7. Cosmology Flashcards
What are the two main properties of the Universe on the largest scales?
Isotropic
- Looks the same in all directions (but not perfectly isotropic or it would appear monochrome)
Homogeneous
- Same at all point (no privileged points)
What are the fluctuations in the CMB?
1 part in 10^5
What are the results after applying the Einstein equations to the de Sitter space?
- There is a constant positive energy density
- However there is a constant negative pressure
How did Einstein account for the dark energy in his equations?
He added the cosmological constant
Describe the proportions of the stress energy momentum tensor that are from dark energy, dark matter, and matter and the consequences of this
- 68% dark energy
- 27% dark matter
- 5% matter
- Universe will evolve into the de Sitter space in the future
What is the main feature of the Friedmann equations?
The scale factor, a, is not constant
- Space time is not stati, and space is dynamic (expanding or contracting)
What are the main features of the acceleration equations?
ä is <= 0. Rate if expansion in the past must have always been at least as fast as it is currently as the universe is expanding (a dot >= 0)
- Going back in time, a = 0 at a finite time in the past = BB
In FLRW cosmology, what do we assume about galaxies
They are test masses that travel along time like geodesics
On cosmological scales, how are the times of emission and observation related
The emission time is approximately equal to the observation time minus a small change in time
How is the fluid equation obtained?
By conserving energy and momentum in the universe as a whole
- Can conserve the stress energy momentum tensor or use the Friedmann equations (but these do not give a closed system)
What is meant by the equation of state for a fluid?
It is the relationship between the pressure and the density
What is the equation of state that we use, and state the key values of the equation of state parameter
p = w (E density)
w = 0: Dust filled U
w = 1/3: Rad filled U
w = -1: Dark E
From the equation that states that:
a^3(1+w) x E density = const, describe the key features that can be interpreted from going into the past
Going back in time, the universe is small and the energy density is large
- Going back far enough, we reach a time where radiation domiantes, and later on matter dominates (think of the graph in DU)
Describe what happens when there is a crossover between the univesre being dominated by radiation and matter
- This is called the cosmological phase transition
- Occured during recombination/photon decoupling
- CMB is a relic of this transition
State what we assume when looking at the exact FLRW solutions
Look at ordinary matter solutions, so the cosmological constant is set equal to 0
