A Little History Of Science: Atoms and the Void

A Little History Of Science: Atoms and the Void

In about 454 bc, the Greek historian Herodotus (c. 485–425 bc) visited Egypt. Just like us, he was astonished by the Pyramids, and by the gigantic statues – sixty feet tall – at Thebes further up the Nile. He could not quite believe just how old everything was. Egypt’s glory had passed and it had already long ago been overrun by the Persians. Herodotus was living in a much younger, more vigorous society that was still on the up, and one that would conquer Egypt a century later under Alexander the Great (356–323 bc).

By Herodotus’s time, people who thought and wrote in Greek dominated a growing part of the eastern Mediterranean. They had written down the works of Homer, the blind poet, such as the story of how the Greeks defeated the Trojans by building and hiding in a giant horse, as well as the fantastic journey home of the Greek soldier Odysseus, who had masterminded the Trojan War. The Greeks were great ship-builders, traders and thinkers.

One of the earliest of these thinkers was Thales (c. 625–545 bc), a merchant, astronomer and mathematician of Miletus, on the coast of what is now Turkey. Nothing that he wrote survives directly, but later authors quote him as well as telling anecdotes that illustrate what he was like. One of them says that he was once so busy looking up at the stars that he forgot to look where he was stepping and fell down a well. In another story, Thales comes out on top: because he was clever, he was able to see that there was going to be a very big olive harvest. He hired all the olive presses long before the harvest, when no one needed them, and then when the harvest came in, he was able to rent them out for a large profit. Thales was not the first absent-minded professor – and we shall meet more later – nor the only one to make money from applying his science.

Thales was said to have visited Egypt and brought back Egyptian mathematics to the Greeks. This may be just another story, like the one about him correctly predicting a total eclipse of the sun (he didn’t know enough astronomy to do that). More likely, though, was the way he tried to explain many natural occurrences, such as the fertilisation of the land by the flooding of the Nile, and the way earthquakes are caused by the overheating of water inside the earth’s crust. For Thales, water was the chief element, and he pictured the earth as a disc floating on an enormous ocean. That sounds very funny to us, but the point is that Thales really wanted to explain things in natural, rather than supernatural, terms. The Egyptians thought that the Nile flooded because of the gods.

Unlike Thales, Anaximander (c. 611–547 bc), also from Miletus, believed that fire was the most important substance in the universe. Empedocles (c. 500–430 bc), from Sicily, came up with the idea of there being four elements: air, earth, fire and water. That idea is familiar to us because it became the default mode of thinkers for almost 2,000 years, until the end of the Middle Ages.

Being the default mode doesn’t mean absolutely everyone accepted the four-element scheme as the last word. Also in Greece, and later in Rome, a group of philosophers known as the atomists believed that the world is actually made up of tiny particles called atoms. The most famous of these early atomists was Democritus, who lived around 420 bc. What we know of his ideas comes from a few fragments of his thought which other authors quoted.

Democritus thought that in the universe there were lots of atoms, and that they had always existed. Atoms could not be broken down any further, nor could they be destroyed. Although they were far too small to be seen, he believed that they must be of different shapes and sizes, for this would explain why the things made of atoms have different tastes, textures and colours. But these larger things only exist because we humans taste, feel and see. In reality, Democritus insisted, there is nothing but ‘atoms and the void’, what we call matter and space.

Atomism was not all that popular, especially Democritus’s and his followers’ view of how living beings ‘evolved’ through a kind of trial and error. One funny version suggested that there had once been a large number of the various parts of plants and animals that could potentially join up in any kind of combination – an elephant’s trunk could attach to a fish, a rose petal to a potato, and so forth – before they finally all fitted together in ways that we see now. The idea was that if a dog’s leg accidentally joined up to a cat, that animal would not survive and so there would be no cats with dogs’ legs. After a period of time, therefore, all the dogs’ legs ended up on dogs, and – thankfully – all the human legs ended up on humans. (Another ancient Greek version of evolution seems more realistic, if still a little icky: all living things were supposed to have gradually come into existence from a very ancient slime.) Because atomism doesn’t see any final purpose or great design in the universe, with things just happening by luck and necessity, most people didn’t like it. It is a pretty bleak view, and most Greek philosophers sought purpose, truth and beauty. The Greeks who lived at the same time as Democritus and his fellow atomists would have heard their full arguments; what we know of them is only through quotations and discussions of philosophers who came later. One atomist who lived in Roman times, Lucretius (c. 100–c. 55 bc), wrote a beautiful scientific poem, De rerum natura (‘On the nature of things’). In this poem he described the heavens, the earth and everything on the earth, including the evolution of human societies, in terms of atomism.

We know the names and some of the contributions of dozens of ancient Greek scientists and mathematicians over a period of almost a thousand years. Aristotle was one of the greatest. His view of nature was so powerful that it dominated long after his death (and we’ll turn to him in Chapter 5). But three people who lived after Aristotle made especially significant contributions to the ongoing development of science.

Euclid (c. 330–c. 260 bc) was not the first person to think about geometry (the Babylonians were pretty good at it). But he was the one who brought together, in a kind of textbook, the basic assumptions, rules and procedures of the subject. Geometry is a very practical kind of mathematics which deals with space: points, lines, surfaces, volumes. Euclid described geometrical ideas such as the way parallel lines never meet, and how the angles of a triangle add up to 180 degrees. His great book, Elements of Geometry, was admired and studied across Europe. You might study his ‘plain geometry’ too one day. I hope you will admire its clear and tidy beauty.

The second of the Big Three, Eratosthenes (c. 284–c. 192 bc), measured the circumference of the earth in a very simple but clever way – using geometry. He knew that on the Summer Solstice, the longest day of the year, the sun was directly overhead at a place called Syene. So he measured the angle of the sun on that day at Alexandria (where he was librarian of a famous museum and library), which was around 5,000 stades due north of Syene. (A ‘stade’ was a Greek measurement of distance, around a tenth of a modern mile.) From these measurements he used geometry to calculate that the earth is about 250,000 stades around. So, was he close? Eratosthenes’ prediction of 25,000 miles is not very far off the actual 24,901.55 miles (around the equator) that we know today.

Notice that Eratosthenes thought that the earth was round. The idea that the earth was a large flat surface and that people could sail off the edge was not always believed, despite the stories that are told about Christopher Columbus and his voyage to America.

The last of the Big Three also worked at Alexandria, the city in northern Egypt founded by Alexander the Great. Claudius Ptolemy (c. 100–c. 178), like many scientists of the ancient world, had very wide interests. He wrote about music, geography, and the nature and behaviour of light. But the work that brought him lasting fame is the Almagest, the title given to it by the Arabs. In this book, Ptolemy brought together and extended the observations of many Greek astronomers, including charts of the stars, calculations of the movements of the planets, moon, sun and stars, and the structure of the universe. He assumed, like everyone else at the time, that the earth is at the centre of everything, and that the sun, moon, planets and stars revolve around it in a circular fashion. Ptolemy was a very good mathematician, and found that by introducing a few corrections he was able to account for the movements of the planets that he, and many people before, had noticed.

It is quite difficult to explain the sun going around the earth when in fact the opposite happens. Ptolemy’s book was essential reading for astronomers in the Islamic lands and in the European Middle Ages. It was one of the first works to be translated into Arabic, and then translated again into Latin, so much was it admired. In fact, Ptolemy was considered the equal of Hippocrates, Aristotle and Galen by many, although for us, these three get their own separate chapters.