Quantum Electrodynamics (QED) is the quantum field theory that describes how light (photons) interacts with matter (such as electrons and positrons). It is one of the most precisely tested theories in all of physics and forms a cornerstone of the Standard Model.
Developed in the 1940s by Richard Feynman, Julian Schwinger, and Sin-Itiro Tomonaga, QED successfully merges quantum mechanics, special relativity, and electromagnetism into a single consistent framework.
Key Concepts in QED:
- Photons are the force carriers of the electromagnetic force.
- Charged particles (like electrons) interact by exchanging photons, even in empty space.
- These interactions can involve emission, absorption, or scattering of photons.
- Feynman diagrams are visual representations used in QED to calculate the probability of different interaction processes.
Why QED Is Important:
- It explains phenomena like the Lamb shift, electron scattering, and magnetic moments with incredible accuracy.
- It predicted the anomalous magnetic dipole moment of the electron, matching experiments to more than 10 decimal places.
- It laid the groundwork for other quantum field theories like quantum chromodynamics (QCD) and electroweak theory.
QED reveals that what appears to be smooth, continuous electromagnetic force is actually the result of countless quantum exchanges of virtual photons. This deep understanding of how light and charged particles interact is essential to modern physics, electronics, chemistry, and even technologies like lasers and semiconductors.