T-duality

T-duality is a concept in string theory where two different-looking spaces, such as a large circle and a tiny circle, can actually describe the same physical reality. Imagine a string wrapped around a circle; its behavior on a very small circle is equivalent to a string on a large circle if you swap certain properties, like momentum and winding modes. This means that at a fundamental level, space can have different shapes or sizes, yet the underlying physics remains unchanged. T-duality reveals that our perception of size and geometry can be more flexible at the quantum level than in everyday experience.