Why do many possible shapes for extra dimensions make string theory difficult to test?

In string theory, the requirement for six extra spatial dimensions presents a significant challenge to experimental verification. Because strings are infinitesimally small, they vibrate within these hidden, "crumpled" dimensions.1

The difficulty arises because the specific geometric shape and size of these extra dimensions directly dictate how the strings vibrate. Since the vibrational patterns of a string determine the fundamental properties of particles—such as their mass and charge—the theory can only produce concrete, testable predictions if the exact geometry of these dimensions is known.1

However, the mathematical equations of string theory allow for a vast number of different geometric forms for these extra dimensions. Because there is no definitive way to determine which of these many possible shapes corresponds to our physical universe, researchers struggle to extract the specific, testable predictions necessary to confirm the theory through experiment.1