Primordial Sound: Listening to the Big Bang Mark Whittle University of Virginia Outline Our Universe & the Big Bang The Microwave Background Sound in the early universe The birth of the first stars and galaxies In the beginning: quantum hiss The Sun: A Normal Star
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University of Virginia
Earth = 100 nm = virus
Sun = 10 μm = cell
Earth orbit = ¼ cm = pin head
Solar system = 20 cm = saucer
Nearest star = 250 m = canteen
They contain 100,000,000,000 stars!
Doppler shifts give galaxy velocities
3 billion light years
(~20% to “the edge”)
Our galaxy is here
Small, un-remarkable region: 1500 galaxies!
The Visible Universe
MW galaxy = 20 m = class room
It contains 100,000,000,000 galaxies!
14 B yrs
14 B light-yrs
hot glowing fog
we see a glowing
wall of bright fog
We cannot see the Big Bang itself
It is hidden behind 400,000 light years of dense fog
CMB is Young and Far
(highlights, there are many others)
Water waves :
high/low level of
Many waves of different sizes, directions & phases
Sound waves :
red/blue = high/low
gas & light pressure
(in this case: moving through a gas)
b) it then rebounds out to make first rarefaction
dimThe first sound waves
c) then back in again to make second compression
the oscillation continues sound wave created
Three important aspects to perceived sound:
Consider each in turn:
What frequencies can we hear ?
20 – 20,000 waves per second (Hertz)
What’s the Cosmic pitch ??
1 wave every 20,000 – 200,000 yrs !!
Too deep to hear, by about 50 octaves!
Sounds usually contain many frequencies
A graph of this is called the Sound Spectrum
Cannot follow waves in time.
Instead use the wave’s spatial appearance
Evaluate spatial power spectrum, of waves on the sphere.
“frequency” is spherical angular harmonic: ℓ
current best data
angular wavelength (degrees)
sky frequency (~180/°)
sound frequency (Hz)
The CMB Power Spectrum
Relative loudness at different pitch
Raw CMB sound
Water waves on the ocean surface illustrate
sound waves on the CMB “surface”
Microwave brightness, greatly contrast stretched.
Brightness differences are also pressure differences
Patches smaller than 2º are sound waves
Open :Ω= 0.8
Flat : Ω= 1.0
The Universe is a poor concert hall !
Distortions are present in the sound spectrum.
One can “remove” distortions by using robust
computer simulations (eg CMBFAST)
The CMB gives only a snapshot of the sound
Use CMBFAST to reconstruct sound from earlier.
These are remarkable features of the sound.
Harmonics usually arise in objects of finite size
The Universe is bounded in time
The harmonics are not as sharp as musical tones
Between major & minor 3rd
C(ℓ) as observed
P(k) pure tones
then galaxies….. clusters…. tapestry
galaxypeaks on peaks on peaks
Movie time flow exponential : 2s for each 10x increase in real (cosmic) time:
0-2s = 102-103 yrs; 2-4s = 103-104 yrs etc; waveform and cosmic color also shown
Movie 5: volume increase included, but artificially reduced so we can hear it all.
Contrast reaches this level after ~100 Myr, when rapid collapse takes over.
Stars/Galaxies/Clusters form from:
small big wavelengths.
Large scale tapestry
1st & 2nd harmonics.
The Big “Bang” was born in utter silence !!
Sound grew later as gas fell into a lumpy landscape
What made the initial lumpiness ?
Quantum fluctuations amplified by inflation
What did this truly primordial sound “sound” like?
The physics of the early Universe can be cast in
terms which are bizarrely familiar, allowing us
access to what must surely be one of the most
remote but important of times.
Strangely, much of this was anticipated in 1680
by poet John Dryden:
From Harmony, from heavenly harmony,
This universal frame began:
When nature underneath a heap
Of jarring atoms lay,
And could not heave her head,
The tuneful voice was heard from high,
“Arise, ye more than dead.”
Then cold, and hot, and moist, and dry,
In order to their stations leap,
And Music’s power obye.
From harmony, from heavenly harmony,
This universal frame began;
From harmony to harmony
Through all the compass of the notes it ran
The diapason closing full in man.