Antimatter is much loved by science fiction writers. Yet it is real: there are looking-glass particles that are counterparts of protons, electrons, and other familiar particles of matter. Below is an excerpt from Frank Close‘s new book Antimatter, which explains that to even begin to understand antimatter you have to first look at the material world, including ourselves. Frank Close previously wrote for OUPblog on CERN’s Large Hadron Collider.
If you were to see a lump of antimatter, you wouldn’t know it; to all outward appearances it looks no different to ordinary stuff. So perfectly disguised that it is seemingly one of the family, its ability to destroy whatever it touches would make it the perfect ‘enemy within’. So, what is antimatter? Saying that it is the opposite of matter is easy on the ear, but what actually is ‘opposite’ about it? Knowing that the briefest contact with antimatter would commit whatever it touched to oblivion is awe-inspiring, but what gives antimatter this power?
To begin to understand antimatter, we need first to take a voyage into ordinary matter, such as ourselves. Our personal characteristics are coded in our DNA, miniature helical spirals made of complex molecules. These molecules in turn are made of atoms, which are the smallest pieces of an element—such as carbon or hydrogen or iron—that can exist and still retain the characteristics of that element.
Hydrogen atoms are the lightest of all and tend to float up to the top of the atmosphere and escape. For this reason hydrogen is relatively rare on earth, whereas in the universe at large it is the commonest element of all. Most of the hydrogen was made soon after the Big Bang and is nearly fourteen billion years old.
Vast balls of hydrogen burst into light as stars, such as our sun. It is in the stars that the full variety of elements is fashioned. Nearly all of the atoms of oxygen that you breathe, and of the carbon in your skin or the ink on this page, were made in stars about five billion years ago when the earth was first forming. So we are all stardust or, if you are less romantic, nuclear waste, for stars are nuclear furnaces with hydrogen as their primary fuel, starlight their energy output and assorted elements their ‘ash’ or waste products.
To give some idea of how small atoms are, look at the dot at the end of this sentence; it contains some 100 billion atoms of carbon, a number far larger than all humans who have ever lived. To see any of those individual atoms with the naked eye you would need to magnify the dot to be 100 metres across.
Elemental carbon atoms can bind in different forms, such as diamond, graphite, and carbon black—soot, charcoal, and coal. Antimatter also consists of molecules and atoms. Atoms of anticarbon would make antidiamond as beautiful and hard as the diamond we know. Antisoot would be as black as soot, and the full stops in an antibook the same as those you see here. They too would need enlarging to 100 metres size for their anticarbon atoms to be seen. Were we able to do that, we would find that these smallest grains of anticarbon are indistinguishable from those of carbon. So even at the basic level of atoms, matter and antimatter look the same: the source of their contrast is buried deeper still.
Atoms are very small, but they are not the smallest things. It is upon entering them and encountering the basic seeds from which they are made that the profound duality between matter and antimatter is disclosed.
Each atom contains a labyrinth of inner structure. At the centre is a dense compact nucleus, which accounts for all but a trifle of the atom’s mass. While enlargement of our ink-dot to 100 metres is sufficient to see an atom, you would need to enlarge it to 10,000 kilometres, as big as the earth from pole to pole, if you wanted to see the atomic nucleus. The same is true for antidots and antiatoms. It is only when they are seen in such fine detail that the subtle choice of matter or antimatter begins to show.
When the profound entangling of space and time that comes with Einstein’s theory of relativity is married with the will-o’-the-wisp ephemeral world of uncertainty that rules within atoms, an astonishing implication emerges: it is impossible for nature to work with only the basic seeds of matter that we know. To every variety of subatomic particle, nature is forced also to admit a negative image, a mirror opposite, each of which follows the same strict laws as do conventional particles. As the familiar particles build atoms and matter, so can these contrary versions make structures that at first sight appear to be the same as normal matter, but are fundamentally dissimilar.