Early 'big bang' theorist
Tuesday 02 October 2007
Ralph Asher Alpher, physicist: born Washington, DC 3 February 1921; married 1938 Louise Simons (died 2004; one son, one daughter); died Austin, Texas 12 August 2007.
You do not have to look far to see what Ralph Alpher discovered. Just turn on your television and tune it between the stations. One per cent of the static on the screen is actually the "afterglow" of the "big bang" fireball in which the Universe was born. Before it was intercepted by your TV aerial, it had been travelling for 13.7 billion years across space, from the beginning of time itself.
You might think that the man who realised that the afterglow of the big bang is still around would be a household name, or at least the toast of the scientific community. However, despite his most strenuous efforts, Alpher's prediction was ignored for most of his life, while others took credit for similar, but much later, work and even carried off the Nobel Prize.
In the early 1940s, Alpher had started night classes at George Washington University in Washington, DC, under the supervision of George Gamow. Gamow, a flamboyant, hard-drinking womaniser, and one of the greats of 20th-century physics, was interested in the origin of the elements – the 92 atoms, from the lightest, hydrogen, to the heaviest, uranium, that make up the world. At one time, it had been assumed that they had been put in the Universe by the Creator, but evidence had mounted to suggest that in fact the Universe had started out with only atoms of the simplest element, hydrogen and all other atoms had been assembled, step by step, from this basic atomic Lego brick. The question was: where?
It had to be somewhere blisteringly hot, because hydrogen Lego bricks repel each other furiously, a repulsion that can be overcome only if they are slammed together at high speed, which in practice means at ultra-high temperature. The stars were hot but Gamow – wrongly, it turned out – had ruled them out as the furnace where the elements were forged. Looking elsewhere, his attention alighted on the Universe as a whole.
In 1929, Edwin Hubble had discovered that the Universe was expanding, its fundamental building blocks – galaxies of stars like our own Milky Way – flying apart like pieces of cosmic shrapnel. If it was expanding, then one conclusion seemed unavoidable: it must have been smaller in the past. Imagining the expansion running backwards, you came to a time when all of Creation was squeezed into a tiny, tiny volume. This was the moment of the Universe's birth – the big bang.
No one had thought much more about this. As the physicist Steven Weinberg has said, the common mistake of physicists is not that they take their theories too seriously but that they do not take them seriously enough. But Gamow did take it seriously. He realised that, if the Universe had once been very small, it must also have been very hot. The big bang would have been a "hot" big bang and Gamow immediately realised this could be the elusive furnace in which the elements had been forged.
Enter Ralph Alpher. Gamow, an ideas man notorious for getting bored quickly, handed to his protégé the problem of working out which atoms could have been cooked in the oven of the big bang and in what proportions. Alpher, meticulous by nature, started grinding through the calculations. There turned out to be a narrow window of opportunity between about 30 seconds and 300 seconds after the big bang when the Universe was hot enough and dense enough for element-building to go on. Then the window closed.
It turned out that Alpher was wrong in many important details – the British cosmologist Fred Hoyle would in the 1950s show that all but the lightest elements were forged inside stars – but he had worked out how the temperature and other properties of the Universe changed as it expanded, laying in 1948 the foundations of the modern big bang theory. Even more importantly, Alpher, working with another young physicist called Robert Herman, showed how to prove he was right.
In retrospect it was stunningly simple. The fireball of the big bang was like the fireball of a nuclear explosion. But, whereas the heat of a nuclear fireball eventually dissipates into its surroundings, the big bang fireball had nowhere to go. It must therefore still be around. Of course, the expansion of the Universe over the past 13.7 billion years has diluted and cooled it. Alpher and Herman calculated that it should no longer appear in the form of visible light but in the form of microwaves invisible to the naked eye. Remarkably, 99 per cent of the Universe's photons – particles of light – were tied up in this "cosmic background radiation" and a mere 1 per cent in the light of stars.
Alpher and Herman published their results in the scientific journal Nature in 1948. But for them, it was the beginning of the wilderness years. Though they repeatedly asked radio astronomers whether the fireball radiation was detectable, they were repeatedly told – incorrectly – that it wasn't. Gamow, a prolific populariser, referred to the afterglow of creation in magazines and books. But nobody noticed.
Then, in 1965, two radio astronomers at the Bell Telephone Laboratories in Holmdel, New Jersey, stumbled on a mysterious static which at one point they attributed to the microwave glow of pigeon droppings from birds nesting in their telescope. By accident, they had found the afterglow of the big bang. (Rarely in the history of science can so profound a discovery have been mistaken for something so mundane.)
Coincidentally, a team at Princeton University, just 30 miles away, were looking for the afterglow of an early hot phase of the Universe. Neither team knew of Alpher and Herman and, when they published the results that would earn Arno Penzias and Robert Wilson the 1978 Nobel Prize for Physics, Alpher was dismayed to see no mention of his work.
The years passed. Misunderstandings between the groups made things worse. Gamow died in 1968, still bitter. Just weeks after Penzias and Wilson went to Stockholm to pick up the prize, stress gave Alpher a heart attack.
The tragedy is that nobody was really to blame. When Alpher, Gamow and Herman started thinking about the earliest moments of the Universe, for most physicists they were straying into theological territory. And, in the 1940s, there was no field of cosmology – the science of the origin, evolution and fate of the Universe – so future scientists might be forgiven for overlooking papers scattered about the journals. To add to this, Alpher vanished from academia in 1955 to work for General Electric, on everything from colour television to energy conversion.
But Alpher died a contented man. A turning point was the launch in 1989 of Nasa's Cosmic Background Explorer (COBE) satellite. On the morning of 18 November, the scientists and engineers who had worked on the project stood about in the freezing pre-dawn darkness waiting for the launch of the Delta rocket that would carry COBE into space. Among them in the crowd, stamping their feet to keep warm, were Alpher and Herman. COBE's project scientist, John Mather (who in 2006 would win the Nobel Prize), had made a special point of inviting them. At long last, everyone recognised Alpher's prescience in predicting the afterglow of the big bang.
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