Chapter 12 Flashcards
How was the conclusion reached that the early universe was hot?
If the universe was cool, then everything would have ended up as Helium
What was predicted by Gamow?
light from long distances away will not be visible but instead will be redshifted
What does the fusion of two helium nuclei produce?
The unstable isotope Beryllium
This promptly decays back into 2 nuclei
What is the stability gap?
The issue of getting over the hump of creating Beryllium.
When Beryllium is formed, it decays. How can this give way to any other element?
How can helium be converted to carbon?
Through the Triple Alpha Process
How does the triple alpha process work?
Though Beryllium is unstable, there will be some of it present that can capture helium nuclei at high temperatures and densities. This will form Carbon
Where was Carbon formed?
Stars. The early universe never had sufficiently high densities or temperatures to make Carbon
What is responsible for all elements heavier than carbon?
Stars (up to Iron formed in the actual lifetime of the stars, the rest are made in type 1a supernovae)
How does CMB prove that the Big Bang happened?
CMB was a natural outcome of the Big Bang but it did not logically follow from the steady state theory
What happens to the state of the universe the further back in time you go?
The universe gets denser and hotter
What is the radiation era?
The first several thousand years of the Earth’s existence where radiation dominated over matter
What is radiation pressure?
The buffeting of photons
EG comets tails point away from the sun because they are buffeted by the Suns photons
When does a pressure force arise?
When the energy contained in a volume is able to exert a net force on a surface
What effect des pressure have on the rate of expansion of the universe?
It decelerates the rate of expansion
This is because it is stress (energy) which participates in gravity
How can you create matter?
Matter can be create from energy as denoted in e=mc^2
What is the state of thermal equilibrium?
The state where all photons have the same energy
At a sufficient temperature, what can happen when two photons collide?
They create a particle and its antiparticle
How hot approximately does the temperature need to be to make a particle and an antiparticle?
10^13 K
What happens when an antiparticle and a particle are created?
The particle and the antiparticle annihilate each other
If the particle and the antiparticle destroy each other, how are we in a matter dominated world now?
There is a tiny bit of leftover matter when the particle and the antiparticle react. This accumulated over time
What is the ultimate goal of particle physics?
To find a ‘theory of everything’
What is the Theory of Everything?
A theory that encompasses all particles and forces, showing them to be manifestations of an underlying simplicity
What is the weakest fundamental force?
Gravity
What is the Planck time?
The earliest time that our modern physics can explain
How far back does the Planck time go?
10^-43 seconds
What is the Planck Epoch?
The time in between the creation of the universe and the Planck time
What were the fundamental forces like in the Planck epoch?
They were all one unified force
Why is the CMB so faint?
It has been redshifted away
What is nucleosynthesis?
The creation of atomic nuclei through nuclear reactions
In what epoch did nucleosynthesis begin to occur?
The nucleosynthesis epoch
What is Deuterium?
An isotope of hydrogen that contains one proton and one neutron in its nucleus
What does the number of protons in an element represent?
The chemical element of something
What does the number of neutrons in a element represent?
The nuclear properties of the isotope
How is helium created from deuterium?
deuterium keeps gaining things (protons and neutrons) until it gets to be He4, the most common isotope o Helium
Why could deuterons not survive early on? What changed?
They would be blasted apart. Once the temperature of the universe dropped some deuterons could survive
What led Gamow to predict the existence of background radiation?
There must have been hot protons or else all of the protons would have combined with neutrons
They also realised that after nucleosynthesis finished, these photons would continue to permeate the universe, redshirting to ever lower temperatures
What controlled the eventual abundance of helium?
The balance between free neutrons that immediately decayed and those that combined with protons
Why was helium the most abundant nucleus?
Because the single neutrons decayed, whilst the single protons could survive
What is the relationship between the density of the universe and the amount of deuterium to be found?
The denser the universe, the less deuterium there will be
What does the relationship between the density of the universe and the amount of deuterium allow us to calculate?
The overall density of the universe
What is produced in nucleosynthesis reactions other than the element?
Light
What is the major limit to nucleosynthesis?
The amount of neutrons. Single neutrons decay and if there is to be construction off anything more than hydrogen, then neutrons are required
What is the heaviest element that can form in nucleosynthesis?
Lithium 7
Universe got too cold to make anything else
What is the omega (density) of the baryons in the universe?
0.04
What can nucleosynthesis not tell us about the density of the universe?
The density of non-baryonic material that is in it
What does the abundance of H4 determine?
The number of neutrino species that exist
Why must the value of H4 in the universe be near 0.23?
Since a lower value would mean only 2 neutrino species can exist when we know of 3§
What is recombination?
The phenomena of the universe being cold enough for most free electrons to be captured by the protons to form hydrogen
What kind of end for the universe will we see in a spherical universe?
the big crunch
What kind of send to the universe will we see in a flat universe?
a whimper
