News

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News
Large Hadron Collider 27 km long loop at a depth
of 50-150 m Smashes 7 Tev protons together,
moving at 99.999999 the speed of light! First
experiments in November 2007
Why isotropic?
Why 2.726 K?
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Questions
Is there a Higgs field which endows particles
with mass? If so the LHC will detect a Higgs
boson. Is there a theory that unifies the
strong, electro-weak, and gravity? This may be a
string theory, where particles arise as
excitations of a string. In string theory the
universe has more than 4 dimensions - maybe 10 or
26. But the other dimensions are small or thin.
The LHC will produce microscopic black
holes! Perhaps it will detect extra-dimensions
Why isotropic?
Why 2.726 K?
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Questions
Is there a Higgs field which endows particles
with mass? If so the LHC will detect a Higgs
boson. Is there a theory that unifies the
strong, electro-weak, and gravity? This may be a
string theory, where particles arise as
excitations of a string. In string theory the
universe has more than 4 dimensions - maybe 10 or
26. But the other dimensions are small or thin.
The LHC will produce microscopic black
holes! Perhaps it will detect extra-dimensions
Why isotropic?
Why 2.726 K?
Lisa Randall
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• The history of the Galaxy got a little muddled,
  for a number of reasons partly because those who
  are trying to keep track of it have got a little
  muddled, but also because some very muddling
  things have been happening anyway.
• From Mostly Harmless, by Douglas Adams
• There is a theory which states that if ever
  anybody discovers exactly what the Universe is
  for and why it is here, it will instantly
  disappear and be replaced by something even more
  bizarre and inexplicable. There is another theory
  which states that this has already happened.
• Douglas Adams

X-ray image of Cygnus X-1 from NASAs Marshall
Flight Center.
COSMOLOGY
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The Large-Scale Structure of the Universe is
Dominated by Galaxies
A Spiral Galaxy
An Elliptical Galaxy
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The Milky Way

• The Milky Way is a spiral galaxy and appears as a
  bright band in the night sky.
• It contains 100 billion (1011) stars.
• There are 100 billion galaxies in the universe.

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Olberss Paradox Why is the sky dark at night?

• If the universe were infinite and the density of
  galaxies was the same everywhere in the universe,
  then there should be a star in every single
  direction the sky should be bright at night, but
  it is not.

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Resolution

• Distant stars are dim, so we receive little light
  from them.
• Wrong. Though we receive less light from distant
  stars there are also more distant stars and this
  makes up for the dimming with distance.
• Theres invisible dust between us and the distant
  stars
• Wrong. The dust would eventually heat up and
  emit its own radiation. We dont see this.

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Resolution The universe is not infinite!

• The universe has a finite age and size.
• Right. These two concepts are closely related.
  When we look to great distances in the universe
  we are looking far back in time. If we look to
  distances so great that we are seeing times
  before the formation of stars, then the sky in
  that direction is dark.

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The force of gravity is always attractive. Why
then doesnt the universe collapse under its own
gravitational attraction?
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Is the Universe Stable?

• The force of gravity is always attractive. Why
  then doesnt the universe collapse under its own
  gravitational attraction?
• Newton said it was an act of God (Give him credit
  though, no one else realized that there was a
  problem).
• Einstein realized the same problem occurred with
  his theory of gravity and, in what he called the
  biggest blunder of his life, fudged the equations
  so that the universe would be stable.

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Answer

• Despite these deep-seated prejudices from
  mankinds two greatest luminaries, the answer is
  simple the universe is not stable, it is
  expanding.

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Doppler Shifts
A stationary (with respect to an observer) light
source emits radiation with a wavelength ? (the
green wave). If that same source is moving
towards the observer, the waves get compressed
and the wavelength is less than ? (the blue
wave). If the source is moving away from the
observer, the waves are stretched out and the
wavelength is greater than ? (the red
wave). Light from approaching objects is called
blue shifted and light from receding objects is
called red shifted, because blue and are on the
short-wavelength and long-wavelength ends of the
visible spectrum. The light is not necessarily
blue or red.
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We can tell if light is blue or red shifted by
examining the characteristic spectral lines of
the elements. In the spectrum shown above the
entire pattern of spectral lines is shifted to
either the blue or red. Because we can recognize
the pattern, we can identify the spectral lines
and therefore know what the un-shifted
wavelengths should be.
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Hubble, Galaxies and Red Shifts
In 1925, Hubble accumulated radial velocities for
40 galaxies.
63 Mly
Shown to the right are images of galaxies and
their spectra. The distance of the galaxies from
Earth in millions of light years (Mly) is listed
under the images and the velocity deduced from
the Doppler shift appears under the spectra. The
bright bands above and below the spectra are used
for calibration. The two dark bands in central
stripe are used to measure the Doppler shift.
The size of the Doppler shift is indicated by the
red arrow. The more distant galaxies show larger
Doppler shifts.
990 Mly
1440 Mly
2740 Mly
3960 Mly
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The Relationship Between Distance and Velocity
Mpc stands for Mega Parsec. 1 Mpc 3.3 million
light years
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Hubbles Law Suggests that Galaxies were once
much closer together
Imagine that all the galaxies were once much
closer together and had a spread of velocities
some were moving fast and some slow. After a
period of time (billions of years) the fast
moving galaxies would be very far away, but the
slow moving galaxies not so far away. The faster
a galaxy was moving, the further away it would
be. This is just what Hubble measured. Thus, it
seems that galaxies were once much closer
together. Notice that, no matter where you are,
everything seems to be moving away.
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Balloons and Raisin Bread
As the bread rises the distance between raisins
increases in a more or less uniform manner. It
would look the same no matter what raisin you
were sitting on. Think of the raisins as
galaxies.
A better analogy is the expanding balloon. As
the balloon expands the dots on the balloon get
further apart however, there is no center to the
surface of the balloon and the expansion would
look the same no matter where you were.
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General Relativity the Big Bang
The most beautiful thing that we can experience
is the mysterious. It is the source of all true
art and science. - Albert Einstein
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Space is curved
Forget forces. Planets travel in orbits,
following the curvature of space.
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Ubiquitous Radio Noise
In 1964, Arno Penzias and Robert Wilson adapted a
radio dish previously used for communication
satellites, to observe radio emissions from a
distant supernova. They hoped to map radio
emissions of the Milky Way.
Chance favors only the mind that is prepared -
Louis Pasteur
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Scientific Method
They were startled to find that no matter where
they pointed the antenna, they measured the same
low-level radio signal. So they tested the old
horn to make sure it was not defective. They also
cleaned the antenna of a thin white dielectric
film left by pigeons. They concluded that the
signals were real and a property of the universe.
Chance favors only the mind that is prepared -
Louis Pasteur
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Cosmic Background Radiation
Unknown to Penzias and Wilson, a Russian
Astrophysicist, George Gamov, had predicted the
existence of these radio signals as a consequence
of something we now call the Big Bang.
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COBE Measurements
Data prediction of emission from a 2.726 K
body.
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Why microwave radiation?
Why isotropic?
Why 2.726 K?
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Explanation 1
Gas gets hot when it is compressed and cool when
it expands. The same is true for the Universe.
The early Universe was a mixture of matter and
radiation. Shortly after the Big Bang, the
universe was tightly compressed, and thus
extremely hot. Its radiation was typical of that
for warm bodies (i.e. it obeyed Weins law). As
the universe expanded both the matter and
radiation cooled. In fact, the radiation cooled
from unimaginably high temperatures to 2.726 K,
the temperature of the universe today.
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Explanation 2
We get the same answer by considering that when
we look very far away we are seeing diffuse
radiation from the hot big bang. However, this
radiation comes from great distances (10-20
billion light years) and has been Doppler shifted
to very long wavelengths. In fact, it has been
Doppler shifted all the way from gamma rays to
radio waves the radio waves discovered by
Penzias and Wilson.
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Evidence for the Big Bang

• The universe is expanding at a rapid rate and
  seems to have been doing so since its creation.
• The Cosmic Background Radiation can be explained
  as the afterglow of the Big Bang.
• The cosmic abundances of hydrogen, deuterium, and
  helium are consistent with expectations based on
  synthesis by nuclear reactions in the Big Bang.

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The Big Bang solves the problem of the stability
of the universe the force of gravity does, in
fact, pull the universe together however, it is
not collapsing because it is still flying apart
at high speeds. This raises the question, will
the universe continue to fly apart or is gravity
strong enough to stop the expansion and pull all
the pieces back together in a Big Crunch? Put
another way, is the escape velocity of the
universe greater or lesser than the rate at which
it is expanding?
The collision of 2 galaxies.
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Fate of the Universe

• The amount of luminous matter in the universe
  appears to be too small to stop its expansion.
  This might imply that the universe would continue
  expanding forever, except that there seems to be
  a dark matter in the Universe. If there is
  enough dark matter, the universe could be
  closed, i.e. it may someday stop expanding and
  start contracting.
• Careful studies of the velocities of galaxies
  should be able to reveal if the rate of expansion
  is slowing down. However, the latest studies
  found a big surprise the rate of expansion is
  increasing! If true, the universe will probably
  expand forever, but the results are only a few
  years old and deserve more careful scrutiny
  before firm conclusions are adopted.

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Evidence for Dark Matter
Stars far from the galactic center obey Keplers
3rd law, but they indicate the presence of far
more mass in the galaxy than expected based on
visible light, hence the term dark matter.
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Is the Expansion Speeding Up?
V H D H Hubble constant, V
velocity, Ddistance
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The Age of the Universe
If the universe has been expanding at a constant
rate V H x D We can figure out H from
measures of D and V. It is estimated to be 70
km / sec Mpc Now the age of the universe is
related to the distance And velocity of objects
t D/V Therefore t D/HD 1/H Or
14 x 109 years for H70 km/s Mpc
1 pc 3.26 lyr 3.1x1013 km 1 Mpc
3.1x1019 km
Hubbles Law V H D H Hubbles
constant, V velocity, Ddistance
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Summary

• The solution to Olberss paradox is that the
  night sky is dark because the universe is a
  finite age.
• The universe is expanding from a primordial
  creation event 10-20 billion years ago.
• The universe is filled with thermal radiation at
  a temperature of 3 K that is the modern residue
  of the primordial fireball.
• There is far more mass in the universe than can
  be seen. The nature of this dark matter is
  unknown.
• Were not sure if the universe will keep
  expanding forever or if gravity will cause it to
  contract to a Big Crunch. The latest evidence
  favors expansion forever.

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