HW 10: The Universe
The objects that made it possible for astronomers to discover the acceleration in the expansion of the universe were
Type Ia supernovae
If you want to check on what conditions were like in the universe a few hundred thousand years after the Big Bang, what sort of instrument would it be best to use:
a satellite with infrared and microwave telescopes on board
Which of the following statements about dark matter is FALSE:
astronomers have a pretty good idea what the dark matter is made of
Where in space did the expansion of the universe begin?
everywhere at once
How do we think our Universe will end?
A big rip!
At first, right after the Big Bang, the universe was too hot for nuclei and electrons to combine into the kinds of neutral atoms that are familiar to us today. How soon after the beginning did it become cool enough for neutral atoms to form? (i.e. nucleons with electrons, not just the nucleons)
a few hundred thousand years
Factoring in everything we currently know about the history of the universe, our best estimate for the age of the universe is
about 13.8 billion years
Today, we believe that only a small number of elements were actually formed during the Big Bang. Which of the following was NOT one of these:
carbon
What have scientists suggested is causing the Universe to expand faster?
dark energy
Which of the following is the Earth not located in?
globular cluster M-13
Which of the following did NOT happen during the first few minutes after the Big Bang?
some very massive early stars formed
What is the present best estimate of Hubble's constant?
~70 km/s/Mpc
What created the Cosmic Microwave Background, or CMB?
Heat left over from the Big Bang
The cosmic microwave background is sometimes referred to as "relic radiation" -- light left over from a truly ancient time. But it isn't a relic of the universe's first moments, of the hot plasma posited by theorists; instead, it's thought to come from about 380,000 years after the very beginning, just after an epoch called "recombination." What happened during this time period?
Neutral hydrogen and helium atoms formed.
What is meant in cosmology by "critical density"?
The density that determines whether the Universe expands forever or re-collapses.
Why is the CMB so cool now?
The expansion of the Universe has cooled the radiation and stretched its wavelengths
What does a larger red-shift indicate?
The galaxy is moving away faster
The rate of expansion of the universe is?
accelerating
Hubble's law indicates that...
all of these The universe is expanding. The universe must have had a beginning. Nearly all other galaxies are moving away from us.
In the very distant future, given our best model of the accelerating universe, what will the universe look like?
all the stars will die and the galaxies will be dark
According to the models of the universe we discussed in this course, why do the galaxies move apart (why do we have Hubble's law)?
as a result of the Big Bang, space itself is stretching, and this stretching carries the galaxies away from each other
In our modern view of the expansion of the universe, we understand that it is space that is stretching; individual galaxies don't speed away from each other as if they were rockets. In that case, why do galaxies show a red-shift?
as space stretches, the waves of radiation in space also stretch and their wavelength increases
Which of the following statements about the early universe (as envisioned by the standard model of cosmology) is FALSE?
at the very beginning, the energies were so great that the universe was actually contracting for a while
Based on many surveys of the average density of matter in the universe (regular matter and dark matter), astronomers now conclude that the average density of the universe is: (To answer this, think about the role an increase in density (and thus gravity) has on the expansion of the universe)
essentially equal to zero (density is super low)
If the universe were decelerating, our calculated age of the universe would be:
less than 1/H
How many galaxies show a red-shift?
nearly all of them
When do astronomers now think that the "dark energy" began to accelerate the expansion of the universe?
several billion years after the Big Bang
When we determine the age of the universe using the Hubble Time, what important simplifying assumption goes into our calculations?
that the expansion of the universe has been happening at the same rate - neither speeding up or slowing down
Which of the following is pretty good evidence that the universe began with a Big Bang?
the 3-degree cosmic microwave background radiation
The reciprocal of the Hubble constant (1/H) is a rough measure of the:
the age of the universe
According to the most recent data from satellites making precise measurements of the properties of the cosmic microwave background,
the dark energy makes up just a little less than 70% of the density of the universe, making it the most significant constituent of the mass-energy
After the Big Bang, in order for the universe to become transparent to light and other electro-magnetic radiation, what had to happen?
the density of the universe had to decrease (to 1000 nuclei per cubic centimeter or less)
Recent observations indicate that the universe is expanding faster today than it was a few billion years ago (that, in other words, the expansion of the universe is accelerating.) What kind of observations have led astronomers to this surprising conclusion?
the measurement of galaxy distances using Type Ia supernovae
