis published in Physical Review, is more famous for its byline than its content. Gamow, a merry prankster, listed the paper’s authors as Alpher, Bethe, and Gamow, even though noted physicist Hans Bethe never participated in the work. Gamow couldn’t resist the pun on the first three letters of the Greek alphabet: alpha, beta, gamma. That the paper chanced to be published on April Fool’s Day in 1948 only added to the fun. 

The twenty-seven-year-old Alpher had been working at the Applied Physics Laboratory of Johns Hopkins University where, upon earning his PhD, he continued to collaborate on Gamow’s campaign to study the physics of the Big Bang model, joined by fellow APL employee Robert Herman. There the two young scientists went on to develop a detailed evolution of the newborn universe, work later described by physicist Steven Weinberg as “the first thoroughly modern analysis of the early history of the universe.” 

Robert Herman
In their investigations, the pair eventually came to realize that Alpher’s original recipe for elemental cooking had a tragic flaw: while his scheme could make a few light elements, the cosmic expansion both dispersed and cooled the primordial plasma before the heavier elements had any chance of forming. With better stellar models, others would later prove that stars could do the job after all. But no matter. In the course of their work, Alpher and Herman made a historic calculation that has stood the test of time.

This result was revealed in an unusual manner. On October 30, 1948, Gamow had published an article in the British journal Nature titled “The Evolution of the Universe.” But in checking over Gamow’s reported results, Alpher and Herman found some errors. They soon dashed off a correction, a brief letter to the editor only four paragraphs long that was published within two weeks. With their more accurate figures, Alpher and Herman compared the density of matter to the density of radiation as the universe evolved. In doing so, they curtly noted at the end of their letter that “the temperature in the universe at the present time is found to be about 5° K [five degrees kelvin].” That’s a mere five degrees above absolute zero (− 459.67° Fahrenheit), the point at which all motion ceases.

With little fanfare, Alpher and Herman were telling the world that the present-day universe is bathed in a uniform wash of radiation leftover from the flood of highly energetic photons released in the fury of the Big Bang. Cooled down over the eons with the expansion of the cosmos, the waning fire now surrounds us as centimeters-long radio waves. Today it is known as the cosmic microwave background radiation (CMBR).

When their note was published, the primordial atom theory was still highly controversial. Many astronomers preferred the steady-state model of the universe, a theory that postulated that space-time had neither a beginning nor an end. But Alpher and Herman’s calculation was a clear-cut means of deciding between the two opposing theories of the universe’s behavior. Yet no one followed up. Looking back, it’s hard to fathom why astronomers didn’t jump at the chance at pointing their instruments at the sky to capture this primordial whisper of creation. But some thought radio telescopes weren’t yet sensitive enough for the task, and when a few did peg an overall temperature of interstellar space at around 3 kelvin, they didn’t link it to cosmology at all. Some thought it was an error in their instruments.

Radio astronomers may have been unresponsive because their field was just establishing itself after World War II and cosmological tests were not taken seriously. As Weinberg noted, they “did not know that they ought to try.” The radio sky was all so new. There were too many objects—radio stars, radio nebulae, radio galaxies—grabbing their attention. Amid such distractions, Alpher and Herman’s prediction was either dismissed or utterly overlooked. The two tried pumping up interest—at one point even holding a press conference to generate attention. But since both men later went into industrial research, they didn’t have the opportunity to keep pushing astronomers to take a look.

The idea didn’t resurface until 1964-65, when astrophysicists at Princeton University again reasoned that the Big Bang’s residual heat must be permeating the universe (with no mention in the team’s Astrophysical Journal paper that Alpher and Herman did it first). Two Bell Lab researchers, Arno Penzias and Robert Wilson, accidentally detected the primeval microwaves with a horn antenna in New Jersey as they were preparing to study our galaxy. For this achievement, Penzias and Wilson received the 1978 Nobel Prize in Physics.

Herman died in 1997, Alpher ten years later. Both were deeply pained that the scientific rewards for making their momentous prediction never came to pass for them—election to prestigious academies, sizable research grants, prized promotions. The honors that were bestowed (Alpher received the National Medal of Science in 2005) arrived late. “But we should not indulge in sermonizing about the nature of science,” the two noted about this oversight in a scientific memoir of their work published in 2001. “On to more about the CMBR….” And so I shall. 

Over the last two decades detectors in space have measured the cosmic microwave background, now pegged at 2.7° K, in exquisite detail. By mapping the barely perceptible ups and downs of this signal, across the breadth of the celestial sky, astronomers have revealed a wealth of cosmological information: they’ve viewed the quantum jiggles that led to galaxy formation, tallied the exact amount of ordinary matter contained in the universe, verified that there is five times more cosmic stuff of an unknown nature (called dark matter), and confirmed that space-time is permeated with an energy that is causing the universe to not just steadily expand but accelerate outward like a runaway drag racer. 

And to think, all this knowledge was gleaned from a radio murmur, a faint heat first mentioned unceremoniously in a note tucked away on the back pages of a scientific journal sixty-two years ago.

1 comment:

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