# Does a single photon have a wavelength?

• feynmann
In summary, the conversation discusses the relationship between a single photon and Heisenberg's Uncertainty Principle. It is argued that a single photon with a definite wavelength would violate the principle, as it would have infinite uncertainty in position. The concept of adding multiple wavelengths to define a position is also mentioned. The conversation concludes with the statement that no one can accurately answer the question being discussed.
feynmann
If a single photon has a wavelength, would it violate Heisenberg Uncertainty principle?
Since photon is a particle, that means it can be represented by a wave packet. But wave packet can not have definite wavelength, only pure wave can have wavelength

backward
One form of the uncertainty principle is that the uncertainty in momentum (delta p) multiplied by the uncertainty in position (delta x) is greater than some minimum number. A single photon with a definite wavelength (uncertainty zero) is one limiting case. With definite wavelength, you know it has a definite momentum. The uncertainty principle implies that you have infinite uncertainty in the position. Consider that a single wave stretches across infinite space. So you can't define a position for an infinite wave. In order to try and make the wave start to have a shape at some position, you have to add other wavelengths. So the uncertainty in momentum starts to go up while the uncertainty in the position starts to come down. At the other end of this that you have to add an infinite number of wavelength together in order to put the wave packet at a single location. So you now have definite (zero uncertainty) position but infinite uncertainty in the momentum.

I have diffracted monoenergetic photons through a Bragg diffraction crystal with an angular resolution of a few seconds of arc at a very low counting rate. every photon had the same wavelength within about 1 part in 1000.

No one can answer this question correctly.

For example, when you accelerate one electron to the definite momentum,

It is a ridiculous thing of the uncertainty principle.

## 1. What is a single photon?

A single photon is the smallest unit of light and is often referred to as a particle of light. It is an elementary particle that carries energy and does not have a mass.

## 2. Does a single photon have a wavelength?

Yes, a single photon does have a wavelength. According to the wave-particle duality theory of light, photons exhibit both particle-like and wave-like properties. This means that, while it behaves like a particle, it also has a wavelength associated with it.

## 3. How is the wavelength of a single photon determined?

The wavelength of a single photon is determined by its frequency and speed. The equation c = λν (speed of light = wavelength x frequency) is used to calculate the wavelength of a photon, where c is the speed of light and ν is the frequency of the photon.

## 4. Can a single photon have different wavelengths?

No, a single photon can only have one specific wavelength. This is because the wavelength of a photon is directly related to its energy. Each photon carries a specific amount of energy, and this energy determines its wavelength.

## 5. How is the wavelength of a single photon measured?

The wavelength of a single photon can be measured using various techniques, such as interferometry or diffraction. These techniques involve passing the photon through a set of slits or mirrors, and observing the resulting interference or diffraction pattern. The distance between the slits or mirrors and the pattern can then be used to determine the wavelength of the photon.

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