ASTR368 Cosmology Timeline Loren Anderson – Shanghai – May 14, 2013

If universe were 1) infinite 2) unchanging 3) everywhere the same Then, stars would cover the night sky Olbers’ Paradox

The early universe must have been extremely hot and dense As it cooled and expanded, particles formed Review: Density, temp of Early Universe

Before s ???? No one knows Big Bang Timeline (Planck Era)

Lasts from Planck time (~ sec) to end of GUT force (~ sec) Forces united (except gravity) into one force – possibly elementary particles Big Bang Timeline (GUT Era)

Four known forces in universe: Strong Force Electromagnetism Weak Force Gravity Who knows? (String Theory) Maybe (GUT) Yes! (Electroweak) Forces at High Temperature

Ends about s Length unknown Big Bang Timeline (Inflation)

Lasts from ~ sec to ~ sec Elementary particles Big Bang Timeline (Electroweak Era)

s to s Amounts of matter and antimatter nearly equal (Roughly 1 extra proton for every 10 9 proton- antiproton pairs) Big Bang Timeline (Particle Era)

0.001 s to 3 min Nucleosysnthesis: The creation of atomic neclei (matter) Nuclei begin to fuse Universe is a plasma of H, He neclei Big Bang Timeline (Era of Nucleosysthesis)

3 min to 300,000 years Nucleosynthesis from 3m to 20m after Big Bang Universe has become too cool to blast helium apart Big Bang Timeline (Era of Nuclei)

380,000 to 1 billion years Atoms form at age ~ 380,000 years (captured electrons are what decouple matter+light) CMB Big Bang Timeline (Era of Atoms)

Galaxies form at age ~ 1 billion years Big Bang Timeline (Era of Galaxies)

Hubble’s Law: velocity = H 0 x distance Hubble’s Law The value of H 0 has been studied for many years

Hubble’s Law We can turn this around and use Hubble’s Law to estimate distances. We won’t need to find cepheids or supernovae, we just need to know how fast something is going away….

The Fate of the Universe If the Universe has enough mass, gravity will eventually re-collapse it We will have successive Big Bangs If the Universe has exactly the correct amount of mass (called the “critical density”), it will eventually stop its expansion and never re-collapse If the Universe does not have enough mass, it will expand forever

Universe Expansion Critical density of matter Not enough dark matter Lots of dark matter ????

Universe Expansion Eventual stop to expansion Expansion forever Recollapse This is our Universe! Expansion forever, but increasingly fast

WHAT WOULD CAUSE AN ACCELERATION OF THE EXPANSION???

So What is Causing the Expansion? Dark Energy! Dark energy makes up about 75% of the Universe It is the repulsive force, in contrast the gravity which is always attractive, that is driving the expansion of the Universe It is our best hypothesis, although this is an area of very active research.

Dark Energy Dark energy is “the cost of having space-time”. As far as we know it is fundamental to the fabric of the Universe. 8/16/11

Loren Anderson – Shanghai – May 14, 2013

SN 1a and Expansion If all SN type 1a are the same luminosity, are the dim supernovae nearby or far away? Therefore, are the dim supernovae early in the history of the universe, or late in the history of the universe? If we find that far supernovae are dimmer than we expected based on their distance, and near ones are as bright as we expected, does this mean that far supernovae are further or closer than we thought? If far supernovae are further than we thought, what does this tell us about the expansion of the universe? Far Away Early Further The universe must have expanded slower in the past and is now accelerating in its expansion.

Accelerating universe is best fit to supernova data The Accelerating Universe

Estimated age depends on both dark matter and dark energy old older oldest