12.3 Flashcards
What state did the universe start in?
very hot and dense
which then cooled and expanded
What was the big bang?
The creation of an expanding region of space and time
everything that exists is inside the big bang
How can we tell that the universe is expanding?
Spectra from distant galaxies is red shifted, meaning that they are receding and the universe is expanding
Which galaxies are receding fastest?
The further away a galaxy is, the faster it is receding
What is the equation for a galaxy’s speed of recession?
v = Ho x r
v=speed of recession
Ho=hubble constant
r=distance of galaxy
What is Ho?
The hubble constant
What does a larger hubble constant mean?
Faster expansion and so a younger universe
How old can the universe be?
It must be younger than 1/Ho (starting at the hot, dense state)
How/why is light from distant galaxies red shifted?
The light is travelling through expanding space time, stretching the wavelength
what is z?
red shift
Δλ/λ
If z is the red shift, by what factor has the universe expanded?
1+z
1 is the original size, z is the expansion on top of this
When can red shift be interpreted as a relative velocity?
when z is much smaller than 1
If a spectra received is red shifted 37%, how much smaller was the universe when the light was emitted?
Smaller by a factor of 1.37
What are stars made from?
Mostly hydrogen and 10% helium
How could helium have been created in stars?
Nuclear fusion of hydrogen when the universe was in a hot, dense state
What is cosmic background microwave radiation?
Radiation which is left over from the fusion of hydrogen to helium when the universe was in its hot, dense state. It can be detected in all directions.
What has the biggest red shift detected in the universe?
Cosmic background radiation
Why did the universe become ‘transparent’ to photons?
When atoms formed as electrons were held in orbit by nuclei of protons and neutrons. Photons no longer interact as easily with atoms so can travel through space
How far is it possible to look back?
To the point at which the universe became transparent to radiation
What was the initial state of the universe?
Very hot and dense
A plasma of elementary particles in which energy is exchanged with photons of EM radiation
When did the universe become transparent to photons?
300,000 years after the big bang
At what temperature did the universe become transparent to photons?
3000K
What temperature is the current universe?
2.7K
Why is the universe cooling?
As space time expands, the wavelength of photons increases. Wavelength is inversely proportional to frequency so frequency decreases. Frequency is proportional to photon energy so photon energy decreases, decreasing the temperature.
How long ago is the big bang thought to have happened?
about 14 billion years ago
How can you tell that the early universe was very uniform?
There are currently only small temperature variation across the universe. Any variation would be exaggerated by expansion, so the early universe must have had a very uniform temperature
What are the problems with the current model of the universe?
dark matter, too little variation in the early universe
What is dark matter?
The way stars move in galaxies shows that galaxies should be surrounded by large amounts of unseen matter which would be about 10x the amount of seen matter
Why is too little variation in the early universe a problem for the current model of the universe?
Galaxies and stars form, where there are non-uniform areas, if the early universe was too uniform then it is not known how stars and galaxies could have developed
What is the equation which links red shift,z, and the radius of the universe now compared to the universe when the shifted radiation was emitted?
radius of universe now/radius of universe then = z + 1
