Post-concert note #1: musical notes and gravitational waves


A few people have asked us about this and the answer is yes: the inspiration for our concert “Lost in the stars … that are aligned” was a scientific discovery and yes, it was mankind’s first-ever detection of gravitational waves in 2015.

Below are a few more details:

  1. The detection. In September 2015, we humans detected for the first time in history something that Albert Einstein has been postulating for exactly 100 years, waves called “gravitational waves” that were produced from the collision of 2 black holes (or neutron stars too). These were detected at both the LIGOs in Hanford, Washington and in Livingston, Louisiana in the US (the event is called “GW150914”).  The measured data supported what was predicted by theory too; it was estimated that the 2 black holes were about 29 and 36 times the mass of the sun, and the collision took place 1.3 billion years ago, with about 3 times the mass of the sun being converted into gravitational waves.
  1. The connection with music. The detected gravitational waves were sound waves that were within the audible range; put in another way, the energy from the collision of black holes does not come out as light but as sound and so we can hear but not see them.  Furthermore, intriguingly, one of the originators of the LIGO that was the instrument with two 4-mile long “arms” set at right-angles to each other that detected the gravitational waves had said, “LIGO covers the same frequency range as the piano”
  1. The significance of 75Hz.  The detection of the sound wave is experienced as a “chirp” – the time interval during which the signal is in the sensitive band of the detector (and hence is visible) corresponds to gravitational wave frequencies in the between 30 and 150 Hz, with that time interval being ~0.2 seconds and increasing in frequency and amplitude in about 8 cycles from 35 Hz to 250 Hz [an audible range].  The orbital frequency of the 2 black holes when they merged was 75 Hz, and at maximum amplitude, the waves (the “gravitational wave frequency”) were around 150Hz.  This is what it (i.e. “the chirp”) sounded like as presented at the LIGO website.
  1. The connection with Rachmaninoff’s Prelude in D. Well, a low D (what’s often called a D2) is at the lower end of the human voice, and has a frequency of ~72 Hz. And the low D is the note on which Prelude in D starts.  And so, here is the piece again – there are no gravitational-wave-style chirps.  (And here’s our pre-concert hommage to Rachmaninoff’s Preludes.)

And the above photo shows the “chirp”.

We hope we answered your question.  In the meantime, thoughts that black holes are singing Bass melodies (30Hz to 250 Hz … totally within the Bass range!) while rotating and merging with each other at high energies is a nice thought though it is true that scientists from antiquity onwards have talked about the music of the spheres (here’s our pre-concert hommage to music about stars)!

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