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Experiments Reveal That Deformed Rubber Sheet Is Not Like Spacetime
KentuckyFC writes "General relativity is mathematically challenging and yet widely appreciated by the public. This state of affairs is almost entirely the result of one the most famous analogies in science: that the warping of spacetime to produce gravity is like the deformation of a rubber sheet by a central mass. Now physicists have tested this idea theoretically and experimentally and say it doesn't hold water. It turns out that a marble rolling on deformed rubber sheet does not follow the same trajectory as a planet orbiting a star and that the marble's equations of motion lead to a strangely twisted version of Kepler's third law of planetary motion. And experiments with a real marble rolling on a spandex sheet show that the mass of the sheet itself creates a distortion that further complicates matters. Indeed, the physicists say that a rubber sheet deformed by a central mass can never produce the same motion of planet orbiting a star in spacetime. So the analogy is fundamentally flawed. Shame!"
I'm not sure the analogy was ever meant to be a rigorous and exact model, but more of a kind of way of visualizing space-time. All analogies break down if you try to map them exactly to the phenomenon you're trying to explain. After all, it's an analogy, not a model.
The world's burning. Moped Jesus spotted on I50. Details at 11.
... that anyone who had a grasp of high school phsyics, and who understood the analogy - of 3D matter flattened to represent a 2D metaphor for our real 3D world, which lives in 4D spacetime - or who understood that gravity attracted mass towards mass and not towards the "down" direction perpendicular to the sheet - would think for a second that such a demonstration would create the same exact trajectory as actual interaction between 3D objects in 4D spacetime.