String theory and quantum electrodynamics (QED) are both theoretical frameworks that aim to describe the fundamental forces and particles in the universe, but they approach this task from different perspectives.
Quantum electrodynamics is a quantum field theory that describes the electromagnetic force and its interaction with charged particles. It successfully combines quantum mechanics with special relativity to explain phenomena such as the behavior of electrons, photons, and the electromagnetic interactions between them. QED is considered one of the most well-established and successful quantum field theories, with accurate predictions that have been experimentally verified.
On the other hand, string theory is a theoretical framework that attempts to unify all fundamental forces, including gravity, into a single coherent framework. It proposes that elementary particles are not point-like objects but rather tiny, one-dimensional strings or loops of energy. The properties and behavior of these strings determine the particle's characteristics, such as mass, charge, and spin.
String theory incorporates quantum mechanics, and it naturally includes a spin-2 particle that behaves like a graviton, the hypothetical particle that mediates gravity. This allows string theory to potentially reconcile quantum mechanics with general relativity, which describes gravity on larger scales.
The connection between string theory and quantum electrodynamics arises from the fact that QED can emerge as a low-energy approximation or limit of string theory. When the energy scale and the size of the strings are much larger than the string length scale, the behavior of the strings can effectively be described by quantum field theories like QED. In this limit, string theory reduces to a theory that includes particles and interactions consistent with QED.
Therefore, while QED focuses specifically on the electromagnetic force and its quantum behavior, string theory provides a more comprehensive framework that aims to unify all fundamental forces, including gravity, and can incorporate QED as a specific case under certain conditions.