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Spacetime and GravitySpacetime and Gravity

Albert Einstein (1879 – 1955)Swiss/American physicist

Einstein’s Second RevolutionEinstein’s Second Revolution

• Gravity is the primary topic of the general theory of relativity.• What is the equivalence principle?• What is spacetime?

Isaac Newton saw gravity as a mysterious “force.”

Einstein theorized that the “force” of gravity arises from distortions of space (or spacetime) itself!

spacetime…the 4-dimensional combination of space & time that forms the very fabric of the Universe

Matter Distorts SpacetimeMatter Distorts Spacetime

• Matter distorts spacetime like weights on a taut rubber sheet.• The greater the mass, the greater the distortion of spacetime.

Warping of space and timeWarping of space and time

The Equivalence Principle The Equivalence Principle

For Einstein• intuition -- all motion should be relative• his equivalence principle: The effects of gravity are

exactly equivalent to the effects of acceleration.

Weak equivalence principleWeak equivalence principleIn a small region of space, the physical effects of a gravitational field as perceived by an observer are indistinguishable from the physical effects reported by another observer accelerating at a constant rate in the absence of a gravitational field. (A. Zee, p. 18)

Working with: Time Lines in SpaceTimeWorking with: Time Lines in SpaceTime

http://physics.syr.edu/courses/modules/LIGHTCONE/events.html

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