Lee Smolin (born 1955 in New York City) is an American theoretical physicist, a researcher at the Perimeter Institute for Theoretical Physics, and an adjunct professor of physics at the University of Waterloo.
Smolin is best known for devising several different approaches to quantum gravity, in particular loop quantum gravity. He advocates that the two primary approaches to quantum gravity, loop quantum gravity and string theory, can be reconciled as different aspects of the same underlying theory. His research interests also include cosmology, elementary particle theory, the foundations of quantum mechanics, and theoretical biology.
Smolin's most famous suggestion may be his theory of fecund universes, also known as cosmological natural selection, which attempts to apply principles of biological evolution to cosmology, suggesting that universes evolve in favor of the production of black holes. Leonard Susskind who now promotes a similar string theory landscape, stated:
"I'm not sure why Smolin's idea didn't attract much attention. I actually think it deserved far more than it got.He writes many articles for the popular media, often promoting loop quantum gravity and criticizing the strength of support for string theory in the physics community.
Smolin also points out that string theory landscape is not Popper falsifiable if other worlds are not observable. There are then only two ways out: traversable wormholes connecting the different parallel worlds and "signal nonlocality", as described by Antony Valentini, a scientist at the Perimeter Institute.
The theory surmises that a collapsing black hole causes the emergence of a new universe on the "other side", whose fundamental constant parameters (speed of light, Planck length and so forth) may differ slightly from those of the universe where the black hole collapsed. Each universe therefore gives rise to as many new universes as it has black holes. Thus the theory contains the evolutionary ideas of "reproduction" and "mutation" of universes, but has no direct analogue of natural selection. However, given any universe that can produce black holes that successfully spawn new universes, it is possible that some number of those universes will reach heat death with unsuccessful parameters. So, in a sense, fecundity cosmological natural selection is one where universes could die off before successfully reproducing, just as any biological being can die without having children.
The claims, many of which are controversial, that the book make include:
The book also focuses on the difficulties faced by current efforts at theories of unification of physics and approaches to quantum gravity.
The publication of The Trouble with Physics generated much controversy and debate about the merits of string theory, and the book was criticised by some leading physicists including string theorists Joseph Polchinski and Luboš Motl.
Smolin has expressed the opinion that quantum mechanics is not a "final theory".