Scientists know that the universe is expanding by 4. The Doppler effect shows stars with red-shifted light.
What scientists said that the universe is growing?
Edwin Hubble
In 1929, Edwin Hubble, an astronomer at Caltech, made a remarkable discovery that quickly led to scientific answers to these questions: he found that the universe is expanding.
How do we know that the universe is growing?
Hubble identified his much-needed candles - bright stars, shining even higher than Cepheids, at 46 galaxies - concluding that galaxies are moving away from each other at a speed equal to their distance. Relationships are now known as Hubble's law, simple relationships that define how space expands.
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