# Light is only a photon - no wave by feynamn?

• jd12345
In summary: In this limit, the wave equation has a single solution that is the wavefunction of the particle.In summary, Feynman says that light is a particle, while the lecture you are referring to describes the behavior of light in a semi-classical limit.
jd12345
I have been studying light and learned that light has a dual character. But then i saw one of the lectures of Feynman out of my interest - http://vega.org.uk/video/programme/45

He says light is not at all wave and he sticks to the photon concept.
But now we describe light pretty much both as a wave and particle but he didnt. So was he wrong or did i miss anything?

okay - according to today's physics we have found that the rules( quantum physics ) of the behaviour of light
But if anyone has seen the video http://vega.org.uk/video/programme/45
Feynman says that light is a particle. He doesn't give it a dual character or anything like we do today. He just sticks to the particle theory

I should further add that the photon is a massless particle, i.e. it is always ultra-relativistic. One consequence of this is that one cannot ascribe a position as an observable for the photon. The role of a wave-function is given to a field operator that creates/annihilates a photon at a particular space-time point. Mathematically, this field operator coincidences with the 4-potential $A^\mu(x)$.

As for classical waves, such as radio-waves emitted from an antenna, they are best described by so called coherent states.

Op, what is referred to as a particle in Modern Quantum Field Theory are excitations of the vacuum corresponding to simple poles in the 2-point correlators. These have a definite energy-momentum relationship (called a dispersion relation), remain stable for a definite time, and have various characteristics (mass, spin, El. charge, color, etc.). Even classical fields, such as the electromagnetic field, have single-particle excitations. For example, the photon is the one for the EM-field. Usually, the fields are named according to the name of the elementary particle that is their excitation.

These particles are not the billiard balls from Classical Mechanics. Feynman, as the co-founder of one of the more successful Qunatum field theories, Quantum Electrodynamics (QED), was certainly aware of this. Thus, he referres to particles in the above sense.

But, the video that you are referring to describes Quantum Mechanics of a single particle. In this case , one may construct a wave equation that describes the evolution of the particle. This wave is the wave of De Broglie's wave-particle duality hypothesis. It corresponds to the semi-classical (non-quantum) limit of the equation of motion for the quantum field, in an approximation where decays and collisions of the particle with others may be neglected, or the vacuum is different (the above coherent state).

## What is the concept of "Light is only a photon - no wave by feynamn"?

The concept of "Light is only a photon - no wave by feynamn" is based on the theory proposed by physicist Richard Feynman, which suggests that light behaves only as a particle (photon) and not as a wave. This theory challenges the traditional understanding of light as having both particle and wave-like properties.

## What evidence supports the idea that light is only a photon?

There are several experiments that support the idea that light is only a photon. One of the most famous is the double-slit experiment, which showed that light behaves as a particle when observed and as a wave when not observed. Additionally, the photoelectric effect and Compton scattering also demonstrate the particle-like behavior of light.

## How does this theory impact our understanding of light?

This theory challenges the traditional understanding of light and forces scientists to rethink the nature of light and its behavior. It also has implications for the field of quantum mechanics and how we understand the fundamental particles of the universe.

## Are there any criticisms of this theory?

Yes, there are some criticisms of this theory. Some scientists argue that while light may behave as a particle in certain experiments, it also exhibits wave-like behavior in other situations. This theory also goes against the established understanding of light as having both particle and wave-like properties.

## How does this theory impact other fields of science?

This theory has implications for other fields of science, such as optics, where the wave-like behavior of light is crucial for understanding phenomena such as diffraction and interference. It also has implications for our understanding of the electromagnetic spectrum and how light interacts with matter.

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