A well-known scientist (some say it was Bertrand Russell)once gave a public lecture on astronomy. He described howthe earth orbits around the sun and how the sun, in turn,orbits around the center of a vast collection of stars called ourgalaxy. At the end of the lecture, a little old lady at the backof the room got up and said: “What you have told us isrubbish. The world is really a flat plate supported on the backof a giant tortoise.” The scientist gave a superior smile beforereplying, “What is the tortoise standing¹ on.” “You’re very clever,young man, very clever,” said the old lady. “But it’s turtles allthe way down!”
Most people would find the picture of our universe as aninfinite tower of tortoises rather ridiculous, but why do we thinkwe know better? What do we know about the universe, andhow do we know it? Where did the universe come from, andwhere is it going? Did the universe have a beginning, and if so,what happened before then? What is the nature of time? Will itever come to an end? Can we go back in time? Recentbreakthroughs in physics, made possible in part by fantasticnew technologies, suggest answers to some of theselongstanding questions. Someday these answers may seem asobvious to us as the earth orbiting the sun - or perhaps asridiculous as a tower of tortoises. Only time (whatever that maybe) will tell.
As long ago as 340 BC the Greek philosopher Aristotle, inhis book On the Heavens, was able to put forward two goodarguments for believing that the earth was a round sphererather than a Hat plate. First, he realized that eclipses of themoon were caused by the earth coming between the sun andthe moon. The earth’s shadow on the moon was always round,which would be true only if the earth was spherical². If theearth had been a flat disk, the shadow would have beenelongated and elliptical, unless the eclipse always occurred at atime when the sun was directly under the center of the disk.
Second, the Greeks knew from their travels that the North Starappeared lower in the sky when viewed in the south than itdid in more northerly regions. (Since the North Star lies overthe North Pole, it appears to be directly above an observer atthe North Pole, but to someone looking from the equator, itappears to lie just at the horizon. From the difference in theapparent position of the North Star in Egypt and Greece,Aristotle even quoted an estimate that the distance around theearth was 400,000 stadia. It is not known exactly what lengtha stadium was, but it may have been about 200 yards, whichwould make Aristotle’s estimate about twice the currentlyaccepted figure. The Greeks even had a third argument thatthe earth must be round, for why else does one first see thesails of a ship coming over the horizon, and only later see thehull?

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