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Famous Thought Experiments
Since ancient times, great thinkers have used thought experiments to understand our Universe. In the first century B.C.E., the philosopher and poet Lucretius used a thought experiment to show that space is infinite: if the Universe had a boundary, that would mean you could throw a spear at it. If it pierced the boundary, there is something on the other side. If it bounced back, there must be some kind of wall existing in further space. Either way, there could be no edge of the Universe. In the 17th century, the physicist and mathematician Isaac Newton wondered, if he shot a cannonball hard enough, would it circle the planet without touching the ground? Later, this thought experiment would be carried out by satellites. In orbit, things are "falling" towards the Earth, but at speeds fast enough so that they never reach the ground.