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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 (Earth-centered)
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)
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)
Hubble expansion: Implies finite age of Universe: Bike race analogy
• 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
Sp
eed
(m
ph
)
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
As Universe expanded, it cooled
Age = 300,000 yr
T = 3,000 K
Age = 13.7 Byr
T = 3 K
Sidebar: Large-scale structure as expected from
irregularities in CBR
Predicted large-scale structure
Observed large-scale structure (2 million galaxies)
Cecilia Payne-Gaposchkin
(First Harvard PhD.
in Astronomy 1923)
Prof. Henry Norris Russell
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
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%
Big Bang Model Prediction for Abundance of Elements
Helium 24%Helium ~75%
Deuterium (2H) 0.002%
Lithium (7Li) 0.00000002%
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)
• Anthropic principle: If constants were even a little different, we wouldn’t be here to puzzle about them!
3. Why is energy density of the vacuum so close to the energy density of matter?
• Particle physics predicts ratio should be ~10120 !)
4. Is there only one Universe or are there ‘many Universe bubbles?’ • Inflation allow for such disconnected space-time ‘bubbles’
5. What was before the Big Bang?• String theory avoids singularity at t=0 [in 10-dimensional space-time]