Big Bang Acoustics : The Sound of Creation

1. Big Bang Acoustics :The Sound of Creation Mark Whittle University of Virginia

2. Setting the Stage • Studies of the Cosmic Microwave Background (CMB) • have revealed SOUND WAVES in the early Universe. • It is possible to make this sound audible to humans. • These sounds offer a wonderful opportunity for teaching: • Cosmology: structure formation • Acoustics: science of sound • Music: musical instruments; harmonics; scales • Much of astronomy is visual. • This gives us auditory access to Nature…. and Creation.

3. 1. The Microwave Background Look far away and we see back in time. Look far enough, and you can see the “Big Flash”

4. red-shift Our view of the Universe includes space and time The Early Universe was filled with hot glowing gas

5. 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 = 4ft in 26 mile marathon = 12 hours in human lifetime

6. Observing the Microwave Background Bell Labs (1963) (highlights, there are many others) COBE satellite (1992) WMAP satellite (2003)

7. The Celestial Sphere Optical Sky Microwave Sky Microwave Sky Stretched

8. The CMB Sound Spectrum sound Loudness Frequency Wavelength Lower Pitch Higher Pitch 2. Raw Sound from the CMB • Measure the pressure waves in the CMB: • The amplitudes (Δ P/P) ~ 10-4≡ 110 dB ! • The pitch is 50 octaves below A440 ! • The sound spectrum has harmonics !

9. DEEP? Why is primordial sound so BIG Because the Universe is so: Cathedral Organ Universe Pan Pipes 400,000 light years

10. 7 octaves 7 octaves 7 octaves 7 octaves 7 octaves 7 octaves 7 octaves Transpose up by ~50 octaves = 7 pianos (~7 octaves each) cosmic concerto human concerto deeper An Ultra-BassPiano

11. Bow+string your ears microphone amplifier antenna aerial amplifier speakers radio waves sound sound few 100 miles Listener Concert hall few µsec delay sound waves glow your ears telescope computer speakers light gravity + hills/valleys sound sound microwaves very long way ! Listener Big Bang 14 Gyr delay ! How does sound get to us ? Consider listening to a live concert on the radio:

12. 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

13. Fraction of Baryons (atoms) reality

14. Fraction of Baryons (atoms) reality

15. Total Cosmic Density reality

16. 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%)

17. 4. 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)

19. Into the Fog: Evolving Sound The CMB gives only a snapshot of the sound Use CMBFAST to reconstruct sound from earlier.

20. Evolution of Sound Spectra : P(k,t)

21. The First 400,000 years Movie 1 1.5 Mb

22. Post Recombination: From Sound to Stars • After recombination, pressure drops to ~zero • Cavity oscillations in time cease: true sound dies • However, the roughness grows quickly: • the baryons fall into dark matter “valleys” • the dark matter itself gets more clumpy • after 100 Myr the peaks collapse  stars ! • Continue to create sound from P(k)

23. 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

24. The Growing Hiss 1 3 5 7

25. 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.

26. 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. Log frequency x-axis Log (decibel) y-axis Constant volume Linear frequency x-axis Log (decibel) y-axis Varying (fake) volume Movie 6 Movie 5 1.5 Mb 1.5 Mb

27. The Harmonics 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

28. 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

29. What’s the Chord ? } Between major & minor 3rd C(ℓ) as observed P(k) undistorted P(k) pure tones

30. raw Creation’s Opening Chord pure both

31. All sounds: 104 – 106.5 years exponential time constant volume Chord Analysis microtonal tempered one octave

32. The Opening Crescendo

33. 4×105 yrs raw pure both microtonal tempered

34. 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?

35. Low pitch High pitch Long wavelength Short wavelength

36. 9. 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:

37. 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.

38. http://www.astro.virginia.edu/~dmw8f