Redshift is a phenomenon in which the frequency of light decreases.
Redshift is divided into: relative redshift and absolute redshift.
1.Relative redshift.
The relative redshift is determined by the relative velocity of the light source and the observer.
Relative redshift law] The light source and the observer are redshifted close to each other and blueshifted far from each other. (Wang 2020).
Assuming that the observer is flying at a speed of 100 million meters and seconds, the frequency of the light source will be blueshifted when the observer moves in the direction of the light source. When the observer moves in the opposite direction of the light source, the frequency of the light source is redshifted; As the observer moves to the left and right of the light source, the frequency of the light source does not change.
Suppose the spacecraft is flying at a speed of 100 million meters and seconds, and when the spacecraft emits light in front of it, the light observed in front of it will be blueshifted. When the spacecraft emits light to the rear, the light observed in the rear is redshifted; When the spacecraft emits light in the left and right directions, the frequency of the light observed in the left and right directions does not change.
2.Absolute redshift.
The absolute redshift is determined by the distance of the light source from the observer.
Wave commonality: The frequency of waves in any medium will continue to decay during propagation and eventually disappear.
For example, the sound of thunder in the near distance is crisp and high-frequency, and the thunder in the distance is thick and low-frequency, indicating that the frequency of the sound wave is constantly attenuating during propagation. The frequency of water waves also decays as they propagate. The frequency of light is constantly attenuated as it travels, so the maximum distance that light travels in the universe is 13.8 billion light-years.
Absolute Redshift Law] The spectrum of distant objects undergoes redshift during propagation, and the frequency of redshift is inversely proportional to distance. (Wang 2020).
The difference between relative redshift and absolute redshift
1.The relative redshift is determined by the relative velocity of the light source and the observer. The absolute redshift is determined by the distance of the light source from the observer.
2.The relative redshift is reversible, and the absolute redshift is irreversible.