1. Matter Unit
BIG BANG NOTES

2. Edwin Hubble First to realize that galaxies
lie outside the Milky Way …
… by measuring their distances using Cepheid variables as ‘standard candles’
Edwin P. Hubble ( ) was trained as a lawyer, before boredom made him turn to astronomy instead
Cepheid variables oscillate in brightness with a regular period that depends on their luminosity. By measuring this period, they can be used as standard candles.

3. Cosmic Speedometer
When a galaxy is receding, light waves travelling to us are red-shifted
Hubble measured the spectrum of these galaxies and found the spectral lines to be red-shifted
The faster the recession, the greater the red-shift

4. Doppler Effect
Doppler Effect is the shift in frequency and wavelength of waves which results from a source moving with respect to the medium, a receiver moving with respect to the medium, or even a moving medium.

6. Expansion of the Universe
… ‘winding’ backwards, the universe must have had a beginning

8. Georges Lemaître
Proposed that the universe began with the explosion of a ‘primeval atom’
His model was improved by George Gamow and others, who proposed that elements were forged during this hot and dense stage
Known as the Big Bang theory today; coined by Fred Hoyle who proposed a rival theory ...
Georges Lemaître ( ) was a Belgian Catholic priest who was fond of saying there is no conflict between science and religion

9. Steady State Model
Universe is expanding, but maintains a constant average density
Matter is continually being created in the voids to form new stars, galaxies
Universe has no beginning and no end
But disproved with the discovery of …

10. Cosmic Microwave Background (CMB)
Background radiation from the sky that is isotropic (same strength in all directions)
Corresponds to a temperature of just 2.7 Kelvins
Identified as the radiation left over from the Big Bang explosion
Arno Penzias (right) and Robert Wilson of Bell Laboratories, next to the horn antenna with which they discovered the CMB in 1965

11. Tests of the Big Bang Theory
Expansion of the universe
Cosmic microwave background
Relative abundances
of hydrogen,
deuterium,
helium and lithium

12. Obtaining the Age of the Universe
Extrapolate the current expansion rate (Hubble constant) back to the Big Bang
10 to 20 billion years old
Look for the oldest stars (in globular clusters)
11 to 18 billion years old
Best current estimate is ± 1.6 billion years
M10 Globular Cluster

13. Summary: Timeline of the Universe

15. Big Bang Timeline
The universe began with an expansion of all the matter and energy of the universe.
The universe begins to cool off.
Gravity begins to take effect and subatomic particles form.
The basic elements (hydrogen and helium) form.

16. The Cat's Eye Nebula has an AGB star at its center.
These gaseous supernova remnants glow in colors determined by the elements they contain. For example, the dark blue areas are rich in oxygen and the red material is rich in sulfur.
Orion nebula, a region of intense star formation.
Much of the brightness in this infrared view of the Horsehead nebula comes from PAH emissions.

17. Big Bang Timeline
As the enormous cloud of hot gas cools electrons fuse with the basic elements to make heavier elements.
Stars begin to form and galaxies are formed.
Stars are starting to die and putting heavier elements into space.
Heavier elements combine to form planets that orbit a central star.

18. The Big Bang Theory
The violent expansion of an extremely small, hot, and dense body of matter between 12 and 18 bya (billion years ago).

21. Fusion of Stars Smaller nuclei collide and fuse releasing
a large amount
of energy and creating
heavier
elements.

22. Elements up to the weight of iron are manufactured in stars.
Elements heavier than iron are formed when a supernova explodes.

23. Major Evidence
We are reasonably certain that the universe had a beginning.
Galaxies seem to be moving apart from each other.
We have found remnants of the heat believed to be from the big bang.
The abundance of hydrogen and helium in the universe seems to support the theory.