general relativity

Galileo’s Thoughts on Gravity

believed all objects fall at the same speed unless air \n resistance or some other force acts upon them

Newtonian Picture

gravity is the attractive force that exists between two objects. \n • a property of the space in the presence of an object with mass the gravitational field.

Einstein’s ‘Happiest \n Thought’

This means that gravity can be cancelled \n out by acceleration !!

Einstein’s ‘Equivalence Principle

gravity is equivalent to acceleration

The Equivalence Principle

The effects of gravity are exactly \n equivalent to the effects of acceleration

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Suppose you were in a closed room. \n • on Earth or accelerating through space at 9.8 m/s2 \n • you would never know the difference \n • your weight would be the same

Matter Distorts Spacetime

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

Space-time Curvature

Einstein’s theory of General Relativity says that \n space-time is curved by the presence of a mass

the curvature then \n explains the the \n movement of the matter.

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What is Gravity

The curvature of the spacetime continuum is produced by the presence of mass. \n Massive object distorts spacetime continuum more.

mass and spacetime

orbits can now be explained in a new way

an object will travel on as ++straight a path as possible++ through ++spacetime++

The Strength of Gravity

• The more spacetime curves, the stronger gravity \n • increase gravity/curvature of spacetime: increased mass greater curvature \n at distances away from it

•curvature is greater near \n denser object

Bending of Light under Gravity

\++Light will always travel at a constant velocity.++ \n • therefore, it will follow the straightest possible path through spacetime \n • if spacetime is curved near a massive object, so will the trajectory of light

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Bending of light by gravity

E = mc2 \n energy is equivalent to \n mass

Gravitational Lensing

• Since that time, more examples \n of gravitational lensing have \n been seen. \n • They usually involve light paths from \n quasars & galaxies being bent by \n intervening galaxies & clusters