The red shift suggests that the universe is expanding
Explanation:
The phenomenon described here is called Doppler effect.
The Doppler effect occurs when there is a source of a wave in motion relative to an observer. When this occurs, the frequency (and the wavelength) as perceived by the observer are different from the proper frequency of the wave emitted by the source.
In particular:
- If the source of the wave is moving towards the observer, then the frequency perceived by the observer is higher than the real frequency (while the wavelength is shorter)
- If the source of the wave is moving away from the observer, then the frequency perceived by the observer is lower than the real frequency (while the wavelength is longer)
This phenomenon occurs also with light waves: therefore,
- if a source of a light wave is moving towards us, the visible light emitted by the source is shifted towards blue color (shorter wavelength). This phenomenon is called blue shift
- If a source of a light wave is moving away from us, the visible light emitted by the source is shifted towards red color (longer wavelength). This phenomenon is called red shift
Observation of light from distance objects in the universe (e.g. galaxies) show for nearly all of them that their light is red-shifted. This means that all the distant objects of the universe are moving away from us, and therefore, the only possible conclusion is that the universe is expanding.
Learn more about waves and wavelength:
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