It was almost like kindergarden. One by one, decked out with our nametags and matching knapsacks, each of us chose a boxed lunch and filed into the classroom. There we sat, in a circle, waiting for the woman whose job it was that day to teach us something new. But when Dr. Bonnie Fleming of Yale University arrived, it wasn't a group of five year olds that she stood before; instead, it was a small group of science journalists from around the country, all gathered there to eat, relax, and listen to the latest news in neutrino physics.
"Neutrino physics is a field with many great stories," Fleming began. She then went on to explain that one of the most well-known of these stories is that of flavor oscillation. As it turns out, neutrinos have a sort of quantum mechanical ADD. Rather than sticking with one identity, neutrinos tend to change states spontaneously over the course of their travels. An electron neutrino may suddenly become a tau neutrino, and then a muon neutrino, and then a tau neutrino once more long before you or I have had the chance to ask, "what the- ?"
Regardless of flavor, however, all neutrinos have been said to interact via the same fundamental force: the weak force. As we sat dutifully munching on our sandwiches, Dr. Fleming invited each of us to lay one of our palms on the table and count to three. During that short time, she explained, over a trillion neutrinos had passed through every one of our outstretched hands. Indeed, a neutrino could pass straight through 200 Earths before having any appreciative chance of hitting anything. Physicists call it the "weak" force for a reason.
However, new research at Fermilab has suggested that there may be a fourth, even lazier type of neutrino - one that, unlike its electron, muon and tau counterparts, interacts via the gravitational force rather than the weak force. Perhaps surprisingly, gravity is actually the weakest of the four fundamental forces. If you're not convinced, just rub a balloon against your hair, stick it to the wall, and rest easily in the knowledge that you have just overcome the gravitational influence of the entire planet. Gravity's unbelievable frailty would make directly detecting the alleged new flavor of neutrino, dubbed the sterile neutrino, one of the most daunting tasks yet undertaken by the particle physics community. As it is, neutrinos are notoriously difficult to pin down. "We can only detect their flavor by whatever charged lepton they turn into," said Fleming.
As if neutrinos weren't hard enough to wrap your head around. Rather than exhaust myself by asking any more questions, I just sat there, ate my cookie, and let Dr. Fleming do rest of the talking.