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Our owls can also use 'Willa Audiobook' for free! If you type 'Review Owl' in the coupon registration, you can get 'Willa Audiobook' for 1 month free + 3 months 50% discount! Register Review Owl coupon https://www.welaaa.com/membership/pur... If you sign up through this link, the coupon will be pre-filled! The universe is so huge that its end is unknown. There are 170 billion galaxies in the observable universe alone, and there are over 400 billion stars in our galaxy alone. This universe is so huge that the world-renowned astronomer Carl Sagan said, "If life were to exist only on our planet, it would be a truly enormous waste of space." It may be arrogant to claim that we humans are the only living creatures in this vast universe! In fact, mankind has been continuously exploring the existence of aliens for a very long time. However, scientist Enrico Fermi asked, "There are so many alien civilizations, but where are they all?" This is the Fermi paradox. Why haven't we seen alien civilizations yet, despite the high possibility of their existence? Source: Willa Audiobook Carl Sagan's Cosmos Chapter 3 https://www.yna.co.kr/view/AKR2019031... https://www.dongascience.com/news.php... https://www.hani.co.kr/arti/culture/b...