Post on 15-Jan-2016
Dwarf galaxies & Cosmology
Let’s start from the beginning …
Jorge Peñarrubia & Matt Walker
The Universe is expanding!
Hubble 1929
Cosmology: The Equations
space-time vs mass/energy
mass/energy = density/pressure
IF the Universe is isotropic and homogeneous Friedman-Lemaitre-Robertson-Walker (FLRW)metric
Combining the above formulae …
Friedman eqs : scale factor vs time
a(t)
equation of continuity
Hubble parameter
Cosmology: The Equations
Equation of state of the Universew=0 Matterw=1/3 Relativistic particles
Matter
Relativistic particles
Accelerating Universe
Cosmology: The Issues
1. The Homogeneity Problem “The Universe becomes less homogeneous with time due to gravity. How can we explain a Universe so smooth in the past?”
2. The curvature Problem
3. The Horizon Problem
observations: Ω0 ≈1
theory:
“The curvature of the Universe was very small at t≈0 “
Co-moving Horizon (aH)-1 tends to zero as t≈0
“How can the CMB be so homogeneous if different regions were not casually-connected at t≈0 ?”
Solution: Inflation
1. Curvature
2. Horizon
aH=exp[Ht] H H as t 0Curvature k is not arbitrarily low ab initio
{1 –exp[-H (ti -t) ]} H-1
Horizon is not arbitrarily small at t≈0