Big Bang Acoustics: Movie and Sound Files


Welcome, from the New York Times Site

If you have arrived from the NY Times site, there is a fuller account of Big Bang Acoustics, one level up on my  Homepage

Play &/or Download Sound & Movie Files

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). Remember, small "laptop" speakers miss the deeper frequencies.
The sound & movie order follows the "3b) Full Presentation" on my homepage.

1) first1Myr.wav   (0.5Mb, from slide 6): The sound from the first million years after the big bang, compressed to 5 seconds (1 second per 200,000 years), and with the volume held constant.

2) CMB_CofL.wav   (0.5Mb, from slide 34): the simple sound from the angular power spectrum of the microwave background, as seen on the sky.

3) geometry_seq.wav (0.74Mb, from slide 49) : the sound from three different universes spliced together to hear the change in sound. These are an underdense (open); critical density (flat) and overdense (closed) universe. The power spectra were calculated using CMBFAST -- the computer simulation of the early universe.

4) atom_seq.wav (0.73Mb, slide 51) : as above but for three universes with different amount of atomic matter (baryons), again spanning the "correct" value of 4%.

5) pure_PofK.wav (0.43Mb, slide 61, lower) : the "observed" sound (CofL) corrected for all the various kinds of distortions -- again using CMBFAST to extract the power spectrum. This pure sound is called P(k) ie "PofK". The epoch at which this P(k) has been evaluated has been chosen to roughly match the spacing and relative amplitude of the integrated curve Cof L.

6) (3.9Mb, slide 67) : a quicktime movie which simply moves a horizontal bar down the figure to show which part is generating the sound at any given instant. The sound sequence is from 100 years after the Big Bang, up to recombination, at about 400,000 years. The figure shows the peaks of the power spectum (red is loud, blue/black is quiet), with frequency horizontally and time running down from top to bottom.

7) movie1_sound.wav (0.34Mb, slide 67) : the sound file separate from the movie.

8) (4.1Mb, slide 68) : as above, but with the x-axis flipped to show wavelength, rather than frequency, and the y-axis now portraying the SIZE of the Universe, from zero up to 0.1% of current size. The sound sequence is arranged so that sound-time increases proportionally to the size.

9) movie2_sound.wav (0.34Mb, slide 68) : The sound file for movie2.

10) pure_notes.wav (0.43Mb, slide 71, lower) : an artificial sound with each harmonic in P(k) replaced by a single frequency (a spike in the sound spectum). This removes the acoustic "blurring" caused by having a fat spike, which our ears tend not to hear as a single note. In a sense, this sound is the "note" or "chord" that the universe is playing at the time of recombination (ie when we see the sound on the microwave background). One can follow the descending note/chord in time, as in slide 73 ( harmV7v.wav 0.62Mb); or keeping the fundamental fixed so the chord is easier to recognize, as in slide 75 -- either keeping the full 3 octave spread ( harm7v3n.wav 0.22Mb, or repacked into a single octave harm7v1n.wav 0.22Mb).

11) (1.0Mb, slide 94, left) : the first 100,000 years played forward in proportional time, with the volume increasing as it should (earlier sounds are either constant because they are just a single power spectrum, or because the actual change in volume is so great that it would be difficult to hear properly). The graph is essentially the same as in movies 3 and 4, but this time with the y-axis plotted linearly. Now it is easier to see the evolution of the separate harmonics.

12) movie3_sound.wav (0.43Mb) : goes with movie3

13) (1.1Mb, slide 94, right) : similar concept to movie3 but covering the time period 100,000years up to 1 million years. Again the sound volume is allowed to increase. In this case, it is very obvious how the sound volume grows soon after recombination, when the gas has been released by the radiation and is free to follow the dark matter. Notice that the starting volume of this SHOULD be the same as the ending volume of movie5 (they are both at 100,000 years). Obviously, to follow the later increase in volume the whole volume level of movie6 has been decreased significantly relative to movie3.

14) movie4_sound.wav (0.43Mb) : goes with movie4

15) movie4_const_sound.wav (0.43Mb) : also goes with movie4 but this has been created at constant volume, suppressing the large increase in volume at the end to allow one to hear the earlier sounds as we move through the interesting period of recombination.

16) (1.0Mb, slide 96, left) : This plays the sound from the big bang forward for the first 100 million years (way past recombination, almost up to the formation of the first stars). The movie shows a graph of the atomic gas power spectrum (green) and the cold dark matter power spectrum (purple) evolving with time. The x-axis is LINEAR in frequency (arranged for the human range) but the y-axis is LOGARITHMIC (which for sound, matches the decibel scale). In this movie, the sound is played in such a way that as each second passes the "real" time interval increases by a factor of 10. This allows one to follow both very short time intervals at the beginning (eg alot happens in the first 10,000 years), but also when things slow down (eg things happen more slowly in the last 90 million years). One sees the atomic gas powerspectrum grow after recombination as the gas falls into the gravitational valleys generated by the dark matter. (Strictly speaking, the post-recombination hiss is not truely acoustic -- but here we've interpreted the spatial power spectrum as a temporal power spectrum)

17) (1.7Mb, slide 96, right) : as above, but with a log frequency axis. This graph is essentially the same, but has been labelled in a more technical way (preserving the original spatial frequency parameter "k" and noting that the y-axis is in fact k**2P(k).

18) movie3and4_sound.wav (0.5Mb, slide 89, center) : the sound file which plays with both movies 3 and 4.

19) primordial3IPS.wav (0.13Mb, slide 116, top) gives the 3-D "sound" of the initial power spectrum -- the fluctuations that came from the pre-inflation quantum world. These are frozen in place shortly after the big bang and so do not oscillate like true sound waves, so here I've cheated and released them all simultaneously. These same fluctuations can also be seen on the CMB on scales larger than a few degrees, and the projected "sound" of these is here : primordial3flat.wav (slide 117, 0.13Mb).


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