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Astronomy 101 > Class Notes > Flashcards

Class Notes Flashcards

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1
Q

How do you calculate the Hubble time?

A

1/hubble constant

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2
Q

what happens to the size of the objects when the universe expands and why?

A

The objects do not change size

The force of gravity holding them together is too strong

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3
Q

What is Cosmological Redshift?

A

As things are further away, they become more redshifted

This is caused by the expansion of the universe

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4
Q

Is the rate of cosmological expansion constant?

A

No, it changes over time

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5
Q

what is R(t)

A

The radius of the universe essentially

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6
Q

What is Rdot?

A

the rate of change of the radius of the universe (R)

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7
Q

What is Hubble’s Constant as of right now?

A

67.74km per sec

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8
Q

Is Hubble’s Constant actually constant?

A

NO

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9
Q

What is the issue with Hubble’s constant being too large and making the age of the universe younger?

A

We know things in the universe to be at least 13bn years old. The universe cannot be younger than some of the things in it

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10
Q

What happens if outward expansion is greater than inward gravity?

A

The universe will continue to expand forever

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11
Q

What is k?

A

The curvature constant

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12
Q

What are the possible values of k?

A

1
0
-1

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13
Q

What is the shape of the universe when k=1

A

the universe is closed/spherical

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14
Q

What is the shape of the universe when k=0

A

the universe is flat

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15
Q

What is the shape of the universe when k=-1

A

the universe is hyperbolic

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16
Q

In which universe could you hypothetically see the back of your head in?

A

closed

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17
Q

What is the critical density?

A

The density of the universe where, if it is larger than the critical density the universe will collapse and if the density is smaller than it the universe will expand forever

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18
Q

What is the density of the universe?

A

6 protons per metre cubed

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19
Q

What is the variation to the idea of Hubble’s expansion?

A

Hubble time is only true for a handful of special arrangements (such as in a totally empty universe). In reality, gravity should slow down the universe’s expansion

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20
Q

If the universe’s expansion rate is slowing down, will the universe be older or younger?

A

Younger

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21
Q

What would the age of the universe be for a closed universe?

A

less than 2/3 of the Hubble time

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22
Q

What would the age of the universe be for a flat universe?

A

2/3 of the Hubble Time

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23
Q

What would the age of the universe be for a hyperbolic/open universe?

A

more than 2/3 of the Hubble Time

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24
Q

What does Friedman’s equation describe?

A

The relationship between the rate of expansion, size of the universe and stuff within the universe

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25
Q

What does Hubble’s expansion imply about the Big Bang?

A

Since the universe is constantly expanding, there must have been a small beginning point to the universe

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26
Q

How are matter and energy related? What does this mean?

A

e=mc(squared)

This means that you can start with pure matter and get energy and vice versa

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27
Q

what can light create?

A

matter and antimatter

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28
Q

What happens when matter and antimatter interact?

A

They annihilate each other

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29
Q

If matter and antimatter annihilate each other, and they are both created when the earth begins, why is there matter last over?

A

when they annihilate each other, there is a tiny bit of matter left over. This matter accumulates

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30
Q

What do up quarks and down quarks form?

A

Protons and neutrons

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31
Q

What are the 3 element that are created in the Big Bang?

A

Deuterium, Helium, Lithium

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32
Q

Why did the reactions from the Big Bang slow down?

A

The temperature cooled off

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33
Q

Why is Lithium the heaviest element created?

A

The temperature was not warm enough to create anything else at this point

Nuclei with 8 protons are not stable

34
Q

What are Population I stars?

A

Stars that are abundant in metals

35
Q

What are Population II stars?

A

Global cluster stars that have low metal abundances

36
Q

What are Population III stars?

A

The first generation of stars with virtually no metals

Only a few have ever been observed

37
Q

What are metals to astronomers?

A

anything but hydrogen or helium

38
Q

What is the density of baryons in the universe?

A

0.04

39
Q

what does the density of baryons mean for the fate of the universe?

A

Because omega is 0.04 (less than 1) the universe will continue expanding forever

40
Q

Why is there more Helium and less Hydrogen than there was 3 minutes after the Big Bang?

A

Stars have consumed Hydrogen and created Helium

41
Q

What happens if R is negative in the Friedmann equation?

A

The universe will contract

42
Q

What happens if R is positive in the Friedman equation?

A

The universe will expand

43
Q

Who discovered CMB?

A

Penzias and Wilson

44
Q

How much of TV static is from CMB?

A

about 1%

45
Q

What did Gammov say about light from far away?

A

It will not be visible as it will have redshifted

Therefore we need radiotelescopes

46
Q

Why does ionised Hydrogen trap photons in it?

A

It is opaque

47
Q

Why can’t we see anything from approx 380,000yrs AB?

A

The universe was filled with ionised Hydrogen and so photons couldn’t escape

48
Q

What happened 380,000yrs AB to help us see what happened?

A

the universe cooled down enough for the protons and electrons to come together to form a neutral gas which was transparent

49
Q

How can we prove that CMB isn’t cosmic?

A

WE put things above the earth’s atmosphere

50
Q

What does the discovery of the Dipole Doppler Shift show about CMB?

A

Proves that it is not created in the Earth’s atmosphere

It is bigger then the Milky Way so it has to be cosmic

51
Q

What can we tell about the source of CMB?

A

Because it has a blackbody spectrum, we know it was hot and dense

52
Q

What is the clumsiness problem?

A

If the universe is clumpy, then shouldn’t CMB be too?

53
Q

What is the satellite that found ‘clumps’?

A

COBE

54
Q

What can we tell from the date from COBE and WMAP?

A

That the universe is flat

55
Q

What is the temperature of CMB and how is it deduced?

A

3K

Wein’s law

56
Q

What causes the clumps in the universe?

A

The variations in the density ofd the universe

57
Q

How big will the clumps be if the universe is expanding fast?

A

small

58
Q

How big will the clumps be if the universe is expanding slowly?

A

big

59
Q

What are the axes in the graph to examine these clumps?

A

x=size of the clumps

y=number of clumps

60
Q

What is the omega of Dark Matter in the universe?

A

0.25

61
Q

How much more DM is there than regular matter?

A

Since the omega of baryons is 0.04, there is more than 5x as much DM

62
Q

Who first discovered the idea of DM?

A

Zwicky

63
Q

How did Zwicky first discover DM?

A

Galaxy clusters were attracted to each other because of gravity, but they were moving too fast to just be explained by the gravitational pull of regular gravity

64
Q

How much of the mass did Zwicky see as ‘unseen’?

A

90%

65
Q

What is the mass to light ratio of a typical galaxy

A

20

This means that there is 20x more unseen matter than visible matter

66
Q

What did Vera Rubin discover

A

Stars at the ends of galaxies were moving at the same speed as those in the middle. This means that there must be extra unseen matter in the galaxy somewhere.

this is shown by a flat rotation curve graph

67
Q

What is the phenomenon of extra dark matter around an object called?

A

a dark halo

68
Q

How does gas relate to DM?

A

The gas is in a bubble around a galaxy. It is hot enough that it should have the necessary escape velocity to leave, but something (DM) is keeping it in

69
Q

How can we use Einstein’s equation about light bending to see the true mass of objects

A

Instead of using mass to find light bending, use light bending to find mass

70
Q

What are the 4 forces?

A

Strong Nuclear
Electromagnetic
Weak nuclear
Gravity

71
Q

What is the strongest force?

A

Strong nuclear

72
Q

What is the weakest force?

A

Gravity

73
Q

Which forces have infinite ranges?

A

Electromagnetic and gravity

74
Q

What is the Theory of Everything?

A

A theory that seeks to unite gravity with Grand Unified Theory

75
Q

What is Grand Unified Theory?

A

A theory that unites electroweak with strong nuclear force

76
Q

What is Electroweak theory?

A

unites electromagnetism with weak nuclear force

77
Q

What was the order of the Eras of the Big Bang?

A

Quantum
Grand Unified
Quark
Hadron/Lepton

78
Q

What was the Quantum Gravity?

A
  • All forces were united as one

- matter light and energy coexisted in a primordial soup

79
Q

What was the Grand Unified Era?

A

4 forces united in a single force

gravity was distinct

80
Q

What was the quark era?

A

Free quarks roamed the universe

Quarks merged with antiquarks to form photons and the photons formed a quark and an anti quark (energy to matter)

81
Q

What were the Hadron and Lepton eras?

A

Hadron
- Universe cooled enough for baryons to form
Lepton
- All antimatter had been wiped out and electrons formed were able to survive

Astronomy 101 (15 decks)

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