From the Ends of the Earth to the Beginning of the Universe Buried over a mile beneath the Antarctic ice, the IceCube Neutrino Observatory is a one-of-a-kind particle detector devoted to studying cosmic neutrinos: high-energy travelers from outside our solar system. Scientists believe that cosmic neutrinos, also known as ghost particles, may be formed by powerful events such as black holes at the centers of galaxies, gamma ray bursts, supernovas, star formations, and pulsars. The international IceCube Collaboration, led by UW-Madison physicists, hopes its findings will provide valuable glimpses into the origins of the universe. These nearly massless subatomic particles carry no electrical charge, which is what makes them so hard to detect. That’s why IceCube was built at the bottom of the world: the clear, abundant ice shields sensors from the distracting cosmic rays that bombard Earth’s atmosphere. With over 5,000 optical sensors the size of basketballs, IceCube can observe and capture the light that occurs when a neutrino slams into another particle. The shape of that light tells researchers both the energy of the neutrino and the direction from which it came. The elusive ghost particle may tell us a lot about our universe. Neutrinos could help us understand why the universe is built of matter rather than antimatter, and provide clues to greater astrophysical mysteries such as dark matter, the mysterious, invisible substance that scientists believe makes up over a quarter of our universe. By decoding cosmic neutrinos and their origins, UW-Madison researchers are seeking to expand our fundamental knowledge of the universe. Their work will spur astrophysics—and science as a whole—forward.