Explaining gravity to a small child is simple: All you have to say is, what goes up must come down.
Until the kid asks why.
What can you say? It’s just the way things work. All masses attract each other. Maybe to bright middle schoolers you could explain that spacetime is warped by mass. Or, to high schoolers, you could say that without gravity, the laws of physics would differ for people moving at changing velocities. Yet all those increasingly sophisticated answers merely invite another “Why.” As Sir Isaac Newton himself replied in response to similar questions, “hypotheses non fingo.” Which roughly translates as “I don’t have a clue.”
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