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What keeps the planets in orbit

  1. May 22, 2013 #1
    If the reason why the planets orbit around the sun is the deviations in the fabric of spacetime,what keeps the planets from crashing into each other? Like if I put a boulder on a trampoline and then I put a baseball next, the baseball would go toward the boulder. I think it could be dark matter pushing the planets away and gravity bringing them closer in equilibrium. But who knows the correct answer ( if there is one).
  2. jcsd
  3. May 22, 2013 #2


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    Staff: Mentor

    You're one of many people who have been misled by the trampoline analogy. It makes for nice pictures and non-technical descriptions of kinda sorta what's happening, but it's very misleading if you want to really understand what's going on.

    You can search this forum for some of the previous criticism of the trampoline analogy (try searching on "rubber sheet").
  4. May 22, 2013 #3
    While I'm firmly in the "the rubber sheet analogy is horrible" camp, it can handle OP's question just fine. Planets are in orbit around the sun. If they didn't have orbital velocity, they would crash into the sun just like OP is suggesting. As it is, they do have tangential velocity so they effectively "fall around" the sun. You can simulate this perfectly well with a boulder and a baseball on a trampoline, though friction will damp things pretty quickly.

    It's still a bad analogy though.
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