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Physics

The laws of physics were broken in 2023 - by sperm

New Scientist's most popular story of the year was about the discovery that sperm break Isaac Newton's third law of motion

By Karmela Padavic-Callaghan

20 December 2023

Take that, Newton

Christoph Burgstedt/Alamy

Breaking the laws of physics is a big no-no – unless you happen to be a sperm. Earlier this year, a team of researchers at Kyoto University in Japan found that microorganisms such as sperm and some algae propel themselves in a way that apparently breaks Isaac Newton’s third law of motion.

These micro-sized swimmers are equipped with long, slender filaments called flagella that jut out of their bodies like hair. These possess…

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