The eighth of the Top Eleven is an experiment by the man who set the gold standard for arrogance in physics.
Who: Ernest Rutherford (1871-1937), a New Zealand-born physicist who famously declared “In science, there is only physics. All the rest is stamp collecting.” He was awarded the Nobel Prize in Chemistry in 1908.
When: He’s nominated for the alpha-particle scattering experiments that showed the existence of the nucleus, an 1909.
What: Rutherford is famous for carrying out early experiments with radioactive substances. Among other achievements, he coined the terms “alpha, beta, and gamma” for the different types of particles emitted in radioactive decays, showed that alpha particles are helium-4 nuclei, and demonstrated that radioactive atoms decay into different atomic species.
His most famous experiments involved the scattering of alpha particles off a thin gold foil. At the time, it was believed that atoms consisted of negatively charge electrons embedded in a sort of positively-charged mush (“Like raisins in a pudding” in one famous description). Rutherford hoped to learn something about their structure by bombarding a sample of gold with alpha particles– the positively charged alphas passing through the foil should be deflected by the positive charges in the atom, and the angle of deflection should convey some information about the structure.
In the “plum pudding” model of the atom, you would expect that alpha particles would only be deflected by small angles. Rutherford therefore set a couple of new students, Marsden and Geiger, to measuring background levels by placing their detector (a fluorescent screen that would light up when hit by an alpha particle) at a very large scattering angle– to get to the detector, particles would have to hit the foil and be deflected almost straight backwards, which was thought impossible.
To everyone’s surprise, Marsden and Geiger saw lots of particles deflected at large angles. The always quotable Rutherford later described it thus:
It was quite the most incredible event that ever happened to me in my life. It was almost as incredible as if you had fired a 15-inch shell at a piece of tissue paper and it came back and hit you.
Why It’s Important: Such large-angle scattering is absolutely impossible in the “plum pudding” model of the atom. In order for the alpha particles to be deflected backwards, the atoms would need to contain a very compact and very massive positively charged nucleus, accounting for most of the mass of the atom.
Rutherford worked this out, and was able to both derive a formula that exactly matched Marsden and Geiger’s data, and to deduce the size of the nucleus. This led to a radical re-thinking of the atomic model, into the “solar system” type picture everybody learns in grade school. Problems in that model led to Bohr’s semi-classical model of hydrogen, and then to the development of the full quantum theory.
Rutherford’s scattering experiments also pretty much established the standard techniques of nuclear and particle physics. Everything we know about the structure of matter at the subatomic scale, we’ve learned by flinging tiny energetic particles at one another.
Reasons to Vote for Him:: Completely revolutionized our understanding of the atom, invented nuclear physics, produced a number of fabulous quotes, paving the way for future curious characters in physics.
Reasons to Vote Against Him: Physics envy.