SimpleQuestionswithNoAnswers七件没有答案的简单现象.ppt

7SimpleQuestionswithNoAnswers,Askaphysicistabouttheradiusoftheblackholeatthecenterofthegalaxyandshelltellyoumorethanyouwantedtoknow.Askherhowabicycleworks,andshellshrug.Itmaysurpriseyoutolearnthatscientistslackexplanationsforsomeofthesimplestquestionsyoumightthinktoask.Readonforatasteofthemanyseeminglymundanequestionsnoknowcananswer.,Whatcausesstaticelectricity?,Staticshocksareasmysteriousastheyareunpleasant.Whatweknowisthis:Theyoccurwhenanexcessofeitherpositiveornegativechargebuildsuponthesurfaceofyourbody,dischargingwhenyoutouchsomethingandleavingyouneutralized.Alternatively,theycanoccurwhenstaticelectricitybuildsuponsomethingelseadoorknob,saywhichyouthentouch.Inthatcase,youaretheexcesschargesexitroute.,Butwhyallthebuildup?Itsunclear.Thetraditionalexplanationsaysthatwhentwoobjectsrubtogether,frictionknockstheelectronsofftheatomsinoneoftheobjects,andthesethenmoveontothesecond,leavingthefirstobjectwithanexcessofpositivelychargedatomsandgivingthesecondanexcessofnegativeelectrons.Bothobjects(yourhairandawoolhat,say)willthenbestaticallycharged.Butwhydoelectronsflowfromoneobjecttotheother,insteadofmovinginbothdirections?Thishasneverbeensatisfactorilyexplained,andastudybyNorthwesternUniversityresearcherBartoszGrzybowskifoundreasontodoubtthewholestory.AsdetailedlastyearinthejournalScience,Grzybowskifoundthatpatchesofbothexcesspositiveandexcessnegativechargeexistonstaticallychargedobjects.Healsofoundthatentiremoleculesseemedtomigratebetweenobjectsastheyarerubbedtogether,notjustelectrons.Whatgeneratesthismosaicofchargesandmigrationofmaterialhasyettobedetermined,butclearly,theexplanationofstaticischanging.,Whyisyawningcontagious?,Lastyear,AustrianresearcherswonanIgNobelPrizefortheirdiscoverythatyawnsarenotcontagiousamongred-footedtortoises.Weknowsomuchabouttortoises,buthumanyawning?Stillanenigma.Thesightofapersonsgapingjaws,squintingeyesanddeepinhalationhijacksyourbodyandinducesyoutoreplicatetheobservedbehavior,writestheUniversityofMaryland,BaltimoreCounty,psychologistRobertProvineinhisnewbook,CuriousBehavior(BelknapPress,2012).Butwhy?,Preliminarybrain-scandataindicatethatregionsofthebrainassociatedwiththeoryofmind(theabilitytoattributementalstatesandfeelingstooneselfandothers)andself-processingbecomeactivewhenpeopleobserveotherpeopleyawning.Manyautisticandschizophrenicpeopledonotexhibitthisbrainactivity,andtheydonotcatchyawns.Thesecluessuggestcontagiousyawningreflectsanabilitytoempathizeandformnormalemotionaltieswithothers,Provineexplained.Butwhyshouldoursocialconnectionswithoneanothercirculatethroughyawning,asopposedtohiccuppingorpassinggas?Nooneknowsforsure,andthatsbecausenooneknowsquitewhyweyawn.Embryosdoittosculptthehingeoftheirjaws.Fullyformedpeopledoitwhenweresleepyandbored.Buthowdoesyawningamelioratethesecomplaints?,Whyaretherelefties(andrighties)?,One-tenthofpeoplehavebettermotordexterityusingtheirleftlimbsthantheirright.Nooneknowswhytheseleftiesexist.Andnooneknowswhyrightiesexisteither,forthatmatter.Whydopeoplehavejustonehandwithtop-notchmotorskills,insteadofadoubledoseofdexterity?Onetheoryholdsthathandednessresultsfromhavingmoreintricatewiringonthesideofthebraininvolvedinspeech(whichalsorequiresfinemotorskills).Becausethespeechcenterusuallysitsinthebrainslefthemispherethesidewiredtotherightsideofthebodytherighthandendsupdominantinmostpeople.Asforwhythespeechcenterusually(butnotalways)endsupintheleftsideofthebrain,thatsstillanopenquestion.Thetheoryaboutthespeechcentercontrollinghandednessgetsabigblowfromthefactthatnotallright-handedpeoplecontrolspeechinthelefthemisphere,whileonlyhalfofleftiesdo.So,whatexplainsthoseleftieswhosespeechcentersresideintheleftsidesoftheirbrains?Itsallveryperplexing.,Whyaremothsdrawntolights?,Look!Thatmothjustflewstraightintothatlightbulbanddied!saidnooneever.Weseeithappensooftenthatitsmorelikelytoinvokeyawnsthandiscussion.But,surprisingly,thereasonfortheseinsectssuicidalnosedivesremainsatotalmystery.Sciencesbestguessesaboutwhytheydoitarentevenverygood.Someentomologistsbelievemothszoomtowardartificiallightsourcesbecausethelightsthrowofftheirinternalnavigationsystems.Inabehaviorcalledtransverseorientation,someinsectsnavigatebyflyingataconstantanglerelativetoadistantlightsource,suchasthemoon.Butaroundman-madelights,suchasacampfireoryourporchlight,theangletothelightsourcechangesasamothfliesby.JerryPowell,anentomologistattheUniversityofCalifornia,Berkeleysaidthethinkingisthatmothsbecomedazzledbythelightandaresomehowattracted.,Butthistheoryrunsintotwomajorstumblingblocks,Powellexplained:First,campfireshavebeenaroundforabout400,000years.Wouldntnaturalselectionhavekilledoffmothswhoseinstincttellsthemtogokamikazeeverytimetheyfeelblindedbythelight?Secondly,mothsmaynotevenusetransversenavigation;morethanhalfofthespeciesdontevenmigrate.Alternatetheoriesareriddledwithholes,too.Forexample,oneholdsthatmalemothsareattractedtoinfraredlightbecauseitcontainsafewofthesamelightfrequenciesgivenoffbyfemalemothspheromones,orsexhormones,whichglowveryfaintly.Inshort,malemothscouldbedrawntocandlesunderthefalsebeliefthatthelightsarefemalessendingoutsexsignals.However,Powellpointsoutthatmothsaremoreattractedtoultravioletlightthaninfraredlight,andUVdoesntlookabitlikeglowingpheromones.Mothdeaths:notasyawn-inducingasyoumightthink.,Whydoeslightninghappen?,Weknowwhylightningstrikes:Ithappensbecausepositiveelectricchargesbuildupnearthetopsofthundercloudsandnegativechargesbuildupatthebottoms.Theelectricalattractionbetweentheseoppositecharges,andbetweenthenegativechargesandpositivechargesthatbuilduponthegroundbelow,eventuallygrowsstrongenoughtoovercometheairsresistancetoelectricalflow.Thechargessuddenlyshoottowardoneanotherandconnect,completinganelectricalcircuitandtriggeringaflashoflightningaschargesshootalongthecircuittheyhaveformed.Butwhydooppositechargesbuildupindifferentpartsofclouds?,Itsasubjectofgreattheoreticaldebate.Onetheoryholdsthatwheniceparticleswithinacloudcollide,theytendtofractureintosmallerparticleswithpositivecharge,andlargerparticleswithnegativecharge.Gravitypullsthelarger,negativelychargedparticlesdownward,andupdraftsliftthesmaller,positivelychargedparticlesupward,resultinginanimbalance.Butmeasuredvaluesofelectricfieldsinthundercloudsdontseemtomatchthosescientistswoudlexpecttoresultfromthisprocess.Anothertheoryholdsthathigh-energyelectronsdeliveredbycosmicraysfromspaceshootdownthroughthecloud,strippingoffmorenegativelychargedelectronsastheygoanddraggingthemtowardthebottomofthecloud,causingthechargeimbalance.Whichistherightexplanation?Thejuryoflightningscientistsisstillout.,Howdobicycleswork?,Wevebeenridingthemforaboutacentury,allthewhilethinkingsomeoneouttherehadahandleonhow,exactly,theyworked.Butasitturnsout,noonedid.Andtheystilldont.Bikescanstayuprightallbythemselves,aslongastheyremovingforward;itsbecauseanytimeamovingbikestartstolean,itssteeringaxis(thepoleattachedtothehandlebars)turnstheotherway,tiltingthebikeuprightagain.Thisrestorativeeffectwaslongbelievedtoresultfromalawofphysicscalledtheconservationofangularmomentum:Whenthebikewobbles,theaxisperpendiculartoitswheelsspinningdirectionthreatenstochange,andthebikeself-correctsinordertoconservethedirectionofthataxis.Inotherwords,thebikeisagyroscope.Additionally,thetraileffectwasthoughttohelpkeepbikesstable:Becausethesteeringaxishitsthegroundslightlyinfrontofthegroundcontactpointofthefrontwheel,thewheelisforcedtotrailthesteeringofthehandlebars.,Butrecently,agroupofengineersledbyAndyRuinaofCornellUniversityupturnedthistheoryofbicyclelocomotion.Theirinvestigation,detailedina2011articleinthejournalScience,showedthatneithergyroscopicnortraileffectswerenecessaryforabiketowork.Toproveit,theengineersbuiltacustombicyclewhichcouldtakeadvantageofneithereffect.Thebikewasdesignedsothateachofitswheelsrotatedasecondwheelaboveitintheoppositedirection.Thatway,thespinningofthewheelscanceledoutandthebikestotalangularmomentumwaszero,erasingtheinfluenceofgyroscopiceffectsonthebikesstability.Thecustombikesgroundcontactpointwasalsopositionedinfrontofitssteeringaxis,destroyingthetraileffect.Andyet,thebikeworked.Theengineersknowwhy:theyaddedmassestothebikeinchoiceplacestoenablegravitytocausethebiketoself-steer.Buttheworkshowedtherearemanyeffectsthatgointothestabilityofbicyclesincludinggyroscopicandtraileffectsinthecaseofbikesthathavethemwhichinteractinextremelycomplexways.Thecomplexinteractionshavenotbeenworkedout.Mysuspicionisthatwewillnevercometogripswiththem,butIdontknowthatforsure,RuinatoldLifesLittleMysteries.,Whydocatspurr