The question of whether a cat is a liquid has become a popular internet meme, fueled by countless images of felines poured into sinks, bowls, and boxes. These viral photographs showcase the domestic cat’s ability to conform precisely to the shape of any container. This observation, while humorous, raises questions that reach into the fields of physics and anatomy. This article explores the scientific definitions of matter and the unique biological structure of the cat to determine if this phenomenon holds up to scientific scrutiny.
Defining States of Matter
The scientific distinction between a solid and a liquid is based on how a material responds to force and how it maintains its shape. A liquid is defined as a substance that maintains a constant volume but has no fixed shape, easily adapting to fill the container it occupies under the influence of gravity. Furthermore, a liquid is a type of fluid, defined as a material that flows continuously when subjected to any shearing force.
In contrast, a solid resists shearing forces and possesses a relatively defined shape, which it attempts to retain. The study of how materials deform and flow is known as rheology, which recognizes that the line between a solid and a liquid is not always absolute. Many complex materials, such as glass or soft biological matter, exhibit properties of both states, often categorized as viscoelastic materials.
A more nuanced definition in rheology involves the concept of relaxation time, which is the time required for a material to adjust to a new shape. If the time over which a material is observed is much longer than its relaxation time, the material acts like a liquid and flows. Conversely, if the observation time is shorter than the relaxation time, the material behaves like a solid.
Feline Flexibility: Anatomy of Conformation
The cat’s remarkable ability to appear liquid is rooted in a highly specialized musculoskeletal system optimized for extreme flexibility and agility. Cats possess a spine with significantly more vertebrae than humans, contributing to a greater range of motion. The joints between these vertebral bones are exceptionally flexible, allowing a cat to twist and contort its body.
Crucially, the cat’s forelimbs are connected to the body by a unique shoulder structure that lacks a traditional fixed clavicle, or collarbone. Instead of a rigid bony connection, the clavicles are small, free-floating bones embedded in muscle. This permits the shoulders to move much closer together, allowing a cat to compress its chest cavity and pass through any opening that is wide enough for its head.
The flexibility is further enhanced by the elastic cushioning disks between the vertebrae, which allow the spine to rotate and absorb impacts. This combination of numerous, flexible vertebrae and a non-fixed clavicle grants the cat the anatomical capacity to simulate a liquid when occupying a container.
The Scientific Verdict
Synthesizing the definitions of matter with the anatomical facts leads to a clear scientific verdict: a cat is a highly deformable solid, not a true liquid. While a cat can take the shape of a container, it does so by rearranging its internal skeletal and muscular structure, not by spontaneously flowing under its own weight. Unlike a liquid, which requires no internal energy to conform, a cat must exert muscular effort and possess the biological capacity to compress and mold its body.
The question of the cat’s state of matter was explored seriously enough to win a 2017 Ig Nobel Prize in Physics, which recognizes research that first makes people laugh, then makes them think. The research applied the principles of rheology to determine that, over a long enough time scale, a cat could technically be considered liquid. This classification is based on the idea that the cat’s relaxation time—the time it takes to conform to the container—is shorter than the time the cat is observed.
The conclusion highlights that the cat’s apparent liquidity is a matter of time scale, not a fundamental property of matter. The cat retains its internal structure and does not have the zero shear modulus that defines a true fluid. The feline is a sophisticated biological machine that uses its unique anatomy to mimic the behavior of a liquid, making it an excellent model system for studying the flow of complex materials.