The Big Bang Model Flashcards
What is the cosmological principle?
On a large scale the universe is homogeneous and isotropic - so it doesn’t have a centre
What does homogeneous mean?
Every part is the same as every other part
What does isotropic mean?
Everything looks the same in each direction - so it doesn’t have a centre
Why do astronomers disagree on the value of Hubble’s constant?
Distance is difficult to measure
Why did Hubble suggest the universe was expanding?
He observed red shift and blue shift.
He used type 1a supernovae as standard candles
Which galaxies show redshift?
all (apart from very close ones)
What does redshift determine?
Recessional velocity
What is recessional velocity?
How fast the galaxy is moving away
What is proportional to recessional velocity?
Distance:
Further away = faster it’s travelling
What is Hubble’s law?
Why must the universe have been smaller and hotter in the past?
Because it is expanding and cooling down (because it’s a closed system) today.
So further back it must have been denser and hotter
What is the Hot Big Bang theory?
The universe was in a hot dense state.
14 million years ago expansion started.
What does the rate of expansion of the universe all around us show?
Uniform expansion away from us.
We appear to be at the centre.
What equation can estimate the age of the universe if it has been expanding at the same rate its whole life?
t = distance/velocity
v = Hd
1/H = d/v
Therefore,
t = 1/H
How do scientists describe the limit of the size of the OBSERVABLE universe?
+How old do they think it is, with and without taking into account expansion of the universe?
A sphere - earth in the centre.
Radius = maximum distance light can travel during the age of universe (taking into account the expansion of space).
If H = 75kms^-1 Mpc^-1,
then this sphere would have a radius of about 13 billion light years.
Taking into account the expansion of the universe, it is though to be more like 46-47 billion light years
