#2 A Brief History of Time - Space and time

Chapter 2:

1. Motion

   1. Aristotle: the natural state of a body is at rest, and motion is driven by a force or impulse

   2. Newton: 3 laws of motion

   3. Galileo's experiment: when falling, each body increases its state at the same rate, no matter what its weight is

   4. The denial of absolute motion and the understanding of relative motion

2. Light

   1. Light does not follow Newton laws, it has a fixed relative speed

   2. Since v is fixed, the disagreement on the distance light particles traveled, all of the observers has only one solution, that time is not absolute

3. Space-time

   1. It is not flat, but curved by the distribution of mass and energy in it

   2. In general relativity, bodies follow straight lines in 4d space-time, but they appear to us to move along curved path in 3d space-time (gravity)

   3. Light rays follow geodesics as well, so it can be bent