Transcript History of the Universe

History of the Universe
If the universe was 1 year old . . .
If the universe was 1 year old . . .
Our goals for learning:
• Science/religion – either/or?
• How do we predict the conditions of
the early universe?
• What are the different eras in the
early universe?
• What key lines of evidence support
the Big Bang model?
• What is the cosmic microwave
background?
Why are we here?
How did we get here?
• Questions of purpose can’t be answered by
science
• Questions of mechanics can be answered by
science
The Big Bang
• Were you THEEEEERE???
• How can we possibly know what happened?
• Three lines of evidence:
– Galaxies moving away from each other
– Types/amounts of elements present in the
universe
– Observe light from Big Bang
Evidence for the Big Bang:
Galaxies are moving apart
• Our own Milky Way Galaxy is just one of countless galaxies of stars that
fill the observable universe.
• If anything, we might expect all these galaxies, including our own, to be
falling towards each other, attracted by their mutual gravity.
• But in 1929, the astronomer Edwin Hubble made the unexpected
discovery that distant galaxies are moving away from Earth. In fact, the
more distant the galaxy, the faster away from us it is moving.
• Since the galaxies are moving apart, they must have been much closer
together in the past.
• Based on the speeds and directions of the galaxies' motions,
astronomers conclude that all the galaxies would have originated from
the same spot about 14 billion years ago.
• Red shift: Observing Movement video; video
Evidence for the Big Bang:
Elements present in the universe
• In the 1940's, the physicist George Gamow and his colleagues
realized that the early universe must have been extremely hot
as well as dense.
• Scientists were just beginning to understand that under great
heat and density, chemical elements can be transformed from
one into the other.
• Gamow and his colleagues calculated that for a hot, dense,
and expanding universe about one-quarter of the simplest
chemical element - hydrogen - would have been "cooked"
into the element helium.
• Astronomers have measured the proportion of hydrogen
and helium scattered through our universe, and it matches
the prediction perfectly.
• This was strong evidence that the early universe was hot as
well as dense.
Evidence for the Big Bang:
Leftover Light
• According to the Big Bang model, the Big Bang took place everywhere
in space (not just at a point). For thousands of years after the Big Bang,
all of space was filled with matter so hot that it glowed - much like the
pottery oven at right. This afterglow of the Big Bang should still fill the
universe today.
• In fact, a steady stream of this light is continuously arriving at Earth,
from distant regions of space, having traveled for billions of years to
get here. The light is no longer visible with the unaided eye – having
dimmed and reddened as the universe expanded and cooled – but it is
detectable with special instruments.
• In 1964, the radio astronomers Arno Penzias and Robert Wilson
became the first to discover this afterglow of the Big Bang.
• Then in 1991, NASA's COBE spacecraft captured the first image of this
ancient light coming from all directions in the sky, confirming the Big
Bang scenario. The achievement has been hailed as one of the greatest
triumphs of scientific exploration.
Cosmic Microwave Background
• The Universe is immersed in a sea of radiation.
• This is the same radiation which was unleashed at the end of the
Era of Nuclei.
• 380,000 years after the Big Bang, the Universe had cooled enough for
free electrons to become bound into atoms of H & He
• without electrons to scatter them, photons were able to travel
unhindered throughout the Universe
• the Universe became transparent
• Its existence first predicted by
George Gamov in 1940s
The temperature of the Universe was 3,000 K
at this time.
Cosmic Microwave Background
• Video here
• The spectral distribution of this
radiation was the same as radiation
from a 3,000 K object.
• like the surface of a red giant
• Since then, the Universe’s size has
expanded 1,000 times.
• cosmological redshift has turned this
radiation into microwaves.
• So the temperature of the background
is 1000 times lower
• Gamov predicted that we should
have a 3 K background
• At this temperature, most radiation
comes in the wavelength of
microwave  the cosmic
microwave background
Fig. 19-6, p.394
• 1964 – 1965:
Discovery of the Cosmic
Microwave Background
– Arno Penzias and Robert
Wilson using the 20-foot
radio antenna at Bell Lab
for their research
– Discovery of faint, uniform,
persistent “noise” at 3K.
– Meanwhile, Princeton team
led by Robert Dicke was
building a radio telescope
to detect the big-band
afterglow predicted by
Gamov
– The discovery of CMB won
Penzias and Wilson the
1978 Nobel Prize
Penzias and Wilson with their horn
Shaped antenna at Bell Lab
Two Key Predictions of the CMB
• The CMB is thermal – “black body radiation”
• The CMB is highly uniform (< 10-5) difference
from one spot to another
Cosmic Microwave Background…
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…was mapped by the COsmic Background Explorer (COBE) in 1990s
Thermal radiation of 2.728 +/- 0.004 K
While very smooth and uniform across the sky…
COBE did find slight temperature variations from place to place on
the level of a few parts in 100,000.