SCIENTIFIC INSTRUMENTS THAT CAN DETECT GRAVITATIONAL WAVES. This article on the sciencemag website by Adrian Cho announces the observation of a gravitational wave, a phenomenon which was predicted by Einstein’s general theory of relativity but had never been observed until five months ago. Cho describes gravitational waves as “ripples in the fabric of space and time”.

I don’t have a chance of understanding what this means, but I can understand the immense scale of the scientific effort—both in terms of how big are the distances of the two black holes whose collision is studied and of how small is the phenomenon that is studied.

How large: The collision of the two black holes took place about 1.3 billion years ago.

How small: The Laser Interferometer Gravitational-Wave Observatory (LIGO), a pair of gigantic instruments in Hanford, Washington, and Livingston, Louisiana, “sensed a wave that stretched space by one part in [ten to the 21st power—or 1 with 21 zeros after it], making the entire Earth expand and contract by 1/100,000 of a nanometer, about the width of an atomic nucleus”.

Robert Lee Hotz in the Wall Street Journal (February 12) made a different comparison: Even before a recent (and crucial) improvement, the instruments could find “distortions in local space-time as small as [one thousandth] of the diameter of a proton—equal to measuring the distance from Earth to the nearest star outside the solar system to within the width of a hair”.

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