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General relativity

Einstein’s theory of general relativity

General relativity (GR) is the geometric theory of gravitation published by Albert Einstein in 1915

It is the current description of gravitation in modern physics.

Luke Mastin writes (physicsoftheuniverse.com)

It generalizes Einstein’s theory of special relativity and Newton’s law of universal gravitation, providing a unified description of gravity as a geometric property of space and time (spacetime.)

As we have seen, matter does not simply pull on other matter across empty space, as Newton had imagined. Rather matter distorts space-time and it is this distorted space-time that in turn affects other matter.

Objects (including planets, like the Earth, for instance) fly freely under their own inertia through warped space-time, following curved paths because this is the shortest possible path (or geodesic) in warped space-time.

Its central premise is that the curvature of space-time is directly determined by the distribution of matter and energy contained within it.

What complicates things, however, is that the distribution of matter and energy is in turn governed by the curvature of space.

This leads to a feedback loop and a lot of very complex mathematics.

The presence of mass/energy determines the geometry of space – and the geometry of space determines the motion of mass/energy.

In practice, in our everyday world, Newton’s Law of Universal Gravitation is a perfectly good approximation.



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Learning Standards

2016 Massachusetts Science and Technology/Engineering Curriculum Framework

HS-ESS1-2. Describe the astronomical evidence for the Big Bang theory, including the red shift of light from the motion of distant galaxies as an indication that the universe is currently expanding, the cosmic microwave background as the remnant radiation from the Big Bang, and the observed composition of ordinary matter of the universe, primarily found in stars and interstellar gases, which matches that predicted by the Big Bang theory (3/4 hydrogen and 1/4 helium).

SAT Subject Test: Physics

Quantum phenomena, such as photons and photoelectric effect
Atomic, such as the Rutherford and Bohr models, atomic energy levels, and atomic spectra
Nuclear and particle physics, such as radioactivity, nuclear reactions, and fundamental particles
Relativity, such as time dilation, length contraction, and mass-energy equivalence

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