Class Notes Flashcards
How do you calculate the Hubble time?
1/hubble constant
what happens to the size of the objects when the universe expands and why?
The objects do not change size
The force of gravity holding them together is too strong
What is Cosmological Redshift?
As things are further away, they become more redshifted
This is caused by the expansion of the universe
Is the rate of cosmological expansion constant?
No, it changes over time
what is R(t)
The radius of the universe essentially
What is Rdot?
the rate of change of the radius of the universe (R)
What is Hubble’s Constant as of right now?
67.74km per sec
Is Hubble’s Constant actually constant?
NO
What is the issue with Hubble’s constant being too large and making the age of the universe younger?
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
What happens if outward expansion is greater than inward gravity?
The universe will continue to expand forever
What is k?
The curvature constant
What are the possible values of k?
1
0
-1
What is the shape of the universe when k=1
the universe is closed/spherical
What is the shape of the universe when k=0
the universe is flat
What is the shape of the universe when k=-1
the universe is hyperbolic
In which universe could you hypothetically see the back of your head in?
closed
What is the critical density?
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
What is the density of the universe?
6 protons per metre cubed
What is the variation to the idea of Hubble’s expansion?
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
If the universe’s expansion rate is slowing down, will the universe be older or younger?
Younger
What would the age of the universe be for a closed universe?
less than 2/3 of the Hubble time
What would the age of the universe be for a flat universe?
2/3 of the Hubble Time
What would the age of the universe be for a hyperbolic/open universe?
more than 2/3 of the Hubble Time
What does Friedman’s equation describe?
The relationship between the rate of expansion, size of the universe and stuff within the universe
What does Hubble’s expansion imply about the Big Bang?
Since the universe is constantly expanding, there must have been a small beginning point to the universe
How are matter and energy related? What does this mean?
e=mc(squared)
This means that you can start with pure matter and get energy and vice versa
what can light create?
matter and antimatter
What happens when matter and antimatter interact?
They annihilate each other
If matter and antimatter annihilate each other, and they are both created when the earth begins, why is there matter last over?
when they annihilate each other, there is a tiny bit of matter left over. This matter accumulates
What do up quarks and down quarks form?
Protons and neutrons
What are the 3 element that are created in the Big Bang?
Deuterium, Helium, Lithium
Why did the reactions from the Big Bang slow down?
The temperature cooled off
Why is Lithium the heaviest element created?
The temperature was not warm enough to create anything else at this point
Nuclei with 8 protons are not stable
What are Population I stars?
Stars that are abundant in metals
What are Population II stars?
Global cluster stars that have low metal abundances
What are Population III stars?
The first generation of stars with virtually no metals
Only a few have ever been observed
What are metals to astronomers?
anything but hydrogen or helium
What is the density of baryons in the universe?
0.04
what does the density of baryons mean for the fate of the universe?
Because omega is 0.04 (less than 1) the universe will continue expanding forever
Why is there more Helium and less Hydrogen than there was 3 minutes after the Big Bang?
Stars have consumed Hydrogen and created Helium
What happens if R is negative in the Friedmann equation?
The universe will contract
What happens if R is positive in the Friedman equation?
The universe will expand
Who discovered CMB?
Penzias and Wilson
How much of TV static is from CMB?
about 1%
What did Gammov say about light from far away?
It will not be visible as it will have redshifted
Therefore we need radiotelescopes
Why does ionised Hydrogen trap photons in it?
It is opaque
Why can’t we see anything from approx 380,000yrs AB?
The universe was filled with ionised Hydrogen and so photons couldn’t escape
What happened 380,000yrs AB to help us see what happened?
the universe cooled down enough for the protons and electrons to come together to form a neutral gas which was transparent
How can we prove that CMB isn’t cosmic?
WE put things above the earth’s atmosphere
What does the discovery of the Dipole Doppler Shift show about CMB?
Proves that it is not created in the Earth’s atmosphere
It is bigger then the Milky Way so it has to be cosmic
What can we tell about the source of CMB?
Because it has a blackbody spectrum, we know it was hot and dense
What is the clumsiness problem?
If the universe is clumpy, then shouldn’t CMB be too?
What is the satellite that found ‘clumps’?
COBE
What can we tell from the date from COBE and WMAP?
That the universe is flat
What is the temperature of CMB and how is it deduced?
3K
Wein’s law
What causes the clumps in the universe?
The variations in the density ofd the universe
How big will the clumps be if the universe is expanding fast?
small
How big will the clumps be if the universe is expanding slowly?
big
What are the axes in the graph to examine these clumps?
x=size of the clumps
y=number of clumps
What is the omega of Dark Matter in the universe?
0.25
How much more DM is there than regular matter?
Since the omega of baryons is 0.04, there is more than 5x as much DM
Who first discovered the idea of DM?
Zwicky
How did Zwicky first discover DM?
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
How much of the mass did Zwicky see as ‘unseen’?
90%
What is the mass to light ratio of a typical galaxy
20
This means that there is 20x more unseen matter than visible matter
What did Vera Rubin discover
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
What is the phenomenon of extra dark matter around an object called?
a dark halo
How does gas relate to DM?
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
How can we use Einstein’s equation about light bending to see the true mass of objects
Instead of using mass to find light bending, use light bending to find mass
What are the 4 forces?
Strong Nuclear
Electromagnetic
Weak nuclear
Gravity
What is the strongest force?
Strong nuclear
What is the weakest force?
Gravity
Which forces have infinite ranges?
Electromagnetic and gravity
What is the Theory of Everything?
A theory that seeks to unite gravity with Grand Unified Theory
What is Grand Unified Theory?
A theory that unites electroweak with strong nuclear force
What is Electroweak theory?
unites electromagnetism with weak nuclear force
What was the order of the Eras of the Big Bang?
Quantum
Grand Unified
Quark
Hadron/Lepton
What was the Quantum Gravity?
- All forces were united as one
- matter light and energy coexisted in a primordial soup
What was the Grand Unified Era?
4 forces united in a single force
gravity was distinct
What was the quark era?
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)
What were the Hadron and Lepton eras?
Hadron
- Universe cooled enough for baryons to form
Lepton
- All antimatter had been wiped out and electrons formed were able to survive
