General relativity / Elementary Tour part 4: The light side of gravity
For the propagation of light, Einstein's theory makes a clear prediction: Light is deflected by gravity. Just as test particles move on the straightest-possible lines in curved spacetime (i.e. on spacetime geodesics), so does light. The most basic example: ...
General relativity / Elementary Tour part 3: A planet goes astray
The first test of general relativity concerned a situation in which Newton's and Einstein's theories give almost the same result - with a small but crucial difference. The scene: our cosmic backyard, the solar system. The protagonist: Mercury, the planet ...
General relativity / Elementary Tour part 1: Einstein’s geometric gravity
The key idea of Einstein's theory of general relativity is that gravity is not an ordinary force, but rather a property of spacetime geometry. The following simplified analogy, which substitutes a two-dimensional surface for four-dimensional spacetime, serves ...
General relativity / Elementary Tour part 2: The cosmic dance
In this new picture, there is no gravitational force that masses exert on other masses. Instead, there are spacetime distortions. Spacetime in the presence of a mass is curved. In flat, empty spacetime, small test particles follow straight lines. However, ...
