SPERM DEFY NEWTON'S THIRD LAW: SCIENTISTS STUNNED BY ASTONISHING DISCOVERY

 

"For every action (force) in nature there is an equal and opposite reaction"

The fundamental criterion for determining whether an entity is alive hinges on its capability for motion, with Newton's laws playing a crucial role in our understanding of this motion. However, it can be said that sperm cells have disrupted or challenged this traditional perspective, deviating from these established principles.

Numerous phenomena, ranging from balanced rocks to the layout of Seinfeld's apartment and now even human sperm, appear to defy or challenge the laws of physics, particularly Newton's third law of motion. This law states that when one object exerts a force on another, an equal and opposite force is exerted in return. However, this principle seems to be violated by biological swimmers like sperm.

In a recent study, scientists investigated Chlamydomonas algae and human sperm cells, discovering non-reciprocal mechanical interactions, which they term "odd elasticity," that run counter to Newton's third law.

Both Chlamydomonas and sperm cells employ hair-like extensions known as flagella for propulsion. These flagella protrude from the cell, behaving like tails, enabling forward movement by changing shape as they interact with the surrounding fluid. Importantly, they do so in a non-reciprocal manner, meaning their actions do not trigger an equal and opposite reaction from their environment, effectively challenging Newton's third law.

However, the elasticity of the flagellum alone does not provide a complete explanation for how these cells move. This is where the concept of odd elasticity becomes crucial. Odd elasticity permits these cells to wiggle their flagella with minimal energy transfer to their surroundings, which would typically inhibit their motion.

The degree of odd elasticity, expressed as an odd elastic modulus, determines the ability of a flagellum to move without significant energy loss, enabling the cell to move in a manner that seems to defy the laws of physics.

It's worth noting that sperm and algae are not the sole organisms with flagella; many microorganisms have them. Therefore, there may be other rule-breaking instances waiting to be discovered. Understanding and categorizing cells or organisms capable of non-reciprocal movement could have valuable applications, according to the study.

Furthermore, researchers suggest that their approach could have implications for the development of small, flexible robots capable of defying Newton's third law. Additionally, the odd elastic modulus can be computed for any closed-loop system, making it applicable to a wide array of biological data, including active elastic membranes and bulk dynamics.

In this context, breaking the law is not only intriguing but potentially beneficial for various scientific and practical applications.

REFERENCE

Ishimoto K, Moreau C, Yasuda K. Odd elastohydrodynamics: Non-reciprocal living material in a viscous fluid. PRX Life. 2023;1(2). doi:10.1103/prxlife.1.023002