21 February 2008

Cat de sigura e cunoasterea stiintifica?

Putine lucruri mi se par mai obositoare decat discutiile epistemologice cu filosofi. Pozitia mea e radical empirista: orice afirmatie descriptiva care are sens (are un oarecare continut informational) are in mod necesar o anumita conectare la realitate, iar aceasta conectare la realitate poate fi folosita pentru a determina experimental (daca esti suficient de ingenios incat sa inventezi o retea potrivita de experimente - care sa se contranga unele pe altele si sa nu lase urme de interpretari alternative) daca propozitia respectiva e adevarata sau falsa. In practica, avem mult prea putine experimente pentru a determina in mod clar valoarea de adevar a propozitiilor, asa ca trebuie sa ne multumim cu judecati probabiliste, si pe masura ce avem mai multe experimente probabilitatea tot mai multor propozitii tinde la 0 sau la 1. Genul asta de pozitie pare complet absurda celor mai multi filosofi pe care i-am intalnit pentru ca ei au impresia ca intotdeauna poti avea interpretari alternative, sau chiar ca intotdeauna poti interpreta oricum vrei tu datele experimentale. Aceasta poveste cu "interpretarile" nu mi se pare ca sta in picioare pentru ca inventeaza un dualism inexistent intre "interpretari" si afirmatiile propriu-zise pe care le judeci. Interpretarea e la randul ei un set de premize. Asa ca la fel cum testezi empiric o afirmatie, tot la fel testezi si o interpretare. Prin urmare ideea asta ca intotdeauna poti interpreta datele cum vrei este de fapt credinta in existenta unor adevaruri sintetice a priori (acest gen de filosofi relativisti neaga in general existenta unor asemenea adevaruri, asta cred ca pe buna dreptate). Ceea ce este frustrat sunt exemplele care sunt aduse.
  • De pilda un argument foarte popular pare sa fie: noi pur si simplu presupunem ca lumina merge in linie dreapta (pentru ca poate asta e cel mai simplu lucru de presupus) si toate impresiile noastre despre lume pleaca de la aceasta premiza imposibil de testat. Insa oricine a frunzarit o carte de optica (chiar si in manualul de liceu!) ar trebui sa stie ca faptul ca lumina merge in linie dreapta nu e deloc ceva luat de bun si cunoastem foarte bine in ce conditii lumina merge pe traiectorii curbe (refractiedifractieinterferentalentile gravitationale).  De asemenea, stim inclusiv care ar fi consecintele experimentale  ale neomogenitatii si neizotropiei spatiului (nu s-ar conserva impulsul si momentul cinetic).
  • Un alt exemplu popular este faptul ca noi chipurile nu avem nici cea mai mica idee daca toti percepem culorile la fel; pur si simplu fiecare dintre noi a fost educat sa numesca "rosu" ceea ce fiecare percepe cand i se arata culoarea rosie etc. Acest argument ignora complet faptul ca nu exista decat 3 culori independente (de pilda rosu, verde, albastru), toate celelalte fiind combinatii de acestea. Din acest motiv este foarte usor sa-ti dai seama daca cineva are o vedere anormala. Daca eu as vedea invers sa zicem albastrul si rosu atunci ar trebui sa vad invers (si sa fi fost invatat invers) si turcoaz-ul si galben-ul si asa mai departe.
  • Un alt exemplu este matematica. 2 + 2 fac 4 iar asta e ceva dat. Adevarul insa e ca 2 + 2 = 4 e o teorema care decurge din axiomele aritmeticii, iar faptul ca aceste axiome ale aritmeticii sunt utile la modelarea fenomenelor naturale este o concluzie stabilita empiric si nicidecum un adevar a priori.
  • La 15 ani de la publicarea Consciousness Explained Dennett inca se mai chinuie sa le explice astora ca ideea de zombi e aberanta (Sweet Dreams incepe cu o discutie despre zombi).
  • Searle inca bate campii cu camera chinezeasca.
  • De 20+ de ani tot nu s-au saturat sa discute despre Mary cea crescuta in camera alb-negru (!).
  • Etc.
  • Etc.
Ceea ce este ridicol la genul asta de argumente filosofice este siguranta cu care ei cred ca aceste lucruri sunt pur si simplu teoretic imposibil de verificat experimental in conditiile in care de foarte multe ori (poate cu exceptia chestiilor de filosofia mintii unde nu exista inca stiinta) oamenii de stiinta au rezolvat deja problema verificarii lor experimentale. Dintr-un motiv sau altul ei au impresia ca aceste argumente sunt de o subtilitate coplesitoare, iar oamenilor de stiinta cu siguranta ca nu le-a trecut prin cap sa le verifice, pentru ca lipsa lor de profunditate filosofica este legendara. (Definitia mea: un experiment mental este o metoda de a genera un maxim de confuzie cu un minim de cuvinte.) In opozitie cu acest gen de siguranta iluzorie, care se bazeaza pe o incredere exagerata in puterea gandirii abstracte, este siguranta care are la baza descoperirile de natura empirica si teoriile ale caror predictii au fost testate empiric. Despre genul asta de siguranta am gasit doua articole cu exemple din fizica care acopera cam tot ce e de zis: Sean Carroll de la Cosmic Variance despre de ce nu exista telekinezie, telepatie si alte asemenea fenomene, si Phil Plait de la Bad Astronomy.
The scientific method makes one assumption, and one assumption only: the Universe obeys a set of rules. That’s it. There is one corollary, and that is that if the Universe follows these rules, then those rules can be deduced by observing the way Universe behaves. This follows naturally; if it obeys the rules, then the rules must be revealed by that behavior. A simple example: we see objects going around the Sun. The motion appears to follow some rules: the orbits are conic sections (ellipses, circles, parabolas, hyperbolas), the objects move faster when they are closer to the Sun, if they move too quickly they can escape forever, and so on. From these observations we can apply mathematical equations to describe those motions, and then use that math to predict where a given object will be at some future date. Guess what? It works. It works so well that we can shoot probes at objects billions of kilometers away and still nail the target to phenomenal accuracy. This supports our conclusion that the math is correct. This in turn strongly implies that the Universe is following its own rules, and that we can figure them out. (Phil, Is science faith-based?)
Sean explica super bine din ce cauza incertitudinea stiintifica exista la marginile teoriilor, acolo unde incercam sa le extindem dincolo de domeniul lor de valabilitate deja testat. Insa chiar daca descoperim vreo noua teorie revolutionara, acea teorie nu o sa dea peste cap toata baza de date experimentale deja adunata, dimpotriva, ea va trebui sa fie conforma cu ea.
The main point here is that, while there are certainly many things that modern science does not understand, there are also many things that it does understand, and those things simply do not allow for telekinesis, telepathy, etc. [...] If we can show that psychic phenomena are incompatible with the laws of physics we currently understand, then our task is to balance the relative plausibility of “some folks have fallen prey to sloppy research, unreliable testimony, confirmation bias, and wishful thinking” against “the laws of physics that have been tested by an enormous number of rigorous and high-precision experiments over the course of many years are plain wrong in some tangible macroscopic way, and nobody ever noticed.” The crucial concept here is that, in the modern framework of fundamental physics, not only do we know certain things, but we have a very precise understanding of the limits of our reliable knowledge. We understand, in other words, that while surprises will undoubtedly arise (as scientists, that’s what we all hope for), there are certain classes of experiments that are guaranteed not to give exciting results — essentially because the same or equivalent experiments have already been performed. [...] We are creatures of the universe, subject to the same laws of physics as everything else. As everyone knows, there are many things we don’t understand about biology and neuroscience, not to mention the ultimate laws of physics. But there are many things that we do understand, and only the most basic features of quantum field theory suffice to definitively rule out the idea that we can influence objects from a distance through the workings of pure thought. The simplest example is telekinesis, the ability to remotely move an object using only psychic powers. For definitiveness, let’s consider the power of spoon-bending. [...] Could either gravitation or electromagnetism be responsible for bending spoons? No. In the case of electromagnetism, it would be laughably easy to detect the kind of fields necessary to exert enough force to influence a spoon. Not to mention that the human brain is not constructed to generate or focus such fields. But the real point is that, if it were electromagnetic fields doing the spoon-bending, it would be very very noticeable. (And the focus would be on influencing magnets and circuits, not on bending spoons.) In the case of gravitation, the fields are just too weak. Gravity accumulates in proportion to the mass of the source, so the arrangement of particles inside your brain will have a much smaller gravitational effect than just the location of your head — and that’s far too feeble to move spoons around. A bowling ball would be more efficient, and most people would agree that moving a bowling ball past a spoon has a negligible effect. Could there be a new force, as yet undetected by modern science? Of course! I’ve proposed them myself. Physicists are by no means closed-minded about such possibilities; they are very excited by them. But they also take seriously the experimental limits. And those limits show unambiguously that any such new force must either be very short-range (less than a millimeter), or much weaker than gravity, which is an awfully weak force. The point is that such forces are characterized by three things: their range, their strength, and their source (what they couple to). As discussed above, we know what the possible sources are that are relevant to spoons: quarks, gluons, photons, electrons. So all we have to do is a set of experiments that look for forces between different combinations of those particles. And these experiments have been done! The answer is: any new forces that might be lurking out there are either (far) too short-range to effect everyday objects, or (far) too weak to have readily observable effects. [...] That’s it. We are done. The deep lesson is that, although science doesn’t know everything, it’s not “anything goes,” either. There are well-defined regimes of physical phenomena where we do know how things work, full stop. The place to look for new and surprising phenomena is outside those regimes. You don’t need to set up elaborate double-blind protocols to pass judgment on the abilities of purported psychics. Our knowledge of the laws of physics rules them out. Speculations to the contrary are not the provenance of bold visionaries, they are the dreams of crackpots. (Sean Caroll, Telekinesis and Quantum Field Theory)
Articolul meu mai vechi despre diferenta dintre stinta si religie.