… ist auch nach dem letzten, von erstaunlichen physikalischen Innovationen und „Revolutionen“ gekennzeichneten Jahrhundert unter theoretischen Physikern stark umstritten. Freeman Dyson schrieb für die New York Review of Books 8/2004 einen lesenswerten Artikel* zum Thema, in dem er sich mit dem neuen Buch von Brian Greene, einem Proponenten der Stringtheorie, beschäftigt: „The Fabric of the Cosmos: Space, Time, and the Texture of Reality“. Diese Theorie ist zumindest mathematisch in der Lage, eines der größten physikalischen Probleme unserer Zeit zu lösen, nämlich die Inkonsistenz zwischen Relativitäts- und Quantentheorie. Greene kann das sehr schön erläutern:
Superstring theory tells a different story. It does not deny the key role played by electrons, quarks, and the other particle species revealed by experiment, but it does claim that these particles are not dots. Instead, according to superstring theory, every particle is composed of a tiny filament of energy, some hundred billion billion times smaller than a single atomic nucleus (much smaller than we can currently probe), which is shaped like a little string. And just as a violin string can vibrate in different patterns, each of which produces a different musical tone, the filaments of superstring theory can also vibrate in different patterns. But these vibrations don’t produce different musical notes; remarkably, the theory claims that they produce different particle properties. A tiny string vibrating in one pattern would have the mass and the electric charge of an electron; according to the theory, such a vibrating string would be what we have traditionally called an electron. A tiny string vibrating in a different pattern would have the requisite properties to identify it as a quark, a neutrino, or any other kind of particle. All species of particles are unified in superstring theory since each arises from a different vibrational pattern executed by the same underlying entity.
Leider hat dieser elegante Ansatz einen großen Haken, der mit der Art und Weise zu tun hat, wie Naturwissenschaften funktionieren, nämlich dass kein Experiment denkbar ist, das fundamentale Aussagen über den Wahrheitsgehalt der Stringtheorie erwarten lässt: Sie ist empirisch nicht testbar. Ähnliches gilt für den Nachweis von Gravitonen (den postulierten Schwerkraft-Teilchen):
I propose as a hypothesis to be tested that it is impossible in principle to observe the existence of individual gravitons. I do not claim that this hypothesis is true, only that I can find no evidence against it. If it is true, quantum gravity is physically meaningless. If individual gravitons cannot be observed in any conceivable experiment, then they have no physical reality and we might as well consider them non-existent. They are like the ether, the elastic solid medium which nineteenth-century physicists imagined filling space. Electric and magnetic fields were supposed to be tensions in the ether, and light was supposed to be a vibration of the ether. Einstein built his theory of relativity without the ether, and showed that the ether would be unobservable if it existed. He was happy to get rid of the ether, and I feel the same way about gravitons.
Das ist ein Grund, warum Dyson auf dem unorthodoxen Standpunkt beharrt, dass Relativitäts- und Quantentheorie gut nebeneinander existieren können, und man nicht krampfhaft nach einer vereinheitlichenden Theorie suchen müsse.
* Der Artikel ist mittlerweile Teil des kostenpflichtigen NYRB-Archivs
