Cosmological Constant Flashcards
When is the cosmological constant used?
When H = 0 (unstable)
What is the Ω_matter and Ω_Λ?
Ω_matter = 0.3
Ω_Λ = 0.7
1+z = 1.3
What is p total?
0 + 3(-ρ_Λc^2)/c^2 ∝ -3Ω_Λ,0
What is ρ total?
Ω_matter + Ω_Λ = 1
What is Ω_total?
Ω_Λ + Ω_matter + Ω_radiation = 1
(up to 1 is in Hubble time and there is not age problem of cosmological constant)
At what redshift does ρ of Λ start to dominate?
z = 0.5
(1 + z = 1.5)
What can the cosmological constant cause?
Acceleration which makes universe older
What is the w value for the cosmological constant?
w = -1 (causes acceleration on its own)
Why was the cosmological constant introduced?
To fix the stable static universe theory
What is the pressure of the cosmological constant?
no time derivative so Δρ_Λ = 0
p_Λ = - ρ_Λ c^2
What does the negative pressure caused by the cosmological constant imply?
(negative pressure = anti-gravity)
anti gravity implies a continuous driving force pushing on going expansion
How do K and ρ change in the Steady State model?
ρ_matter = constant (even though universe is expanding)
K = 0
Why was Steady State model discounted?
Due to the need of Λ and real matter term (matter term needed as Λ on its own doesn’t match low redshift of universe
If w = -1/3, is universe accelerating?
no acceleration or deceleration
If w > -1/3, is universe accelerating?
it is decelerating
If w < -1/3, is universe accelerating?
it is accelerating
What is Ω_Λ + Ω_matter for flat universe?
Ω_Λ + Ω_matter = 1
What is Ω_Λ + Ω_matter for closed universe?
Ω_Λ + Ω_matter > 1
What is Ω_Λ + Ω_matter for open universe?
Ω_Λ + Ω_matter < 1
What can a small positive Ω_Λ stop?
Can stop high density matter dominated universe from collapsing
For H_o t_o vs Ω_matter,0 graph, what does H_o t_o > 1 indicate?
Universe is older than Hubble time
What is H_o t_o for observations made of Supernovae Ia?
1
What does the data from Supernovae Ia which are observed out to significant distances suggest?
Λ ≠ 0 as matter-only model don’t fit
What is the effect of introducing Λ?
Makes things further away K =0 as the universe is now expanding rapidly
What dominates the late universe?
cosmological constant (as scale factor increases, constant wins)
How is a scale factor for every choice of Ω_matter and K derived?
Using the 1+z vs Ω_vac graph
