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24 Cards in this Set

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What is the cosmological principle?
the universe is homogeneous and isotropic on sufficiently large scales

-structures are present but they tend to repeat.
If the universe is constantly expanding according to Hubble's law, this suggests that at one point all galaxies were together. When was this? what was this called? where did this happen?
THE BIG BANG; EVERYWHERE; 13-14 BILLION YEARS AGO
The big bang occured at
time= distance/velocity= 1/Ho = 14 billion years ago!
When the first galaxies and clusters of galaxies were forming (i.e. gravitationally collapsing and forming stars, etc.),
they had to overcome the overall expansion of space.
So, while gravity is making things collapse on a small scale,
it is also slowing the expansion of the Universe
Within the Hubble Flow, there are self-gravitating systems like galaxies and clusters of galaxies that
are not expanding at the rate of Hubble's flow or not expanding at all.
Galaxies experience a cosmological redshift, why?
not due to their velocity through space but due to the expansion of space.
Whether or not the universe continues to expand forever or eventually collapses depends on its
density
What is the outcome if the universe has high density? low density?
High density= more mass--> more gravity to halt the expansion of the universe.

Less density= less gravity--> expansion will continue.
What is the critical density?
the exact amount of density that is required to halt the expansion of the universe.
The ratio of the actual density of the universe to the critical density is called the
cosmic density parameter
Sigma = cosmic density parameter
1; in a marginally bound
What would be the result of too much mass (larger than the critical density?
The Big crunch. all of the universe would be crunched to a point (reverse of big bang)
WHEN OMEGA >1
WHEN OMEGA =1
WHEN OMEGA <1

What kind of universe is it?
Bound

Flat (marginaly bound)

Open
So how dense is the universe to determine wheteher we live in an open, marginaly bound or closed universe?
between 0.21 - .031 are best estimates which suggests we live in an OPEN UNIVERSE!
BUT WE MAY NOT DIRECT OBSERVATIONS SUGGEST WE LIVE IN A
BOUND UNIVERSE
Using standard candles methods research suggested that teh universe was actually accelerating. How could this be?
A vaccum pressure force known as cosmological constant.
recall that the age of the universe was determined using the ACCELERATING UNIVERSE model to be 14 billion years old. But the critical density age (which takes into count the fact taht gravity has tried to halt expansion) suggests the age is
9 billion years old.
Because the big bang was such a large event releasing so much heat and radiation, we should be able to find some cooled-off remnants. on what form do we find them?
Primordial background radiation. workers in a telephone company recieved a background weak signal that created a blackbody curve with a temperature of 2.7K
Why is the radiation so weak?
When the big bang occured the radiation released was infact gamma rays. but with the expansion of the universe the radiation has red-shifted to the radio/microwave wavelength
History of the universe.

-t=0
-t=1 minute
-t=2 minute
-t=15 minute
t= few thousand years
t=0: the universe is all radiation. NO MATTER.

T=1: photons of light have enough energy to form themselves into matter

T=2: Primordial nucleosynthesis occurs -protons and neutrons fuse to form deuterium. As the universe continues to cool and expand, the heavier helium-4 nuclei are formed

t=15 minutes: the universe is 25% helium and 75% hydrogen (like most is now)

t=15,000: matter begins to dominate over radiation
What major event occurs at a few hundred thousand years?
atoms form and the universe becomes transparent to light

(decoupling or recombination)- realize before this it was too hot for electrons to stay on atoms.
why is this so important?
This is the point at which we observe the microwave background radiation. The decoupling of photons from matter form a “surface of last scattering” around the Earth. At this point photons are no longer absorbed by atoms where they were before as subatomic particles.
how did structures eventually develop?
universe started out as mostly dark matter and normal matter were evenly distributed.

Then the DARK MATTER CLUMPED FIRST. bringing together the normal matter to form present day stars and galaxies.