Transcript Foundation 1 - Discovering Astronomy

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
The 2.7K cosmic microwave background radiation
that fills all space is evidence for the BIG BANG
Penzias and Wilson (1965)
COsmic Background Explorer
(COBE) Satellite (1990)
Cosmic Microwave Background Radiation
By COBE 1990
Cosmic Microwave Background Radiation
By WMAP 2001
Structure of the Universe
Figure 17.18
The Inflationary Universe
Cosmological Timeline
Figure 17.15
E=mc2:
Energy
turn into massparticle and
antiparticle pairs
Fire and Ice
“Some say the world will end in fire,
Some say in ice.
From what I’ve tasted of desire
I hold with those who favor fire.
But if it had to perish twice,
I think I know enough of hate
To 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 the
Universe, 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 that
it 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