One of the predictions of general relativity is that the motion of large masses, such as a binary system of black holes or neutron stars, should produce gravitational waves. When most people think of waves they typically think of water waves. Drop a pebble in a calm pond and you can watch the waves spread out over the surface of …
Matters of Gravity
By the principle of general relativity, free fall under gravity and the absence of gravity feel the same because they are the same. The idea seems ridiculous because we can see the space station orbit the Earth, so something must be pulling it. But remember that space and time are not absolute.
Circling the Drain
It turns out that the rotation of a mass also distorts space and time. For example, as the Earth rotates, it drags the nearby space along with it (an effect known as frame dragging). Similar to water spiraling down a drain, this effect builds up, and as a result, space spirals a bit around the Earth. You have to be a bit careful with this comparison. Spacetime doesn’t “flow” the way water does, but the spiral effect is somewhat similar.
Gravitational Lensing
Einstein said space was curved, but how to we know it really is? It turns out we can observe that curvature by watching light bend around a large mass such as a galaxy.
The Attraction of Curves
When we say gravity is a curvature of space, what does that really mean? It all has to do with the fact that the laws of physics are the same from any vantage point.
Black Holes
Black holes are objects that are so dense that not even light can escape them. But that’s only if you get too close.
Frame Dragging
Frame dragging is one of those strange effects that occurs in general relativity. It happens when a rotating mass twists space. Strange as it is, we’ve observed the effect near Earth.
Equivalent Principles
The equivalence principle states that everything falls at the same rate in a gravitational field. But what about antimatter? We think it would fall just like regular matter, but we haven’t yet been able to put that assumption to the test.
Dark Matters
The first evidence of dark matter came from observing the motion of stars in our own galaxy. It turns out stars were moving far more quickly than they should. Ever since then astronomers have tried to determine just what dark matter is.
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