What is the current understanding of the photon and its interaction with matter?

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In summary, the paper "Evolution of the modern photon" by Kidd, Ardini, and Anton, published in 1989, discusses the various models of photons that have been proposed over time, including the corpuscular, singularity, wave packet, and QED models. The author emphasizes that in 1989, the QED model was the most accurate in explaining observed phenomena. However, it remains unclear if this is still the case in recent years. The QED model is a quantum field theory in which the electromagnetic field is quantized and the photon is the quantum of that field, contrary to the belief that the field is unquantized. In simpler terms, the photon can be thought of as a discrete unit of energy
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Karthiksrao
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I have been going through the paper "Evolution of the modern photon" by Kidd,Ardini and Anton. This was published in 1989.

In the paper, he describes the various 'models' of photons that have come up over time including the corpuscular model, the singularity model, wave packet model and the QED model.

He lays stress on the fact that 'at present' (in 1989) the QED model seems to fit the bill quite well, in the sense that most of the phenomena observed can be explained using this model.

I wish to know what has changed in the last 20 years. Is the QED model still holding its ground.

Also, I've understood the QED model as that which postulates that interaction of light with matter as being quantized but the field or radiation itself is un-quantized/continuous. Have I understood it correctly?

Thanks,
Karthik
 
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  • #2
QED is a quantum field theory. This means that all particles (photons included) are treated as excitations of a quantized field. So, no, you have not understood it correctly. In QED, the EM field is quantized and the photon is the quantum of that field. A model in which unquantized (or "classical") EM fields interact with quantum mechanical matter is usually termed a "semi-classical" model.
 
  • #3
By 'excitation', do you mean a ripple, which propagates through space at speed of light?
 
  • #4
Not a terrible analogy, provided you include the understanding that ripples of a given frequency can only have discrete quantities of energy, with the size of the discrete unit being proportional to the frequency of the ripple.
 

1. What is a photon?

A photon is a fundamental particle that is the smallest unit of light. It is an elementary particle that carries electromagnetic radiation and has no mass or charge.

2. How is a photon created?

A photon can be created through various processes, such as the emission of light from atoms, nuclear reactions, or the acceleration of charged particles. It can also be created through the conversion of energy into light, as in the case of bioluminescence or fluorescence.

3. How does a photon travel?

A photon travels at the speed of light in a vacuum, which is approximately 299,792,458 meters per second. It has both wave-like and particle-like properties, which allows it to travel through space and interact with other particles.

4. What is the energy of a photon?

The energy of a photon is directly proportional to its frequency and inversely proportional to its wavelength. This relationship is described by the equation E = hf, where E is energy, h is Planck's constant, and f is frequency. The higher the frequency, the more energy the photon carries.

5. How is a photon detected?

A photon can be detected by its interaction with matter. When a photon is incident on a material, it can be absorbed, reflected, or transmitted. These interactions can be detected by specialized instruments, such as photodetectors, which convert the energy of the photon into an electrical signal.

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