Richard Dawkins - The Magic of Reality

The mass of an object depends almost entirely on how many protons and neutrons it has in all its atoms added together. The number of protons in the nucleus of any atom of a particular element is always the same, and is equal to the number of electrons in orbit around the nucleus, although the electrons don’t contribute noticeably to the mass because they are too small. A hydrogen atom has only one proton (and one electron). A uranium atom has 92 protons. Lead has 82. Carbon has 6. For every possible number from 1 to 100 (and a few more), there is one and only one element that has that number of protons (and the same number of electrons). I won’t list them all, but it would be easy to do so.

The number of protons (or electrons) that an element possesses is called the ‘atomic number’ of that element. So you can define an element not just by its name but by its own unique atomic number. For example, element number 6 is carbon; element number 82 is lead. The elements are conveniently set out in a table called the periodic table – I won’t go into why it’s called that, although it is interesting. But now is the moment to return, as I promised I would, to the question of why, when you cut a piece of, say, lead into smaller and smaller pieces, you eventually reach a point where, if you cut it again, it is no longer lead. An atom of lead has 82 protons. If you split the atom so that it no longer has 82 protons it ceases to be lead.

The number of neutrons in an atom’s nucleus is less fixed than the number of protons: many elements have different versions, called isotopes, with different numbers of neutrons. For example, there are three isotopes of carbon, called Carbon-12, Carbon-13 and Carbon-14. The numbers refer to the mass of the atom, which is the sum of the protons and neutrons. Each of the three has six protons. Carbon-12 has six neutrons, Carbon-13 has seven neutrons and Carbon-14 has eight neutrons. Some isotopes, for example Carbon-14, are radioactive, which means they change into other elements at a predictable rate, although at unpredictable moments. Scientists can use this feature to help them calculate the age of fossils. Carbon-14 is used to date things younger than most fossils, for example ancient wooden ships.

Well then, does our quest to cut things ever smaller and smaller end with these three particles: electrons, protons and neutrons? No – even protons and neutrons have an inside. Even they contain yet smaller things, called quarks. But that is something I’m not going to talk about in this book. That’s not because I think you wouldn’t understand it. It is because I know I don’t understand it! We are here moving into a wonderland of the mysterious. And it is important to recognize when we reach the limits of what we understand. It is not that we shall never understand these things. Probably we shall, and scientists are working on them with every hope of success. But we have to know what we don’t understand, and admit it to ourselves, before we can begin to work on it. There are scientists who understand at least something of this wonderland of the very small, but I am not one of them. I know my limitations.

All the elements are special in their different ways. But one element, carbon, is so special that we will end the chapter by talking briefly about that. Carbon chemistry even has its own name, separating it from the whole of the rest of chemistry: ‘organic’ chemistry. All the rest of chemistry is ‘inorganic’ chemistry. So what is so special about carbon?

The answer is that carbon atoms link up with other carbon atoms to form chains. The chemical compound octane, which, as you may know, is an ingredient of petrol (gasoline), is a rather short chain of eight carbon atoms with hydrogen atoms sticking out to the sides. The wonderful thing about carbon is that it can make chains of any length, some literally hundreds of carbon atoms long. Sometimes the chains come around in a loop. For example, molecules of naphthalene (the substance that mothballs are made of) are also made of carbon with hydrogen attached, this time in two loops.

Carbon chemistry is rather like the toy construction kit called Tinkertoy. In the laboratory, chemists have succeeded in making carbon atoms join up with each other, not just in simple loops but in wonderfully shaped Tinkertoy-like molecules nicknamed Buckyballs and Buckytubes. ‘Bucky’ was the nickname of Buckminster Fuller, the great American architect who invented the geodesic dome. The Buckyballs and Buckytubes scientists have made are artificial molecules. But they show the Tinkertoyish way in which carbon atoms can be joined together into scaffolding-like structures that can be indefinitely large. (Just recently the exciting news was announced that Buckyballs have been detected in outer space, in the dust drifting near to a distant star.) Carbon chemistry offers a near-infinite number of possible molecules, all of different shapes, and thousands of different ones are found in living bodies.

One very large molecule called myoglobin, for example, is found, in millions of copies, in all our muscles. Not all the atoms in myoglobin are carbon atoms, but it is the carbon atoms that join together in these fascinating Tinkertoy-like scaffolding structures. And that is really what makes life possible. When you think that myoglobin is only one example among thousands of equally complicated molecules in living cells, you can perhaps imagine that, just as you can build pretty much anything you like if you have a large enough Tinkertoy set, so the chemistry of carbon provides the vast range of possible forms required to put together anything so complicated as a living organism.

This chapter has been unusual in that it didn’t begin with a list of myths. This was only because it was so hard to find any myths on this subject. Unlike, say, the sun, or the rainbow, or earthquakes, the fascinating world of the very small never came to the notice of primitive peoples. If you think about this for a minute, it’s not really surprising. They had no way of even knowing it was there, and so of course they didn’t invent any myths to explain it! It wasn’t until the microscope was invented in the sixteenth century that people discovered that ponds and lakes, soil and dust, even our own bodies, teem with tiny living creatures, too small to see, yet complicated and, in their own way, beautiful – or perhaps frightening, depending on how you think about them.

Dust mites are distantly related to spiders but too small to see except as tiny specks. There are thousands of them in every home, crawling through every carpet and every bed, quite probably including yours. If primitive peoples had known about them, you can imagine what myths and legends they might have invented to explain them! But before the invention of the microscope, their existence was not even dreamed of – and so there are no myths about them. And, small as it is, even a dust mite contains more than a hundred trillion atoms.

Dust mites are too small for us to see, but the cells of which they are made are smaller still. The bacteria that live inside them – and us – in vast numbers are smaller even than that.

And atoms are far far smaller even than bacteria. The whole world is made of incredibly tiny things, much too small to be visible to the naked eye – and yet none of the myths or so-called holy books that some people, even now, think were given to us by an all-knowing god, mentions them at all! In fact, when you look at those myths and stories, you can see that they don’t contain any of the knowledge that science has patiently worked out. They don’t tell us how big or how old the universe is; they don’t tell us how to treat cancer; they don’t explain gravity or the internal combustion engine; they don’t tell us about germs, or nuclear fusion, or electricity, or anaesthetics. In fact, unsurprisingly, the stories in holy books don’t contain any more information about the world than was known to the primitive peoples who first started telling them! If these ‘holy books’ really were written, or dictated, or inspired, by all-knowing gods, don’t you think it’s odd that those gods said nothing about any of these important and useful things?