It has been known if you put several metronomes (set to the same frequency, or same number of ticks per minute) on a movable platform, then no matter how out-of-sync you set them up to be at the beginning, eventually all of the metronomes will tick at the same time in the same direction.
A team of engineers at Saitama University, just outside of Tokyo, lead by Professor Tohru Ikeguchi decided to do an experiment with 24 metronomes. All of them are placed onto a board which hangs from a solid frame by pieces of string. You can see one of the researchers setting off each metronome quite randomly. After two or three minutes, they are (pretty much) in synchronisation.
I’m not a metronome expert, but what I do know is that when one metronome’s pendulum bob swings to the right, the base is pushed to the left (because that’s what Newton’s third law of motion says will happen). The moving base makes the hanging board move left, which then gives the neighbouring metronome’s pendulum bob an extra push to swing to the right. This is how each metronome influences each other. The total effect of the tiny movements created by each metronome on one another will be that they eventually swing in the same direction at the same time. This is true whether it be two metronomes or 24.
If you want to get a better explanation about synchronisation, and how it’s used in real life, here’s a fun TED talk by mathematician Steven Strogatz I found: http://www.ted.com/talks/steven_strogatz_on_sync.html