Visualizzazione post con etichetta principio antropico. Mostra tutti i post
Visualizzazione post con etichetta principio antropico. Mostra tutti i post

domenica 15 dicembre 2019

USI IMPROPRI DEL PRINCIPIO ANTROPICO

Il principio antropico ci dice che una certa proprietà del nostro universo è così com' è perché altrimenti non saremmo qui per parlarne. La cosa è approssimativamente corretta se si intende che l'universo deve avere determinate proprietà perché altrimenti la nostra stessa esistenza non sarebbe possibile. In questa versione la nostra esistenza non è né necessaria né inevitabile. È semplicemente un fatto osservato che porta a vincoli sulle leggi della natura.
Si tratta di un principio che ha facilitato alcune scoperte scientifiche, la più nota è la previsione di Fred Hoyle secondo cui un certo isotopo del carbonio deve avere una certa risonanza perché, senza quella risonanza, la vita come la conosciamo non sarebbe possibile. Tale previsione si rivelò corretta. Come è facile vedere non c'è nulla di non scientifico in tutto cio'
Un altro esempio è che puoi usare il semplice fatto che siamo qui per dire che una certa costante cosmologica deve essere tarata in un certo intervallo microscopico. Se la costante cosmologica fosse sballata l'universo sarebbe collassato da tempo, oppure si espanderebbe troppo velocemente per formare le stelle. Ancora una volta, non c'è nulla di a-scientifico in tutto questo.
il principio antropico non è né scientifico, né inutile. Ma allora perché è così controverso?
Per questioni filosofiche più che scientifiche. Di solito viene propugnato da chi crede che il nostro universo è solo uno tra gli infiniti che esistono. Se credi in questa ipotesi, allora il principio antropico può essere riformulato per dire che la probabilità di trovarci qui non sia affatto minuscola come sembrerebbe.
Tuttavia, questo utilizzo è improprio: il principio antropico è corretto indipendentemente dal fatto che tu creda o meno nel multiverso. Il principio si limita a dire che le leggi della natura devono essere tali da consentire la nostra esistenza, né più né meno. Che questo derivi da una coincidenza incredibile o dall'esistenza del multiverso è assolutamente indifferente.

YOUTUBE.COM
In this video, I explain why the anthropic principle is a good, scientific principle. First I explain the difference between the strong and the weak anthropi...

venerdì 21 dicembre 2018

lunedì 22 ottobre 2018

A che serve il multiverso?

A che serve il multiverso?

Carissimo, tutte le volte che discuto con te si va a parare sempre lì: l’esistenza di Dio. Non so perché ma nemmeno con i preti il tema ricorre tanto spesso. In realtà  una risposta posso immaginarmela: come è possibile infatti osservare la volta celeste senza un pensiero alla creazione? La cosmologia è una disciplina dove il miracolo della matematica si disvela in tutta la sua pienezza lasciandoci attoniti, annaspiamo così in cerca di spiegazioni. Per altro verso la tua mentalità è quella dello scienziato  moderno e quindi restia ad accogliere un’ipotesi razionale di Dio. Come è giusto che sia sei sempre a caccia di alternative, e il tuo genio, in questo senso, è prodigo di offerte. Ma poiché c’è un punto particolare in cui ci incartiamo di continuo, qui vorrei prenderlo di petto per trattarlo un po’ più a fondo.
Partiamo allora dai fatti, una roba su cui è difficile non concordare. Secondo i tuoi stessi  colleghi, le condizioni richieste per l’esistenza della vita nel nostro universo sono molto-molto-molto-molto particolari (fine tuning). Ci sono cioè tutta una serie di parametri fisici che devono assumere valori ben precisi da ricomprendersi in un intervallo estremamente ristretto, e devono farlo contemporaneamente. Se per esempio la costante di gravitazione differisse anche solo di 1/10 alla quarantesima rispetto al suo valore standard tutto crollerebbe. Una roba del genere vale anche per grandezze quali la massa dei protoni, la forza nucleare debole e quella forte, la forza elettromagnetica, i valori entropici nella fase iniziale dell’universo, eccetera.
Ora, per un credente come me è del tutto istintivo interpretare questo stato di cose come indizio dell’esistenza di un progettopresente sin dall’inizio. Ma tu, caro amico cosmologo, hai sempre avuto la risposta pronta su questo punto: un’alternativa atea in realtà esiste e si chiama “universo multiplo”.
A questo punto urge chiarimento: il fatto che un universo compatibile con la vita sia tanto improbabile supporta davvero l’esistenza di molteplici universi? In caso affermativo, questa singolare ipotesi entrerebbe in legittimaconcorrenza con quella teistica.
La cosa migliore per portare a casa una risposta attendibile all’enigma è farsi aiutare da un logico di professione con una certa dimestichezza nel calcolo probabilistico, propongo di interpellare il filosofo Mike Huemer– ateo convinto ma non sospettabile di professione ideologica – che fortunatamente dedica il suo saggio “Self-Locating Beliefs” proprio a questi temi.
Mike Huemer mi piace perché anziché impantanarsi nel gergo filosofico professionale ragiona per analogie comprensibili a tutti. Per soppesare l’ipotesi del multiverso  ne propone diverse tra cui mi permetto di estrapolarne  tre rilevanti. Partiamo con la prima. (1) Immagina allora, carissimo, di essere un condannato a morte che attende l’esecuzione a cura di un plotone di fucilieri scelti. Dopo essere messo al muro il capitano ordina di fare fuoco, i soldati sparano ma tu ti ritrovi ancora vivo: tutte le pallottole partite dalle canne ti hanno solo schivato.  Questo evento è così improbabile che la tua testa si metterà subito al lavoro per cercare una spiegazione plausibile dell’evento. Penserai subito che c’è sotto qualcosa, una cospirazione ordita per salvarti la vita. Poi però qualcuno ti riferisce un’ipotesi alternativa: altrove nell’universo potrebbero esserci trilioni di trilioni di plotoni di esecuzione, pertanto la tua sorte non è poi così improbabile: numeri elevati rendono tutto più probabile. Tra tante esecuzioni che una sia andata storta è del tutto normale, non c’è quindi bisogno di pensare a complotti e cospirazioni.
Ovviamente un ragionamento del genere è strampalato: quand’anche esistano miliardi di esecuzioni in giro per l’universo cio’ spiegherebbe il fatto che una possa andare male ma non che questa debba essere proprio la tua. L’evidenza che devi spiegare riguarda te stesso, non una persona qualsiasi. In altri termini, il fatto che su Alpha Centauri stiano fucilando un poveraccio non influenza le probabilità che chi ti sta sparando manchi il bersaglio.
In questo caso il trucco di  moltiplicare gli eventi per giustificare l’improbabile non funziona.
Altra analogia (2). Lanci una moneta dieci volte e fai dieci “teste” consecutive.  Ma aspetta, ecco un’ulteriore informazione: qualcuno nella stanza accanto sta lanciando come te una moneta. Questo ha reso più probabile la tua impresa? No, e non è questione di numeri. Allo stesso modo il fatto che miliardi e miliardi di persone lancino insieme a te una moneta non sembra agevolare il quasi-miracolo delle dieci teste consecutive.
Siamo nella stessa situazione precedente: la moltitudine spiega al massimo che qualcuno farà dieci teste consecutive ma non che le farai tu, ovvero l’evidenza che devi spiegare.
Le due analogie precedenti sembrano invalidare il ragionamento sottostante all’ipotesi dei molti universi: in questi casi l’esistenza di molte situazioni simili alla tua non spiega cio’ che di singolare ti sta capitando. Ciò significa allora che il fatto di ritrovarci vivi nell’universo non è reso più probabile  dal fatto che esistano molti universi? Non affrettiamo conclusioni, ci sono infatti anche analogie più favorevoli al multiverso.
Veniamo alla terza analogia (3): apri gli occhi e ti ritrovi a vivere sulla terra. Come giudichi questa evidenza? E’ forse resa più probabile dal fatto che nel nostro universo esistano molti pianeti simili alla terra? Bè, direi di sì: quanti più pianeti simili alla terra esistono, tanto più è probabile che io mi sia svegliato proprio in un posto del genere.
Questa volta ipotizzare una moltiplicazione dell’evento di base rende l’evidenza disponibile decosamente più probabile.
Ma che differenza c’è allora tra (1), (2) e (3)? In tutti e tre i casi, in fondo, cerchiamo di spiegare l’improbabile ipotizzando che certe premesse a eventi unici siano presenti in gran quantità (si tratti di esecuzioni, di lanci o di pianeti).
Provo a rispondere: in (1) l’esperienza che ho io, ovvero quella di sopravvivere alla fucilazione, è fondamentalmente diversa da quella che avrebbe un “io” destinato a soccombere.
In (2) la cosa si ripete: l’esperienza di fare dieci teste consecutive è qualitativamente diversa da quella di fare una serie anonima.
Ma in (3) le cose sono molto diverse: tra la mia vita su Terra1e la mia vita su Terra2 non ci sono grandi differenze. In realtà, per quanto ne so, non sarei mai in grado di distinguerle in senso qualitativo.
Ora torniamo a bomba: l’ipotesi dei molti universi assomiglia più a (1), a (2) o a (3)?
Di primo acchito direi a (3), tra “pianeti” e “universi” in fondo c’è una certa affinità. Ma poiché, come abbiamo appena visto, la forza che distingue (3) da (1) e (2) sta nel fatto che io potrei esistere su uno qualsiasi dei tanti pianeti gemelli della Terra, occorre chiedersi se lo stesso si possa dire quando si ragiona in termini di universi. Ebbene, poiché le condizioni per ospitare la vita sono così particolari la quasi totalità dei “tanti” universi sarà sterile, tuttavia è anche possibile pensare che i “tanti” universi siano così tanti che un numero ristretto di loro accolga la vita e che quindi io possa pensare di trovarmi in uno di loro. In questo caso l’ipotesi dei molti universi diverrebbe un’alternativa concreta all’ipotesi di Dio.
C’è ancora qualcosa da aggiungere, però: difficile coniugare il materialismo con l’ipotesi dei molti universi, te ne sei accorto? Per il materialista ogni individuo è solo un oggetto fisico e se un oggetto fisico è “qui” non puo’ essere “lì”. E’ una questione di molecole. L’ oggetto fisico può esistere solo nell’universo in cui si trova, se esisti in questo come potresti immaginarti altrove? L’ipotesi del “multiverso” pensata dal materialista, dal punto di vista logico, si apparenta più a (1) e (2) che a (3) non potendo così  competere con quella divina.
Personalmente non sono materialista, quindi sono propenso a vedere l’ipotesi del multiverso e quella di dio sullo stesso piano. Se scelgo la seconda è solo per la sua maggiore semplicità, un tema su cui qui non mi soffermo. Tuttavia, se continuerai a professarti materialista, carissimo, prevedo per te qualche problema nel contrapporre l’idea dei “molti universi” a quella di un Dio creatore.

venerdì 19 ottobre 2018

11. Self-Locating Beliefs

11. Self-Locating Beliefs
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11.1 The Sleeping Beauty Paradox
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At the beginning of the week, they put a person (“Sleeping Beauty”, as we will call her) to sleep by chemical means. Then they flip a fair coin. If it comes up heads, the scientists wake up Sleeping Beauty on Monday, talk to her briefly, then put her back to sleep, using a drug that causes her to forget
Note:DESCRIZIONE

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If, on the other hand, the coin comes up tails, then the scientists wake up Beauty twice: once on Monday, and again on Tuesday. Each time, the scientists talk to her briefly, then put Beauty back to sleep using the same drug,
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When the scientists wake Beauty, they ask her one question: “What is your credence that the coin came up heads?”
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If she is perfectly rational, what answer should Beauty give?
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Answer 1:
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Coins have a ½ probability of coming up heads when flipped.
Note:RISPOSTA ELEMENTARE

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Answer 2:
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Suppose that the experiment were repeated with 200 subjects.
Note:100 TESTE 100 CROCI E 300 RISVEGLI. A CHE GRUPO APOARTENGO? AL PIÙ NUMEROSO QUELLO DEI "RISVEGLI CROCE". PUOI ANCHE IMMAGINARE UNA SOLA SB CHE RIPETE L ESPERIMENTO X 200 SETTIMANE E CONSIDETA I SUOI 200 RISVEGLI NOTANDO CHE BEN 200 AVVENGONO IN SEGUITO A UNA CROCE E AI 100 IN SEGUITO A UNA TESTA

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There would then be a total of 300 occasions on which someone was woken up,
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100 wakings in which the coin had come up heads, and it was now Monday 100 wakings in which the coin had come up tails, and it was now Monday 100 wakings in which the coin had come up tails, and it was now Tuesday
Note:Cccccc DETTAGLIO DEI 300 RISVEGLI

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300 wakings, of which you believe roughly 1/3 are “heads wakings”
Note:1/3 VS 2/3

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11.2 The Fine Tuning Argument
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According to many scientists, the conditions required for life to exist are extremely specific.
Note:IL DATO DI PARTENZA

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a number of physical parameters of the universe that must take on values in an extremely narrow range,
Note:LO SPECIFICO

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if the gravitational constant differed by more than 1/1040
Note:Es...1/10 ALLA 40...O TROPPO CALDO O TROPPO FREDDO

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the strength of the strong nuclear force, the strength of the electromagnetic force,
Note:ES DI ALTRI PARAMETRI

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it is very lucky that the universe started with extremely low entropy.
Note:ALTRO ESEMPIO

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the best explanation for the universe’s having such properties is that our universe was designed
Note:PER ALCUNI

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The most popular non-theistic alternative is the Multiple Universes (“Multiverse”)
Note:ALTERNATIVA

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In the many other universes where life is impossible, there just is no one around to notice this fact.
Note:DESERTO

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Does the fine tuning evidence – the fact that the universe has parameters falling within very narrow ranges that are necessary for life to exist – support the existence of multiple universes? If so, does this neutralize whatever reason we would otherwise have for accepting the Design hypothesis?
Note:LE DOMANDE CHE MI PONGO

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11.3 The Doomsday Argument
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How much longer will the human species last?
Note:LA DOMAMDA

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nuclear war.
Note:APOCALISSE 1

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biological weapon
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giant asteroid
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superintelligent robots
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Short-lived Species:
Note:PER SEMPLICITÀ CONSIDERIAMO SOLO DUE CASI...1

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extinct within the next ten thousand years.
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Long-lived Species:
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species will continue for more than ten thousand more years.
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human beings have existed for at least 50,000 years
Note:PRIMO DATO

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number of humans who have ever existed is surprisingly low, only about 108 billion, of which around 7.4 billion are alive now.
Note:SECONDO

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you are somewhere between the 100 billionth and the 108 billionth human
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that is, your “birth order”
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The probability of finding that one’s birth order is less than 108 billion is greater if one belongs to a short-lived species than it is if one belongs to a long-lived
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the fact that your birth order is less than 108 billion is evidence that you belong to a short-lived species,
Note:POICHÈ RAPPRESENTI LA MEDIA

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the hat contains either ten slips of paper, with the numbers 1 through 10 written on them, or a hundred slips of paper, with the numbers 1 through 100. You know it’s one of those two alternatives,
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It turns out to be the number 8.
Note:PESCHI...

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what should you think about the contents of the hat?
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you are a random person chosen from the human species.
Note:NEL DA...ANCHE ASSUNTI I TASSI DI NATALITÀ IL NUMERO CHE PESCHI È MOLTO BASSO...QUINDI...

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Since your birth order number is relatively small,
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all three issues can be resolved in a similar manner.
Note:TESI SU DA FINE TUNING E SLEEPY

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11.4 The Multiverse : Pro and Con
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11.4.1 The “This Universe” Objection
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Imagine that you are scheduled to be executed by a firing squad.
Note:ANALOGIA

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you find yourself still alive.
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this event seems so unlikely that there must be some explanation.
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TUA RIFLESSIONE

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suppose it occurs to you that there might perhaps be a trillion trillion other firing squads elsewhere in the universe.
Note:SUPPOSIZIONE

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Therefore, you conclude (?), you now have good reason to think there actually are all these other firing squads.
Note:LA STRANA CONCLUSIONE

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there is no need to postulate any sort of conspiracy
Note:IN QS CASO

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I take it that this pretty obviously is not good reasoning.
Note:GIUDIZIO

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your evidence is not that at least one person somewhere in the universe has experienced this; your evidence is that you experienced this.
Note:MOTIVAZUONE DEL GIUDIZIO

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what needs to be explained is the fact that you personally survived the firing squad.
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If someone starts up a firing squad on Alpha Centauri, that doesn’t make your firing squad suddenly more likely to miss.
Note:COME SI INFLUENZANO LE PROB

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You are about to flip a coin. What is the probability that it will come up heads? 50%. But wait, here is an additional piece of information: someone in the next room is flipping a coin too. Does that make it more likely that you will flip heads? No. That makes it more likely that at least one of the coins will come up heads, but the probability that this coin will do so remains 50%.
Note:ANALOGIA DELLA FALLACIA

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Champions of the Multiverse appear to be committing the very fallacy that we have just criticized.
Note:TORNIAMO A BOMBA

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This assumes that our evidence is merely that life exists in at least one universe. But this is not correct; our evidence is that life exists in this universe.
Note:LA LORO CONCLUSIONE NN DICE NULLA SUL NS UNIVERSO

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11.4.2 In Defense of the Multiverse
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Earth contains peculiar features that make it especially hospitable to life.
Note:ALTRA ANALOGIA CHE RIABILITA L OPZIONE MT

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distances from the sun,
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appropriate size,
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large amount of surface water,
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it is only on the few planets suitable to life that any intelligent beings could have evolved to wonder about the characteristics of their planet.
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Now imagine someone pressing the “this planet” objection:
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Our evidence is not merely that at least one planet somewhere is habitable; our evidence is that this planet is habitable. And however many other planets there may be, they don’t affect the habitability of this one.
Note:THIS PLANET OBJ...MA QUI NN SEMBRA AVERE FORZA...PERCHÈ?

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11.4.3 Four Cases Resolved
Note:Ttttttttttttttttt COSA CONTA 1) TEORIA...2) DESCRIZIONE EVIDENZA 3) QUALITÀ E SOSTITUIBILITÀ

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a theory that accounts for all four of the above cases: the Firing Squad, the Coin Flip, Planet Earth, and the Uranium case.
Note:COSA CERCHIAMO

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Your evidence supports a hypothesis, H, provided that the truth of H would make it more likely that you would receive that qualitative evidence than it would be if H were false.
Note:LA TEORIACENTRALE DESCRIVERE CORRETTAMENTE L'ESPERIENZA. ESEMPIO FUCILAZIONE: IO SOPRAVVIVO (IL FATTO CHE ESISTANO MILIARDI DI PLOTONI NON SPIEGA CHE UNO SOPRAVVIVERA' NON CHE QUELL'UNO SIA IO...NN C È SOSTITUIBILITÀ). ESEMPIO DIECI TESTE: IO LE FACCIO (IL FATTO CHE SIAMO MILIARDI DI PERSONE A LANCIARE NON ALZA LA PROB CHE SIA PROPRIO IO A FARE LE DIECI TESTE, SPIEGA SOLO CHE UNO LE FARA'...NN C È SOSTITUIBILITÀ). MULTIVERSO: IL NOSTRO UNIVERSO OSPITA LA VITA (SE ESISTONO MOLTI UNIVERSI IN GRADO DI OSPITARE LA VITA AUMENTA LA PROB DELLA NOSTRA EVIDENZA. MA SE GLI ALTRI UNIVERSI SONO STERILI NN C È SOSTITUIBILITÀ)

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what needs to be explained is always your having a certain set of evidence, not merely someone’s
Note:PRIMA PRECISAZIONE...TU...NN UNO QUALSIASI

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The evidence itself should be understood qualitatively.
Note:SECONDA...QUALITÀ NN QUANTITÀ...ES CONTA IL COLORE NN IL NUMERO...ASSUNTO NECESSARIO X GARANTIRE LA SOSTITUIBILITÀ NEI MULTIPLI. Es SU QS O SU UN ALTRA TERRA GEMELLA LA MIA ESPERIENZA È LA MEDESIMA SOLO SE CONTA ESCLUSIVAMENTE LA QUALITÀ

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explanatoriness of a hypothesis is evaluated relative to the alternatives.
Note:TERZA CONDIZIONE

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In the Firing Squad case, your evidence consists of an experience of surviving a firing squad.
Note:PRIMO CASO

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The existence of other firing squads raises the probability that there will be some other people having that experience, but it does not affect your probability of having that experience.
Note:NN PASSA IL TEST

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In the Coin Flip case, your evidence is your experience of flipping a coin ten times and seeing it come up heads every time.
Note:SECONDO CASO

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The probability of your receiving this evidence if there are many other coins being flipped elsewhere by other people is also (1/2)10.
Note:NN PASSA IL TEST

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In the Planet Earth case, your evidence consists of your experience of living on a life-sustaining planet.
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if there were many planets in the universe, it is much more likely that you would find yourself existing,
Note:PASSA IL TEST...UN PÒ- AL CONTRARIO - COMEVINCERE LA LOTTERIA...IL M DEI PARTECIPANTI CONTA: È PIÙ PROBABILE SE I PARTECIPANTI SONO POCHI

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Why not describe the evidence as being that this specific planet that you find yourself on is life-sustaining, rather than merely that you find yourself on some life-sustaining planet?
Note:OBIEZIONE..XCHÈ NN CONSIDERARE QLCS DI PIÙ INFORMATIVO

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The answer is that your evidence does not really identify a specific, individual planet. If you had instead found yourself on another planet, qualitatively like Earth but located in another galaxy, you would not have noticed the difference; thus, we should count the evidence you would have had in that case as being the same as the evidence you actually have.
Note:RISPOSTA....ECCO A COSA SERVE LA QUALITÀ

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why not include in the evidence more information, besides just that you are on a life-sustaining planet?
Note:ALTRA OBIEZIONE

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number of continents
Note:ES ALTRE INFO

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number of other planets in its solar system,
Note:INFO 2

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shapes of the constellations visible
Note:INFO 3

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It is irrelevant because the theories under consideration do not differentially impact the probabilities of these details.
Note:RISPOSYA

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A refined version of the total evidence requirement, then, would state that we should take a more informative characterization of the evidence rather than a less informative one, whenever this makes a difference to the relative probabilities of the evidence
Note:X EVITARE ERRORI

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in the case of the uranium atoms, your evidence is that an atom named Bob decayed in the last five minutes.
Note:CASO DELL URANIO

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You would be much more likely to receive this evidence if the box contained many atoms than if it contained few.
Note:SUPERA IL TEST

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11.4.4 Personal Identity and the Multiverse Theory
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Now at last, what of the Multiverse theory ?
Note:PASSIAMO AL NS CASO

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more likely to happen if there were many universes than if there were only one.
Note:LA NS ESPERIENZA

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the argument requires the assumption that you could have existed in a universe other than this one.
Note:CAVEAT!!!!!!!

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You might well doubt this.
Note:Ccccccccccc

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you are an individual, physical object. And a particular physical object can only exist in the universe it is in.
Note:IL PROBLEMA

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if you had not existed in this universe, you could not have existed at all,
Note:Cccccccccccc

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An alternative view is that you would exist as long as an organism with a brain sufficiently like your actual brain had come into existence
Note:ALTERNATIVA LASCA

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perhaps your identity is tied to a particular, immaterial soul,
Note:LASCA BIS

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if a person in another universe could count as you, then the fine tuning evidence supports multiple universes.
Note:CONCLUSIONE RIPETUTA

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if a person in another universe could not count as you, then the fine tuning evidence gives you no reason at all to believe in other universes.
Note:COROLLARIO

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11.5 Against Doomsday
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It misunderstands our evidence by characterizing it in an overly general way.
Note:L ERRORE DA

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The probability of your being born at the time you were actually born is completely unaffected by anything that happens after that time. Therefore, that you were born at that time does not provide any evidence about what will happen later;
Note:INFATTI

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Notice how this case differs from the case of picking numbers from a hat. In the hat case, when you pick a small number, you can infer that the hat probably contains few numbers rather than many numbers. This inference is legitimate because the size of the hat can in fact affect what number you draw.
Note:DISANALOGIA

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The slip numbered “501”, for example, can prevent the slip numbered “8” from being chosen, by getting in the way and getting itself drawn out of the hat instead.
Note:DISANALOGIA

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in the Doomsday Argument, since individuals who exist later in time could not have prevented you from being born when you were.
Note:Ccccccc

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Multiverse argument does not require any problematic backward causation, since the many universes are supposed to exist simultaneously.
Note:IL VANTAGGIO DI MT RISPETTO A DA

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There could be a version of the Multiverse theory that makes the same mistake as the Doomsday Argument: suppose we claimed that because we find ourselves existing at all, there probably will be many universes in the future.
Note:LA FALLACIA DELL UNIVERSO CICLICO

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11.6 Sleeping Beauty: For a Third
Note:Ttttttttttt

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In the Firing Squad case, it is important that your evidence is that you survived your firing squad, not merely that someone survived
Note:L IMPORTANZA DI DESCRIVERE BENE L EVIDENZA

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In the Doomsday case, it is important that your evidence is that you were born at the time you were, not merely that some random person from the species’
Note:ANCORA

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E1 I am woken up at least once.
Note:MODI DI DESCRIVERE L EVIDENZA DELLA BELLA ADDORMENTATA 1

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E2 I am woken up now.
Note:2

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she in fact has no new evidence, since she knew from the start that she would be woken up at least once regardless of whether the coin came up heads or tails.
Note:CASO E1.....MI HANNO SVEGLIATO ALMENO UNA VOLTA...SI REALIZZA SIA CON TESTA CHE CON CROCE

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In the statement of E2, “now” refers to the specific time at which Beauty has just found herself awoken.
Note:CASO E2…INFO SPECIFICA CHE SI AGGIUNGE

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But times at which a subject of this experiment is woken up are more likely to be Mondays than to be Tuesdays.
Note:QUINDI LUNEDÌ QUINDI TESTA...NB SB SI RITROVA XFETTAMENTE SOSTITUIBILE TRA LUNEDÍ E MARTEDÌ

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Beauty has no reason to think she is special
Note:Ccccccccc

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E2 is in fact the correct characterization of the evidence, given the total evidence principle: we should use the most informative accurate characterization of the subject’s evidence. Beauty knows both E1 and E2, but E2 is more informative: that Beauty is woken up now logically entails that she is woken up at least once,
Note:E2>E1

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The theories are not empirically equivalent;
Note:MULTIVERSO VS DESIGN@@@@@@@@@@NELLE NOTE

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Multiverse predicts, roughly, that we should find ourselves to be fairly typical examples of the sort of conscious beings who would exist in a multiverse filled with universes with randomly chosen parameter values.
Note:ESEMPIO 1 SEMBREREBBE SFAVOREVOLE A MT

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Multiverse might lead us to expect the initial entropy of the universe to be approximately the highest that it could be, compatible with life later being likely to evolve; Design would probably lead us to expect a lower initial entropy, perhaps the minimal physically possible initial entropy.
ESEMPIO 2…ANCORA SFAVOREVOLE A MT@@@@@@@@@NOTE

venerdì 5 maggio 2017

L'uomo che disegnava bersagli intorno ai fori di pallottola

Bad Stats - Bad Science by Ben Goldacre
Noi non sappiamo leggere le statistiche se non ci vengono “tradotte” in un linguaggio naturale.
L’umile assunzione di questa verità appartiene ad ogni persona di buon senso.
Prendiamo i “miracoli del colesterolo”…
… Let’s say the risk of having a heart attack in your fifties is 50 per cent higher if you have high cholesterol. That sounds pretty bad. Let’s say the extra risk of having a heart attack if you have high cholesterol is only 2 per cent. That sounds OK to me. But they’re the same (hypothetical) figures…
Noi non sappiamo leggere le statistiche perché il cervello umano non comprende il reale significato delle probabilità e dei fattori di rischio. Siamo fatti così, inutile insistere.
Su questo fatto i giornali ci giocano, evitando accuratamente di proporre i medesimi risultati in termini di frequenze naturali, ovvero di numeri assoluti, qualcosa che il nostro cervello afferra meglio…
… Out of a hundred men in their fifties with normal cholesterol, four will be expected to have a heart attack; whereas out of a hundred men with high cholesterol, six will be expected to have a heart attack. That’s two extra heart attacks per hundred. Those are called ‘natural frequencies’. Natural frequencies are readily understandable, because instead of using probabilities, or percentages, or anything even slightly technical or difficult, they use concrete numbers, just like the ones you use every day to check if you’ve lost a kid on a coach trip, or got the right change in a shop. Lots of people have argued that we evolved to reason and do maths with concrete numbers like these, and not with probabilities, so we find them more intuitive…
Rischio. Tra assoluto e relativo ci passa il mare, e i giornali ci giocano…
… you could have a 50 per cent increase in risk (the ‘relative risk increase’); or a 2 per cent increase in risk (the ‘absolute risk increase’); or, let me ram it home, the easy one, the informative one, an extra two heart attacks for every hundred men, the natural frequency…
La carne rossa causa il cancro. Ovvio. Ma in che misura? Al prof in TV è richiesto di impressionare il pubblico senza mentire. Che fa? Ecco un tipico dialogo con l’anchorman…
… Try this, on bowel cancer, from the Today programme on Radio 4: ‘A bigger risk meaning what, Professor Bingham?’ ‘A third higher risk.’ ‘That sounds an awful lot, a third higher risk; what are we talking about in terms of numbers here?’ ‘A difference … of around about twenty people per year.’ ‘So it’s still a small number?’ ‘Umm … per 10,000…’…
Antidepressivi e infarti
… The reports were based on a study that had observed participants over four years, and the results suggested, using natural frequencies, that you would expect one extra heart attack for every 1,005 people taking ibuprofen…
Ecco la notizia sul nesso come riportata dai media, ancora il giochetto di prendere il rischio assoluto anziché quello relativo…
… ‘British research revealed that patients taking ibuprofen to treat arthritis face a 24 per cent increased risk of suffering a heart attack.’ Feel the fear. Almost everyone reported the relative risk increases…
E i ricercatori non sono meno nel drammatizzare. A volte cercano le luci della ribalta più avidamente di una soubrette.
***
H.G. Wells previde che la statistica sarebbe stata il fulcro della civiltà a venire. Giusto. Ma previde anche che ci saremmo abituati ad interpretarle correttamente. Sbagliato, sbagliato, sbagliato…
… Over a hundred years ago, H.G. Wells said that statistical thinking would one day be as important as the ability to read and write in a modern technological society. I disagree; probabilistic reasoning is difficult for everyone, but everyone understands normal numbers…
***
Facciamo un esempio: lo sapevate che la cannabis attualmente in circolazione è molto più potente di quella di una volta? La notizia…
… The Independent was in favour of legalising cannabis for many years, but in March 2007 it decided to change its stance. One option would have been simply to explain this as a change of heart, or a reconsideration of the moral issues. Instead it was decorated with science—as cowardly zealots have done from eugenics through to prohibition—and justified with a fictitious change in the facts… Twice in this story we are told that cannabis is twenty-five times stronger than it was a decade ago… The data from the Laboratory of the Government Chemist goes from 1975 to 1989. Cannabis resin pootles around between 6 per cent and 10 per cent THC, herbal between 4 per cent and 6 per cent. There is no clear trend. The Forensic Science Service data then takes over to produce the more modern figures, showing not much change in resin, and domestically produced indoor herbal cannabis doubling in potency from 6 per cent to around 12 or 14 per cent. (2003–05 data in table under references)…. The rising trend of cannabis potency is gradual, fairly unspectacular, and driven largely by the increased availability of domestic, intensively grown indoor herbal cannabis…. ‘Twenty-five times stronger’, remember. Repeatedly, and on the front page. If you were in the mood to quibble with the Independent’s moral and political reasoning, as well as its evident and shameless venality, you could argue that intensive indoor cultivation of a plant which grows perfectly well outdoors is the cannabis industry’s reaction to the product’s illegality itself… In the mid-1980s, during Ronald Reagan’s ‘war on drugs’ and Zammo’s ‘Just say no’ campaign on Grange Hill, American campaigners were claiming that cannabis was fourteen times stronger than in 1970. Which sets you thinking. If it was fourteen times stronger in 1986 than in 1970, and it’s twenty-five times stronger today than at the beginning of the 1990s, does that mean it’s now 350 times stronger than in 1970? That’s not even a crystal in a plant pot. It’s impossible…
Ricorda un’altra vicenda, quella dell’alluvione di cocaina in arrivo nelle nostre città (marzo 2006). L’articolo…
… ‘Use of the addictive drug by children doubles in a year,’ said the subheading. Was this true?…
I dati erano tratti da fonti governative.
Ma la fonte sembrava minimizzare nel suo commento, parlava di “nessun aumento”. Per fortuna che il fiero giornalista investigativo aveva fiutato il marcio, ovvero aveva scoperto che in realtà i consumatori di cocaina erano raddoppiati!…
… If you read the press release for the government survey on which the story is based, it reports ‘almost no change in patterns of drug use, drinking or smoking since 2000’. But this was a government press release, and journalists are paid to investigate…
La fonte documentale
… You can download the full document online. It’s a survey of 9,000 children, aged eleven to fifteen, in 305 schools. The three-page summary said, again, that there was no change in prevalence of drug use. If you look at the full report you will find the raw data tables: when asked whether they had used cocaine in the past year, 1 per cent said yes in 2004, and 2 per cent said yes in 2005. So the newspapers were right: it doubled? No. Almost all the figures given were 1 per cent or 2 per cent…
Ecco: nel 2003 l’1% degli intervistati diceva di aver consumato cocaina. Nel 2004 il 2%. Possiamo davvero parlare di raddoppio?
Senza contare dell’ “arrotondamento perduto”…
… The actual figures were 1.4 per cent for 2004, and 1.9 per cent for 2005, not 1 per cent and 2 per cent…
Traduciamo tutto in termini di rischio, ma di rischio relativo…
… What we now have is a relative risk increase of 35.7 per cent, or an absolute risk increase of 0.5 per cent. Using the real numbers, out of 9,000 kids we have about forty-five more saying ‘Yes’ to the question ‘Did you take cocaine in the past year?’ Presented with a small increase like this, you have to think: is it statistically significant?…
Nonostante questo, sembrerebbe che l’incremento sia statisticamente significativo. Allora perché gli estensori della statistica dicevano che non vi era alcun incremento? Perché?
Partiamo dall’inizio, cos’è la significatività statistica?…
… It’s just a way of expressing the likelihood that the result you got was attributable merely to chance. Sometimes you might throw ‘heads’ five times in a row, with a completely normal coin, especially if you kept tossing it for long enough… The standard cut-off point for statistical significance is a p-value of 0.05, which is just another way of saying, ‘If I did this experiment a hundred times, I’d expect a spurious positive result on five occasions, just by chance.’…
Ma attenzione: la significatività statistica assume che i casi osservati siano indipendenti, il che non è mai vero del tutto nel mondo reale. Il comportamento degli studenti, per esempio, è influenzato da tanti fattori comuni (mode, eventi, trend…). Tanto è vero che se replichiamo nel mondo concreto il sondaggio non otteniamo mai il 5% canonico…
… To ‘data mine’, taking it out of its real-world context, and saying it is significant, is misleading. The statistical test for significance assumes that every data point is independent, but here the data is ‘clustered’, as statisticians say. They are not data points, they are real children, in 305 schools. They hang out together, they copy each other, they buy drugs from each other, there are crazes, epidemics, group interactions… The increase of forty-five kids taking cocaine could have been a massive epidemic of cocaine use in one school…
Urge correggere il risultato. Gli statistici chiamano questa correzione “clustering” (una tecnica per far la tara alla dipendenza insita tra i data points)…
… As statisticians would say, you must ‘correct for clustering’. This is done with clever maths which makes everyone’s head hurt. All you need to know is that the reasons why you must ‘correct for clustering’ are transparent, obvious and easy, as we have just seen… When you correct for clustering, you greatly reduce the significance of the results…
Cosa resta dopo questa correzione?
Ben poco, anche perché, nel caso di specie, bisogna apportarne una ulteriore.
Quando testi molte relazioni in teoria puoi scegliere quelle che ti fanno più comodo. Aumenta così la possibilità che alcune siano positive per puro caso, viene la tentazione di assumerle scartando le altre. Il metodo scientifico, infatti, imporrebbe di fare delle ipotesi tramite un modello e poi di verificarle. Guardare ai dati per costruire delle ipotesi non è il modo corretto di procedere…
… Will our increase in cocaine use, already down from ‘doubled’ to ‘35.7 per cent’, even survive? No. Because there is a final problem with this data: there is so much of it to choose from. There are dozens of data points in the report: on solvents, cigarettes, ketamine, cannabis, and so on. It is standard practice in research that we only accept a finding as significant if it has a p-value of 0.05 or less. But as we said, a p-value of 0.05 means that for every hundred comparisons you do, five will be positive by chance alone. From this report you could have done dozens of comparisons, and some of them would indeed have shown increases in usage—but by chance alone, and the cocaine figure could be one of those…
Analogia: se lancio ripetutamente il dado potrò poi scegliere ad hoc delle serie di 6 in modo da dimostrare che non c’è casualità…
… If you roll a pair of dice often enough, you will get a double six three times in a row on many occasions…
Lo studio in oggetto contiene una miriade di confronti tra variabili le più disparate. E’ quindi uno studio che induce i ricercatori in tentazione. In casi del genere occorre procedere con la “correzione di Bonferroni”, una rettifica deontologica/metodologica che si applica comunemente in casi del genere…
… This is why statisticians do a ‘correction for multiple comparisons’, a correction for ‘rolling the dice’ lots of times. This, like correcting for clustering, is particularly brutal on the data, and often reduces the significance of findings dramatically…
Dopo quest’ultima correzione, del “raddoppio” di cui parla l’alacre giornalista investigativo non resta più niente.
I nerd che hanno stilato lo studio in oggetto, oltre ad interpretare correttamente il passaggio dall’1% al 2%, conoscevano bene la “correzione per cluster” e la “correzione di Bonferroni”, per questo concludevano che “non si registra alcun aumento nel consumo di cocaina. Per questo, e non per tacere al popolo una “scomoda” verità.
***
Ma la piaga più vistosa delle statistiche sono i campioni mal selezionati
… There are also some perfectly simple ways to generate ridiculous statistics, and two common favourites are to select an unusual sample group, and to ask them a stupid question. Let’s say 70 per cent of all women want Prince Charles to be told to stop interfering in public life. Oh, hang on—70 per cent of all women who visit my website want Prince Charles to be told to stop interfering in public life…
Esempio: disponibilità dei medici a fare aborti
… Telegraph in the last days of 2007. ‘Doctors Say No to Abortions in their Surgeries’ was the headline. ‘Family doctors are threatening a revolt against government plans to allow them to perform abortions in their surgeries… ‘Four out of five GPs do not want to carry out terminations even though the idea is being tested in NHS pilot schemes, a survey has revealed.’…
La fonte della notizia…
… It was an online vote on a doctors’ chat site that produced this major news story. Here is the question, and the options given:   ‘GPs should carry out abortions in their surgeries’ Strongly agree, agree, don’t know, disagree, strongly disagree…
Primo: dubbi sulla formulazione della domanda
… Is that ‘should’ as in ‘should’? As in ‘ought to’?… Are they just saying no because they’re grumbling about more work and low morale? More than that, what exactly does ‘abortion’ mean here?…
***
Un altro caso esemplare. Avete presente quanti omicidi commettono gli psicopatici?…
… In 2006, after a major government report, the media reported that one murder a week is committed by someone with psychiatric problems. Psychiatrists should do better, the newspapers told us, and prevent more of these murders. All of us would agree…
Non si potrebbe fermarli prima? Non si potrebbe trattenere i soggetti più pericolosi?
Chi pensa a soluzioni del genere non ha chiaro il concetto di frequenza di base e di falso positivo
… the blood test for HIV has a very high ‘sensitivity’, at 0.999. That means that if you do have the virus, there is a 99.9 per cent chance that the blood test will be positive. They would also say the test has a high ‘specificity’ of 0.9999—so, if you are not infected, there is a 99.99 per cent chance that the test will be negative. What a smashing blood test.* But if you look at it from the perspective of the person being tested, the maths gets slightly counterintuitive. Because weirdly, the meaning, the predictive value, of an individual’s positive or negative test is changed in different situations, depending on the background rarity of the event that the test is trying to detect. The rarer the event in your population, the worse your test becomes, even though it is the same test. This is easier to understand with concrete figures. Let’s say the HIV infection rate among high-risk men in a particular area is 1.5 per cent. We use our excellent blood test on 10,000 of these men, and we can expect 151 positive blood results overall: 150 will be our truly HIV-positive men, who will get true positive blood tests; and one will be the one false positive we could expect from having 10,000 HIV-negative men being given a test that is wrong one time in 10,000. So, if you get a positive HIV blood test result, in these circumstances your chances of being truly HIV positive are 150 out of 151. It’s a highly predictive test. Let’s now use the same test where the background HIV infection rate in the population is about one in 10,000. If we test 10,000 people, we can expect two positive blood results overall. One from the person who really is HIV positive; and the one false positive that we could expect, again, from having 10,000 HIV-negative men being tested with a test that is wrong one time in 10,000. Suddenly, when the background rate of an event is rare, even our previously brilliant blood test becomes a bit rubbish. For the two men with a positive HIV blood test result, in this population where only one in 10,000 has HIV, it’s only 50:50 odds on whether they really are HIV positive…
L’esame psichiatrico dei soggetti pericolosi ha falsi positivi notevoli abbinati poi a frequenze di base comunque piuttosto basse. Assurdo fermare dei soggetti in condizioni tanto incerte…
… Let’s think about violence. The best predictive tool for psychiatric violence has a ‘sensitivity’ of 0.75, and a ‘specificity’ of 0.75. It’s tougher to be accurate when predicting an event in humans, with human minds and changing human…
Basta fare qualche calcolo…
… Let’s say 5 per cent of patients seen by a community mental health team will be involved in a violent event in a year. Using the same maths as we did for the HIV tests, your ‘0.75’ predictive tool would be wrong eighty-six times out of a hundred. For serious violence, occurring at 1 per cent a year, with our best ‘0.75’ tool, you inaccurately finger your potential perpetrator ninety-seven times out of a hundred. Will you preventively detain ninety-seven people to prevent three violent events?…
Mettere praticamente in gabbia 96 persone per salvare tre vite è un po’ esagerato. O no?
***
Il caso Clark
… In 1999 solicitor Sally Clark was put on trial for murdering her two babies…
La prova della sua colpevolezza…
… At her trial, Professor Sir Roy Meadow, an expert in parents who harm their children, was called to give expert evidence. Meadow famously quoted ‘one in seventy-three million’ as the chance of two children in the same family dying of Sudden Infant Death Syndrome (SIDS)….
Troppo improbabile che due bambini muoiano insieme per ragioni naturali: doveva averli assassinati lui per forza!
Cosa c’è che non va in questo ragionamento.
Innanzitutto si commette una “fallacia ecologica”: certi fatti non sono indipendenti e l’operatore logico “contemporaneamente” non si rende fattorizzando…
… The figure of ‘one in seventy-three million’ itself is iffy, as everyone now accepts. It was calculated as 8,543 × 8,543, as if the chances of two SIDS episodes in this one family were independent of each other. This feels wrong from the outset, and anyone can see why: there might be environmental or genetic factors at play, both of which would be shared by the two babies…
Poi c’è la “fallacia dell’accusatore”, il quale tiene conto solo dell’improbabile innocenza. E l’improbabile colpevolezza che fine ha fatto?…
… Many press reports at the time stated that one in seventy-three million was the likelihood that the deaths of Sally Clark’s two children were accidental: that is, the likelihood that she was innocent… Once this rare event has occurred, the jury needs to weigh up two competing explanations for the babies’ deaths: double SIDS or double murder. Under normal circumstances—before any babies have died—double SIDS is very unlikely, and so is double murder… If we really wanted to play statistics, we would need to know which is relatively more rare, double SIDS or double murder. People have tried to calculate the relative risks of these two events, and one paper says it comes out at around 2:1 in favour of double SIDS… the rarity of double SIDS is irrelevant, because double murder is rare too…
***
A posteriori nessun caso puo’ essere definito sorprendente: Richard Feynman in merito alla cosa…
… You know, the most amazing thing happened to me tonight. I was coming here, on the way to the lecture, and I came in through the parking lot. And you won’t believe what happened. I saw a car with the license plate ARW 357. Can you imagine? Of all the millions of license plates in the state, what was the chance that I would see that particular one tonight? Amazing… Richard Feynman…
Ecco il caso dell’infermiera assassina: troppi morti durante i suoi turni…
… A nurse called Lucia de Berk has been in prison for six years in Holland, convicted of seven counts of murder and three of attempted murder. An unusually large number of people died when she was on shift, and that, essentially, along with some very weak circumstantial evidence, is the substance of the case against her… The judgement was largely based on a figure of ‘one in 342 million against’….
Calma: mai fidarsi delle “previsioni” fatte dopo. Le previsioni si fanno prima: una cosa è rara solo se imprevedibile…
… It’s only weird and startling when something very, very specific and unlikely happens if you have specifically predicted it beforehand…
L’uomo che disegnava bersagli intorno ai fori di pallottola…
… Imagine I am standing near a large wooden barn with an enormous machine gun. I place a blindfold over my eyes and—laughing maniacally—I fire off many thousands and thousands of bullets into the side of the barn. I then drop the gun, walk over to the wall, examine it closely for some time, all over, pacing up and down. I find one spot where there are three bullet holes close to each other, then draw a target around them, announcing proudly that I am an excellent marksman…
Prima le ipotesi, poi le evidenze. Ecco come opera la scienza…
… a cardinal rule of any research involving statistics: you cannot find your hypothesis in your results…
I rischi dell’indagine a ritroso
… To collect more data, the investigators went back to the wards to see if they could find more suspicious deaths. But all the people who were asked to remember ‘suspicious incidents’ knew that they were being asked because Lucia might be a serial killer. There was a high risk that ‘an incident was suspicious’ became synonymous with ‘Lucia was present’…
Qui bisogna essere chiari: alcuni fenomeni non possono essere verificati, cosicché puo’ essere interessante formulare delle ipotesi a posteriori, è tutto quel che abbiamo in mano. pensiamo solo al caso del principio antropico. Tuttavia, bisogna essere ben consapevoli della differenza tra il metodo scientifico più rigoroso e questo modo di agire.