Transcript Document

The Big Bang Evidence
The Science of Creation
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Goals
• What is the evidence for the Big Bang?
– What predictions does the Big Bang theory make?
– What observations can we make?
• How good of a theory is the Big Bang?
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How do scientists estimate the
age of the universe?
A.They take the distance to a nearby galaxy and
divide it by its speed of recession (time =
distance/velocity).
B. They take the distance to a very distant galaxy and
divide it by its speed of recession (time =
distance/velocity).
C.They take the distances to all galaxies and divide
them by their speed of recession (time =
distance/velocity).
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What does it mean to say that our
universe is expanding?
A.Galaxies are moving apart through space.
B. Space itself is expanding.
C.Everything is expanding, including galaxies, star
clusters, and star systems.
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Olbers’ Paradox
• Why is it dark at
night?
• In an infinite and
unchanging universe:
Every line of sight
should end at the
surface of a star.
• Either:
– Universe has edge.
– Universe has a
beginning.
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Concept Test
• Olbers’ paradox asks why the night sky is dark,
when every line of sight must eventually fall on
a star. Which of the following reasons would
best explain the darkness at night? It is because
the universe is:
a.
b.
c.
d.
e.
Infinite and mostly empty.
Clumpy, so not every sightline intercepts a star.
Expanding, so distant stars are red-shifted.
Young, so there are only stars to a finite distance.
None of the above.
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Cosmological Principle
• Isotropy – The view from
here is the same in all
directions. (observation)
• Homogeneity – We live
in an average place the
same as any other.
(statistics)
• This is the cosmological
principle.
• Implies:
– Universe has no edge!
– Universe has no center!
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What observed feature of the
universe motivated scientists to
propose the big bang theory?
A.There is lots of debris in space, as would be
expected
from an explosion.
B. The universe is expanding, and the expansion must
trace back to a specific point and time of origin in
the past.
C.Everything has a beginning, middle, and end.
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Scientific Evidence
• A scientific model must do two things:
– Explain what is seen.
– Predict what will happen accurately.
– Or, predict what can be seen before one thinks to
look.
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What does the big bang theory
predict can
be seen today if there really was a
big bang?
A. Radiation from the big bang might be detected. It was gamma
rays 14 billion years ago, but today it is cooler and would
look like weak microwaves coming from all of space.
B. The Big Bang produced three elements, which might be seen
in the oldest stars: 75% hydrogen, 25% helium, 1 part in a
billion lithium.
C. The universe must be finite in mass and dimension.
D. all of the above
E. A and B
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At the beginning of the universe,
A.the temperature was billions of degrees.
B. the density was enormously high.
C.matter could turn into energy and vice
versa.
D.all of the above
E. A and B
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Cosmic Microwave
Background
• The Big Bang:
– Massive amount of energy.
– Very high temperature  thermal radiation
• As Universe expands:
– Temperature cools  thermal radiation gets redder.
or
– Cosmological redshift  same thing.
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Origin of the CMB
Once cool
enough for
atoms, radiation
could move
freely through
space.
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The Temperature of Space
• After 500,000 yrs: T=3000K
lpeak a 1/T
lpeak = near infrared.
• The Universe was red.
• After 16 billion yrs:
Universe 1000x bigger.
lpeak = 1000x longer.
lpeak = microwaves (radio).
T = 3K!
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Where do you look?
•
•
•
•
Recall Lookback time.
Universe is a time machine.
Look beyond the youngest galaxies.
Look everywhere.
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What We See
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Cosmic Microwaves
• Big Bang theory predicted cosmic microwave
background.
• In 1965: discovery of radio waves
(microwaves) from sky.
• Prediction confirmed.
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COBE
• Early 1990s:
NASA Cosmic
Background
Explorer
• Measure the
intensity of
radiation at many
wavelengths.
• 3K thermal
emission!
l peak
const .

T
lpeak = (3 x 10-3 m/K) / 3 K = 0.001m = 1mm
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COBE cont.
• Also measure the (temperature) intensity and
wavelength in various directions.
• Look for fluctuations out of which galaxies came.
V = 600 km/s
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Large Scale
Structure
WMAP
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Concept Test
• The cosmic background radiation is visible
in every direction because:
a.
b.
c.
d.
We are at the center of the universe.
It is just now passing by us at the speed of light.
It pervades all space.
It has reflected in every direction over the age of
the universe.
e. All of the above.
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Evidence of Eras
• Can’t see what happened before origin of
CMB.
• Can estimate given change of temperature
and density with time.
• Look for Proof.
– CMB (Age of Nuclei)
– Ratio of H/He and Li (Age of Nucleosynthesis)
– Weak Bosons (Electroweak Era)
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Which of the two main
predictions of the big
bang theory turned out to be
true?
A.Radiation has been found coming from all of space,
just as predicted.
B. The oldest stars are made of hydrogen, helium, and
lithium, in the proportions predicted.
C.both A and B
D.neither A nor B
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A Good Theory?
• The Big Bang is a very successful theory.
• Makes predictions:
–
–
–
–
CMB.
Hydrogen, Helium, Lithium abundances.
Formation of structure.
Expansion of Universe.
• Are other Creation theories:
– Scientific?
– Successful?
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What do we see when we look
beyond the cosmological
horizon?
A.Galaxies that are just about to form.
B. Galaxies that are about to enter the universe.
C.White dwarfs that are about to go supernova.
D.The beginning of the universe.
E. We cannot look beyond the cosmological horizon
because we cannot look back to a time before
the universe began.
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Homework #22
• For Friday: Come prepared to discuss your
observing projects with your groups. What
have you seen? What did you think you’d
see? How do they compare?
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