The Launch Pad
Friday, 8/27/10
Which of the following provide compelling evidence for
the Big Bang theory?
A.The universe is expanding
B.We can detect cosmic background
radiation noise in all parts of space.
C.Most galaxies are moving away from
each other.
D.All of the above are evidence.
In ongoing observations of one
of the universe's earliest, most
distant cluster of galaxies using
NASA's Spitzer Space
Telescope, an international
team of researchers led by
Texas A&M's Dr. Kim-Vy Tran
has discovered that a
significant fraction of those
ancient galaxies are still actively
forming stars.
Assignment Currently
Open
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Date of Notes on
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Date Issued
Date Due
Information Sheet
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8/23
8/24
Class Procedures
and Expectations
1-4
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8/23
8/25
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Einstein’s Theory of General Relativity
Albert Einstein's theory of general relativity
indicates that the universe (i.e., the space-time
metric) was described by a metric tensor that was
either expanding or shrinking (i.e., was not
constant or invariant), this result coming from an
evaluation of the field equations of the general
theory. Friedmann derived the expanding-universe
solution to general relativity field equations in
1922.
Expansion of the
Universe
Diffuse cosmic
background radiation
(COBE spacecraft)
Relative abundances
of elements
The end:
Expansion forever
or the Big Crunch?
The Doppler Effect is the apparent change in
frequency of waves (pitch) due to the motion of
the source or observer.
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
Note: The higher the frequency the higher the pitch.
A great example is an ambulance’s siren coming
toward you and then passing you. The pitch drops
as the ambulance passes.
The Doppler Effect
• The Doppler Effect is the apparent change in wavelength
of radiation caused by the relative motions of the source
and observer. It is used to determine:
 direction of motion.
 increasing distance – wavelength is longer
(“stretches.”)
 decreasing distance – makes wavelength
shorter (“compresses.”)
 velocity – larger Doppler shifts indicate higher
velocities.
The Doppler Effect
• So, the Doppler Effect is the change in the
wavelength of light emitted by an object due to
its motion.
 Movement away stretches the wavelength
Longer wavelength
Light appears redder
 Movement toward “squeezes” the wavelength
Shorter wavelength
Light shifted toward the blue
Figure 23.2
The Doppler Shift
• The amount of the Doppler shift
indicates the rate of movement .
•Large Doppler shift indicates a high
velocity
•Small Doppler shift indicates a lower
velocity
The Expanding Universe
• Most galaxies exhibit a red Doppler shift ,
meaning they are moving away from us.
• Far galaxies
•Exhibit the greatest shift
•Greater velocity
• Discovered in 1929 by Edwin Hubble
• Hubble’s Law – the recessional speed of galaxies is
proportional to their distance
• Accounts for red shifts
•
If a yellow star is stationary, the light waves it
emits are neither bunched together nor
stretched out; therefore, it appears yellow.
• If the same yellow star is approaching rapidly,
its light waves will be bunched together;
therefore, it appears blue.
• If the same yellow star is receding rapidly, its
light waves will be stretched out; therefore, it
appears red.
•
•
When a star (or galaxy) is
approaching us or receding from us,
the light waves emitted as a particular
color (e.g., yellow) are bunched
together or stretched out.
This shifts the object’s light (both the
maximum  and all spectral lines)
toward the blue or red part of the
spectrum.