Not understanding the actions of neutrinos seems to be a common theme for scientists. As discussed in last weeks ADYK, claims that neutrinos travel faster than the speed of light are currently stumping scientific theory, but neutrinos have always been mysterious particles...
We discussed last week that neutrinos are neutral subatomic particles that are created in large quantities inside the sun. Astronomers in the 1940's hypothesized this, and decided to build detectors on Earth that would measure the amount of incoming solar neutrinos here on Earth. Based on the then current theories of solar fusion, astronomers predicted how many neutrinos they would expect to see in their detectors. Long story short, they measured only one third of the expected number of neutrinos, and the solar neutrino problem was born. Astronomers spent the next 50+ years trying to figure out where their theories went wrong. It was originally thought that neutrinos were massless particles, like light, and therefore existed in one form only. This turned out to be the problem, as was hypothesized by particle physicists in the 1960's and 1970's. If neutrinos had a tiny bit of mass, then quantum theory says that they have the ability to switch between three different "flavors" of neutrinos (electron, muon, tau), each with slightly different properties. If this were true, electron neutrinos would be created and released by the sun, then on their travels towards Earth, probability suggests that 33% would switch to tau neutrinos, and 33% would switch to the muon neutrinos. The detectors in the 1940's were only sensitive to electron neutrinos, and thus never detected the other two types (aka the other 66% of the missing neutrinos!). This sounded like a fantastic solution, but astronomers and physicist had to wait until the years 1962 and 2000 for the first detection of the muon and tau neutrino, respectively, thus confirming the theory. It was a long wait, but proving that neutrinos come in three flavors allowed scientists to refine the standard model of particle physics, and astronomers to really understand what was happening in the interior of stars.
