NOTES FOR THE DAY: General Theory of Relativity (a gravity theory):

Ingredients:

The Principle of Equivalence: acceleration ~ gravity

Riemann's Curved Geometry: acceleration ~ curved space-time

( ' ~ ' means 'is equivalent to'.)

This implies: gravity ~ curved space-time (Einstein's Field Eqns.)

This is important when objects are massive, like sun or black hole. Supercedes Newton's Law in these cases.

Three experimental-observational proofs of General Relativity:1. Perihelion precession of Mercury's orbit. (Slow rotation of

ellipse.2. Light bends near the sun.3. Time slows in a strong gravity field. (Ex. Gravitational redshift, and clocks flown in planes vs those on ground.)

The General Theory of Relativity (GTR)is a new theory of gravity, beyond Newton’s, & based on two ingredients:

1. The Principle of Equivalence: acceleration ~ gravity

Conceived byErnst Mach1838-1902

~ means ‘is equivalent to’.

Einstein can’t tell whether he is on the earth or in space, accelerating at 1 g.

2. Riemann's Curved Geometry was another ingredient, implying acceleration ~ curved space-time

George Riemann1826-1866

The essential idea of Einstein’s GTR

acceleration ~ gravity and acceleration ~ curved space-time imply

gravity ~ curved space-time (Einstein's Field Eqns.)

This is important when objects are massive, like sun or black hole. Supercedes Newton's Law in these cases.

Black hole—HELP! We need Einstein!

Three experimental-observational proofs of General Relativity:

1. Perihelion precession of Mercury's orbit (slow rotation of elliptical orbit 16 degrees/10,000 yrs).

Three experimental-observational proofs of General Relativity:

2. Light bends near the sun.

Arthur Eddington went to South Africa during a total eclipse of the sunTo test the bending of light by the sun’s gravity. He was the first to suggest this.It was later confirmed by anotherobservation.

Three experimental-observational proofs of General Relativity:

3. Time slows in gravity

The frequency of light (time-dependent) is decreased by a massive star (toward the red end of the spectrum).

This is called a gravitational red shift.