Cosmology Flashcards
regard galaxies as ___ test ___
cosmic/particles
galaxies follow a ___ and ___ distribution
homogeneous/isotropic
___ in the microwave background radiation is ___ in all directions
temperature/the same
some time ago all galaxies we see today must be at ___ point
the same
motion of galaxies is due to ___ forces acting on them by other objects superimposed with general ___ caused by expansion of space
gravitational/receding velocity
___ force much stronger than ___ force
EM/gravitational
___ and ___ forces exert no significant forces between atoms as they are ___ ranged
strong/weak/short
___ and ___ forces influence over very large scales as it is a ___ distance to decay and vanish
electromagnetic/gravitational/long
___ is the dominant force as the attraction of very massive objects is felt over vast distances
gravity
gravitational attraction makes a uniform distribution of mass ___
unstable
small fluctuations in ___ attract more than their surroundings
density
universe looks the same in every position
homogeneity
universe looks the same in every direction
isotropy
___ implies ___ but not necessarily the reverse
isotropy/homogeneity
universe with uniform distribution of matter rotating around some point looks ___ but it is not ___ as its rotation velocity differs in different directions
homogeneous/isotropic
Olber’s paradox: if the universe were infinite, every ___ will eventually intersect a star somewhere
line of sight
we assume the universe is:
finite in ___ (modern view)
infinite in ___
___
___
space is ___
time/
space/
static/
homogeneous/
euclidean
hubble flow is relevant only on ___ scales
large
___ velocity: velocities induced by ___ effects of structures which have detached from hubble flow
peculiar/gravitational
___ velocity dominates over hubble flow for ___
peculiar/galaxies
___ coordinate is a coordinate system that expands with space
comoving
energy density of universe is dominated by ____ matter and does not include contributions from ___ and ___
non-relativistic/photons/dark matter
test bodies move along ___ trajectory - not necessarily a ___ line
shortest/straight
matter tells space how to ___, space tell matter how to ___
curve/move
proper separation of two events is ___ and independent of observer
invariant
___ specifies rules that govern how distance is ___and ___ in a given space time
metric/defined/measured
positive curvature ___ universe
closed
negative curvature ___ universe
open
flat curvature ___ universe
flat
friedmann,___ and ___ equations are not all independent
acceleration/fluid
some particles have such ___ interactions that they would pass through without being ___
weak/reflected
relativistic particles are called ___ in cosmology, and they have large ___ motions
radiation/random
___ pressure: a particle moving towards the right will meet a counterpart particle with the same ___ moving towards the left
radiation/momentum
non-relativistic particles have ___ random motions
negligible
any of the friedmann, acceleration and fluid equations can be derived from ___
the other two
dark energy does not participate in ___ interactions so its existence is inferred through ___ effects and density remains near ___ as the universe expands
EM/gravitational/constant
as universe expands, newly created space has ___ energy as density can stay constant
vacuum
in a vacuum, pairs of particles and antiparticles are ___ and ___ after a short time
created/annihilate
critical density is an ___ estimate of the density in the universe and is very small
order of magnitude
density greater than critical density ___ universe
closed
density equal to critical density ___ universe
flat
density less than critical density ___ universe
open
density parameter is roughly the ___ of a given matter species to the universe’s expansion rate
fractional contribution
expansion halts at ahalt and universe starts to ___ eventually collapsing back to a ___
contract/singularity
k=0, density par0.=0 then universe would ___ forever but its rate ___ as time passes
expand/diminishes
k<0, density par0.<0 the universe ___ forever but at an asymptotically ___ speed
expands/constant
attractive gravity between matter tends to ___ expansion but can be reversed if there is enough matter
slow down
ahalt gets closer to 1 if density par0. ___, adding more matter more quickly ___ and ___ expansion
increases/slows down/reverses
open universe: expands forever and approaches an ___ or ___ universe in the distant future
empty/constant
closed universe: expansion ___ and ___ in future
halts/recollapses
flat universe: expands forever, expansion rate becomes ___ in the distant future
smaller
___ becomes dominant energy as we go to earlier times
radiation
in a ___ universe, density par. of matter species i is the fraction of the total density contributed by the species
flat
as long as we are not too close to the ___ time, the expansion history can be well approximated by the ___-component solution
equality/single
when we observe objects at red-shift we are seeing the universe ___ than is it today
younger
Hubble constant as a state parameter is the current Hubble ___
expansion rate
Hubble constant as a cosmological parameter directly determines ___ and ___ scales in cosmology
distance/time
luminosity of cepheids calibrated in our own galaxy allows us to calculate ___ to cepheids in other galaxies
distances
___ speed is found to correlate with total galaxy luminosity
rotation
path of light from distant galaxies can be bent by the ___ field of an intervening massive galaxy
gravitational
time flows at different rates in places of different ___
curvature
standard candles are astronomical objects with known ___ (regardless of their distance)
luminosity
provided the ___ is high enough, other particle species than photons can become ultra relativistic and become radiation
temperature
small fluctuations mean universe at last scattering is not exactly ___
homogeneous
photons play ___ role in present-day dynamics of the universe
negligible
there is a point beyond which photons dominate the ___ content of the universe
energy
if timescale for reactions is short compared with the age of the universe then ___ is reached
thermodynamic equilibrium
timescale for interactions is ___ to square of Fermi’s weak coupling constant
proportional
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
larger/younger/higher
longer half-lie implies ___ weak coupling tau and so smaller reactions and ___ freeze out
smaller/earlier
luminosity of galaxies is total luminosity of ___ they contain
stars
massive stars produce more ___ per unit mass so mean value M/L depends on fraction of stars that are more or less ___
light/massive
close universe: light rays from opposite sides of hot spot ___ each other
bend towards
flat universe: light rays from opposite sides of hot spot ___
do not bend at all
open universe: light rays from opposite sides of hot spot ___ each other
bend away from
closed universe: structures appear ___ and therefore ___ (CMB peak towards ___)
larger/closer/left
open universe: structures appear ___ and therefore ___ (CMB peak towards ___)
smaller/further/right
positive galaxy correlation indicates that galaxies ___
clump together
zero galaxy correlation function implies that galaxies are ___ distributed
randomly
___ matter density than environment means it pulls more matter
higher
in the ___ model there was a period of very rapid expansion before the radiation-dominated era
inflation
horizon size increases with time due to propagation of ___ and the ___ of space
photons/expansion
horizon size increases ___ during inflation
exponentially
