String theory is a proposal about nature on an unbelievably small scale, over a billion times smaller than the distances studied at the Large Hadron Collider (LHC). We may never be able to detect strings themselves. Despite decades of research the physics community is divided about its practical and philosophical implications. Here we explore what the future might hold.
How do we go about deciding whether string theory is right? And will we ever completely grasp the nature of reality? These are really questions for philosophers, who set out rules for accepting scientific theories.
The biggest hurdle facing string theorists is making testable predictions. Are the concepts in our toolbox simply pretty mathematics, or do they describe the real world? A definitive answer requires experimental evidence.
There remain many things that we don’t understand about string theory, limitations to what it tells us. Will further research in string theory provide the answers, or do we need to look elsewhere?
There are also several alternative proposals for quantum gravity. These can look very different from string theory. Perhaps they are related at a deeper level, but they might be fundamentally distinct. Will one idea emerge victorious, or do we need to combine elements from all of them? Maybe we are still missing essential ingredients.