What if Einstein was wrong? In developing his Theory of Relativity in 1905, he stated that nothing could travel faster than the speed of light. That pronouncement hasn’t prevented physicists from searching for faster-than-light particles, and the tachyon is the most sought-after—and elusive—prize.
This hypothetical particle was proposed 50 years ago, and in 2011 physicists at Geneva’s CERN laboratory, whose work focuses on fundamental physics, claimed to have found evidence for its existence. Though the experiment’s findings were later proven wrong, some physicists are continuing the search.
Several lines of evidence are used to support that quest. A recent analysis of neutrinos emitted from supernova 1987A, approximately 168,000 light-years away, and an analysis of data involving high-energy cosmic rays suggest that one of the neutrinos is a tachyon. If proven, the existence of tachyons could prompt a wholesale re-evaluation of the standard model of particle physics and cause physicists to rethink how the cosmos works. For example, a hypothetical technology using tachyons is claimed to be capable of sending messages backward in time. (Wouldn’t it be nice to tell your earlier self to get in on Google stock when it was first offered?)
Robert Ehrlich, professor of physics and astronomy at George Mason University, discusses the nature of the evidence for tachyons, the motivation for the idea, whether their existence conflicts with relativity, philosophical implications (including backward time-signaling), current empirical searches for tachyons, and proposed tests that he thinks might prove—or disprove—the existence of this mysterious but potentially powerful particle.