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COSMOLOGY 2
Harrison B. Prosper
Florida State University
YSP
Topics
 Big Bang Cosmology
 The Accelerating Universe
 Summary
BIG
BANG
COSMOLOGY
3
In the distant past the visible Universe was much smaller than it
is today and therefore much, much hotter.
Therefore, the Universe must have been filled with very short
wavelength photons.
As the universe expanded, it cooled and all wavelengths were
stretched by the same factor by which the universe expanded.
Big Bang Cosmology – Predictions
Prediction 1
 The universe should be expanding
Prediction 2
 The universe should be made of roughly ¾
hydrogen and ¼ helium and not much else
Prediction 3
 Today, the universe should be filled with
microwaves, with a perfect thermal spectrum.
The Abundance of Elements
Element
 Hydrogen
 Helium-4
 Deuterium
 Helium-3
 Lithium
Structure
(p)
(2p,2n)
(p,n)
(2p,n)
(3p,4n)
Abundance (%)
77
23
10-3
10-3
10-8
Cosmic Microwave Background
(CMB)
Arno Penzias and
Robert Wilson (1965)
 While preparing a
radio telescope at Bell
Labs to observe the
Milky Way they
discovered the CMB!
 1978 Nobel Prize
Cosmic Background Explorer (COBE)
 Launched November 1989
 T = 2.725 +/- 0.002 K
COBE – (1991)
Measured temperature fluctuations of 1 part in 100,000.
Snapshot of universe when it was ~ 300,000 years old
when photons could finally travel freely.
Wilkinson Microwave Anisotropy Probe
June 30, 2001
Kennedy Space Center
http://map.gsfc.nasa.gov
(Optional) Challenge Problem!
Problem 9:
Show that the distance of L1
from the Earth is given
by the implicit equation:
Me 
R3
 M E Me
r
 2 

2
(Me  M E )  r
R
(R  r)2 
1. Assume circular orbits for which the centripetal
acceleration in F = ma is v2 / r
2. Remember objects orbit about the center of mass, but
the gravitational force depends on the objects separation
3. The orbital period T at L1 is the same as that of Earth
12
WMAP Measurements
Planck Mission to L2 (2009)
14
Planck Measurements (2013)
15
17
Big Bang Cosmology – Puzzles
The Flatness Problem
Why is the global geometry of space Euclidean?
The Horizon Problem
Why is the temperature of the CMB the same at opposite
sides of the Universe?
The Smoothness Problem
Why, on very large scales is the Universe so smooth?
Why, on smaller scales, are galaxies distributed in huge
sheets, separated by great voids?
THE
ACCELERATING
UNIVERSE
19
Breakthrough of the Year, 1998
20
21
22
23
24
THE PHANTOM MENACE
25
26
27
28
29
30
Summary
Big Bang Cosmology
 The universe began a finite time ago
 The universe had a hot dense beginning
 Space is globally flat
 Galaxies were seeded by quantum fluctuations
Big Bang Puzzles
 What caused the big bang?
 Why this particular universe?
 What is causing the accelerated expansion? Is it dark energy?
If so, what is dark energy?
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