From Tom Siegfried at ScienceNews::
Maybe, string/brane/M theory would explain the amount of that mysterious “dark” energy in space and all would be well. But no. Working with physicist Raphael Bousso, Polchinski found that string theory did not specify how much energy the vacuum of space contained. Instead the theory predicted a virtually countless number of vacuum states, with nearly any amount of repulsive energy you could imagine. In other words, string theory described a giga-gaggle of different universes — a multiverse.
Polchinski’s modesty manifested itself in his reaction to this situation. He hated the idea of a multiverse, because it implied that some questions had no answers that physicists could calculate. No equation could specify the amount of dark energy; it would just be luck — determined by which universe had the right amount of dark energy to make it hospitable to life (an idea known as the anthropic principle). Polchinski once vowed to quit physics if dark energy existed and implied the need for anthropic reasoning. But unlike many physicists who adamantly defend their views against contrary evidence, Polchinski changed his mind. More.
No serious evidence has ever turned up for string theory and the multiverse is — as Polchinski seems to have grasped — science’s assisted suicide. Dark energy or no, today’s multiverse community is beyond such trivia as falsifiability.
Perhaps it’s best to see Polchinski as a nice and helpful Jacques Derrida (1930-2004). He adopted a disastrous intellectual assumption in good faith and will, happily, not live to address the consequences of his immensely destructive idea. That task is left to others. Requiem aeternam dona ei.
From the obit: “One of the boldest and most innovative string theorists has died.”
See also: Peter Woit: 15th anniversary of multiverse mania, “a concerted attack on conventional notions of science”
and
The multiverse is science’s assisted suicide