Transcript The Life of the Universe - University of Minnesota

The Life of the Universe
From Beginning to End
• Early Universe is
extremely hot and dense
• All 4 forces were merged
• As Universe cooled,
forces became unique
• Energy of photons high
enough to create matter
and vice versa
• GUT – strong and
electroweak
forces united
• SuSy – GUT and
Gravity united
The Big Bang Theory
• The early Universe was
exceedingly hot and dense
• Big Bang theory explains how the
early Universe cooled and evolved
into the Universe we observe today
• Relies on Theoretical and
Observational data
Planck Era
• t < 10-43 s
• T > 1032 K
• Current physics is unable to
understand times before the
Planck era
– Need to unite physics of large
scales (general relativity) with
physics of small scales
(quantum mechanics)
GUT Era
• 10-43 s < t < 10-38 s
• 1029 K < T < 1032 K
• Supersymmetry force splits
into GUT force and gravity
Electroweak Era
• 10-38 s < t < 10-10 s
• 1015 K < T < 1029 K
• GUT force splits into strong
and electroweak forces
– Huge release of energy 
Inflation
• Inflation expands Universe at
exponential rate
Particle Era
• 10-10 s < t < 10-3 s
• 1012 K < T < 1015 K
• Electroweak splits into weak
force and electromagnetism
– All four forces distinct
• T too low for spontaneous
conversion of photons to
particles
• Photons became quarks,
which merge into protons
and neutrons
Era of Nucleosynthesis
• 0.001 s < t < 5 min
• 109 K < T < 1012 K
• Fusion begins
– T still so high that most He
nuclei will break apart again
• Expansion reduces density
so fusion ceases despite T
being so high
• 75% H, 25% He, trace others
Era of Nuclei
• 5 min < t < 380,000 years
• 3000 K < T < 109 K
• Photons still hot enough to
ionize, so electrons and
nuclei stay separated
• Photons cannot travel far
because they are scattered
by electrons
Era of Atoms
• 380,000 yrs < t < ~109 yrs
• T < 3,000 K
• T drops low enough for
atoms to form
• With electrons bound to
nuclei, photons can travel
long distances
– Cosmic Microwave
Background
Era of Galaxies
• t > 109 years
• Universe filled with nearly
homogeneous distribution of
matter and dark matter after
era of atoms
• Slightly overdense regions
collapse to form first stars
and galaxies
• Gravity dominates on large
scales
A Few Questions
• Where did the large scale structure
come from?
• Why is the Universe so uniform?
• Why is the density of the Universe
so close to the critical density?
Inflation
• Separation of strong force from GUT force
would release enormous amount of energy
• Energy would cause the Universe to
expand by factor of 1030 in 10-36 sec
Inflation and Structure
• Huge expansion would
make tiny quantum
fluctuations in density
large ripples
• A ripple the size of a
nucleus would become
the size of our solar
system
• Creates density
enhancements that give
rise to the structure we
observe today
Inflation and Uniformity
• No reason why things so far away should
be similar
• Things close by should be
• Inflation takes things that were very close
together and spreads them out a lot
– Universe was all close together, so everything
was uniform, then inflation spread it out
Inflation and Density
• Density implies
curvature of
spacetime
– Think general relativity
– Critical density has flat
geometry
• If Universe started
somewhat curved,
inflation would make it
seem much flatter
Evidence for the Big Bang
The Cosmic Microwave Background
The CMB
• Line – a theoretically
calculated thermal
radiation spectrum
based on the Big
Bang Theory
• Dots – Observed data
• They match!
The Fate of the Universe
Two Things to Consider
• Expansion of the Universe
• Gravity – makes things collapse
• Critical density – the density required to balance
gravitational attraction and expansion
• Dark energy – a repulsive force  opposite of gravity
An Accelerating Universe
• SN Ia data show that
we most likely live in
an accelerating
universe
• Acceleration is driven
by some force that is
not well-understood
– Dark energy
The Big Rip
The End