Lecture 8 Flashcards
what was redshift now vs big bang
0 now, infinity big bang
what was the scale factor for temp, a now vs big bang
now 1, big bang 0
what was temp of cmb photons now vs past
3k now, bigger in past
what happened before the big bang and how can we test the theories
several speculative theories, not enough data to say for sure
can use cmb to test some
examples of before big bang
big bang could be one of many, causing different universes with different properties
cyclic universe possibly
3 phases of early universe
force decoupling before 10^-10 s
particle production 10^-10s to 380k years
structure formation after 380k years
timeline of universe epochs, trend with temperature
planck - gravity separates
GUT - inflation, strong force separates
inflation - rapid expansion of cosmic size
electroweak - em/weak forces separate
particle - antimatter annihilation, particle formation
nucleosynthesis - creation of H and He nuclei
Recombination - dark matter dominates, nuclei bind to elections, CMB generated
dark ages - formation of first stars
reionization - universe ionises again
galaxy formation - formation of galaxies and clusters
temp decreases from 10^32k to 6k
what are the 4 fundamental forces
Gravity, electromagnetism, weak nuclear, strong nuclear
what are the 4 forces believed to be
aspects of one underlying force with one unified explanation
what did we think of electrical and magnetic forces previously
thought of them as separate but found them to be apart of the same phenomenon, electroweak theory explains the forces together
how do EM and weak forces behave at different energy levels
at normal energy they settle down to tow seperate behaviours but at higher energy a wider range is possible
what are particles that carry forces
lowest energy forms of more general type
what do we expect to have happened to all 4 forces at the early universe
high energy so expect all 4 forces merged, forces decoupled during first phase
what happened in the Planck epoch to do with fluctuations
density fields, like the early universe, have tiny fluctuations, zero-point energy according to quantum theory
small fluctuation in high density can be large
in early times, these were large enough that classically should form black holes
planck epoch black holes
black holes = GR
zero points energy = quantum mechanics
theories independent, need quantum gravity to understand this thus understand Planck epoch
what happened to gravity in Planck epoch
gravity decouples from the other 3 forces
GUT epoch meaning
grand unified theory - hypothetical theory combining strong and electroweak forces
what happened in GUT epoch
strong force split off from electroweak
this is only marginally understood better than Planck era
what happened in the inflation epoch
theorised period
short but ultra rapid acceleration of cosmic expansion
lasted 10^-36 seconds
scale factor 10^26 bigger
increased size of an atom to size of solar system
what happened in electroweak epoch
electroweak separated into electromagnetic and weak forces at the end
particles continuously created and annihilated
mix of fundamental particles
can reach these energies I particle accelerators - above 10^15k
Behaviour of W and Z bosons match theories
understood fairly well
what happened in the particle epoch
universe cooled, spontaneous creation of particles stopped. photons dominated energy forms
quarks form protons and neutrons
lots of annihilation
asymmetry meant matter left over: every billion anti protons, billion and one protons
unknown why asymmetric
first 5 min of nucleosynthesis
nucleosynthesis - production of nuclei
universe was hot
at high temp neutrons convert to protons and vice versa
low temp, proton production favoured as neutrons are more massive so need more energy
protons and neutrons fused to form deuterium
deuterium fused to form helium
explain light element abundances
fusions forming helium stopped at 5 minutes as density too low for proton neutron reactions
ratio was frozen - 7p per n
if all neutrons are in helium, will have. 1 helium nucleus per 12 hydrogens
so mass ratio is 75% hydrogen, 25% helium
how does light element abundances provide evidence for big bang
observed ratios matches nucleosynthesis predicted ratios very closely
energy vs matter in early universe
more energy in radiation than matter in early universe, radiation energy decreases faster as universe expands, after 50k years it drops lower than matter density
radiation has pressure which counteracts gravity stopping cosmic structure growing, from here seeds of early galaxies can grow
what happened after recombination
dark ages - 500m years of not much happening
what happened in the dark ages
tiny over dense regions in CMB maps slowly pull more matter towards them, eventually form stars, starts galaxy formation phase and the period of universe we can directly observe
what is cosmic dawn
big clouds of hydrogen become galaxies of stars
it is unclear how this actually works
21cm radio signature should detect and characterise but it is hard to detect
what is reionisation
before CMB. universe ionised, all photons bounced around knocked electrons off protons
lower energy after cmb meant they stayed bounded
after galaxies start to form they reionize the particles again, high energy radiation from early stars or quasars splits off electrons
