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hawking
physics.subha.peperonity.net

STEPHEN HAWKING: To boldly go (my life in physics)

by STEPHEN HAWKING

INTRODUCTION:
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What's it like to live your life as the ringleader of obscurity? Stephen Hawking - renowned cosmologist, celebrated physicist and bestselling author - describes his journey of inspiration and discovery.
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I did my first degree in Oxford. In my final examination, I was asked about my future plans. I replied:

"If you give me a first class degree, I will go to Cambridge. If I only get a second, I will stay in Oxford." They gave me a first.

I arrived in Cambridge as a graduate student, in October 1962. I had applied to work with Fred Hoyle, the principal defender of the steady state theory of cosmology, an alternative to the big bang theory. Hoyle was the most famous British astronomer of the time.

I say astronomer because cosmology was at that time hardly recognized as a legitimate field, yet that was where I wanted to do my research, inspired by having been on a summer course with Hoyle's student, Jayant Narlikar.

However, Hoyle had enough students already so, to my great disappointment, I was assigned to Dennis Sciama, of whom I had not heard.

But it was probably for the best. Hoyle was away a lot, seldom in the department, and I wouldn't have had much of his attention. Sciama, on the other hand, was usually around and ready to talk. I didn't agree with many of his ideas, particularly on Mach's principle, but that stimulated me to develop my own picture.

When I began research, the two areas that seemed exciting were cosmology and elementary particle physics. Elementary particle physics was the active, rapidly changing field that attracted most of the best minds, while cosmology and general relativity were stuck where they had been in the 1930s.

Richard Feynman has given an amusing account of attending the conference on general relativity and gravitation, in Warsaw in 1962.

In a letter to his wife he said, "I am not getting anything out of the meeting. I am learning nothing. Because there are no experiments, this field is not an active one, so few of the best men are doing work in it. The result is that there are hosts of dopes here and it is not good for my blood pressure. Remind me not to come to any more gravity conferences!"

Of course, I wasn't aware of all this when I began my research. But I felt that elementary particle physics at that time was too like botany. Quantum electrodynamics, the theory of light and electrons that governs chemistry and the structure of atoms, had been worked out completely in the 1940s and 1950s.

Attention had now shifted to the weak and strong nuclear forces between particles in the nucleus of an atom, but the field theory approach that worked so well for quantum electrodynamics didn't seem to work for these other forces. Indeed, the Cambridge school, in particular, held that there was no underlying field theory.

Instead, everything would be determined by unitarity, that is, the idea that probabilities always add to one, and certain characteristic patterns in the scattering of particles.

With hindsight, it now seems amazing that it was thought this approach would work, but I remember the scorn that was poured on the first attempts at unified field theories of the weak nuclear forces. Yet it is these field theories that are remembered, and the analytic S matrix work is forgotten.

I'm very glad I didn't start my research in elementary particle physics. None of my work from that period would have survived.

Cosmology and gravitation, on the other hand, were neglected fields, that were ripe for development at that time. Unlike in elementary particle physics, there was a well-defined theory, Albert Einstein's general theory of relativity, but it was thought to be impossibly difficult.

People were so pleased to find any solution of the Einstein field equations they didn't ask what physical significance, if any, it had.

This was the old school of general relativity that Feynman encountered in Warsaw. But the Warsaw conference also marked the beginning of the renaissance of general relativity, though Feynman could be forgiven for not recognising it at the time.

A new generation entered the field and new centres of general relativity appeared. Two of these were of particular importance to me.

One was in Hamburg, Germany, under the direction of Pascal Jordan. I never visited it, but I admired their elegant papers, which were such a contrast to the previous messy work on general relativity.

The other centre was at King's College, London, under the direction of Hermann Bondi. Bondi was another proponent of the steady state theory of cosmology, but he was not ideologically committed to it, like Hoyle.

I hadn't done much mathematics at school, or in the very easy physics degree at Oxford, so Sciama suggested I work on astrophysics. But having been cheated out of working with Hoyle, I wasn't going to do something boring like Faraday rotation. I had come to Cambridge to do cosmology, and cosmology I was determined to do.

So I read old text books on general relativity, and travelled up to lectures at King's College, London, each week, with three other students of Sciama. I followed the words and equations, but I didn't really get a feel for the subject. Also, I had been diagnosed with motor neurone disease, or ALS, and given to expect I didn't have long enough to finish my PhD.

Then suddenly, towards the end of my second year of research, things picked up. My disease wasn't progressing much, and my work all fell into place, and I began to get somewhere.

Sciama was very keen on Mach's principle, the idea that objects owe their inertia to the influence of all the other matter in the universe. He tried to get me to work on this, but I felt his formulations of Mach's principle were not well defined.

However, he introduced me to something a bit similar with regard to light, the so-called Wheeler-Feynman electrodynamics. This said that electricity and magnetism were time-symmetric.

However, when one switched on a lamp, it was the influence of all the other matter in the universe that caused light waves to travel outward from the lamp, rather than come in from infinity and end on the lamp.

For Wheeler-Feynman electrodynamics to work, it was necessary that all the light travelling out from the lamp should be absorbed by other matter in the universe. This would happen in a steady state universe in which the density of matter would remain constant, but not in a big bang universe where the density would go down as the universe expanded. It was claimed that this was another proof, if proof were needed, that we live in a steady state universe.

In Cornell in 1963, there was a conference on Wheeler-Feynman electrodynamics and the arrow of time [a term coined in 1927 by British astronomer Arthur Eddington to distinguish a direction of time that, according to Eddington, can be determined by a study of organisations of atoms, molecules, and bodies].

Feynman was so disgusted by the nonsense that was said about the arrow of time that he refused to let his name appear in the proceedings. He was referred to as Mr. X, but everyone knew who X was.

I found that Hoyle and Narlikar had already worked out Wheeler-Feynman electrodynamics in expanding universes and had then gone on to formulate a time-symmetric new theory of gravity. Hoyle unveiled the theory at a meeting of the Royal Society in 1964.

I was at the lecture, and in the question period I said that the influence of all the matter in a steady state universe would make his masses infinite. Hoyle asked why I said that, and I replied that I had calculated it. Everyone thought I had done it in my head during the lecture, but in fact, I was sharing an office with Narlikar and had seen a draft of the paper.

Hoyle was furious. He was trying to set up his own institute and threatening to join the brain drain to America if he didn't get the money. He thought I had been put up to it to spoil his plans.

However, he got his institute, and later gave me a job, so he didn't harbour a grudge against me.

The big question in cosmology in the early 1960s, was did the universe have a beginning. Many scientists were instinctively opposed to the idea, because they felt that a point of creation would be a place where science broke down. One would have to appeal to religion and the hand of God to determine how the universe would start off.

Two alternative scenarios were therefore put forward. One was the 'steady state theory', in which as the universe expanded, new matter was continually created to keep the density constant on average. The steady state theory was never on a very strong theoretical basis because it required a negative energy field to create the matter.

This would have made it unstable to run away production of matter and negative energy. But it had the great merit as a scientific theory, of making definite predictions that could be tested by observations.

By 1963, the steady state theory was already in trouble. Martin Ryle's radio astronomy group at the Cavendish Laboratory in Cambridge did a survey of faint radio sources. They found the sources were distributed fairly uniformly across the sky.

This indicated that they were probably outside our galaxy, because otherwise they would be concentrated along the Milky Way. But the graph of the number of sources against source strength did not agree with the prediction of the steady state theory. There were too many faint sources, indicating that the density of sources was higher in the distant past.

Hoyle and his supporters put forward increasingly contrived explanations of the observations, but the final nail in the coffin of the steady state theory came in 1965 with the discovery of a faint background of microwave radiation.

This could not be accounted for in the steady state theory, though Hoyle and Narlikar tried desperately. It was just as well I hadn't been a student of Hoyle, because I would have had to have defended the steady state.

The microwave background indicated that the universe had had a hot dense stage in the past, but it didn't prove that was the beginning of the universe.

One might imagine that the universe had had a previous contracting phase, and that it had bounced from contraction to expansion at a high, but finite density. This was clearly a fundamental question, and it was just what I needed to complete my PhD thesis.

Gravity pulls matter together, but rotation throws it apart. So my first question was: could rotation cause the universe to bounce? Together with George Ellis, I was able to show that the answer was no if the universe was spatially homogeneous, that is, if it was the same at each point of space.

However, two Russians, Lifshitz and Khalatnikov, had claimed to have proved that a general contraction without exact ...
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