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.
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?
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.
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”
13.
14.
15.
16.
17.
18.
19.
20.
21.
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
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
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)
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.
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!
35.
36.
37.
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
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
53.
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.”
