If you place 32 metronomes on a static object and set them rocking
out of phase with one another, they will remain that way indefinitely.
Place them on a moveable surface, however, and something very
interesting (and very mesmerizing) happens.
The metronomes in
this video fall into the latter camp. Energy from the motion of one
ticking metronome can affect the motion of every metronome around it,
while the motion of every other metronome affects the motion of our
original metronome right back. All this inter-metranome "communication"
is facilitated by the board, which serves as an energetic intermediary
between all the metronomes that rest upon its surface. The metronomes in
this video (which are really just pendulums, or, if you want to get
really technical, oscillators) are said to be "coupled."
The math
and physics surrounding coupled oscillators are actually relevant to a
variety of scientific phenomena, including the transfer of sound and
thermal conductivity. For a much more detailed explanation of how this
works, and how to try it for yourself, check out this excellent video by condensed matter physicist Adam Milcovich.