Friday, February 6, 2015


In the world of particle physics, there is a clear divide between the theorists and the experi-mentalists. While all are interested in the same big questions — what is the fundamental nature of the world, what is everything made of, and how does it interact, how did the universe come to be and how might it end — the two specialties have very different approaches and tools.

The theorists develop new models of elementary particle interactions and forces, and apply formidable mathematical machinery to develop predictions that experimenters can test. The experimenters develop novel instruments, deploy them on grand scales, and organize large teams of researchers to collect data from particle accelerators and the skies, and then turn those data into measurements that test the theorists’ models. The work is intertwined, but ultimately lives in different spheres. I admire what theorists do, but I also know that I am much better equipped to be an experimentalist.

It is the rule of scientific advancement that a theory must fit all the known data and characteristics the theory attempts to explain, but must also predict some new behavior, phenomenon, or measurement. Einstein’s famous theory of General Relativity predicted that gravity would bend light. After the photographs of a solar eclipse demonstrated this phenomenon, Einstein’s theory was praised as “proven.”

However, unlike a mathematical proof, physical theories can only be validated, never proven. Every experiment and observation in the last 90 years has validated Einstein, but that doesn’t prove the theory correct. After all, Newton’s theory of gravity held for well over 200 years before Einstein demonstrated its weakness and corrected it for large masses and velocities. Just as Newton's laws had corrected the results of Kepler, allowing for a center of mass in orbital calculations, Einstein's theory makes small corrections to Newton.

The experimentalist also needs the theorist. In many cases the experiments are designed to verify (or falsify) a given theory. Like the right and the left hand, these two classes of physics practitioners work together to advance the realm of understanding and explain the natural world we all live in.

This dance between theory and measurement has occurred over and over throughout the history of science. Sometimes it is the experimentalist who leads as when the Michelson–Morley experiment demonstrated that the speed of light was a constant, which was later explained by Einstein's special theory of relativity. Other times it is the theorist first as with Einstein's general theory's description of gravity.

Or it may be while testing a given theory that some new variance or attribute is found which is then fit into existing theories as a correction, or it is the theorists trying to more accurately explain a given experimental result. The neutrino was invented by a theorist to explain the results of known experiments. The first step of quantum theory was a refutation of the extreme result of the existing explanation or theory, the so-called "Ultraviolet catastrophe." Then this new theory was expanded and tested and ended up replacing the previous opinions on the behavior of tiny particles. The dance goes on.

But there is a bit of a bias or preference in the “business.” Many consider the theorists the top dogs and hold the experimentalists in somewhat lesser esteem. Revenge is taken by the many funny comments from an eminent experimentalist, Leon M. Lederman, when he describes theorists in his book The God Particle: If the Universe Is the Answer, What Is the Question? He notes the short hours and napping habits of the theorist in comparison to the sleep-deprived experimentalist sitting freezing in a sub zero chamber in the middle of the night gathering data, poking fun at the supposed easy life of a theoretical physicist.

Dr. Lederman is a winner of the Nobel Prize for Physics for "the neutrino beam method and the demonstration of the doublet structure of the leptons through the discovery of the meson neutrino." He is Director Emeritus of Fermi National Accelerator Laboratory (Fermilab) in Batavia, Illinois. His sense of humor is well known. Here’s one little anecdote that he tells.

The neutrino was postulated first by Wolfgang Pauli in 1930 to explain how beta decay could conserve energy, momentum, and angular momentum or "spin." Neutrinos, literally “little neutral ones” in Italian, are extremely difficult particles to detect due to their small mass relative to other sub atomic particles and their electrical neutrality. They weren't actually discovered until 1942.

In Lederman's work, he was performing measurements on neutrinos. He needed to collimate a beam of the elusive particles. That means get them all lined up, moving in parallel, sort of like focusing. He received the barrel from a 16 inch gun as a donation from the US Navy. His plan was to aim the beam of neutrinos down the barrel. The thick metal would absorb many of the neutrinos as they spread outward, leaving a collated beam coming out the end.

However, when he took delivery of the barrels, he learned they had rifling. Those are deep spiraling grooves to spin the shell as it travels through the barrel. These grooves would interfere with the experiment, but he had a plan to fill up the grooves with steel wool.

The barrel was over 30 feet long. He had his skinniest graduate assistant crawl into the barrel and begin stuffing the steel wool in the grooves. After about four hours of this difficult and hot work, the student climbed out of the barrel and declared his plan to “quit.” The doctor responded that he couldn’t quit. “Where will we find another student of your caliber.”

OK. Enough levity. Let’s examine some well known scientists. The TV comedy The Big Bang Theory has four scientists. And, although they are just actors, the science on the show is actually quite accurate due to real physics advisors.

The top scientist on the show is Sheldon Cooper. He is a theorist. His roommate is Leonard Hofstadter. (A name chosen to recognize Douglas Hofstadter, a well known computer researcher and columnist for Scientific American.) Leonard is an experimentalist.

The other two are Rajesh Koothrappali, PhD., an Astrophysicist (what we used to call an “astronomer’) and Howard Wolowitz, an engineer with only a Master’s degree. You can see the pecking order demonstrated in that show’s cast of characters with the theorist in the top spot.

Of course, the show also assumes that Sheldon has the highest IQ, although he is completely unable to identify satire.

Although there is a nice term “Astrophysicist” to describe those that study space and cosmology, Sheldon and Leonard are most likely focused on “Particle Physics” or the old term “Atomic Physics.”

Just for those that are curious, my focus is in particle physics. Based on my skills and experience in electronics engineering and programming, as well as mechanics and project management, I always thought I would be an experimental physicist, so I’ll be the one asking my graduate assistants to crawl into the gun barrel … assuming they are the right caliber.

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