Primal Scream: Sounds from the Infant Universe

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Primal Scream Sounds from the Infant Universe

• Mark Whittle
• University of Virginia
• brief version
• (see full presentation for more details and
  narrative)

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Introduction

• This project began in 2003, following the WMAP
  results, and was
• developed for public outreach education.
• It unpacks many aspects of modern cosmology via
  the novel, yet
• scientifically accurate, use of sound.
• This is not new science, rather it uses existing
  data and computer
• models to create the sounds.
• Disclaimer I am not an cosmologist (I study
  active galaxies)

Acknowledgments Im delighted to thank the
following for assistance Joe Wolfe Alex
Tarnopolsky (UNSW) for help with acoustics.
Constantinos Skordis (Oxford) for help with
CMBFAST DASh. Charlie Lineweaver (UNSW), Pedro
Ferreira (Oxford) Louise Ord (UNSW), for help
with CMB physics. Mike Tuite (UVa) for help with
movie making.
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Last sound first

• Heres one version of the cosmic sound in this
  case the first million years, compressed to 5
  seconds, shifted up by 50 octaves, and played at
  constant volume

Click on the speaker icon to play. These are
.wav files
Note three stages descending scream deep roar
growing hiss.

• What do these stages mean, and how can we
  possibly know this?
• Observations of the Cosmic Microwave Background
  (CMB)
• Detailed computer simulations of the early
  Universe

Lets begin, then, with this Microwave
Background..
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The Origin of the CMB
atomic transparent
we see a glowing wall of bright fog
orange light
microwaves
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The CMB is Young and Far
380,000 yr
10
5
Time (Gyr)
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0
Big Bang
here now
nearby galaxies
HST
CMB
JWST
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The Big Bang is all around us !

• Since looking in any direction looks back to the
  foggy wall
• we see the wall in all directions.
• the entire sky glows with microwaves
• the flash from the Big Bang is all around us!

Big Bang
Near Far
Now red-shift Then
Far Near
Big Bang
Then red-shift Now
Big Bang
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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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Three all-sky maps of the CMB
The CMB is highly uniform, as illustrated here.
This means the young Universe is extremely smooth.
The oval shapes show a spherical surface, as in a
global map. The whole sky can be thought of as
the inside of a sphere.
But not completely COBEs 1992 map showed
patchiness for the first time. red ?? blue
tiny differences in brightness. Resolution 7o.
Patches in the brightness are about 1 part in
100,000 a bacterium on a bowling ball 60
meter waves on the surface of the Earth.
WMAPs now famous 2003 map of CMB patchiness
(anisotropy). Resolution ¼o.
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Two ways to view patchiness

• Seeds of cosmic structure
• Gravity amplifies density variations
• peaks ? stars/galaxies troughs ? voids

• 2. Sound waves
• peaks troughs in pressure sound waves
• the Big Bang has both light and sound
• ? acoustic analysis reveals cosmic properties

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Sound waves in the sky
This slide illustrates the situation. Imagine
looking down on the ocean from a plane and seeing
far below, surface waves. The patches on the
microwave background are peaks and troughs of
distant sound waves.
Water waves high/low level of water surface
many waves of different sizes, directions
phases all superposed
Sound waves red/blue high/low gas light
pressure
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Sound in space !?!

• Surely, the vacuum of space must be silent ?
• ? Not for the young Universe
• Shortly after the big bang (eg _at_ CMB 380,000
  yrs)
• all matter is spread out evenly (no stars or
  galaxies yet)
• Universe is smaller ? everything closer together
  (by 1000)
• the density is much higher (by 109 a billion)
• 7 trillion photons 7000 protons/electrons per
  cubic inch
• all at 5400ºF with pressure 10-7 (ten millionth)
  Earths atm.
• There is a hot thin atmosphere for sound waves
• unusual fluid ? intimate mix of gas light
• sound waves propagate at 50 speed of light

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How does sound get to us ?
Consider listening to a concert on the radio
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Nature of Cosmic Sound

• Three important aspects to consider
• Volume
• pressure variations 1/10,000
• corresponds to about 110 dB (decibels)
• ? as loud as a rock concert
• Pitch
• measured wavelengths 20,000 200,000 lyr
• wave periods 40,000 400,000 years
• pitch 10-12 10-13 Hz (sound speed 0.5c)
• 48 52 octaves below concert A (440 Hz)
• Way too deep to hear !!

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An Ultra-Bass Piano
Transpose up by 50 octaves 7 pianos (7
octaves each)
human concerto
cosmic concerto
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Nature of Cosmic Sound (ii)

• Quality
• Sounds usually contain many frequencies
• Relative amount of each ? sound quality
• A graph of this is called the Sound Spectrum
• The next figure shows two real sound spectra

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Flute power spectra
Joe Wolfe (UNSW)
B? Clarinet
piano range
Modern Flute
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Sky Maps ? Power Spectra
We see the CMB sound as waves on the sky. Use
special methods to measure the strength of each
wavelength. Shorter wavelengths are smaller
frequencies are higher pitches
peak
trough
Lineweaver 1997
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CMB Angular Power Spectrum
CBI
ACBAR
BOOMERANG
DASI
Lineweaver 2003
Frequency (on the sky)
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CMB Sound Spectrum
Click for sound
acoustic
non-acoustic
Lineweaver 2003
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Why so un-musical ?

• With a strong fundamental harmonics, why
• doesnt the CMB sound more like a note or chord ?
• Musical instruments are designed to give pure
  notes.
• ? their P.S. have very sharp peaks

• The CMB gas is not a good resonator
• The fundamental harmonics are broad
• they contain many frequencies
• they dont sound like a note or a chord
• this is obvious with a log (decibel) scale ?

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CMB
fundamental
h a r m o n i c s
C(l)
Cosmic sound spectrum
P(k)
Y axes for both plots are on a decibel
scale (log intensity).
fundamental
Flute
h a r m o n i c s
Flute sound spectrum
0
1
2
kHz
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How does sound get started ?

• Ironically, the Big Bang starts out silent
• only pure expansion no other lateral motion
• however, there are initial density variations
  everywhere
• (these arise from quantum fluctuations amplified
  by inflation)
• As time passes, regions begin to feel their
  surroundings, and gas can begin to move

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The first sound waves

1. gas falls into valleys, gets compressed, glows
   brighter

b) it overshoots, then rebounds out, is
rarefied, gets dimmer
c) it then falls back in again to make a second
compression
? the oscillation continues ? sound waves are
created

• Gravity drives the growth of sound in the early
  Universe.
• The gas must also feel pressure, so it rebounds
  out of the valleys.
• We see the bright/dim regions as patchiness on
  the CMB.

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Sound as diagnostic tool

• The sound of a vibrating object tells you about
  its structure composition.
• eg a wineglass teacup sound differently when
  hit.
• a smaller wineglass sounds higher
• Likewise CMB sound ? Universes properties
• Two examples

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Geometry of the Universe
Open O 0.8
Flat O 1.0
Closed O1.2
Low pitch
High pitch
Long wavelength
Short wavelength
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Geometry ?? Sound Pitch
Region size outstretched hand
The Universes density affects its pitch. How? By
changing the geometry of space. A denser universe
makes space curve more. This bends the light from
the CMB on its way to us like a convex lens, thus
magnifying our view of the patchiness. The
patches appear bigger, with longer wavelengths
and smaller associated frequencies hence deeper
pitch! This effect is in fact more like a
distortion to the sound rather than an actual
change to the waves moving through the gas. The
effect occurs between us and the CMB.
Real Data
Simulated data for different densities
critical flat geometry flat lens medium
blobs medium pitch
high density ve curvature convex lens big
blobs deep pitch
low density -ve curvature concave lens small
blobs high pitch
Affects apparent wavelength of harmonic peaks
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Atomic content of the Universe
8 atoms
4 atoms
2 atoms
Low pitch
High pitch
Long wavelength
Short wavelength
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Properties of the Universe

• Property
  Value Uncertainty
• 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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The cosmic concert hall

• The CMB patterns are not all sound waves, other
  effects are important
• Eg Doppler shifts from moving gas
• Gravitational red blue shifts
• The Universe is not a perfect concert hall
• Carpet drapes deaden high pitches
• Ceiling walls give reverberation
• The pure sound can be recovered by using a
  sophisticated computer simulation (CMBFAST)
• Observed C(l) ? Pure P(k)

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C(l) as observed
P(k) pure/corrected
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A broad note sounds quite different from a pure
tone The difference seems greatest for the lowest
note.
Single tone Pure sine wave
Spread of tones 200 Hz range
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Whats the Chord ?
Between major minor 3rd

(evolves major 3rd ? minor 3rd)
P(k) pure/corrected
P(k) single notes
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Into the fog yet earlier times

• The CMB shows the sound at 380,000 yrs ABB
• What was the sound like before then ?

• We cant see beyond the CMB foggy wall !
• Use CMBFAST to access earlier times

• 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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Evolution of Power Spectra P(k,t)
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Growth of Cosmic Sound
Movie 1
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Growth of Cosmic Sound
Movie 2
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From sound to stars

• Sound waves grow to spawn the first stars, but
• Two serious initial difficulties
• The gas is trapped by the radiation, it cannot
  collapse
• The sound is too quiet, collapse would take 40
  Byr
• Two wonderful solutions
• Gas becomes transparent, no longer trapped.
• Dark Matter has much louder variations
• ? gas free to fall into the dark matter potential
  wells
• Sound quickly evolves
• Becomes much louder 120 dB ? 200 dB by 1 Myr
• Quality changes from deep roar to high pitched
  hiss

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After Recombination
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First 100 Myr
Movie time flow exponential 1s for each 10x
increase in real (big bang) time 0-1s 102-103
yrs 1-2s 103-104 yrs 2-3s 104-105 yrs
3-4s 105-106 yrs, etc Volume level constant
throughout
log frequency x-axis decibel (log) y-axis ( more
technical info)
linear frequency x-axis decibel (log) y-axis
Movie 4
Movie 3
1.7 Mb
1 Mb
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The First Million Years
These two movies also include the increase in
loudness as time passes Time flows linearly in
each. Movie 5 1s 20,000 yr, Movie 6 1s
200,000 yr Both axes are plotted linearly (y-axis
loudness is not decibels) Y-axis scale changes
from Movie 5 to 6 (volume is also turned down for
Movie 6)
Movie 5
Movie 6
const volume
1 Mb
1 Mb
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Quick recap

• The CMB fluctuations show, in part, sound waves
• They are loud deep (110 dB 50 octaves below
  A440)
• Their Power Spectrum has a fundamental
  harmonics
• Shifting up by 50 octaves ? deep rasping roar
• Other kinds of Universe would sound slightly
  different
• Computer simulations allow access to the pure
  sound
• The chord of harmonics is between a major
  minor 3rd
• At earlier times, the sound pitch is higher, so
  the first
• 400,000 years sounds like a decending scream ?
  roar
• After recombination, the gas falls into the dark
  matter
• potential wells ? the sound becomes a deafening
  hiss.
• This short wavelength hiss becomes the first
  stars.

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Sound Waves in the Sky
The CMB Power Spectrum Relative loudness at
different pitch
NASAs WMAP satellite
sound
Loudspeaker
Loudness
Frequency
Wavelength
The Full Microwave Sky
Lower Pitch
Higher Pitch
Water waves on the ocean surface illustrate sound
waves on the CMB surface
short plus medium plus long all mixed together
Microwave brightness, greatly contrast
stretched. Brightness differences are also
pressure differences Patches smaller than 2º are
sound waves
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THE END
http//www.astro.virginia.edu/dmw8f See also
full presentation