Perhaps the most well-known equation in all of physics is Einstein’s E = mc². Does mass or energy increase, then, near the speed of light?
One of the most puzzling features of nature is this: as you approach the speed of light, everything you commonly understand about motion changes. If you’re on a train moving forward at 30 m/s (about 67 mph) and you throw a baseball forward at 30 m/s from it, to someone on the ground, they’ll see the baseball move forward at 60 m/s: much faster than any human could throw it from the ground. But if that train were moving at 60% the speed of light and the baseball were thrown at 60% the speed of light, that same observer on the ground wouldn’t see that baseball moving at 120% the speed of light, but rather only at 88% the speed of light. The familiar rules of how velocities add-or-subtract is different, and more complicated, at speeds close to the speed of light.
Other, familiar rules change as well: distances appear contracted, times appear dilated, and the energy of a fast-moving particle is greater than a slow-moving particle or one at rest, too. But, particularly when it comes to energy, how can we make sense of that? Does the particle’s mass change as well? That’s what Jerry…
