Portuguese scientists discover why pendulum clocks swing together

Pair of physicists bust a 350-year-old conundrum in a report that proposes a transfer of energy through a sound pulse causes clocks to synchronise

Almost 350 years ago, Dutch inventor and scientist Christiaan Huygens observed that two pendulum clocks hanging from a wall would synchronise their swing over time.

What causes the phenomenon has led to much scientific head-scratching over the centuries, but no consensus to date.