Download Announcements

Announcements
•The last Dark Sky Night is tonight. Set-up
will start at 7:30pm. Cancellation notice, if needed,
will be posted immediately after class. If it is cancelled we
will try again Thursday night
•Don’t forget about your project.
Presentations will be Monday May 1 at
3:20pm. A written paper is also due at the
same time. Exam 4 is after the presentations
The Early Universe
What was the universe like before the CBR? How about
before nucleosynthesis? How far back can we go if we
can’t see anything farther than this?
Matter density decreases differently
than energy density
This term is due to the
decrease in energy from
the expansion of space
Thus, there must have been a time
when energy dominated over matter
Solving the Friedmann equation for
an energy dominated universe
Energy decreases as 1/R4 so
 R(t1 ) 
E (t)  E (t 1 ) 

 R(t ) 
4
But energy density is proportional to T4 so
 R(t1 ) 
T (t )  T (t1 ) 

 R(t ) 
At the extremely high density of the
early universe, the density term
dominates the Friedmann equation
2
R
8 G   kc
2
  2
  H 
3
3 R
R
2
Putting it all together gives a simple
relationship between time and size
R (t )  t
During the energy dominated era, the universe
expands as the square root of time
So the
farther
back in
time we
go, the
higher the
density
gets and
the hotter it
gets
What was a universe dominated by
energy like?
Virtual particles of all types of elementary particles were
popping in and out of existence everywhere
If only particleantiparticle
pairs are
produced there
would not be
any matter in
the universe
There must have been
particle production
processes that did not
conserve baryon number
So to understand the early universe
we must understand high-energy
particle physics
At the elementary particle level we
talk about particle fields
Some fields are easy to picture
The photon is
the exchange
particle for the
electromagnetic
field
One of the important things in
particle physics is symmetry
Spontaneous Symmetry Breaking
is like a phase transition
Before the Planck time (10-43
seconds) we know nothing
?
Some theories say that space-time is so
warped during this time that space and time
can no longer be separated so that the very
concept of “before this time” is meaningless
During
the
Planck
Epoch
Quantum
Gravity
Rules
Eventually gravity “freezes out”
and we enter The Unified Epoch
Only two fields
govern everything:
The Unified Field
and gravity. We
don’t understand
what gravity is like
at this time but we
are starting to
understand GUT’s.
In the Unified Era there are
only two forces
Quantum Gravity
Current theories are called
looped quantum gravity
GUT’s are Grand Unified Theories
which unify the electromagnetic,
weak and strong nuclear forces
GUT’s deal with elementary particles
The strong nuclear, electromagnetic and weak nuclear
forces are united in a single Grand Unified Theory
Baryogenesis occurs during the
Unified Epoch
More particles than antiparticles are created by symmetry
breaking processes which are not well understood. We
know they must have occurred, though, because our
universe only contains matter and not much antimatter.
Because of baryogenesis,
protons must decay
One mechanism is the proton decays into a
positron (e+) and a pion (0) which quickly decays
into a pair of gamma rays. Another is the creation
of a mini charged black hole.
The Unified Epoch is when Inflation
occurred
The universe
expanded at
tremendously
superluminal
speeds during
Inflation
1m 1050 m
35 m
26

10

3
.
33

10
c
s
35
37
10 s  10 s
During Inflation, the temperature
actually rose!
After Inflation, the strong nuclear
force “freezes out” and the universe
enters the Quark Epoch
The universe is now
a quark-gluon
plasma. The quarks
were created in the
Unified Era and
move around almost
unbound during the
Quark Era