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Observational Evidence of Creation
1) The sky is dark! (Olber’s Paradox)
If the Universe were infinite in space and time, every line of sight
would eventually end on a star. Even if it were very far away and
faint, that would be made up for by having more of them in a
smaller patch of sky. The sky should have the same brightness as
the Sun (or at least an M star!). This resolved by the fact that the
Universe started a finite amount of time ago (the expansion helps
too with the redshift).
Observational Evidence of Creation
2) The Universe is observed to be expanding (so in the past it was smaller).
The Steady State Universe tried to get around this by supposing that new
galaxies appear out of nowhere to fill the increasing volume
(no more unreasonable than supposing that the Universe appeared).
But then the past shouldn’t look different than the present (on average)
3) The Universe was hot and opaque in the distant past.
This is proven by the thermal cosmic background radiation. Only if all
space were opaque would all space be filled with thermal photons (and their current
temperature is reasonable given the expansion factor)
4) A theory which supposes the Universe evolves in this way can predict how the
composition of the Universe arose from the primordial fireball. These predictions are
borne out well by the current observed composition.
It seems inescapable that the Universe is only 10-20 billion years old
(actually about 14 billion) and that it started at a set and knowable
point of time. The moment of Creation is now an empirical fact.
Conceptual Framework for the Big Bang
1) As you run the movie backwards (look back in time), the Universe shrinks and
gets hotter.
2) The average photon increases in energy with decreasing time, and the photon
density goes up like T4 (matter density like T3).
3) Energy and mass are equivalent, so they will freely exchange when
E average>mparticlec2 for a given particle.
4) The particles created from energy must be equal numbers of matter and
antimatter (to conserve all quantum numbers).
5) Once the matter froze out (going forward in time), all the antimatter would
annihilate with the matter, leaving energy (which gets redshifted down below
the threshold energy to make particles again). Since there is matter now, there
must have been a slight overproduction of matter compared with antimatter.
This tiny symmetry violation (1 per 100 million) produced all the particles
now in the Universe. You can infer that there are 100 million photons for
every proton. Where are they…?
Energy
matter +
antimatter
Energy
Big Bang Nucleosynthesis
From t=1-200 sec the Universe had about the density of water and a temperature
of about a billion degrees. Protons and neutrons froze out of the radiation field
(fewer neutrons because they are a little more massive), and neutrons began to
decay. There were 14 protons for 2 neutrons. The neutrons fused to make
deuterium, and then helium. This left 12 protons and 1 helium (He4), or about 8%
He by number or 25% helium by mass. Just as we see everywhere today! A little
bit of deuterium and lithium was also left, and we see that too. The exact density
of those then determines the amount left today (so we know what it was).
The Recombination Era
Age of Universe: about 300,000 years
The light comes to us from
the time when hydrogen
atoms were able to
recombine and stay that
way. The interaction of
photons with matter was
then restricted to the
hydrogen spectral lines,
leaving almost all photons
free to fly unimpeded.
We see such photons
redshifted by z=1000
(meaning the Universe
was 1000 times smaller at
that time).
All Around Us – The Fireball
COBE
(1990)
The Cosmic Background Radiation
Those photons should be all around, but very
cool (redshifted). And they are…
Cosmic dipole (motion)
Penzias & Wilson
1965 (and Dicke)
A perfect blackbody
(thermal) spectrum:
2.736 K
Imperceptible structure then
 galaxies today
The fireball had to have some structure,
or we wouldn’t have any now. The
effort to find it was epic; it was only
seen at one part in 100,000.
Galactic plane
The Formation of Large Scale Structure
The Universe hasn’t
really been around long
enough for the gravity
from all the galaxies we
see to have caused the
collapse of matter into
this foamy structure.
Computer models show
this could only happen if
there is a lot more “cold,
dark matter”out there –
invisible, but dominating
the mass in the Universe.
Dark Matter - rotation curves
Rotation curves imply the mass-to-light ratios of galaxies go up as we
look on larger scales: Sun M/L=1,
solar neighborhood  M/L=3,
galaxy  M/L=50
Dark Matter – cluster speeds
galaxy clusters  M/L=200-500
From average speed of galaxies – the cluster would fly apart
From X-ray gas held in – several million degrees and extensive
Dark Matter :gravitational lensing
The mass required
to produce the
observed lensing is
much higher than
the luminous mass.
This is a direct
observation of
gravity due to dark
matter.
What could the dark matter be?
1) Normal but dark matter (“baryonic”) : rocks, white or brown dwarfs?
2) Black holes or neutron stars? Too much metals would have been produced.
Anyway, Big Bang nucleosynthesis tell us this can’t be it…
WIMPS and Cold Dark Matter
Could dark matter be some kind of new particles which
interact very weakly with matter (like neutrinos do) but
massive, and not moving relativistically? Experiments
at Berkeley and elsewhere are looking for them
(guaranteed Nobel prize!).
A Brief History of Time
The Horizon Sets the Limit of the Observable Universe
The observable Universe has a horizon
(in light years) set by its age. Each point
has the same size horizon. Not only has
light beyond the horizon not had enough
time to reach us, but the redshift at the
horizon is infinite. This is an event
horizon (like a black hole’s).
14 billion light years
14 billion light years
28 billion light years
Cosmic Microwave Background Anisotropy spectrum
The details of the features on
the fireball (CMB) tell us
what the curvature of
spacetime is. They confirm
that it is flat, which means the
Universe will not recollapse,
but will expand forever.
Mysteries in the Big Bang Theory
• The Horizon Problem
– The cosmic background in all directions has the same temperature, yet
opposite sides of the sky are not in “causal contact” (they are outside each
other’s horizons). The largest COBE structures are also larger than their
own horizons!
• The Flatness Problem
– The geometry of the Universe now appears to be flat. But it has expanded
by a factor of 1060, so at the beginning it had to be flat to within a factor
of 10-60! And yet it had to have enough density fluctuations to produce
today’s structure. How was that arranged?
• The Matter Problem
– Matter and antimatter should be created in exactly equal amounts, but
they weren’t (by a tiny bit).
• The Creation Problem
– How did spacetime suddenly spring into being, with lots of mass and
energy, and violently expand?
The Solution : Inflation!
The Flatness Problem
Solved
Geometrically, it is easy to see
how inflation can remove any
initial curvature to spacetime (at
least within the horizon).
But remember that the geometry
of spacetime is tied up with the
density of the Universe. We call
this W (Omega) and set it equal to
1 if it has the critical value.
If inflation is correct, then we
must have W =1, and the question
becomes: how is that
accomplished? We know that
matter can only supply W =0.05,
and dark matter gives about
W =0.25. Where’s the other 0.7?
Another measure
of curvature
If we have an independent
way of getting distances
to very distant objects, we
could try to measure the
change in the Hubble
constant with time, and
get the behavior of the scale in the
distant past. Then we’d know which
curve we are on, and whether the
Universe really is flat or doing
something else.
Type I supernovae provide such an
opportunity…
Exploding White Dwarfs as “Standard candles”
We need to find them very
far away, but be able to
distinguish them from the
light of the host galaxy.
A Major Surprise!
Something is giving us a push…
A very Berkeley project…
A detailed view of the cosmic fireball. Results:
The Universe is 13.7+/-0.2 billion years old.
The curvature of observable spacetime is flat.
Galaxies began to form after 200 million yrs.
W-MAP
Density and Composition of the Universe
Based on what we can see, stars fall short of providing the critical
density by a factor of 200. Neutrinos don’t seem to help. Indeed, the
results of Big Bang nucleosynthesis shows that matter of all forms is a
factor of 20 short. But there are good theoretical reasons to believe the
curvature is flat. Dark matter (?) provides about a third of what is
needed. The rest appears to be in the form of “dark energy” (eh???)
What’s in the Universe:
VACUUM (with dark energy)
Counting particles in 100 sq meters
1 heavy (more than O) atom
100 atoms of C,N,O
100,000 atoms of helium
1,000,000 atoms of hydrogen
30 times that mass in dark matter
(particles of unknown mass)?
100,000,000,000,000 cosmic photons
and as many cosmic neutrinos
The History and Fate of the Universe
Define time by “cosmic decade”: time=10 t years (t is decade)
Primordial Era
t = -50: Planck epoch
t = -35: symmetry breaking, inflation
t = -12: formation of “normal” particles
t = -6 : production of helium
t = 4 : end of radiation domination
t = 5.5: atoms form, cosmic microwave background
Stellar Era
t = 7 : first stars form
t = 9 : Milky Way, galaxies form
t = 9.5: formation of solar system
t =10.2: Sun dies
t = 14 : end of star formation, smallest stars die
The History and Fate of the Universe
Define time by “cosmic decade”: time=10 t years (t is decade)
Degenerate Era
t = 16 : colliding brown dwarfs
t = 19 : most brown dwarfs, planets ejected
t = 30 : remaining dwarfs fall into central black hole
t = 37 : free protons decay, neutron stars decay
t = 39 : protons in dwarfs and planets decay
Black Hole Era
t = 42 : dark matter particles decay into photons
t = 66 : stellar black holes evaporate
t = 84 : galactic black holes evaporate
t = 98 : cluster black holes evaporate
t = 141 : last positronium decays
(see “The Five Ages of the Universe” by Adams and Laughlin)