Big Bang Acoustics : The Sound of Creation

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Big Bang Acoustics The Sound of Creation

• Mark Whittle
• University of Virginia

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Setting the Stage

• Studies of the Cosmic Microwave Background (CMB)
• have revealed SOUND WAVES in the early Universe.
• It is possible to make this sound audible to
  humans.
• These sounds offer a wonderful opportunity for
  teaching
• Cosmology structure formation
• Acoustics science of sound
• Music musical instruments harmonics scales
• Much of astronomy is visual.
• This gives us auditory access to Nature. and
  Creation.

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1. The Microwave Background
Look far away and we see back in time. Look far
enough, and you can see the Big Flash
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red-shift
Our view of the Universe includes space and time
The Early Universe was filled with hot glowing
gas
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We cannot see the Big Bang itself It is hidden
behind 400,000 light years of dense fog 4ft in
26 mile marathon 12 hours in human lifetime
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Observing the Microwave Background
Bell Labs (1963)
(highlights, there are many others)
COBE satellite (1992)
WMAP satellite (2003)
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The Celestial Sphere
Optical Sky
Microwave Sky
Microwave Sky Stretched
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2. Raw Sound from the CMB

• Measure the pressure waves in the CMB
• The amplitudes (? P/P) 10-4 110 dB !
• The pitch is 50 octaves below A440 !
• The sound spectrum has harmonics !

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Why is primordial sound so
DEEP?
BIG
Because the Universe is so
Cathedral Organ
Universe
Pan Pipes
400,000 light years
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An Ultra-BassPiano
deeper
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How does sound get to us ?
Consider listening to a live concert on the radio
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Sound as Diagnostic

• Quality of sound reveals the nature of an object
• True also for the Universe
• The sound spectrum reveals many properties
• Use computer simulations to match data
• Two examples baryon fraction total density

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Fraction of Baryons (atoms)
reality
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Fraction of Baryons (atoms)
reality
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Total Cosmic Density
reality
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The Concordance Model

• Age of Universe 13.7 Gyr
  (2)
• Flatness
  1.02 (2)
• Atoms
  4.4 (9)
• Dark matter 23
  (15)
• Dark energy 73
  (5)
• Hubble constant (km/s/Mpc) 71
  (6)
• Photon/proton ratio 1.6x109
  (5)
• Time of first stars 180 Myr
  (50)
• Time of CMB 380,000yr
  (2)

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4. Removing Distortion C(l) ? P(k)
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)
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Into the Fog Evolving Sound
The CMB gives only a snapshot of the sound Use
CMBFAST to reconstruct sound from earlier.
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Evolution of Sound Spectra P(k,t)
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The First 400,000 years
Movie 1
1.5 Mb
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Post Recombination From Sound to Stars

• After recombination, pressure drops to zero
• Cavity oscillations in time cease true sound
  dies
• However, the roughness grows quickly
• the baryons fall into dark matter valleys
• the dark matter itself gets more clumpy
• after 100 Myr the peaks collapse ? stars !
• Continue to create sound from P(k)

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From Sound to Stars
100 million years
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The Growing Hiss
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3
5
7
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stars
galaxies
clusters
tapestry
Contrast reaches this level after 100 Myr, when
rapid collapse takes over. Stars/Galaxies/Cluste
rs form from small ? big wavelengths. Large
scale tapestry forms from 1st 2nd harmonics.
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First 100 Million yrs
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.
Log frequency x-axis Log (decibel)
y-axis Constant volume
Linear frequency x-axis Log (decibel)
y-axis Varying (fake) volume
Movie 6
Movie 5
1.5 Mb
1.5 Mb
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The Harmonics
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
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Why does it sound so unmusical?

• Because the Universe is not a good resonator
• the harmonics are broad (fuzzy)
• we do not easily notice the hidden notes

Compare the Universe with a flute
decibel scales
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Whats the Chord ?

Between major minor 3rd
C(l) as observed
P(k) undistorted
P(k) pure tones
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Creations Opening Chord
raw
pure
both
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Chord Analysis
All sounds 104 106.5 years
exponential time constant volume
microtonal
tempered
one octave
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The Opening Crescendo
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4105 yrs
raw
pure
both
microtonal
tempered
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In the Beginning Quantum Hiss
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?
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9. Closing thoughts
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
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John Dryden (1687)
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 Musics 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.
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http//www.astro.virginia.edu/dmw8f