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The Theory of Everything (Robert B. Laughlin & David Pines)

dandan | 13 Junio, 2008 22:30 | Share and Enjoy:

Acabo de leer el artículo que Robert B. Laughlin publicó con David Pines antes de escribir "Un universo diferente". El artículo se llama "The Theory of Everything" (está aquí), y es una crítica más directa a la teoría del todo de la que luego aparece en el libro. El libro ya no insiste en la polémica, sino que explora lo que puede haber después. La teoría del todo fue el sueño de Einstein, la posibilidad de explicar la física a partir de una única teoría. Después de integrar el electromagnetismo de la relatividad especial con la gravedad en la teoría de la relatividad general, Einstein estuvo trabajando durante años en la misma dirección para integrarlo todo en una única teoría. No lo consiguió. Mientras él seguía trabajando con el mismo método en Estados Unidos, en Europa descubrían el universo cuántico que descolocaba todo el escenario. Einstein nunca aceptó la indeterminación que supone la física cuántica.

A partir de entonces, la física ha quedado dividida en dos sectores poco comunicados: la teoría general de la relatividad, que explica satisfactoriamente el universo macro, y el modelo estandar, que explica también satisfactoriamente el universo micro. El problema que las mantiene separadas es que la segunda no consigue integrar la gravedad. En los últimos años ha aparecido una nueva teoría que intenta recuperar el sueño de Einstein, la teoría de las cuerdas, que consigue integrar la gravedad, pero, pero, que no es verificable experimentalmente con los recursos que tenemos ahora. Es una teoría matemática en donde las ecuaciones encajan entre si, pero en donde falta por saber si el universo está dispuesto a encajar en ellas. De momento no responde porque no se ha encontrado la manera de preguntarle.

La teoría de las cuerdas trabaja con el mismo método que Einstein: integrar los diversos fenómenos físicos en ecuaciones-raiz y reducirlos a leyes. Si encuentras la ecuación adecuada, toda la física hace click y encaja. En la misma línea trabajan otras propuestas alternativas a la teoría de las cuerdas, como la gravedad cuántica de bucles de Lee Smolin o la reciente teoría topológica de Garrett Lisi. Pero lo que propone Laughlin, que ganó el Nobel por temas sobre la superconductividad, es decir, trabajos en la frontera entre la teoría general de la relatividad y el modelo estandar, es cambiar este método jerárquico de la física y aprender de los tratos con la incertidumbre a que se ha acostumbrado la biología porque, a nivel cuántico, se dan fenómenos imprevisibles que dependen de la organización del contexto, de la emergencia de un patrón en un momento dado (como el cambio de fase del agua al hervir de líquido a vapor, o al revés con el frío, de líquido a hielo sólido), que depende de una "decisión" de los átomos colectivamente implicados. como lo fenómenos de emergencia en biología de que parte Steven Johnson. Lo que propone Laughlin es cambiar el método y limitarse a como responde el universo (macro y micro) a las preguntas que se le plantean a partir de experimentos. Una actitud un poco radical, pero que creo que intenta desactivar los riesgos de una excesiva confianza en las ecuaciones, avisando de que lo que ha visto por ahí no encaja en ese modelo.

Bueno, voy a copiar aquí el final del artículo. Queda pendiente un buen resumen (o algo) del libro, pero es que todavía lo estoy digiriendo. De momento aquí va esto:

The fact that the essential role played by higher organizing principles in determining emergent behavior continues to be disavowed by so many physical scientists is a poignant comment on the nature of modern science. To solid-state physicists and chemists, who are schooled in quantum mechanics and deal with it every day in the context of unpredictable electronic phenomena such as organogels (47), Kondo insulators (48), or cuprate superconductivity, the existence of these principles is so obvious that it is a cliché not discussed in polite company. However, to other kinds of scientist the idea is considered dangerous and ludicrous, for it is fundamentally at odds with the reductionist beliefs central to much of physics. But the safety that comes from acknowledging only the facts one likes is fundamentally incompatible with science. Sooner or later it must be swept away by the forces of history.

For the biologist, evolution and emergence are part of daily life. For many physicists, on the other hand, the transition from a reductionist approach may not be easy, but should, in the long run, prove highly satisfying. Living with emergence means, among other things, focusing on what experiment tells us about candidate scenarios for the way a given system might behave before attempting to explore the consequences of any specific model. This contrasts sharply with the imperative of reductionism, which requires us never to use experiment, as its objective is to construct a deductive path from the ultimate equations to the experiment without cheating. But this is unreasonable when the behavior in question is emergent, for the higher organizing principles---the core physical ideas on which the model is based---would have to be deduced from the underlying equations, and this is, in general, impossible. Repudiation of this physically unreasonable constraint is the first step down the road to fundamental discovery. No problem in physics in our time has received more attention, and with less in the way of concrete success, than that of the behavior of the cuprate superconductors, whose superconductivity was discovered serendipitously, and whose properties, especially in the underdoped region, continue to surprise (49, 50). As the high-Tc community has learned to its sorrow, deduction from microscopics has not explained, and probably cannot explain as a matter of principle, the wealth of crossover behavior discovered in the normal state of the underdoped systems, much less the remarkably high superconducting transition temperatures measured at optimal doping. Paradoxically high-Tc continues to be the most important problem in solid-state physics, and perhaps physics generally, because this very richness of behavior strongly suggests the presence of a fundamentally new and unprecedented kind of quantum emergence.

In his book "The End of Science" John Horgan (51) argues that our civilization is now facing barriers to the acquisition of knowledge so fundamental that the Golden Age of Science must be thought of as over. It is an instructive and humbling experience to attempt explaining this idea to a child. The outcome is always the same. The child eventually stops listening, smiles politely, and then runs off to explore the countless infinities of new things in his or her world. Horgan's book might more properly have been called the End of Reductionism, for it is actually a call to those of us concerned with the health of physical science to face the truth that in most respects the reductionist ideal has reached its limits as a guiding principle. Rather than a Theory of Everything we appear to face a hierarchy of Theories of Things, each emerging from its parent and evolving into its children as the energy scale is lowered. The end of reductionism is, however, not the end of science, or even the end of theoretical physics. How do proteins work their wonders? Why do magnetic insulators superconduct? Why is 3He a superfluid? Why is the electron mass in some metals stupendously large? Why do turbulent fluids display patterns? Why does black hole formation so resemble a quantum phase transition? Why do galaxies emit such enormous jets? The list is endless, and it does not include the most important questions of all, namely those raised by discoveries yet to come. The central task of theoretical physics in our time is no longer to write down the ultimate equations but rather to catalogue and understand emergent behavior in its many guises, including potentially life itself. We call this physics of the next century the study of complex adaptive matter. For better or worse we are now witnessing a transition from the science of the past, so intimately linked to reductionism, to the study of complex adaptive matter, firmly based in experiment, with its hope for providing a jumping-off point for new discoveries, new concepts, and new wisdom.