Midterm 1 Flashcards
Name four observations that support the hot Big Bang model of the Universe and briefly note why they lend support to this model
Olber’s Paradox, Redshift of Galaxy Spectra, Cosmological Principle, CMB
A distant galaxy emits light at a wavelength λe and we receive it at wavelength λ0.
How is the redshift z of the source defined?
z = λ0 - λe / λe
How is the redshift related to recession velocity and distance?
v = cz = H0d
What is the value of the Hubble constant? (Include units)
~ 68 Km/sec/Mpc
Why is the Hubble constant such an important number in cosmology?
It gives the value of the expansion rate of space at a given time
What is the scale factor a(t)?
The factor by which the universe has expanded at a given time; it is different across time.
What is its present day value, a(t0)?
a(t0) = 1
How is the scale factor related to the Hubble parameter?
adot / a = H(t)
How is the scale factor related to redshift?
a = 1 / 1+z
Why does the energy density of matter scale as εm = εm,0 a-3 and the energy density of radiation scale as εm = εm,0 a-4 ? (Explain the physical reason - simply quoting ⍵ for matter and radiation is not sufficient.)
Em : volume dilution (a^3)
Er : volume dilution + stretching of photon wavelength (a^4)
Consider two galaxies with no peculiar velocity (this is a quantitative question):
How does their distance in comoving coordinates change from z = 2 to the present?
Their distance in comoving coordinates would NOT change, by definition
Consider two galaxies with no peculiar velocity (this is a quantitative question):
How does their proper distance change from z = 2 to the present?
a = 1/1+z = 1/1+2 = 1/3
dp(t) = r/a(t) = r / (1/3) = 3r
Increases by a factor of 3
What does the benchmark model refer to?
Important cosmological parameters
How is Ω(t) defined?
Ω(t) = Ωr,0 + Ωm,0 + Ωlambda,0
Ωi = E/Ec
What is the value of Ωmatter,0 ?
~ 0.30
