Science past and present

Tom Siegfried



‘Gravity waves’ is an OK way to refer to gravitational radiation

gravitational waves illustrated

Scientists announced February 11 that they have detected the ripples in spacetime caused by a black hole merger, regardless of whether you call those ripples “gravitational waves” or “gravity waves.” 

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It’s OK to call them “gravity waves.”

Purists insist that the spacetime ripples just discovered by the Advanced LIGO observatories should be called “gravitational” waves. Which in itself is just a shorthand way of saying radiation of gravitational energy via oscillations in the fabric of spacetime. Further shortening that to “gravity wave” is considered by some to be scientifically illiterate, because “gravity wave” is already taken by scientists who study fluid mechanics. In that context, “gravity wave” refers to disturbances in fluids that occur when two fluids meet or layers of different densities (such as in the atmosphere) come together.

For some people unfamiliar with the concept of homonyms, the use of “gravity wave” in fluid mechanics renders illicit its use to describe gravitational radiation. On the other hand, it’s a general rule of good writing to use no more syllables than necessary. Besides, there’s plenty of justification for using the “gravity” shorthand.

Merriam-Webster’s collegiate unabridged dictionaries recognize the astrophysical meaning of gravity wave, for instance. Physicists often use the phrase in casual conversation. And while “gravitational wave” is more common in the scientific literature, plenty of published papers use the shorter form. You can find it in papers published in Astrophysical Journal Letters, for instance, or Physical Review D, or even Physical Review Letters. And the late John Archibald Wheeler, America’s foremost expert on general relativity in the 20th century, once wrote a book with a whole chapter titled “Gravity Waves.”

So if you encounter anybody who chastises you for saying “gravity waves” because the phrase also has a meaning in fluid mechanics, tell them to spend eight minutes listening to Led Zeppelin’s “Stairway to Heaven.” ’Cause you know sometimes words have two meanings.

Follow me on Twitter at @tom_siegfried

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