Have you ever figured out just exactly what you would do if the Earth were to suddenly disappear from the universe, leaving just you and whatever’s around to fall towards whatever the nearest heavenly bodies are? No, me neither. Asked to improvise one, I suppose I’d suffocate within minutes and then everything else becomes not so interesting to me, although possibly my heirs might be interested, if they’re somewhere.
My mother accidentally got me thinking about this fate. She’s taking a course about the science and world view of the Ancient Egyptians. (In talking about it she asked if I knew anything about the science of the Ancient Egyptians, and I tried to say I didn’t really know more than the average lay reader might, although when I got to mentioning that I knew of their awareness of the Sothic Cycle and where we get the name “Sothic Cycle” I realized that I can’t really call myself ignorant about the science of the Ancient Egyptians.) But the class had reached the point where astrological beliefs of the ancients were under discussion, and apparently some of the students insisted that astrology really and truly works, and my mother wanted me to figure out how strong the force of gravity of the Moon is, compared to the force of gravity of another person in the same room. This would allow her to go into class armed with numbers which have never dissuaded anyone from believing in astrology, but, it’s fun for someone.
I did double-check, though, that she meant the gravitational pull of the Moon, rather than its tidal pull. The shorthand reason for this is that arguments for astrology having some physical basis tend to run along the lines of, the Moon creates the tides (the Sun does too, but smaller ones), tides are made of water (rock moves, too, although much less), human bodies are mostly water (I don’t know what the fluid properties of cytoplasm are, but I’m almost curious enough to look them up), so there must be something tide-like in human bodies too (so there). The gravitational pull of the Moon, meanwhile, doesn’t really mean much: the Moon is going to accelerate the Earth and the people standing on it by just about the same amount. The force of gravity between two objects grows with the two objects’ masses, and the Earth is more massive than any person on it. But this means the Earth feels a greater force pulling it towards the Moon, and the acceleration works out tobe just the same. The force of gravity between two objects falls off as the square of the distance between them, and the people on the surface of the Earth are a little bit closer or a little bit farther away from the Moon than the center of the Earth is, but that’s not very different considering just how far away the Moon is. We spend all our lives falling into the Moon, as fast as we possibly can, and we are falling into the Moon as fast as the Earth is.