View Post

Wandering Stars

In Relativity by Brian Koberlein

One of the consequences of general relativity is that light can be deflected by nearby masses. Mass curves space, and this curvature causes light to bend slightly. It was first observed during a total eclipse in 1919. The effect is extremely small unless the light passes close to a large mass, so gravitational lensing (as it is typically known) is usually only noticed with objects such as lensed galaxies, or specific tests of general relativity. But even though the effect is small as you get further from a mass, it isn’t zero. As our astronomical measurements become more precise, the effects of gravity are starting to become something we can’t ignore.

View Post

Flight Delay

In Relativity by Brian Koberlein

It’s a well known law of physics that the speed of light (in a vacuum) is always the same, regardless of your frame of reference (essentially your vantage point). But this isn’t entirely true. It actually depends on how you define “speed”.

View Post

In the Red

In Relativity by Brian Koberlein

If you toss a ball into the air, it will slow down as it rises. The Earth’s gravity pulls on the ball as it moves upward, causing it to slow down until it comes to a momentary stop at its highest point. Then it will begin to move downward, speeding up as it does. Suppose, then, that you were to shine a flashlight upward. What would happen? You might argue that gravity would pull on the photons, causing them to slow down, but we know that light has a constant speed, and can’t slow down. You might argue that since photons are massless gravity doesn’t affect them, but we know that the Earth’s mass, like any other mass, can cause light to change directions. So neither of these can be the answer. The real answer is pretty interesting, and it turns out to be one of the tests of Einstein’s theory of relativity.