What foundational relationship did Edwin Hubble establish concerning galaxies based on redshift measurements?
Answer
Recessional velocity is proportional to distance
The consistent measurement of spectral lines shifting toward the red end of the spectrum across numerous galaxies led Edwin Hubble to a key cosmological realization. By observing how much the spectral lines from distant galaxies were shifted—indicating how fast they were moving away (recessional velocity)—he determined a direct correlation: the farther away a galaxy is, the faster it appears to be receding from the observer. This foundational discovery established that the universe is not static but is actively expanding, with the velocity of recession scaling linearly with the distance separating the galaxies.
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