Fred Hoyle An observer of the world and a ponderer on its problems ...

The idea that the chemical elements were produced by nuclear reactions inside stars had its flowering in the 1950s. Today, however, I would like to speak of the previous decade, the 1940s. Especially of a paper I wrote in 1946, of which a well-known nuclear astrophysicist once said when in a kindly mood:

“I don’t know how he ever came to write it.”

So I thought I would explain how I came to write it, even though in doing so I will be destroying any mystique it may seem to have had.

The first of a long chain of accidents that led to its writing was the outbreak of war in 1939. It was decided by a committee of senior British scientists to recommend to the Government that younger scientists in the universities should not be enlisted as they had been in the First World War. Instead they should be recruited by personal contacts. This had the effect that, on recruitment, one immediately had a definite job to do. Instead of drifting aimlessly around some centralised agency.

When scientists left their universities they told few beyond their immediate family where they were going. When I left Cambridge it didn’t occur to me to tell my college where I was going. There were no forwarding addresses, no telephone numbers. People just disappeared. Add to this sociological fog that in the summer of 1940 all road signs were removed throughout Britain. Maps were taken out of the shops and nobody, either in town or country, would give you information about where you were. Let the slightest glimmer of light out through a window at night and a warden, followed likely enough by the police, would soon be banging on your door. So here was a nation in near total blackness, in which you didn’t know where anybody had gone. Or where you were, should you be unwise enough to get off known paths or roads. This was what our Prime Minister, Mr Chamberlain, apparently meant when on 3 September 1939, he said he was ready for war.

As I come into the system as an unknown quantity at its junior end it can well be understood how in this confusion it was all very obscure. But by 1942-43 the skies had cleared quite a bit. By then I was a member of a small unit that was dedicated to the investigation of jobs nobody else wanted.

When the first aerial photographs of the German rocket testing sites at Peenemunde were circulated in the British scientific establishments there were plenty of people who said they didn’t look like a new form of radar. But it fell to us to write a report saying they were not. Which nobody else wanted to do.

Then when the first really short wavelength radars came into operation, it was confidently expected that the detection of enemy ships would cut off sharply at the horizon. But early operational reports showed sporadic detections going far beyond the optical horizon. The disposition in London was to say this was impossible and therefore the operational reports must be wrong.

But my friend Maurice Pryce, to whom the problem then fell, soon satisfied himself from talking to a number of young officers that this was not so. What could be going on then became the question?

Pryce noticed that molecules of water vapour had an exceedingly high dipole moment. But the amount of water in the air seemed to him to still be too small to have much effect. I believe at this point I made a contribution by pointing out that it wouldn’t really be the amount of water that was relevant but the water vapour gradient. And that water vapour is notorious for its sharp gradients. The thought sent me off to Cambridge to search around in the libraries there. I chose Cambridge because the phenomenon had a very high security clearance and I could gain access to the Cambridge libraries without exciting any comment.

A month or two of mathematical work followed as we worked out possibilities for various kinds of water vapour distributions. Two years later in 1944 all this had become generally accepted. Also by 1944 this water vapour effect on high frequency radar had gained a new importance. The enemy didn’t need to make an entire radar in order to detect our ships and planes. They could do so with a high frequency receiver only. I don’t think the Japanese in the Pacific ever had such receivers but the Germans certainly did. Making the water vapour phenomenon a high security problem.

In October 1944 I was asked to make a trip to Washington. To discuss these matters with American radar experts. One day our small local administrative office received instructions for me to present myself on a certain day at 8 o’clock in the morning at an obscure dockyard on the lower River Clyde near Glasgow. To board a boat bound for New York, where at a certain hotel I would receive further instructions. Money I would receive when I reached the British Embassy in Washington. There was nothing to say how I should return. But by 1944 it was generally assumed that if you were competent enough to get from A to B, then you should also be competent enough to get from B to A.

I was further informed that a certain Commander, who I knew to be most sunk-at-sea officer in the British Navy – sunk once from a cruiser and once from an aircraft carrier – would be making the same trip. When a while later I ran into him in London he informed me that our boat was something of a rust bucket, with a speed 5 knots short of the latest U-boats. This intelligence sent me hot foot into the London financial district, where a broker for Lloyds gave me odds of 20 to 1 on making the voyage successfully. Odds that greatly relieved me, since they were much better than my friend the Commander had led me to expect.

The nuclear astrophysicist who wondered how my paper of 1946 ever came to be written would probably be surprised to hear that all this was very relevant. As was the strange circumstance that friends and colleagues from my pre-war Cambridge days were again going missing. By now I thought I knew where most of them were located. So it was with some surprise that an attempt to contact one of them was met by a denial that any such person had ever existed. Then the same thing happened with another. Then with a third. People really were vanishing into thin air.

One problem remained before I was off at last. The 500 mile journey from the English South Coast to some obscure dockyard on the Lower Clyde, contriving to arrive there at 8 am in the morning. The problem was solved by ‘bagging’ an official car. By ‘bagging’ I mean that one moment the car was there in its usual official position and the next moment it was not. I took good care then to pick up my friend the Commander, since his uniform gave respectability to this manoeuvre. I have always thought that it was because the Germans didn’t do this kind of thing that they were at a serious disadvantage.

The Commander and I still had to acquire some American money. At least we had to do so if life was to be at all worth living once we reached New York. This problem we solved fairly easily. On the boat we ran into a director of the British General Electric Company. One moment he had a lot of American money – the next he didn’t.

Discussions on short wavelength transmission problems continued beyond Washington, far to the west to the big US Naval base at San Diego. Since I had a day or two to spare in San Diego I obtained a lift by car to Los Angeles. Then by tram to Pasadena, and so to the offices of the famous Mt Wilson Observatory, where I was fortunate to have a letter of introduction to Walter Adams, the Director.

Adams then introduced me to his most distinguished astronomer then in residence, by an ironical twist the German, Walter Baade. When Baade found that, unlike some of the residents of Pasadena, I had no interest in tormenting him with questions about the war, but wanted to talk about astronomy, he became enthusiastic. I had intended to discuss novae. But Baade quickly switched the subject to supernovae, all of which was new to me. Hundreds of times more powerful than novae, Baade said, and another bit of the story had fallen into place.

When I implied just now that Germans don’t indulge in the unconventional I am being unfair. Walter Baade did the most unconventional thing I ever saw. For three years he drove around Pasadena without a driving licence. The reason being that, although he was a superb astronomer, he was a shockingly bad driver. His system was to discover the patrol schedules of the Pasadena police, taking care never to drive any street or avenue where a car would be operating,

I was scheduled to fly back from San Diego to Boston. Then the night train to Montreal. Then a bomber flight back to Glasgow. Followed finally by an almost motionless train from Glasgow to the English South Coast. But when I reached Montreal I fell into the hands of the Canadians who wanted to talk about radar problems. Which interlude occupied the time up to the Christmas period. When to my surprise I at last discovered what had happened to my friends who had gone seriously missing over the previous months.

It was on this chance discovery that my paper of 1946 turned. In pre war Cambridge I had been a nuclear physicist. Understandably my friends from those days had been weighted by nuclear physicists, and it was these who had gone missing. A sinister fact which had been somewhat obvious. But now I found them all safe and well at a Canadian nuclear establishment called Chalk River near Montreal.

Why were they there was of course the question. Already in 1939 it had been clear that a nuclear bomb could be made, if sufficient effort were expended in the making. By 1942 it had also become clear that the necessary effort was too great for the British Government. But was it too great for the Americans? After the immense number of war ships I had seen in San Diego Harbour perhaps it wouldn’t I thought. If so I could understand why these people should have been transferred so secretly here to Chalk River.

With these thoughts, everything now fell into place. Bombs and supernovae was the crucial connection. Just as a bomb had to be triggered, so would a supernova need to be triggered in some way. The idea occurred to me on the very last stages of my homeward journey. It also seemed attractive that I could work on the triggering of a bomb inside a star without having to ask permission from anyone. That I could talk about it without needing permission from anyone. Although my wife reminds me that, after the publication of my 1946 paper, I had a visit from two Secret Service Officers. They were distinctly surprised to hear that bombs occur in the stars, and my wife says they departed looking very depressed about it.

Anyway, about four months after my American visit the war in Europe ended. I had recently been appointed to a junior teaching post in Cambridge. And under the terms of my employment by the British Admiralty I was then free to return to Cambridge. In fact in time for the beginning of the Cambridge October term. This was still 1945, and it was in the next three months that the paper which appeared in the following year was written.

The paper explained the production of the transition metals in supernovae centred at iron. Since the natural abundances of the chemical elements as they occur here on Earth were known to possess just such a peak , I felt emboldened from 1946 to stick to the production of chemical elements inside stars. When in the immediately succeeding years George Gamow suggested what for a while became a more popular view, that the elements came from the origin of the universe, I felt that at least on the transition metals George had to be wrong, and that supernovae would come out the winners in the long run. The conference beginning here tomorrow shows that they did.

I don’t find memories come in orderly fashion nor in any particular sequence. So the kaleidoscope of feelings I have experienced in recent weeks flashes out in something of a brightly painted picture – the unexpected first visit to the delightful town and ancient university of Lund and, again unexpected, the chance to revisit the grandeur of Stockholm with its beauty and symmetry, rare indeed in capital cities these days. Impressions to carry always woven into the fabric of memory.

From the time of the first message from Professor Norrby informing me of the great honour to be bestowed on Professor Saltpeter and myself of the award of the Crafoord Prize, it has been a tremendous boost to morale and the greatest encouragement to have one’s work chosen for recognition.

And it is to the Crafoord family that our warmest thanks go for this prestigious and much appreciated prize. .

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