Big bang and early universe Flashcards
Describe big bang
•occurred everywhere-all space
•is a process/era, not a point
•may have followed in from an earlier phase
What does universe expanding mean for past of universe?
•it was all much closer together-big bang
•or it has gradually been created as it expands-steady state
What were earliest attempts to test bb v ss?
•used numbers of radio sources per volume as function of redshift
•if universe not evolving should not change
•favoured bb
Why is cosmic microwave background evidence for bb?
•uniform across sky
•if interpreted as black body then temperature about 3 K
•as predicted by bb cosmology
What happens when you heat up gas enough?
Plasma
•free electrons and protons
•scatters photons so opaque
What happened when universe cooled?
•electrons bound to protons(recombination)
•universe became transparent and photons escaped-travelling ever since
When was universe hot enough for plasma?
380,000 years after bb
How does CMV preserve density structure?
Tiny variations in temperature
How much do hot spots caused by gravitational redshift vary?
1 part in 10^5
What are structures visible in density pattern of early universe?
Progenitors of galaxies
What measured CMB spectrum?
COBE space telescope
•perfect black body spectrum
What must any theory of the universe confront?
CMB measurements such as temp fluctuations, energy, shape measures
What completely killed steady state theory?
CMB measurements
What are the four known forces?
Gravity, electromagnetism, weak and strong nuclear
What are known forces believed to be?
Aspects of one underlying force
What is proof for general relativity?
Black holes
What is proof for quantum mechanics?
Zero point energy
Are GR and QM compatible?
No but both compatible with classical physics
What theory do we need to understand QM and GR?
Quantum gravity
What is zero point energy?
Quantum theory implies density fields have tiny fluctuations
In early universe what do fluctuations mean?
•early universe incredibly dense
•small fluctuation in high density field can be very large
•so in early universe fluctuations large enough that they should be black holes
What is Grand Unified Theory(GUT)?
Theory combining strong and electroweak forces
What happened in GUT era?
Gravity and GUT force only forces acting
What happened at end of GUT era?
GUT Force split into strong and electroweak force
What was the inflation era?
A short but ultra-rapid acceleration of cosmic expansion
How long did inflation era last?
10^-36 seconds and made scale factor 10^26 times bigger (size of atom to solar system)
What was inflation era driven by?
One or more scalar fields going through a transition and releasing energy
What are motivations for inflation?
•cosmic structure
•horizon problem
•flatness
What’s the link between inflation and structure?
Could have blown up atom sized fluctuations in density to solar system sized ones- progenitors of structure today
What is the universes horizon?
14 billion light years away but horizon changes with time
What did inflation expand?
A tiny region that was close together in thermal equilibrium
Can the universe as a whole have an overall curvature?
Depends on matter of density compared to a critical value
What is flat geometry?
A special case where density perfectly matches expansion
What shape is universe if p<pcritical?
Hyperbolic
What shape is universe if p>pcritical?
Spherical
What predicts flatness of universe?
Inflation
As space enlarges quickly it gets closer and closer to flat. So any pre inflation curvature would be flattened out and only detectable on scales larger than horizon
What happened at end of electroweak era?
Electroweak force split into electromagnetic and weak forces
What happened during electroweak era?
Particles continuously created and annihilated (soup of fundamental particles)
How can we reach energy of electroweak era?
In particle accelerators above 10^15K. W and Z boson behaviour matches theories
When did photons become dominant energy?
When universe cooled and spontaneous creation of particles stopped. (Particle era)
What happened to quarks in particle era?
Coalesced into protons and neutrons
What happened to matter and antimatter in particle era?
Annihilated
What is baryon asymmetry?
In particle era, for every billion anti-protons there was a billion and one protons
When was universe hot enough to produce nuclei(nucleosynthesis)?
<5 minutes
What happens to neutrons at high temps?
Convert to protons and vice versa
Why is proton production favoured at lower temps?
Neutrons more massive so need more energy to produce
What did protons and neutrons fuse to form in nucleosynthesis era?
Deuterium and then deuterium fused to form helium
What era was after nucleosynthesis?
Recombination (formation of CMB)
What happened after recombination?
Dark ages( 500M years of not much)
What happened during dark ages?
Tiny over dense regions in CMB maps slowly pull more matter towards them by gravity, growing. Then grow enough so smallest ones can start to form stars
When does galaxy formation begin?
In first billion years after bb
What is the current era?
Dark energy era
What is dark energy era?
When matter decreases below density of dark energy
