The Quantum Physics Sequence

This is an in­clu­sive guide to the se­ries of posts on quan­tum me­chan­ics that be­gan on April 9th, 2008, in­clud­ing the di­gres­sions into re­lated top­ics (such as the differ­ence be­tween Science and Bayesi­anism) and some of the pre­limi­nary read­ing.

You may also be in­ter­ested in one of the less in­clu­sive post guides, such as:

My cur­rent plan calls for the quan­tum physics se­ries to even­tu­ally be turned into one or more e-books.


  • Prob­a­bil­ity is in the Mind: If you are un­cer­tain about a phe­nomenon, this is a fact about your state of mind, not a fact about the phe­nomenon it­self. There are mys­te­ri­ous ques­tions but not mys­te­ri­ous an­swers. The map is not the ter­ri­tory.

  • Re­duc­tion­ism: We build mod­els of the uni­verse that have many differ­ent lev­els of de­scrip­tion. But so far as any­one has been able to de­ter­mine, the uni­verse it­self has only the sin­gle level of fun­da­men­tal physics—re­al­ity doesn’t ex­plic­itly com­pute pro­tons, only quarks.

  • Joy in the Merely Real: If you can’t take joy in things that turn out to be ex­pli­ca­ble, you’re go­ing to set your­self up for eter­nal dis­ap­point­ment. Don’t worry if quan­tum physics turns out to be nor­mal.

  • Zom­bies! Zom­bies? and The Gen­er­al­ized Anti-Zom­bie Prin­ci­ple: Don’t try to put your con­scious­ness or your per­sonal iden­tity out­side physics. What­ever makes you say “I think there­fore I am”, causes your lips to move; it is within the chains of cause and effect that pro­duce our ob­served uni­verse.

  • Belief in the Im­plied In­visi­ble: If a space­ship goes over the cos­molog­i­cal hori­zon rel­a­tive to us, so that it can no longer com­mu­ni­cate with us, should we be­lieve that the space­ship in­stantly ceases to ex­ist?

Ba­sic Quan­tum Me­chan­ics:

  • Quan­tum Ex­pla­na­tions: Quan­tum me­chan­ics doesn’t de­serve its fear­some rep­u­ta­tion. If you tell peo­ple some­thing is sup­posed to be mys­te­ri­ous, they won’t un­der­stand it. It’s hu­man in­tu­itions that are “strange” or “weird”; physics it­self is perfectly nor­mal. Talk­ing about his­tor­i­cal er­ro­neous con­cepts like “par­ti­cles” or “waves” is just ask­ing to con­fuse peo­ple; pre­sent the real, unified quan­tum physics straight out. The se­ries will take a strictly re­al­ist per­spec­tive—quan­tum equa­tions de­scribe some­thing that is real and out there. Warn­ing: Although a large fac­tion of physi­cists agrees with this, it is not uni­ver­sally ac­cepted. Stronger warn­ing: I am not even go­ing to pre­sent non-re­al­ist view­points un­til later, be­cause I think this is a ma­jor source of con­fu­sion.

  • Con­figu­ra­tions and Am­pli­tude: A pre­limi­nary glimpse at the stuff re­al­ity is made of. The clas­sic split-pho­ton ex­per­i­ment with half-silvered mir­rors. Alter­na­tive path­ways the pho­ton can take, can can­cel each other out. The mys­te­ri­ous mea­sur­ing tool that tells us the rel­a­tive squared mod­uli.

  • Joint Con­figu­ra­tions: The laws of physics are in­her­ently over math­e­mat­i­cal en­tities, con­figu­ra­tions, that in­volve mul­ti­ple par­ti­cles. A ba­sic, on­tolog­i­cally ex­is­tent en­tity, ac­cord­ing to our cur­rent un­der­stand­ing of quan­tum me­chan­ics, does not look like a pho­ton—it looks like a con­figu­ra­tion of the uni­verse with “A pho­ton here, a pho­ton there.” Am­pli­tude flows be­tween these con­figu­ra­tions can can­cel or add; this gives us a way to de­tect which con­figu­ra­tions are dis­tinct. It is an ex­per­i­men­tally testable fact that “Pho­ton 1 here, pho­ton 2 there” is the same con­figu­ra­tion as “Pho­ton 2 here, pho­ton 1 there”.

  • Distinct Con­figu­ra­tions: Since con­figu­ra­tions are over the com­bined state of all the el­e­ments in a sys­tem, adding a sen­sor that de­tects whether a par­ti­cle went one way or the other, be­comes a new el­e­ment of the sys­tem that can make con­figu­ra­tions “dis­tinct” in­stead of “iden­ti­cal”. This con­fused the liv­ing daylights out of early quan­tum ex­per­i­menters, be­cause it meant that things be­haved differ­ently when they tried to “mea­sure” them. But it’s not only mea­sur­ing in­stru­ments that do the trick—any sen­si­tive phys­i­cal el­e­ment will do—and the dis­tinct­ness of con­figu­ra­tions is a phys­i­cal fact, not a fact about our knowl­edge. There is no need to sup­pose that the uni­verse cares what we think.

  • Where Philos­o­phy Meets Science: In ret­ro­spect, sup­pos­ing that quan­tum physics had any­thing to do with con­scious­ness was a big mis­take. Could philoso­phers have told the physi­cists so? But we don’t usu­ally see philoso­phers spon­sor­ing ma­jor ad­vances in physics; why not?

  • Can You Prove Two Par­ti­cles Are Iden­ti­cal?: You wouldn’t think that it would be pos­si­ble to do an ex­per­i­ment that told you that two par­ti­cles are com­pletely iden­ti­cal—not just to the limit of ex­per­i­men­tal pre­ci­sion, but perfectly. You could even give a pre­cise-sound­ing philo­soph­i­cal ar­gu­ment for why it was not pos­si­ble—but the ar­gu­ment would have a deeply buried as­sump­tion. Quan­tum physics vi­o­lates this deep as­sump­tion, mak­ing the ex­per­i­ment easy.

  • Clas­si­cal Con­figu­ra­tion Spaces: How to vi­su­al­ize the state of a sys­tem of two 1-di­men­sional par­ti­cles, as a sin­gle point in 2-di­men­sional space. A pre­limi­nary step be­fore mov­ing into...

  • The Quan­tum Arena: In­stead of a sys­tem state be­ing as­so­ci­ated with a sin­gle point in a clas­si­cal con­figu­ra­tion space, the in­stan­ta­neous real state of a quan­tum sys­tem is a com­plex am­pli­tude dis­tri­bu­tion over a quan­tum con­figu­ra­tion space. What cre­ates the illu­sion of “in­di­vi­d­ual par­ti­cles”, like an elec­tron caught in a trap, is a plaid dis­tri­bu­tion—one that hap­pens to fac­tor into the product of two parts. It is the whole dis­tri­bu­tion that evolves when a quan­tum sys­tem evolves. In­di­vi­d­ual con­figu­ra­tions don’t have physics; am­pli­tude dis­tri­bu­tions have physics. Quan­tum en­tan­gle­ment is the gen­eral case; quan­tum in­de­pen­dence is the spe­cial case.

  • Feyn­man Paths: In­stead of think­ing that a pho­ton takes a sin­gle straight path through space, we can re­gard it as tak­ing all pos­si­ble paths through space, and adding the am­pli­tudes for ev­ery pos­si­ble path. Nearly all the paths can­cel out—un­less we do clever quan­tum things, so that some paths add in­stead of can­cel­ing out. Then we can make light do funny tricks for us, like re­flect­ing off a mir­ror in such a way that the an­gle of in­ci­dence doesn’t equal the an­gle of re­flec­tion. But or­di­nar­ily, nearly all the paths ex­cept an ex­tremely nar­row band, can­cel out—this is one of the keys to re­cov­er­ing the hal­lu­ci­na­tion of clas­si­cal physics.

  • No In­di­vi­d­ual Par­ti­cles: One of the chief ways to con­fuse your­self while think­ing about quan­tum me­chan­ics, is to think as if pho­tons were lit­tle billiard balls bounc­ing around. The ap­pear­ance of lit­tle billiard balls is a spe­cial case of a deeper level on which there are only mul­ti­par­ti­cle con­figu­ra­tions and am­pli­tude flows. It is easy to set up phys­i­cal situ­a­tions in which there ex­ists no fact of the mat­ter as to which elec­tron was origi­nally which.

  • Iden­tity Isn’t In Spe­cific Atoms, Three Dialogues on Iden­tity: Given that there’s no such thing as “the same atom”, whether you are “the same per­son” from one time to an­other can’t pos­si­bly de­pend on whether you’re made out of the same atoms.

  • De­co­her­ence: A quan­tum sys­tem that fac­tor­izes can evolve into a sys­tem that doesn’t fac­tor­ize, de­stroy­ing the illu­sion of in­de­pen­dence. But en­tan­gling a quan­tum sys­tem with its en­vi­ron­ment, can ap­pear to de­stroy en­tan­gle­ments that are already pre­sent. En­tan­gle­ment with the en­vi­ron­ment can sep­a­rate out the pieces of an am­pli­tude dis­tri­bu­tion, pre­vent­ing them from in­ter­act­ing with each other. De­co­her­ence is fun­da­men­tally sym­met­ric in time, but ap­pears asym­met­ric be­cause of the sec­ond law of ther­mo­dy­nam­ics.

  • The So-Called Heisen­berg Uncer­tainty Prin­ci­ple: Un­like clas­si­cal physics, in quan­tum physics it is not pos­si­ble to sep­a­rate out a par­ti­cle’s “po­si­tion” from its “mo­men­tum”. The evolu­tion of the am­pli­tude dis­tri­bu­tion over time, in­volves things like tak­ing the sec­ond deriva­tive in space and mul­ti­ply­ing by i to get the first deriva­tive in time. The end re­sult of this time evolu­tion rule is that blobs of par­ti­cle-pres­ence ap­pear to race around in phys­i­cal space. The no­tion of “an ex­act par­tic­u­lar mo­men­tum” or “an ex­act par­tic­u­lar po­si­tion” is not some­thing that can phys­i­cally hap­pen, it is a tool for an­a­lyz­ing am­pli­tude dis­tri­bu­tions by tak­ing them apart into a sum of sim­pler waves. This uses the as­sump­tion and fact of lin­ear­ity: the evolu­tion of the whole wave­func­tion seems to always be the ad­di­tive sum of the evolu­tion of its pieces. Us­ing this tool, we can see that if you take apart the same dis­tri­bu­tion into a sum of po­si­tions and a sum of mo­menta, they can­not both be sharply con­cen­trated at the same time. When you “ob­serve” a par­ti­cle’s po­si­tion, that is, de­co­here its po­si­tional dis­tri­bu­tion by mak­ing it in­ter­act with a sen­sor, you take its wave packet apart into two pieces; then the two pieces evolve differ­ently. The Heisen­berg Prin­ci­ple definitely does not say that know­ing about the par­ti­cle, or con­sciously see­ing it, will make the uni­verse be­have differ­ently.

  • Which Ba­sis Is More Fun­da­men­tal?: The po­si­tion ba­sis can be com­puted lo­cally in the con­figu­ra­tion space; the mo­men­tum ba­sis is not lo­cal. Why care about lo­cal­ity? Be­cause it is a very deep prin­ci­ple; re­al­ity it­self seems to fa­vor it in some way.

  • Where Physics Meets Ex­pe­rience: Meet the Eb­bo­ri­ans, who re­pro­duce by fis­sion. The Eb­bo­rian brain is like a thick sheet of pa­per that splits down its thick­ness. They fre­quently ex­pe­rience di­vid­ing into two minds, and can talk to their other selves. It seems that their unified the­ory of physics is al­most finished, and can an­swer ev­ery ques­tion, when one Eb­bo­rian asks: When ex­actly does one Eb­bo­rian be­come two peo­ple?

  • Where Ex­pe­rience Con­fuses Physi­cists: It then turns out that the en­tire planet of Eb­bore is split­ting along a fourth-di­men­sional thick­ness, du­pli­cat­ing all the peo­ple within it. But why does the ap­par­ent chance of “end­ing up” in one of those wor­lds, equal the square of the fourth-di­men­sional thick­ness? Many mys­te­ri­ous an­swers are pro­posed to this ques­tion, and one non-mys­te­ri­ous one.

  • On Be­ing De­co­her­ent: When a sen­sor mea­sures a par­ti­cle whose am­pli­tude dis­tri­bu­tion stretches over space—per­haps see­ing if the par­ti­cle is to the left or right of some di­vid­ing line—then the stan­dard laws of quan­tum me­chan­ics call for the sen­sor+par­ti­cle sys­tem to evolve into a state of (par­ti­cle left, sen­sor mea­sures LEFT) + (par­ti­cle right, sen­sor mea­sures RIGHT). But when we hu­mans look at the sen­sor, it only seems to say “LEFT” or “RIGHT”, never a mix­ture like “LIGFT”. This, of course, is be­cause we our­selves are made of par­ti­cles, and sub­ject to the stan­dard quan­tum laws that im­ply de­co­her­ence. Un­der stan­dard quan­tum laws, the fi­nal state is (par­ti­cle left, sen­sor mea­sures LEFT, hu­man sees “LEFT”) + (par­ti­cle right, sen­sor mea­sures RIGHT, hu­man sees “RIGHT”).

  • The Con­scious Sorites Para­dox: De­co­her­ence is im­plicit in quan­tum physics, not an ex­tra law on top of it. Ask­ing ex­actly when “one world” splits into “two wor­lds” may be like ask­ing when, if you keep re­mov­ing grains of sand from a pile, it stops be­ing a “heap”. Even if you’re in­side the world, there may not be a definite an­swer. This puz­zle does not arise only in quan­tum physics; the Eb­bo­ri­ans could face it in a clas­si­cal uni­verse, or we could build sen­tient flat com­put­ers that split down their thick­ness. Is this re­ally a physi­cist’s prob­lem?

  • De­co­herece is Pointless: There is no ex­act point at which de­co­her­ence sud­denly hap­pens. All of quan­tum me­chan­ics is con­tin­u­ous and differ­en­tiable, and de­co­her­ent pro­cesses are no ex­cep­tion to this.

  • De­co­her­ent Essences: De­co­her­ence is im­plicit within physics, not an ex­tra law on top of it. You can choose rep­re­sen­ta­tions that make de­co­her­ence harder to see, just like you can choose rep­re­sen­ta­tions that make ap­ples harder to see, but ex­actly the same phys­i­cal pro­cess still goes on; the ap­ple doesn’t dis­ap­pear and nei­ther does de­co­her­ence. If you could make de­co­her­ence mag­i­cally go away by choos­ing the right rep­re­sen­ta­tion, we wouldn’t need to shield quan­tum com­put­ers from the en­vi­ron­ment.

  • The Born Prob­a­bil­ities: The last se­ri­ous mys­te­ri­ous ques­tion left in quan­tum physics: When a quan­tum world splits in two, why do we seem to have a greater prob­a­bil­ity of end­ing up in the larger blob, ex­actly pro­por­tional to the in­te­gral of the squared mod­u­lus? It’s an open prob­lem, but non-mys­te­ri­ous an­swers have been pro­posed. Try not to go funny in the head about it.

  • De­co­her­ence as Pro­jec­tion: Since quan­tum evolu­tion is lin­ear and uni­tary, de­co­her­ence can be seen as pro­ject­ing a wave­func­tion onto or­thog­o­nal sub­spaces. This can be neatly illus­trated us­ing po­larized pho­tons and the an­gle of the po­larized sheet that will ab­sorb or trans­mit them.

  • En­tan­gled Pho­tons: Us­ing our newly ac­quired un­der­stand­ing of pho­ton po­lariza­tions, we see how to con­struct a quan­tum state of two pho­tons in which, when you mea­sure one of them, the per­son in the same world as you, will always find that the op­po­site pho­ton has op­po­site quan­tum state. This is not be­cause any in­fluence is trans­mit­ted; it is just de­co­her­ence that takes place in a very sym­met­ri­cal way, as can read­ily be ob­served in our calcu­la­tions.

Many Wor­lds:

(At this point in the se­quence, most of the math­e­mat­i­cal back­ground has been built up, and we are ready to eval­u­ate in­ter­pre­ta­tions of quan­tum me­chan­ics.)

  • Bell’s The­o­rem: No EPR “Real­ity”: (Note: This post was de­signed to be read as a stand-alone, if de­sired.) Origi­nally, the dis­cov­er­ers of quan­tum physics thought they had dis­cov­ered an in­com­plete de­scrip­tion of re­al­ity—that there was some deeper phys­i­cal pro­cess they were miss­ing, and this was why they couldn’t pre­dict ex­actly the re­sults of quan­tum ex­per­i­ments. The math of Bell’s The­o­rem is sur­pris­ingly sim­ple, and we walk through it. Bell’s The­o­rem rules out be­ing able to lo­cally pre­dict a sin­gle, unique out­come of mea­sure­ments—rul­ing out a way that Ein­stein, Podolsky, and Rosen once defined “re­al­ity”. This shows how deep im­plicit philo­soph­i­cal as­sump­tions can go. If wor­lds can split, so that there is no sin­gle unique out­come, then Bell’s The­o­rem is no prob­lem. Bell’s The­o­rem does, how­ever, rule out the idea that quan­tum physics de­scribes our par­tial knowl­edge of a deeper phys­i­cal state that could lo­cally pro­duce sin­gle out­comes—any such de­scrip­tion will be in­con­sis­tent.

  • Spooky Ac­tion at a Dis­tance: The No-Com­mu­ni­ca­tion The­o­rem: As Ein­stein ar­gued long ago, the quan­tum physics of his era—that is, the sin­gle-global-world in­ter­pre­ta­tion of quan­tum physics, in which ex­per­i­ments have sin­gle unique ran­dom re­sults—vi­o­lates Spe­cial Rel­a­tivity; it im­poses a preferred space of si­mul­tane­ity and re­quires a mys­te­ri­ous in­fluence to be trans­mit­ted faster than light; which mys­te­ri­ous in­fluence can never be used to trans­mit any use­ful in­for­ma­tion. Get­ting rid of the sin­gle global world dis­pels this mys­tery and puts ev­ery­thing back to nor­mal again.

  • De­co­her­ence is Sim­ple, De­co­her­ence is Falsifi­able and Testable: (Note: De­signed to be stan­dalone read­able.) An epis­tle to the physi­cists. To prob­a­bil­ity the­o­rists, words like “sim­ple”, “falsifi­able”, and “testable” have ex­act math­e­mat­i­cal mean­ings, which are there for very strong rea­sons. The (minor­ity?) fac­tion of physi­cists who say that many-wor­lds is “not falsifi­able” or that it “vi­o­lates Oc­cam’s Ra­zor” or that it is “untestable”, are com­mit­ting the same kind of math­e­mat­i­cal crime as non-physi­cists who in­vent their own the­o­ries of grav­ity that go as in­verse-cube. This is one of the rea­sons why I, a non-physi­cist, dared to talk about physics—be­cause I saw (some!) physi­cists us­ing prob­a­bil­ity the­ory in a way that was sim­ply wrong. Not just crit­i­ciz­able, but out­right math­e­mat­i­cally wrong: 2 + 2 = 3.

  • Quan­tum Non-Real­ism: “Shut up and calcu­late” is the best ap­proach you can take when none of your the­o­ries are very good. But that is not the same as claiming that “Shut up!” ac­tu­ally is a the­ory of physics. Say­ing “I don’t know what these equa­tions mean, but they seem to work” is a very differ­ent mat­ter from say­ing: “Th­ese equa­tions definitely don’t mean any­thing, they just work!”

  • Col­lapse Pos­tu­lates: Early physi­cists sim­ply didn’t think of the pos­si­bil­ity of more than one world—it just didn’t oc­cur to them, even though it’s the straight­for­ward re­sult of ap­ply­ing the quan­tum laws at all lev­els. So they ac­ci­den­tally in­vented a com­pletely and strictly un­nec­es­sary part of quan­tum the­ory to en­sure there was only one world—a law of physics that says that parts of the wave­func­tion mys­te­ri­ously and spon­ta­neously dis­ap­pear when de­co­her­ence pre­vents us from see­ing them any more. If such a law re­ally ex­isted, it would be the only non-lin­ear, non-uni­tary, non-differ­en­tiable, non-lo­cal, non-CPT-sym­met­ric, acausal, faster-than-light phe­nomenon in all of physics.

  • If Many-Wor­lds Had Come First: If early physi­cists had never made the mis­take, and thought im­me­di­ately to ap­ply the quan­tum laws at all lev­els to pro­duce macro­scopic de­co­her­ence, then “col­lapse pos­tu­lates” would to­day seem like a com­pletely crack­pot the­ory. In ad­di­tion to their other prob­lems, like FTL, the col­lapse pos­tu­late would be the only phys­i­cal law that was in­for­mally speci­fied—of­ten in du­al­is­tic (men­tal­is­tic) terms—be­cause it was the only fun­da­men­tal law adopted with­out pre­cise ev­i­dence to nail it down. Here, we get a glimpse at that al­ter­nate Earth.

  • Many Wor­lds, One Best Guess: Sum­ma­rizes the ar­gu­ments that nail down macro­scopic de­co­her­ence, aka the “many-wor­lds in­ter­pre­ta­tion”. Con­cludes that many-wor­lds wins out­right given the cur­rent state of ev­i­dence. The ar­gu­ment should have been over fifty years ago. New phys­i­cal ev­i­dence could re­open it, but we have no par­tic­u­lar rea­son to ex­pect this.

  • Liv­ing in Many Wor­lds: The many wor­lds of quan­tum me­chan­ics are not some strange, alien uni­verse into which you have been thrust. They are where you have always lived. Egan’s Law: “It all adds up to nor­mal­ity.” Then why care about quan­tum physics at all? Be­cause there’s still the ques­tion of what adds up to nor­mal­ity, and the an­swer to this ques­tion turns out to be, “Quan­tum physics.” If you’re think­ing of build­ing any strange philoso­phies around many-wor­lds, you prob­a­bly shouldn’t—that’s not what it’s for.

Time­less Physics:

(Now we de­part from what is nailed down in stan­dard physics, and en­ter into more spec­u­la­tive realms—par­tic­u­larly Ju­lian Bar­bour’s Machian time­less physics.)

  • Mach’s Prin­ci­ple: Anti-Epiphe­nom­e­nal Physics: Could you tell if the whole uni­verse were shifted an inch to the left? Could you tell if the whole uni­verse was trav­el­ing left at ten miles per hour? Could you tell if the whole uni­verse was ac­cel­er­at­ing left at ten miles per hour? Could you tell if the whole uni­verse was ro­tat­ing?

  • Rel­a­tive Con­figu­ra­tion Space: Maybe the rea­son why we can’t ob­serve ab­solute speeds, ab­solute po­si­tions, ab­solute ac­cel­er­a­tions, or ab­solute ro­ta­tions, is that par­ti­cles don’t have ab­solute po­si­tions—only po­si­tions rel­a­tive to each other. That is, maybe quan­tum physics takes place in a rel­a­tive con­figu­ra­tion space.

  • Time­less Physics: What time is it? How do you know? The ques­tion “What time is it right now?” may make around as much sense as ask­ing “Where is the uni­verse?” Not only that, our physics equa­tions may not need a t in them!

  • Time­less Beauty: To get rid of time you must re­duce it to non­time. In time­less physics, ev­ery­thing that ex­ists is perfectly global or perfectly lo­cal. The laws of physics are perfectly global; the con­figu­ra­tion space is perfectly lo­cal. Every fun­da­men­tally ex­is­tent on­tolog­i­cal en­tity has a unique iden­tity and a unique value. This beauty makes ugly the­o­ries much more visi­bly ugly; a col­lapse pos­tu­late be­comes a visi­ble scar on the perfec­tion.

  • Time­less Causal­ity: Us­ing the mod­ern, Bayesian for­mu­la­tion of causal­ity, we can define causal­ity with­out talk­ing about time—define it purely in terms of re­la­tions. The river of time never flows, but it has a di­rec­tion.

  • Time­less Iden­tity: How can you be the same per­son to­mor­row as to­day, in the river that never flows, when not a drop of wa­ter is shared be­tween one time and an­other? Hav­ing used physics to com­pletely trash all naive the­o­ries of iden­tity, we re­assem­ble a con­cep­tion of per­sons and ex­pe­riences from what is left. With a sur­pris­ing prac­ti­cal ap­pli­ca­tion...

  • Thou Art Physics: If the laws of physics con­trol ev­ery­thing we do, then how can our choices be mean­ingful? Be­cause you are physics. You aren’t com­pet­ing with physics for con­trol of the uni­verse, you are within physics. Any­thing you con­trol is nec­es­sar­ily con­trol­led by physics.

  • Time­less Con­trol: We throw away “time” but re­tain causal­ity, and with it, the con­cepts “con­trol” and “de­cide”. To talk of some­thing as hav­ing been “always de­ter­mined” is mix­ing up a time­less and a time­ful con­clu­sion, with para­dox­i­cal re­sults. When you take a per­spec­tive out­side time, you have to be care­ful not to let your old, time­ful in­tu­itions run wild in the ab­sence of their sub­ject mat­ter.

Ra­tion­al­ity and Science:

(Okay, so it was many-wor­lds all along and col­lapse the­o­ries are silly. Did first-half-of-20th-cen­tury physi­cists re­ally screw up that badly? How did they go wrong? Why haven’t mod­ern physi­cists unan­i­mously en­dorsed many-wor­lds, if the is­sue is that clear-cut? What les­sons can we learn from this whole de­ba­cle?)

  • The Failures of Eld Science: A short story set in the same world as Ini­ti­a­tion Cer­e­mony. Fu­ture physics stu­dents look back on the cau­tion­ary tale of quan­tum physics.

  • The Dilemma: Science or Bayes?: The failure of first-half-of-20th-cen­tury-physics was not due to stray­ing from the sci­en­tific method. Science and ra­tio­nal­ity—that is, Science and Bayesi­anism—aren’t the same thing, and some­times they give differ­ent an­swers.

  • Science Doesn’t Trust Your Ra­tion­al­ity: The rea­son Science doesn’t always agree with the ex­act, Bayesian, ra­tio­nal an­swer, is that Science doesn’t trust you to be ra­tio­nal. It wants you to go out and gather over­whelming ex­per­i­men­tal ev­i­dence.

  • When Science Can’t Help: If you have an idea, Science tells you to test it ex­per­i­men­tally. If you spend 10 years test­ing the idea and the re­sult comes out nega­tive, Science slaps you on the back and says, “Bet­ter luck next time.” If you want to spend 10 years test­ing a hy­poth­e­sis that will ac­tu­ally turn out to be right, you’ll have to try to do the thing that Science doesn’t trust you to do: think ra­tio­nally, and figure out the an­swer be­fore you get clubbed over the head with it.

  • Science Isn’t Strict Enough: Science lets you be­lieve any damn stupid idea that hasn’t been re­futed by ex­per­i­ment. Bayesi­anism says there is always an ex­actly ra­tio­nal de­gree of be­lief given your cur­rent ev­i­dence, and this does not shift a nanome­ter to the left or to the right de­pend­ing on your whims. Science is a so­cial free­dom—we let peo­ple test what­ever hy­pothe­ses they like, be­cause we don’t trust the village el­ders to de­cide in ad­vance—but you shouldn’t con­fuse that with an in­di­vi­d­ual stan­dard of ra­tio­nal­ity.

  • Do Scien­tists Already Know This Stuff?: No. Maybe some­day it will be part of stan­dard sci­en­tific train­ing, but for now, it’s not, and the ab­sence is visi­ble.

  • No Safe Defense, Not Even Science: Why am I try­ing to break your trust in Science? Be­cause you can’t think and trust at the same time. The so­cial rules of Science are ver­bal rather than quan­ti­ta­tive; it is pos­si­ble to be­lieve you are fol­low­ing them. With Bayesi­anism, it is never pos­si­ble to do an ex­act calcu­la­tion and get the ex­act ra­tio­nal an­swer that you know ex­ists. You are visi­bly less than perfect, and so you will not be tempted to trust your­self.

  • Chang­ing the Defi­ni­tion of Science: Many of these ideas are sur­pris­ingly con­ven­tional, and be­ing floated around by other thinkers. I’m a good deal less of a lonely icon­o­clast than I seem; maybe it’s just the way I talk.

  • Faster Than Science: Is it re­ally pos­si­ble to ar­rive at the truth faster than Science does? Not only is it pos­si­ble, but the so­cial pro­cess of sci­ence re­lies on sci­en­tists do­ing so—when they choose which hy­pothe­ses to test. In many an­swer spaces it’s not pos­si­ble to find the true hy­poth­e­sis by ac­ci­dent. Science leaves it up to ex­per­i­ment to so­cially de­clare who was right, but if there weren’t some peo­ple who could get it right in the ab­sence of over­whelming ex­per­i­men­tal proof, sci­ence would be stuck.

  • Ein­stein’s Speed: Albert was un­usu­ally good at find­ing the right the­ory in the pres­ence of only a small amount of ex­per­i­men­tal ev­i­dence. Even more un­usu­ally, he ad­mit­ted it—he claimed to know the the­ory was right, even in ad­vance of the pub­lic proof. It’s pos­si­ble to ar­rive at the truth by think­ing great high-minded thoughts of the sort that Science does not trust you to think, but it’s a lot harder than ar­riv­ing at the truth in the pres­ence of over­whelming ev­i­dence.

  • That Alien Mes­sage: Ein­stein used ev­i­dence more effi­ciently than other physi­cists, but he was still ex­tremely in­effi­cient in an ab­solute sense. If a huge team of cryp­tog­ra­phers and physi­cists were ex­am­in­ing a in­ter­stel­lar trans­mis­sion, go­ing over it bit by bit, we could de­duce prin­ci­ples on the or­der of Gal­ilean grav­ity just from see­ing one or two frames of a pic­ture. As if the very first hu­man to see an ap­ple fall, had, on the in­stant, re­al­ized that its po­si­tion went as the square of the time and that this im­plied con­stant ac­cel­er­a­tion.

  • My Child­hood Role Model: I looked up to the ideal of a Bayesian su­per­in­tel­li­gence, not Ein­stein.

  • Ein­stein’s Su­per­pow­ers: There’s an un­for­tu­nate ten­dency to talk as if Ein­stein had su­per­pow­ers—as if, even be­fore Ein­stein was fa­mous, he had an in­her­ent dis­po­si­tion to be Ein­stein—a po­ten­tial as rare as his fame and as mag­i­cal as his deeds. Yet the way you ac­quire su­per­pow­ers is not by be­ing born with them, but by see­ing, with a sud­den shock, that they are perfectly nor­mal.

  • Class Pro­ject: From the world of Ini­ti­a­tion Cer­e­mony. Bren­nan and the oth­ers are faced with their midterm ex­ams.

  • Why Quan­tum?: Why do a se­ries on quan­tum me­chan­ics? Some of the many morals that are best illus­trated by the tale of quan­tum me­chan­ics and its mis­in­ter­pre­ta­tion.