520美书楼

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第13部分（第4页）

Ted　began　to　position　the　pieces　of　fruit。　〃This　orange　is　the　sun。　And　these　are　the　planets；　which　move　in　circles　around　the　sun。　So　we　have　the　solar　system　on　this　table。〃

〃Okay。〃

＇＇85＇＇　〃Fine；〃　Ted　said。　〃Now；　the　sun〃…he　pointed　to　the　orange　in　the　center　of　the　table…〃is　very　large；　so　it　has　a　lot　of　gravity。〃

〃Right。〃

Ted　gave　Norman　a　ball　bearing。　〃This　is　a　spaceship。　I　want　you　to　send　it　through　the　solar　system；　so　it　passes　very　close　to　the　sun。　Okay？〃

Norman　took　the　ball　bearing　and　rolled　it　so　it　passed　close　to　the　orange。　〃Okay。〃

〃You　notice　that　your　ball　rolled　straight　across　the　flat　table。〃

〃Right。〃

〃But　in　real　life；　what　would　happen　to　your　spacecraft　when　it　passed　near　the　sun？〃

〃It　would　get　sucked　into　the　sun。〃

〃Yes。　We　say　it　would　fall　into　the　sun。　The　spacecraft　would　curve　inward　from　a　straight　line　and　hit　the　sun。　But　your　spacecraft　didnt。〃

〃No。

〃So　we　know　that　the　flat　table　is　wrong；〃　Ted　said。　〃Real　space　cant　be　flat　like　the　table。〃

〃It　cant？〃

〃No；〃　Ted　said。

He　took　the　empty　bowl　and　set　the　orange　in　the　bottom。　〃Now　roll　your　ball　straight　across　past　the　sun。〃

Norman　flicked　the　ball　bearing　into　the　bowl。　The　ball　curved；　and　spiraled　down　the　inside　of　the　bowl　until　it　hit　the　orange。

〃Okay；〃　Ted　said。　〃The　spacecraft　hit　the　sun；　just　like　it　would　in　real　life。〃

〃But　if　I　gave　it　enough　speed；〃　Norman　said；　〃itd　go　right　past　it。　Itd　roll　down　and　up　the　far　side　of　the　bowl　and　out　again。〃

〃Correct；〃　Ted　said。　〃Also　like　real　life。　If　the　spacecraft　has　enough　velocity；　it　will　escape　the　gravitational　field　of　the　sun。〃

〃Right。〃

〃So；〃　Ted　said；　〃what　we　are　showing　is　that　a　spacecraft　passing　the　sun　in　real　life　behaves　as　if　it　were　entering　a　＇＇86＇＇　curved　region　of　space　around　the　sun。　Space　around　the　sun　is　curved　like　this　bowl。〃

〃Okay　。。。〃

〃And　if　your　ball　had　the　right　speed；　it　wouldnt　escape　from　the　bowl；　but　instead　would　just　spiral　around　endlessly　inside　the　rim　of　the　bowl。　And　thats　what　the　planets　are　doing。　They　are　endlessly　spiraling　inside　the　bowl　created　by　the　sun。〃

He　put　the　orange　back　on　the　table。　〃In　reality；　you　should　imagine　the　table　is　made　out　of　rubber　and　the　planets　are　all　making　dents　in　the　rubber　as　they　sit　there。　Thats　what　space　is　really　like。　Real　space　is　curved…and　the　curvature　changes　with　the　amount　of　gravity。〃

〃Yes。。。〃

〃So；〃　Ted　said；　〃space　is　curved　by　gravity。〃

〃Okay。〃

〃And　that　means　that　you　can　think　of　gravity　a

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