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Planets and Cosmology > Cosmology > Flashcards

Cosmology Flashcards

1
Q

regard galaxies as ___ test ___

A

cosmic/particles

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2
Q

galaxies follow a ___ and ___ distribution

A

homogeneous/isotropic

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3
Q

___ in the microwave background radiation is ___ in all directions

A

temperature/the same

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4
Q

some time ago all galaxies we see today must be at ___ point

A

the same

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5
Q

motion of galaxies is due to ___ forces acting on them by other objects superimposed with general ___ caused by expansion of space

A

gravitational/receding velocity

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6
Q

___ force much stronger than ___ force

A

EM/gravitational

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7
Q

___ and ___ forces exert no significant forces between atoms as they are ___ ranged

A

strong/weak/short

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8
Q

___ and ___ forces influence over very large scales as it is a ___ distance to decay and vanish

A

electromagnetic/gravitational/long

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9
Q

___ is the dominant force as the attraction of very massive objects is felt over vast distances

A

gravity

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10
Q

gravitational attraction makes a uniform distribution of mass ___

A

unstable

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11
Q

small fluctuations in ___ attract more than their surroundings

A

density

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12
Q

universe looks the same in every position

A

homogeneity

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13
Q

universe looks the same in every direction

A

isotropy

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14
Q

___ implies ___ but not necessarily the reverse

A

isotropy/homogeneity

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15
Q

universe with uniform distribution of matter rotating around some point looks ___ but it is not ___ as its rotation velocity differs in different directions

A

homogeneous/isotropic

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16
Q

Olber’s paradox: if the universe were infinite, every ___ will eventually intersect a star somewhere

A

line of sight

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17
Q

we assume the universe is:
finite in ___ (modern view)
infinite in ___
___
___
space is ___

A

time/
space/
static/
homogeneous/
euclidean

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18
Q

hubble flow is relevant only on ___ scales

A

large

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19
Q

___ velocity: velocities induced by ___ effects of structures which have detached from hubble flow

A

peculiar/gravitational

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20
Q

___ velocity dominates over hubble flow for ___

A

peculiar/galaxies

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21
Q

___ coordinate is a coordinate system that expands with space

A

comoving

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22
Q

energy density of universe is dominated by ____ matter and does not include contributions from ___ and ___

A

non-relativistic/photons/dark matter

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23
Q

test bodies move along ___ trajectory - not necessarily a ___ line

A

shortest/straight

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24
Q

matter tells space how to ___, space tell matter how to ___

A

curve/move

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25
Q

proper separation of two events is ___ and independent of observer

A

invariant

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26
Q

___ specifies rules that govern how distance is ___and ___ in a given space time

A

metric/defined/measured

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27
Q

positive curvature ___ universe

A

closed

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28
Q

negative curvature ___ universe

A

open

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29
Q

flat curvature ___ universe

A

flat

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30
Q

friedmann,___ and ___ equations are not all independent

A

acceleration/fluid

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31
Q

some particles have such ___ interactions that they would pass through without being ___

A

weak/reflected

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32
Q

relativistic particles are called ___ in cosmology, and they have large ___ motions

A

radiation/random

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33
Q

___ pressure: a particle moving towards the right will meet a counterpart particle with the same ___ moving towards the left

A

radiation/momentum

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34
Q

non-relativistic particles have ___ random motions

A

negligible

35
Q

any of the friedmann, acceleration and fluid equations can be derived from ___

A

the other two

36
Q

dark energy does not participate in ___ interactions so its existence is inferred through ___ effects and density remains near ___ as the universe expands

A

EM/gravitational/constant

37
Q

as universe expands, newly created space has ___ energy as density can stay constant

A

vacuum

38
Q

in a vacuum, pairs of particles and antiparticles are ___ and ___ after a short time

A

created/annihilate

39
Q

critical density is an ___ estimate of the density in the universe and is very small

A

order of magnitude

40
Q

density greater than critical density ___ universe

A

closed

41
Q

density equal to critical density ___ universe

A

flat

42
Q

density less than critical density ___ universe

A

open

43
Q

density parameter is roughly the ___ of a given matter species to the universe’s expansion rate

A

fractional contribution

44
Q

expansion halts at ahalt and universe starts to ___ eventually collapsing back to a ___

A

contract/singularity

45
Q

k=0, density par0.=0 then universe would ___ forever but its rate ___ as time passes

A

expand/diminishes

46
Q

k<0, density par0.<0 the universe ___ forever but at an asymptotically ___ speed

A

expands/constant

47
Q

attractive gravity between matter tends to ___ expansion but can be reversed if there is enough matter

A

slow down

48
Q

ahalt gets closer to 1 if density par0. ___, adding more matter more quickly ___ and ___ expansion

A

increases/slows down/reverses

49
Q

open universe: expands forever and approaches an ___ or ___ universe in the distant future

A

empty/constant

50
Q

closed universe: expansion ___ and ___ in future

A

halts/recollapses

51
Q

flat universe: expands forever, expansion rate becomes ___ in the distant future

A

smaller

52
Q

___ becomes dominant energy as we go to earlier times

A

radiation

53
Q

in a ___ universe, density par. of matter species i is the fraction of the total density contributed by the species

A

flat

54
Q

as long as we are not too close to the ___ time, the expansion history can be well approximated by the ___-component solution

A

equality/single

55
Q

when we observe objects at red-shift we are seeing the universe ___ than is it today

A

younger

56
Q

Hubble constant as a state parameter is the current Hubble ___

A

expansion rate

57
Q

Hubble constant as a cosmological parameter directly determines ___ and ___ scales in cosmology

A

distance/time

58
Q

luminosity of cepheids calibrated in our own galaxy allows us to calculate ___ to cepheids in other galaxies

A

distances

59
Q

___ speed is found to correlate with total galaxy luminosity

A

rotation

60
Q

path of light from distant galaxies can be bent by the ___ field of an intervening massive galaxy

A

gravitational

61
Q

time flows at different rates in places of different ___

A

curvature

62
Q

standard candles are astronomical objects with known ___ (regardless of their distance)

A

luminosity

63
Q

provided the ___ is high enough, other particle species than photons can become ultra relativistic and become radiation

A

temperature

64
Q

small fluctuations mean universe at last scattering is not exactly ___

A

homogeneous

65
Q

photons play ___ role in present-day dynamics of the universe

A

negligible

66
Q

there is a point beyond which photons dominate the ___ content of the universe

A

energy

67
Q

if timescale for reactions is short compared with the age of the universe then ___ is reached

A

thermodynamic equilibrium

68
Q

timescale for interactions is ___ to square of Fermi’s weak coupling constant

A

proportional

69
Q

if neutrino species is larger than 3 then at a given temperature, density rel is___ hence Hubble parameter is larger. At given temperature Universe is ___ thus freeze out occurs at ___ temperature

A

larger/younger/higher

70
Q

longer half-lie implies ___ weak coupling tau and so smaller reactions and ___ freeze out

A

smaller/earlier

71
Q

luminosity of galaxies is total luminosity of ___ they contain

A

stars

72
Q

massive stars produce more ___ per unit mass so mean value M/L depends on fraction of stars that are more or less ___

A

light/massive

73
Q

close universe: light rays from opposite sides of hot spot ___ each other

A

bend towards

74
Q

flat universe: light rays from opposite sides of hot spot ___

A

do not bend at all

75
Q

open universe: light rays from opposite sides of hot spot ___ each other

A

bend away from

76
Q

closed universe: structures appear ___ and therefore ___ (CMB peak towards ___)

A

larger/closer/left

77
Q

open universe: structures appear ___ and therefore ___ (CMB peak towards ___)

A

smaller/further/right

78
Q

positive galaxy correlation indicates that galaxies ___

A

clump together

79
Q

zero galaxy correlation function implies that galaxies are ___ distributed

A

randomly

80
Q

___ matter density than environment means it pulls more matter

A

higher

81
Q

in the ___ model there was a period of very rapid expansion before the radiation-dominated era

A

inflation

82
Q

horizon size increases with time due to propagation of ___ and the ___ of space

A

photons/expansion

83
Q

horizon size increases ___ during inflation

A

exponentially

Planets and Cosmology (12 decks)

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