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Timeisverytroublesome.The19thcenturyprovidedasimplemathematical
descriptionoftimebutbehindithidesaphysicalphenomenonthatishardto
grasp.Thereisalsoasubjectivesenseoftime.Thetwoareconnected.Explana-
tionofthisconnectionisataskofnaturalsciences:forphysics,physiology,and
psychology.Inspiteofitsvagueness,timeissubjectivelythemostcontinuous
ofallcontinuities:ifwecannotimagineabreakinthespacethenwecannot
possiblyimagineabreakintime.
Itseemsthattimeisastreamofeventswithadirection.Itisn3tclearwhether
thenotionofdirectionoftimeisduetooursensesorispartofthenatureof
things.Timeseemstoflowcontinuously.Ifnotmuchisgoingon,thenwenotice
changesoftheintensityofitsflow,momentaryatrophiesandturnings.Weseem
toflowwiththestream.Wedonotknowiftheflowoftimeiseverywhere
thesameandwhetheritwillalwaysbethesame.Wecannotimagineitsever
comingtoanendanditseverbeginning.Weexperiencethephysicalnature
oftimemosthavingintenselywhenwecanturntimeback.Preconditionsfor
thisare:asmallnumberofphenomenaandnotmuchhappening.Thenwecan
turnthetimebackbyrestoringearlierpositionsofmovedobjects.Toturnthe
timebackinthefullsenseofthewordwewouldneedalltheenergyinthe
world,ifnotmore.Aristotle,withPlatoinmind,saidthat“Someclaimsthat
timeisthemotionofthewholeworld.”St.AugustineagreedwithPlatoand
thoughtthattimebeganatthemomentofcreation,andaddedthatbeforethat
momenteternityruled.
Wetendtothinkofamomentasapointseparatingthepastofthefuture.
Thismeansthatwearewillingtotreattimeastheorderedcontinuum,auni-
versalcontinuumforallphenomena,but,strictlyspeaking,weneverascertain
thisuniversality.Eachrangeofphenomenaseemstohaveitsowntimestream.
Thetimenotionweuseisalwaysastrandweattributetothestreamofphe-
nomenainwhichwemove.Inthatstrandamomentseemstohaveadefinite
content.Inmathematicalproblemswerestrictphenomenasothattimetakes
onthestructureofastraightline.
Theancientsremovedtimefromtherangeofmathematics.Theirgeometry
1asAristotlestatedsuccintly1waslimitedtoconsiderationofmotionless
existences.Theyhaddefinitereasonsforsodoing.Wewilltalkoftheserea-
sons.Modernmathematicshasincludedtimeinitsdeliberationasaschematic
existencedevoidofallthevariedpropertiessuggestedbyitsnature.
Wespeakofspaceandtimeasofthings.Wehavenorighttodothisbe-
causethesearequalitiesofthingsratherthanthings,qualitieswemightcall
spacenessandvariability.Butwhenspeakingaboutqualitiesofthingswesome-
timesfinditconvenienttoelevatethemtothelevelofthings.Thenweforget
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