Primal Scream : Sounds from the CMB

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Primal Scream Sounds from the CMB

• Mark Whittle
• University of Virginia

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Sound waves red/blue high/low gas light
pressure
Many waves of different sizes, Directions
phases, all superposed
Water waves high/low level of water surface
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Nature of Cosmic Sound

• Volume
• pressure variations 1/100,000
• corresponds to about 90 dB
• Loud but not cacophonous
• Pitch
• measured wavelengths 20,000 200,000 lyr
• pitch 10-12 10-13 Hz (v 0.6c)
• ? 48 52 octaves below concert A (440 Hz)
• Quality
• need to construct the power spectrum

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MWB power spectrum Combined binned data
Low frequency
High frequency
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Region size outstretched hand
Real data
Simulated data for different densities
critical flat geometry flat lens medium blobs
high density ve curvature convex lens big blobs
low density -ve curvature concave lens small blobs
Affects apparent wavelength of harmonic peaks
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Closed 1.2
All three
Flat 1.0
Open 0.8
Low pitch
High pitch
Long wavelength
Short wavelength
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All three
8 atoms
4 atoms
2 atoms
Low pitch
High pitch
Long wavelength
Short wavelength
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Why the Harmonics ?

• There are hills and valleys of all sizes
• It takes time for gas to fall into a valley
  longer for bigger
• valleys.
• At a given time, there is a largest valley which
  has just
• experienced its 1st compression. The size of
  this is
• speed of sound x age of universe
• e.g. 0.6 c x 380,000 yr
  230,000 lyr
• ? this is the wavelength of the 1st harmonic
  !
• 4. Valleys of 1/2 1/3 1/4 this size have
  2nd 3rd 4th compressions
• ? these are the higher harmonics !

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The cosmic concert hall
The universe is not a perfect concert hall There
is distortion en-route and local noise
Similar to carpetdrapes in a concert hall plus a
noisy audience adding distractions
Correct for these problems using
detailed computer calculations of the early
universe
Observed C(l) ? Pure P(k)
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Into the fog yet earlier times
The CMB shows the sound at 380,000 yrs What was
the sound like before then ?
We cant see beyond the CMB foggy wall ! But
computer models can take us there

• Earlier times
• Gas only had time to fall into smaller valleys
• Wavelengths are shorter, frequencies higher
• Amplitudes lower, sound is quieter

Examples
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The first sound striking the bell
Although gravity amplifies sound, there must be
initial irregularities, what caused these ?

• Deep mystery, but recent progress
• Quantum roughness in early universe
• Amplified by 1050 during inflation at 10-35 sec
• Inaudible quantum hiss made audible by inflation
• All structure in the universe due to quantum
  effects !

• What did the quantum hiss sound like ?
• Its power spectrum is flat ? white noise
• Gravitys amplifier then distorts the sound to
  make the final power spectrum with its harmonics

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Both
All three
Primordial
Final CMB
Low pitch
High pitch
Long wavelength
Short wavelength
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From sound to structure
Gravity amplifies sound into structure, right?

• Wrong !! .. it is too quiet
• at the CMB, the maximum fluctuations are 10-5 at
• the 1st peak (size 2 x 105 lyr), all others are
  weaker.
• This is too small to grow quickly into stars
  galaxies.
• We need something else with greater variation ??

• Dark matter comes to the rescue
• it feels no pressure
• it keeps collapsing from early times (no rebound)
• At CMB, fluctuations are large (10-2)
• P.S. shows no harmonics, power at high
  frequencies

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first
next
last
stars
galaxies
Large scale structure
0-1 Myr
Z400
Z600
Z800
Z1000
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