Title: COSMOLOGY
1COSMOLOGY HOW IT BEGAN
Chris Impey University of Arizona
2Norton, 2010
3Space
Science is Seeing
4A Scale Model
Set the Earth to the size of a walnut, or a
1500,000,000 scale model
- The Moon is a pea at arms length
- The Sun is a 3 m ball 300 m away
- Neptune is a softball 9 km away
- Nearest star is 80,000 km away
5And at this scale, light is reduced to very slow
walking speed. Theres no way information in the
universe can travel any faster
- The Moon is a seconds walk away
- The Sun is 8 minutes walk away
- 10 hours to walk the Solar System
- 4 years to walk to the nearest star
6Reduce the scale by a factor of 10,000,000
- The Solar System is a grain of sand
- The distance between stars is 20 m
- The Milky Way is the size of the U.S.
- The MW has 400,000,000,000 stars
7Now reduce by another factor of 10,000,000
- The Milky Way is like a small plate
- The nearest galaxy is 5 m away
- The universe is the size a large city
- Billions of galaxies within this space
8The Contents
9Galaxies
100 billion galaxies
- Scattered in a universe 46 billion light years
across
10Stars
100,000 billion billion stars
- The Milky Way is typical with 400 billion stars
11Atoms
1080
Atoms
- Almost all the simple elements hydrogen and helium
12Photons
1089
- A billion photons for every particle
13Mediocrity
- We therefore live on an
- Average planet around
- An average star in an
- Average galaxy in a
- Very large universe
Copernicus
14Composition of the Universe
Universal Pie
Dark matter 22
Dark energy 73
15Cosmology
16Cosmology
Slipher
17Lookback Time
If the speed of light were infinite, light from
everywhere in the universe would reach us at
exactly the same time and we would see the entire
universe as it is now.
But it is not, so we see distant regions as they
were in the past.
Distant Light Old Light
18Cosmology What We Know
- Redshift its a universal
- expansion of space-time,
- not a Doppler shift.
- The microwave background radiation (CMB), a
signal that is close to perfectly thermal, at
temp of 2.726K.
19- Deuterium and Helium synthesized (much higher
temperatures in the past).
Hubble Ultra Deep FieldHSTACS
- Galaxies in past look younger (smaller and more
irregular).
20Big Bang
21Evidence
- A good scientific model should always make
predictions which can be verified. - The big bang model makes two predictions which
have been verified since the 1960s - the existence and characteristics of the cosmic
microwave background (CMB) - the expected Helium abundance in the Universe
- The model predictions agree with all current
observations. There is much indirect evidence the
universe was smaller and hotter in the past
22Cosmic Microwave Background
- The universe is immersed in a sea of radiation.
- 380,000 years after the big bang, the universe
had cooled enough for free electrons to become
bound into atoms of Hydrogen and Helium - Without electrons to scatter them, photons were
able to travel unhindered throughout the universe - The universe became transparent
- The temperature of the universe was 3,000 K at
this time, similar to a stellar photosphere - It has expanded by a factor of 1000 since then,
reducing the temperature to 3000/1000 3 Kelvin
23The CMB has highest redshift of anything we can
see (z 1000).
When we look at the CMB, we look at the surface
of the glowing fog that filled the entire early
universe!
24(No Transcript)
251 of the specks on any TV tuned between stations
are interactions with the big bang
26Origin
Science is Seeing
27The big bang was extraordinary? the instantaneous
creation of all of space and time, containing
energy to drive the expansion and enough matter
for 100 billion galaxies. The initial state was
so compact that it can only be described by a
theory that unites gravity and the quantum world.
We do not have such a theory at present. The big
bang can be thought of as a quantum event,
originating from very chaotic space-time in which
the other quantum fluctuations might have led to
other parallel universes.
28Cosmic Inflation
The standard big bang has trouble explaining why
the universe is as smooth and flat as it is,
leading to the idea of an epoch of extremely
rapid inflation, just 10-35 sec after the big
bang. The mechanism is unclear but probably
associated with the Grand Unified theories that
seek to unite all the forces except gravity.
29Status of Inflation
Inflation makes the universe flat and smooth (by
design!), and it implies vast region of space
that are beyond view. It has tentative support
from CMB satellite data.
30Beyond the Horizon
The universe is bounded in time and not space.
General relativity sets no speed limit to the
expansion. As time goes by, ever more distant
regions come into view.
At z 1.3, an object was moving away from us at
c at the time the light was emitted.
At z 1000, two distant points were moving apart
at 60c at the time the radiation was emitted.
Consequence of standard big bang The physical
universe is much larger than the observable
universe, we are subject to a horizon.
Consequence of the inflationary big bang A
microscopic region of space-time became our
universe the universe is a quantum entity.
31THE UNIVERSE AND US
Us
Earth
Solar System
Milky Way
Universe
Multiverse?
32Multiverse
33Beyond the Horizon
Science is Seeing
Life occurs in a range of scales that extends
from galaxies to the atomic nucleus, as
symbolized by the ancient symbol of the
ouroboros, the snake that eats its own tail
34Quantum fluctuations are a mechanism for multiple
realizations of the universe
leading to the concept of the multiverse
35 String Theory Landscape
500
Perhaps 10 different vacua
de Sitter expansion in these vacua create quantum
fluctuations and provide the initial conditions
for inflation. String theory provides context for
the multiverse
36The ekpyrotic universe has a big bang, but it
is not ever at an infinite temperature and
density, and it is not the origin of all
space-time So our universe emerged from a
collision of two 4D branes that are embedded in
5D space-time. The collision is the engine for
expansion and matter creation.
37Eternal Universe
38Dark matter binds galaxies and dark energy is
currently driving the cosmic acceleration.
39Nature of the Expansion
The early expansion was rapid, driven by intense
radiation. It slowed down as the dark matter
began to dominate, and more recently has begun to
accelerate due to the relative growth of dark
energy.
40Within the expanding and cooling universe
gravity formed stars, galaxies
, and people.