Guardian Shorts: Science That Changed The World By Tim Radford, Chapter 3
Follow this link to read Chapter 2The big bang and the cosmological aftermath
In 1882 my favourite mad Victorian cosmologist, Samuel Kinns tried to square the biblical and scientific stories of creation in Moses and Geology, or The Harmony of the Bible with Science. He identified 15 scripturally-recorded stages by which God made the world, starting with the words ‘And the Earth was without form, and void, and darkness was upon the face of the deep.’ Science, he reports ‘says that matter existed first in a highly attenuated gaseous condition, called aether, without any form, and non-luminous.’ This aether condensed to form nebulae, and then suns and worlds, which is matched by the next command ‘And God said, Let there be light.’ And so on. There were 1,307,674,368,000 ways in which 15 events could be sequentially arranged, says Kinns, and for science and the story of Genesis to be in such precise agreement at every stage could not possibly be by chance: obviously, God had revealed the story of creation to Moses, and Moses had (presumably) reported the timetable of events in the language and imagery appropriate to a Bronze Age tribe on the run in the desert of Sinai. The churchman was quite right about aether – that is, quite consistent with the science of the time – and even in 1909, Sir Oliver Lodge in his book The Ether of Space advocated ‘a view of the Ether which makes it not only present and all pervading, but also massive and substantial beyond conception. It is turning out to be the most substantial thing – perhaps the only substantial thing – in the material universe.’ Luminiferous aether or ether was a very old idea, invoked by Isaac Newton, and only reluctantly abandoned after Einstein’s 1904 paper on special relativity, and I quote Kinns and Lodge only to demonstrate that right up until 1965, anybody could believe and argue anything they liked about creation. There were really only three options. One was that the universe had no beginning. It was eternal and probably infinite and everything had always existed and although distant galaxies were indeed moving away, the universe would always look like that because new matter was being created continuously, to fill the gaps. The second was that the universe really did have a beginning and could possibly have an end. The second view had some religious support: Jewish, Christian and Islamic faiths all subscribed to the proposition that heaven and Earth were created, along with all the things on Earth, by Jehovah, God or Allah, but although these beliefs were enshrined in a Christian creed – and even non-believers knew this creed through choral masses composed by Bach, Palestrina, Byrd, Mozart and Beethoven – it is fair to say that nobody thought much about the details, and very few people subscribed to the precise sequence of events recounted in the Hebrew book of Genesis. To astronomers, the evidence of the receding galaxies was what mattered: if they were receding now, as if propelled by some initial force, then at a much earlier era they must have been much closer together and before that, all the stars and galaxies must have been just one big bursting blob of incredibly hot, dense stuff, and space-time would have been contorted in a very strange way called a singularity.
There were powerful scientific proponents for each proposition. Leader and spokesman for the continuous or continual creationist team was the astronomer-royal of Great Britain, Sir Fred Hoyle, and it was he who dismissively coined the term the big bang, to mock his opponents. His team-mates, Hermann Bondi and Thomas Gold, postulated that – to keep the visible galaxy quotient more or less steady – matter was continually created, from nothing, everywhere in the universe. It wasn’t such a big postulate. To replace disappearing galaxies, all the universe had to do was deliver one brand-new atom of hydrogen per litre of volume every billion years. Gold, Bondi and Hoyle were all distinguished scientists with formidable and enduring achievements behind them. On the opposing team were a number of scientists of equal distinction. Among these was a Belgian priest called Georges-Henri Lemaître who in 1931 had proposed a beginning for the universe in a ‘primeval atom’ or a ‘cosmic egg.’ Another was the Russian-born George Gamow, who in a famous paper known as Alpher-Bethe-Gamow (the real author was Gamow’s PhD student Ralph Alpher, but Gamow thought it would be fun to co-opt the name of the nuclear weapons scientist Hans Bethe to exploit a joke about the Greek alphabet and it was published on 1 April 1948) calculated that the proportions of hydrogen and helium in the universe could be explained by the cookery conditions in a very hot dense moment of creation. If the universe began hot, and then expanded, it must have cooled but still be detectably warm. So Gamow took a guess at the temperature of space itself: the space not just between the stars, but between the galaxies. The real point of all these stories – from eccentric clerics to fun-loving physicists – is that for most of the rest of the world, they were just stories: made up to explain the world in which we lived. I cannot now remember when I first heard someone say that there was speculation, and then there was wild speculation, and then there was cosmology, but it was probably already an old joke. Right up till 1965 there was no way of knowing who was right: whether the universe and everything in it, had a beginning, or whether it had always been there.
And then in 1965, two papers appeared in the same edition of Astrophysical Journal Letters. In the first of these, four physicists from Princeton proposed that if the universe had begun as an incredibly hot, small region of space-time – perhaps 10 billion degrees Kelvin – then all that heat would still be there, spread throughout the universe. The universe would cool as it expanded, and if the universe had been expanding for 10 billion years or more, then there would be no glow. This remnant temperature would in fact be ferociously low: a few degrees above absolute zero. But the dark wastes of space would still radiate something that might be ‘heard’ with sensitive antennae. Two of the four scientists had set about the technically challenging task of trying to devise antennae that could tune into this radiation. But, they wrote, two other scientists working for Bell Telephone Laboratories had already tuned into the distant cosmos and – wherever they pointed a sensitive antenna originally designed for communication with the satellite Telstar – they had detected radiation at 7.3cm wavelength, with an intensity that, converted to temperature, would be about 3.5°K, give or take a degree. In the same issue, the two Bell Telephone boffins, Arno Penzias and Robert Wilson, reported that they had detected an excess temperature that was ‘within the limits of our observations, isotropic, unpolarized and free from seasonal variations.’ That is, it wasn’t radiation from pigeon nests in the antenna structure; it wasn’t something in the atmosphere: it came from outer space and it came from everywhere. They had discovered the cosmic microwave background radiation that should exist if the universe had begun in a blast of heat and violence; they had detected the faint and fading rumbles of the big bang. Someone had predicted the discovery. Someone else, working independently and not even looking for that particular result, had discovered it. Once again, humanity’s picture of the universe had changed. The universe was not eternal or infinite. It had a beginning. Matter, space and time had come into existence at some point in the measurable past.
So suddenly, serious cosmological researchers had somewhere to start: a beginning. They could contemplate the cosmos as it seemed to be now, and speculate about the initial conditions that made stars, galaxies, gas and dust fall out of some unimaginably hot, dense moment. They could use the Copernican principle to assure themselves that the physics that seemed to be true in the solar system would be just as reliable far away and long ago, nearer the beginning of time. They could use the laws of thermodynamics to begin to compose a budget of mass and energy that would account for the things they could see through optical telescopes and hear with radio telescopes and detect with x-ray telescopes delivered above the atmosphere by experimental rockets. They could use logic, mathematical physics and observation to collect data, frame hypotheses and test them. Within a dozen years, Penzias and Wilson were heading for a Nobel prize, and another Nobel laureate, Steven Weinberg, could compose a popular science classic called The First Three Minutes, which provided an account of exactly that: the things that must have happened in the first three minutes of time, in tiny, detailed, blow-by-blow stages when the world was brand new, and expanding at the speed of light. The universe, wrote Weinberg when he reached the end of his self-allotted third minute ‘will go on expanding and cooling, but not much of interest will happen for another 700,000 years’ when electrons and protons become cool enough to form stable atoms, and get on with the job of making stars and planets. That he could write such a book at all was made possible by Penzias and Wilson in 1965. The most important thing accomplished by their discovery ‘was to force us all to take seriously the idea that there was an early universe.’ The intellectual energy released by the publication of the two papers in 1965 drove research in a number of unexpected directions: theorists used mathematical logic, known physics and a series of ‘what-if’ scenarios to explore the seemingly unknowable – the first few minutes of creation – and ended up with a series of predictions, some of which have been confirmed, both by observation of the distant heavens with ever-more sophisticated instruments, many of them mounted on orbiting spacecraft, and by experiments in a series of increasingly powerful accelerators and colliders in which they could explore the creation of sub-atomic particles and – even more satisfyingly – actually spot the ones that their theories told them should exist. The hectic race to chronicle the brief history of time led researchers to unexpected conclusions.
One of the most stylish intellectual advances happened in the 1980s, in pursuit of a particle that theory said should exist, and should be difficult to miss, but experience said didn’t exist or at least had never been spotted. The notional missing object was called the magnetic monopole: that is, a tiny magnet with only one pole, which in itself would be pretty strange. It would also be massive, and difficult not to observe. A number of different theories predicted these oddities: no sighting has ever been confirmed. Alan Guth, a young US physicist, picked up the entirely academic challenge of explaining why a particle that should be as easy to find as currants in a bun didn’t seem to exist anywhere. He proposed a strange, short episode in the very early universe – well inside the first trillionth of a second – when space itself did something strange and expanded far faster than light. This bizarre period of inflation ended with a universe so large that the initial pool of monopoles would, in effect, have been diluted out of existence. If a currant bun suddenly became as big as the solar system, you’d not expect to ever see a currant. In fact, cosmic inflation turned out to be a very neat idea: it explained why the universe was more or less the same in every direction, and it explained why the critical density of the universe seemed so nicely balanced between two alternative fates, continual expansion and eventual collapse. Cosmic inflation is not something that can be tested, even in the most powerful particle collider. So it cannot be demonstrated, the way gravitational force is demonstrated with every rocket launch, and every throw of a cricket ball: but it explains so many things that it is now orthodoxy. Physicists still argue about how and why it happened and why and when it stopped, and what exactly happened during the inflationary period, but they seem inclined to accept that there was one. They also accept that something very strange happened when the energy of creation started to condense into matter (the equation that absolutely everybody knows – the one that says that e=mc2 – means exactly what it says: energy and mass are equivalent and interchangeable) then what dropped into being should have been equal quantities of matter and antimatter. This is what happens routinely in particle accelerators; it is what theorists had predicted even before the first discovery of antimatter. But we live in a universe composed seemingly only of matter, and quite a lot of this matter has yet to be identified – most of the masses of galaxies are made up of something unexplained and unidentified, but massive, called ‘dark matter’ – so there remain a number of partly-answered or unanswered questions.
The joyous investigation of the cosmos also raised interesting questions about space and time and the future of everything. What, actually, is time? Does it exist? If you can go in two directions in space, why can you go only in one direction in time? And if space can expand, then it must be something, it must have some sort of fabric: it cannot be nothing, it cannot be emptiness. It must have some sort of energy because the farthest galaxies are receding faster than predictions say they should. The upshot is that physicists can be very precise about some things – that the universe, for instance, is 13.798 billion years old – and very vague about others. They can explain and account for the stars and galaxies but these add up to only about 4% of the mass of the observable universe. The other 96% remains unexplained. They know to great precision the fundamental values and measurements of gravitational, electromagnetic and other forces and so on, but they cannot explain why these forces have the values they do have: on the other hand, they know that if these forces were even the slightest bit different, we would not be here. Matter would not have condensed at the right pace into nebulae, and then into stars. Stars would not have slowly ‘cooked’ hydrogen into carbon, oxygen and iron and all the other elements, and planets would not have formed, and without planets, water, carbon and oxygen, there would have been no life, and no curious, wondering forms of intelligent life. The adventure that began with the 1965 papers has answered some questions with unexpected precision and left others wide open. So it is possible to have some sympathy with the ridiculous Samuel Kinns with whom we began the chapter. It is worth pointing out that 120 years on, we are still left with a universe filled with something that seems to be highly attenuated and without any detectable form, and non-luminous. Aether wouldn’t be the right word, but – since nobody ever found a specimen of aether, or even a proper definition of it – it would not be the wrong word either. And the expectations implicit in Kinns’s argument haven’t gone away. Does it look as though the universe was made so that intelligent life could exist? Or does intelligent life exist because universes are forever popping into random existence and we just happen to be in the one that looks exactly right for the only intelligent life we know about? Freeman Dyson, one of the giants of modern physics, once observed that the universe ‘in some sense must have known that we were coming.’ Albert Einstein once said that the most incomprehensible thing about the universe was that it was comprehensible. Steven Weinberg’s last paragraph in his book The First Three Minutes went even further. ‘The more the universe seems comprehensible,’ he wrote ‘the more it also seems pointless.’
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