Big Bang Acoustics
Movie and Sound Files for Playing & Download
Left click hyperlink filename to play sound or movie.
Right click to copy file to your own computer.
Sound files are .wav and Movies are .mov (Quicktime) or .mpg (mpeg).
Remember, small "laptop" speakers miss the deeper frequencies, so it is best
to play the sounds over at least the larger type of computer speakers.
First, a small selection of the most important sound and movie files.
Evolving Sounds: the First 100 Million Years
s_1e6_lin_V.wav (313 kb sound) lilili_1e6V.mov (1500 kb movie)
s_1e6_lin_C.wav (313 kb sound) lilgli_1e6C.mov (1500 kb movie)
The first million years. The sound files take the first million
years of cosmic sound and compress it into 10 seconds. The first
allows the loudness to vary (V) correctly (it increases with time), while the
second holds it constant (C). Two Quicktime movies show
slightly different versions of the changing sound spectrum, along with
the changing sound waveform and sky color. (from slide 107).
s_1e8_log_Vfake.wav (376 kb sound) lilglg_1e8Vfake.mov (1600 kb movie)
s_1e8_log_C.wav (376 kb sound) lglglg_1e8C.mov (1800 kb movie)
The first 100 million years. These sound files take the first 100
million years of cosmic sound and compresses the time "exponentially" so
that the first 2 seconds span 100 to 1000 years; the next
two seconds span 1000 to 10,000 years; and so on, with 2
seconds for each factor of 10 increase in time, all the way up
to 100 million years (total of 14 seconds). The true volume increase
is too great to render correctly. Instead, the first version fakes an
increase to illustrate reality (Vfake), while the second keeps the volume
constant (C). Two Quicktime movies show slightly different
versions of the changing sound spectrum, along with the changing sound
waveform and sky color. (from slide 109).
Raw/Pure Sounds: Measuring the Universe
s_cofl_conc_R_5s.wav (157 kb) :
s_cofl_minute_44.m4a (524 kb) :
s_cofl_minute_44.wav (10.8 Mb) :
s_cofl_minute_5s.aif (10.8 Mb) :
The raw sound constructed from the observed angular power spectrum of
the microwave background. This is the fundamental observational basis
for Big Bang Acoustics. In practice, a number of distortions are present
in these raw sounds, which have been removed using a sophisticated
program (CMBFAST) for all but the next two sounds. (from slide 43).
s_curve_three_9s.wav s_bary_three_9s.wav (282 kb each) :
The raw sounds from different types of Universe, calculated using CMBFAST.
The first plays the sound of three Universes of different density --
the densest Universe has the deepest voice, while the middle sound
matches the sound of our real Universe. The second plays the sound
of three Universes with different atomic content : 2%, 4% and 8% of
the total content are atoms (the rest is dark matter and dark energy).
These are more difficult to tell apart, but the middle one (4%) matches
the raw sound of our real Universe. (from slide 58 and slide 61).).
s_CandP_8s_R.wav (251 kb) :
Comparison of the "Raw" sound (calculated from the sound spectrum
of the microwave background) and the "Pure" sound (calculated using
CMBFAST). The pure sound removes many distortions which find their way
into the microwave background and is a much closer match to the true
acoustic sound. In this clip, the raw and pure sounds alternate, with
the raw sound first. [For those in the know, the raw sound comes from C(l)
while the pure sound comes from P(k).] (from slide 71).
Cosmic Music: Replacing the Harmonics.
s_4e5_lin_V_7s.wav & h_4e5_lin_V_7s.wav & hs_4e5_lin_V_7s.wav
h_1e6_lin_NF3mVD.wav & h_1e6_lin_NF3nVD.wav (all are 219 kb):
The first 400,000 years compressed to 10 seconds with varying volume.
The s_ version is the pure (undistorted) sound. This, amazingly, includes
a number of broad harmonics, suggesting the young Universe was behaving
like a musical instrument. However, because the harmonics are broad,
they dont sound like pure tones. To help bring out the "musical nature"
of the sound, one can replace each broad harmonic with a pure tone
of the same pitch and loudness. h_ gives this Musical version. The hs_
version adds these two together, to help our ear hear the harmonics while
keeping its more authentic "rough" form.
s_1e2_1e7_log_C.wav & h_1e2_1e7_log_UCD.wav & hs_1e2_1e7_log_C.wav (862 kb each)
The next two sounds repeat the h_ Musical version but with the downward
slide removed (by fixing the 1st harmonic to the A below concert
A) This now allows our ears to hear the subtly changing chord. The
NF3mVD version has the exact (microtonal) pitches while the NF3nVD
version has the pitches forced to our tempered scale, which gives the
discrete changes as the true tones wander between our tempered notes.
(From Slide 88 which shows the
changing harmonics graphically & musically)
h_1e4_3e6_log_NF3mCD.wav & h_1e4_3e6_log_NF3nCD.wav & h_1e4_3e6_log_NF1nCD.wav (219 kb each)
Essentially exactly the same as the versions above, but for the first
10 million years played with exponential time (2 seconds per factor of
10 in time) and constant volume. There is one additional version (NF1nCD)
which places all harmonics into a single octave, giving a compact chord.
(from slide 83 and slide 85).).
Sounds From The Newborn Universe
This selection includes essentially all sounds and movies from the main narrative ("3b: Full Presentation" found on my
There are 16 themes spanning 168 slides, which is how the files are organized here, with the slide number indicated. A small GIF image of the slide is also
available, as well as a few selected slides which don't have associated
sounds or movies.
1: Introduction & Overview
Slide 7 : s_1e6_lin_C.wav (313 kb):
The sound from the first million
years after the big bang, compressed to 10 seconds (1 second per 100,000 years),
and with the volume held constant.
2: The First Million Years
Slide 11 & Slide 12 & Slide 13
3: The Microwave Background
Slide 22 & Slide 26
4: Cosmic Acoustics
Slide 29 & Slide 47
Slide 34 : clarinet.wav (215 kb) and flute.wav (92 kb) :
The sounds from a Clarinet and Flute playing the same note. The difference
in sound is visible in the two sound spectra. (Taken from Joe Wolfe's
work at UNSW).
5: The CMB Sound Spectrum
Slide 43 : s_cofl_conc_R_5s.wav (157 kb) :
The raw sound constructed
from the observed angular power spectrum of the microwave background.
Slide 44 & Slide 45
6: Origins of Cosmic Sound
Slide 50 & Slide 51
7: Using Sound to Measure the Universe
Slide 58 : c_curve_50_150.wav (313 kb) :
A sequence of raw sounds for Universes spanning a range of density,
from 50% of "closure" density, to 150%. The denser Universes have the
deeper voice. The true Universe seems to have exactly the closure density,
ie 100%. The power spectra were calculated using CMBFAST --
the computer simulation of the early universe.
Slides 60 & 61 : c_bary2C_10_90.wav and c_bary1_2_10.wav (313 kb each) :
Two sequence of raw sounds for Universes spanning a range of atomic
content. The first sequence spans the range 10% to 90% of the "closure"
density in atoms. The second spans the range 2% to 10%. The true Universe
has 4% atomic content.
8: Removing Distortion: From C(l) to P(k)
Slide 66 & Slide 69
Slide 71 : s_CandP_8s_R.wav (251 kb) :
Comparison of the "Raw" sound (taken directly from the power spectrum of
the microwave background) and the "Pure" sound (calculated using CMBFAST).
The pure sound has now removed many distortions which find their way
into the microwave background. It is a much closer match to the true
acoustic sound. In this clip, the raw and pure sounds alternate, with
the raw sound first.
Slide 72 : spike_200_both.wav & spike_600_both.wav & spike_1000_both.wav (251 kb each) :
Comparison of pure frequency and spread of frequencies, centered on 200 Hz; 600 Hz and 1000 Hz. This shows how a range of frequencies makes an indistinct note. Similarly, the cosmic harmonics don't sound like notes to our ears because
they too contain a spread of frequencies.
9: Evolving Sounds
Slide 75 : s_z1050_t4e5_4s.wav & s_z3400_t5e4_4s.wav & s_z26000_te3_4s.wav (126 kb each) :
Pure cosmic sounds from three different times: 400,000 years; 50,000 years;
1000 years. Earlier times have higher pitches. (The z values in the names
signify the redshift corresponding to the time, ie by what factor the Universe
Slide 77 : lilili_4e5C.mov (1400 kb movie) :
Quicktime movie showing the changing sound spectrum across the first 400,000 years, together with the changing sound waveform and sky color. Bars at the
top allow you to follow the changing cosmic size and time.
Slide 78 : bar_linF.mov (362 kb movie) & s_4e5_lin_C.wav (313 kb matching sound)
bar_linW.mov (381 kb movie) & s_4e5_lin_V.wav (313 kb matching sound)
Quicktime movies of the same time period (first 400,000 years) but showing
just the sound spectrum, with a simple bar crossing to track time. bar_linF uses frequency, while bar_linW uses wavelength to plot the sound spectrum.
The accompanying sounds are also given as a separate files. lin_C plays
the sound a constant volume, while lin_V follows the true change in volume
(the volume increases as time passes).
10: Fun with Chord Analysis
Slide 80 & Slide 82
Slide 81 : spike_z1700_all_three.wav (438 kb) :
Compares Raw, Pure, and Musical versions of the sound from about 300,000
years. The Raw and Pure versions were played in slide 71. The Musical
version has replace all the broad harmonics with single tones of the
appropriate frequency and loudness. This renders the sound suitable
for our ears, since we don't discern notes from broad harmonics (see
slide 72). The Musical version is essentially a chord with a number of
interesting intervals in it, including a major third and a minor third.
Slide 83 : s_1e2_1e7_log_C.wav & h_1e2_1e7_log_UCD.wav & hs_1e2_1e7_log_C.wav (862 kb each):
Three versions of the first 10 million years of sound, played with an
exponential time such that 2 seconds elapse for the intervals: 100 to 1000
years, 1000 to 10,000 years, 10,000 to 100,000 years, etc. In all cases
the volume has been held fixed (otherwise the latter times would drown
out the earlier times). s_.wav gives the "Pure" sound, with distortions
removed (using CMBFAST) but keeping the broad harmonics. h_.wav gives
the Musical sound, where the first 8 harmonic peaks have been replaced
by pure tones. hs_.wav has added these together so that one hears both
the natural sound as well as the hidden harmonics. Related versions, but
with the downward slide removed are given in slide 85.
Slide 85 : h_1e4_3e6_log_NF3mCD.wav & h_1e4_3e6_log_NF3nCD.wav & h_1e4_3e6_log_NF1nCD.wav (219 kb each):
Three Musical versions (ie harmonic peaks replaced by pure tones) of
the period 10,000 to 3 million years, played with exponential time as
in slide 83. In these versions the downward slide in pitch has been
removed (by anchoring the first harmonic to 220 Hz), allowing
our ear to hear the subtle changes in the chord. NF3mCD gives the
"microtonal" version, which means that the true frequencies relative to
the lowest harmonic are reproduced exactly. In this case, tones which
are not on our musical scale are included. The NF3nCD version
forces all tones to be played at the pitch of the closest note in our
musical (tempered) scale. These notes change abruptly as the slowly
drifting harmonics shift closer or further from specific tempered notes.
The NF1nCD version also uses the tempered scale, but puts all harmonics
into a single octave, making a compact chord. In all these versions,
the overall volume has been set to a constant, though the loudness of
the individual harmonics has been allowed to vary appropriately (eg, for
reasons explained in the Presentation, the even numbered harmonics
gradually get weaker after about 200,000 years, and by 1 million years
have essentially gone).
Slide 88 : s_4e5_lin_V_7s.wav & h_4e5_lin_V_7s.wav & hs_4e5_lin_V_7s.wav (219 kb each):
The same as slide 83, but for the first 400,000 years with normal
(linear) time and a (correctly) varying volume. As before, the s_
version is the pure (undistorted) sound with broad harmonics. h_ gives
the Musical version, with broad harmonics replaced by pure tones, while
the hs_ version adds the two together.
Slide 88 : h_1e6_lin_NF3mVD.wav & h_1e6_lin_NF3nVD.wav (219 kb each):
The same as slide 85 but for the first 400,000 years at linear (normal)
time and with varying (increasing) volume. Once again, the downward
slide has been removed to allow our ears to hear the subtly changing
chord. The NF3mVD version has the exact (microtonal) pitches while
the NF3nVD version has the pitches forced to our tempered scale. In
these examples, the volume changes correctly, both overall and for the
individual harmonics. (A single octave version wasn't made).
11: From Sound to Stars
Slide 102 & Slide 103
Slide 98 : s_z1100_baryons.wav & s_z1100_cdm.wav (126 kb each):
Pure (undistorted) sound for the atomic matter (baryons) and dark matter
(cdm) around the time of the microwave background (400,000 years).
Of course, the dark matter doesn't generate true pressure waves,
but this sound has been constructed in the same way as for the atomic
matter, from the spectrum of density variations. The dark matter has
not been subject to the high pressure forces of radiation, and so it
has been able to clump up on very small scales which gives yields the
high pitches giving the hiss. Furthermore, because the dark matter has
not participated in any pressure oscillations, its spectrum contains no
harmonics, hence the hiss is similar to that of "white noise".
Slide 100 : s_z1050_t4e5_4s.wav & s_z400_t2e6_4s.wav & s_z150_te7_4s.wav (126 kb each):
Pure (undistorted) sound for times after the microwave background,
when the atomic gas is free to fall into dark matter clumps, inheriting
its increasingly loud white noise hiss. (The three times are 400,000;
2 million; and 10 million years). In truth, during these later times,
the atomic gas has lost most/all its former pressure and so it does not
sustain pressure (sound) waves. However, its density structure continues
to evolve, and this is what's been used to create these late-time
12: The First 100 Million Years
Slide 106 & Slide 108
Slide 107 : lilgli_1e6C.mov (1500 kb movie) & s_1e6_lin_C.wav (313 kb matching sound)
lilili_1e6V.mov (1500 kb movie) & s_1e6_lin_V.wav (313 kb matching sound)
Quicktime movies of the evolving sound spectrum for the first 1 million
years, including the changing sound waveform and sky color. Time unfolds
linearly (normally) in both. The first (lilgli) plots log-loundess
(decibels) and plays the sound at constant volume, while the second
(lilili) plots linear loudness and plays the sound at (correct) varying
volume. The accompanying sounds are also given separately.
Slide 109 : lilglg_1e8Vfake.mov (1600 kb movie) & s_1e8_log_Vfake.wav (376 kb matching sound)
lglglg_1e8C.mov (1800 kb movie) & s_1e8_log_C.wav (376 kb matching sound)
Quicktime movies of the evolving sound spectrum for the first 100 million
years, including the changing sound waveform and sky color. Time unfolds
exponentially in both (2 seconds for each factor of 10 starting at 100
years). The first (lilglg) has a linear frequency axis while the second
(lglglg) has a logarithmic frequency axis. The true volume changes too
much to render, so a "faked" varying volume is given to the first, to
give the feel for the extreme increase in volume. At the end of this
time period, 100 million years after the Big Bang, the first generation of
stars is about to be born.
13: Expanding Horizons
14: Quantum Hiss
Slide 119 & Slide 123 & Slide 125 & Slide 127
Slide 129 : s_prim_IPS_4s.wav & s_prim_steps_pofk_N_6s.wav (126 & 190 kb):
The so-called "Initial Power Spectrum" (IPS) rendered acoustically. This
is the spectrum to emerge from inflation and provides the template for
all future development of sound and structure. Only as time passed, and
causal horizons moved out, could the gas begin to form sound waves. So
this sound is really a "latent" sound, waiting to emerge. The second
sound file illustrates the response of the Universe, after 400,000 years,
to this initial spectrum. After repeating the IPS sound, we then hear the
dark matter and the atomic matter. Both have had their higher pitches
supressed, though for rather different reasons -- the dark matter only
experiences the supression associated with perturbations entering the
horizon, while the atomic matter has also experienced a high radiation
pressure which prevents significant compression. Thus, the dark matter
is transformed into a less shrill hiss, while the atomic matter is deep
and laced with harmonics.
15: The CMB Microscope
Slide 132 & Slide 133
16: From Sound to the Present
Slide 138 & Slide 139
Slide 144 : movie7_bate_large.avi (54 Mb avi video)
WARNING this is a large, 54 Mega-byte, file. It shows a computer
simulation of the formation of a star cluster, and illustrates the kind
of processes that might have ocurred 100 million years after the Big Bang
during the birth of the first stars. The simulation is by Matthew Bate.
Slide 148 : movie8_group_merge.mpg (2.4 Mb mpeg movie)
WARNING this is a moderately large, 2.4 Mega-byte, file. It shows a
computer simulation of several galaxies merging, and illustrates the kind
of processes that might have been common in the first two billion years
after the Big Bang. The simulation is by Lars Hernquist (I think?!).
Slide 151 : movie9_cluster.mpg (900 kb mpeg movie)
This shows a computer
simulation of the formation of a large galaxy cluster. The simulated duration
is the entire age of the Universe, starting from an almost uniform distribution
of material. In this simulation, only the dark matter is followed, but it
also illustrates roughly how the stars would also collect. The simulation
is by (yikes, I cant' remember, sorry).
Slide 154 : movie10_LSS (400 kb mpeg movie)
This shows a computer simulation of a giant region, several billion
light years across, containing millions of galaxies. The brief movie
spans the full age of the Universe, and shows the formation of "Large
Scale Structure" -- the Tapestry of galaxies that fills the present
day Universe. Recently, the structure of the tapestry has been analysed
and the wavelength of the deepest harmonic has been found, a relic of
the acoustic era, 14 billion years ago. The simulation is by (yikes,
I cant' remember, sorry).
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