Text 1 String theory attempts to reconcile general relativity (gravity) and quantum mechanics. It proposes that the fundamental constituents of the universe are not point-like particles, but one-dimensional 'strings' vibrating at specific frequencies. Text 2 A major criticism of string theory is its lack of testability. The theory requires extra dimensions that are compacted at scales too small for current technology to probe. Without experimental verification, some physicists argue it belongs to philosophy, not science.