Big Bang Theory – A History

1927: Belgian priest Georges Lemaître proposes that the universe began with the explosion of a "primeval atom".

Einstein develops a mathematical model of how gravity works on the scale of the entire universe and discovers that his equations suggests that the universe should be expanding. Believing this to be nonsense he adds a “fudge factor” called the cosmological constant to recreate a steady-state universe.

1930s: Hubble observes the expansion of the universe – Hubble's law

George Gamov suggests that if the universe is expanding then at one point intime it must have been very small, and very hot

Fred Hoyle an opponent of the expanding universe theory coins the term Big Bang to ridicule the theory.

Hoyle's steady-state theory explained the expansion in a way that didn't requirethe universe to have ever been small

The debate continued until the discovery of the Cosmic Microwave Backgroundradiation.

Proves that the universe was once small!

George Gamov's theory suggested that once the universe was so small that it must have been hot enough to generate nuclear reactions – like in the centre of a star.

This early universe would have initially been opaque to light, but then as it expanded the light would escape as a hot blackbody radiation.

The Cosmic Microwave Background

This radiation would cool as the universe expanded until after 13 billion years (the present age of the universe) it would be 2.7 K, or microwave radiation.

Penzias and Wilson from Bell Labs in the early 1960s built a microwave receiver for satellite communications and noticed that where ever they pointed their receiver they picked up a strong background noise. Turns out that they were receiving thismicrowave radiation created from beginning of the universe.

The COBE satellite in 1990 revealed that the radiation is not perfectlysmooth but has ripples – the formation of galaxies and structure in the universe

Solves Olber's paradox

Future of theuniversedepends uponit's densitycomparedto the critical density

Dark Matter

COBE showed us that the universe is flat (ripples look the same inall directions)

BUT not enough visible matter in the universe to reach critical density

In fact for the universe to be flat it must contain over 90% dark matter!

Also the rotation curves of galaxies suggest that galaxy halos are dominatedwith dark matter.

Maybe galaxies formed in dark matter gravitational wells.

What is Dark Matter?

MACHOs

WIMPs

MOND

Dark Energy

In fact the universe is expanding more quickly than it should be.

Supernova observations.

Big Rip