The Evidence for the Big Bang

Student Resource Sheet 5Science and Religion in Schools: Unit 4a

Unit 4a

Evidence for the Big Bang

The Big Bang model is a concise explanation for 3 independent observations:

The red shift of light from distant galaxies The presence of large amounts of helium in the universe The cosmic microwave background radiation

Each can possibly be explained in other ways, but the Big Bang model draws all of them together into a convincing story

Unit 4a

The red shift

Spectrum of light from the sun Fraunhoffer lines

Light from a cluster of galaxies 109 light years away

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z =λ2 − λ1λ1

=Δλ

λ1

Unit 4a

Hubble’s original data

Red shift due to expansion Further away, the longer the light

has been traveling Universe has expanded more Red shift is bigger

The velocity (speed) is basically how much the distance to the galaxy has changed in the age of the universe

Unit 4a

Much improved data

Distance scale 250 x bigger Much more convincing!

Implication - the universe had a start

Unit 4a

Expansion of the universe

Expansion of the universe is NOT a rushing to fill empty space

The WHOLE universe is expanding - there is no empty space

the universe as a box filling with galaxies

the universe as expanding space

Unit 4a

Helium abundance

Universe is 24% He (by mass) Stars fuse hydrogen into helium

In 14 billion years, stars have not burned hot enough, or long enough to make this much helium

The oldest stars (11 billion years) also have ~ 24% Heso this He cannot have been made in stars!

Big Bang - in early history the whole universe was the same temp as the inside of a star!

Fusion in the first three minutes of history made the helium This shows that the universe was hot in earliest times

Unit 4a

Cosmic Microwave Background

Arno PenziasRobert W Wilson (Nobel Prize, 1978)

Persistent microwave noise independent of time and direction

Relic radiation from Big Bang Thermal radiation now redshifted so it

is in the microwave part of the spectrum

Unit 4a

CMB (Cosmic Microwave Background) for fun and profit

Dates to 300 000 years into history Epoch of recombination (bad name!)

Before then, all matter ionized At this time temp of universe down to the

point at which atoms could form All free electrons captured Thermal radiation decouples from the

matter Imprint of matter density on temperature

variations

The density fluctuations ‘seed’ galaxy formation

WMAP whole sky map±200 K