We believe the Universe is infinite. But if it is infinite and there are infinite stars, why isn't the sky fully bright, with stars filling every spot we look at? This is called Olber’s Paradox.
While many have posed this question over the ages, Olber’s Paradox is attributed to amateur astronomer Heinrich Wilhelm Olbers, who described it in 1823. At the time, this was one of the most convincing theories to suggest that the Universe must have an end and must be finite. Only later in the 20th century were we able to explain how the universe can be infinite, yet the sky remains dark.
First, we discovered that the Universe is expanding, and distant stars are moving away from us. Their light is redshifted (stretched to longer wavelengths) to a point where it's no longer visible to the naked eye. Later, we embraced the theory of the Big Bang, which posited that even if the Universe is infinite, it has a finite age. Hence, we can only see light from stars that have had enough time to reach us. Both theories can explain on their own, why the sky looks much more sparse in terms of stars.
We still understand very little about the vastness of the Universe. But thanks to people like Olbers and others, we continue to push the boundaries of our knowledge, asking questions and formulating hypotheses that enhance our understanding of the immense space we inhabit.
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