Final Stretch 1 (50% of Final) Flashcards
What does the size of the universe mean about the distance between the objects in the universe?
If the universe is getting bigger, then the space between the objects is getting bigger too
What happens to the size of the objects as the universe expands?
The gravitational energy keeps them together so they do not change size. Gravity is much stronger than the expansion for
What happens to the wavelength of light waves as they travel through the universe?
They stretch and their wavelength increases.
What is cosmological redshift?
The redshifting of light waves as they travel through space
What is the relationship between redshift and the distance from an object?
The further away you are, the more redshifted it becomes
Is the of expansion of the universe constant over time?
NO
What is Rdot?
The rate of change of the expansion of the universe
What is H?
Hubble’s constant (the rate of expansion of the universe)_
What is the current value of H?
Around 68km/sec
How do you calculate th Hubble Constant?
1/Hubble time
Is the Hubble Constant actually constant?
NO. It has changed over time
What does it mean for the age of the universe when Hubble’s constant is larger?
Th universe is younger; the speed of the universe expanding is faster, so there is less time for it to have grown
What is the issue with the Hubble constant being too large?
Wee know there to be objects in the universe that are 13bn years old. If the constant is too large, then the age of the universe will be younger than the age of these objects.
What is Hubble Time?
The age of the universe as it applies to the Hubble constant
How does the Hubble time actually relate to the ag of the universe?
The Hubble Time is only true for a handful of conditions in thee universe. It does not likely indicate the true age of the universe
What does the cosmological principle mean for the expansion of the universe?
The Hubble constant will be the same everywhere
What is k?
The curvature constant
What are the 3 possible values of k?
0, 1, -1
What happens when k=0?
The universe is flat
What happens when k=1?
the universe is closed/spherical
What happens when k=-1
the universe is open
What is R(t)?
Essentially, it is the radius of the universe
What happens if outward expansion is greater than the force of gravity?
The universe will continue to expand forever
In which universe could you hypothetically see the back of your head in?
closed universe
What is critical density?
Th density of the universe where if the density is large than it, the universe will eventually collapse and if it is smaller it will expand forever
What is the current density of the universe?
6 protons per metre cubed
What would the age of the universe be in a close universe with reference to the Hubble time?
less than 2/3 of the Hubble time
What would the age of the universe be for a flat universe with reference to the Hubble time?
2/3 of the Hubble time
What would the age of the universe be for an open universe with reference to the Hubble time?
greater than 2/3 of the Hubble time
What does the Friedman Equation describe?
The relationship between the rate of expansion, size of the universe and stuff within the universe
What does Hubble’s theory of expansion imply about the Big Bang?
Since the universe is constantly expanding, there must have been a singular point at which it began
How are matter and energy related? What does this mean?
e=mc squared
This means that you can start with pure energy and get matter (and vice verse)
What can light create?
matter and antimatter
If matter and antimatter both annihilate each other, and both of these were created when the earth begins, then why do we have any matter at all?
When matter and antimatter annihilate each other, there is a tiny bit of matter left over. This accumulates over time
What do up quarks and down quarks form?
Protons and neutrons
What are the 3 elements that are created from the Big Bang?
Deuterium, Lithium, Helium
Why did the reactions from the Big Bang slow down?
The temperature cooled off
Why was Lithium the heaviest element that was created in the Big Bang?
The temperature was not high enough to create anything past this point
Nuclei with more than 8 protons were not stable
What are population I stars and where are they primarily found?
These are stars that are primarily found in the Milky Way and are abundant in metals
What are population II stars?
Stars with lower metal abundances
What are population III stars?
Stars with virtually no metals. These are the first generation of stars and only a few have ever been observed
What are ‘metals’ to astronomers?
Anything but H or He
What do baryons make up?
protons and neutrons and therefore matter in the univrsee
What is the baryon density in the universe?
0.04
Why is there less hydrogen and more helium in the current atmosphere than in the initial conditions of the universe?
Stars have consumed H and created He
What is nucleosynthesis?
The creation of matter in the Big Bang through heat and the condensation of the particles
What does it mean about the shape of the universe when omega = 1
The universe is flat
What does it mean about the shape of the universe when omega = -1
The universe is open
What does it mean about the shape of the universe when omega = 1
The universe is closed
What does it mean when R is positive?
The universe is expanding
What does it mean when R is negative?
The universe is contracting
What happened to all of the light from nucleosynthesis?
it is coming from far away and as such will have redshifted to a point where we will need radiotelescopes to see it
What did Wilson and Penzias discover?
Their horn antenna had a constant background noise that would not go away. This was CMB
How much of TV static is made up of CMB?
About 1%
Why can we not see past 380,000 years AB?
It was so hot before this point that the hydrogen in the universe ionised. Ionised Hydrogen is very opaque
How can we prove that CMB is not in the Earth’s atmosphere but rather is cosmic?
We can go outside of the Earth’s atmosphere and still detect it. Also, w can observe the Dipole Doppler Shift
What is the Dipole Doppler Shift?
This is the shift in the CMB due to the motion of the earth. There can be a redshift on one side and a blueshift on the other
How can we tell that the source of CMB photons is further away than the Milky Way?
We can measure the Dipole Doppler shift with the speed of the Milky Way
What is the clumsiness problem and how was it discovered?
If the universe is clumpy, the shouldn’t there be clumpiness in the CMB?
This was discovered by COBE
What do the WMAP and Planck satellites say about omega?
They say that omega = 1, which means that the universe is flat
What is the temperature of CMB? How is it deduced?
3K
It is deduced using Wein’s law
What causes the clumps in the CMB?
Variations in the density of the universe
What does it mean for the six of the clumps if the universe is expanding quickly?
The clumps will be smaller.
vice versa if the universe is expanding slowly.
What is the relation between the size of the clumps and the amount of matter in the universe?
The more matter there is in the universe, the more gravity will attract matter together
Vice versa if there is less matter
What can a graph of the size of the clumps against the number of clumps tell us?
The universe is flat
The baryon density of the universe is 0.04
What is the density of Dark Matter?
0.25 (5 times larger than the baryon density)
What did Zwicky discover about the movement of galaxies that links to Dark Matter?
Galaxies were moving as though they were attracted by something else. They were moving too fast for this to be gravity alone so there must be more matter somewhere
What percentage of the mass did Zwicky deem to be ‘unseen’?
90%
What is the Mass-to-Light ratio?
The ratio of light that is unseen to the amount that is seen
What is the typical mass-to-light ratio of a galaxy and how does this apply to Dark Matter?
The typical ratio is 20, implying that there is a LOT of Dark Matter
What does the orbital velocity of stars at the edge of galaxies imply about Dark Matter?
the orbital speed is not slower than the stars toward the centre of the galaxy
This can only be explained by there being extra matter around the galaxy
This was discovered by Vera Rubin
What is the ‘dark halo’?
The halo caused by gas that should have enough energy to supersede the escape velocity of the atmosphere, however the greater mass of the DM is keeping it contained in the object’s atmosphere
How can we use Einstein to tell what the actual size of galaxies?
Instead of using the mass of an object to discover the amount of light bending, w use the amount of light bending to calculate mass
When we do this, we find that many galaxies are approx. 100x bigger than previously thought
What are the 4 forces?
strong nuclear force
weak nuclear force
electromagnetic force
gravity
What is the strongest force?
strong nuclear force
What is the weakest force
gravity
What forces have infinite ranges?
gravity and electromagnetic force
What is the Theory of Everything?
A theory that seeks to unite gravity with the grand unified theory
What is Grand Unified Theory?
A theory that seeks to unite electroweak force with strong nuclear force
What is Electroweak Theory?
A theory that seeks to combine electromagnetic and weak nuclear force
What is the order of the theories in the big bang?
Quantum
Grand Unified
Quark
Hadron/Lepton
What was the quantum gravity era?
When all of the 4 forces were united
Matter, light, and energy all coexisted in a primordial soup
What was the Grand Unified era?
When all of the forces were united except for gravity, which was separated
What was the quark era?
free quarks roamed the universe
quarks began to form photons and the movement from energy to matter began
What were the Hadron and Lepton Eras?
Hadron
- Universe cooled enough for baryons to form
Lepton
- All antimatter was wiped out and electrons were able to survive
