The wavelength of light we observe from distant galaxies is typically longer (redshifted) than its original wavelength when it was emitted due to the expansion of the universe. This phenomenon is known as cosmic redshift. As the universe expands, the space between galaxies also expands causing light from distant galaxies to stretch as it travels towards us. This stretching causes the observed wavelength to appear longer (i.e., more red) than its original wavelength, which is what we call redshift.
The redshift (z) can be used to calculate the ratio of the observed wavelength (λ_observed) to the emitted wavelength (λ_emitted). The relationship is given as:
1 + z = λ_observed / λ_emitted
Given a redshift of z = 7, we can calculate the ratio:
1 + 7 = 8 = λ_observed / λ_emitted
This means that the observed wavelength of light from galaxies with a redshift of 7 is 8 times longer than the wavelength of the light when it was emitted.
How does the wavelength of light we observe from those galaxies compare with its original wavelength when it was emitted?
The most distant galaxies observed to date have a redshift of approximately z =7.
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