3 Sources Of Evidence Towards The Big Bang

The Big Bang theory suggests the the Universe originated in a very hot and very dense state from which it has expanded and cooled.

Red Shift

Red shift of light from distance galaxies is evidence that the universe is expanding because:
• Light from all galaxies is red shifted suggesting that all galaxies are moving away from us (and from each other).
• If all galaxies are moving apart it suggests that they started from some common point and expanding outwards.

Cosmological Microwave Background Radiation

The cosmological microwave background radiation (CMBR) is evidence that the universe used to be very hot because:
• If the universe used to be much hotter, nuclear fusion of hydrogen would have taken place producing helium and EM radiation.
• This radiation would still be around today, but red shifted because of the expansion of the universe.
• This is CMBR.

Cosmological Red Shift

• For light from objects that are very far away the red shift is due to the expansion of space itself as the waves travel through it (rather than due to an object moving through fixed space).
• This is called cosmological red shift, Z.
• From the cosmological red shift we can calculate how much the universe has expanded since the light set off.
From this, we can produce the equation:

R observed / R emitted = λ observed / λ emitted

But, the observed λ wavelength will be equal to λ emitted λ.
• R observed / R emitted = (λ emitted λ) / λ emitted.
• R observed / R emitted = λ / λ emitted.
The cosmological red shift is given as λ / λ emitted = Z. Therefore…

λ / λ emitted = 1 + Z

Summary

We can provide evidence towards the big bang theory:

• Red shift of light from distance galaxies (wavelength increases therefore moves towards the red spectrum).
• Cosmological Microwave Background Radiation (CMBR). The radiation from the nuclear fusion of hydrogen atoms can still be picked up which is present in every direction. However, the radiation has red shift due to the expansion of the universe (we on Earth know the wavelength of radiation from Hydrogen fusion by performing fusion of Hydrogen atoms on Earth). This gives evidence towards the universe being extremely hot.
• Cosmological red shift. The expansion of space itself has stretched waves that were emitted at the time of the big bang. We can tell from this how much the universe expanded since the light set off.