Two thousand years ago, according to Matthew the Evangelist, three men saw a star in the east, and took it for a portent. It may have been a comet. Comets have a 2,000-year-old reputation for portending momentous things. Right now, a robot spacecraft called Stardust is on a three billion-mile journey to encounter a rare comet. It will overtake the portent-bearer at 13,000 mph, scoop up fragments of the coma less than 25,000ths of an inch across, with a catcher of aerogel, a glassy substance so weird that its makers dubbed it "frozen smoke", and then deliver the precious fragments of the leftover fabric of the solar system back to earth in 2006.
How we got from Matthew to Mars landers, from Plutarch to plutonium, from Vitruvius to vitreous enamel, is a story of seeing. It is a story of how people looked further and further towards bigger and bigger and bigger horizons, and at smaller and smaller fragments of matter, until they could see (they like to think) the whole picture.
One agent of seeing has been a form of vitrified silica called glass. The Romans made glass. They knew, through the writings of Vitruvius Pollo, about engineering structures such as arches and domes, they knew about plumbing, they knew about the link between drainage and health and they knew (when they thought about it) that the earth was a sphere, with temperate, torrid and frigid zones. They hurled missiles from machines called ballistas, so that intercontinental ballistic missiles were already there 2,000 years ago, just waiting for a bit more science and technology. They knew (at least Lucretius did) that matter had to exist as accretions of atoms; they knew (at least Lucretius did) that there could be other worlds beyond this one; they knew (from Galen) that the heart was a pump and the pulse rate was an indication of health; and that effective medicines could be distilled from plants.
They knew that glass could keep the wind out and let the light in but it was more than 1,000 years after the fall of Rome that a Latin-speaking Italian looked through a glass brightly and began to change the world forever. Glass is a maker of miracles, a word derived from the Latin miraculum, a thing to be wondered at. Hold it one way and it refracts light and makes rainbows; hold it another and it focusses light and makes fire.
It did more than that; it made people wonder. Aristotle had helped Christians believe in a perfect geocentric universe with a sad, bad planet at its core but in 1609 Galileo Galilei put two glass lenses together and looked down them one way to see tiny insects writ large, and then he looked through them the other way, and saw the stars as pinpoints of light, and the planets as globes, and the moon as the pale light reflected from the sun, and he deduced from it all that the moon was nearest, the planets near and the stars very, very far away.
Furthermore, he saw mountains on the moon, and spots on the sun, and he saw the moons on Jupiter and from it all, he deduced that Copernicus and Tycho Brahe were right. The earth wasn't the centre of the universe, and the universe looked like a piece of machinery that obeyed laws, if only you could work out what they were. The day Galileo died, Isaac Newton was born, and Newton became the genius of the revolution begun by Galileo. But besides hammering out the laws of motion and the mathematics of gravity and inventing a proper telescope he began to think about light itself: he looked at the spectrum cast by a prism and realised that white light was an amalgam of colours, and he theorised that light exists as unimaginable particles, now known as photons.
With a telescope you can begin to see things on the most distant horizon. The next step is to go there. You can't sail there safely without finding a treatment for scurvy - the first great scientific link between diet and health. Once there, you have to establish exactly where you are so you can find your way back again. Explorers had to establish ways of measuring and calculating distance and time with ever-greater precision which leads to questions about measuring other things, like heat, and cold, and wind, and sound. You can't do things like that without asking: "What is time?" "What is space?" "What is heat?"
More than a century after Newton, the largely uncelebrated Count Rumford (why do we not rejoice in a man who invented the first efficient firegrate, the first efficient kitchen range and the first proper coffee pot?) showed that heat wasn't a sloshy invisible liquid called caloric that flowed from one thing to another: heat was energy, work, effort - heat was a happening. Rumford was a bit of a happening himself: he founded the Royal Institution in London and hired Humphry Davy to do things in it, like run electricity through solutions in glass retorts and jars and precipitate elements and begin to establish what is now called chemistry. Davy hired an apprentice helper called Michael Faraday who helped take electricity, magnetism and chemistry from the world of the laboratory to multinational corporate industry, but there was one other figure in the story of Count Rumford. He also hired (for a year or two) Thomas "Phenomenon" Young.
Young was a phenomenon who could speak 12 languages and play the bagpipes before he had finished growing up. Every time you worry whether a strip of elastic is elastic enough you need Young's modulus. Young also started the work on deciphering the Rosetta stone, so he also launched Egyptology and the systematic exploration of the past.
But most of all, he looked again at light itself: he saw that three primary colours would together account for all the other hues; he shone light through two tiny slits and watched them interfere with each, and concluded that light travelled in waves (you have to think of light as waves sometimes and photons sometimes) and that these wavelengths could be measured. He had discovered that light is a form of information, and that different wavelengths and different absorption patterns could tell you different things. He had founded spectroscopy. With a spectroscope, you can look at the light from the sun and see evidence of an element then unknown on earth, and name it helium. With a spectroscope, you can detect the signature of hydrogen cyanide in a comet, oceans of water in Orion's belt, vast lakes of pure alcohol in the dust between the distant stars.
PEOPLE like Newton and Davy and Young were taking big problems, like "Where are we?" and "Why is the world like it is?", and reducing them into tiny little questions, like "What is light doing, when it does this?" and, "Why does a candle go out when you put it in something airtight?", and then thinking up ways of putting the question so that there could only be one answer, and not six possible explanations.
They were inventing modern science, and the headlong stampede to answer more and more, and bigger and bigger questions - the road to the periodic table, and relativity, and quantum theory, and the electromagnetic spectrum and x-rays and the plutonium bomb - stems from astonishing experiments with candles, and glass, and salt and water, and the electricity you could get from rubbing two bits of glass together (it was known, at the time, as vitreous electricity). Once you started down this road, you were really motoring. Once you got up speed, you could really take off. Flights of fancy became flights of Lancaster bombers, and flights to the moon.
With each step, God as the maker and sustainer of the universe was pushed further back ("I have no need of that hypothesis," Laplace told Napoleon) but many great scientists were doing what they did because they thought knowledge of God's creation would lead them closer to God.
Naturalists like John Ray thought that by considering the ant and its ways - by looking at the exquisite work of God - they would discern His hand and His purpose. What they saw was the intricate way that living things dovetailed with each other, and depended on each other. Naturalists like William Buckland thought that by looking at bones in caves and hillsides, left behind by Noah's Flood no doubt, they could establish the literal truth of the Book of Genesis, and then rediscover the short history of the world.
To do that properly, he and fellow puzzlers had to invent stratigraphy, and palaeontology, and make the discovery that the well of the past was unimaginably deep, and grew more dark with each recovered fragment of evidence of awesome entrances and exits upon the earth's rocks: vast bones, huge teeth, appalling footprints in the limestone of the Jurassic, not to mention small things like trilobites and vitreous foraminifera.
Darwin's conclusion that all life was from one source, sculpted to its astonishing variety by tiny random changes which either met or did not meet the demands of a heedless environment, is so profound that philosophers - and societies - are still wrestling with it. But it was an idea fashioned from evidence already gathered by Believers, and many who had taken up biology for the glory of God looked at Darwin's argument and said, yes, that's the way it is.
Out of that acceptance of a new kind of relationship - life as competition with the other creatures - modern medicine began to make astounding strides. Once physicians accepted that people died of disease because of germs, they could stop making airy observations about miasmas, choler, bilious humours or vitreous phlegm, and get on with hygiene - at last, a vital role for vitreous enamel in bathtubs - and sterilisation and vaccination. They could ask about the chemical weapons that plants use to fight off insects, and go from aspirin in meadowsweet and digitalis in foxgloves to the alkaloids found in the Madagascar rosy periwinkle now used to treat two cancers. They could ask how germs compete with each other and then suddenly realise that penicillin would only be a beginning: that there would be other antibiotics, with other properties.
ONCE people knew all these things, they could see off old terrors like syphilis, and smallpox, and (for a while) tuberculosis. And when some of them came back, they could say: but of course, we should have expected it. They could even ask: what is it that unites life, orders it, orchestrates its differences? It was a step from that question to DNA. If all life is from one source, assembling itself from one set of chemical tools, then surely if you were missing a bit in one species you could lift one from another, and tweak it to your purpose? Once they had understood Darwin and the gene theory proposed by Mendel and the DNA of Watson and Crick, they could think about transplanting organs, growing new heart valves in laboratory dishes, and engineering sheep that provide human proteins like alpha-1 antitrypsin in their milk for children with cystic fibrosis.
It has been a long journey, with a slow start, but gathering bewildering speed. There has been a revolution in knowledge, but not, so far, in the capacity of humans for understanding either each other, or the planet they have begun to alter forever. Geneticists have begun to close in on the question of life itself while other humans are busy obliterating species on a scale unparalleled in a 4.5 billion year history of earth. Cosmologists who at mid-point in this century had no answer to whether the universe was eternal or created now say that they are sure of the entire history of the universe, except for the first thousandth of a second of time itself.
Ironically, all cosmologists can quote St Augustine of Hippo, a Roman who in 400 AD concerned himself with some very modern questions. He asked if space had always existed?
No, he thought, because then you'd have to explain why God made the world here, and not there. And had time always existed? No, because then you'd have to ask what God was doing before he created the world. So, he reasoned: "We are not to think about infinite time before the world, any more than about infinite space outside it. As there was no time before it, so there is no space outside it."
When he put a question like that, he demonstrated the power of the human brain. He also raised questions nobody can answer, such as why evolution had produced a brain the weight of a bag of sugar containing enough neuronal connections to cope with questions about life, the universe and everything, and still have some left over for the Sistine Chapel and Father Ted.
Albert Einstein worried about that, too. "The most incomprehensible thing about the universe," he said "is that it is comprehensible."
Tim Radford is science editor of The Guardian