Big Bang
Extraterrestrial Life and Death
Lecture Seven, Jan. 29, 2003
Pre-project Essay
• In one or two typewritten pages discuss
some of the events important for life on
Earth between the Big Bang and the
evolution of man.
• Due Friday Jan. 31, 2002.
Evolution
• Evolution and survival of fittest is very powerful.
• Evolution needs stable environment for long
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time and way to store information (DNA).
Is evolution enough to explain Man and
intelligence from primitive life?
A number of mass extinctions have occurred on
Earth. Some probably from asteroid/ comet
impacts.
Mass extinctions can be important for evolution.
Genesis
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This completes overview of first third of class.
Origin of Universe in Big Bang.
Origin of first stars and Milky Way galaxy.
Origin of chemical elements in stars that died before the
solar system formed.
Origin of solar system: Earth, Sun and planets.
Origin of primitive life.
Evolution of intelligence and Man.
Man very recent, sophisticated multicell organsims 6-700
Mya, life 3.8 Bya, formation of Earth 4.6 Bya, formation
of elements 5-12Bya, Milky Way galaxy 12 Bya, Big Bang
~13 Bya.
Here is a reverse timeline of some of these events in
terms of the evolution of the Earth.
Big Bang
• Grand explosion that created the Universe.
• Who banged? God.
• What banged? The Universe.
• When was the big bang? ~13 B.y. ago.
• Where was the big bang? Everywhere. It
created space.
• Why the big bang? For life???
Who banged? God
• As a physicist part of my definition of God is that
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which created the Universe.
Hey, it is in his job description.
What banged. Tremendous explosion that
created the mass, energy, space, and time of
the Universe.
When? We measure an expansion rate for the
Universe today. The faster the rate, the faster
the galaxies got to their present positions hence
the younger the Universe is.
Where was the Bang?
• Everywhere.
• The explosion created the space and time
of the Universe. It also created the
reference frame to ask where any event
occurred.
• The Universe has no center and no edge!
Just like the surface of the round Earth
has no center or edge.
What is outside the Universe?
• What is the Universe expanding into?
• What happened before the big bang?
• What is the sound of one hand clapping,
Grasshopper?
• There was no time or space before the big
bang.
• You will not be responsible, in this class,
for anything which occurred before the
big bang.
We now know that distant galaxies
are moving away from us as the
Universe expands.
Expanding
Universe
Click here for 10
second animation of
expanding universe
• Dots represent galaxies. Each dot moves away from all
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others as the Universe expands. Note, Universe shown
as expanding surface, should show it as expanding 3 dim
space in 4 dimensions.
Scientific visualization from "Galactic Odyssey“ produced
by NCSA for NHK, the Japanese Broadcasting Co.
Dots are Galaxies
–Island Universes
Single dot is M31 Galaxy
Hubble deep field showing lots of galaxies
Image of M31 from my driveway with an 8” telescope and a homemade CCD
camera.
Great Scale of the Universe
• E. Hubble in 1920s used great 100” Hooker telescope to
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resolve M31 into stars. He enlarged the image until the
uniform white “milky way” gave may to individual stars.
M31 is made out of lots of stars just like our own Milky
Way! We are but one of very many galaxies!
Stars were very dim. This implied M31 is very far away.
Of order 3 million light years! [Note, today we think of
this distance as a very close neigbor.]
Read discussion and debate in the Perfect Machine.
Expansion of Universe and the
Motion of Distant Galaxies
• How do we know that distant galaxies are
moving away from us?
• These galaxies are so far away that it
would take a very long time, even given
their very high velocities, to see them
move appreciably.
• Instead, we infer their velocities from the
Doppler shifts of their spectral lines.
Spectral Lines
• How do we know the composition of distant Stars and
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Galaxies?
Each chemical element has a set of unique spectral lines.
These are particular frequencies of light (electromagnetic
radiation) that the element absorbs or emits.
Chemical elements are characterized by their atomic
number Z. This is the number of electrons that orbit the
nucleus. Hydrogen Z=1, Helium Z=2, Lithium Z=3 …
Uranium Z=92.
Quantum mechanics says these electrons can only have
discrete energies when they are orbiting the nucleus. A
spectral line is emitted when an electron jumps from one
energy to another.
Hydrogen has Z=1, Carbon has Z=6 and Sodium (Na) has Z=11 electrons.
Example, Sodium Glows Yellow
• Spectrum of Sodium shows green, bright yellow, orange.
and red spectral lines. Light from a glowing discharge
containing the element sodium is split by a prism with
short wavelengths (blue) on the left and long (red)
wavelengths on the right.
• Seeing these lines in the spectrum of a star or galaxy
implies that the distant object contains sodium.
• Remember electromagnetic spectrum.
Composition of Other Stars
• Spectral lines show that other stars, in
general, have a similar chemical
composition to our Sun.
• Therefore, the Sun is just another star!
• The Earth was no longer the center of the
universe since it orbits the Sun.
• Now the Sun is not the center of the
universe because it is just one of billions
of stars in the galaxy.
• Spectra of some stars. Spectra are shown in order of
decreasing temperature for normal stars, whose names
are listed on the right. Spectral types are labeled on the
left, and the wavelengths and associated elements are
shown at the top and bottom for selected spectral lines.
Doppler shift of Spectral Lines
• If an object is moving away from you, the sound
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or light that it emits is Doppler shifted to lower
frequencies.
The lowest frequency visible light is red.
Therefore we call this a red shift.
If the object is moving towards us, the light is
shifted to higher frequencies and we call it a
blue shift.
Can use the Doppler shift to measure the
velocity of distant galaxies.
Doppler Shift of Light from Galaxy
• The top figure compares spectral line (black line) from
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distant galaxy to same spectral line on Earth, yellow
marks at top and bottom.
If galaxy is moving away (middle figure) spectral line is
shifted to the red. If galaxy is moving towards us
(bottom), spectral line is shifted towards blue.
Hubble’s Law
• E. Hubble found that light from distant galaxies
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was red shifted by an amount proportional to
distance (from us).
The velocity of a distant galaxy v (inferred from
the red shift) is related to its distance d,
v=H d
Hubble’s constant H has dimensions of 1/time.
Age of universe is about 1/H. Exact value
depends on how expansion rate depends on
time.
This expansion age is about 13 B. years.
Expanding
Universe
Click here for 10
second animation of
expanding universe
• Dots represent galaxies. Each dot moves away from all
•
others as the Universe expands. Note, Universe shown
as expanding surface, should show it as expanding 3 dim
space in 4 dimensions.
Scientific visualization from "Galactic Odyssey“ produced
by NCSA for NHK, the Japanese Broadcasting Co.
Age of Universe
• Age of oldest stars. Stars turn into red giants
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(such as Betelgeuse) when they burn their
hydrogen fuel. More massive stars are hotter
and burn their fuel much faster.
Our Sun will take a total of 10 billion years to
use up its hydrogen. Note, Sun has been
shinning for 4.6 B. years so it has about 5 B.
more years to go before becoming a red giant.
More massive stars, last much less then 10 B.
years. Less massive stars last longer.
Globular Star Clusters
• Contain up to a million
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stars which all formed at
nearly the same time.
Look for smallest mass
star that has already
become a red giant.
Many clusters in our
galaxy have red giants
with masses slightly less
then the Sun.
Thus the clusters are
about 12-13 B. years old.
Universe is about 1 B.
years older
Ancient Globular Star Cluster M13
Radioactive dating of Stars
• New! With a great deal of effort one can
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determine amounts of radioactive Thorium and
Uranium in ancient stars in halo of Milky Way
galaxy. This is done by observing spectral lines
(particular frequencies of light) from U and Th in
the star light.
This gives a direct radioactive age of these stars
of 12 +/- 3 B. years.
Three independent ways to date Universe:
expansion rate, globular cluster red giants, and
radioactive dating. All say Universe is about 13
B. years old.
Big Bang Summary
• Universe contains countless galaxies like Milky Way.
• A single galaxy can have 100s of billions of stars.
• Spectrum (characteristic frequencies) of star light similar
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to Sun. Sun is just nearest star.
Each chemical element has characteristic spectral lines.
Doppler shift of spectral lines from distant galaxies
shows universe is expanding.
Measured expansion rate implies about 13 billion years
ago all galaxies on top of each other: age of universe.
This was Big Bang that created a very hot and dense
universe that has been expanding and cooling ever
since.
For next time
• Read chap. 3 of Jakosky about the history of the
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Earth and read “Alchemy of the Heavens", pages
25-58 in course packet about origin of chemical
elements.
Pre-project Essay: In one or two typewritten
pages discuss some of the events important for
life on earth between the Big Bang and the
evolution of man. Due Friday Jan. 31, 2002.
Next lecture, “Death Stars and Alchemy of the
Heavens” about the origin of the chemical
elements.