Complete History of the Universe Abridged

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Complete History of the Universe (Abridged)

• Thursday, March 6

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t 0
The Big Bang
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t0 The Big Bang
How do we know that this happened?
Universe was denser in the past if we daringly
extrapolate backward to infinite density, that
was a finite time ago.
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t0 The Big Bang
Why do we care that this happened?
If the universe had remained dense, it wouldnt
have cooled enough for nuclei, atoms, galaxies,
and us to form.
(Speaking to an audience of humans, I make no
apologies for my human chauvinism.)
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t 10-35 seconds
Inflation
A brief period when the expansion of the universe
was greatly accelerated.
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t10-35 sec Inflation
How do we know?
The universe is nearly flat now it was
insanely close to flat earlier.
Inflation flattens the universe.
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t10-35 sec Inflation
Why do we care?
If the universe hadnt been flattened, it would
have long since collapsed in a Big Crunch or
fizzled out in a Big Chill.
No inflation, no galaxies.
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t 7 minutes
Primordial Nucleosynthesis
A period when protons and neutrons fused to form
helium.
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t7 min Primordial Nucleosynthesis
How do we know?
The earliest stars contain 75 hydrogen, 25
helium, as predicted from primordial
nucleosynthesis.
(Later stars contain more helium, made in
previous generations of stars.)
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t7 min Primordial Nucleosynthesis
Why do we care?
It shows we understand what the universe was like
when it was less than 10 minutes old.
No nucleosynthesis, no periodic
table (until the 1st stars).
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t 350,000 years
Transparency
A period when protons electrons joined to form
neutral atoms.
after
before
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t350,000 years Transparency
How do we know?
Cosmic Microwave Background is the leftover
light from when the universe was hot opaque.
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t350,000 years Transparency
Why do we care?
If the universe were still opaque, we wouldnt be
able to see distant galaxies.
No transparency, no astronomers.
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t 500 million years
The First Galaxies
A period when gas cools, falls to center of dark
halos, and fragments into stars.
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t500 million years First Galaxies
How do we know?
We see galaxies with large redshift (implying
large distance, implying distant past).
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t500 million years First Galaxies
Why do we care?
We live in a galaxy, orbiting a star.
No stars, no photosynthesis.
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t 14 billion years
Now
A period when (more-or-less) intelligent life on
Earth wonders about how the universe works.
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Where do we come from? What are we? Where are we
going?
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Lets try predicting the future.
Sometimes even short-term predictions are wrong
but Ill base my predictions on known laws of
physics.
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t 19 billion years (5
billion years from now)
Sun becomes a red giant star.
Sun as red giant
Sun now
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t19 billion years Sun red giant
How do we know?
We see what happens to older stars when they
start to run out of hydrogen.
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t19 billion years Sun red giant
Why do we care?
The Earth will be toast.
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After its last hurrah as a red giant, the
remnants of the Sun will become a white dwarf.
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t 1 trillion years
Last stars run out of fuel.
Galaxies remain filled with stellar
corpses
White dwarfs, neutron
stars, black holes.
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t1 trillion years Last stars die.
How do we know?
Lifespan is longest for the thrifty subcompact
stars barely massive enough for fusion.
Eventually, though, they run out of gas.
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t1 trillion years Last stars die.
Why do we care?
Even if our remote descendents huddle around a
dim, low-mass star, the light will eventually go
out.
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t 100 trillion trillion (1027) years
The end of galaxies.
Encounters between stellar remnants fling some of
them out of galaxy, others into a central black
hole.
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t 1031 years
The growth of black holes.
Clusters of gargantuan black holes (1011 solar
masses) in place of clusters of galaxies.
Moving black holes radiate gravitational waves
(ripples in space-time).
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Gravitational waves carry away energy (just like
electromagnetic waves).
Black holes spiral in toward each other, merging
to form hyper-gargantuan (1015 solar masses)
black holes.
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t 1045 years
The end of protons neutrons.
Protons neutrons decay into photons, electrons,
positrons (anti-electrons)
White dwarfs, neutron stars, planets
disintegrate into expanding clouds of photons,
electrons, positrons.
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Black holes aint so black. Stephen
Hawking
Black holes emit radiation - if quantum mechanics
is taken into account.
Particle - antiparticle pairs pop out of vacuum,
annihilate shortly afterward.
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One member of a pair can fall into a black hole,
while the other escapes.
The black hole appears to be spitting out
particles antiparticles. Where does the
particles energy come from?
The mass of the black hole.
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t 10106 years
The end of black holes.
Hyper-gargantuan black holes evaporate by the
emission of particles antiparticles.
An ever-expanding universe, containing electrons,
positrons, photons, neutrinos, at
ever-decreasing density.
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BrrrrThe Big Chill
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Some say the world will end in fire, Some say in
ice. From what Ive tasted
of desire I hold with those who favor
fire. But if it had to perish twice,
I think I know enough of hate To say
that for destruction ice Is also great
And would suffice.
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Tue, Mar 11, 130 pm Final Exam
Comprehensive Same
format as midterm
Practice mini-exam available on the class website
starting Friday at 5 pm.