The Surprising Secret of Synchronization

The second law of thermodynamics tells us that everything in the universe tends towards

disorder. And in complex systems, chaos is the norm. So you'd naturally expect the universe

to be messy. And yet, we can observe occasions of spontaneous order, the synchronization

of metronomes, the perfectly timed orbits of moons, the simultaneous flashes of fireflies,

and even the regular beating of your heart. What puts these things in order in spite of

nature's tendency for disorder.

London was opened to much excitement. But as crowds filled the bridge, it began to wobble

back and forth. Police started restricting access to the bridge, but that only resulted

in long lines to get on the wobble was unaffected. Two days later, the bridge which had cost

18 million pounds, was fully closed, and it wouldn't reopen for another two years. So

what went wrong?

Well, it's long been known that armies should break step when crossing bridges. This dates

back to an accident in 1831. When 74 men from the 60 of Rifle Corps were marching across

the Broughton suspension bridge in northern England. It collapsed under their synchronized

footsteps. 60 men fell into the river 20 of whom suffered injuries like broken bones or

concussions. Luckily, no one was killed. But after this, the British Army ordered all troops

to break step when crossing bridges.

Now look at the people walking across the Millennium Bridge. Most of them are walking

in step with each other. But they are not part of an army. They're random members of

the public so why are they walking together? And why couldn't a modern bridge designed

for heavy pedestrian traffic handle this? Well, to understand it, we have to go back

350 years.

In 1656, famous Dutch physicist Christian Huygens created the first working pendulum

clock. The goal was to help sailors figure out where they were on the globe. Latitude

can be judged by measuring the position of the sun or stars. But for longitude you also

need to know the time at some fixed location, say your home port. But clocks at the time

were routinely out by around 15 minutes a day. So they were effectively useless. wagons

pendulum clocks by contrast, were accurate to around 10 to 15 seconds per day. Huygens plan

was to attach his clocks to a heavy hanging mass on the ship, so they wouldn't get tossed

around by the rolling seas. His plan called for two clocks in case one stopped or was

damaged.

But testing out this arrangement while at home sick in February 1665. He made a remarkable

discovery. To have his clocks hung from a wood beam across some chairs. Watching the

pendulums sway back and forth for hours. He noticed after half an hour or so they would

spontaneously synchronize. As one clock swung one way, the second would swing the other

way. As one would tick, the other would talk.

So he tried disturbing the clocks. He set them ticking out of sync but again, within

30 minutes or so they were back to the same lockstep. Wiggins thought this strange sympathy

of clocks must have been caused by air currents between the pendulums, so he placed a large

board in between them, but their clocks continued to sync up. It wasn't the air currents.

When he separated the clocks, the synchrony would disappear, their times drifting apart.

But when he brought them back together, the synchrony returned. Wiggins realized the two

clocks were synchronizing because they were hung from the same wood beam. He transferred