1) Early cosmologists like Einstein, Friedman, and Lemaître developed the foundations of the Big Bang theory, proposing an expanding universe from an initial hot, dense state. 2) Hubble discovered that distant galaxies are receding from us, providing observational evidence the universe is expanding according to Hubble's law. 3) The cosmic microwave background radiation discovered in 1964 provided crucial evidence for the Big Bang theory, confirming the hot, dense state of the early universe predicted by Gamow. 4) Precise measurements of the CMB have since established a highly accurate age of the universe and supported the Big Bang as the dominant cosmological model.

1. In The Beginning
big bang cosmology

3. Einstein
Problem: Gravitational
attraction would cause the
universe to collapse.
Solution: Addition of the
cosmological constant to the
general theory creates an
anti-gravitational effect
Result: Preservation of the
eternal, static universe.

4. Modified Field Equation
Spacetime MatterConversion
Factors
Cosmological
Constant

5. Alexander Friedman
1888 - 1925
“On the possibility of a world
with constant negative
curvature of space” (1924)
What happens if the
Cosmological Constant (Λ)
has different values?
What happens if the universe
is expanding?

6. Friedman Equations

9. Georges Lemaître
1894 - 1966
Suggested that in an expanding
universe, galaxies should be
retreating at a velocity proportional
to their distance from us (1927)
Proposed a compact,“primeval
atom” or “Cosmic Egg” that
exploded, expanded and evolved
into the universe as we see it today.

10. William Herschel
1738 - 1822

11. Charles Messier
1730 – 1817
Catalog of 103 nebulous
and “deep sky” objects
(1781)

12. William Parsons,
Earl of Rosse, 1800 - 1867
Able to distinguish between
elliptical and spiral-shaped
nebulae.
Managed to make out
individual point sources in
some of these nebulae,
“Leviathan”

22. Henrietta Leavitt
1868 – 1921
Studying variable stars and
found that brighter ones
appeared to have longer
periods.
Estimating period of
variability allowed estimation
of their distance

26. Small Magellanic Cloud

27. Cepheids in the SMC
The Cepheids are huddled together and can be
assumed to be relatively close together
compared with distance to earth [200,000 light
years]
Therefore, a Cepheid in this sample that
appears twice as bright as another in the
sample is twice as intrinsically luminous.

28. Leavitt, Henrietta S. "1777 Variables in the Magellanic Clouds". Annals of Harvard College Observatory. LX(IV)
(1908) 87-110.
Period (days) Log Period (days)
Brightness

29. 800x Sun 10,000x Sun

30. So What?
Cepheids are easily identifiable
They are relatively plentiful and scattered
throughout the universe
We can measure intrinsic luminosity from
period
Need calibration (direct measurement 1913 by
Ejnar Hertzsprung)

31. Stellar
Parallax

32. A “standard candle”
Find a Cepheid
Measure the period and thus derive the
intrinsic luminosity (how bright it is)
Measure the apparent luminosity (how bright
it appears to be)
Work out the distance that accounts for the
difference.

33. Doppler
Effect
Redshift (objects moving away)
Blueshift (objects getting closer)

34. Edwin Hubble
1889 - 1953
In 1923, found a cepheid in
Andromeda and (measuring
the distance) found it to lie
beyond the Milky Way
The nebulae were galaxies
and the universe was full of
them!

38. Hubble’s Law - 1929
Linear relationship between a
galaxy’s distance and
“apparent” recessional velocity
Implies universe is expanding
First observational support for
Lemaître’s prediction in 1927

39. Hubble’s Law - 1929

40. A B C D E F G
EDC F

42. Georges Lemaître
1894 - 1966
There was both “creation” and
“evolution” of the universe.

45. Friedmann-Lemaître-Robertson-
Walker (FLRW) Model
Howard Robinson (US) and Arthur Walker
(England) independently explored these ideas in the
1930’s.
Offers an exact solution of Einstein's field equations
of general relativity
Describes a simply connected, homogeneous [same
properties in all locations], isotropic [same
properties when viewed in any direction from any
location], expanding or contracting universe.

46. The αβγ
Paper
Ralph Alpher, [Hans Bethe]
& George Gamow pictured
the early universe as a
dense “soup” of protons,
neutrons and electrons.
Bigger and bigger atoms
were built by fusion in the
heat of the Big Bang.

47. The αβγ
Paper
Success: Model could
explain why the universe is
currently 90% Hydrogen
and 9% Helium.
Failure: Model could not
explain the formation of
elements heavier than
Helium.

48. George Gamow
1904 - 1968
With Alpher & Robert
Herman (1948) predicted an
“echo” of the Big Bang
Alpher & Herman (1949)
predicted that the radiation
should be in the radio
region of the EM spectrum

49. Fred Hoyle
1915 – 2001
With Thomas Gold &
Hermann Bondi proposed the
Steady State Model
The Universe was indeed
expanding but new matter was
being formed in the gaps
between the galaxies
Thus the universe evolves but
remains unchanged and eternal

50. Radio Astronomy
Discovery of young
galaxies and quasars at the
far reaches of the universe
Uneven distribution went
against Steady State model
which claimed the
universe should be similar
everywhere

51. Robert Wilson &
Arno Penzias
“Discovery” of the Cosmic
Microwave Background (CMB)
radiation as a background noise
(1964)
Nobel Prize in 1978
Was this sufficient evidence for
acceptance of the Big Bang?

52. Confirms black-body spectrum of CMB as
expected
Discovery of variations (anisotropies) in the
CMB which indicated tiny variations in the
density of the early universe

54. Stephen Hawking
The COBE results are “the
greatest discovery of the
century, if not of all times”.

55. The Nobel committee
stated that COBE can
“be regarded as the
starting point for
cosmology as a
precision science.”

58. High-precision CMB mapping yields age of the
universe of 13.73 ± 0.12 billion years

63. The End
Heat Death (Kelvin)
Big Rip
Big Crunch
Big Bounce
Multiverse