At least 3,700 years ago, Babylonian mathematicians approximated the ratio o
f a circle’s circumference to its diameter. They inscribed their answer, th
e first discovered value of pi, on a humble clay tablet: 25/8, or 3.125. Now
Carl-Johan Haster, a theoretical astrophysicist at the Massachusetts Instit
ute of Technology, has managed to do almost as well: in a study uploaded to
the preprint server arXiv.org, he measured pi to be about 3.115.
In the intervening years, researchers have calculated the true value of the
ratio to a modest 50 trillion decimal places with the aid of powerful comput
ers (you probably know how it starts: 3.141592653 … and on into infinity).
Haster’s approximation of it may be a couple of millennia behind in terms o
f accuracy, but that fact is of little relevance to his real goal: testing E
instein’s general theory of relativity, which links gravity with the dynami
cs of space and time.
Information about the laws of physics is effectively baked into gravitationa
l waves, the ripples in spacetime created when massive objects such as black
holes spiral into one another. Haster, a member of the Laser Interferometer
Gravitational-Wave Observatory (LIGO) Scientific Collaboration, noticed pi
appeared in several terms of an equation describing the waves’ propagation.
https://www.scientificamerican.com/article/pi-in-the-sky-general-relativity-passes-the-ratios-test/
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