Will We Ever Prove String Theory?

Vibrating strings the size of atoms may hold the key to unifying physics, but string theory's vast landscape of possible universes has left scientists searching for our cosmic address. Harvard physicist Cumrun Vafa is working to narrow the field by identifying which hypothetical universes are incompatible with observed reality.

"We have learned that even if you are not interested in quantum gravity, per se...questions that have nothing to do with gravity have been answered using string theoretic ideas," Vafa explains. His "swampland" concept aims to cull theories that fail to match known physics.

While critics argue string theory lacks testable predictions, Vafa counters that it actually limits possibilities: "String theory gives you a finite number of possibilities. And cutting the possibility from an infinite set to a finite set is a remarkable reduction."