This means that if the glare of the Sun were blocked, like it is during an eclipse, he would be able to see stars that should be behind it. Eddington knew that if mass curves spacetime, then light would travel in a curved path as it approaches a massive object like the Sun. 8.2 Confirmation of general relativityĪrthur Eddington confirmed general relativity after the 1919 solar eclipse. These ideas were formalised by the British astronomer Edward Milne in the 1930s, and verified by NASA’s WMAP (Wilkinson Microwave Anisotropy Probe), which launched in 2001. Homogeneity assumes that our observations are representative of the whole universe, and isotropy means that the universe is the same in whichever direction we look. This assumes that the universe is homogeneous and isotropic when averaged over very large scales. In order to apply his theories to the universe as a whole, Einstein applied the cosmological principle. This meant general relativity predicted that the path of light is bent by heavy objects, like the Sun. The shortest path, which may be curved, is known as a geodesic. Light moves through curved spacetime taking the shortest possible path, however, the shortest path across a curved surface is not necessarily a straight line. This means that the curvature of space and hence the force of gravity is invariant. General relativity shows that observers in any frame will agree on how spacetime is curved by objects and hence their gravitational field, whether they are moving relative the object or not. A tensor contains more than two properties, which may be written in a matrix - numbers or symbols that are arranged in rows and columns. Velocity, for example, is a vector as it represents speed in a given direction. The energy-momentum tensor is the source of the gravitational field, just as mass is the source of the gravitational field in Newton’s equations.Ī tensor is like a vector, which contains two properties. g μ ν is the metric tensor for Minkowski space, which describes all the intrinsic properties of the spacetime manifold, including time periods, distances, volumes, and the curvature, and finally, T μ ν is the energy-momentum tensor, which describes the distribution of matter. R μ ν is the Ricci tensor, which describes the relationship between Euclidean and non-Euclidean geometry. Here, G μ ν is the Einstein tensor, which describes the curvature of spacetime.
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