Tonight I watched one of the random Nova episodes that TiVo catches for me from time to time. This one was titled “The Ghost Particle”.
I’m no physicist, but Nova has a way of bringing even the most esoteric of scientific studies within the reach of normal folks and making them interesting. This episode was all about the neutrino. I found especially interesting the “drama” surrounding this particle over the years. It’s known as the solar neutrino problem, and it surrounded two scientists, Ray Davis and John Bahcall. To shorten things a bit, Bahcall helped develop a model which predicted the number of neutrinos which should be emitted by the sun (and thus how many we should be able to detect here on earth). Davis and Bahcall headed a huge experiment to measure these neutrinos. The problem was that the measurements were showing only about a third of the predicted number of neutrinos.
For years, many people assumed that either the experiment or the predictive model was wrong. Davis kept refining the measurements, but the experiment ran for decades with basically the same results. Bahcall insisted that his model was accurate.
To shorten this up, a definitive experiment was finally run which had the potential to resolve the conflict. It turned out that they were both right. The problem was an assumption in the Standard Model that neutrinos have no mass.
In other words, a scientific theory which had been perhaps surprisingly predictive for many years contained an assumption which had just been proven wrong by experimental result.
I love the following quote. It’s by an experimental physicist and Columbia University (and now MIT) professor named Janet Conrad who specializes in neutrinos:
Scientists have searched for so long—my whole scientific career—to find a problem with the Standard Model, and it has been very resilient. And that is why it is so exciting to suddenly come up with this new information that neutrinos have mass, because that doesn’t fit within our theory. And so, it’s like opening a door, and of course when you open a door, behind that, you find a lot more doors.
(from the episode transcript)
To me, this perfectly exemplifies what true science is. Conrad is excited that a longstanding theory has been (partially) proven wrong by real, hard, experimental result. Why? Because it reveals information. It points out new questions that need to be asked (and answered). Real science looks for things that are wrong with the current theory. It expects change, and it does not seek to find “truth” so that the “right answer” can be known once and for all. However, it also does not allow established theories to be toppled by just any old hypothesis.
People who back a certain hypothesis which I will not name are fond of pointing out that a theory is not a fact. I wholeheartedly agree. Theory is so much more powerful than fact because of its ability to predict future observations (AKA facts). And don’t you know that John Bahcall was thrilled when he learned that the theory that he helped create was able to predict the results of experiments performed decades later.
A lot more doors, indeed.
One reply on “A Lot More Doors”
Around 1997 I got to hear a colloquium on the Super-Kamiokande experiment, and then later another with what they’d found. It was great to get to see people grappling with the data. Plus it’s really fun to say “Super-Kamiokande” a lot.