Astronomy Second Midterm - Chapt. 17

Front 1

What is the Universe expanding into?

Back 1

Nothing, the universe is all there is...there is no per-exisiting space into which the galaxies expand (just uniform expansion of the universe)

ex. don't need the white background behind the balloon to account for observations that the balloon itself is expanding

Front 2

What is Hubble time?

Back 2

how long it would take galaxies to reach their current separations expanding at the observed rate...

Hubble time = 300/H0 (22km/s/Mly)

= ~14 billion years

-the average separation b/w galaxies was more now than it was in the past (14 billion years ago the galaxies would have been coincident)

Front 3

What is Olber's Paradox?

Back 3

Why is the night sky dark?
-after all, the universe is made up of stars...

Front 4

How did Olber (and Edgar Allan Poe) solve the Olber's Paradox of the Night Sky?

Back 4

The light from sources further away has not had time to reach us
-the finite age of the universe (14 billion years) represents a cosmic horizon, in which we cannot look back further than this

Front 5

What is the He Problem? What is its solution?

Back 5

The He Problem:
-He is present everywhere in the Universe and is about 25% of the mass
-these amount of He are seen in very distant objects (which we see as they were long ago)
-it does not seem possible for stars in the Universe to make all this He

Solution:
-14 billion years ago the universe was much denser and hotter, so nuclear reactions in the Universe could have made all the He itself (but then hot things emit light though...so where did all the light go from these nuclear reactions?)

Front 6

Where did all the light go from the making of He near the Big Bang when the universe was hot and dense enough to have nuclear reactions?

Back 6

Cosmic Microwave Background Radiation!
-radio waves that are uniform in all directions in the sky, with the same temperature (2.73 degrees) and spectra
-fluctuations in CMBR are about 1 in 100,000 (minor fluctuations)

Front 7

What was the recombination era?

Back 7

When the universe cooled to allow atoms to form, the universe became transparent (releasing background radiation)
-380,000 years after the big bang, universe dropped below critical temp of 3000K
-light was scattered before this era b/c electrons weren't bound to atoms, so light bounced off electrons

Front 8

Why is the Cosmic Microwave Background Radiation in microwaves?

Back 8

Since the universe is uniformly expanding, and light is stretched out by this expansion, once visible light has now been stretched out into microwave radiation (universe has stretched about 1000 times since the recombination era)

Front 9

What was the nucleosynthesis era? Why didn't the BB produce all of the other elements?

Back 9

-Universe was even hotter and denser in nucleosynthesis era than in the recombination era
-this is when H --> He (the 25% of He we see today)
-but this era lasted for only a few minutes
-in nuclear reactions have to over come gap between elements like in a ladder (became too cool too quickly for the stable nucleus atomic mass 5 to be overcome, so stopped at He (with He, H, and deuterium being made)

Front 10

What is the observational pillars of the BB?

Back 10

1) Expansion of the Universe (Hubble constant)
2) Cosmic Microwave Background Radiation (from making of He in nucleosynthesis era - light released during recombination era)
3) Nucleosynthesis of light elements (deuterium and He)

Front 11

New observations revise the value of Hubble's constant from 22km/s/Mly to 11 km/s/Mly. What is the implication of this for the age of the Universe or (Hubble Time)?

Back 11

Hubble Time = 300/H0

So if H0 is smaller, Hubble time will be larger

The Universe would now thought to be older than a previous estimate

Front 12

How was the Term Big Bang coined? Why is it ironic who it was formed by? What theory did they support instead?

Back 12

-Coined in a BBC program by Hoyle

-Hoyle did not believe in the BB, believed in Steady-State Theory (cosmological principles)

-Hoyle explained how chemical elements in the Universe are built up by the nucleosynthesis era

Front 13

What are the Cosmological principles supported by Hoyle?

Back 13

1) Ordinary Principle
-There is nothing special about our location in the universe
-universe is homogenous and isotropic (so we have a fair sample of the elements in the universe)

2) Perfect Principle
-There is nothing special about our location in the universe either in space or time

Front 14

Which are likely implications of the perfect cosmological principle?

Back 14

There can be no BB and no CMBR (but we see CMBR so we know this theory to be false)
&
Matter must be continuously created throughout the universe (to have an expanding universe, have to be constantly making matter)

Front 15

What is the difference b/w the density of galaxies seen as time went on between the BB and Steady-state models?

Back 15

BB:
-density of galaxies falls as universe expands (galaxies moving away from each other - uniform expansion)

Steady State Model:
-density of galaxies remains constant - so matter has to be continuously created

Front 16

Are the physical conditions thought to be present at the origin of the universe (BB) accessible to experimental tests?

Back 16

YES - Large Hadron Collider
-huge ring that accelerates charged particles to high speeds so they collide to see what fragments are produced

-at a given temp., we can figure out the typical speed (energy) particles are moving
-so we can compare the temp predicted by the BB with the collision speeds in the particle accelerator

Front 17

How soon after the BB can the Large Hadron Collider probe the physical conditions of the Universe?

Back 17

5 x 10^-15 seconds
-have very high energy photons that can turn their energy into mass and make particles (particle creation) and collide to turn mass into photons (particle annihilation)

Front 18

What 4 forces are present in the universe currently to allow for particle creation and annihilation? What forces were thought to be present at the BB?

Back 18

Now:
-gravitational, electro-magnetic, weak force, strong force

BB:
-forces were unified together (at higher temps)
-electroweak force
-maybe a gravitational-strong force? - string theory

Front 19

What are the three possible geometries that GR theory allows for the Universe? - curving space-time

What is the significance of the Universe's geometry?

Back 19

1) Flat - requires a critical amount of mass/energy (if more = closed, if less = open)
2) Closed (sphere)
3) Open (saddle)

-Global geometry determines the Universe's ultimate fate

Front 20

Typically, how far apart on the sky are the temperature fluctuations in the CMBR? What is the flatness problem of the Universe?

Back 20

1 degree
-this scale of temp fluctuations in the CMBR provide convincing evidence that the geometry of the Universe is flat

BUT if this is true, for the Universe to appear flat today, it had to start of exceedingly flat at the BB...

Front 21

What is the horizon problem?

Back 21

-different regions of the universe have not contacted each other (too far apart), but have the same temp and other physical properties...how?

The uniform temp of the CMBR is a problem, b/c the universe does not seem old enough to allow all parts of it to be in thermal contact

-we'd like to think that the microwave radiation needed time to exchange heat with its surroundings in order to come into "equilibrium" (like a cooled down cup of coffee), BUT are universe seems too big for this

Front 22

What is the inflation solution? How does inflation help solve the flatness problem and horizon problem?

Back 22

The universe went through an extremely brief period of rapid expansion in the first fraction of a second after the BB

-explains why CMBR are event distributed & why the universe is flat