In an op-ed piece in the New York Times on June 10, 2012 titled, "Physicists, Stop the Churlishness," essayist Jim Holt criticizes the public disdain that many top contemporary physicists unfortunately hold for philosophy. Holt quotes the late Richard Feynman as mocking "cocktail party philosophers" for thinking that they can discover things about the world "by brainwork rather than experiment." I have not been able to find the precise quotation, which Holt does not reference. However, Feynman does mention "cocktail-party philosophers" (note: not professional philosophers) several times in chapter 16, volume 1, of his classic Lectures on Physics. In any case, Holt remarks, "Leucippus and Democritus ... didn't come up with [the idea of atoms] by doing experiments."
He is dead wrong. While is true that Leucippus, Democritus, nor any other ancients performed the type of carefully controlled experiments that mark science today, the idea of atoms did not arise from pure thought alone.
The philosophy of the ancient atomists, in particular Epicurus, was recorded for posterity in the epic poem De rerum natura (The Nature of Things) written in Latin hexameter at the time of Julius Caesar by the Roman Lucretius Carus. The following excerpts make it clear that careful observation played an important part in the thinking of ancient atomists (translation by A. E. Stallings).
Just in case you start to think this theory [atoms] is a lie,
Because these atoms can't be made out by the naked eye,
You yourself have to admit there are particles
Which are but which cannot be seen. . . (I, 165-169)
For example:
Thus clearly there are particles of wind you cannot spy
That sweep the ocean and the land and clouds up in the sky. (I, 277, 278)
Most significantly, in Book II Lucretius adds
There's a model, you should realize,
A paradigm of this that's dancing right before your eyes --
For look well when you let the sun peep in a shuttered room
Pouring forth the brilliance of its beams into the gloom,
And you'll see myriads of motes all moving many ways
Throughout the void and intermingling in the golden rays. (II, 112-117)
...
Such turmoil means that there are secret motions, out of sight,
That lie concealed in matter. For you'll see the motes careen
Off course, and then bound back again, by means of blows unseen. (II, 126-128)
This last, remarkable passage precisely describes the Brownian motion that Einstein and Jean Baptiste Perrin used in the early twentieth century to demonstrate conclusively the existence of atoms. Gaston Bachelard has suggested that observations involving dust provided the essential notion of atoms so that it was not just a product of pure thought:
Without this special experience, atomism would never have evolved into anything more than a clever doctrine, entirely speculative, in which the initial gamble of thought would have been justified by no observation. Instead, by virtue of the existence of dust, atomism was able to receive from the time of its inception an intuitive basis that is both permanent and richly evocative.
In his Critique of Pure Reason, Immanuel Kant argued that experience was not the only source of knowledge, that in addition our minds have certain built-in a priori concepts. One of his major examples was our intuition that space is described by Euclidean geometry. Of course, we now know that other geometries exist and that Einstein used non-Euclidean geometry to describe space in his general theory of relativity. So much for what Kant called the synthetic a priori.
Another belief, still common today, is that we can reason ourselves to knowledge about reality. How often have you read "proofs" of the existence, or non-existence, of God or some other deep question? A logical deduction can tell you nothing that is not already embedded in its premises. All a logical deduction does is enable you to determine whether or not some conclusion is consistent with some set of premises.
- Gaston Bachelard, Les Intuitions Atomistiques (Atomistic Intuitions): Essai De Classification, 2nd ed., (Paris: J. Vrin, 1975).
- Richard P. Feynman, Robert B. Leighton, and Matthew L. Sands. The Feynman Lectures on Physics. New millennium ed. (New York: Basic Books, 2011).
- Jim Holt. "Physicists, Stop the Churlishness." New York Times, June 10, 2012.
- A.E. Stallings, and Richard Jenkyns. Lucretius: The Nature of Things. (London; New York: Penguin, 2007).