The nature of spacetime, whether it is emergent or fundamental, is a topic of ongoing research and debate in physics. Different theories and approaches provide various perspectives on this question, but there is no definitive consensus at present.
In classical physics, spacetime is treated as a fundamental background in which all physical phenomena occur. However, in the context of quantum mechanics and attempts to reconcile it with general relativity, such as in the pursuit of a theory of quantum gravity, the nature of spacetime becomes more intricate.
Some theories and ideas propose that spacetime could be emergent, meaning that it arises from more fundamental entities or degrees of freedom. For example, certain approaches within string theory, such as the AdS/CFT correspondence, suggest that in certain cases, a higher-dimensional spacetime can be described by a lower-dimensional quantum field theory. This implies that spacetime itself may not be fundamental but emerges as a collective behavior of underlying quantum fields or other fundamental entities.
Other approaches, such as loop quantum gravity, also propose that spacetime could have a fundamentally discrete structure at the smallest scales. According to this perspective, spacetime could be composed of discrete units or quanta, analogous to the quantization of other physical quantities in quantum theory.
On the other hand, there are also viewpoints that argue for the fundamental nature of spacetime. Some theories, like causal set theory, propose that spacetime is the fundamental structure, with discrete elements ordered in a causal relation. These theories maintain that spacetime is not emergent but rather a foundational aspect of reality.
It is important to note that the exploration of the nature of spacetime at the fundamental level is an active area of research, and further theoretical and experimental investigations are required to gain a clearer understanding. As our knowledge and understanding evolve, the question of whether spacetime is emergent or fundamental may be resolved or refined in the future.