Week 10 Cosmology: evolution of the Universe Flashcards
what are the 2 properties of the Cosmological principle
Homogeneous - same in all places
Isotropic - same in all direction
what is the idea of Galilean invariance
no matter what velocity you were travelling at without any reference points you wouldn’t be able to determine your velocity
what can be said about the acceleration of galaxy
it is proportional to the galaxies distance from us
what is the critical density of a galaxy equation
ρcr = 3H0^2 / 8πG
if the density of the universe is the critical density what can be said
gravity can halt the hubble flow so galaxies keep moving away but at gradually slower velocities
if the density of the universe is greater than the critical density what can be said
gravity will reverse the hubble flow causing the universe to collapse
if the density of the universe is less than the critical density what can be said
the galaxies will escape the effects of gravity and the Universe will expand forever
what is the density parameter equation
Ω = ρ0 / ρcr
as the density parameter value changes what can I say
when Ω is < 1 we have an open unbound universe
when Ω is = 1 we have a critical universe
when Ω is > 1 we have a closed universe
what does the scale factor do
it describes the expansion factor of the Universe
how does the scale factor(a) vary as time varies
for current time t0, a = 1
for future time t, a > 1
for past time t
what two quantities can be used to describe the expansion of the Universe
hubble flow
scale factor
what is the hubble flow scale factor equation
H = 1/a da/dt
what is the redshift scale factor equation
1 + z = 1 / a
what does the Friedmann equation do
it describes how the scale factor changes with time based on density and k for the whole universe
