"Human sperm cells don't think about Newton's third law of motion, and scientists don't know why" seems like an oversimplification of the complex biological and physical processes involved in sperm motility.

 

Newton's laws of motion have revolutionized science and have stood the test of time, being applicable in most situations, with some exceptions appearing on the microscopic scale and when matter approaches the speed of light. However, a confusing scene unfolds within our own bodies, where Newton's third law seems to break down.

Consider human sperm cells, with their distinctive features—a blob-like head and an unusually long tail. Despite their appearance, these tiny entities seem to defy the laws of physics by their very existence.

Both human sperm cells and the Chlamydomonas algae propel themselves through the motion of waving their tails or flagella. This seemingly inexorable movement puzzles physicists because, in theory, the surrounding fluid dissipates all the energy these cells expend, essentially immobilizing them.

The secret to their motility lies in the inherent elasticity of their shape-changing flagella. This remarkable property defies Newton's third law, enabling them to move without losing significant amounts of energy to their environment. This phenomenon is known as the 'odd elastic modulus', a relatively new concept that was introduced to the scientific community around 2019 to explain these microscopic interactions.

The precise mechanisms that drive these agile swimmers are shrouded in a complex process of evolution. Understanding and calculating the elastic modulus peculiar to different microorganisms can shed light on what enables them to operate outside the limits of Newton's laws. Furthermore, this knowledge could prove invaluable to scientists seeking to develop soft, elastic robots capable of using this "non-reciprocity" for innovative applications..