32 asynchronous metronomes fall into line

October 4, 2012 • 11:40 pm

I shamelessly stole this video from a post by Julianne Dalcanton at Cosmic Variance because it’s so cool. 32 metronomes start out ticking asynchronously, buit miraculously fall into synchrony. Why? It’s based on the platform on which they’re standing, but go to Cosmic Variance to see the answer.

If you’re a physics geek, try to answer by watching the video before you read Julianne’s explanation.

46 thoughts on “32 asynchronous metronomes fall into line”

    1. One version of the steady state theory of the universe has photons falling into step to form particles in interstellar space.
      It explains why the night sky isn’t white.

  3. Isn’t this a (partial) analog to natural selection, where the misfit metronomes (each click is a generation) get weeded out, or at least their non-survival characteristics are suppressed? And the ones that fit (resonate with) their environment survive and spread?

    Does the math of the metronomes match (in some way) the math of population genetics?

    1. I’d have thought natural selection would be subject to too much randomness – in the source of mutation and the coincidental environments that allow any particular mutation to survive.

      Within an individual organism there there are enough potentially synchronous rhythms from the many biological processes, that working in the same organism could have this effect. In the extreme I would see some such ‘coordination’ being the basis of athletes being ‘in-tune’ with their own bodies and their surroundings. This appears to be what’s going on with horse rider and horse, for example.

      And synchronised menstrual cycles? The regulating stimuli might be psychological and chemical, but it seems to be a real effect.

      And religion and other dogmas; and even atheism, and science, … all human endeavours? Why do we have a tendency to get in line with our fellow proponents of our belief systems? Because we get in tune with similar intellectual and emotional stimuli?

      The military seems to be the most conscious and intentional example of human synchronicity.

  4. Could it be the swing of the shelve that causes the synchronization of all metronomes?

    1. Yes!

      I’d say, even before the movement of the shelf is visually obvious, it’s moving with a small imperceptible movement (imposed by whichever colection of metronomes happens to be almost in sync) and this is enough to encourage other metronomes that are almost on the same frequancy and phase to ‘fall into line’.

      And as more metronomes come into synchronisation, so the shelf movement becomes more pronounced and the influence on out-of-sync metronomes gets stronger.

      1. Well, yes, that much is clear from the video. But the question is how exactly does that influence work? What specific physical mechanism acts selectively on out-of-sync metronomes to convert shelf motion into phase-shift to bring them into sync?

        You’re not a true Physics Geek until you’ve answered that question. (My guess is below.)

        1. Your guess looks quite plausible to me (I hasten to add I’m not an expert!). I must admit I was too lazy to try and work out the detailed mechanics of it. Mea culpa.

    2. Yes. This is similar to the swaying of the Millennium Bridge in London.

      That had to be closed for 2 years to fix the resonance effects of whose steps, though obviously uncorrelated, became correlated and caused the bridge to sway. See Wiki for more.

      1. I was going to mention this but you got there first. I immediately thought of the bridge when I saw this and it does indeed seem to be the same effect in action.

        1. It used to be a commonplace that soldiers crossing a bridge would be ordered to “Break step!” because a large number in step could cause the bridge to sway and eventually fall. There was even a cartoon (Punch?) of an officer commanding about four soldiers to “Break step!” while crossing some huge bridge (the Forth, from memory).

          Does anyone know if any bridge anywhere ever has fallen as a result of such marching or is it just an urban myth? (Snopes is silent.)

          (It’s true about the voice and the wineglass, though. Here is a really annoying kid doing it on camera.)

          2. Further to that, there are a lot of wire suspension footbridges in New Zealand that illustrate the resonance phenomenon quite nicely. They have minimal damping. Even one person, walking across at the critical frequency, can start the bridge oscillating like a plucked string. Or, bouncing up and down at certain points along the span will excite particular resonances. (No prizes for guessing how I know this).

    3. Yes. This is similar to the swaying of the Millennium Bridge in London.

      That had to be closed for 2 years to fix the resonance effects of walkers, whose steps, though obviously uncorrelated, became correlated and caused the bridge to sway. See Wiki for more.

  5. Here’s my hypothesis (before looking up the answer):

    Contrary to Galileo, the frequency of a pendulum is not perfectly constant; there’s a small dependency on amplitude. Metronomes that are in sync with the pack tend to have smaller amplitude (because of the contrary motion of the platform) and therefore slightly higher frequency. Those that are out of sync (like the one near the front right corner) get an amplitude boost from the platform’s motion; this slows them down a bit and shifts their phase until they’re in sync with the pack, at which point the amplitude decreases and the frequency increases to keep pace with the pack.

  6. Make sure to check out the simulation codes by Andy Rundquist (in Mathematica) and Paul Gribble (in Python) linked in addenda to Julianne Dalcanton’s original post: short pieces full of insight.

    As it happens, I’m trying to model the influence of local information flow on housing price oscillations in my area, and Andy Rundquist’s code provided one key idea I had been missing.

  7. As a physics geek, I can authoritatively state that the reason for the synchronisation is that God has OCD & has to tweak them all until they match. This also explains why he didn’t want the Hebrews to wear clothes made from differing fibres.
    Man, this theology stuff’s easy!

    1. No, the reason is the same one that makes all females living in the same door room have their periods at the same time. Which is god’s doing, I guess. You win.

  8. Have to post link to the contemporary music classic Poème Symphonique by Györge Ligeti. You have to jump to 5.30 in this link to experince the music, until then there is a talk in Russian/Slavic language I don’t understand.
    Enjoy
    Ligeti Poéme Symphonique

      1. Come to think of it Phase Patterns can be seen as a musical way of describing this phenomenon, couldn’t it?

    3. OK – synchronicity of another kind 😀 My son just returned from school, threw jacket in hall went to the piano and immediately started both our oldfashioned metronomes so now the livingroom is filled with non-synchronising metronome tic-tocs

  9. This video is scary! Marching soldiers comes to mind. From my point of view (leftist Norwegian Chomskyist) this examplifies how little it takes to subvert democracy and manifacture concent …

  11. I think they are obviously watching and listening to each other and are concerned about group pressure.

    indianpeaks-runner.blogspot.com

  12. And toward the end notice the one on the extreme right wing. It is completely out of phase but does eventually come to agreement with its compatriots!

    2. And there I was thinking that the sound track to the video made me think very Orwellian thoughts from about 2 minutes in.

      1. Yes, I noticed that too. There is something very – totalitarian (regimented? militaristic? authoritarian? – plenty of adjectives come to mind) about all those metronomes ticking in unison.

  13. “Tide goes in, tide goes out. Never a miscommunication. You can’t explain that…” C’est tout! 🙂

    I wonder if the number/weight of the metronomes matters–perhaps a critical mass of a variable/constant is necessary for their becoming synchronized. Off to read the explanation now…

    1. The probability of that is 2^32. Order does not occur without an Orderer. It must be Designed.
      Another example of pseudodesign produced through natural principles.
      Thank you Michelle.

  15. What if the metronomes were a variety of types from different manufacturers? What if, instead of 32, there were 4? 16? 50? What if the shelf had more or less springiness?

    Cool experiment! Great metaphor for human behavior.

  16. I immediately had the answer and then started doubting myself. I decided that these simple nudges were not sufficient to produce significant change. Does that remind you of another concept that some find to be counterintuitive?

    1. No, wait. It’s the way the colors are arranged in order. Yeah, that’s it.

  19. This is a great example of the “double thrill” science can provide. #1 is the phenomenon itself (metronome synch-up; Milky Way in night sky; leopard’s spots). Thrill #2 is the study, analysis, and sometime explanation. Certain gauzy-eyed wet blankets (Marilynne Robinson comes to mind) claim #2 sucks all the marvel out of #1. T’ain’t so!

  20. Not quite the same thing, I know, but I used to work in a factory that used big thumpy presses. Sometimes there would be only two presses running at very close to the same speed. I used to find the rhythm interesting as they went into phase together and then gradually went into the opposite and then gradually back again. Of course, in this case the two presses had no effect on one another, it was simply that the speeds were just slightly off.

  22. I’m reminded of some classic films, which reminds mo of how truly fantastic the Internet is, because thes used to be really hard to see.

    Jean Mitry Symphonie Mecanique
    Fernand Leger Ballet Mechanique
    Dziga Vertov The Man With The Movie Camera

    Regarding the physics in this film, a metronome is not just a pendulum; it also has an energy source, either electronic or spring to replace lost energy. I’m not sure how significant ths is, but I suspect if these were simple pendulums (pendula?) they would be dampened fairly soon by the table. The work of moving the table would drain energy from the oscillators. The more a metronome is out of phase with the table, the more work it does, the more its oscillation is dampened. This dampening would slow the angular velocity more if the metronome is out of phase, which would be resisted by the metronomes internal energy, which should tend to shift it into phase with the rocking of the table. This is from the stand point of each metronome, which only interacts with the table, but not directly with the other metronomes. From the standpoint of the table, it is curious what starts it rocking. If you could exactly synchronize two groups of 16 to be precisely 180 degrees out of phase, perhaps the table would not rock at all. The combined randomly phased pendula apply a net average force, which because of all the cancelations of randomly out of phase movements, is just slightly different from zero, just enough to give the table a directional nudge. But this initiates a feedback with the pendula, which want to get in phase with the table as described above, which increases the net force on the table, which increases its amplitude until equilibrium occurs when all the pendula are in phase.

    This could probably be expressed compactly with a few equations, but my physics is way to rusty to go to that length.

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