Download 5.2.1 Doppler Hubble Toil and Trouble

Shakespeare jokes up in here, son
*drops mic, drives off in 78 Coupe de Ville
with the g-funk bumping*
Christian Doppler

Doppler Shift

 Austrian mathematician/physicist Christian Doppler
predicted this effect in 1842.
 As a source of waves moves towards you, the
frequency (pitch, in the case of sound waves) rises.
 As the wave source moves away, the frequency
drops.
Doppler Shift

 Since light is a wave, the light from any star moving
towards us is shifted towards a higher frequency,
making it slightly bluer than we’d expect. (blue shift)
 A star moving away appears slightly redder. (red
shift)
 The faster it’s moving, the greater the Doppler shift.
Edwin Hubble

Edwin Hubble

 Hubble had access to the world’s finest telescope,
and worked on measuring the red shift of nearby
galaxies.
 Remember that we know what color stars really are
because they are made of H and He, and emit and
absorb very specific wavelengths of light.
Edwin Hubble

 Hubble found that not only were almost all galaxies
moving away, but the more distant galaxies were
retreating even faster.
 Therefore the Universe was expanding in all
directions.
 Does that put us at the center of the Universe?
 Nah, bro. Observe this little demonstration with a
balloon.
Hubble Space Telescope
(HST)

 In 1990, the HST was finally launched.
 Free from the interference caused by Earth’s
atmosphere, HST recorded stunning images of our
Universe.
 There are coffee table books and everything.
 Phwoar.
Hubble Deep Field

Hubble Space Telescope
(HST)

 Thanks to the HST, we found earlier and earlier
galaxies.
 We can see back in time because the light from those
galaxies takes billions of years to reach our
telescopes.
 HST data tells us that when the Universe was only
600 million years old, there were already stars and
galaxies and other familiar things.
Beyond HST

 But what about before that? When did the first
galaxies form?
 To answer that, we use computer models to simulate
the early Universe. If your model produces
something that looks like what we observe, you are
probably on the right track.
Beyond HST

 You want observational
data? We’re gonna need a
bigger telescope.
Beyond HST

 Enter the James Webb Space Telescope (JWST)
 Much-delayed, this beast will finally launch in 2018.
 It’s so huge, it will have to unfold in space, because
it’s too large for any rocket.
JWST

JWST

JWST

 Like a squinting teen who suddenly gets a pair of
glasses, JWST will be able to see much farther than
Hubble can, and hopefully see the earliest galaxies of
all, catching them in the act of formation.
 Theorists will then compare this data to their
computer programs and see who got it right!
Before That?

 Singularity
 Radiation-dominated era
 Inflation
 Matter-antimatter production and annihilation
 Nucleosynthesis
 Matter-dominated era
 Recombination
 Dark Age
 Reionization
Singularity

 As discussed earlier this week, attempts to logically
have an infinitely old Universe have all failed.
 It does seem that our Universe had a beginning,
13.80 billion years ago.
 A singularity is a point of near-infinite energy in an
infinitesimal volume.
 From this “seed”, our Universe exploded outwards.
Inflation (t=10-36-10-33s)

 Proposed in 1980 by American Alan Guth.
 Although nothing can move faster than light, there is
no physical law preventing space-time from
expanding faster than light.
 Inflation suggests that in a billionth of a trillionth of
a trillionth of a second, the Universe expanded from
the size of a proton to about the size of a grapefruit.
Inflation

 The inflation hypothesis explains a couple of
puzzling things about the Universe, including how
patches of space on opposite sides of the Universe
can be the same temperature.
 Gas clouds separated by tens of billions of lightyears are not just “about the same temperature”. The
difference between the hot spots and cold spots is 30
millionths of a Kelvin. This is bizarre, unless they
were once in close contact.
Matter-antimatter
Production

 Since the 1930s, we have known that at very high
energies, pairs of particles – 1 matter, 1 antimatter –
can spontaneously pop into existence.
 They fly around until the antimatter particle hits
matter, and then both are turned back into energy (a
photon) according to E=mc2.
 We live in a matter-dominated universe.
Matter-antimatter
Production

 In the baby Universe, the incredible energy levels led
to production of protons and antiprotons, and
electrons and positrons.
 Somehow (and this is one of the biggest questions in
physics today), we ended up in a universe with only
matter.
 We think that there was a tiny asymmetry in the
matter-antimatter production. (If there hadn’t been,
we couldn’t be here to observe it!)
Matter-antimatter
Production

 After about 14 seconds, the temperature/energy
density of the Universe dropped below the threshold
for particle production to occur (3x109K). All the
protons and neutrons in the Universe were already
made.
 Between 14 seconds and 3 minutes, the protons and
neutrons couldn’t stick together to form deuterium
because the temperature was so high that photons
(light) would literally blast them apart again!
Matter-antimatter
Production

 There were 1,000,000,001 matter particles for every
1,000,000,000 antimatter particles.
 Matter and antimatter annihilated one another like a
game of Advanced Warfare.
 The numbers come from this equation, but don’t ask
me to explain it:
 η ≡ nb/nγ = 5.4 × 10−10 (Ωbh2/0.02)
Nucleosynthesis

 This means that there were 1 billion photons for
every particle of matter.
 The Sun, you, me, Jessica Alba and yo momma are
made of the leftovers.
 As we saw earlier this week, between 3 and 20
minutes, a chunk of the hydrogen was fused into
helium via our old friend the proton-proton chain.
Ions! Ions Everywhere!

 The Universe continued to expand, and cool.
 As the temperature was still extremely high, the
Universe was actually made of plasma – ionized
atoms. The electrons had far too much kinetic energy
to settle into orbits around nuclei.
 Ain’t nobody got time for dat.
 No stars, no galaxies, just plasma.
Recombination (t=378,000yr)

 Once the background temperature of the Universe
dropped below 3000K (about half the surface
temperature of the Sun), electrons finally combined
with nuclei to form the first atoms.
 As they did so, they released photons. It is this light
(now red-shifted beyond what our eyes can see) that
Penzias and Wilson detected as the CMB. This is the
earliest detectable light in the Universe.
Recombination

 Note: There were photons before that, but they were
constantly being absorbed and reemitted by protons
and electrons.
 This is usually described as a foggy or opaque
Universe. Recombination meant that the fog cleared
and some of that light – the CMB – has traveled
through space for 13.8bn years before reaching our
telescopes.
Dark Age (t=378,000yr-?)

 So now the Universe is “only” a couple of thousand
Kelvin, and made entirely of hydrogen, helium, and
a few stray atoms of lithium and beryllium.
 Some regions are a tiny bit denser than others.
 That’s all the opening gravity needs, and it pulls the
gas together. Stephen Hawking explains it better
than me.
Reionization (t=~4x108years)

 Once the first stars ignited, the Universe was no
longer the same temperature throughout – we had
dense regions (nebulae that gave birth to stars)
heating up to thousands or millions of Kelvin, and
less dense regions that continued to cool (CMB is
2.7K today)
 Ions, and plasma, were back. Yeah! And at last, there
was starlight.
 JWST’s job is to study the reionization epoch.