Scientists have observed several microorganisms, including human sperm, moving in ways that contradict Newton’s Third Law.
Specifically, researchers at Kyoto University (Japan) have identified a characteristic known as strange elasticity in various organisms, allowing them to swim without expending energy. This discovery could aid in designing future microscopic robots.
The field of classical physics serves as a pillar for our understanding of the world, based on fundamental laws that describe the behavior of matter at all scales, except at the subatomic level.
Human sperm swimming defies Newton’s Third Law. (Illustration: Futura Science).
In the 17th century, Isaac Newton studied and proclaimed a law that has been considered unshakeable in the realm of physics: Newton’s Third Law.
This law states that for every action, there is always an equal and opposite reaction.
A simple illustration of this law is that if a person exerts force on a wall, the wall will exert an equivalent pressure back, preventing the person from passing through it.
However, physicists have observed phenomena that seemingly do not comply with this law. In this context, the action of pushing an object may not produce an equal and opposite reaction.
This implies a contradiction to what we have always been taught, leading scientists to speculate that there may be situations where forces do not necessarily balance each other.
Algae and Human Sperm
The movement of cells, especially at the microscopic scale, is a complex phenomenon dependent on various factors, including the interaction between the cells and their liquid environment.
The study led by scientist Kenta Ishimoto and his team at Kyoto University highlighted these behaviors in two types of organisms, including human sperm and Chlamydomonas algae.
Although they are vastly different, they share a common characteristic: they use flagella to move.
The research team identified a unique feature of these flagella, which is that they possess “strange elasticity.”
Unlike normal elasticity, which allows an object to return to its original shape after deformation, strange elasticity enables an object to retain some deformation, which is beneficial for movement in fluid.
This strange elastic property is essential for cells as it allows them to move efficiently without wasting energy. In other words, even though the surrounding fluid creates resistance, the strange elasticity of the flagella allows the cells to continue moving with minimal energy loss.
This discovery enables scientists to identify characteristics, adaptations, and evolutionary traits that provide advantages for these microorganisms in their environments, defying Newton’s law.
A tool like this would be invaluable for researchers, facilitating studies, collaborations, and paving the way for many new discoveries in the field of biophysics. The authors believe that these advancements will impact the design of extremely small swimming robots.
