1. A New Vision of the Cosmos
Albert Einstein
A New Vision of the Cosmos

2. Einstein’s Vision Space + Time = Spacetime
Four dimensions: 3 of space and 1 of time
Cosmos has only these 4 dimensions
Must know where and when

3. Natural Motion
Newton: Natural motion is constant speed along a straight line (constant velocity, no acceleration)
Straight line: Shortest distance between two points
Assumed: A flat (Euclidean) geometry

4. Einstein
NO assumption about local or global geometry of cosmos (flat or curved)
Options: flat (Euclidean), open (saddle), closed (sphere), in four dimensions (spacetime)
Natural motion: Freefall (weightlessness)

5. General Theory of Relativity
Gravity not a force! Natural motion in a curved spacetime.
Objects follow straight (4-dimensional!) lines in spacetime
“Matter tells space how to curve, and space tells matter how to move.”

6. Gravity-Two Views Newton: Forces (interactions at a distance)
Einstein: Courses (local paths in spacetime)
Predicts bending of light (eclipses, gravitational lenses), expansion of universe; used in GPS satellites

7. General Theory Cosmology
Physics of cosmological models
Explains past, predicts future
Big Bang (any geometry)
Big Bore (flat or open)
Big Crunch (closed)
Compare actual density to critical density (open, flat ≤ critical; closed > critical)