The Story of Astronomy (26 page)

There are many theories about the nature of the universe we live in, and one of the most fascinating is that the universe itself is contained inside a black hole. The Schwarzschild radius of a black hole is given by the simple formula
r
= 2
GM
/
c
²
. Here
G
is the gravitational constant,
M
is the mass of the black hole and
c
is the velocity of light. Thus it is the mass of the black hole, the only variable in this equation, that determines the radius and therefore the boundary of the black hole. A black hole with the mass of the Earth, for example, would be about the size of a cherry, and it hardly needs saying that it would be an incredibly dense object. A black hole with twice the mass of the Earth would have a radius twice that of a cherry; it would be eight times the volume, and the density of the matter in it would still be very high but only one quarter that of the smaller black hole. If the black hole had the same radius as the Earth it would be incredibly massive, but the density would be only 5 × 10
¹⁸
times the density of the cherry-sized black hole. For very large black holes, with radii measured in millions of light years, the density of the matter inside comes down to manageable proportions. It is not necessary for a black hole to contain incredibly dense matter inside its horizon. The next question we need to ask therefore is: “what would be the radius of a black hole with a mass equal to
that of the whole universe?” If we knew the mass of the universe then we could calculate the Schwarzschild radius of such a hole very easily, and we know that the radius would be a distance of astronomical proportions. This would mean that the whole universe was contained inside a black hole. Nothing can escape from the universe. Anything trying to escape even at the speed of light would be drawn back to it by the gravity of all the mass in the universe. If we really were inside this black hole then how would it appear to us? It has to be admitted that it may well appear to be very similar to the universe we do actually observe.

The “black hole” description of the universe complements the idea of a three-dimensional but finite universe quite well. We would not be able to find the edge of our universe. We could send off a light beam in what we think is a straight line to the edge of the universe. After traveling for a few billion light years we think that our light beam has traveled in a straight line, but the four-dimensional being looking from the outside can see that it has followed a curve. He or she can calculate how long it will take for the beam to travel in a great circle and to come back from the opposite direction to the point from where it started. Looking in the direction of the light beam we are unaware that it is not straight; light from any bright object from the sky behind is bent in exactly the
same way by the gravitational field of the universe inside the black hole.

Similar arguments can be used to answer the question of where the universe was first created. Where should we point our telescopes to see the place where the Big Bang took place? The answer is that we can point the telescope anywhere in the universe and we are looking toward the place where it all began. It seems a very unsatisfactory answer, but from what we are able to deduce about the universe it does not seem to matter what point we choose, for to look at the universe from that point would show the same results as we see from our own vantage point. It is true that we see everything rushing away from us, faster and faster the further away it is. It can be argued from our three-dimensional minds that we are at the center of the universe, where the Big Bang took place, otherwise we would see galaxies and quasars at the edge of the universe traveling at different speeds away from us with the direction of the center of the Big Bang as the point where those speeds are the greatest. But this is not the case. We are like the raisins in a cake expanding as it is cooking. Each raisin “sees” all the other raisins rushing away from it in every direction, but it does not have a privileged position in its space.

Exploring the Boundaries of Space

For many years our understanding of the universe was based on the interpretation of data painstakingly collected through countless hours of observing the heavens with optical and, later, radio telescopes. But then came a major advancement: ground-breaking astronomical discoveries about the universe brought about with the aid of complicated mathematics.

There was a public lecture in the university town of Cambridge. The speaker had to be lifted onto the stage in his wheelchair by several assistants. He was wired up to a computer and a voice synthesizer was plugged into a public address system. On the arm of the wheelchair were a set of computer discs containing text and diagrams for the lecture. Pictures and diagrams appeared on the screen. The speaker addressed his audience by tapping the controls on a keyboard to operate the speech
synthesizer. A stilted, metallic, computerized voice rang out with a slight American accent. There were gaps between the words and sentences but the presentation was still fully comprehensible to the audience. Sometimes the speaker raised his head. Sometimes he lifted his eyebrows and turned to face the audience with a wicked grin. The lecture lasted for about 40 minutes and was greeted with rapturous applause. Professor Stephen Hawking acknowledged the ovation.

It used to be said that Isaac Newton was born in the year that Galileo died. This claim can only be made because the English and the Italians were using different calendars at the time; thus when Newton was born it was still 1642 on the Julian calendar in England but it was 1643 on the Gregorian calendar in Rome. Stephen Hawking was born on January 8, 1942—299 years after Isaac Newton was born and 300 years to the day after Galileo died. His career parallels that of both his predecessors.

Hawking's birthplace was at the “other place”; the university town of Oxford. This came about because his family moved out of Highgate in London at the outbreak of World War II. The family moved back to Highgate when the war ended and in 1950 they moved on again to live in St. Albans. It was there, at the local grammar school,
that Stephen Hawking received his secondary education and where he achieved the academic standard necessary to return to his birthplace at Oxford as an undergraduate student. As a bright student he was able to enjoy the social side of undergraduate life to the full and still manage to pass his examinations. By the time he approached his finals he had decided that he wanted to devote his life to an academic career. He was well aware of the rapid progress being made in astronomy and cosmology and he wanted these subjects to be the mainstays of his career. There is a story about his viva interview at Oxford, to determine his class of degree.
“If you award me a first,”
he said,
“I will go to Cambridge. If I receive a second, I shall stay in Oxford, so I expect you to give me a first.”
Did Oxford want to get rid of Stephen Hawking or were they perfectly fair in their dealings? It is hard to believe that the examination board took his words to be any more than a joke but the outcome was that they awarded him first class honors.

In the astronomical community the man that Hawking admired above all others was the blunt, outspoken and brilliant Fred Hoyle (1915–2001) at Cambridge. Hoyle was the main reason why Hawking chose Cambridge over Oxford for his postgraduate career when he had such strong connections with the latter university. The other reason for choosing Cambridge was that he had already
decided that he wanted to follow a career in cosmology and at that time Cambridge was much better placed to offer him that career. He quickly settled into postgraduate life, but it was not all roses. When he began his PhD he quickly discovered that his knowledge of mathematics was inadequate. To follow the research he had chosen to undertake he had to work hard to master the tensor calculus—a necessary requirement to be able to understand the work of Einstein and the complex calculations required for general relativity.

It was at Cambridge that Stephen Hawking met a young lady called Jane Wilde. She found him an eccentric and fascinating character, but she also soon discovered that there was to be a tragic side to him.

“There was something lost,”
she said later.
“He knew something was happening to him of which he wasn't in control.”

Hawking was 21 at this time. He knew that he was suffering from a medical problem and so he arranged to have an examination and a professional diagnosis. The result of the examination was not good news. The diagnosis showed that he was exhibiting the early symptoms
of a rare disease called amyotrophic lateral sclerosis (ALS), better known in Britain as motor neuron disease. It affects the nerves of the spinal cord as well as the part of the brain that controls the movement of the muscles and limbs. It was a terrible thing to happen to a young man in his prime, and Stephen Hawking knew that his problem could only get worse. There was no cure for the condition. According to the statistics of those suffering from the disease he had very few years left to live. But although he could never get better, there was a small consolation. The motor neuron disease did not affect his brain. He was still capable of doing his research and following the academic career he wanted.

In July 1965 Hawking married Jane Wilde. She knew that he was by this time suffering from crippling motor neuron disease and was fully aware of what she was taking on. Nevertheless she was firmly of the belief that he had a great future in spite of his growing disability. By this time Hawking had taken to using a walking stick to help himself to get around. Soon afterward his speech deteriorated and also his mobility. He had to change his stick for a pair of crutches. For a few years the illness progressed slowly, but his speech continued to deteriorate and there came a point when only his closest associates could understand what he
was saying. His mobility became seriously affected and from 1969 he was issued with a standard National Health Service three-wheeler invalid carriage to get around. However, by 1974 he found it more convenient to use an electric wheel-chair. By 1985 his speech had deteriorated so much that, after struggling on for a decade, he was obliged to use a speech synthesizer to give his lectures and to communicate with other people. This was actually a great help to him and he quickly found that he could communicate faster and better with the speech synthesizer than he had been able to do for many years without it.

Hawking is an exceptional case as far as motor neuron disease is concerned. Not only has he lived far longer than is usual for someone suffering from this condition, but he is still solving new and complex problems in cosmology at an age when many mathematicians are seen as well past their prime. We cannot help but admire a man who has pursued a demanding fulltime career while having to compete with the ravages of motor neuron disease. There are many anecdotes of his reckless wheelchair driving, his sense of humor and his methods of coping with his disability, but he will no doubt not wish to be remembered for his illness but by his contribution to cosmology. In his chosen field of study Stephen Hawking became the most charismatic figure in the second half of the 20th century.

As a young man Hawking had no difficulty using a telescope, but the direct observation of the universe was not his first priority. He was quite content simply to read about new observations in the astronomical press. He knew from the outset that he wanted to be a cosmologist. He was much more interested in aspects of astronomy other than direct observations. He was fascinated by the links with nuclear physics and by the mathematics of the remarkable objects such as neutron stars—and in particular black holes—that were very much at the cutting edge of cosmology in his time. He knew as much as most physicists about general relativity, and he also knew about the strange world of quantum mechanics. But whereas Einstein wanted nothing to do with quantum mechanics, Hawking was keen to bring relativity and quantum mechanics together, and this was an ambition in which he eventually succeeded.

He always entered enthusiastically into debate and was never backward in stating his own opinions. One of the best examples of his approach occurred at a meeting of the Royal Society in the early 1960s. At this time Hawking was just a young researcher, but at the meeting he challenged a statement made by his idol, Fred Hoyle. Hawking claimed that one of the quantities that Hoyle had specified in his equations as convergent was actually
divergent. Hoyle asserted again that the function converged, but the younger man stood his ground. Hoyle was furious at being challenged in public but he later accepted that Hawking's proof was correct. They were both scientists. It was the truth that mattered. Hoyle held no grudge against Hawking, and any friction between the two cosmologists was quickly forgotten.

Fred Hoyle (1915–2001), Hermann Bondi (1919–2005) and Thomas Gold (1920–2004) are the names chiefly associated with the steady-state theory of the universe, but in fact another British astronomer, James Jeans (1877–1946), put forward the idea in the 1920s. The steady-state theory, a competing cosmological view to the Big Bang, proposes that new matter is constantly created as the universe expands. After the discovery of background radiation thought to have come from the Big Bang, the steady-state theory quickly lost ground.

However, Hoyle went on to make a notable contribution to astronomy with his work on the evolution of the stars and in particular the way elements were created inside the stars. At first it was difficult to explain how the heavy elements could be created, but he showed that the necessary conditions for this to happen existed inside an exploding supernova. His classic paper on this subject,
known as the B
²
FH paper, was published with William Fowler (1911–95), Margaret Burbidge (b. 1919) and Geoffrey Burbidge (b. 1925) in 1957.