Cosmic Music : Sounds from the Infant Universe

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Cosmic Music Sounds from theInfant Universe

• Mark Whittle
• University of Virginia

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Map of the universe this talk

• Our destination is the edge of the universe the
  beginning of time.

• We need to build a bridge from here to there
• Stars, galaxies, clusters, walls/voids ?
  expansion
• Ways to access the past observe it directly (!)

• We can then
• Describe the initial fireball (seen as the CMB)
• Unpack the sound waves, and listen to them !

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Properties of the Universe

• Isotropic (same in all directions)
• Homogeneous (same at all locations)

• Expanding

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Hubble law tells us the Universe ..

• Has no centre
• Will get emptier in the future
• Was denser in the past
• ? its youth was very different
• Was all together 14 Byr ago
• ? it was born in a Big Bang

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Uncovering the Past

• Archeology
• infer the past from the present

2. Watch History Now (?!?) Astronomers
have access to a natural time machine
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HDF
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The Microwave Background
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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Two ways to view patchiness

• Seeds of cosmic structure
• Gravity amplifies density variations
• peaks grow into clusters of galaxies
• troughs grow into voids
• ? computer models of structure formation

• 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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Model evolution of this region Gravity amplifies
density contrasts
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SDSS ? million galaxies
More detailed similation
3 billion light years (20 to the edge)
Our galaxy is here
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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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Power spectra
Sounds are not usually just one frequency, many
frequencies are simultaneously present.
The relative amount (loudness) of each frequency
is called the power spectrum.

• Thus sounds can be graphed in two ways
• waveform pressure vs time (or location)
• power spectrum loudness vs frequency (pitch)

Some examples
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Baroque
Baroque
Modern
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MWB power spectrum Combined binned data
Low frequency
High frequency
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Generating Cosmic Sound

• Shortly after the Big Bang (gt 1 hr), the universe
  contains an expanding, almost uniform gas.
• There are small variations in density from place
  to place (these originate from an earlier time).
• This creates a rough gravitational landscape,
  with
• local highs and lows (hills valleys)
• 4. The gas starts falling away from hills,
  into valleys

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Generating cosmic sound
c) then back in again to make second compression
? the oscillation continues ? sound wave created
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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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Sound as Measuring Tool
Power spectra depend on structure of object e.g.
flute violin playing G have different
P.S. understanding the P.S. ? structure of object
Use cosmic P.S. ? structure of universe.
e.g. WMAP data ( other observations) have
yielded 12 parameters with high accuracy.
Two examples
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Density of the Universe

• Whats the mass of the universe ?
• tricky. if size is infinite, so is mass.
• better to ask what the density is.

• Measure by its affect on the shape of space-time
• ? Mass ( energy) bend space light beams
• Universe acts like a giant lens
• high density convex lens magnify
• critical flat glass same
• low density concave lens de-magnify

• Do the sound waves appear bigger or smaller ?

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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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Atomic content of Universe
1. protons (atomic nuclei) electrons have
inertia exert pressure
2. their abundance affects the efficiency of
rebound ie the higher harmonics
3. compare observed P.S. with models of, low
(2), intermediate (4) , high (8) atomic
content.
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All three
8 atoms
4 atoms
2 atoms
Low pitch
High pitch
Long wavelength
Short wavelength
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Properties from the CMB

• Age of Universe 13.7 Byr
  (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 MWB 380,000yr
  (2)

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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
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