The basic idea on which the measurement of the frequency of light is based on the following realization:
As light passes through the diffraction grating, it changes the wavelength.
The wavelength of light can be changed as it passes through the diffraction grating. Whether and how its wavelength changes are not yet measured and documented, although this measurement may solidify the basis of physics. The measurement represents a white spot in physical measurement.
Direct measurements form the basis of physics. A measurement is often considered a priori as unnecessary, if we think that everything is clear to us, however, in this way, we do not make progress towards the objective knowledge. Here I describe one of the measurements that can solidify physical science, regardless of the measured result.
We measure the wavelength of visible light coming from a moving light source. The speed of the light source should be at least a few km/s. There must be no turbulence at the light source thus ensuring the same speed of the light source to all light waves. The light source can be a comet or one of the planets (Mars, Jupiter).
When measuring the wavelength of light on Earth without the use of a diffraction grating, the measured spectral line has a different wavelength than when placing a diffraction grating in front of the wavelength meter so that the beam travels through the grating. The wavelength meter is for example the Fabry-Perot etalon, which is sensitive to the wavelength but not on the frequency of the light.
We measure the deflection beam (m = 0), which travels straight through the grating and does not deflect on it. Any spectral line can be selected for measurement.
Expected measurement result
When the beam passes through a diffraction grating, we detect the spectral line shifts as a function of the speed of the light source. At light source speeds of 5 – 20 km/s, the expected shift of the spectral line is from 0.015 nm to 0.05 nm, which is measurable.
Similar measurements of light from the comet (6300 Large Aperture Photometry of Comet Hale-BOPP), or light coming from planets, have been described in the scientific literature. The expected results of the measurements are based on the records in these articles.
Measurement is not technicali difficult. The expected measurement results cause measurement problem. A change in the wavelength on the diffraction grating means a change in the speed of light as it passes through the grid, and this casts doubt on the postulate of always the same speed of light.
The expected result of a measurement often deters astrophysicists from measuring. Such measurements can be made successfully by someone who is in favor of it. The article might give a new insight in such measurements and motivate physicists to perform this measurement with commitment.
Physics is the science that measures everything that is measurable. Regardless of the measured result of this measurement, it is necessary to publish the results of this measurement. The measurement should not be a white spot, where everyone answers the question in his own way, differently, according to his own beliefs.