Matter Unit BIG BANG NOTES

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 (1889-1953) 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.

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

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.

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

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 (1894-1966) was a Belgian Catholic priest who was fond of saying there is no conflict between science and religion

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 …

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

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

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 13.4 ± 1.6 billion years M10 Globular Cluster

Summary: Timeline of the Universe

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.

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.

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.

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).

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

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

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.