HZ Quiz 3 Astron 101

What is recombination/decoupling?

400,000 years after the Big Bang, the universe cooled enough to form neutral H and the universe became transparent for the first time.

What is evidence for the cosmic microwave background?

Spy planes above the Earth's atmosphere measured dipoles (two poles: a red shifted side and a blue shifted side) which can only be explained by the motion of Earth with respect to the CMB.

What are the different eras of the early universe?

(1) Planck (2) Quark (3) Hadron (4) Lepton

T/F: Cepheid variable stars with higher luminosities have shorter periods.

False; they have longer periods.

T/F: Einstein initially did NOT support the idea that the universe was expanding.

True

Who were the two astronomers who theorized that the universe was expanding?

(1) Friedman (2) Lemeitre

What was the impact of Hubble discovering cepheid variable stars in the Andromeda Nebula?

Knowing the period of the variable stars, he could find the luminosity of the stars. Thus, he could compute the distance away from Earth that the Andromeda Nebula was. It was way outside the Milky Way Galaxy thus supporting the argument that the Andromeda Nebula was another galaxy.

How far is the Andromeda Nebula from Earth?

2.5 mn light years away.

T/F: Nebulas are separate galaxies.

True

What did Hubble discover about stars in 1929?

If you graphed the relationship between the distance in parsecs against the velocity in km/s of the stars, they formed a linear relationship. V \= md

What is Hubble's law?

The observation that galaxies are moving away from Earth at speeds proportional to their distance. The farther they are, the faster they are moving away from Earth.

T/F: All galaxies are moving away from us.

False; almost all galaxies. The Andromeda Nebula is moving towards the Milky Way Galaxy because the gravitational force between the two galaxies is greater than the expansion of space.

What is the equation for Hubble's Law?

V \= Ho*d (Ho \= Hubble's constant)

T/F: Stars are pinned to their location and space itself is expanding.

True

T/F: There is a center to the expansion of the universe.

False

How can we use the Hubble-Lemaitre Law to measure the distance of cosmological objects?

If we can measure the velocity of the object moving away from us, we can use V \= Ho*d to find the distance.

What is the rate of the expansion of the universe determined by?

Ho

What is the formula for the age of the universe?

Age \= 1/Ho

What is the approximate value of Ho? Include units.

70 km/sec/Mpc

What happens when Ho is too large?

The universe would be younger than the Earth.

What is the approximate age of the universe?

13.8 bn years

What is cosmological redshift?

As light travels towards us from distant galaxies, it is stretched over time by the ever-expanding space it is traveling through (according to supporters of the Big Bang Theory).

T/F: Cosmological redshift has the same effect as the doppler effect.

True

What does R-dot represent?

The rate of change of R or the speed at which the universe is expanding or shrinking.

What are the different implications of having a constant R-dot and having a variable R-dot?

(1) Constant rate of change. (2) The universe is changing sizes at different rates over time.

What does Ho equal? or How do you calculate Ho?

R-dot(now) / R(now)

Why is Ho called Hubble's constant? How is it constant?

Every observer in the entire universe will measure the same value for Ho at any given moment.

T/F: The two ways of measuring Ho (cepheid variable stars and cosmic microwave background) are equal.

False; and we don't know why.

T/F: We can predict if our universe is open, flat, or closed.

False; we are too early in the process to know.

What is the formula that predicts if our universe is open, flat, or closed?

Omega \= density(actual) / density(critical)

What does the critical density of our universe equal? State the formula and the approximate value.

(1) 6 Hydrogen atoms per m^3. (2) (3/8piG) Ho^2*

What is the evidence for the Big Bang Theory?

(1) Hubble and others discovered that nearly all galaxies are moving away from us. (2) The farther away from us they are, the faster the galaxies are moving. (3) This motion is due to an expansion of space itself and not because Earth is the center of the expansion. (4) Expansion implies a beginning to the universe.

What is the cosmological principle?

The universe is isotropic (uniform in all directions) and homogeneous (same in all places) over large scales.

Is the cosmological principle a bad theory?

Not necessarily. It's not possible to be proved but it's possible to be disproved.

What is the "perfect" cosmological constant?

The universe is the same in all directions, places at all times.

T/F: The "perfect" cosmological constant is true.

False

T/F: Nearly all the elements in the universe were created 3 minutes after the Big Bang.

True

What are CERN and Fermilab?

They are particle accelerator facilities.

What are the fundamental building blocks?

(1) Electrons (2) Up quark (3) Down quark

Why is studying the Big Bang the only way to probe high temperature and energy?

(1) Fermilab and CERN can only create high temperatures for a short period of time. (2) Conditions that created the Big Bang cannot be recreated on Earth.

What was the early universe dominated by?

Light (aka radiation).

Gamma rays + gamma rays \=

matter + antimatter (aka electrons + positron)

As the universe expanded, what happened?

It cooled down and the radiation lost energy due to cosmological red shift. Particles could exist for longer.

T/F: Our physics can't explain before the Planck Era.

True

Planck Era

Age < 10^-43 sec

Quark Era

(1) 10^-35 < Age < 10^-6 sec (2) Free quarks formed from pure energy and survived.

Hadron Era

(1) 10^-6 Age < 10^-4 sec (2) Quarks fused together into baryons

Lepton Era

(1) 10^-4 < Age < 10 sec (2) Electrons formed from pure energy and survived.

Why is the amount of matter in the universe fixed?

A few seconds after the Big Bang, the universe cooled so much that photons couldn't form electrons.

How can we test the hypothesis that the amount of matter in the universe is fixed?

We can look at distant objects to see if particles existed in quantities predicted by the Big Bang.

What are baryons made of?

3 quarks (1) Protons: uud (2) Neutron: ddu

What is an example of a lepton?

Electron

What is primordial nucleosynthesis?

The production of nuclei other than those of the lightest isotope of hydrogen (hydrogen-1, 1H, having a single proton as a nucleus) during the early phases of the Universe.

What are the problems with the Big Bang theory in explaining the creation of elements past Lithium?

(1) There are no stable nuclei with atomic masses of 5 or 8 so nuclear reactions have a problem building any elements more complex than lithium. (2) By about 100s, the universe had cooled so much that nuclear reactions began to slow. (3) By about 3 minutes, nucleosynthesis had pretty much stopped.

T/F: The evidence supports primordial nucleosynthesis.

True

Big Bang nucleosynthesis happened \______ and \______ in the young universe.

(1) everywhere (2) at the same time

What do the spectral lines of distant galaxies tell us about the early universe? Why do they constrain the Big Bang model?

(1) The amount of H, D, He, and Li (2) The predicted chemical abundance of the early universe is constrained by the observed chemical abundance.

What was allowed to happen three minutes after the Big Bang?

Protons and neutrons could form to make H and He.

Why is nucleosynthesis evidence for the Big Bang?

The chemical abundance predicted matches the measurements from spectral lines of distant galaxies.

What happened to the gamma rays produced by the Big Bang?

As the universe expanded, the rays had cosmological redshift and were stretched into radio waves.

Who discovered the cosmic microwave background in 1965?

Wilson and Penzias.

T/F: The cosmic microwave background is everywhere.

True; because nucleosynthesis occurred everywhere. That's why Wilson and Penzias kept on hearing this hissing noise when they were measuring using the radio telescope.

For about 400,000 years after the Big Bang, what was the universe like?

There was a cloud plasma of protons and electrons (Ionized H and light) that was opaque to light.