13 - Cosmological Models & Concordance

What is our current model of the Universe called?

Concordance model or Lamda CDM model

What does this Concordance model describe?

The universe is homogenous on large scales and contains baryonic matter (5%), cold dark matter (25%), and dark energy (70%)

What does “cold” mean in the context of cold dark matter?

Non-interacting and slow-moving compared to the speed of light

In the early universe (up to CMB), the fluctuations in density are _____, specifically _ part in ______.

Small, 1, 100000

What mathematical approximation can we use to predict the CMB fluctuation spectrum and Galaxy density spectrum (on large scales)?

Perturbation theory

What are the cosmological parameters in perturbation theory?

Numbers in the theory that are not predefined in the model or measured in labs

What is the Hubble Parameter?

The current expansion rate of the Universe.

What is the critical density?

The specific density of matter and energy required for the universe to be flat.

Dark energy likely doesn’t _______ at all, whilst dark matter does a bit and Baryons do the most.

Cluster

All density parameters add up to ____ implying that the universe is ____.

100%, flat

Where is dark matter distributed primarily?

Between stars and galaxies

How is the curvature density calculated?

1 - all other densities

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

What are the two main questions about structure in the early universe?

How much structure is there (variations of fluctuations)? How does this vary with physical size (short or long)?

What is the concordance of measurements?

Different measurements are sensitive to different parameters.

What are the issues with Hubble parameter?

You get different values whether using Cepheid stars or CMB to compute H_0