by Adrian Berry
The behaviour of matter at supercold temperatures has much in common with its opposite in the realm of the extremely hot. Inside fast-spinning, superdense pulsar stars, where the heat exceeds 100 million degrees, matter is also in a superfluid state. Supercold helium will give astrophysicists an excellent idea of what happens inside these remnants of giant stars whose very atoms have been crushed out of existence.
The most bizarre of all phenomena which supercold matter is helping scientists to understand are ‘cosmic strings’. These are believed to be strings of matter of huge mass but almost infinite thinness. An inch of such a string, according to , of Tufts University, Boston, would weigh 10 million billion tons. Such strings may still exist.
Millions of light-years long, their huge gravitaitonal attraction is believed to have formed the galaxies in the earliest epoch of the universe. Their superfluid behaviour is thought to be analogous to that of liquid helium near absolute zero. They may still exist.
But the most practical use for this refrigeration may be in high-speed computing by means of superconductivity. There is almost no ‘noise’ or resistance to an electric current at near absolute zero where atoms are so still, and a signal can travel unimpeded. The lower the temperature, the more thinking that can be done with less and less energy.
Brightest of the Bright
What is the difference in brightness between the brightest star and the faintest? This would make a good quiz question, but I will give the answer at once: the difference between the Sun, with an apparent magnitude of-26, and the faintest known stars that the Hubble Space Telescope can only see after an hour’s time exposure, magnitude 30, encompasses a brightness ratio of more than 1022, or 100 billion trillion.
The whole system of magnitudes, invented by in the second century bc, has become extremely complicated and is surely due for revision.
It seemed simple enough at first. The brightest stars, like the best athletes, were of the ‘first magnitude’ or the ‘biggest’, going down to the sixth. This worked well so long as nobody knew of any connection between distance and brightness, and so long as there were only six magnitudes. Ptolemy, four centuries later, slightly complicated matters by using the words ‘greater’ and ‘smaller’ to distinguish between stars within the same magnitude. But it was still ’s system.
Then Galileo’s new telescope upset everything. ‘With this new glass,’ he proclaimed in 1610, ‘you will detect below stars of the sixth magnitude such a crowd of others that escape natural sight that it is hardly believable.’
Today, with magnitudes down to at least 30 and all measured logarithmically (each magnitude is 2.512 times fainter than the last), the brightness of most classes of objects is well known. The full Moon is -12, a quarter Moon is -10, and at its brightest is about -5. Sirius is -2, is 0 (implying, confusingly, that has no magnitude at all), and the naked eye limit is of course 6.
Beyond that, binoculars can distinguish stars down to 9, amateur telescopes down to 14, and a five-metre to 20. The can see magnitudes of 24 and fainter.
But how bright are distant stars in reality? Absolute magnitude provides that answer, by assuming that we see them at a theoretical distance of 32.6 light-years. By this scale the Sun is a mere 4.85 while Rigel is a dazzling -8. (I’m glad I do not live too close to Rigel.)
On top of this, we have photographic magnitude, showing how bright stars seemed on black and white film, and a new kind of magnitude based on the difference between a star’s natural appearance and its photographic magnitude called the ‘colour index’.
Add to that bolometric magnitude ( a name based on an ancient device called a bolometre) which measures a star’s total radiation, in all wavelengths except radio. Astronomers say this is the simplest classification that can be devised, but I have my doubts.
Meanwhile here is another quiz question. If it is true that a network of telescopes on the Moon will have 100,000 times the resolution of the , what will be the faintest magnitude it will be able to detect? The answer, assuming a long time-exposure made possible by 14-day lunar nights, is a staggering 42. In short, when astronomers reach the Moon, the brightness ratio between brightest and faintest will be nearly 2.512 , which is 10 or 1 followed by 27 zeros.
Smallest of the Small
The 1957 film The Incredible Shrinking Man shows the hero - or rather the victim - suffering from an unexplained radiation accident which causes him to become inexorably smaller. First he is the size of his cat, then of an insect, and finally he vanishes. At this point, unfortunately, the film stops and, unlike the London University physicist and his colleagues, we have no chance to explore the realms of the almost infinitely small.
These scientists are not concerned even with the structure of atoms, but with ‘superstrings’, objects that compare in size with atoms as an atom compares with a planet. With a diameter in centimetres of 10 , a decimal point followed by 33 noughts and then a 1 - the constant - superstrings form the bedrock of all matter.
Everything is made of them, including the supposedly empty space between the stars. They are the smallest objects that can exist. ‘Without them, nothing else would exist,’ said. ‘There would be neither time nor space nor matter. There would be no stars or planets. There would be no universe.’
‘The theory of superstrings is beautiful, wonderful, majestic - and strange,’ says his colleague, of Princeton University. ‘But it’s not weird.’
At the level of superstrings, there is a world of unbelievable turbulence, of tossing and foaming and continuous change. In the words of John Wheeler of the University of Texas, Austin: ‘Space is like an ocean which looks flat to the aviator who flies above it, but which is a tossing turmoil to the hapless butterfly which falls upon it. Regarded more and more closely, it shows more and more agitation until the structure is permeated everywhere with strings and holes. ’s general theory of relativity forces this foam-like character on all space.’
Why should these mysterious superstrings exist? There is no experimental evidence for them and, given their size, there may never be. Despite the scepticism of many physicists, Green and , of Princeton, devoted the Eighties to pursuing the superstring. ‘I never worked with such intensity in my life,’ says . ‘I’ve never been so immersed in a subject.’
Green was eventually able to tell a meeting of the British Association for the Advancement of Science that he had at last reached the definite conclusion that superstrings are the only elegant way to reconcile the two principal theories that have underpinned twentieth-century physics: one that predicts the behaviour of planets, stars and galaxies, the other that describes the sub-atomic world.
The first of these, ’s general theory, states that the gravity of a planet (or any large mass) creates the time and space surrounding it. In other words, time and space have a physical structure as real as that of matter.
The other theory, of quantum mechanics, describes three of the fundamental forces of the universe which operate at extremely small distances: electromagnetism; the weak nuclear force that causes radioactivity; and the strong nuclear force that binds atoms.
But quantum mechanics says nothing about gravity, the fourth and weakest of the fundamental forces, which seems to work without needing any quantum esoterics to explain it. Yet gravitational waves, although felt across vast distances - by stars holding planets in their orbits - must travel.
By introducing the concept of the ‘graviton’, a particle that transmits gravity just as a photon transmits light, Green and Schwarz have been able to explain how superstrings work. At the tiny distances of the superstring world, gravity distorts and twists everything. It is responsible for the continuous turbulence that describes.
Some mathematics even more abstruse than this suggests also that, in the very early universe, a few fractions of a second after the Big Bang, there were ten dimensions instead of the familiar four (length, breadth, height and time) we know today. The other six dimensions are still there. But in the words of physicist ,
‘they remained curled up like rosebuds that never bloomed, locked in tight geometries of the immeasurably small.’
Yet this means that at the instant of the Big Bang all ten dimensions would have been, in some manner, equal. They would have been responsible for all four fundamental forces. Thus, superstring theory provides a grand unity of the forces, a ‘theory of everything’.
But will the theory ever be of any practical use? ‘We must be cautious in saying that it won’t,’ said. ‘Remember how , who split the atom, described the idea of usable atomic energy as moonshine . . .’
An Odyssey of the Sun
Did the earliest humans, when they looked up into African skies three million years ago, see the same Sun as we do? The difference would have been almost impossible to detect. But it was there none the less, for the size and brightness of the Sun has increased by a third since its formation some 5,000 million years ago. This process is going to continue until it eventually grows so huge that it will eat up the inner planets Mercury and and come close to devouring the Earth.
Last week three astronomers announced the results of their ‘Odyssey of the Sun’. They had fed the vital statistics of our parent star into a computer, programmed the machine to understand the laws of thermonuclear fusion, and foretold its vast and mysterious future.
‘Predictions about the future of the Sun have been made before,’ said one of them, Arnold Boothroyd, of the University of Toronto. ‘But ours is superior because it was the first to be tailor-made for the Sun itself, rather than some hypothetical Sun-like star. We used all the correct numbers. We fed in its radius, mass, age, surface temperature and known composition. And then we told the machine to prophesy its future.’
Their findings foretell a series of stellar adventures, each stranger than the last, that can only be called an odyssey of the skies. The most unpleasant surprise is that the Earth will only be habitable for a quarter of the time than had been expected. It had been supposed that 5,000 million years – a time equal to the Sun’s past age - would elapse before its growing heat became intolerable to terrestrial life. But the computer model reveals that we shall have to start evacuating Earth within a ‘mere’ 1,100 million years, as the Sun brightens by another 10 per cent and its ever increasing heat drives all the carbon dioxide out of our atmosphere. Without photosynthesis, plant life will perish and it will be time for humans to migrate from this barren rock.
Some 2,400 million years after this the Sun will have started to exhaust the supply of hydrogen fuel in its core, which will have been creating energy steadily for all these billions of years as it was being converted into helium. Now the helium itself starts to undergo nuclear burning, and the Sun grows even bigger, and now redder.
‘The expanding Sun will stop just short of eating up the Earth and Moon - another surprise finding,’ said Boothroyd. ‘It will have become a red giant star with a diameter 200 times what it is at present and a brightness some 5,000 times greater. But here the expansion must end. Because it is a star of comparatively small mass, its helium will not become hot enough to ignite and burn to become another element. Instead, because of this lack of further fuel to burn, the Sun will throw out mass that will form into vast rings of luminous gas and dust thousands of millions of kilometres around it.’
Unable to expand any further, the Sun must now contract. Within a period of about 100 million years, its nuclear fuel exhausted, it will shrink to the size of the Earth, a mere 13,000 kilometes in diameter, but with three-quarters of the Sun’s original mass squashed into it. This will make it a ‘white dwarf star, an object so dense that a piece of its material the size of a matchbox will weigh about ten tons. , of the University of Illinois at Urbana-Champagne, said: ‘This will be an extraordinary object, faint, half planet and half star, still smouldering from the remains of the nuclear power in its core. About a fifth of the stars in our Milky Way galaxy are such white dwarfs.
‘Its gravitational compression will be so strong that mountain ranges on its surface will be no more than a few inches high. Any astronaut who ventures to tread on it will be instantly squashed flat. Yet it will still have an atmosphere about half a mile thick.’
Another 1,000 million years pass, and all nuclear activity has ceased. The Sun has lost all luminosity and has become a ‘black dwarf. It will retain its density but be invisible. While not to be confused with a black hole, it will have something of its character, for it will be an object of deadly peril to astronauts who, unaware of its existence, might become trapped in its orbit.
An incredible journey, indeed, and a terrible inevitable fate for the sole source of warmth and life on Earth - and, of course, for Earth itself.
Going Bats in the Basement
Science, like many other activities, is a random mixture of the sublime and the ridiculous. Seldom has this combination been more apparent than in an extraordinary correspondence in an American journal about the creation of new universes.
This speculation has been brought right down to earth with a statement in the journal Science by , a physicist at the Massachusetts Institute of Technology, who says: ‘We now have the tools to seriously discuss the prospect of creating a universe in your own basement.’
To most people space is just empty nothingness. But to physicists, this statement ceases to be true at the sub-sub-sub-microscopic level. If we could examine empty space of a hundred-millionth of a trillionth of a trillionth of a millimetre, (on the scale of Planck’s Constant), we would find a cauldron of activity. It would be full of interconnecting ‘worm-holes’, through which objects would vanish into the past or future. To Guth and many of his colleagues, these ‘worm-holes’ are the gateways to other universes, regions that might not be microscopic at all. A person who compressed himself to a tiny size, like going through a very small looking-glass, would find himself in an expanding region with dimensions which were of light-years in extent. (See Through a Wormhole to the Stars?, p. 234.) Hence the professor’s bold and quite serious conclusion that new universes may be constantly coming into existence, even in the empty space of one’s basement.
So much for sublimity: now for the ridicule. , a psychologist from Hunter College, New York City University, has written this reply to Guth in Science. ‘I was particularly interested to learn that mathematical tools are now available to create a universe in the basement. I was able to locate an empty room in the basement of Hunter College, and I persuaded several colleagues to join me in creating a new universe during ’s hours on Wednesday afternoon.
‘But we encountered numerous theoretical problems: Hunter College is short of space. Since the newly created universe is expected to expand exponentially, the problem of finding intergalactic space must first be discussed with administration.
‘Who will be of the universe, and will it be run on hard or soft money? What if new life emerges within this universe? Hunter College is unionized, and so it would be very difficult not to grant tenure to any new life-form, regardless of its chemical basis.
‘What if the universe was composed of (violently explosive) anti-matter? It would be just my dumb luck to have a universe expand out of the basement up to the sixth floor, and annihilate the psychology department. Isn’t it enough to have to worry about perishing for lack of publishing?
‘Our conclusion is that it is currently much too dangerous to attempt the creation of a new universe in the basement. If at all possible, we recommend the roof instead.’
Running Water on Mars
Water in liquid form exists on the surface of Mars. This discovery - a crucial advance in planetary science - removes one of the great obstacles to establishing settlements on the Red Planet. It also increases the probability that primitive life exists there although it does not prove it. If, in fact, this were proved it would be an epochal event - the first discovery of life beyond Earth.
But first, the evidence for Martian water. It has been discovered, not by a space probe, but by an examination of meteorites which once lay on the sur
face of Mars and have fallen to Earth. This is caused by a large asteroid striking Mars. Stones lying on the planet’s surface are thrown into space by the ‘splash’ of the impact. They fly around the solar system for a few million years and then, sometimes, land here.
of Michigan University at Ann Arbor explained, in Nature magazine, how studies of a large number of these meteorites showed that the air in the thin Martian atmosphere is interacting with water at its surface. For these meteorites contain hydrous, or water-bearing, minerals. The ratio in them between two types of hydrogen, light and heavy, proves that water is coming to the surface and evaporating.
‘The rest of the water will not be far below,’ says Donahue. ‘If it was spread on the surface uniformly, it would cover Mars to a depth of 25 metres. All that colonists on Mars will need to do is sink wells to get it out. This will make the establishment of settlements much easier and cheaper than it has seemed until now.’
However, Mars is an extremely cold and dry world. Where did all this water come from?
It is already known from the shape of basins on its surface, especially in its northern hemisphere, that some three billion years ago it was much warmer than it is today, and that it had widespread oceans and rivers. Then there occurred some vast cosmic accident which ruined Mars as a habitable world. Perhaps a massive asteroid strike pushed the planet out to an orbit much further from the Sun -where it now remains - and, as Mars grew colder, much of this water evaporated.
But, not all. The rest would have drained away underground. Until now, it was thought to lie in the form of deeply frozen ice which future colonists would have to melt, perhaps by atomic explosions. The new discovery, that the water is easily available without such industrial violence, is a most encouraging surprise.