Gamow: Father of the Big Bang

Time for a plug for one of the people who introduced me to science, through his “Mr Tompkins” books:

WHEN NASA’s COBE satellite reported the discovery of “ripples” in the background radiation that filled the Universe, this was heralded as the final confirmation of the hot Big Bang theory, the idea that the Universe was born in a superdense, superhot fireball, some 14 billion (thousand million) years ago. But in all the press coverage of this great discovery, one name was conspicuously absent. It was that of George Gamow, a Russian emigre scientist who almost single-handedly invented the hot Big Bang theory, more than half a century ago. He also found time to predict the existence of the background radiation now probed by COBE and its successors, to explain how the Sun stays hot, to investigate the structure of the molecule of life (DNA), to play scientific practical jokes that still bring a wry smile to the lips of astronomers, and to write a series of best-selling books explaining new ideas in quantum physics, relativity and cosmology to the public. Born in the Ukraine, at Odessa, in 1904, Gamow lived through the turmoil of revolution and civil war in Russia, and studied at the University of Leningrad, where he learned about the new discoveries in quantum physics and Albert Einstein’s new theory of the Universe, the general theory of relativity. Between 1928 and 1931, the newly- qualified young physicist travelled to the University of Göttingen, to the Institute of Physics in Copenhagen, and to the Cavendish Laboratory in Cambridge — the three main centres at the heart of the quantum revolution. It was during his visit to Göttingen that he made his first major contribution to science.

At the end of the 1920s, physicists were puzzled at the way in which an alpha particle (now known to be the nucleus of a helium atom) could escape from radioactive nuclei. Within the nucleus, the particles are held tight by a force, now known as the “strong nuclear” force. This has a very short range, but overcomes the tendency of all the particles in the positively charged nucleus to repel each other electrically. A little way outside the nucleus, the strong force cannot be felt. An alpha particle just outside the nucleus, itself carrying two units of positive charge, would be repelled by the nucleus electrically, and fly away. It is as if the alpha particle in the nucleus sits in a dip at the top of a mountain — like the crater of an extinct volcano. If it could climb out of the crater, it could roll away down the mountainside. But it turned out that the energy of alpha particles emerging from radioactive nuclei was too low for this to be possible. They did not carry enough energy to climb out of the crater — so how did they escape?

Gamow’s explanation was the first successful application of quantum physics to the nucleus. He took up the idea that each particle is also a wave. Because a wave is a spread-out entity, its location is not restricted to a point inside the “crater”. Instead, the wave spreads right through the surrounding walls, and under the right circumstances the alpha “particle” can tunnel through those walls, without having to climb to the top of the mountain.

This quantum tunneling also explains an astrophysical puzzle. Inside the Sun, nuclei of hydrogen (protons) collide and fuse together, in a step by step process, to make helium nuclei. The process releases energy, and that keeps the Sun hot. But protons are positively charged, and repel each other. According to calculations carried out in the 1920s, the protons inside the Sun do not move fast enough (they are not at a high enough temperature) to overcome their mutual electrical repulsion when they collide, and get close enough together for the strong force to take over. They do not have enough energy, that is, to climb in to the volcano from outside, and settle in the crater where the strong force dominates.

But tunneling can work both ways. Because protons are also waves, they only have to come close enough together for their waves to overlap before the strong force does its work. So Gamow’s tunneling process explains how the Sun generates heat.

In 1931, Gamow was called back to the USSR, where he was appointed Master of Research at the Academy of Sciences in Leningrad, and Professor of Physics at Leningrad University, at the tender age of 27. But his ebullient nature and independence of mind hardly suited him to a happy life under Stalin’s regime, and when he was allowed to attend a scientific conference in Brussels in 1933 he seized the opportunity to stay away, moving to George Washington University in Washington DC, where he was Professor of Physics from 1934 to 1956, and then to the University of Colorado in Boulder, where he stayed until his death in 1968.

The idea of sticking protons together to make helium nuclei led Gamow to puzzle over the way particles must have interacted under the conditions of extreme heat and pressure in the Big Bang in which the Universe was born. In the 1930s, it became clear from observations of galaxies beyond the Milky Way that the Universe is expanding, with empty space between the galaxies stretching in a way predicted by the equations of Einstein’s general theory of relativity.

Taking the theory and those observations at face value implied that the Universe started out from a hot, dense soup of particles — protons, neutrons and electrons mingled together — in the beginning. Very few people had that much faith in the equations or the observations in the 1930s and 1940s, but Gamow persisted in trying to explain how the stuff stars and galaxies are made of could have been cooked up by nuclear reactions from such a primeval particle soup.

Stars are essentially made of hydrogen (roughly 75 per cent) and helium (roughly 25 per cent). Everything else, including the elements such as carbon, oxygen and nitrogen that are so important for life, makes up less than 1 per cent of the visible mass of the Universe (astronomers now think that there are also vast quantities of so-called “dark matter” in the Universe, but this does not affect Gamow’s discoveries about where star stuff comes from). The protons and electrons, combined together to make atoms, would provide the hydrogen. So the key problem is to manufacture helium.

In the 1940s, Gamow was joined at George Washington University by Ralph Alpher, a graduate student. He gave Alpher the task of working out the details of how helium could have been built up from protons and neutrons in the Big Bang.

All eminent scientists like to have graduate students to do such donkey work. But it was particularly important for Gamow to have someone to do the calculations for him, since although he was a brilliant physicist he was always hopeless at getting the details of his arithmetical calculations right, and had trouble adding up his bank statements. Together, they found that it was indeed possible to produce a mixture of 75 per cent hydrogen and 25 per cent helium out of the Big Bang, but that as the Universe expanded and thinned out the nuclear reactions would quickly come to a halt making it impossible to build up more complicated elements.

Gamow wasn’t worried about this. After all, as he used to tell anyone who was interested, the theory explained where more than 99 per cent of the visible material in stars and galaxies came from, and that was good enough to be going on with. (In case you are wondering, the other elements are made inside stars; Fred Hoyle showed this in the 1950s.)

The detailed calculations formed part of Alpher’s PhD thesis, which was submitted in 1948. They clearly deserved a wider audience, however, and Alpher and Gamow wrote a joint paper on the work for submission to the Physical Review. It was at this point that Gamow’s sense of fun overcame him, and he perpetrated his most famous scientific joke. Without telling his friend Hans Bethe of his plan, he decided that it was “unfair to the Greek alphabet to have the article signed by Alpher and Gamow only, and so the name of Dr Hans A. Bethe (in absentia) was inserted in preparing the manuscript for print.” To Gamow’s delight, and entirely by coincidence, the paper duly appeared in print on 1 April 1948, under the names Alpher, Bethe, Gamow. To this day, it is known as the “alpha, beta, gamma” paper. This is a suitable reflection of the fact that it deals with the beginning of the Universe, and also can be taken as referring to the contents of the paper, since helium nuclei are also known as alpha particles, beta ray is another term for electrons, and gamma rays are high energy photons (particles of light) involved in the nuclear reactions. It was the fate of those gamma rays that next caught the attention of Gamow and his students.

The calculations showed that the proportion of helium produced in the Big Bang depends on the temperature of the fireball in which the Universe was born. To match the observations that stars contain 25 per cent helium, Gamow’s team had to set the temperature of the Big Bang rather precisely. But Einstein’s equations then predict how the temperature of that radiation will fall as the Universe expands. Later in 1948, Alpher and another of Gamow’s students, Robert Herman, published a paper in which they calculated that the temperature of this leftover radiation today must be about five degrees on the absolute, or Kelvin, scale — that is, some -268 oC. The calculation is simple. In its modern form (updated slightly from 1948) it sets the temperature now, in Kelvin, as 1010 divided by the square root of the age of the Universe in seconds. One second after the moment of creation, the temperature was 10 billion degrees; after 100 seconds, it had already cooled to 1 billion degrees; and after an hour it was down to 170 million degrees. For comparison, the temperature at the heart of the Sun today is about 15 million degrees.

Gamow’s team predicted, almost fifty years ago, that the Universe must be filled with radiation left over from the Big Bang, cooled all the way down to about 5 K. The radiation would be in the form of microwaves, just like those used in radar or in a microwave oven. In effect, the Universe is an “oven” with a temperature of a few K. Microwaves are in the radio part of the spectrum, and could be detected by radio telescopes. But radio astronomy was only just getting into its stride in the early 1950s, and Gamow didn’t realise that it might actually be possible to measure this microwave background.

His own career soon took a new path, or he might have learned how much progress the radio astronomers were making and urged them to look for this background radiation.

In 1953, Francis Crick and James Watson, working in Cambridge, reported that they had discovered the structure of the molecule of life, the now-famous double helix of DNA. It soon became clear that the information carried by DNA — the information which tells a fertilised egg how to grow to become a human being, and which tells each cell in that human being how to function — is in the form of a genetic “code”, spelled out on chemical units along the DNA double helix. But nobody knew how the code worked.

At the time, Gamow was visiting the Berkeley campus of the University of California, and, as he later recalled: I was walking through the corridor at the Radiation Lab, and there was Luis Alvarez going with Nature in his hand . . . he said “Look, what a wonderful article Watson and Crick have written.” This was the first time that I saw it. And then I returned to Washington and started thinking about it. Gamow was hooked. Scientific code-breaking was just the kind of thing to intrigue him, and he soon wrote to Watson and Crick, introducing himself and presenting some ideas about how the DNA code might be translated into action inside the cell. His first paper on the subject was published in 1954, and presented the key idea that hereditary properties could be characterised by a long number in digital form. This is exactly the way computers work, expressing everything in terms of binary numbers, long strings of 0s and 1s, and it was eventually confirmed that the DNA code does indeed work like this, but with four “digits” (like having the numbers 0, 1, 2, 3) instead of two. But it took a long time for the code to be cracked and read. Some of the key work was carried out in Paris, by Jacques Monod, Francois Jacob and their colleagues; but Gamow kept in touch with all of the researchers involved, contributing stimulating ideas to the debate. The code was finally cracked in 1961, and it is no coincidence that Crick and Watson received their Nobel Prize the following year.

By then, Gamow had almost forgotten his team’s pioneering investigation of the temperature of the Universe. But in 1963 two young radio astronomers, Arno Penzias and Robert Wilson, began to puzzle over some strange “interference” they were getting with their telescope, a microwave detector built on Crawford Hill in New Jersey. The puzzle was that everywhere they pointed the telescope they found a persistent hiss of radio noise, corresponding to microwaves with a temperature of about 3 K. They tried everything to locate the source of the interference, even taking the whole antenna apart and cleaning off the pigeon droppings that had accumulated on it, then putting it back together. Nothing made any difference. It seemed that the Universe was filled with a background of microwave radiation. News of the discovery was published in 1964, and the radio noise was quickly explained by other researchers as the leftover radiation from the fireball of the Big Bang. By then, the work of Gamow and his team had been so neglected for so long that the first accounts failed to mention them, and the fact that they had predicted the existence of this radiation, at all. Understandably, this upset Gamow, Alpher and Herman greatly. But the omission was later rectified, and there is now no doubt in the mind of any astrophysicist that the radiation discovered by Penzias and Wilson accidentally in the early 1960s is the radiation predicted by Gamow’s team in the 1940s.

The importance of the discovery cannot be over-emphasised. Before it was made, even the cosmologists did not really “believe” in the Big Bang — and there were very few people who even called themselves cosmologists. They regarded cosmology rather like a great game of chess, in which they could work out theories and construct mathematical “models” of the Universe, with no expectation that the equations they scribbled on their blackboards actually described the real world.

The discovery of the background radiation changed all that. After 1964, those equations had to be taken seriously. With the realization that cosmology was indeed a real science, many physicists turned to its investigation, leading to the situation today, thirty years later, where the study of the Big Bang is possibly the most important branch of theoretical physics. As Steven Weinberg, one of those physicists who turned to cosmology after 1964, has summed up the situation: Gamow, Alpher and Herman deserve tremendous credit above all for being able to take the early universe seriously, for working out what known physical laws have to say about the first three minutes.

Gamow died in 1968, ten years before the Nobel Committee gave their award for physics to Penzias and Wilson. Nobel Prizes are never awarded posthumously, but it would surely be right, on this occasion, to include the name of Dr George Gamow “in absentia”. He had shown how the stars shine, almost single-handedly invented the Big Bang theory, and contributed to explaining the secret of life itself. The “ripples” discovered by COBE, and hailed in 1992 as “the greatest scientific discovery of all time” (by no less an authority than Stephen Hawking), are, in fact, just a secondary feature of the background radiation predicted by Gamow.

But his most enduring legacy is the series of books he wrote describing the mythical adventures of Mr Tompkins, a mild-mannered bank clerk who has vivid dreams in which he visits the world of the very small, inside the atom, and the world of the very large, the Universe itself. Although they first appeared in the 1940s, they still provide an excellent and entertaining guide to basic physics. Many readers seem to agree — the collected edition was reprinted in England every single year during the 1980s, and are now available with a foreword by Roger Penrose, one of the founding fathers of black hole theory.

The irony would probably have amused Gamow himself. Eminent scientists may have forgotten his seminal contribution to so much of twentieth century science; but generations of schoolchildren know him as a witty raconteur who explains science painlessly for beginners. Perhaps some things are more important than Nobel Prizes, after all.

 

For more, see my book In Search of the Big Bang. 

http://www.amazon.co.uk/Search-Bang-Penguin-Press-Science/dp/0140269894

 

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One comment on “Gamow: Father of the Big Bang

  1. RhEvans says:

    I’ve never understood why Gamow’s work of the late 1940s went so unnoticed. I met Ralph Alpher in 1995, when I was offered a professorship at Union College in Schenectady, he was a professor there. He had no explanation for how his, Hermann and Gamow’s work was so overlooked by the physics and cosmology communities. Dicke seems (or claimed) to have been completely unaware of their work when he developed his own theory of the CMB in the early 60s.

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