GENERAL RELATIVITY Structure of the Universe
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GENERAL RELATIVITYStructure of the Universe
1. Stars and Galaxies 2. Expansion of the Universe3. Creation of the Universe
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Sizes Enormous distances measured in
= Distance travelled by light in one year(1 light second = 186,000 miles)
Light Years
Earth-Sun = 8 light minutes
Milkyway = 100,000 light years
Universe = billions of light years
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• Stars like the Sun collect in (typically) rotating spiral galaxies• Each galaxy contains billions of stars, dust, and Dark Matter• There are billions of galaxies in the universe
The Universe
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According to GR, mass/energy of matter determines geometry of space-time.
Apply to entire universe:
Curvature = Mass of Matter - Vacuum Energy
Gravity attracts galaxies (matter) to one another
Empty space acts to pushmatter apart
So what does our universe do?
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Hubble first discovered galaxies are moving away from us (receding)
Speed of recession grows with distance from us (linearly)
Universe is expanding
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Where is the center, edge of the expansion ? Need have no answer
Imagine space is surface of sphere:
• As surface expands, galaxies move apart• There is no center• There is no edge(finite but unbounded)• Space is `created’
Universe could be infinite or finite, with or without boundary(we haven’t seen a boundary yet)
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Imagine rewinding expansion….. GR retrodicts there was a beginning of space-time
BIG BANG
GR describes a singularityat which all Space*Time*** Matter*** was created.
*Not created `inside’ anything.**No `before’.***No cause.
Microwaves fill the universe from the initial heat of the
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Imagine fast-forwarding the expansion….. GR predicts it will expand for ever
Energy of empty space (Dark Energy) is now stronger than gravity pulling galaxies back together
expansion of universe is accelerating