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The Scientific Case for The Standard Big Bang
Cosmological Model: A 30 minute synopsis
And the Lord said, “Let there be light….” (Genesis 1:2)
The Big Bang (inaccurate artist’s conception!!
Is the Big Bang ‘just a theory’?
George Deutsch, a presidential appointee in NASA headquarters, told a Web
designer [October 2005] working for the agency to add the word “theory” after
every mention of the Big Bang,
The Big Bang is “not proven fact; it is opinion” stated Deutsch in a email to
NASA scientists (Deutsch later resigned his post after it was discovered that he
had misrepresented his education (didn’t graduate from Texas A&M in
journalism) on his application to NASA.
“Standard Model”
of the Universe
c.100AD-1600AD
Geocentric (Earthcentered)
Cosmological Model
• Valid scientific
model (testable,
falsifiable)
• Not in conflict with
observations until
Galileo (c. 1610)
Galileo’s discovery (1610) of Jupiter’s moons
with his telescope showed that Earth was not
the center of all orbits strongly supported a
heliocentric (Sun-centered) model
The Three Observational Foundations of the
Big Bang Theory
1. Hubble Expansion of the Universe
(1920’s)_
2. Cosmic Microwave Background Radiation
(1965)
3. Elemental Abundances (1960’s – 1980’s)
First, we need a tutorial on spectral
analysis…
Importance of stellar spectra 1: :
Lines determine what are stars
made of (like fingerprints)
Spectral lines allow
identification of
elements
(Example: Star Formation region,
showing line of Hydrogen, Helium,
Oxygen, Neon)
Importance of spectra, 2:
Line Shifts Determines speeds of stars
(and galaxies)
State’s Evidence 1:
Expansion of the Universe
Speed (km/s)
Edwin Hubble (1920): “Universe is expanding in all directions”
Distance to galaxy
•
Three bike racers:
– Lance: 30 mph
– Bob: 20 mph
– Fred: 10 mph
– Start race at time = 0
•
Slope of line determines
time since race started
Time = D/V, ‘age’ of race!)
•
•
Edwin Hubble (1920’s)
measured speed (Doppler
shift) and distance for
galaxies –got a straight
line
• Slope determines
age of Universe:
13.7 Billion yrs
Speed (mph)
Hubble expansion: Implies finite age of Universe:
Bike race analogy
Oldest detected object in Universe
(Quasar, 12.5 billion light-yrs distance)
Infrared
Historical origins of the Big Bang model
•
Georges LeMaitre, a Belgian priest and
mathematician, proposed (1927) that the
expansion of the universe can be traced to
an exceedingly dense ‘primeval atom’
•
… when the whole universe exploded in
“fireworks of unimaginable beauty” and with a
“big noise”
•
Einstein, after listening to a lecture by
LeMaitre said ‘This is the most beautiful and
satisfactory explanation of creation to which I
have ever listened.”
•
LeMaitre used the term ‘Cosmic Egg’. Now
known as the Big Bang theory
State’s Evidence 2:
Cosmic Background Radiation
Penzias and Wilson
(Discoverers of CMB
Radiation (1965)
As Universe expanded, it cooled
Age = 300,000 yr
T = 3,000 K
Age = 13.7 Byr
T=3K
CBR spectrum is exactly thermal,
as expected from Big Bang model
Sidebar: Large-scale
structure as expected from
irregularities in CBR
Predicted
large-scale
structure
Observed large-scale
structure (2 million galaxies)
State’s Evidence 3:
Csomic Abundance of Elements
What is Universe made of?
Cecilia Payne-Gaposchkin
(1925) determines that Sun
(and all stars) are primarily:
• Hydrogen (75%)
• Helium (25%),
• All other elements <2%
 Payne-Gaposchkin:
“Hydrogen, helium
dominate solar
abundance” (1925 Ph.D.
thesis)
 Professor Russell:
“Clearly impossible”
 Payne-Gaposchkin
adds “almost certainly not
real” to her final Ph. D.
draft
Cecilia Payne-Gaposchkin
(First Harvard PhD.
in Astronomy 1923)
Prof. Henry Norris Russell
Harvard College Observatory Director Edward Pickering and his ‘computers’ c. 1912
I’m the
boss!
Big Bang Model Prediction for Abundance of Elements
Helium ~75%
Helium 24%
Deuterium
(2H) 0.002%
Lithium (7Li)
0.00000002%
Observed light element
abundances agree with
Big Bang Model!
What is still uncertain?
Plenty! For example…
1.
Why did inflation occur?
2.
Standard model doesn’t predict fundamental constants (masses,
charges, speed of light, etc)
•
3.
Anthropic principle: If constants were even a little different, we
wouldn’t be here to puzzle about them!
Why is energy density of the vacuum so close to the energy
density of matter?
•
Particle physics predicts ratio should be ~10120 !)
Is there only one Universe or are there ‘many Universe bubbles?’
4.
•
5.
Inflation allow for such disconnected space-time ‘bubbles’
What was before the Big Bang?
•
String theory avoids singularity at t=0 [in 10-dimensional space-time]