Matter UnitMatter Unit

BIG BANG NOTESBIG BANG NOTES

The Big Bang TheoryThe Big Bang Theory The violent expansion of an The violent expansion of an

extremely small, hot, and dense extremely small, hot, and dense body of matter between 12 and 18 body of matter between 12 and 18 bya (billion years ago).bya (billion years ago).

Edwin HubbleEdwin Hubble

First to realize that galaxies First to realize that galaxies

lie outside the Milky Way …lie outside the Milky Way …

… … by measuring their distances by measuring their distances using Cepheid variables as using Cepheid variables as ‘standard candles’ ‘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 periodthat depends on their luminosity. By measuring this period,they can be used as standard candles.

Cosmic SpeedometerCosmic Speedometer When a galaxy is receding, light When a galaxy is receding, light

waves travelling to us are red-waves travelling to us are red-shifted shifted

Hubble measured the spectrum Hubble measured the spectrum of these galaxies and found the of these galaxies and found the spectral lines to be red-shiftedspectral lines to be red-shifted

o The faster the recession, the greater the red-shift

Doppler EffectDoppler Effect

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

Expansion of the UniverseExpansion of the Universe

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

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

Georges LemaîtreGeorges Lemaître

Proposed that the universe began with the Proposed that the universe began with the explosion of a ‘primeval atom’explosion of a ‘primeval atom’

His model was improved by George Gamow His model was improved by George Gamow and others, who proposed that elements were and others, who proposed that elements were forged during this hot and dense stageforged during this hot and dense stage

Known as the Big Bang theory today; coined Known as the Big Bang theory today; coined by Fred Hoyle who proposed a rival theory ...by Fred Hoyle who proposed a rival theory ...

Steady State ModelSteady State Model Universe is expanding, but maintainsUniverse is expanding, but maintains

a constant average densitya constant average density

Matter is continually being created in Matter is continually being created in the voids to form new stars, galaxiesthe voids to form new stars, galaxies

Universe has no beginning and no endUniverse has no beginning and no end

But disproved with the discovery of …But disproved with the discovery of …

Cosmic Microwave Cosmic Microwave Background (CMB)Background (CMB)

Background radiation from the sky that is Background radiation from the sky that is isotropic (same strength in all directions)isotropic (same strength in all directions)

Corresponds to a temperatureCorresponds to a temperatureof just 2.7 Kelvinsof just 2.7 Kelvins

Identified as the radiation left Identified as the radiation left over from the Big Bang explosionover 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 TheoryTests of the Big Bang Theory

Expansion of the universeExpansion of the universe

Cosmic microwave backgroundCosmic microwave background

Relative abundances Relative abundances

of hydrogen, of hydrogen,

deuterium, deuterium, helium and lithium

Obtaining the Age of the Obtaining the Age of the UniverseUniverse

Extrapolate the current expansion rate Extrapolate the current expansion rate (Hubble constant)(Hubble constant) back to the Big Bangback to the Big Bang

• 10 to 20 billion years old10 to 20 billion years old Look for the oldest stars Look for the oldest stars

(in globular clusters)(in globular clusters)

• 11 to 18 billion years old11 to 18 billion years old Best current estimate is Best current estimate is

13.4 ± 1.6 billion years13.4 ± 1.6 billion years

M10 Globular Cluster

Summary: Timeline of the Summary: Timeline of the UniverseUniverse

Big Bang TimelineBig Bang Timeline

1.1. The universe began with an The universe began with an expansion of all the matter and expansion of all the matter and energy of the universe.energy of the universe.

2.2. The universe begins to cool off. The universe begins to cool off. 3.3. Gravity begins to take effect and Gravity begins to take effect and

subatomic particles form.subatomic particles form.4.4. The basic elements (hydrogen and The basic elements (hydrogen and

helium) form.helium) form.

Big Bang TimelineBig Bang Timeline

1.1. As the enormous cloud of hot gas As the enormous cloud of hot gas cools electrons fuse with the basic cools electrons fuse with the basic elements to make heavier elements.elements to make heavier elements.

2.2. Stars begin to form and galaxies are Stars begin to form and galaxies are formed.formed.

3.3. Stars are starting to die and putting Stars are starting to die and putting heavier elements into space.heavier elements into space.

4.4. Heavier elements combine to form Heavier elements combine to form planets that orbit a central star.planets that orbit a central star.

Fusion of StarsFusion of Stars

Smaller nuclei Smaller nuclei collide and collide and

fuse releasing fuse releasing

a large amount a large amount

of energy and of energy and creating creating

heavier heavier

elements.elements.

Elements up to the weight of iron are manufactured

in stars.

Elements heavier than iron are

formed when a supernova explodes.

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.

The Cat's Eye Nebula has an AGB star at its center.

Major EvidenceMajor Evidence1.1. We are reasonably certain that the We are reasonably certain that the

universe had a beginning.universe had a beginning.

2.2. Galaxies seem to be moving apart Galaxies seem to be moving apart from each other.from each other.

3.3. We have found remnants of the heat We have found remnants of the heat believed to be from the big bang.believed to be from the big bang.

4.4. The abundance of hydrogen and The abundance of hydrogen and helium in the universe seems to helium in the universe seems to support the theory.support the theory.