Sperm manages to defy Newton’s third law of motion
Scientists have been left stunned after learning that sperm seems to defy one of Isaac Newton’s laws of motion.
We all have a basic understanding of sperm — that little tadpole-like cell that swims toward an egg, ready to fertilize it. But what if we told you that sperm can break one of the most fundamental laws of physics?
Kenta Ishimoto, a mathematical scientist, and his team at Kyoto University recently made a jaw-dropping discovery: sperm defy Newton’s third law of motion. According to this law, “for every action, there is an equal and opposite reaction,” meaning forces act in opposition to one another. This is what happens when two marbles collide — they transfer their energy and bounce off each other.
But sperm doesn’t play by these rules.
Ishimoto and his team discovered that sperm can propel themselves through thick, viscous fluids without encountering the usual resistance. Instead of creating a force that pushes back against them, they seem to move without the expected equal and opposite reaction.
To figure out how this happens, the team dove deep into the mechanics of non-reciprocal interactions, studying experimental data on human sperm and modeling the motion of green algae called Chlamydomonas. Their findings challenge long-standing assumptions in fluid dynamics and could open up exciting new avenues of research.
Both sperm and certain types of algae use flagella — the tiny tails — to propel themselves forward. But here’s the fascinating twist: while highly viscous fluids usually sap the energy of most cells, sperm’s flagella seem to defy that by continuing to push them forward.
The researchers found that sperm tails possess what they described as an “odd elasticity.” This unique property allows the flagella to whip through the fluid without losing much energy. But even with this, the propulsion caused by the wave-like motion of the flagella still wasn’t fully explained.
To unravel the mystery, the team introduced a new concept: the “odd elastic modulus.” This term describes the internal mechanics of the flagella as they bend and respond to the liquid around them. Remarkably, this flexibility allows them to bypass the equal and opposite reaction that would normally resist their movement, conserving energy as they go.
In their statement, the researchers explained: “From simple solvable models to biological flagellar waveforms for Chlamydomonas and sperm cells, we studied the odd-bending modulus to decipher the nonlocal, nonreciprocal inner interactions within the material.”
They further clarified, “Odd elasticity isn’t just a term for activity in solids. It’s a well-defined physical mechanism that generates active forces in solids or other systems where generalized elasticity can be defined without needing an elastic potential.” This breakthrough could reshape our understanding of how cells move through fluids and open up new possibilities in physics and biology.
The research team’s breakthrough could have some serious real-world implications. Their findings may pave the way for the development of small, self-assembling robots that mimic living materials. These robots could be used in a variety of fields, including medicine and engineering. Additionally, the discovery may help us understand the underlying principles of collective behavior, potentially informing everything from swarm robotics to the study of how organisms work together in nature.
But as cool as this discovery is, there’s another sperm-related fact that might make you cringe.
Elon Musk, the richest man in the world, is not just known for his ventures in space, cars, and tech—he’s also made headlines for his unique approach to addressing the birth rate crisis. Musk has frequently voiced his concerns about declining birth rates and how it poses a serious threat to civilization.
He tweeted, “A collapsing birth rate is the biggest danger civilization faces by far,” and continued, “Many countries are already well below replacement rate, and the trend is that almost all will be. This is simply a fact, not a ‘debunked theory.’ 2.1 kids is replacement rate, and obviously the world as a whole will soon drop below that point.”
According to a report from The New York Times, Musk has taken his concerns a step further by offering his sperm to friends and acquaintances over the years. While that’s a piece of information most of us would rather not know, it certainly adds a bizarre layer to his already unconventional persona.
