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

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

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**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. • 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 by Ernst Mach 1838-1902 ~ means ‘is equivalent to’.**Einstein can’t tell whether he is on the earth or in**space, accelerating at 1 g.**George Riemann**1826-1866 2. Riemann's Curved Geometry was another ingredient, implying acceleration ~ curved space-time**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.**Three experimental-observational proofs of General**Relativity: • 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 sun To test the bending of light by the sun’s gravity. He was the first to suggest this. It was later confirmed by another observation.**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.