1. To do:
Run through the ppt on Big Bang and Cosmology (resources.faulkes-telescope.com > GCSE Astronomy > Class Exercises > Cosmology
Complete the following worksheets:
Expansion of the Universe
Cosmic Microwave Background Radiation
Hubble Trouble
Galaxies Wordsearch

2. Age of the Universe Hubbleʼs Law is given by: v = H0d (1)
If a galaxy has travelled at a speed v for a time t since the Universe began, it will have travelled a distance d given by:
d=vt (2)
Putting (2) into (1) gives:
v=H0vt (3)
Cancelling out the vʼs gives:
t=1/H0

3. The Big Bang

4. What was the Big Bang? Big Bang theory says…
Universe started from an explosion

5. Evidence?
A glow - Cosmic Microwave Background

6. Echoes of the Big Bang
Penzias & Wilson found a faint background ‘hiss’
Leftover radiation from Big Bang!
Universe was originally filled with very high energy blackbody radiation
As Universe expanded, the radiation cooled, and predicted to be at microwave wavelengths – with T approx. 3K
Figure 26-6 The Bell Labs Horn Antenna
Using this microwave horn antenna, originally built for communications purposes,
Arno Penzias and Robert Wilson detected a signal that seemed to come from
all parts of the sky. After carefully removing all potential sources of
electronic “noise” (including bird droppings inside the antenna) that could
create a false signal, Penzias and Wilson realized that they were actually
detecting radiation from space. This radiation is the afterglow of the Big
Bang. (Bell Labs)

7. WMAP
Studied the whole sky and mapped the microwave emissions to very accurate levels.
WMAP has:-
Confirmed the age of the Universe as 13.7 billion years
Shown the existence of dark energy
Limited the effects of dark matter
Defined the stages of development of the Universe more accurately
Produced data on events of the first fraction of a second of the Universe
NASA’s Wilkinson Microwave Anisotropy Probe (WMAP)
The better the data that cosmologists have, the more accurate the explanations of what has taken place in the Universe.

9. Expansion of the Universe
What is the Universe expanding into?
Not an expansion into space, but an expansion of space itself.
Matter is more or less fixed. We are not expanding, nor is the Earth, the solar system, galaxy, or local group of galaxies. These are all held together by gravitational and chemical (i.e. electrical) forces.

10. Evidence? Galaxies are rushing away from each other
Observations from HST have found extremely high redshifted galaxies and quasars – shows they are moving away from us faster and faster….

11. The future of the Universe
An analogy:
Balance between kinetic energy
and gravitational energy
Can model expansion of Universe by thinking about a rocket leaving the Earth. A rocket leaving earth with vel less than esc vel will slow down and fall bk down.
One that travels with speed equal to escape vel will stop, but only when at an infinite dist away at an infinite time
Esc speed = 2GM/R^1/2
Density = mass/vol
Hubble Law says V=Hd
Subbing in gives critical density for Uni to expand forever. (Critical density for esc vel to be achieved)

12. The future of the Universe
As with the rocket, so with the Universe
Open Universe:
kinetic energy wins
Closed Universe:
gravitational energy wins
Esc speed = 2GM/R^1/2
Density = mass/vol
Hubble Law says V=Hd
Subbing in gives critical density for Uni to expand forever.

13. Fate of the Universe The future depends on the density of the Universe
High density : gravity wins : Universe is ‘closed’
Low density : expansion wins : Universe is ‘open’
Dividing line = critical density
Critical density = where the average density of matter is just high enough so the galaxies come to a halt in an infinite time when they’re infinitely far apart
Will the Universe expand forever? Depends on knowing the av density of matter it contains
As Uni expands, gravity will act continuously to slow it down and decelrate the expansion
If grav strength generated by this matter is too weak, Uni will carry on expanding and galaxies will continue to move away from each other. Universe = unbounded
If the density of matter is high enough, gravity will halt the expansion and the Uni will reach a max size sometime in the future. Gravity will then pull back allthe galaxies towards each other and the Universe will contract – BIG CRUNCH

14. Universe can be ‘open’, ‘flat’ or ‘closed’ depending on its density
We can investigate the fate of the Universe by using the interactive applet.

15. The bit we think we probably know a bit about…

16. Dark Matter Matter that is invisible to us (doesn’t emit EM radiation)
We can only ‘see’ it due to its gravitational influence
Evidence:
galaxy rotation curves
gravitational lensing
Could be: black holes, neutrinos, WIMPs (exotic particles)

17. Dark Energy
In 1998, astronomers found evidence that the expansion of the Universe was accelerating
Repulsive force of negative gravity – dark energy
Look at:

18. Summary
Observations suggest the Universe began ~13.7 billion years ago
It is expanding
It is expanding faster now than in the past…Dark Energy?
Most of the mass of the Universe is not “normal matter”…