Transcript: How do we know that atoms are real? Most people have never seen atoms. Even the Greeks, when they speculated about the existence of atoms, were just doing a thought experiment. There’s a simple experiment you can do that shows that the fundamental units of nature must be hundreds of thousands of times smaller then the eye can see. If you take the surface of a bath and sprinkle it finely with pepper and then put a single drop of heavy oil on it, an interesting thing will happen. The oil will spread out on the surface of the water and displace the pepper to the side. You can easily see that a single spherical drop has covered the whole bath after a little while. If you turn the height of the oil layer into a number given the area of the oil and the volume of the original drop you will deduce that atoms must be hundreds of thousandths of an inch or less. If you did this experiment on a lake or a pond you could actually produce a monolayer of atoms or molecules from a single drop of oil. In the modern age atoms have been isolated absolutely. The way we see atoms individually is by using radiation to detect them that is much smaller in wavelength then atoms themselves, typically x-rays or gamma rays. Atoms are real and scientists observe them everyday in labs around the world.