Cosmology

Question 1

What is the theory of the Big Bang?

Answer 1

• 14 billion years ago, the universe began from a very hot and dense point
• Here there was a giant explosion known as the Big Bang
• This caused the universe to expand, cooling as it did so as it became less dense - it is still expanding today
• Each point is expanding away from each other - galaxies move away from each other but are always separated by even amounts, and the further away they are the faster they move

The lighter objects will also move at a faster speed to heavier objects

Question 2

What is galactic red shift?

Answer 2

• Due to the doppler effect, light spectrums from supernovae in other galaxies appear to have a higher wavelength (so a lower frequency)
• This means they are red-shifted, and can appear to look more red
• This means they are moving away from earth
• The galaxies moving the fastest exhibit the largest red shift - these are the ones which are now further away

The opposite effect - when a light emitting object is moving towards you and the wavelength appears lower and the frequency higher - is known as blueshift (as blue light has a lower wavelength)

Question 3

How does galactic red shift provide evidence for the big bang?

Answer 3

• Galaxies moving away from earth means that the universe is still expanding as galaxies are moving away from each other
• This is what would be expected after a large explosion such as the big bang - matter moving out in all directions with differing speeds depending on mass

Question 4

What is the relationship between change in wavelength, reference wavelength, velocity of a galaxy and speed of light in order to calculate the doppler shift of light from galaxies?

Answer 4

• Change in wavelength/reference wavelength = velocity of a galaxy/speed of light
• λ -λ₀/λ₀ = v/c

Question 5

How is red shift different depending on which galaxy we are observing?

Answer 5

• Light spectrums produced by more distant galaxies are redshifted more than galaxies closer to us
• This is because these galaxies are moving away from us at a higher velocity
• If anything was moving towards us (no galaxies are due to the big bang), the light would be blueshifted

Question 6

What is the cosmic microwave background radiation theory and how does it provide evidence for the Big Bang?

Answer 6

• Radiation in the microwave region was detected in space coming from all directions at a uniform temperature
• This was most likely from the early stages of the universe which were very hot and dense and would have emitted thermal radiation in the form of microwaves
• At first, it would have been very high energy and gamma but the wavelength expanded as the universe expanded (redshift)
• There is no other credible source for these waves, so it must have been from the hot material in the early stages of the universe

Some areas of the universe have CMBR of a slightly lower temperature, indicating a lower density of galaxies, though it is mostly uniform