String theory and quantum electrodynamics (QED) are both theoretical frameworks that aim to describe the fundamental interactions of particles and fields in the universe. However, they approach this task from different perspectives and have different scopes of application.
Quantum electrodynamics is a quantum field theory that specifically deals with the electromagnetic force, which includes the interactions between charged particles and the electromagnetic field. It provides a framework for understanding and calculating the behavior of electrons, positrons, and photons, which are the elementary particles associated with electromagnetic interactions. QED successfully combines quantum mechanics and special relativity to describe the electromagnetic force with remarkable precision. It is one of the most well-tested and successful theories in physics.
String theory, on the other hand, is a theoretical framework that attempts to provide a more fundamental description of the universe by postulating that the fundamental building blocks of matter are not point-like particles but tiny, vibrating strings. These strings are hypothesized to be one-dimensional entities, and their different modes of vibration give rise to the various particles and forces observed in nature. String theory goes beyond the scope of QED and aims to encompass all the fundamental forces, including gravity, within a single unified framework.
In certain limits, string theory reduces to quantum field theories such as QED. This means that in certain situations where the interactions can be well-described by QED, string theory should reproduce the predictions of QED. In fact, when string theory is compactified to lower dimensions, under certain conditions, it can give rise to effective quantum field theories that include QED as a specific component.
However, it is important to note that string theory is still a work in progress and has not yet been fully formulated or experimentally confirmed. It is an active area of research, and physicists are working to understand its mathematical and conceptual foundations better. Therefore, the exact relationship between string theory and QED, as well as its other implications, are still subjects of ongoing investigation and debate within the physics community.