Both string theory and loop quantum gravity are active areas of research within theoretical physics, but it is challenging to determine which theory produces more testable hypotheses at this time.
String theory is a theoretical framework that seeks to reconcile quantum mechanics and general relativity by considering fundamental particles as tiny, vibrating strings. It has led to various mathematical developments and has provided insights into the behavior of black holes and the early universe. However, due to its mathematical complexity and the difficulty of accessing the energy scales at which strings would manifest, string theory has not yet produced experimentally testable predictions that can be verified directly.
On the other hand, loop quantum gravity is a competing approach to the unification of quantum mechanics and general relativity. It suggests that spacetime is quantized at a fundamental level, consisting of discrete "atoms" or "quanta" of space. Loop quantum gravity has generated testable predictions in certain scenarios, such as the behavior of black holes at the Planck scale, the existence of a minimum length scale, and potential effects on the cosmic microwave background radiation.
However, it's important to note that both string theory and loop quantum gravity are still in active development, and neither has reached the level of experimental confirmation or definitive empirical predictions. They are highly complex theories that are still being refined and explored by physicists.
Ultimately, the testability of hypotheses depends on various factors, including the mathematical consistency of the theory, the availability of experimental techniques to probe the relevant energy scales, and the development of novel observational or experimental methods. As research progresses and new insights emerge, the testability of hypotheses in both string theory and loop quantum gravity may evolve.