It’s a lot less poetic than “we are made of stardust” (the second sentence of John and Mary Gribbin’s book Stardust), which is meant to inspire feelings of awe akin to the kind religion can elicit, but it’s true that we’re all made of empty space. Well, mostly, empty space. Perhaps.
Like pretty much everything else, we’re made of atoms. Atoms are composed of protons, neutrons, electrons, and empty space. More specifically, protons and neutrons make up an atom’s tiny nucleus, around which its electrons are distributed in space in probability distributions called orbitals. To get an idea of the scale of an atom’s nucleus relative to where it’s electrons are mostly likely to be, if the atom was an American football stadium, the nucleus would be a pea on the field (thanks, first year Chemistry text-book written in the USA! Also, thanks for cruelly saying that “room temperature” is a summery 21 degrees).
Of course, we’re not just made of isolated atoms. Atoms form molecules and more and more complex compounds, from water to DNA, fats, proteins, and ever more larger structures. But even these compounds are mostly electron clouds surrounding tiny nuclei.
There are people with neurological disorders, often caused by particular types of brain damage, whose mental picture of their bodies is damaged such that they do not perceive a limb or even an entire hemisphere of their bodies as their own. But besides such unfortunate individuals, we each perceive ourself as a unitary whole—a complete and solid being with a clearly defined border, separate from other people, animals, and objects. The idea that we may be little more than a lattice work of subatomic particles inside a larger cloud of subatomic particles in space can be unsettling to say the least.
So are we mostly empty space?
I recently put this question to a physics student: we’re made of atoms, and atoms are mostly space, so does that mean that we’re mostly made of space? He said “Yes… well, no” and argued that the “football field” was not empty space but a space in which electrons have a certain probability of residing. “Yes” I said, “but surely at any one time, any one of an atom’s electrons is in one particular place in that field” (I don’t care what you might hear, I can totally speak in well-formed sentences no matter how much beer I drink). The physics student replied “actually … no” and explained that each electron occupies all space in its probability field at once. Man, physicists and their cats in boxes, eh?
What he was talking about was Schrödinger’s description of the three-dimensional wave functions surrounding atomic nuclei which characterise the probability distribution of an atom’s electrons: according to quantum physics, electrons are composed of both waves and particles—you can look for an electron and find something particle-like, but when you’re not looking, the electron is a wave that carries information about where the electron probably is: the electron isn’t in any one particular place when you’re not looking. I know, physics is mental.
While we’re on the subject of what we’re made of, what makes protons, neutrons and electrons our smallest parts? Or does it get even smaller?
The same physicist from a couple of paragraphs previous described to me a famous and very old thought experiment posited by the Greek philosopher Leucippus and his pupil Democritus in the fifth century BC: take a bar of gold and cut it in half. Then take one of the halves and cut it in half again. Continue in this way cutting smaller and smaller, and imagine you have some fantastic equipment that allows you to see the gold no matter how small it gets. When does the gold disappear? Half of something isn’t nothing. When do you reach something that cannot be divided any further? Leucippus and Democritus proposed that all matter was made up of atoms, which are essential and indivisible (they used the word atomos meaning “uncuttable”).
For most of history the atom was believed to be as small as you could get, until our friends the electron, proton and neutron were discovered in 1897, 1911, and 1932 respectively. And this isn’t it either: today, there are over 200 subatomic particles known. Scientists are even smashing protons together in a giant underground tunnel beneath the Franco-Swiss border to find the God particle (or the “goddamn particle” as the author of a book about Higgs boson wanted to call it before the book met his editor’s red pen).
What are we made of? Stardust? Empty space? Three-dimensional probability waves? They’re possibilities that can seem almost mystical, and maddeningly confusing at times. Is Chuck Norris made of the same subatomic particles as the rest of us, or some super-tough particles that would make anyone else explode? Is that meme even relevant anymore? Man, I’m so out of touch. All these questions have gotten me all flustered, I need to go lie down. On my bed, which is not so much a solid object as mostly empty space … or waves … or dust … arrrrrrggghh.