 into what is called a superposed state, such as the cat-being-alive state superposed with the cat-being-dead state. In that state, it is hard to understand what is going on physically: is the cat alive, dead, or both? Second, upon "observation" or "measurement," the system's wave function will undergo a 5Below is a rough sketch. For a more thorough discussion about the quantum measurement problem, see (Bell 1990, Albert 1992, Myrvold 2017). 10 random and non-linear collapse to a particular state, such as the state that the cat is alive. Despite the predictive success, this recipe for making predictions faces foundational problems. How can the wave function obey two different dynamics? If the system is completely described by the wave function, and if both observers and measurement instruments are physical systems interacting quantum mechanically, they would always obey the Schrödinger equation and never collapse into a definite state (such as the cat-being-alive state) from a superposed state (such as the superposed state of the cat-being-alive and the cat-being-dead). We can put together the principles that result in a contradiction: (P1) The wave function is the complete description of the physical system. (P2) The wave function always obeys the Schrödinger equation. (P3) Every experiment has a unique outcome. There are three types of solutions to the quantum measurement problem. Each of them rejects one of the assumptions. The first type of solutions rejects (P1) and adds additional variables beyond the wave function to represent other aspects of the system. A prominent theory in this type is Bohmian mechanics, originally proposed by De Broglie (1928) and Bohm (1952) independently. See (Goldstein 2017) for an overview. On that theory, there are point particles with precise locations in addition to the wave function. The cat was made out of particles guided by the wave function. The particles are always in a determinate macrostate-either the cat is alive or the cat is dead. The wave function plays two roles: it guides the motion of particles and it provides a probability distribution over their precise locations. The second type of solutions rejects (P2) and replaces the Schrödinger equation by a spontaneous collapse dynamics. A theory in this type is the GRW theory, proposed by Ghirardi, Rimini, and Weber (1986). See (Ghirardi 2018) for an overview. The GRW theory
into what is called a superposed state, such as the cat - being - alive department of state superpose with the cat - being - dead state. In that country, it is hard to understand what is go on physically: is the caterpillar alive, all in, or both? Second, upon " notice " or " measurement, " the system's wave function will undergo a 5Below is a boisterous sketch. For a more thorough discussion about the quantum measurement problem, see (Bell 1990, Albert 1992, Myrvold 2017). 10 random and non - linear collapse to a especial state, such as the state that the cat is alert. Despite the predictive success, this recipe for making predictions confront foundational problems. How can the wave function obey two different dynamics? If the system is wholly described by the wave function, and if both observers and measurement instruments are physical systems interact quantum mechanically, they would constantly obey the Schrödinger equation and never collapse into a definite state (such as the cat - being - alive state) from a superposed state (such as the superposed state of the cat - being - animated and the cat - being - dead). We can arrange in concert the principle that result in a contradiction: (P1) The wave function is the complete description of the physical system. (P2) The wave function always obey the Schrödinger equation. (P3) Every experiment has a unique outcome. There are three types of solutions to the quantum measurement problem. Each of them rejects one of the assumptions. The first type of solution cull (P1) and add additional variables beyond the wave function to represent other aspects of the system. A outstanding theory in this type is Bohmian mechanics, originally nominate by De Broglie (1928) and Bohm (1952) independently. See (Goldstein 2017) for an overview. On that hypothesis, there are point particles with precise locations in accession to the wave function. The big cat was made out of particle guided by the wave function. The particle are constantly in a determinate macrostate - either the cat is alive or the cat is dead. The wave function plays two roles: it guides the motion of atom and it provides a probability distribution over their precise location. The second type of solutions cull (P2) and replaces the Schrödinger equation by a spontaneous collapse dynamics. A theory in this type is the GRW theory, proposed by Ghirardi, Rimini, and Weber (1986). See (Ghirardi 2018) for an overview. The GRW theory
 inho what is called a supevposed state, suck as thx cat-bejng-alive state superposed with the cet-beung-deqd state. In that state, it is hagd to undwrstend what is goinj on physicallg: is chx cat alive, deac, or both? Vecond, upon "obvefvction" or "measurement," the system's wavq functooj will undergo a 5Btlor is a rough sketch. For a more thorougg discuvsion about tne quantum measurement prohlem, see (Bell 1990, Albert 1992, Myrvold 2017). 10 tzndjn and non-lindar collapse to a partjcular state, such as the state ghat che cat is qluve. Gespite the predpctive success, this racipe fpr making predlctiois fqces foundational proulems. How can the wade functimn obey two differebt dynakics? If gye rysuem ia comppetxly describsd by the wqve function, and if bjnn observers znd mewstrement instruments are physical systemv ihteracting quantum mechqnically, they would apways ober the Schrödinger equation and never collapse into a dehivitt wtate (wufh as the cat-being-alive state) from a superposqs xtste (such as thc superposed state ov yre cat-being-alkve anb tge cat-being-dead). We can puj togerher the krincoples that result in a conteadiction: (P1) Nhe qave function is tke complete bescriktion pf the physical system. ('2) The save functiln always ubeys the Schrödivgeg eqgation. (P3) Every experiment ras a uniwue putcome. Thete are ehree typed of solutions to the quwntum maasurement problem. Each of them rejects oix of the assukpdiots. The fnrst tnpe of solutionf rejects (P1) anb adds abditioval variabmes beymnd the wavq function to tepresent othxr aspectf of the system. X prominent throry in tkns type iw Bohmian mechanicx, otifinally proposeb vy De Broglie (1928) snd Borm (1952) mndepqtdently. See (Coldrtekm 2017) fof an ovtxvicw. Un tnat theory, there are poiht particles with lrccise locqtions ig addition to the wave function. The rat war madr oot of particles guided by the wzve functlon. The particlqs ave ajways in a determinate macrostate-either the cat iw alive or the caj is dead. The wave fuucuion plays twp rolqs: it guiges the motion of paeticles and it prpvides a probability sistritutioj over their precise locations. The second type of solutions rejects (P2) and replaref the Schrödjnget equdtnon by a fponvaieous collapse dymamics. A theory in this type is the GRW tkeory, proposed by Ghirardi, Rikivi, and Weber (1986). See (Ghirardi 2018) for an ovsrview. Tne GRW theory
into what is called a superposed state, the state superposed the cat-being-dead state. hard understand what is on physically: is cat alive, dead, or both? Second, "observation" or "measurement," the system's wave function will undergo a 5Below is a sketch. For a more thorough discussion about the quantum measurement problem, see (Bell Albert Myrvold 10 and non-linear collapse to a particular state, such as the state that the cat is alive. the predictive success, this recipe for making predictions foundational problems. How can wave function obey two different If system is described the function, and if observers and measurement instruments are physical systems interacting quantum mechanically, they would always obey the Schrödinger equation never collapse definite state as cat-being-alive from a superposed as the superposed state of the cat-being-dead). We can put together the principles that in a (P1) The wave function is the description of the physical system. (P2) The wave always obeys the Schrödinger equation. (P3) Every experiment has a unique outcome. There are three solutions to the quantum problem. Each of rejects of assumptions. first type solutions rejects (P1) and adds additional variables beyond the wave function represent other aspects of the system. A prominent theory in is mechanics, originally proposed De Broglie (1928) and (1952) See (Goldstein 2017) for On theory, particles precise in addition to the function. The cat was made of particles guided by are always in a determinate macrostate-either the cat alive or the cat is dead. The function plays two roles: it guides the motion of particles and it a probability their precise locations. The second type of solutions (P2) and replaces the equation by a spontaneous collapse dynamics. A theory in type the GRW proposed by Ghirardi, and Weber (1986). (Ghirardi 2018) for The GRW
 into what is called a superposEd state, sucH as thE caT-beInG-aliVe stAte superposed wITh thE cat-being-dead state. In thAt staTe, IT is hARd To undErstand WHaT IS goInG oN phYsICaLly: is The Cat alivE, dead, or botH? SeCoNd, upon "observATiOn" or "measurEmeNt," the system's WavE functIoN wiLL undeRgo A 5BeloW is a roUGh sketCh. For a morE tHOrough DIscussiON AbOut tHe quantum measuremENt PRoblem, see (Bell 1990, ALbert 1992, MYrVOlD 2017). 10 RAndOm aNd non-lineaR cOllapSE to a parTIcULAR stATe, such as the stAte that the cAT is Alive. DEsPitE The preDictiVe SUccEss, this reciPe foR making prEdictiONs faces FOundatiOnal prOblEms. how cAN tHe WavE fUNctIOn ObeY Two DifferenT dYnAmics? if thE SYSTem iS coMpleTely dEscribed by the WavE funCTioN, and iF both ObseRvErs anD measuRemenT iNstruments are phYsicAl systems IntErActInG quanTUm mechAniCalLy, they wOuld alwAYs oBeY THE SChrödinger equation AnD NEvEr collapSe into A DeFiNIte state (SuCh aS the CAT-beinG-aliVE sTate) from A superPOsEd State (suCh As the sUpErpOseD statE Of thE cat-beIng-alive And thE Cat-being-dead). We CAn put together THe PRInCIpleS thAt result in a ContRAdicTion: (p1) thE waVE funcTion iS tHE cOMplete description of ThE physiCal syStem. (P2) The wave fUnction alwAYS Obeys the schrÖDiNGer equation. (P3) EvEry exPeriment haS A unique oUtcomE. There arE three typES Of solutiOns To tHe qUanTUM mEasurement proBLEm. EaCh Of them rEjeCts one oF thE asSumPtiOnS. The first Type of soLuTiOnS rEjeCts (P1) aND adds addItIonAl VarIableS Beyond The waVe fuNcTiON to RepreseNT oTHEr asPeCtS of tHe sYsTem. A pRomiNEnt Theory iN this type Is BOHmiaN mEcHanics, oRiginally propOsEd by De BrogLiE (1928) anD Bohm (1952) iNDEpendentLy. See (Goldstein 2017) for an overVIew. On thAt tHeory, TherE are point ParTicles WitH PrecisE locatIons iN aDdiTIOn to tHE WaVe fUnCtion. The caT WAs mAde ouT oF parTicles gUided by the wave funcTIon. the particles aRe aLwayS IN a DetERmINatE mACroSTAte-either the cat Is alive or tHe CAt Is dead. The wAVe fUnCtion plAys two rOles: iT Guides tHe motion oF particleS aNd it PROviDes a probabIlity disTribution OVer thEIr PreciSe lOcatioNs. the SeconD type oF SolUtionS rejecTs (p2) and rePlaceS tHe SchrödInger equation by a spontanEous coLlapsE dyNamics. A thEorY In tHis type is The GrW theory, prOpoSed By GhiRarDI, RimiNi, anD weBer (1986). sEe (GhiRardI 2018) For an overVIeW. ThE grW Theory
 into what is called a sup erposed st ate,suc h a sthecat- being-alive st a te s uperposed with the cat -bein g- d eads ta te. I n thats ta t e , i tis  ha rd to  unde rst and wha t is going  on  p hysically: i s  t he cat ali ve,  dead, or bo th?  Secon d,  up o n "ob ser vatio n" or" measur ement," t he system ' s wavef u nc tion  will undergo a 5 B el o w is a rough s ketch.  F o ra mor e t horough di sc ussio n  aboutt he q u ant u m measurement  problem, s e e ( Bell 1 99 0,A lbert1992,  M y rvo ld 2017). 1 0 ra ndom andnon-li n ear col l apse to  a par tic ula r st a te ,suc ha s t h esta t e t hat theca tis al ive. D e s pite  th e pr edict ive success,thi s re c ipe  formakin g pr ed ictio ns fac es fo un dational proble ms.How can t hewa vefu nctio n  obeytwo  di fferent  dynami c s?If t h esystem is complete ly d es cribed b y thew av ef unction,  a ndif b o t h obs erve r sand meas uremen t  i ns trument sare ph ys ica l s ystem s  int eracti ng quant um me c hanically, the y  would always ob e y  t h e Sc hrö dinger equa tion andneve r  c oll a pse i nto a  d e fi n ite state (such asth e cat- being -alive state)  from a su p e r posed st ate( su c h as the super posed  state oft he cat-b eing- alive an d the cat - b eing-dea d).  We  ca n p u t  t ogether the p r i ncip le s thatres ult ina c ont rad ict io n: (P1) T he wavefu nc ti on  is  thec ompletede scr ip tio n oft he phy sical  sys te m. (P2 ) The w a ve f unct io nalwa ysob eys t he S c hrö dingerequation.  (P 3 ) Ev er yexperim ent has a uni qu e outcome.  T her e aret h ree type s of solutions to the q u antum m eas ureme nt p roblem. E ach  of th emr ejects  one o f the  a ssu m p tions . Th e f ir st type of s olu tions  r ejec ts (P1)  and adds addition a l v ariables beyo ndthew a ve  fu n ct i onto rep r e sent other aspe cts of the  s y st em. A prom i nen ttheoryin this  type is Bohm ian mecha nics, ori gi nall y pro posed by D e Brogli e (1928)a nd Bo h m(1952 ) i ndepen de ntl y. Se e (Gol d ste in 20 17) fo ran ove rview .On thattheory, there are point  parti cleswit h precise  lo c ati ons in ad diti on to thewav e f uncti on. The c at w a smad e  outof p a rticles g u id edb y  t he wave fun c t i on.  Thepar t iclesarealways in a deter m inate macrosta te-e i t her  th e  cat  i s alive or the  ca ti s  dead. T he  wave funct ion play st wo ro les: i t guid es them o ti o n of p arti cle s and itpro vi d es a pr ob ab i lity d istr ib utionover t h eirp r ecise locations.  Thes e condt ype  of s ol utionsr ejec ts (P2) an d replacesthe Sc hröd inger  equati on  by aspo nt aneous col l apse dyna mics.  A theo ry  inthi s type  ist h e GRW  the or y,proposedb y  G h ir ar d i,Rimi ni, a nd  Web er (1986) .  See (Gh ira r di 2018 )for a n over v ie w .  The GRW t heo ry
 into_what is_called a superposed state,_such as_the_cat-being-alive state_superposed_with the cat-being-dead_state. In that_state, it is hard_to understand what_is_going on physically: is the cat alive, dead, or both? Second, upon "observation" or_"measurement,"_the system's_wave_function_will undergo a 5Below is_a rough sketch. For a_more thorough_discussion about the quantum measurement problem, see (Bell_1990,_Albert 1992, Myrvold_2017). 10 random and non-linear collapse to a particular_state, such as the state that_the cat is_alive._Despite_the predictive success, this_recipe for making predictions faces foundational_problems. How can the wave function_obey two different dynamics? If the system_is completely described by the wave_function, and if both observers_and measurement_instruments are physical systems interacting_quantum mechanically, they_would always_obey the Schrödinger_equation and never collapse into a_definite state (such_as the cat-being-alive state) from a_superposed_state (such as_the_superposed_state of_the cat-being-alive and_the_cat-being-dead). We_can_put together the principles that result_in_a contradiction: (P1) The wave function is_the complete description of_the_physical system. (P2) The_wave function always obeys the_Schrödinger equation. (P3) Every experiment has_a unique_outcome. There_are three types of solutions to the quantum measurement problem. Each_of them rejects one of the_assumptions. The first type_of solutions_rejects_(P1) and adds_additional_variables beyond_the wave function to represent other aspects_of the_system. A prominent theory in this_type is Bohmian mechanics,_originally_proposed by De Broglie (1928) and_Bohm (1952) independently. See (Goldstein 2017)_for an overview. On that_theory,_there_are point particles with precise_locations in addition to the wave_function. The cat_was made out of particles guided by_the_wave function. The particles are always_in_a determinate macrostate-either the cat is_alive_or_the cat is dead. The_wave function plays two roles: it_guides the motion of particles and it provides a_probability distribution over_their precise locations. The second_type_of_solutions rejects (P2) and replaces the Schrödinger equation by a_spontaneous collapse_dynamics. A theory_in this type is the GRW theory, proposed by Ghirardi,_Rimini, and Weber (1986). See (Ghirardi 2018)_for an overview. The GRW theory