Comments about "Doppler effect" in Wikipedia

This document contains comments about the article Doppler effect in Wikipedia
In the last paragraph I explain my own opinion.




The article starts with the following sentence.
The Doppler effect (or the Doppler shift) is the change in frequency or wavelength of a wave in relation to an observer who is moving relative to the wave source.
There is a physical difference if the Doppler shift is considered with or without an observer. Reflection 1 - Doppler effect versus an observer
For waves which do not require a medium, such as light or gravity in general relativity, only the relative difference in velocity between the observer and the source needs to be considered.
How do we know that the movement of photons does not involve a medium? The medium are the millions of photons surrounding us.
This is a physical issue and has nothing to do with general relativity.

1. History

2 General

3. Analysis

4. Application

5. Inverse Doppler effect

5. See also

Following is a list with "Comments in Wikipedia" about related subjects

Reflection 1 - Doppler effect versus an observer

There is a clear physical distinction with a Doppler effect with or without an observer.
Starting point is a process which creates waves at a certain fixed frequency f when the process is at rest relative to the medium that propagates the waves. The wave pattern is symetric.
It is important to consider the two different types because in the first case this is a physical effect, in the second case not.

Reflection 2 - Doppler effect with photons.

The Doppler effect with photons is physical very different compared to water waves and noise propagation. With water waves it is the combined behaviour of millions of water molecules which causes a wave. With photons it is the combined behaviour but also of individual photons.
A photon is emitted when inside an atom, an electron jumps from an higher energy level to a lower energy level. One photon can be considered as one energy packet (with a certain frequency). That same energy packet can be used that within one atom an electron jumps from a lower to a higher energy level.
For water to produce an interference patern your starting point are parallel waves which are guided through two holes. Behind the holes forms such an interference patern.

Reflection 3


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Created: 22 January 2019

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