What physical process stretches light waves leading to the phenomenon of redshift for distant galaxies?
Answer
Expansion of space itself between galaxies
The redshift observed in distant galaxies is fundamentally different from the simple Doppler shift caused by motion through static space. The primary driver is the expansion of the universe. As the space separating the emitting galaxy and the observer continually grows larger during the light's journey, the physical distance the light must travel increases. This stretching of the intervening space directly stretches the light waves themselves. As the wavelength of light is stretched toward the longer end of the spectrum, this shift is termed redshift, and the effect is cumulative; the farther away the galaxy, the greater the expansion of space along the path, resulting in a larger redshift value.
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