How do you know you’re a person who has lived your life, rather than a just-formed brain full of artificial memories, momentarily hallucinating a reality that doesn't actually exist? That may sound absurd, but it’s kept several generations of top cosmologists up at night. They call it the Boltzmann brain paradox.
Kako znate da ste osoba koja je živela svoj život, a ne tek formiran mozak ispunjen veštačkim sećanjima, koji trenutno halucinira stvarnost koja zapravo ne postoji? Ovo može da zvuči apsurdno, ali je držalo nekoliko generacija najboljih kosmologa budnim po noći. Pojava nosi naziv: paradoks Bolcmanovog mozga.
Its namesake, Ludwig Boltzmann, was a 19th century physicist operating in a period when scientists were passionately debating whether the universe had existed for an infinite or finite time. Boltzmann’s main claim to fame was revolutionizing thermodynamics, the branch of physics that studies energy. He put forward a new interpretation of entropy, which is a measure of the disorder of a system. A glass is an ordered system, whereas a shattered glass is disordered. The second law of thermodynamics states that closed systems tend towards disorder: you won’t see a shattered glass return to its pristine state.
Njen prezimenjak, Ludvig Bolcman je bio fizičar iz XIX veka koji je radio u periodu kada su naučnici strastveno raspravljali da li univerzum postoji beskonačan ili konačan vremenski period. Glavni razlog Bolcmanove slave je to što je unapredio termodinamiku, granu fizike koja izučava energiju. Izneo je novo tumačenje entropije, tj. mere neuređenosti sistema. Čaša je uređen sistem, dok je slomljena čaša neuređen. Drugi zakon termodinamike ističe da zatvoreni sistemi teže neuređenosti: nećete videti polomljenu čašu kako se vraća u iskonsko stanje.
Boltzmann’s insight was applying statistical reasoning to this behavior. He found that a system evolves to a more disordered state because it’s more likely. However, the opposite direction isn’t impossible, just so unlikely that we’ll never witness things like scrambled eggs turning raw.
Bolcmanov doprinos je bila primena statističkog rasuđivanja na ovo ponašanje. Otkrio je da sistem prelazi u neuređenije stanje jer je ono verovatnije. Međutim, suprotan smer nije moguć, toliko je neverovatan da nikad nećemo videti kajganu kako se vraća u sveže jaje.
But if the universe exists over an infinitely long time, extremely unlikely events will happen, including complex things forming out of random combinations of particles. So what does that look like in a hypothetical infinitely old universe? In this unremarkable stretch of near-nothingness, about eight octillion atoms randomly come together to form a replica of the Thinker made of pasta. It instantly dissolves. Over here, these particles suddenly form something like a brain. It’s filled with false memories of a lifetime up to the present moment, when it perceives a video saying these very words, before decaying. And finally, by random fluctuations, all the particles in the cosmos concentrate in a single point, and an entire new universe spontaneously bursts into existence. Of those last two, which is more likely? The brain, by far— despite all its complexity, it’s a blip compared to an entire universe. Every one universe produced by random fluctuations has equivalent odds to heaps upon heaps of insta-brains. So by this reasoning, it seems extremely more likely that everything you believe to exist is actually a brief illusion, soon to be extinguished.
Međutim, ako univerzum postoji tokom beskonačno dugog vremena, krajnje neverovatni događaji će da se dese, uključujući složene stvari koje nastaju od nasumičnih kombinacija čestica. Dakle, kako to izgleda u hipotetički beskonačno starom univerzumu? U ovom neizglednom rasponu skoro pa ništavila, oko osam oktiliona atoma nasumično se spaja kako bi stvorili repliku Mislioca napravljenog od testenine. On se istog trena rastvara. Ovde te čestice iznenada formiraju nešto nalik mozgu. Ispunjen je lažnim sećanjima na život sve do sadašnjeg trenutka, kada spazi snimak koji izgovara baš ove reči, pre nego što se raspadne. I, naposletku, nasumičnim fluktuacijama, sve čestice u kosmosu se koncentrišu u jednoj tački, i potpuno nov univerzum spontano bukne u postojanje. Od dva poslednja primera, koji je verovatniji? Mozak, i to nadaleko - uprkos svoj njegovoj složenosti, tek je zrnce u čitavom univerzumu. Za svaki pojedinačni univerzum stvoren nasumčnim fluktuacijama šanse su jednake hrpama i hrpama instant mozgova. Ovakvim rezonovanjem, čini se daleko verovatnijim da je sve u šta verujete da postoji zapravo prolazna iluzija, koja će uskoro da iščezne.
Boltzmann didn’t get quite that far in his thinking; the brains themselves were introduced by later cosmologists building on his work. But they, like just about everyone else, were pretty sure that they themselves weren't just ephemeral brains. So the paradox was: how could they be correct and the universe be eternal? The resolution is something most take for granted today: that our universe has not existed forever, but rather time and space started with a Big Bang.
Bolcman nije otišao baš toliko daleko u razmišljanju; mozgove su uveli kasniji kosmolozi koji su nastavili njegov rad. Međutim, baš kao i skoro svi ostali, bili su prilično sigurni da oni sami nisu tek efemerni mozgovi. Stoga je paradoks glasio: kako je moguće da su u pravu i da je univerzum večan? Rešenje mnogi danas uzimaju zdravo za gotovo: da naš univerzum nije postojao oduvek, već da su vreme i prostor otpočeli Velikim praskom.
So that’s the paradox over and done with, right? Well, maybe not. In the last century, scientists have found evidence supporting the theory of the Big Bang everywhere we look. Yet while we know that the Big Bang happened, no one knows what, if anything, preceded and caused it. Why did the universe begin in such an extremely ordered, and unlikely, state? Is our universe in an unending cycle of creation and collapse? Or might we be in one of many universes expanding within a multiverse?
Dakle, to je to što se tiče paradoksa, zar ne? Pa, ne baš. U ovom veku, naučnici su otkrili dokaze koji potkrepljuju teoriju Velikog praska gde god da se osvrnemo. Ipak, iako znamo da se Veliki prasak desio, niko ne zna da li mu je nešto, ako išta, prethodilo i uzrokovalo ga. Zašto je univerzum otpočeo u tako izuzetno sređenom, i neverovatnom, stanju? Da li je naš univerzum beskrajni ciklus stvaranja i urušavanja? Ili smo možda jedan od mnogih univerzuma koji se šire unutar multiverzuma?
In this context, Boltzmann’s paradox has found renewed interest by contemporary cosmologists. Some argue that leading models for where the universe came from still imply that Boltzmann brains are more likely than human brains, suggesting something’s amiss. Others counter that slight modifications of the cosmological models would avoid the problem, or that Boltzmann’s brains can’t actually physically form. Some researchers even attempted to calculate the probability of a brain popping out of random quantum fluctuations long enough to think a single thought. They got this incredible number whose denominator is 10 to a number about a septillion times larger than the number of stars in the universe. The Boltzmann brain paradox, despite its absurdity, is useful because it creates a bar that models have to rise to. If, compared to numbers like this one, the current state of the universe is exceedingly unlikely, something in the model is almost certainly wrong. Unless you’re the one who is wrong...
U ovom kontekstu, došlo je do obnovljenog interesovanja za Bolcmanov paradoks od strane savremenih kosmologa. Neki tvrde da vodeći modeli u vezi s poreklom univerzuma i dalje sugerišu da su Bolcmanovi mozgovi verovatniji od ljudskih mozgova, nagoveštavajući da nešto nije kako treba. Drugi protivreče tvrdeći da bi se blagim modifikacijama kosmoloških modela izbegao problem ili da Bolcmanovi mozgovi zapravo ne mogu fizički da nastanu. Neki istraživači su čak pokušali da izračunaju verovatnoću iskrsavanja mozga iz nasumičnih kvantnih fluktuacija taman toliko da smisli samo jednu misao. Došli su do ovog neverovatnog broja čiji je imenilac 10 na broj koji je oko septilion puta veći od broja zvezda u univerzumu. Paradoks Bolcmanovog mozga, uprkos aspurdnosti, koristan je jer pruža lestvicu koju modeli moraju da dosegnu. Ukoliko je, u poređenju sa brojevima poput ovoga, trentuno stanje univerzuma izuzetno neverovatno, nešto u modelu je sasvim izvesno pogrešno. Ukoliko vi niste ti koji greše...