Exam #3 Study Guide:
Exam 3 will have 40 multiple choice questions based on
material covered in lectures from 11-15 to 12-1. Material from HW9-11 may be on
the exam. A few of the questions will involve simple calculations, so you
should bring your calculator. You will not need your clicker. You may bring one
double-sided 8.5x11 inch sheet of paper with notes to the exam.
I String Theory
that science is trying to find one theory that describes everything.
that String Theory tries to describe everything in terms of vibrating
size of the strings is 10-35m.
theory requires at least 10 dimensions to work.The minimum number of
dimensions for M-theory to work is 11.
experience only 4 dimensions. The others are too small to be detected.
problem with String Theory is that it theory as a whole has not yet made
falsifiable predictions that would allow it to be experimentally tested.
So far all the explanations it provides could be explained in other ways.
II The Big Bang
evidence is consistent with the Universe beginning in a very hot (1035K)
fireball 13.7 billion years ago. We call this event the Big Bang.
the three main pieces of evidence for the Big Bang
cosmic microwave background radiation
hydrogen, helium and lithium produced (this is called Big Bang
expansion of the Universe. Beyond our nearest neighbors all galaxies
appear to be moving away from us.
out from Earth is like looking back in time. It takes about 3 million
years for light from the Andromeda Galaxy to reach us.
structure of the Universe
are approximately 200 billion other galaxies
are part of a local group of about 20 galaxies, which includes the
are clumped into groups called clusters.
large scale structure of the Universe is clusters and voids
first person to discover the size of the Universe was Edwin Hubble. He did
this by studying variable stars. Variable stars work because it is
possible to know their luminosity accurately. A measurement of brightness
and a know luminosity can be used to determine a distance.
able to use the inverse square law to guess a distance.
also discovered that on average galaxies are moving away from us and the
farther away the galaxy, the faster it is moving. This is called the
the steps in determining distances in the universe (many of the steps
involved the use of standard candles)
– nearby stars
parallax – stars in our galaxy
stars – distances to nearby galaxies
– to nearby clusters of galaxies
Law – to farther galaxies and quasars
of bright galaxies - to the farthest galaxy clusters..
furthest view of the Universe is of the cosmic microwave background
radiation. This was formed 300,000 years after the Big Bang.
the timeline for the Big Bang.
that at about 10100 years all the stars will have burned out,
and at about 101000 years the universe will be at maximum
entropy and nothing else will happen. This is of course based on what we
know now. It is very likely there is more to the story. (The last two
sentences will not be on the test, but had to be said anyway.)
III Black holes and Worm holes
what is meant by the conservation of energy
energy is energy of motion. Potential energy is energy of position.
in kinetic energy = loss in potential energy
able to use conservation of energy to find a velocity, or from a velocity
is escape velocity? What happens to escape velocity if the mass of the
planet is changed? What happens if the radius is changed?
holes are a large mass in a small region, so that the escape velocity
becomes greater than the speed of light.
inside the event horizon (aka the Schwarzschild radius) not even light can
holes are formed in the collapse of massive stars at the end of their
holes also form at the centers of galaxies. Some galaxies have
supermassive black holes with 109 solar masses.
holes at the centers of galaxies explain active galaxies and quasars.
holes are a possible solution of Einstein’s equations, but to be stable
something would have to keep them open. Know that no corresponding white
holes have been observed. White holes violate the second law of
that the second law of thermodynamics says that entropy always increases
in any process
the two formulas for entropy.
entropy of the early Universe was far too low, hence the probability of
any process increasing entropy is vanishingly small. This gives time its
direction since to go back in time would allow entropy to be decreased.
IV Dark Matter and Dark Energy
- We are
made of atoms, atoms are made of nuclei and electrons, nuclei are made of
… Know all of these steps down to strings at 10-35m.
type of luminous matter only makes up 4% of the universe.
the evidence for dark matter
curves of galaxies
microwave background radiation
indicates that 23% of the universe must be in the form of some type of
cold dark matter. These may be particles that interact by the weak force.
They are called WIMPS.
that 73% of the Universe is made of Dark Energy. We don’t know what this is,
but it acts like an antigravity that is pushing the Universe apart.
about WMAP and the things it has discovered (LONCAPA problem).
a 1% accuracy the Universe is 13.7 billion years old.
don't know what 96% of the Universe is made of.
- The first
stars formed about 200 million years after the Big Bang.
picture of the background microwave radiation is from 379,000 years after
the Big Bang.
the present it appears the Universe will expand forever, but since we
don't know what dark energy is, this conclusion could change.