Lecture 13 Flashcards
what is the current model of the universe
LambdaCDM model, the universe is homogeneous on large scales, described by general relativity
it is cold - non interacting and slow moving compared to speed of light
how are cosmological models used
compute predictions for things we can observe and compare to actual predictions to determine suitability of the model
how do cosmology theories predict
don’t predict specifics but predict statistical quantities
what is the easiest thing to predict from a cosmological model and how
overall average expansion of the universe, relates object redshifts to different kinds of distance
what is perturbation theory
approximation of the fluctuations in density in the early universe
what can perturbation theory predict
CMB fluctuation spectrum, galaxy density spectrum on large scales
what is the issue with late universe perturbations
cant solve relativity equations to get current complicated density patterns at small scales as would take A LONG time
can simulate examples of them by individually simulating large numbers of particles
need these to make predictions for the late universe density spectra for galaxy clustering , lensing and other phenomena
what are the cosmological parameters
numbers In the theory that are not predefined in the model or measured in labs
in lambdaCDM, there are 6
what is the Hubble parameter
current expansion rate of the universe, measured in km/s/Mpc
what is the critical density
specific density needed for the universe to be flat, depends on expansion rate of the universe
what are the density parameters
can compare the actual densities of substances to the critical value
use parameters to describe cosmic densities as a fraction of the critical density
all density parameters add up to 100% indicating the universe if flat - too unlikely to be a coincidence
distribution of dark matter densities
overall dominant, mainly between stars and galaxies
what is the curvature parameter k
flat - k = 0, angles sum to 180
spherical - k > 0, angle sum to > 180
hyperbolic - k < 0, angles sum to < 180
can find by writing as a density
what are the two main question sabot structure in early universe
how much structure is there, variations of fluctuations?
does this vary with physical size, short or long fluctuations?
what is the concordance of measurements
different measurements are sensitive to different parameters and measurements have different sensitivities - these do not have to meet in one place
what are the issues/discrepancies with Hubble parameter
we get H0 to be different if it is based on cepheid stars or extrapolated from the cmb
