When we say that an object has become smaller than its wavelength, we are referring to a situation where the size of the object or the distance between its features is comparable to or smaller than the wavelength of the wave interacting with it.
In the context of electromagnetic waves, such as light, the wavelength corresponds to the distance between successive peaks or troughs of the wave. Objects interact with waves based on their size and the scale of their features relative to the wavelength.
When an object or its features are much larger than the wavelength of the interacting wave, we can treat the object as a macroscopic entity. The wave interacts with the object's overall shape and properties, such as reflection, absorption, or transmission, depending on the material properties.
However, when an object or its features approach or become smaller than the wavelength, we enter a regime known as the "wave-particle duality." This concept arises from quantum mechanics, which describes the behavior of particles at the atomic and subatomic scale. In this regime, both particles (objects) and waves are considered valid descriptions of the underlying physics.
At the quantum scale, particles such as electrons, protons, and even composite objects like atoms or molecules, can exhibit wave-like properties. This means that they can exhibit interference and diffraction effects, similar to waves. The size of these quantum objects is often comparable to or smaller than their associated wavelength.
It is important to note that the "wave-particle duality" does not mean that objects physically occupy and don't occupy space simultaneously. Rather, it refers to the fact that particles at the quantum scale can exhibit behaviors characteristic of both particles and waves, depending on the experimental setup or the nature of the interaction.
In essence, when we say an object has become smaller than its wavelength, we are entering a regime where quantum effects become significant, and the object's behavior may exhibit wave-like characteristics.