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When I was in school, I often wondered how it was possible to know that the matter around us is made up of those strange, tiny “little balls” called atoms and the molecules they talked about so much in class. But this doubt usually didn’t last long. After thinking about it for a while, I always came to the same conclusion: “they must know because they saw them with a microscope.” What I didn’t know until several years later was that this answer that left me so calm was completely wrong.
Although there are special microscopes with a high enough resolution to “photograph” atoms, the first microscope of this type wasn’t invented until 1981, and the idea of the atom is much older. Specifically, the first scientific theories in which atoms began to be discussed date back to the 18th and 19th centuries, but even philosophers in Ancient Greece talked about atoms. So, the idea of the atom couldn’t have arisen because someone simply saw atoms, but rather it emerged as an idea to explain different curious phenomena they encountered: simple and everyday things, like the ones I found one day preparing a coffee for breakfast, which I’m going to tell you about.
Titanium oxide seen through a high-resolution transmission electron microscope. Image by Evgenii Modin, belonging to the Fotciencia17 (FECYT) competition, titled “The Atomic Heart.”
The very fact that we can dissolve substances like coffee and milk is an initial clue that atoms are there. If matter were not made up of atoms, then it would be continuous: this means that within a material there would be no gaps – it would always look the same regardless of whether we looked at it with more or less magnification. If matter were not made up of these tiny balls, when pouring coffee into milk, they would remain separate, as happens with water and oil, and even if we stirred with a spoon using all our strength, the most we would achieve would be small drops of coffee moving through the milk (but never a homogeneous mixture). However, the idea that matter is made up of small balls with gaps between them (that is, by atoms) would much better explain the fact that we can dissolve substances: when the two liquids come into contact, the atoms and molecules that make up the coffee can seep into the gaps left by the atoms and molecules of the milk (and vice versa), forming a solution.
Another thing I studied in high school about atoms, and which can also be learned by looking at a glass of coffee, is the kinetic theory: the idea that atoms are constantly moving and that this movement is responsible for a material being at a certain temperature. The faster the atoms of a material move, the higher its temperature will be. A good clue to this can be found with instant coffee (it also works with chocolate powder drinks, but I don’t want to offend anyone’s preferences). If you pour a spoonful of instant coffee into a glass of water, you will see a very curious phenomenon called diffusion: the instant coffee dissolves, making its way through the water in branched shapes. In the end, these branch shapes become so large and numerous that they all join together, and we end up with a homogeneous solution after some time, and this process occurs faster the higher the temperature.
Comparison between the diffusion of instant coffee in hot water and in cold water.
This fact that the coffee atoms make their way into the water on their own, and that they do so faster the hotter the water is, can be very well explained if we think that the atoms are moving on their own, and if the faster they move, the faster they will dissolve (which is what we see in the glass of hot water).
Although at the time the only idea I had about how to know of the existence of atoms was the most direct one (seeing them), the people who researched centuries ago had to arrive at this idea through a much longer path, putting together many small clues like these examples of coffee and proposing ideas like that of the atom that could well explain all these things. Many of the ideas they proposed ended up being discarded: they couldn’t explain some of these clues well or they led to contradictions. Finally, the idea of the atom was the one that best survived this whole process of putting ideas to the test, which is the scientific method. When advances in technology made it possible to build microscopes with sufficient resolution, encountering atoms when exploring that tiny world was the perfect ending to hundreds of years of scientific work.
Sometimes we think that science is limited to research laboratories with complex equipment and colorful liquids, but the truth is that science is in almost everything we do from breakfast to dinner. Will you look at your breakfast with different eyes tomorrow?
Alberto Martín Pérez
PhD in Applied Physics, currently works as a researcher at the Polytechnic University of Turin (Italy) and runs the online science communication project “Doctor Berti”.
