Ancient Music : The Sound of Creation

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Ancient Music The Sound of Creation

• Mark Whittle
• University of Virginia

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Themes

1. The early Universe
2. Sound in the acoustic era
3. The Universe as a musical instrument
4. Fun with chord analysis
5. How can we know all this ?!
6. Why scientists are interested in primordial sound
7. Sound creates stars and galaxies
8. In the beginning the sound of silence

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1. The Early Universe
History of the first million years (1st day in
the life of a human)
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The early Universe was radically different
Now
Stars/galaxies Vacuum between
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The Primordial Atmosphere

• Everything spread very uniformly (unlike now!)
• three main constituents light atomic matter
  dark matter

• Light hot gas glows, hence very bright
• ? 109 photons per atom (cf. Earth 1012
  atoms/photon)
• ? pressure of gas dominated by light
• Atomic Matter H He nuclei electrons
• hot ? ionized ? foggy ? lightgas are single
  fluid
• Dark matter 7x denser non-interacting.

• Unusual gas of lightmatter, permeated by a
  denser
• independent substrate of dark matter.

• Cosmic expansion ? cooling, dimming, thinning of
  the gas

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Plot of first Myr
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2. Sound in the Acoustic Era
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Sounds are waves of pressure. (in this case
moving through a gas)
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Volume quiet loud
How much does the pressure vary ?
dP/Po decibels volume
10-9 billionth 15 v. quiet
10-6 millionth 75 noisy
10-3 thousandth 135 deafening
Cosmic sound dP/Po 10-4 ? 110 decibels !
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Pitch deep high
What frequencies can we hear ?
20 20,000 waves per second (Hertz)
v. deep
v. high
Cosmic pitch ?? 1 wave every 20,000
200,000 yrs !! Wavelengths 10,000 100,000 ly
yrs
Too deep to hear, by about 50 octaves!
Hz
1000
600
200
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An Ultra-BassPiano
deeper
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Why is primordial sound so
DEEP?
BIG
Because the Universe is so
Cathedral Organ
Universe
Pan Pipes
lin
400,000 light years
log
First 400,000 years ? 10 seconds Transposed up 50
octaves
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Why does the pitch drop?

• Simple the Universe gets bigger
• Subtle the horizon size gets bigger.
• the sphere in causal contact (c age)

But, why is there sound how is it generated?
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Why is there sound?

• Ironically, the Big Bang starts out silent
• However, there is slight unevenness
• As time passes, regions begin to feel their
  surroundings, and gas begins to fall into denser
  patches (valleys)

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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
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3. Universe as a musical instrument
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Sound Quality (color)

• Most sounds have many frequencies present
• ? relative amount of each ? sound quality/color
• A frequency analyzer can show these
• Lets look at some sound spectra ..

Analyzer

• Noise broad spectrum with all frequencies
• Pure tone single frequency
• Musical note one fundamental many harmonics
• Other sounds complex combination of the above

• What about primordial sound?

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Primordial Sound Spectrum First 400,000 yrs
There are fuzzy harmonics !!
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Why are there harmonics?

• Harmonics usually arise from waves crossing
• a finite structure (eg musical instruments)
• But the Universe is not finite in space
• However, it is finite in time it has a finite
  age
• At time t sound has moved a distance ds vs
  t
• for a valley of size ds, gas has just arrived at
  the bottom
• maximum compression loud fundamental (1st
  harm)
• for a valley of size ½ ds, gas has just got
  back out
• ? maximum rarefaction loud 2nd harmonic
• for a valley of size ? ds, gas bounced back out
  for 2nd time
• ? maximum compression loud 3rd harmonic
• and so on. to make a series of harmonics

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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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Make the cosmic harmonics pure
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Combine raw and clean sounds
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Repeat with exponential time 100 yrs ? 10
million yrs
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22 kHz
Pure Harmonics
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Combine real pure harmonics
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Creations Opening Chord
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The Opening Crescendo
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4. Fun with chord analysis
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Removing the downward slide

• The drop in pitch dominates the sound
• Lets remove it (ie. we expand with the
  horizon)
• ? divide each frequency by the fundamental
• ? set the new fundamental to A220 Hz
• How does this new chord evolve with time?
• As before, do linear exponential times
• Include change in volume
• Explore microtonal vs tempered scales

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microtonal
tempered
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Chord Analysis
All sounds 104 106.5 years
exponential time constant volume
microtonal
tempered
one octave
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Perfectly Harmonic Notes

• Many musical instruments have simple harmonic
  sequences
• e.g. strings air columns fn n f1
• An integral number of waves fit between the two
  ends

• We hear the pitch of f1 while the relative
  strength of all
• the harmonics gives the quality or color

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Inharmonic Notes

• Some instruments have more complex modes of
  vibration
• e.g. drums, bells, bars

• Sometimes, hear a ghost strike tone not
  actually present
• some partials are harmonically related (f nfs)
• We hear fs even if fs isnt itself present

• What is the primordial sound?
• It is basically harmonic, but 1st and 2nd are
  inharmonic
• A ghost strike tone defined by the higher partials

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Inharmonic Fundamental
Primordial Harmonics
raw/pure
1
Ghost strike tone at fs fn / n
pure/even-f1
2
pure/even-fS
3
4
5
6
7
8
High Pitch
Low Pitch
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Reduced Harmonics the Strike Tone
microtonal
tempered
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5. How do we know all this !?
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Witnessing the Big Bang !

• Telescopes are time machines
• look 1000 light-years away, you see 1000 years
  ago
• If we look far enough, we can see the Big Bang !
• It was also a Big Flash
• It is all around us !

What we see
Universe at Big Bang
Universe today
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The Microwave Background
So why isnt the sky very bright ? Because the
Universe is expanding This causes a redshift
red-shift
? Early Universe was hot bright
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Bell Labs (1963)
Observing the Microwave Background (highlights,
there are many others)
COBE satellite (1992)
WMAP satellite (2003)
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Rotate
Flyby
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Sound Waves in the Sky
The CMB Power Spectrum Relative loudness at
different pitch
NASAs WMAP satellite
sound
Loudspeaker
Loudness
Raw CMB sound
Frequency
Wavelength
Lower Pitch
Higher Pitch
The Microwave Sky
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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How does sound get to us ?
Consider listening to a live concert on the radio
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Making the CMB
atomic transparent
we see a glowing wall of bright fog
orange light
microwaves
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CMB is Young and Far
380,000 yr
10
5
Time (Gyr)
14
0
Big Bang
here now
nearby galaxies
HST
CMB
NGST
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Robust Computer Simulations

• The raw CMB sound is limited in two important
  ways
• It only reveals sound at one time (380,000 yrs)
• It contains non-acoustic distortions

Motivated by CMB studies, cosmologists have
created accurate computer simulations of the
early Universe. e.g. CMBFAST by Seljak
Zaldarriaga

• These calculations provide
• Undistorted (pure) acoustic information
• Access to times both before after the CMB
• The CMB spectra of other kinds of universe

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Evolving Sound Spectra
Follow sound spectra forward in time. E.g. from
100 yrs to 100 million years. Here, movie time
flows exponentially 1s for each 10x increase in
cosmic time Volume level constant throughout
just 5 seconds
Movie
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Why are cosmologists interestedin primordial
sound ?
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Sound as diagnostic tool

• The sound of a vibrating object tells you about
  its structure composition.
• ? e.g. a wineglass teacup sound different when
  hit.
• Likewise
• ? different kinds of Universe sound different !
• Use CMB sound to measure Universes properties
• Two examples

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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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7. From sound to stars
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Growth of Structure

• Sound waves grow slowly until fog clearing, after
  which
• pressure is lost ? true sound ceases.
• However, lumpiness continues to grow much faster
  as gas
• falls into the dark matter valleys
• After 100 Myr, rapid collapse begins
• Stars, galaxies, clusters, tapestry, begin to form

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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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Tapestry Formation
After 13 billion years, matter from the CMB era
becomes millions of galaxies. The pattern of
sound waves is written in the tapestry of
galaxies.
SDSS ? million galaxies
Computer Simulations
1Gpc 107 gals 13Gyr 2sec
0.1Gpc 105gals 13Gyr 35sec
3 Billion light yrs
10Mpc 103gals 13Gyr 8sec
Our galaxy here
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8. In the Beginning Quantum Hiss
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The Sound of the Initial Silence

• What struck the cosmic bell to set it
  ringing?
• Sound grows when gas falls across a lumpy
  landscape
• What caused the initial lumpiness?
• This is a deep question we think we now have
  an answer!
• Initial quantum fluctuations are amplified by
  inflation
• seconds after the Big Bang, there are very slight
  variations of density from place to place
  lumpiness
• These lumps grow by gravity, first creating
  sound and
• then all the stars and galaxies!
• Although the Universe is born silent, the
  primordial
• lumpiness is really a latent sound what was it
  like?

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(No Transcript)
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9. Closing thoughts
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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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Why is Nature so comprehensible?
Creation was an exceedingly remote and wild
time. Yet, its story can be told in remarkably
human terms. We talk of light and sound and
even harmonics Isnt this unreasonably
familiar? Should we worry that we are making
the Universe in our own image?
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Because we are a product of it.
I think it isnt a puzzle. Why? Because we have
evolved within Nature not only do our senses
reflect its character, but also (to some degree)
our inner world. Consider sight evolved under
the suns photosphere. But the CMB is also a
photosphere. Both arise when electrons are just
bound to atoms ? Both are visible. Consider
sound much of the Universe is gaseous. Sound is
everywhere inside stars, across galaxies, at
creation and, of course, in planetary atmospheres
where its detection encourages the evolution of
hearing.
Evolving within Nature gives us genuine (though
limited) access to many of its fascinating
stories, including its birth.
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THE END
See also http//www.astro.virginia.edu/dmw8f
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CMB Angular Power Spectrum
Lineweaver 2003
Frequency (on the sky)
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Harmonic Vibrations fn nf1
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Complex Vibrations
Cymbals
Bells
e.g. bells cymbals complex modes usually not
harmonic structure adjusted ? more harmonic
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The ghost strike tone
1
2
3
6
5
4
4
3
5
2
1
A bar vibrates with mode frequencies Fm
(2m1)2 ? this is not harmonic in m (it is
quadratic) ? however m4,5,6 are in ratios
81121161 234 Our ear hears the ghost
fundamental at 1 strike tone
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13.7 Gly
0
The Visible Universe
MW galaxy 20 m class room
MW galaxy 20 m class room
Our Galaxy
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Acoustic peak in galaxy distributions
Excess structures of size 110 Mpc (350 M-lyr)
? 300,000 lyr CMB 1st harmonic stretched 1000 by
cosmic expansion
Degree of clustering
Eisenstein et al 2005
Length scale for clustering
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• During presentation
• For real-time analysis, do
• Noise me hiss/crinkle paper/scratch something
• Pure tone prayer bell, or pull in sound file of
  pure note.
• Harmonic notes play flute guitar string voice
• Inharmonic notes cymbal bell bar
• Resonant objects wine-glass tumbler
  bowl-scrape it.
• Evolving sounds speech slide on
  guitar/slide-flute.
• At volume increase slide, explain
• Growth of dark matter valleys (need to really fix
  that idea earlier)
• After fog clearing gas released by light ? falls
  in, hence
• compression peaks grow while rarefaction peaks
  die
• (aside even harmonics missing in clarinet/oboe
  so flute? oboe)