These days, we take the existence of atoms for granted. The concept of everything being built of minuscule balls of matter is relatively simple and it makes sense to us because we’ve all grown up with it. But you only have to go back as far as 1900 to find serious debate in the scientific community about whether atoms were there at all. Photography, telephones, and radio had arrived to herald a new technological age, but there was still no agreement on what “stuff” was actually made of. To a lot of scientists, atoms seemed like a reasonable idea. For example, chemists had discovered that different elements seemed to react in fixed ratios, which made perfect sense if you needed one atom of one sort plus two atoms of another sort to make a single molecule. But the skeptics held out. How could you be sure about whether something so tiny was really there?
Many decades later, a quote was attributed to the scientist and science-fiction writer Isaac Asimov that expresses perfectly the most common path of a scientific discovery: “The most exciting phrase to hear in science, the one that heralds new discoveries, is not Eureka! (I found it!) but rather, ‘Hmm . . . that’s funny . . .’” The final confirmation of the existence of atoms is a perfect example of science taking that route, but it was nearly eighty years in coming. The clock started ticking in 1827, when the botanist Robert Brown was looking through a microscope at pollen grains suspended in water. Tiny particles were breaking off the pollen, and they were pretty much the smallest things that could be seen by an optical microscope, then or now. Robert Brown noticed that even when the water was perfectly still, those tiny particles were jiggling about. At first, he assumed that it was because the particles were alive, but he later observed the same thing with non-living matter. It was weird, and he didn’t have any explanation for it. But he wrote about it, and over the following decades many other people saw the same thing. The weird jiggling became known as “Brownian motion.” It never stopped, and it was only the tiniest particles that jiggled. Various people proposed explanations, but no one really got to the bottom of the mystery.
In 1905, the world’s most famous Swiss patent clerk published a paper based on his PhD dissertation. Einstein is best known for studies on the nature of time and space, and the Theories of Special and General Relativity. But his PhD topic was the statistical molecular theory of liquids, and in papers in 1905 and 1908 he laid out a rigorous mathematical explanation of Brownian motion. Suppose, he said, that the liquid is made of many molecules, and those molecules are bouncing off each other continually. He painted a picture of the liquid as a dynamic, disorganized substance, with molecules hitting each other and speeding up and slowing down and changing direction with each bump. Then, what happens to a larger particle, one that’s much bigger than the molecules? It gets bumped from lots of different directions. But because the bumps are random, sometimes the particle gets hit more on one side than the other. So it moves sideways a bit. And then it gets randomly bumped upward more than downward. It moves a little because of that. So the jiggling of the bigger particle is just the consequence of its being hit by many thousands of much smaller molecules. Robert Brown couldn’t see the molecules, but he could see the bigger particles. The jiggling that Einstein predicted matched what Brown had seen. And that could only be the case if the liquid really was made up of molecules bumping into each other. So individual lumps of matter—atoms—must exist. Even better, one of Einstein’s equations predicted how big the atoms would have to be to cause the jiggling that was seen. And then, in 1908, Jean Perrin carried out even more detailed experiments that fit Einstein’s theory. The last doubters had no alternative but to be convinced by the new evidence. The world was made of many tiny atoms, these atoms constantly jiggled about, and at last everyone could move on. Those two discoveries went hand in hand. The constant vibration of the atoms wasn’t incidental, either. It turns out to explain some of the most fundamental physical laws about the way the world works.
One of the biggest consequences of the new understanding of atoms and molecules was that phenomena like Brownian motion had to be explained using statistics. There wasn’t any point tracking every individual atom, calculating exactly what happened when it hit another one, and keeping track of each of the billions of atoms in a single drop of liquid. Instead, you worked out the statistics of what would happen, given lots of random collisions. On any given day, you couldn’t say that the Brownian particle would go exactly 0.04 inch to the left. But you could say that if you did the experiment lots of times, it would end up 0.04 inch away from its starting point on average. You could calculate that average very accurately, but an average was all you were going to get. It meant that physics was a bit messier than it had been in 1850. But it could explain an awful lot. Once you knew about atoms, even everyday things like sodden clothes looked much more interesting.
The first program I ever presented for the BBC was about the Earth’s atmosphere and the patterns of weather around the globe. And so I got to spend three days in the largest and most famous weather event on the planet: the Indian monsoon. The monsoon is a yearly change in the wind patterns around India, and between June and September each year the reversed winds bring rain. Lots and lots of rain. We were there to talk about where all that water was coming from.
We stayed in tiny wooden huts on a very quiet beach in Kerala, right down on the southern tip of India. The first filming day was long and varied—monsoon weather is very changeable, which is frustrating if you need a couple of hours with the same weather conditions to film one particular section. Hot sunshine was followed by an hour of very intense rain, and then strong winds and then back to the hot sunshine. But it was warm all day, and I never mind being rained on if I’m not cold. Being cold really isn’t fun. Every time it rained, I got drenched, and then I’d have to work out how to make my clothes look slightly drier when the sun came out. The problem with being the one on camera is that you’re the only person who has to wear the same clothes all the time. So I found a sheltered warm sunny nook where things would dry out a bit, and it felt like I spent hours changing into and out of clothes of various degrees of dampness, trying to match the sogginess of my clothes to the current weather conditions. At about 7 p.m., the heavens opened (again), I got drenched (again), and since the sun was going down, we decided to call it a day.