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Primordial Sound: Listening to the Big Bang Mark Whittle University of Virginia Outline Our Universe & the Big Bang The Microwave Background Sound in the early universe The birth of the first stars and galaxies In the beginning: quantum hiss The Sun: A Normal Star

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primordial sound listening to the big bang

Primordial Sound: Listening to the Big Bang

Mark Whittle

University of Virginia

outline
Outline
  • Our Universe & the Big Bang
  • The Microwave Background
  • Sound in the early universe
  • The birth of the first stars and galaxies
  • In the beginning: quantum hiss
slide8

Jewel Box

Cluster

Naked eye

stars

Eagle

Nebula

Crab

Nebula

Our Galaxy

Earth = 100 nm = virus

Sun = 10 μm = cell

Earth orbit = ¼ cm = pin head

Solar system = 20 cm = saucer

Nearest star = 250 m = canteen

Solar system

Galaxy Center

galaxies are
Galaxies are

BIG

They contain 100,000,000,000 stars!

A hundred

thousand

million

slide17

SDSS : ⅓ million galaxies

Doppler shifts give galaxy velocities

3 billion light years

(~20% to “the edge”)

Our galaxy is here

slide24

Hubble Deep Field

Small, un-remarkable region: 1500 galaxies!

HST image

HDF

slide26

SDSS &

2dFGRS

HDF

“Nearby”

galaxies

13.7 Gly

0

The Visible Universe

MW galaxy = 20 m = class room

Our Galaxy

the visible universe is
The Visible Universe is

VERY

BIG

It contains 100,000,000,000 galaxies!

A hundred

thousand

million

slide29

Universe at Big Bang

Universe today

14 B yrs

14 B light-yrs

What we

witness

slide30

400,000 years

Big Bang

Very Hot

CMB

3000 K

cooling

ionized

foggy

atomic

transparent

hot glowing fog

we see a glowing

wall of bright fog

We cannot see the Big Bang itself

It is hidden behind 400,000 light years of dense fog

redshift

z=1000

orange

light

microwaves

slide31

Human lifespan

Conc-

eption

child

teenage

Old age

12hr

Marathon race

Finish

26 miles

Start

4 feet

CMB is Young and Far

380,000 yr

5

Time (Gyr)

10

0

14

Big

Bang

here

now

“nearby”

galaxies

CMB

NGST

HST

observing the microwave background
Observing the Microwave Background

Bell Labs

(1963)

(highlights, there are many others)

COBE satellite

(1992)

WMAP satellite

(2003)

slide33

The

Celestial

Sphere

Optical Sky

Microwave

Sky

Microwave

Sky

Stretched

sound waves in the sky
Sound waves in the sky

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

slide36

Sounds are waves of pressure.

(in this case: moving through a gas)

the first sound waves

gas falls into valleys to make first compression

compression

dim

dim

rarefaction

bright

rarefaction

b) it then rebounds out to make first rarefaction

bright

bright

rarefaction

compression

compression

dim

The first sound waves

c) then back in again to make second compression

 the oscillation continues  sound wave created

slide38

What does the CMB “sound” like?

Three important aspects to perceived sound:

A. Volume

B. Pitch

C. Spectrum

Consider each in turn:

a volume quiet loud

dP

Pressure

dP

Po

 volume

Po

Time or position

(A) Volume : quiet – loud

How much does the pressure vary ?

Cosmic sound : dP/Po = 10-4  110 decibels !

b pitch deep high
(B) Pitch : deep – high

What frequencies can we hear ?

20 – 20,000 waves per second (Hertz)

v. deep

v. high

What’s the Cosmic pitch ??

1 wave every 20,000 – 200,000 yrs !!

Too deep to hear, by about 50 octaves!

why is primordial sound so

DEEP?

Why is primordial sound so

BIG

Because the Universe is so:

Cathedral Organ

Universe

Pan Pipes

400,000 light years

c sound spectrum
(C) Sound Spectrum

Sounds usually contain many frequencies

A graph of this is called the Sound Spectrum

Modern Flute

sky maps sound spectra
Sky Maps  Sound Spectra

Cannot follow waves in time.

Instead use the wave’s spatial appearance

Evaluate spatial power spectrum, of waves on the sphere.

“frequency” is spherical angular harmonic: ℓ

peak

trough

Lineweaver 1997

the observed sound spectrum
The Observed Sound Spectrum

fundamental

current best data

×

harmonics

( model)

angular wavelength (degrees)

Sound “Loudness”

sky frequency (~180/°)

sound frequency (Hz)

sound waves in the sky45
Sound Waves in the Sky

The CMB Power Spectrum

Relative loudness at different pitch

NASA’s

WMAP satellite

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

sound as diagnostic
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
geometry of the universe
Geometry of the Universe

Open :Ω= 0.8

Flat : Ω= 1.0

Closed: Ω=1.2

Low pitch

High pitch

Long wavelength

Short wavelength

atomic content of the universe
Atomic content of the Universe

2% atoms

4% atoms

8% atoms

Low pitch

High pitch

Long wavelength

Short wavelength

the concordance model
The Concordance Model
  • Age of Universe13.7 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%)
removing distortion c p k
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)

into the fog evolving sound
Into the Fog: Evolving Sound

The CMB gives only a snapshot of the sound

Use CMBFAST to reconstruct sound from earlier.

harmonics musical form
Harmonics & Musical Form

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

why does it sound so unmusical

fundamental

Flute

Universe

C(ℓ)

h a r m o n i c s

P(k)

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

what s the chord
What’s the Chord ?

}

Between major & minor 3rd

C(ℓ) as observed

P(k) undistorted

P(k) pure tones

slide57

4×105 yrs

raw

pure

both

microtonal

tempered

4 the first stars galaxies
4. The First Stars & Galaxies
  • After fog clearing, matter is free to clump up
    • expansion within each clump halts
    • clumps collapse to make stars…..

then galaxies….. clusters…. tapestry

from sound to stars

1. Sound wave

peak

peak

trough

trough

2. Contrast grows

3. Collapse begins

4. First stars form

no-star

no-star

star

star

From Sound to Stars

100 million years

peaks on peaks on peaks

stars

stars

stars

galaxy

galaxy

galaxy

peaks on peaks on peaks
  • Dark matter clumps of all sizes are randomly distributed
  • The first clumps to collapse are where all peaks coincide : small on top of medium on top of large
    •  stars are born in groups, which are also in groups

short waves

sum

sum

medium waves

long waves

galaxy cluster

first 100 million yrs
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.

Movie 5

slide62

tapestry

clusters

galaxies

stars

Contrast reaches this level after ~100 Myr, when rapid collapse takes over.

Stars/Galaxies/Clusters form from:

small  big wavelengths.

Large scale tapestry

forms from:

1st & 2nd harmonics.

in the beginning quantum hiss
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?

slide64

Low pitch

High pitch

Long wavelength

Short wavelength

6 closing thoughts
6. 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:

john dryden 1687
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 Music’s 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.