# Tag Info

## Hot answers tagged quantum-electrodynamics

8

Both the wave theory of light and the particle theory of light are approximations to a deeper theory called Quantum Electrodynamics (QED for short). Light is not a wave nor a particle but instead it is an excitation in a quantum field. QED is a complicated theory, so while it is possible to do calculations directly in QED we often find it simpler to use an ...

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This is a perceptive question. Consider the following from the Wikipedia article "Virtual Particle": As a consequence of quantum mechanical uncertainty, any object or process that exists for a limited time or in a limited volume cannot have a precisely defined energy or momentum. This is the reason that virtual particles — which exist only ...

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In this link there exists a mathematical explanation of how an ensemble of photons of frequency nu and energy E=h*nu end up building coherently the classical electromagnetic wave of frequency nu. It is not simple to follow if one does not have the mathematical background. Conceptually watching the build up of interference fringes from single photons in a ...

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Your interpretation is not correct. The propagator $D_{\mu\nu}(x-y)$ describes the amplitude for a photonic field perturbation to go from $x$ to $y$, with the implicit picture that you have a "source" $J(x)$, and a "sink" $J(y)$, which are perturbing the vaccuum. However, a field perturbation is not a real particle (for instance, in the photon case, the ...

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In 1995 Willis Lamb published a provocative article with the title "Anti-photon", Appl. Phys. B 60, 77-84 (1995). As Lamb was one of the great pioneers of 20th century physics it is not easy to dismiss him as an old crank. He writes in the introductory paragraph: "The photon concepts as used by a high percentage of the laser community have no scientific ...

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The question here really is: "When are photons not virtual?". As explained in this article: A virtual particle is one that has borrowed energy from the vacuum, briefly shimmering into existence literally from nothing. Virtual particles must pay back the borrowed energy quickly, popping out of existence on a time scale set by Werner Heisenberg's ...

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Try, for instance, section 9 of Srednicki. The way to do it is to replace the fields in the interaction Lagrangian by functional derivatives with respect to the sources, then write power series for the exponents. Take the first order contribution. Then, use that you need to consider three-point functions where the fields are again replaced by functional ...

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However, I do not observe any visible light between objects around me, repelling each other when I place them on a desk. They also don't appear to heat up, or emit IR light, from just being placed beside each other either. What type of light is being emitted by this matter constantly? The key point is that those photons are not real photons. They are ...

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