The question of whether a cat is a liquid has moved beyond a simple internet meme and into the realm of scientific curiosity. The visual evidence of a cat seemingly pouring itself into a vase, a sink, or a small box challenges our everyday understanding of physical states of matter. This common observation of felines adapting their shape to fill any container suggests a fluidity that appears to defy the properties of a solid body. The intriguing visual phenomenon sparks a genuine inquiry into the physics of materials and the unique biological adaptations of Felis catus.
The Scientific Definition of a Liquid
Physics defines matter by its behavior in terms of shape and volume. A solid is characterized by a definite shape and a definite volume, resisting changes to both unless subjected to significant force. Liquids, by contrast, possess a definite volume but no fixed shape. The molecules within a liquid remain close together, which maintains a constant volume, but they can move around one another, allowing the substance to conform precisely to the shape of its container. Liquids are also considered nearly incompressible, meaning their volume changes very little even when under high pressure. Gases, unlike liquids, have neither a fixed shape nor a fixed volume, expanding completely to fill any vessel they occupy. Therefore, to be classified as a liquid, any material must meet the criterion of adopting the container’s shape without changing its own volume.
Feline Flexibility and Physical Adaptations
The appearance of liquidity in cats is rooted in their specialized anatomy, which allows for extreme flexibility. A cat’s skeletal structure includes several adaptations that enable its seemingly fluid movements and contortions. Cats possess a greater number of vertebrae than humans, including extra lumbar and thoracic vertebrae, which contributes significantly to their spinal mobility. The joints between these vertebral bones have elastic cushioning discs, giving the spine an enhanced range of motion and allowing the cat to twist its body nearly 180 degrees. This spinal elasticity is further supported by muscles rather than rigid ligaments, permitting the back to elongate and contract with agility. The most impactful adaptation is the cat’s clavicle, or collarbone. Unlike the human clavicle, which is firmly connected to the shoulder, the cat’s is greatly reduced in size and floats freely, embedded only in muscle. This non-bony attachment allows the shoulders to compress and move closer together. This unique structure means a cat’s body can pass through any opening that its head can fit through, which creates the illusion of a flowing substance.
Why Cats Are Not Actually Liquids
The Biological Solid
Despite their anatomical adaptations and the convincing visual evidence, cats are not true liquids under the classical definition of matter. A cat is a biological solid composed of cells, tissues, and a skeleton, meaning it inherently possesses a definite shape and volume in its resting state. While a cat can actively change its shape to fit a container, a true liquid does so passively and continuously due to the movement of its particles.
The Rheological Perspective
The question was explored by physicist Marc-Antoine Fardin, who used the field of rheology—the study of flow—to contextualize the phenomenon. Fardin’s analysis applied the Deborah number, a concept that compares a material’s internal relaxation time (the time it takes to deform) to the time of observation. If the observation time is much longer than the relaxation time, the material appears to flow like a liquid, giving the impression of liquidity. For a cat observed over a short period, such as during a quick jump, it acts like a solid. However, when observed as it slowly settles into a container over a period of minutes, its relaxation time is shorter than the observation time, making it appear liquid. Fardin’s conclusion that a cat can be considered a liquid is therefore relative to the time scale of the interaction. Ultimately, a cat is a highly flexible, living solid that uses biological action to mimic the behavior of a fluid.