很有意思-时间的七个箭头 7 Arrows of Time

TonyRothmanDeep(est)ParadoxofPhysics:PhysicsisTimeSymmetricNatureisNotFundamentalTheoriesofPhysicsDon’tCareWhichWayTimeGoes•NewtonianPhysics•Electromagnetism•Relativity•QuantumMechanicsNevertheless,NatureCaresRogerPenroselistssevenwaysinwhichNaturedistinguishespastfromfuture,seven“arrowsoftime”SevenArrowsofTime1.MemoryArrow2.ElectromagneticArrow3.QuantumArrow4.BlackHoleArrow5.CosmologicalArrow6.KaonArrow7.EntropyArrow1.MemoryArrowMemoryonlyworksbackwards(Wedon'trememberthefuture)2.ElectromagneticArrowElectromagneticCausesPrecedeEffects3.QuantumArrowWaveFunctions“Collapse”ButDon’t“Uncollapse”4.BlackHoleArrowBlackHolesExistButWhiteHolesDon’t(Apparently)5.CosmologicalArrowWeliveinanexpandinguniverse,notacontractingone.Wouldtimechangedirectionifuniversestartedcontracting?6.KaonArrowKaondecaynottimesymmetricKoππInatime-reversedworldthisparticledecaysatadifferentratethaninourworld!CPTtheorem“Charge-Parity-Time”Changeelectricchargeofallparticlesinworld(Changeallparticlestoantiparticles);Reflectitinmirror;Runtimebackwards:NewworldisindistinguishablefromoldPrinceton1964Experiment:•KaondecaynotinvariantunderCP-reversal•MustalsochangeunderT-reversal7.EntropyArrowEntropyalwaysincreases(secondlawofthermodynamics)Question:Arearrowsindependent?Hawking:Memoryandentropyarrowslinked(Requiresenergytoreadonebit,increasesentropybycertainamount)RothmantoPenrose:Onearrowarbitrary;onlysixindependentsigns.SudarshantoRothman:AllparticledecayCPTinvariantbutIrreversible:Particle-decayarrow.RothmantoRothman:Temperaturedependent?Entropy•Entropycanbethoughtofaswasteheatgeneratedinanyrealisticprocess•“Disorder”inasystemSecondLaw:Entropyofasystemalwaysincreasesunderrealistic(“irreversible”)processOnlylawofnaturethatexhibitsdirectionoftime!“Thermodynamicsystem”:Systemwithlotsofparticles(Gas)ObeyssecondlawButindividualparticlesobeyNewtonianphysicsCentralParadox:Gasisathermodynamicsystem;obeyssecondlaw.Butifgasparticlesindividuallyobeytime-symmetricNewtonianphysics,howcanarrowoftimearise?BoltzmannattemptstoderiveincreaseofentropyfromNewtonianPhysicsH-TheoremLoschmidtStrikesBackBoltzmanngoestoprobabilistictheoryAnordereddeckofcardsbecomesdisorderedonshufflingGibbsstrikesbackAnotherProblem:EntropyshouldnotalwaysbeequatedwithdisorderPrigogine’sSolution:SecondLawisfundamental.Can’tderive.ChaoticsystemsmanifestirreversibleBehavior.EntropyincreasetiedupwithchaosObjection:Chaoticsystemsaretime-symmetric.Ifasystemischaoticintothefuture,itisalsochaoticintothepastConclusion:Todatenosatisfactoryexplanationfordirectionoftime