We know that the speed of light coming from space is always the same. While the speed of light from space has not yet been measured, its speed is known based on observations and explanations of various phenomena.
Here we are asked why the speed of light coming from space has not yet been measured. Either we don’t know how to measure it, or it can’t be measured. The speed of light from space can be measured and we know how to measure it. The measurements are described later in this text. The speed of light from space should be measured to present it to students based on direct measurement, but not indirectly through the description of various phenomena.
The properties of light are not yet well understood. We are surprised by measuring the speed of an asteroid with an optical prism. The measurement does not detect any Doppler shift of the spectral lines! From the result of the measurement, we can wrongly conclude that the asteroid is at rest.
In science, unexpected measurement results occasionally appear, such as measuring the speed of an asteroid with an optical prism. The measurement shows no Doppler shift of the spectral line, regardless of the asteroids’ velocities.
Accepting the results of this unexpected measurement takes place in several steps. In the first step, the author does not even trust his measurement. He does not know what went wrong with the measurement and abandons the measurement. He keeps some expected results in his mind, which the measurement does not show.
In the second step, the author investigates such measurements in more detail and therefore trusts the measured results. However, he encounters great resistance from his interlocutors. Many think that measurement threatens the foundations of current science.
In the next step, several smaller groups of experts on this topic are formed, who repeat the measurement in their own environment and who are aware that the measurement cannot be faulted technologically or methodologically. Most, of course, still defend current knowledge, even by obstructing mentions of this measurement in the literature.
All the time, the number of those looking for an answer is increasing, and finally the reviewers of the articles allow the first professional article on this measurement. This article is still met with opposition, but at the same time it presents the measurement to the public. New and new implementations of this measurement are appearing, and thus new articles and the measurement with its results are gaining a foothold in science. As a rule, these steps take time, which is measured in decades.
The key insight from measuring the speed of an asteroid with an optical prism is that the speed of the light source affects the frequency of the light, but not its wavelength. The optical prism is not sensitive to the frequency of light, so it does not detect the Doppler shift of the spectral lines in the light of the asteroid. It is different with the diffraction grating, it is sensitive to the frequency of light, so we can use it to measure the speed of the asteroid.
An optical prism is suitable for measuring other properties of light from space. The gravitational shift of the spectral line affects the wavelength of the light instead of the frequency, and this is detected by the optical prism.
The frequency and wavelengths of light can therefore vary independently of each other, which means different speeds of light. Separate measurement of gravitational and Doppler shifts offers a renewed view of the universe, which does not require dark matter to describe.