IB Astrophysics option part 4. See also http://nothingnerdy.wikispaces.com

1. presents
a production
COSMOLOGY
based on the IB Astrophysics option
1

2. COSMOLOGY
Where did the universe come from?
Olbers’ paradox
Red shift
Expanding universe
The Big Bang
Open universe
CMBR
International space research

3. Olbers’ paradox
Why is the night sky dark?
If the universe is infinite and ageless (according to
Newton’s model), the night sky should be uniformly bright
since there will be stars in every direction. If stars are
further, away they will be less bright but more numerous.
The brightness decreases according to the inverse square law,
but the number of stars is proportional to distance cubed.
SOLUTIONS
The universe is not infinite in size.
The universe is not infinitely old. Some light has not yet arrived.
The universe is expanding so some of the light has been
stretched (red-shifted) outside the visible spectrum.

4. Red shift
An application of the Doppler effect
The wavelength of light from an object which is receding will
increase (and the frequency decrease). This means that the
known absorption lines in the hydrogen spectrum will be found
nearer the red end of the electromagnetic spectrum. From this we
can calculate the speed of the object.
For an object which is approaching, the emitted light will be blue-
shifted (shorter wavelength and higher frequency).

5. Expanding universe
In the 1920s, Edwin Hubble realised that the
spectra of all distant galaxies show a redshift,
which means that they are all moving away
from Earth. This lead to the conclusion that the
space-time of the universe is expanding.
At some time in the past, all of the matter in
the universe originated at one point. Space
and time were created when it began to
expand.

6. The Big Bang
13.7 billion years ago, the universe, space and time were
created and the universe began to expand. Before this,
according to the theory, there was NOTHING.

7. CMBR
Cosmic Microwave Background Radiation
Models of the early universe suggest that after 300
thousand years, it became transparent for the first
time (at 4 000 K) and high frequency photons could
pass through it. As the universe has expanded, this
radiation has been red-shifted until it has become
microwave radiation. This represents a temperature
of 2.7 K.
The existence of the CMBR was predicted in 1948,
but at that time it had not been detected.

8. Detection of the CMBR
In 1964, Penzias and Wilson
were working with a microwave
aerial and found that no matter
in what direction they pointed
the aerial it picked up a steady,
continuous background
radiation.
The COBE and WMAP
satellites measured tiny ripples
in the CMBR, the seeds of the
first stars and galaxies.

9. Fate of the Universe
There are different ideas about the
future of the universe depending on
how much mass it contains.
Flat universe has a critical density so
that its expansion will slow down due
to gravity but never stop.
Closed universe has higher
density, gravity will halt its
expansion and it will contract.
Open universe has lower density
and it will expand forever.

10. Measuring density
To predict the fate of the universe
The mass of the matter in the universe can be estimated
by measuring stars and interstellar gas, but we find that
the mass of observable matter is far too small to hold
galaxies together.
To solve this problem, astrophysicists have suggested and
observed dark matter (5 times more abundant than
matter), but they do not know what it is made of.
In 1996, the expansion of the universe was measured to
be increasing. To explain this, dark energy has been
suggested (3 times more abundant than dark matter) but
we do not know what it is.
CONCLUSION: the universe is open

11. The universe is made of
Heavy elements
Neutrinos
Stars
Free hydrogen and helium
Dark matter
Dark energy
Dark matter could be Weakly Interacting Massive Particles
(WIMPs) - preliminary observations have been made.
Or Massive Compact Halo Objects (MACHOs) - normal matter
which doesn’t emit light such as black holes, neutron stars,
brown dwarfs have also been suggested, but theory rules this
out; the Big Bang did not make enough normal matter.

12. Space Research
Many modern space projects are the
result of international cooperation.
Examples: Hubble Space Telescope; International Space Station;
International X-ray Observatory; Very Large Telescope in Chile
12

13. a production
MUCH MORE AT
http://nothingnerdy.wikispaces.com
http://nothingnerdy.wikispaces.com/E4+COSMOLOGY
13