520美书楼

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第14部分（第1页）

〃Yes。。。〃

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

〃Okay。〃

〃And　that　means　that　you　can　think　of　gravity　as　nothing　more　than　the　curvature　of　space。　The　Earth　has　gravity　because　the　Earth　curves　the　space　around　it。〃

〃Okay。〃

〃Except　its　not　that　simple；〃　Ted　said。

Norman　sighed。　〃I　didnt　think　it　would　be。〃

Harry　came　back　into　the　room；　looked　at　the　fruit　on　the　table；　but　said　nothing。

〃Now；〃　Ted　said；　〃when　you　roll　your　ball　bearing　across　the　bowl；　you　notice　that　it　not　only　spirals　down；　but　it　also　goes　faster；　right？〃

〃Yes。〃

〃Now；　when　an　object　goes　faster；　time　on　that　object　passes　slower。　Einstein　proved　that　early　in　the　century。　What　it　means　is　that　you　can　think　of　the　curvature　of　space　as　also　representing　a　curvature　of　time。　The　deeper　the　curve　in　the　bowl；　the　slower　time　passes。〃

Harry　said；　〃Well　。。。〃

〃Laymans　terms；〃　Ted　said。　〃Give　the　guy　a　break。〃

〃Yeah；〃　Norman　said；　〃give　the　guy　a　break。〃

Ted　held　up　the　bowl。　〃Now；　if　youre　doing　all　this　mathematically；　what　you　find　is　that　the　curved　bowl　is　neither　space　nor　time；　but　the　bination　of　both；　which　is　called＇＇87＇＇　space…time。　This　bowl　is　space…time；　and　objects　moving　on　it　are　moving　in　space…time。　We　dont　think　about　movement　that　way；　but　thats　really　whats　happening。〃

〃It　is？〃

〃Sure。　Take　baseball。〃

〃Idiot　game；〃　Harry　said。　〃I　hate　games。〃

〃You　know　baseball？〃　Ted　said　to　Norman。

〃Yes；〃　Norman　said。

〃Okay。　Imagine　the　batter　hits　a　line　drive　to　the　center　fielder。　The　ball　goes　almost　straight　out　and　takes；　say；　half　a　second。〃

〃Right。〃

〃Now　imagine　the　batter　hits　a　high　pop　fly　to　the　same　center　fielder。　This　time　the　ball　goes　way　up　in　the　air；　and　it　takes　six　seconds　before　the　center　fielder　catches　it。〃

〃Okay。〃

〃Now；　the　paths　of　the　two　balls…the　line　drive　and　the　pop　fly…look　very　different　to　us。　But　both　these　balls　moved　exactly　the　same　in　space…time。〃

〃No；〃　Norman　said。

〃Yes；〃　Ted　said。　〃And　in　a　way；　you　already　know　it。　Suppose　I　ask　you　to　hit　a　high　pop　fly　to　the　center　fielder；　but　to　make　it　reach　the　fielder　in　half　a　second　instead　of　six　seconds。〃

〃Thats　impossible；〃　Norman　said。

〃Why？　Just　hit　the　pop　fly　harder。〃

〃If　I　hit　it　harder；　it　will　go　higher　and　end　up　taking　longer。〃

〃Okay；　then　hit　a　low　line　drive　that　takes　six　seconds　to　reach　center　field。〃

〃I　cant　do　that；　either。〃

〃Right；〃　Ted　said。　〃So　what　you　are　telling　me　is　that　you　cant　make　the　ball　do　anything　you　want。　There　is　a　fixed　relationship　governing　the　path　of　the　ball　through　space　and　time。〃

〃Sure。　Because　the　Earth　has　gravity。〃

〃Yes；〃　Ted　said；　〃and　weve　already　agreed　that　gravity　is　a　curvature　of　space…time；　like　the　curve　of　this　bowl。　Any　baseball　on　Earth　must　move　along　the　same　curve　of　＇＇88＇＇　space…time；　as　this　ball　bearing　moves　along　this　bowl。　Look。〃　He　put　the　orange　back　in　the　bowl。　〃Heres　the　Earth。〃　He　put　two　fingers　on　opposite　sides　of　the　orange。　〃Heres　batter　and　fielder。　Now；　roll　the　ball　bearing　from　one　finger　to　the　other；　and　youll　find　you　have　to　acmodate　the　curve　of　the　bowl。　Either　you　flick　the　ball　lightly　and　it　will　roll　close　to　the　orange；　or　you　can　give　it　a　big　flick　and　it　will　go　way　up　the　side　of　the　bowl；　before　falling　down　again　to　the　other　side。　But　you　cant　make　this　ball　bearing　do　anything　you　want；　because　the　ball　bearing　is　moving　along　the　curved　bowl。　And　thats　what　your　baseball　is　really　doing…its　moving　on　curved　space…time。〃

Norman　said；　〃I　sort　of　get　it。　But　what　does　this　have　to　do　with　time　travel？〃

〃Well；　we　think　the　gravitational　field　of　the　Earth　is　strong…it　hurts　us　when　we　fall　down…but　in　reality　its　very　weak。　Its　almost　nonexistent。　So　space…time　around　the　Earth　isnt　very　curved。　Space…time　is　much　more　curved　around　the　sun。　And　in　other　parts　of　the　universe；　its　very　curved；　producing　a　sort　of　roller…coaster　ride；　and　all　sorts　of　distortions　of　time　may　occur。　In　fact；　if　you　consider　a　black　hole…〃

He　broke　off。

〃Yes；　Ted？　A　black　hole？〃

〃Oh　my　God；〃　Ted　said　softly。

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