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Q & A: Democritus' atomic theory

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Most recent answer: 09/20/2013
what is the democratus atomic theory
- toufeeq.ur.rehman (age 26)

I just learned about Democritus from a wonderful book by Scott Aaronson called "Quantum Computing Since Democritus." Since I'm advertising his book, I guess he won't mind if I steal the following passage from his lecture notes (), which are much more fun than anything I write.

" First of all, who was Democritus? He was this ancient Greek dude. He was born around 450BC in Abdera, which was sort of this podunk town. where people from Athens said that even the air causes stupidity. He was a disciple of Leucippus, according to my source, which is Wikipedia. He's called a "pre-Socratic," even though actually he was a contemporary of Socrates. That gives you a sense of how important he's considered: "Yeah, the pre-Socratics -- maybe stick 'em in somewhere in the first week of class." (Incidentally, there's a story that Democritus journeyed to Athens to meet Socrates, but then was too shy to introduce himself.)

Almost none of Democritus's writings survive. (Some of them apparently survived into the Middle Ages, but they're lost now.) What we know about him is mostly due to the fact that other philosophers, like Aristotle, brought him up in order to criticize him.

So, what were the ideas they criticized? Democritus thought the whole universe is composed of atoms in a void, constantly moving around according to determinate, understandable laws. These atoms can hit each other and bounce off, and they can stick together to make bigger things. They can have different sizes, weights, and shapes -- maybe some are spheres, some are cylinders, whatever. On the other hand, Democritus says that properties like color and taste are not intrinsic to atoms, but instead emerge out of the interactions of many atoms. For if the atoms that made up the ocean were "intrinsically blue," then how could they form the white froth on waves?

Remember, this is 400BC. So far we're batting pretty well.

Why does Democritus think there are these atoms surrounded by void? He gives a few arguments, one of which can be paraphrased as follows (following Carl Sagan). Suppose we have an apple, and suppose the apple's not made of atoms but is instead this continuous, hard stuff. And suppose we take a knife and cut the apple into two pieces. It's clear that the points on one side go into the first piece and the points on the other side go into the second piece, but what about the points exactly on the boundary? Do they "disappear"? Do they get duplicated? Does the symmetry get broken? None of these possibilities seem particularly elegant.

Incidentally, some of you might know that there's a debate raging even today between atomists and anti-atomists. ... At issue in this debate is whether space and time themselves are made up of indivisible atoms, at the Planck scale of 10-33 centimeters or 10-43 seconds. Ironically, the physicists have almost no experimental evidence to go on, and are basically in the same situation that Democritus was in 2400 years ago. If you want an ignorant, uninformed layperson's opinion, my money is on the atomist side. And the arguments I'd use are not entirely different from the ones Democritus used: mostly they hinge on inherent mathematical difficulties with the continuum.

One passage of Democritus that does survive is a dialogue between the intellect and the senses. The intellect starts out, saying: "By convention there is sweetness, by convention bitterness, by convention color, in reality only atoms and the void." In my book, this one line already puts Democritus shoulder-to-shoulder with Plato, Aristotle, or any other ancient philosopher you care to name. But the dialogue doesn't stop there. The senses respond, saying: "Foolish intellect! Do you seek to overthrow us, while it is from us that you take your evidence?" "

Mike W.

(published on 09/20/2013)

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