B00B7H7M2E EBOK, page 19
It hadn’t escaped Hubble’s notice that there were connections between the observations that Slipher, Humason and he were making and the solutions that physicists such as Willem de Sitter, Alexander Friedmann and Abbé Georges Henri Lemaître were getting from the equations of Albert Einstein – solutions that implied that the universe must be either expanding or contracting.
The debate about whether the universe is expanding, shrinking or just holding its own has a history that goes back long before the 20th century. Ancient and medieval thinkers regarded the Earth as the region of the universe where change, decay and evil held sway, while all beyond the Moon was unchanging and perfect. Newton echoed these sentiments to the extent of believing that a universe created by God could not be changing dramatically over time, for constancy and stability reflected the nature of God, while change (implying decay and conflict) did not. Newton was also of the opinion that if a system goes far awry, as he realized the planetary orbits would over time, God would set it right again, so things would never be allowed to change too drastically.
As for the specific question whether the universe might be expanding or contracting, Newton decided on logical grounds that it couldn’t be doing either. He reasoned that if it were expanding or contracting, there would have to be a centre to the motion – in other words, a point away from which it was expanding or towards which it was contracting. But matter distributed uniformly through an infinite space (as Newton believed it was) has no centre. Newton couldn’t foresee that others nearly three centuries later would find that his own equations led to the prediction that the universe must be expanding or contracting. In the 18th century, Kant, who took off from Thomas Wright’s picture of the universe as a flattened slab of stars, thought that if the universe were not perfectly balanced between the orbital motion of stars and their gravitational attraction for each other, it would end in destruction and chaos and lack ‘the character of that stability which is the mark of the choice of God’.
Although it was out of fashion from the mid-19th century onwards to include God in scientific statements, the feeling that there was something sublimely rational and sacred about an unchanging universe and something shifty and distasteful about one that changed had by no means disappeared. It had become a doctrine of science rather than of religion. In an interesting turnabout, one of the 20th-century reasons for clinging doggedly to the notion of a static universe (one that isn’t expanding or contracting) was that an expanding universe – which almost surely must have had a beginning – seemed more likely to require a creator. That was a possibility some had considered safely put to rest.
Albert Einstein resisted the idea of an expanding or contracting universe for reasons having to do with his scientific intuition. Soon after he produced his general theory of relativity in 1915, Einstein and the Dutch astronomer Willem de Sitter realized that solutions to Einstein’s equations implied that the universe was either expanding or contracting. Einstein was not necessarily one to cling to old assumptions, but at this juncture he did, and he dug in his heels. Annoyed by the ridiculous upshot of his equations, he wrote, ‘To admit such a possibility seems senseless.’ Such strong aversion did he feel that he decided to adjust his theory to cancel out the offensive prediction. He put in a new constant of nature – a ‘cosmological constant’, a mathematical term that would allow the universe to be static. He was later to regret this move, calling it ‘the biggest blunder of my life’. But the notion of a cosmological constant didn’t disappear when Einstein reneged on it. It still haunts physics.
While Einstein was tinkering with his equations, Russian mathematician Alexander Friedmann decided instead to take Einstein’s theory at face value. Friedmann insisted that if there is a cosmological constant, its value is probably nothing else but zero. He pointed out in one of his first papers dealing with Einstein’s theories that the assumption that the universe is static had always been only an assumption. No observations required one to believe it. Einstein himself was well aware that this was the case.
Friedmann proceeded to find not one, but a number of solutions to the cosmological equations of general relativity. Each solution described a different sort of universe. See Figure 6.1.
Friedmann predicted that regardless of where we were to situate ourselves in the universe, in any galaxy, we would find the other galaxies receding from us. The further away a galaxy is from us, the faster it’s receding, twice as far away, twice as fast. For an analogy, imagine a loaf of raisin bread rising in the oven. Sitting on any raisin while the dough rises and expands between the raisins, we would see every other raisin moving away from us, twice as far, twice as fast. We cannot of course directly observe the universe from any vantage point except our solar system, but at least from here that is the sort of recession that Hubble observed in 1929 with the 100-inch telescope at Mount Wilson. The outward-bound speed of a galaxy is directly proportional to its distance from us. Twice as far away, twice as fast.
Figure 6.1
Three models of the universe: (a) The universe expands to a maximum size and then recollapses; (b) The universe expands rapidly and never stops expanding; (c) The universe expands at exactly a critical rate to avoid recollapse.
Belgian astrophysicist and theologian Abbé Georges Henri Lemaître discovered solutions to Einstein’s equations that were similar to Friedmann’s. What intrigued Lemaître most was what the equations and solutions could reveal about the origin of the universe. It was Lemaître who first described something like what was soon to be dubbed the ‘Big Bang’, though he didn’t give it that name. His suggestion was that there must have been a time when everything that makes up the present universe was compressed into a space only about 30 times the size of our Sun – a ‘primeval atom’. Partly because he was a priest and theologian as well as an astrophysicist, some of Lemaître’s colleagues greeted his idea with derision. It smacked too much of Genesis.
Though Friedmann’s theoretical work ended prematurely – he died at the age of 37 – and he remained largely unknown except among mathematicians, Lemaître’s work came to the attention of observational astronomers, largely through British physics giant Arthur Eddington, whose student Lemaître had been at Cambridge, and another of Eddington’s students, George McVittie.
Thinking about the universe as an expanding lump of raisin bread dough led to interesting speculation. Would it be possible, assuming the necessary technology existed, to travel to the surface of the loaf and find the border of the universe? What would be beyond that? Unfortunately those questions probably have no real meaning. Eddington fielded them by providing an analogy of a balloon and an ant:
The balloon has dots painted all over it. The ant crawls on the surface of the balloon. All that exists for this ant is that surface. It can’t look outward from the balloon’s surface or conceive of an interior to the balloon. Air is let into the balloon and the balloon expands. The ant sees every dot on the surface of the balloon moving away. Anywhere the ant crawls on the balloon, every dot is moving away. The ant may wander forever, like the Flying Dutchman, but it will never find an edge or a border to this universe. Our situation in our own universe is probably similar to the ant’s, but with more dimensions. There is no edge from which we would see galaxies in one direction and absolutely nothing in the other.
The question of a ‘centre’ has cropped up often in this book, most recently in Newton’s objections to an expanding or contracting universe. Where in the universe did the expansion begin? From what centre point is everything retreating? The Big Bang was an explosion that sent everything flying outwards. Even granting that there are no absolute directions in the universe, it would seem that beings riding on a piece of debris from this explosion would have the right to assume there is an answer to the question: Where did the explosion take place in relation to where we are now?
Eddington’s balloon analogy helps with that question as well: Can the ant ask where on the balloon’s surface the expansion began? No. From our vantage point, watching the ant, we can see that that question would be meaningless. No dot on the balloon represents the ‘centre’ of the expansion. Newton failed to imagine a situation in which all points in the universe are moving away from all other points, with no ‘centre’ to the expansion, no direction towards which we can look and insist that it all began there.
Paradoxically, living in an expanding universe means that there is a direction in which we can peer and see something different, perhaps even see an ‘edge’. That direction is the past. What’s more, in any space direction we look, we look towards the origin of the universe, for any direction is towards the past. That is true not only when we gaze deep into space with telescopes. It’s true even in the small area of the room in which I write this paragraph. What I see of the opposite wall is old news. Of course the delay with which the picture of that wall reaches my eyes is not worth considering because light, and thus any picture that comes into my eyes, travels extremely fast, 186,000 miles or 300,000 kilometres per second.
When speaking of cosmic distances – where measurement in light years is more meaningful than measurement in miles or kilometres – light speed isn’t terribly fast, and the delay can’t be ignored. As the history of cosmic measurement continued in the 20th century, measurement of distance in space was to become inextricably bound up with measurement of distance in time. One can no longer ask how far away something is without also implying the other question: How far in the past is it? Questions about what is meant by an ‘edge’ or ‘outside the universe’ become entangled with questions about what is meant by a ‘beginning’ or ‘before the universe’.
In the 1930s, many astronomers and theoretical physicists were taking Hubble’s observations as direct evidence that the universe is expanding, but resistance to the idea had not ended and it was not all from within scientific circles. As was the case with Newton’s Principia, the public were aware of stupendous changes going on in science. Einstein’s theories were popularized in many forms and his name became a household word. When a new discovery or theory is fundamental enough to impinge on everyone’s concept of the universe and reality – not just a few specialized scientists – there tends to be a feeling that others besides scientists should have a say about what is True in this matter.
Nearly everyone who reads popular science books remembers that Einstein didn’t like the idea of an expanding universe. Fewer are aware of the ugly opposition from some who held political power. In 1936, in the Soviet Union, Joseph Stalin began a purge of scientists whose scientific findings and conclusions were not politically correct. One of the forbidden ideas was that the universe was expanding.
In his book Fireside Astronomy, British astronomer Patrick Moore tells of the experiences of his friend Nikolai Kozyrev. Kozyrev was an astrophysicist at the Pulkovo Observatory near St Petersburg. In November 1936 he was arrested and physically assaulted. In May 1937 he came to trial. What his offence was was never clearly stated, but he was sent to prison. After two years Kozyrev ended up in a labour camp, and there a fellow prisoner reported him for holding scientific views about an expanding universe that were contrary to Soviet doctrine.
Kozyrev was resentenced to 10 years’ imprisonment. When he appealed, the sentence was changed to death. There was no firing squad at the labour camp, and a second appeal got the sentence reduced again to 10 years. Gregory Shain, later the Director of the Crimean Observatory, rescued Kozyrev from this appalling situation. He managed to get him transferred to Moscow in 1945 and saw him set free in 1947. Kozyrev returned to his work in astrophysics, having lost 10 years. Other Soviet scientists were less fortunate. Many were executed. The persecution even extended to the scientists’ families. Kozyrev’s wife was imprisoned, though not for such a long period as her husband.
Elsewhere the opposition was less extreme, and it soon focused not so much on whether the universe was expanding as upon whether it had a beginning. It was here that discoveries in astronomy and physics theory trod most seriously on philosophical and religious sensibilities.
One interpretation of Galileo’s trial sees it as a clear contest between the authority of religion and the authority of science. In the 20th century, those who had thought science had won that contest long ago were chagrined to find science seeming to uphold a religious point of view. Anyone for whom the idea of a God was anathema now had to face the unthinkable: a beginning . . . a moment of choice about whether there would be a universe . . . a creator.
Not that all who found the Big Bang philosophically disquieting were self-declared atheists. Many men and women, often without giving much thought to whether this conflicted with their religious beliefs, had put their trust in the power of science to explain the world. Since the time of Newton it had been a growing assumption both in and out of science that scientific laws and explanations underlie everything that occurs, even those things that remain most mysterious and hidden, and that, given time, human minds ought to be able to discover those laws and explanations. The Big Bang threatened that cherished assumption.
A passage from Robert Jastrow’s 1978 book God and the Astronomers sums up the situation. Jastrow is himself an astronomer and an agnostic, but he chides his colleagues for their reaction: ‘the response of the scientific mind – supposedly a very objective mind – when evidence uncovered by science itself leads to a conflict with the articles of faith in our profession’. He goes on to say:
This is an exceedingly strange development, unexpected by all but the theologians. They have always accepted the word of the Bible: In the beginning God created heaven and earth. To which St Augustine added, ‘who can understand this mystery or explain it to others?’ The development is unexpected because science has had such extraordinary success in tracing the chain of cause and effect backward in time . . . Now we would like to pursue that inquiry farther back in time, but the barrier to further progress seems insurmountable. It is not a matter of another year, another decade of work, another measurement, or another theory; at this moment it seems as though science will never be able to raise the curtain on the mystery of creation. For the scientist who has lived by his faith in the power of reason, the story ends like a bad dream. He has scaled the mountains of ignorance, he is about to conquer the highest peak; as he pulls himself over the final rock, he is greeted by a band of theologians who have been sitting there for centuries.
Three Cambridge physicists declined the invitation to sit down with the theologians. Just as there had been excellent alternative ways of explaining Galileo’s findings without having to have a moving Earth (Tycho Brahe’s model, for example), there were excellent alternative ways of explaining Hubble’s and Einstein’s without having to have a beginning.
In 1948 Hermann Bondi and Thomas Gold, both originally from Austria, and Fred Hoyle introduced theories that allowed the expansion of the universe to happen without requiring that the universe have a beginning in time. Their ‘Steady State’ theory became the Big Bang’s major competitor. According to Bondi, Gold and Hoyle’s proposal, the universe hasn’t always contained all the matter that is in it today. As the universe expands, new matter emerges to fill in the broadening gaps, and the average density of matter in the universe remains the same. While the stars in a galaxy like ours burn out and the galaxy dies, new galaxies are forming from the new matter. There would be no beginning or end to a Steady State universe. The unwelcome hint of ‘creation’ suggested by Big Bang theory would be eradicated.
For at least two decades, the scientific and philosophical debate went on between those who favoured one theory and those who insisted on the other, until finally, in the 1960s, new evidence came to light that Steady State theory could not explain and Big Bang theory actually had predicted. It should come as no surprise that Hoyle, one of the inventors of Steady State theory, was the author of one of the most insightful books about the Copernican revolution, a book with considerable sympathy for Ptolemy that points out clearly how both Copernicus and Ptolemy were correct.
The observational evidence that weighed in so heavily in favour of the Big Bang was not evidence from an optical telescope. By then astronomers had discovered that the old phrase ‘I won’t believe it until I see it’ represented a ridiculously limiting attitude. Most of what goes on in the universe can’t be ‘seen’ at all. It happens beyond the visible range of the spectrum.
It was no coincidence that studies of the heavens were for centuries only studies of visible light, and that radio astronomy was the first new astronomy to emerge. In only those two parts of the electromagnetic spectrum – the optical and radio ranges – are there wavelengths that can pass through the Earth’s atmosphere. Radiation in the infrared range can reach as low as the highest mountains. The Earth’s atmosphere blocks other radiation. Study of ultraviolet rays, X-rays and gamma rays coming from space can’t be done at all without telescopes above the atmosphere. It wasn’t possible to put them there until the late 1950s.
Radio astronomy began a quarter of a century before that, almost by accident. In the 1930s, trans-Atlantic phonecalls took place by radio transmission and were plagued by static. The task of finding out what was causing the static fell to Karl Jansky of the Bell Telephone Laboratories in Holmdel, New Jersey. Jansky built a special radio antenna – a long array of metal pipes – to aid him in his investigation.
As Jansky sorted out the static, he found that most of it came from thunderstorms, but there was also a faint hissing static that couldn’t be so easily explained. The hiss was strongest when the region of the sky in the direction of the constellation Sagittarius was overhead. The central regions of our Galaxy lie in that direction. When this part of the sky was below the horizon, the hiss was weaker but it never disappeared entirely. The expectation prior to Jansky’s discovery had been that the Sun would be the strongest source of radio waves in the sky, just as it is the brightest source of light. Now it seemed that a source could be very ‘bright’ in another part of the spectrum but show up not at all in terms of visible light. Jansky knew he had discovered the centre of the Galaxy. What else was out there that we were missing?
