According to our current understanding of physics, there is no known smallest possible number in the universe. The concept of a smallest possible number relates to the idea of discrete quantities, where numbers are considered to be composed of individual units or increments. In classical physics, quantities were often thought to be continuous, meaning they could take on any value within a range.
However, with the development of quantum mechanics, our understanding of the fundamental nature of reality changed. Quantum mechanics introduced the idea of quantization, where certain physical properties are inherently discrete and can only take on specific values. For example, the energy levels of electrons in an atom are quantized.
In the realm of quantum physics, there is a concept called the Planck scale, which is considered to be the smallest scale at which our current understanding of physics holds. The Planck length, for instance, is thought to represent the smallest meaningful "distance" in our current understanding of spacetime. However, it is crucial to note that the Planck scale is a theoretical concept that arises from the combination of quantum mechanics and general relativity. It represents our current theoretical limit of understanding, and whether it corresponds to an ultimate fundamental limit is still an open question.
In summary, while the concept of a smallest possible number is not applicable in our current understanding of the universe, the Planck scale represents a theoretical limit at which our current understanding of physics breaks down. The search for a more comprehensive theory, such as a theory of quantum gravity, may shed further light on the fundamental nature of the universe at scales currently beyond our reach.