AS101 Assignment 6

The redshifts of the galaxies imply that the universe is expanding and that we are at the centre.

False

​The Kelvin temperature scale is based on the freezing point of water.

False

The night sky is dark because the universe is not infinitely old.

True

The cosmological principle states that any observer in any galaxy will see the same general features of the universe.

True

Cosmologists cannot begin their history of the Big Bang at a time of exactly zero because it cannot be explained by current physics.

True

The Big Bang happened everywhere in the Universe at the same time.

True

The Universe is isotropic, but not homogenous.

False

The cosmological redshifts of galaxies are Doppler shifts.

False

All dark matter in our Universe falls into the category of "hot dark matter".

False

The expansion of the Universe is accelerating.

True

Normal matter is baryonic.​

True

What is meant by the term "observable universe"?

the part of the universe where the look-back time is smaller than the age of the universe

How long after the big bang could gas begin to clump together due to gravity?

about a billion years

What does a cosmological redshift tell you?

how much the universe has expanded since the light was emitted

The water molecules in your body contain hydrogen atoms. When did these hydrogen atoms form?

within a few minutes after the big bang

What is the definition of Absolute Zero?

the temperature at which no thermal energy can be extracted from atoms

The temperature of an object is 273K. What is the temperature in degrees Celsius?

0

Is it possible for a red star to emit more energy than a blue star?

Yes, if the red star has a larger area.

You are standing near a railway track and a train is moving toward you at 100 kph and blowing its whistle. What will you notice as the train moves past you?

As the train approaches, the horn will sound higher in pitch than when the train is moving away.

The Doppler effect is useful in measuring the ____.

motion of an object toward or away from the observer

While you are sounding a tone on a toy whistle, you notice a friend running toward you. If you want her to hear the same frequency that you hear even though she is approaching, you must

run away from her at the same speed.

A person standing in the street is unaware of a bird dropping that is falling from a point directly above him with increasing velocity. If the dropping were producing sound of a fixed frequency, as it approaches the person would hear the sound

increase in frequency.

Which of the following statements best describes Olbers's paradox?

The night sky should glow bright.

Why is there a limit to the size of the observable universe?

because the universe has a finite age

What is the point of the raisin bread analogy for the expanding universe?

to show that all observers see other raisins (galaxies) expanding away from them

Which of the following changes would make the raisin bread analogy more similar to the actual expansion of the universe?

Make the raisin loaf infinitely big.

When people hear the phrase "big bang," they often think of an explosion. What word would be a better description than "explosion"?

expansion

What does the resolution of Olbers's paradox say about why it gets dark at night?

It gets dark at night because the universe is not infinite in age.

What is the Hubble time?

an estimate of the age of the universe assuming a constant expansion rate

Where did the cosmic microwave background (CMB) come from?

photons released when electrons and nuclei combined for the first time

The cosmic background radiation comes from a particular time after the origin of the universe. What was that time?

when electrons began to recombine with nuclei to form atoms

What is the assumption of isotropy?

that the large-scale appearance of the universe is the same in every direction

What is the assumption of homogeneity?

that the large-scale appearance of the universe is the same from any point

Under what conditions will space-time be flat?

if the average density of the universe is equal to the critical density

A universe is finite in time if its expansion will eventually stop, and finite in space if it does not extend indefinitely. What would a closed universe be?

finite in both time and space

Which of the following applies if the universe is closed?

The universe is homogeneous and has a high density.

What problems are solved by the theory of inflation?

flatness and horizon

Which of the following does current evidence suggest about the universe?

It is flat, infinite, and its expansion is accelerating.

What is dark energy?

the energy causing the universe's expansion to accelerate

Arno Penzias and Robert Wilson are famous for____.

detecting the large redshift background radiation from the Big Bang