Australian scientists have discovered that light isn’t quite as fast as it used to be.

In October, 1971, American physicists took four super-accurate atomic clocks, kept two on the ground and put two on commercial jets flying at 1000 kmh in opposite directions around Earth.

When the planes landed, the scientists found what they were hoping for: The clocks on the high-speed journeys were ticking a few billionths of a second behind their stationary friends.

Motion, it turns out, slows time – one of the funny effects of the law of relativity. At low speeds, the effect is slight and makes no difference to our daily lives.
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