Editing Lee Smolin (section)

==Theories and work==

===Loop quantum gravity===
Smolin contributed to the theory of [[loop quantum gravity]] (LQG) in collaborative work with [[Ted Jacobson]], [[Carlo Rovelli]], Louis Crane, [[Abhay Ashtekar]] and others. LQG is an approach to the unification of quantum mechanics with general relativity which utilizes a reformulation of general relativity in the language of [[Gauge theory|gauge field theories]], which allows the use of techniques from particle physics, particularly the expression of fields in terms of the dynamics of loops. With Rovelli he discovered the discreteness of areas and volumes and found their natural expression in terms of a discrete description of quantum geometry in terms of [[spin network]]s. In recent years he has focused on connecting LQG to [[Phenomenology (particle physics)|phenomenology]] by developing implications for experimental tests of spacetime symmetries as well as investigating ways elementary particles and their interactions could emerge from spacetime geometry.

===Background independent approaches to string theory===
Between 1999 and 2002, Smolin made several proposals to provide a fundamental formulation of [[string theory]] that does not depend on approximate descriptions involving classical background spacetime models.

===Experimental tests of quantum gravity===
Smolin is among those theorists who have proposed that the [[Phenomenological quantum gravity|effects of quantum gravity can be experimentally probed]] by searching for modifications in special relativity detected in observations of high energy astrophysical phenomena, including very high energy cosmic rays and photons and neutrinos from gamma ray bursts.  Among Smolin's contributions are the co-invention of [[doubly special relativity]] (with [[João Magueijo]], independently of work by [[Giovanni Amelino-Camelia]]), and of [[relative locality]] (with Amelino-Camelia, [[Laurent Freidel]], and Jerzy Kowalski-Glikman).

===Foundations of quantum mechanics===

Smolin has worked since the early 1980s on a series of proposals for hidden variables theories, which would be non-local deterministic theories which would give a precise description of individual quantum phenomena.  In recent years, he has pioneered two new approaches to the interpretation of quantum mechanics suggested by his work on the reality of time, called the real ensemble interpretation and the principle of precedence.

===Cosmological natural selection {{anchor|Fecund universes}}===
{{main|Cosmological natural selection}}
Smolin's hypothesis of [[cosmological natural selection]], also called the ''[[Fecundity|fecund]] universes'' theory, suggests that a process analogous to biological [[natural selection]] applies at the grandest of scales.  Smolin published the idea in 1992 and summarized it in a book aimed at a lay audience called ''[[The Life of the Cosmos]]''.

Black holes have a role in this natural selection. In fecund theory, a collapsing{{clarify|reason=How exactly did he think black holes can "collapse"?|date=December 2013}} [[black hole]] causes the emergence of a new universe on the "other side", whose fundamental constant parameters (masses of elementary particles, [[Planck constant]], [[elementary charge]], and so forth) may differ slightly from the universe where the black hole collapsed.  Each universe gives rise to as many new universes &mdash; its "offspring" &mdash; as it has black holes, giving an evolutionary advantage to universes in which black holes are common, which are similar to our own. The theory thus explains why [[fine-tuned universe|our universe appears "fine-tuned"]] for the emergence of life as we know it. Because the theory applies the evolutionary concepts of "reproduction", "mutation", and "selection" to universes, it is formally analogous to models of [[population biology]].

When Smolin published the theory in 1992, he proposed as a prediction of his theory that no neutron star should exist with a mass of more than 1.6 times the mass of the sun.{{Citation needed|date=April 2011}}  Later this figure was raised to two solar masses following more precise modeling of neutron star interiors by nuclear astrophysicists. Smolin also predicted that inflation, if true, must only be in its simplest form, governed by a single field and parameter.

===Contributions to the philosophy of physics===
Smolin has contributed to the philosophy of physics through a series of papers and books that advocate the relational, or [[Leibnizian]], view of space and time.  Since 2006, he has collaborated with the Brazilian philosopher and Harvard Law School professor [[Roberto Mangabeira Unger]] on the issues of the reality of time and the evolution of laws; in 2014 they published a book, its two parts being written separately.<ref>Smolin L., and Roberto Mangabeira Unger R., (2014), ''The Singular Universe and the Reality of Time: A Proposal in Natural Philosophy'', Cambridge University Press, {{ISBN|978-1107074064}}</ref>

A book length exposition of Smolin's philosophical views appeared in April 2013. ''[[Time Reborn]]'' argues that physical science has made time unreal while, as Smolin insists, it is the most fundamental feature of reality: "Space may be an illusion, but time must be real" (p.&nbsp;179). An adequate description according to him would give a ''Leibnizian universe'': [[Identity of indiscernibles|indiscernibles]] would not be admitted and every difference should correspond to some other difference, as the [[principle of sufficient reason]] would have it. A few months later a more concise text was made available in a paper with the title ''Temporal Naturalism''.<ref>	Smolin L., [https://arxiv.org/abs/1310.8539 arXiv:1310.8539]</ref>