By Don Lincoln, Fermilab
Even a person with the sharpest eyes in all of history could not possibly have seen an atom. And yet, we all know that atoms exist and that they are made of protons, neutrons, and electrons. In fact, none of us probably questioned any of those claims, in spite of the fact that we’ve never seen anything as small as, or smaller than, an atom. So then what do the scientists base their existence on? What is the proof?
Idea of Atoms
Atoms are simply just too small to see. In fact, they are literally smaller than the wavelength of visible light, which means that the inability to see an atom isn’t something that can be fixed with a better set of glasses. That’s because we can only see things using light that are bigger than the wavelength of light. Since atoms are smaller than that, it means that not a single person in the history of all of science has seen an atom. Yet, the idea of atoms is universally accepted. That’s kind of tricky when we think about that fact that scientists mostly believe only what they can see or observe.
It all starts with the claim that matter is made of atoms. Now, one may also have heard about how electrons swirl around the nuclei of atoms in shells. The shells though can have very complicated shapes, and actually, ‘seeing’ this shell structure is devilishly hard. Basically, it’s like while feeding a small flock of pigeons, we try and grab one. While the flock might cluster around us, when we grab at one, they’d scatter, and the flock would look different from when they were eating. So, how did the scientist overcome this atomic stumbling block?
Seeing the Shell Structure of Atoms
When it comes to seeing the shell structure of atoms, certain atoms actually have a simple structure, with the simplest being a hydrogen atom. A hydrogen atom has a single proton, surrounded by a single electron. The electron arranges itself in a spherical shape around the proton. However, the details are still complicated, as the electron sort of spreads itself around in a series of shells around the proton, each shell being a little bigger than the one inside it.
Spotting the electrons, even in a simple shell structure was, to say the least, quite challenging. It was only as recently as 2013, that a group of scientists at the Dutch research institution, called the FOM Institute for Atomic and Molecular Physics, were able to achieve it.
The way spot the electrons was by zapping the hydrogen atoms with an ultra-fast laser pulse and knocking the electrons off the atom. Before they did that, they put the atom in an electric field so that when the electrons got kicked off the atom, the electrons followed a very precisely-determined path to hit an electronic detector. The location where the electron hit the detector was recorded and the process was repeated over and over again.
This article comes directly from content in the video series The Evidence for Modern Physics: How We Know What We Know. Watch it now, on Wondrium.
Seeing the Various Orbital Spheres of Electrons
After many attempts, the locations where the electrons hit the detector started to build up a pattern that looked a lot like a target, with a bullseye at the center, and concentric circles surrounding it. In some circles, there were lots of electron hits, in other circles there were none. This pattern of concentric circles was the exact signature of seeing the various orbital spheres of electrons inside the hydrogen atom. It was an amazing feat, no doubt.
It was a proof that atoms exist! They were not some crazy thing that chemists and physicist just dreamed up. Atoms are real.
Bizarre Science
And yet, on one level, the proof of their existence probably doesn’t shock us very much. We almost certainly knew that atoms were a thing. But all modern science isn’t as familiar. There are much more bizarre sounding topics in physics. Physicists claim that objects shrink at high speeds and that clocks slow down. They also claim that clocks slow-down in areas of strong gravity. Astronomers claim that planets orbit very distant stars—stars so distant that it takes light, that fleetest of messengers, years and years to travel from there to here.
Cosmologists, joining the bandwagon of the bizarre, claim with some authority to know in detail how the universe began and how long ago that happened. They claim to know of invisible matter that outweighs ordinary matter five-fold. They claim that not only is the universe expanding, but it’s expanding faster and faster. When one gets right down to it, the claims of modern physics are huge and dramatic and puzzling, and one can be excused if you wonder just how scientists can be so sure of their claims.
Common Questions about How Do Scientists Know that Atoms are Real?
Atoms are simply just too small to see. In fact, they are literally smaller than the wavelength of visible light, which means that the inability to see an atom isn’t something that can be fixed with a better set of glasses. That’s because we can only see things using light that are bigger than the wavelength of light.
When it comes to seeing the shell structure of atoms, certain atoms actually have a simple structure, with the simplest being a hydrogen atom. A hydrogen atom has a single proton, surrounded by a single electron. The electron arranges itself in a spherical shape around the proton. However, the details are still complicated, as the electron sort of spreads itself around in a series of shells around the proton, each shell being a little bigger than the one inside it.
The scientists zapped hydrogen atoms with an ultra-fast laser pulse and knock the electrons off the atom. They put the atom in an electric field so that when the electrons got kicked off the atom, the electrons followed a very precisely-determined path to hit an electronic detector. The location where the electron hit the detector was recorded and the process was repeated over and over again.
