Quantum Electrodynamics (QED) is the quantum field theory that describes the interactions between charged particles and electromagnetic fields, encompassing phenomena such as the interaction of electrons with photons. QED has been tremendously successful in providing accurate predictions and explaining a wide range of phenomena in the realm of quantum electrodynamics, including the behavior of charged particles in electromagnetic fields, the Lamb shift, and the anomalous magnetic moment of the electron, among others.
However, it is true that QED, as a theory, is not considered complete in the sense that it does not incorporate the other fundamental forces of nature, such as the strong and weak nuclear forces, or gravity. QED is a quantum field theory that describes the electromagnetic interactions based on quantum mechanics and special relativity, but it does not account for the full range of physical phenomena in the universe.
The success of QED despite its incompleteness can be attributed to a few factors:
Limited domain: QED is particularly successful in the regime of low energies and weak electromagnetic fields. In this domain, the theory provides extremely accurate predictions that are experimentally verified. QED calculations have been tested to extraordinary precision and have been found to agree with experimental observations to many decimal places.
Effective theory: QED can be seen as an effective theory that accurately describes a specific range of phenomena within its domain of validity. Effective theories capture the essential physics of a specific energy range while neglecting or approximating the effects of other fundamental interactions. QED is excellent at describing electromagnetic phenomena while ignoring the complexities of other forces.
Renormalization: As mentioned earlier, QED utilizes the process of renormalization to remove divergences and obtain finite predictions. This mathematical technique allows for precise calculations and predictions in the regime where it is applicable.
Consistency with other theories: Although QED does not include other fundamental forces, it is consistent with other well-established theories in their respective domains. For instance, it agrees with general relativity in the weak-field limit, and it is consistent with the standard model of particle physics, which describes the strong and weak nuclear forces.
While QED is not a complete theory, its remarkable success and accuracy within its domain have made it one of the most successful theories in physics. However, a more comprehensive theory, such as a unified theory that includes all fundamental forces, is still actively pursued by physicists in their quest for a more complete understanding of the universe.