Quantum Electrodynamics (QED) and String Theory are both important theoretical frameworks in physics, but they have different scopes and applications.
QED is a quantum field theory that describes the electromagnetic force and its interaction with charged particles, such as electrons and photons. It has been extensively tested and successfully explains a wide range of phenomena, including the behavior of subatomic particles and the electromagnetic interactions observed in experiments. QED is considered one of the most accurate and precise scientific theories, and its predictions have been experimentally confirmed to a remarkable degree.
On the other hand, String Theory is a theoretical framework that attempts to describe the fundamental structure of the universe at a deeper level. It proposes that elementary particles are not point-like objects but rather tiny, vibrating strings or higher-dimensional objects. String Theory aims to unify gravity with the other fundamental forces and provide a consistent description of quantum gravity, which is an unresolved problem in physics. However, String Theory has not yet made testable predictions that can be experimentally verified, and its mathematical complexity makes it challenging to explore.
In terms of relevance to the world, QED has had a more direct impact on our understanding of the physical world and has been successfully applied in various technological advancements, such as the development of quantum mechanics, solid-state physics, and modern electronics.
While String Theory is an intriguing and active area of research, it is still considered a speculative and theoretical framework. It has not yet produced experimental evidence or technological applications that have directly impacted our everyday lives.
In summary, both QED and String Theory are significant in their respective domains, but QED's impact on our understanding of the physical world and its practical applications make it more immediately relevant than String Theory at present.