String theory, which is a theoretical framework in physics that attempts to reconcile quantum mechanics and general relativity, originally formulated in the late 20th century, requires ten dimensions for its mathematical consistency. The fundamental objects in string theory are not point-like particles but rather tiny, vibrating strings. These strings can exist in different vibrational modes, which correspond to different types of particles observed in the universe, such as electrons or photons.
To accommodate the properties of these vibrating strings and ensure mathematical consistency, string theory requires extra spatial dimensions beyond the usual three dimensions of space (length, width, and height) that we are familiar with. These additional dimensions are often referred to as "compactified" dimensions or "curled-up" dimensions because they are extremely small and not directly observable in our everyday experiences.
The specific choice of ten dimensions in string theory is a result of several mathematical reasons. One important reason is that in ten dimensions, the mathematics of string theory becomes mathematically consistent and free of certain inconsistencies that arise in lower-dimensional formulations. In particular, certain anomalies that appear in lower dimensions are canceled out in ten dimensions.
Additionally, when the extra dimensions are compactified in a particular way, the resulting physics can effectively reproduce the observed four-dimensional spacetime (three dimensions of space and one dimension of time) at low energies, which matches our everyday experience.
It's important to note that string theory has evolved over time, and there are different formulations and variants of string theory, such as superstring theory, which include supersymmetry and require eleven dimensions (including time) in some cases. These variations provide different mathematical frameworks to explore the fundamental nature of the universe and attempt to address various open questions in physics.
It's worth mentioning that string theory is still an active area of research, and its complete formulation and experimental verification remain challenging. The number of dimensions, the choice of compactification, and other aspects of string theory continue to be investigated and refined by physicists.