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The entire point of string theory not being testable is not specific to string theory but rather to quantum gravity. Any theory of quantum gravity will only dev

by pontus 5y ago

The entire point of string theory not being testable is not specific to string theory but rather to quantum gravity. Any theory of quantum gravity will only deviate from our current understanding (general relativity) at the Planck Scale. So, if one has an issue with string theory not being testable, one actually has an issue with pursuing any version of quantum gravity. The interesting thing about string theory that sets it apart from all other theories of quantum gravity is that it's actually not just a theory of gravity. Because of this, there is actually hope that string theory could produce nontrivial testable predictions at energy scales much lower than the Planck Scale. However, it turns out that teasing out these predictions is very nontrivial, primarily because of a structure called the string landscape. Basically it turns out that the equations of string theory, while being tidy at high energy, produce a multitude of solutions at low energy and, unless you know which solution to look at, making definitive predictions is hard. Normally the way around a situation like that is to make some observations and try to constrain which solution we should look at. Unfortunately our current best understanding of the landscape is only one-way; we can't currently constrain which solution to look at based on observational evidence. It's sort of like a one-way hash. If we can invert this 'hash function', we could in principle make measurements to constrain which solution we're in and at that point string theory would be falsifiable.

tsimionescu 5y ago
The bigger problem is that some of String Theory's few predictions have in fact been falsified. Supersymmetry has been predicted twice already, once at LHC energy levels and once before. Those predictions turned out wrong, but instead of abandoning the theory, it was easily tweaked to make a new prediction at a slightly higher energy level that LHC can predict. The very fact that such tweaks can be made is a known problem with string theory as a component of physics.

by pontus 5y ago

tsimionescu 5y ago

The bigger problem is that some of String Theory's few predictions have in fact been falsified. Supersymmetry has been predicted twice already, once at LHC energy levels and once before. Those predictions turned out wrong, but instead of abandoning the theory, it was easily tweaked to make a new prediction at a slightly higher energy level that LHC can predict. The very fact that such tweaks can be made is a known problem with string theory as a component of physics.