Transcript Cosmology - Lunar and Planetary Laboratory

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 collisions scheduled for August 2008
News
Why isotropic?
Why 2.726 K?
Fundamental Forces & Particles
Bosons have integral
spin, and are force
carrier particles
Fermions have odd 1/2
integral spin
Proton
Particles are classified in terms of:
Mass
Charge
Spin
Neutron
Unified Field Theory
1970s:
Electromagnetic & Weak Forces are 2 aspects of the same force,
now called the electroweak force.
Present: Are all forces different manifestations of the same “unified” force?
String theory: perhaps particles & forces are vibrations of “stringlike” structures in 10 or more dimensions.
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.
Why isotropic?
Why 2.726 K?
The LHC will produce microscopic black
holes!
Perhaps it will detect extra-dimensions
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.
Why isotropic?
Why
2.726
K?
The LHC will produce microscopic black
holes!
Perhaps it will detect extra-dimensions
Lisa Randall
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
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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 X1 from NASA’s Marshall
Flight Center.
COSMOLOGY
The Large-Scale Structure of the
Universe is Dominated by Galaxies
A Spiral Galaxy
An Elliptical Galaxy
The Milky Way
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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.
Olbers’s Paradox:
Why is the sky dark at night?
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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.
Resolution
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Distant stars are dim, so we receive little light
from them.
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Wrong. Though we receive less light from distant
stars there are also more distant stars and this makes
up for the dimming with distance.
There’s invisible dust between us and the distant
stars
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Wrong. The dust would eventually heat up and emit
its own radiation. We don’t see this.
Resolution:
The universe is not infinite!
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The universe has a finite age and size.
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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.
The force of gravity is always
attractive. Why then doesn’t
the universe collapse under it’s
own gravitational attraction?
Is the Universe Stable?
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The force of gravity is always attractive. Why
then doesn’t the universe collapse under it’s own
gravitational attraction?
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Newton said it was an act of God (Give him
credit though, no one else realized that there
was a problem).
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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.
Answer
Despite these deep-seated prejudices from
mankind’s two greatest luminaries, the
answer is simple: the universe is not stable,
it is expanding.
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 shortwavelength and long-wavelength
ends of the visible spectrum. The
light is not necessarily blue or red.
We can identify blue or red shifts by examining the characteristic
spectral lines of the elements. In the spectrum above the entire pattern
of spectral lines is shifted to either the blue or red. By identifying the
spectral lines*, we know what the un-shifted wavelengths should be.
* These absorptions are formed from hydrogen transitions out of the 1st excited state.
Hubble, Galaxies
and Red Shifts
In 1925, Hubble accumulated radial
velocities for 40 galaxies.
Images of galaxies & 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 which is indicated by the
red arrow.
63 Mly
990 Mly
1440 Mly
2740 Mly
The more distant galaxies show larger
Doppler shifts.
3960 Mly
Wait: how did he measure galactic
distances
Need bright objects of known luminosity.
White dwarf supernova emit 10 billion times the light of the Sun
Relationship Between Distance &
Velocity
The slope of the line is called Hubble’s Constant: H = V/D ~ 70 km/s/Mpc
Mpc stands for Mega Parsec. 1 Mpc = 3.3 million light years. 1 ly = 9.46x1015 m
Hubble’s 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.
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.
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
Space is curved
Forget forces. Planets travel in orbits, following the curvature of space.
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
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
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.
COBE Measurements
Data & prediction of emission from a 2.726 K body.
Why microwave radiation?
Why isotropic?
Why 2.726 K?
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 Wein’s 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.
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.
Evidence for the Big Bang
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The universe is expanding at a rapid rate and
seems to have been doing so since its creation.
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The Cosmic Background Radiation can be
explained as the afterglow of the Big Bang.
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The cosmic abundances of hydrogen,
deuterium, and helium are consistent with
expectations based on synthesis by nuclear
reactions in the Big Bang.
How old is the Universe?
Consider Hubble’s Finding
The beginning of the Universe
The slope of the line is called Hubble’s Constant: H = V/D ~ 70 km/s/Mpc
The Universe appears to be expanding at a constant rate: V = H x D
The Age of the Universe
If the universe expands at a constant rate:
V=HxD
From measurements of D & V: H ~70 km / sec / Mpc
Over the age of the universe, T, galaxies have traveled
a distance D with at a velocity V:
D=VxT
1 pc = 3.26 lyr
= 3.1x1013 km
1 Mpc = 3.1x1019 km
Or:
T=D/V
Therefore:
T = D / (H x D) = 1 / H
H = 70 km/s / 3.1x1019 km
H = 2.26 x 10-18 sec-1
H = 7.13 x 10-11 yr-1
Or:
T = 14 x 109 yrs
for H=70 km/s Mpc
14 Billion years old !
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.
Fate of the Universe
1) 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.
2) 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.
Rotational speeds of stars in our Galaxy
Evidence for Dark Matter
Stars far from the galactic center obey Kepler’s 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.”
Is the Expansion Speeding
Up?
V=H*D
H = Hubble “constant”, V= velocity, D=distance
Convertin
g one
particle
into
another
How was nature
different in the
past?
Summary
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The solution to Olbers’s 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.
We’re 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.