Cosmic Clocks Keep Time in the Search for Gravitational Waves

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By Calla Cofield, Senior Writer

There’s a recurring plot line in science fiction and fantasy stories about clocks that start behaving strangely: In “The X-Files,” digital clocks go haywire and wristwatches show missing time during alien encounters; in “Doctor Who” and “The Magicians,” a clock behaving strangely signals the arrival of a threatening intruder.

With cosmic clocks, an interruption could mean the passing of a ripple in the fabric of space and time.

The clocks in this case are pulsars — objects in the sky that appear to blink rapidly, such as strobe lights. A group of scientists spread out around the world are keeping a careful watch on a handful of pulsars to try to detect those ripples in the fabric of reality, also known as gravitational waves. These pulsar experiments require an incredible amount of patience; some of them have been collecting data for over a decade, and optimistic predictions say it could be another three to five years before they find what they’re looking for.

In February, a U.S.-based experiment known as the Laser Interferometer Gravitational-Wave Observatory (LIGO) made history when it announced the first-ever direct detection of gravitational waves. In June, LIGO announced a second detection, and in what seemed like the blink of an eye, the experiment transformed gravitational-wave astronomy from hypothetical to concrete. Scientists can now use gravitational waves to see powerful and previously invisible cosmic events, such as isolated black holes colliding in space.

But LIGO isn’t the only instrument hunting for these space-time ripples. Just as there are telescopes that search for different wavelengths of light in the universe (such as X-rays, gamma- rays and radio waves), there are searches aimed at finding different frequencies of gravitational waves; those different frequencies would illuminate different objects and events in the universe.

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