Does mass increase when nearing the speed of light?
The concept of ‘relativistic mass’ has been around almost as long as relativity has. But is it a reasonable way to make sense of things?
No matter who you are, where you are, or how quickly you’re moving, the laws of physics will appear exactly the same to you as they will to any other observer in the Universe. This concept — that the laws of physics don’t change as you move from one location to another or one moment to the next — is known as the principle of relativity, and it goes all the way back not to Einstein, but even farther: to at least the time of Galileo. If you exert a force on an object, it will accelerate (i.e., change its momentum), and the amount of its acceleration is directly related to the force on the object divided by its mass. In terms of an equation, this is Newton’s famous F = ma: force equals mass times acceleration.
But when we discovered particles that moved close to the speed of light, suddenly a contradiction emerged. If you exerted too large of a force on a small mass, and forces cause acceleration, then it should be possible to accelerate a massive object to reach or even exceed the speed of light! This isn’t possible, of course, and it was Einstein’s relativity that gave us a way out. It was commonly explained…
