Arthur Macdonald is a Canadian astrophysicist. Born August 29, 1943 in Sydney, Nova Scotia, he obtained his Master of Science degree from Dalhousie University in 1964 and shortly after received a PhD from the California Institute of technology. He is currently the director of the Sudbury Neutrino Observatory Institute. He is most famous for proving neutrinos have mass. He did this by showing experimentally that they oscillate between different types of neutrinos (electron, muon and tau). After knowing that neutrinos oscillate though different types it is easy to show that they have mass: If they didn’t the neutrinos would travel at the speed of light and wouldn’t experience time (according to relativity). If this was true they wouldn’t be able to oscillate between states, therefore they must have mass. He did this work in the Sudbury Neutrino Observatory, a facility located 2.1 km underground made to solve the solar neutrino problem, which it did. The results he obtained from working there were of 5 significance meaning a chance of statistical error are smaller than 1 in a 1 000 000. He was awarded the Nobel Prize in 2015 for that work (it was shared with Professor Takaaki Kajita). His contribution to society was the advancement of human knowledge, doing science for the sake of science itself. In hisown words “”We are very satisfied that we have been able to add to world’s knowledge at a very fundamental level.”He now holds theGordon and Patricia Gray Chair in Particle Astrophysicsin Queen’s University.