Testing GR

All tests of GR can be separated into two types: weak field limit, i.e. testing GR when deviations from Newton's gravity are weak, and strong field limit, when deviations from the Newton's law are large.

Weak field limit test are numerous (but they are less valuable, because there are alternative theories of gravity):

• bending of light by the Sun's gravity field;
• precession of planetary orbits;
• time delay due to the Earth gravity;
• gravitational redshift from white dwarfs.

Strong field limit tests are much more difficult to perform, but only they can convincingly confirm (or reject!) the GR:

• gravitational radiation from a binary pulsar;
• existence of black holes (?).

Conformal diagrams

Conformal diagram is a space-time diagram, in which infinity is (imaginary) squeezed to a finite distance from the center.

Properties of conformal diagrams:

• Light-like world lines still go at 45^o.
• Infinities are always light-like, i.e. they run at 45^o.
• All time-like or space-like world lines begin and end at the intersection of infinities or at singularities.
• All light-like world lines that connect intersections of infinities with singularities are called horizons.
• The full (conformal) space-time diagram can have only infinities or singularities as boundaries.

Here are five conformal disgrams that we will use in this class:

• Minkowski space-time:
  
• Schwarzschild black hole:
  
• Schwarzschild white hole:
  
• Full Schwarzschild space-time:
  
• kerr rotating black hole: