D3 Gravitational Waves

Topic

The key element of this model is the interferometer that detects the passage of a gravitational wave.

Ground-based laser interferometers detect the passage of such a wave by measuring the minute stretching and differential compression it exerts on two perpendicular arms several kilometers long; the sheer smallness of this effect—a change in length far smaller than an atomic nucleus—is precisely why the first confirmed detection (the merger of two black holes) did not occur until 2015, a full century after these waves were first predicted.

Since then, dozens more merger events have been cataloged, each identified by the same characteristic signature: a rising frequency—a "chirp"—as the two compact objects draw closer together in the final moments before merging.

A future space-based detector will extend this detection principle to much lower frequencies, enabling the observation of supermassive black hole mergers that ground-based detectors cannot capture; this is because Earth's own vibrations and the finite length of their arms limit ground-based detectors to higher frequencies. Thus, from the interferometer measuring the wave's passage—with which this document begins—to the future space-based detector with which it concludes, and taking in the first confirmed detection and the characteristic "chirp" of each merger, gravitational wave detection transforms a tremor in spacetime itself—smaller than an atomic nucleus—into a signal that can be cataloged, counted, and studied time and again.

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