Astronomy 1 Final (Chapter 7)

Which of the following observations helps show that the universe is evolving with time?

- the fraction of material that is hydrogen in the most remote stars (compared to the stars around us) - the observation that the amount of deuterium is greater than what we expect from processes inside stars - the number of quasars that can be observed at different distances and thus at different times in the past - the existence of the cosmic background radiation all of the above help show that the universe evolves

To date, physicists have investigated the behavior of matter and energy at temperatures as high as those that existed in the universe as far back as ________ after the Big Bang.

10^-10 second

How long after the Big Bang was the Planck time, before which our current theories are completely unable to describe conditions in the universe?

10^-43 second

How long after the Big Bang was the Planck time, before which our current theories are completely unable to describe conditions in the universe?

10^-43 seconds

Approximately how long did the era of nucleosynthesis last?

3 minutes

At the beginning of the universe:

- the density was enormously high - matter could turn into energy and vice versa - only a and e - the temperature was billions of degrees all of the above

The satellite that has given us the most precise measurements of the characteristics of the cosmic background radiation is

WMAP

Why do we call dark matter "dark"?

We cannot detect the type of radiation that it emits.

Why can't current theories describe what happened during the Planck era?

We do not yet have a theory that links quantum mechanics and general relativity

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

Where do the photons in the cosmic background radiation originate?

the end of the era of nuclei

What causes the expanding universe to decelerate in many of our cosmological models?

the mutual gravity of the galaxies pulls them together

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?

3 minutes

Why might inflation have occurred at the end of the GUT era?

An enormous amount of energy was released when the strong force froze out from the GUT force

Why is the era of nucleosynthesis so important in determining the chemical composition of the universe?

Except for the small amount of matter produced later by stars, the chemical composition of the universe is the same now as at the end of the era of nucleosynthesis

What kinds of atomic nuclei formed during the era of nucleosynthesis?

Hydrogen and helium and trace amounts of lithium, beryllium, and boron

The first scientist to propose a specific model (the primeval atom model) for the big bang was

Lemaitre

The period from about 100 seconds up to 15 minutes after the Big Bang is the

Nuclear Epoch

What direct evidence do we have that the weak and electromagnetic forces were once unified as a single electroweak force?

Particle accelerators on Earth can reach energies equivalent to the high temperatures of this era and have produced particles predicted by the electroweak theory.

The two scientists who first discovered the cosmic background radiation were

Penzias and Wilson

Which of the following particles are baryons?

Protons

If all the "dark matter" in the Universe were to be, somehow, instantaneously removed, which of the following would not happen?

The Solar System would fly apart

What is meant by "dark energy"?

The agent causing the universal expansion to accelerate

Why does the Big Bang theory predict that cosmic background radiation should have a perfect thermal radiation spectrum?

The background radiation came from the heat of the universe, with a peak corresponding to the temperature of the universe.

Evidence that the cosmic background radiation really is the remnant of a Big Bang comes from predicting characteristics of remnant radiation from the Big Bang and comparing these predictions with observations. Four of the five statements below are real. Which one is fictitious?

The cosmic background radiation is expected to contain spectral lines of hydrogen and helium, and it does.

Recent measurements of the expansion rate of the universe reveal that the expansion rate of the universe is doing something astronomers did not expect. What is that?

The measurements show that the expansion is accelerating, rather than slowing under the influence of gravity.

Why do we expect the cosmic background radiation to be almost, but not quite, the same in all directions?

The overall structure of the universe is very uniform, but the universe must have contained some regions of higher density in order for galaxies to form.

Why did the era of nuclei end when the universe was about 300,000 years old?

The universe had expanded and cooled to a temperature of about 3,000 K, cool enough for stable, neutral atoms to form.

Some MACHOs emit radiation. Why are they considered dark matter?

They are not as bright as a normal star and are not visible across great distances of space.

Olbers' paradox is an apparently simple question, but its resolution suggests that the universe is finite in age. What is the question?

Why is the sky dark at night?

Which of the following is an example of baryonic matter?

You

The Hubble Time is

a rough estimate of the age of the universe

According to our studies of the ages of the oldest stars we know, the age of the universe must be

about 13 - 14 billion years

The crossover point from radiation to matter domination occurred

about 50,000 years after the Big Bang, at a temperature of about 16,000 K

The reciprocal of the Hubble constant (1/H) is a rough measure of the

age of the universe

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

Which of the following statements about dark matter is FALSE?

astronomers have a pretty good idea what the dark matter is made of

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

The Planck era refers to the time period

before the Plank time.

According to our modern theories, the geometry of the universe (all of space-time) may be curved or warped. This is a pretty bizarre notion; what other discovery in astronomy has helped us believe that space may be able to curve or warp?

black holes

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

In the closed universe model, the universe will end by

coming together in a "big crunch"

Einstein included a cosmological constant in his equations describing the universe, because he

could not bring himself to imagine a universe in motion

In the open universe model, the universe will

expand forever

In describing the universe using his equations of general relativity, Einstein assumed that it was isotropic (the same in all directions.) What recent observations have confirmed that the universe is isotropic on the large scale?

measurements of the 3-degree cosmic background radiation

Helium originates from

mostly from the Big Bang with a small contribution from stellar nucleosynthesis

At about 1 second after the beginning of the universe, one type of particle was able to start traveling freely through the universe. These particles are still with us, but they are extremely hard to detect. They are called

neutrinos

When we say that the electromagnetic and weak forces "freeze out" from the electroweak force 10^-10 seconds after the Big Bang, we mean that

prior to this time the electromagnetic and weak forces maintained a single identity, but they possessed separate identities following this time.

What did the Big Bang theory predict could be seen today?

radiation from the Big Bang might be detected. It was gamma rays 14 billion years ago, but today it is cooler and would look like weak microwaves coming from all of space

Which of the following is NOT an observation made by the COBE satellite?

that many new elements were being produced at the time that the cosmic background radiation was emitted

Which of the following is pretty good evidence that the universe began with a Big Bang?

the 3-degree background radiation

The universe appears flat; this is explained by

the Inflationary epoch

In which model (theory) of the universe will all the galaxies eventually show a blue shift in their spectrum instead of a redshift?

the closed universe (with positive curvature)

What are the two key observational facts that led to widespread acceptance of the Big Bang model?

the cosmic background radiation and the high helium content of the universe

According to the most recent data from satellites making precise measurements of the properties of the cosmic background radiation (CBR)

the dark energy makes up more than 70% of the density of the universe, making it the most significant constituent of the mass-energy

Measuring the amount of deuterium in the universe allows us to set a limit on

the density of ordinary (baryonic) matter in the universe.

Based on current evidence concerning the amount of deuterium in the universe, we can conclude that

the density of ordinary (baryonic) matter is between 1 percent and 10 percent of the critical density.

The amount of deuterium we find in stars today can give astronomers an important clue about

the density of the universe just a few minutes after the Big Bang

The model of the universe that involves an enormous increase of scale during a very short time in the early universe is called

the inflationary universe model

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

What is the strongest force in the universe?

the strong nuclear force

If the Hubble constant turns out to be larger than we have thought in the past, it means that

the time that has passed since the Big Bang is less than we thought

What did the COBE observations tell cosmologists about the early universe?

there are tiny but important "ripples," temperature fluctuations that are perhaps the seeds of galaxies that form later

What happened to the quarks that existed freely during the particle era?

they combined in groups to make protons, neutrons, and their antiparticles

How many forces operated in the universe during the GUT era?

two, gravity and the GUT force

A GUT (grand unified theory) refers to theories that

unify the strong force and the electromagnetic and weak forces.

To measure whether the expansion of the universe is decelerating or accelerating, we need an independent way of measuring the distance to really remote galaxies. Which of the following holds some promise as a way of measuring such very large distances?

using the brightness of type I supernovae as standard bulbs

What do we mean by inflation?

what happened the instant after the Big Bang

The redshift of the universe at decoupling was about

z = 1,100