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Cosmology
Some important questions
• Did the universe have a beginning or has it always existed?
• Will the universe end?• If it ends, what will happen at the end?• Is the Universe infinite or does it have a
boundary?
The Universe is expanding!
• During the 1920s, Edwin Hubble and Milton Humason found that galaxy spectral lines were redshifted
The distant galaxies are moving away from us!
The Universe is expanding!
Hubble’s Law The most distant galaxies had the largest redshifts and speeds.
Hubble’s Law
velocity of galaxy = Hod=(Hubble’s constant) (distance to the galaxy)
Expansion without a Center
The Universe is not infinitely old!
• If the universe is expanding, it must have been smaller in the past
• In the beginning of time all material was in a
“singularity” with infinite density
• The Universe is 14 billion years old
An “event” called the BIG BANG created the Universe and caused it to expand
COsmic Background Explorer(COBE) Satellite (1990)
Penzias and Wilson (1965)
The 2.7K cosmic microwave background radiation that fills all space is evidence for the BIG BANG
Cosmic Microwave Background RadiationBy COBE 1990
Cosmic Microwave Background RadiationBy WMAP 2001
Structure of the Universe
Figure 17.18
The Inflationary Universe
Figure 17.15
E=mc2: Energy
turn into mass-particle and
antiparticle pairs
Fire and Ice
“Some say the world will end in fire,Some say in ice.From what I’ve tasted of desireI hold with those who favor fire.But if it had to perish twice,I think I know enough of hateTo say for destruction ice Is also great And would suffice”
- Robert Frost
Fire?
• If we live in a high density closed Universe: The expansion of the Universe will stop. The Universe will collapse; all matter and energy will be squeezed back into a singularity at high temperatures
• If we live in an oscillating Universe:
Cycle of Collapse then rebirth in another “Big Bang”
Ice?If we live in a low density open or critical density flat
Universe, the Universe will expand forever:
1. stelliferous era: lots of stars
2. degenerate era: brown dwarfs, white dwarfs, black dwarfs, neutron stars, black holes, planets
3. black-hole era: only objects left are black holes which will eventually evaporate
4. dark era: low-energy photons, neutrinos, and some elementary particles (10110 years)
The Universe would be a cold, lifeless, lonely world!
Geometry and Fate of the Universe
Critical Density:
Flat
and Infinite in Size
High Density:
Closed
and Finite in Size
Low Density:
Open
and Infinite in Size
In the past we thought we live in a low density Universe...
The Universe is open and will expand forever!!
If the force of gravity is acting on theUniverse, the expansion should be slowing down
But there may be a force that is speeding up the expansion of the
Universe!
• If the Universe is speeding up, there must
be a force that acts opposite to gravity
• This “fifth” force should be a long range repulsive force -“anti-gravity”
• Suggests that vacuum has a nonzero, positive energy density called dark energy
Dark Energy Dominates all of Space!
• Dark Energy causes space to expand faster with time
• Energy density due to dark energy + the density to matter exactly = The Critical Density!
Now...
There is enough density so thatit equals the critical value for the Universe to be flat!
Only 30% is made of matter and 70% is made of dark energy!
Something to think about…
Is our Universe the only universe or could it be one of many???
Do they exist in other dimensions???
Can we access them through wormholes???
Multiverse Theory
New universes can sprout out within any black hole?
The Superstring Theory
• Each fundamental particle (quark, electron, neutrino) is a different vibration mode of a tiny, elongated, one-dimensional energy packet called a “string”
• “strings” are so small (10-33 cm), they are almost point-like
• Universe is 11-dimensional, but 7 of the dimensions are too small to see
