Gravity (notes on others)
Principle of equivalence: unlike charge, gravitational field is a property of mass itself. i.e. inertial mass = gravitational mass. The force required to make things move is same as force of gravity. When an body is in gravitational free fall under earths gravity, it experiences no weight force since it creates a movement (inertial) field which balances out the gravitational one.
[Q. need these be exactly the same direction always e.g. are inertial and gravitational field equiv. to electrical and magnetic fields]
General relativity is largely a geometry problem based upon the following geometry:
2d Pythag: l^2 = x^2 + y^2
3d Pythag l^2 = x^2 + y^2 + z^2
4d Pythag l^2 = w^2 + x^2 + y^2 + z^2
but time dimension is diff, therefore:
space-time T^2 = t^2 - x^2 - y^2 - z^2
The Curved Space Time of General Relativity is to Minkowski Flat 4D space time as Riemann n dimensional curved geometry is to Euclidian geometry.
Singularities exist(ed) for black holes and the Big Bang
Black hole entropy is very high
Big Bang entropy is very low
Collapse into a singularity does not require a symmetric collapse (Penrose)
The Big Bang singularity was exceedingly unlikely
Penrose suspects that a quantum gravity would require an adjustment to quantum theory to make it time asymmetric, probable adjustment to Schrodinger wave equation. This is a maverick view.