David W. Snoke | |
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Scientific career | |
Fields | Physics |
Institutions | University of Pittsburgh in Pennsylvania American Physical Society |
David W. Snoke is a Distinguished Professor of Physics at the University of Pittsburgh and co-director of the Pittsburgh Quantum Institute. In 2006 he was elected a Fellow of the American Physical Society "for his pioneering work on the experimental and theoretical understanding of dynamical optical processes in semiconductor systems." [1] In 2004 he co-wrote a controversial paper with prominent intelligent design proponent Michael Behe. In 2007, his research group was the first to report Bose-Einstein condensation of polaritons in a trap. [2] Snoke and theoretical physicist Jonathan Keeling recently published an article announcing a new era for polariton condensates saying that polaritons are arguably the "...best hope for harnessing the strange effects of quantum condensation and superfluidity in everyday applications." [3]
Snoke received his bachelor's degree in physics from Cornell University and his PhD in physics from the University of Illinois at Urbana-Champaign. He has worked for The Aerospace Corporation and was a visiting scientist and Fellow at the Max Planck Institute. [4]
His experimental and theoretical research has focused on fundamental quantum mechanical processes in semiconductor optics, i.e. phase transitions of electrons and holes. Two main thrusts have been Bose-Einstein condensation of excitons [5] [6] [7] [8] [9] and polaritons. [10] [2] He has also had minor efforts in numerical biology, and has published on the topic of the interaction of science and theology.
In 2007, Snoke's research group at the University of Pittsburgh used stress to trap polaritons in confined regions, [2] similar to the way atoms are confined in traps for Bose–Einstein condensation experiments. The observation of polariton condensation in a trap was significant because the polaritons were displaced from the laser excitation spot, so that the effect could not be attributed to a simple nonlinear effect of the laser light. Later milestones from Snoke and collaborators include showing a clear difference between polariton condensation and standard lasing, [12] showing quantized circulation of a polariton condensate in a ring, [13] and the first clear demonstration of Bose-Einstein condensation of polaritons in equilibrium [11] (see Figure 1), in collaboration with the Keith Nelson group at MIT. Prior to this result, polariton condensates were always observed out of equilibrium. [14] [15] For a general discussion of Bose-Einstein condensation of polaritons, see this page.
The basic questions of how systems out of equilibrium approach equilibrium (“equilibration”, or “thermalization”) have involved longstanding deep questions of physics, sometimes called the thermodynamic “arrow of time,” with debates going back to Boltzmann. In 1989 Snoke was one of the first to perform simulations of the equilibration of a Bose-Einstein condensate, using numerical solution of the quantum Boltzmann equation . [16] In 1994 Snoke showed agreement of time-resolved experimental measurements of a particle distribution to solution of the quantum Boltzmann equation . [17] In 2012 he and theorist Steve Girvin published a seminal paper [18] on the justification of the Second Law of Thermodynamics based on analysis of the quantum Boltzmann equation, which has impacted the philosophy of the Second Law. [19] Other work by Snoke has included nonequilibrium dynamics of electron plasma [20] and the Mott transition from exciton gas to electron-hole plasma. [21]
Snoke recently published a book entitled "Interpreting Quantum Mechanics: Modern Foundations" [22] which discusses basic philosophy of quantum mechanics, included an extended critique of the many-worlds interpretation. The later chapters of this book include discussion of his original work on objective-collapse theory (also called spontaneous collapse), which proposes a modification of quantum field theory that gives wave function collapse due to local environmental fluctuations. [23] [24] [25]
In 2004, Snoke co-authored an article with Michael Behe, a senior fellow of the Discovery Institute's Center for Science and Culture, in the scientific journal Protein Science, [26] which received widespread criticism. Snoke's contribution to the paper was an appendix which verified the numerical results with analytical calculations that showed the relevant power law, namely that for a novel feature requiring multiple neutral mutations, the time to fixation has a sublinear dependence on population size.
Behe has stated that the results of the paper support his notion of irreducible complexity, based on the calculation of the probability of mutations required for evolution to succeed. However, the published version did not address the concept directly; according to Behe, all references to irreducible complexity were eliminated prior to the paper's publication at the behest of the reviewers. [27] Michael Lynch authored a response, [28] to which Behe and Snoke responded. [29] Protein Science discussed the papers in an editorial. [30] Protein Science received letters that "contained many points of disagreement with the Behe and Snoke article", including the points that: [30]
- Substantial variation in the rate of mutation fixation occurs, both between lineages and between sites on a protein during evolution. This is a central concept of modern population genetics [citations removed]
- Changes in one site are known to cause changes in the mutation and acceptance rate at other sites in a protein, generally called "compensatory" changes [citations removed]
- Recombination strongly accelerates the rate of joining of independent mutations at multiple sites and of grafting new domains with additional functions and sites of interaction to proteins to create new modes of action or regulation [citations removed]
- Selection acts continuously, and cumulative effects, rather than a single strongly adaptive change, are the basis of evolution under a Darwinian model. Thus, intermediate states must also be assumed to be selected.
The paper's assumptions have been severely criticised and the conclusions it draws from its mathematical model have been both criticised and contradicted:
On May 7, 2005, Behe described the paper in presenting arguments for irreducible complexity in his testimony at the Kansas evolution hearings. [34] At the Kitzmiller v. Dover Area School District trial later that year it was the one article referenced by both Behe and Scott Minnich as supporting intelligent design. In his ruling, Judge Jones noted that "A review of the article indicates that it does not mention either irreducible complexity or ID. In fact, Professor Behe admitted that the study which forms the basis for the article did not rule out many known evolutionary mechanisms and that the research actually might support evolutionary pathways if a biologically realistic population size were used." [35]
Despite the controversy, this article has continued to inspire further work on the problem of the time scale for novel function, with over 100 citations. [36] [37] [38]
In 2014 Snoke, along with coauthors Jeffrey Cox and Donald Petcher, published a numerical study of the evolution of novel structures, in the journal Complexity. [39] The model claimed to address the fundamental problem of the tradeoff of the cost of allowing novel structures which are not yet functional, versus the benefit of the eventual new function.
His book, A Biblical Case for an Old Earth (Baker Books, 2006) was described in a review by Law Professor David W. Opderbeck, in the American Scientific Affiliation's Perspectives on Science and Christian Faith as "succeed[ing] admirably" in "establish[ing] that the 'day-age' view is a valid alternative for Christians who hold to biblical inerrancy", but as "less persuasive" at "argu[ing] for a concordist understanding of the Genesis texts and modern science." [40] Snoke was elected a Fellow of the American Scientific Affiliation in 2006. [4] In 2014 he published a review article for the Discovery Institute, [41] arguing that the prevailing paradigm of modern systems biology favors an intelligent design perspective, namely that systems biologists commonly assume a “good design” paradigm. In 2022 he published a paper in Biocosmos [42] that argues that the second law of thermodynamics implies that the original of life corresponds to an extremely unlikely, low-entropy state. Chapter 7 of his book, Interpreting Quantum Mechanics: Modern Foundations", gives an extended discussion of how quantum mechanics does and does not impact certain theological questions, including a critique of the use of the Copenhagen interpretation to justify mind-over-matter spiritualism, and a critique of attempts to argue that quantum fluctuations can generate something from nothing. [43]
In condensed matter physics, a Bose–Einstein condensate (BEC) is a state of matter that is typically formed when a gas of bosons at very low densities is cooled to temperatures very close to absolute zero. Under such conditions, a large fraction of bosons occupy the lowest quantum state, at which microscopic quantum-mechanical phenomena, particularly wavefunction interference, become apparent macroscopically. More generally, condensation refers to the appearance of macroscopic occupation of one or several states: for example, in BCS theory, a superconductor is a condensate of Cooper pairs. As such, condensation can be associated with phase transition, and the macroscopic occupation of the state is the order parameter.
In physics, polaritons are quasiparticles resulting from strong coupling of electromagnetic waves with an electric or magnetic dipole-carrying excitation. They are an expression of the common quantum phenomenon known as level repulsion, also known as the avoided crossing principle. Polaritons describe the crossing of the dispersion of light with any interacting resonance. To this extent polaritons can also be thought of as the new normal modes of a given material or structure arising from the strong coupling of the bare modes, which are the photon and the dipolar oscillation. The polariton is a bosonic quasiparticle, and should not be confused with the polaron, which is an electron plus an attached phonon cloud.
In theoretical physics, a roton is an elementary excitation, or quasiparticle, seen in superfluid helium-4 and Bose–Einstein condensates with long-range dipolar interactions or spin-orbit coupling. The dispersion relation of elementary excitations in this superfluid shows a linear increase from the origin, but exhibits first a maximum and then a minimum in energy as the momentum increases. Excitations with momenta in the linear region are called phonons; those with momenta close to the minimum are called rotons. Excitations with momenta near the maximum are called maxons.
Wolfgang Ketterle is a German physicist and professor of physics at the Massachusetts Institute of Technology (MIT). His research has focused on experiments that trap and cool atoms to temperatures close to absolute zero, and he led one of the first groups to realize Bose–Einstein condensation in these systems in 1995. For this achievement, as well as early fundamental studies of condensates, he was awarded the Nobel Prize in Physics in 2001, together with Eric Allin Cornell and Carl Wieman.
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In physics, a quantum vortex represents a quantized flux circulation of some physical quantity. In most cases, quantum vortices are a type of topological defect exhibited in superfluids and superconductors. The existence of quantum vortices was first predicted by Lars Onsager in 1949 in connection with superfluid helium. Onsager reasoned that quantisation of vorticity is a direct consequence of the existence of a superfluid order parameter as a spatially continuous wavefunction. Onsager also pointed out that quantum vortices describe the circulation of superfluid and conjectured that their excitations are responsible for superfluid phase transitions. These ideas of Onsager were further developed by Richard Feynman in 1955 and in 1957 were applied to describe the magnetic phase diagram of type-II superconductors by Alexei Alexeyevich Abrikosov. In 1935 Fritz London published a very closely related work on magnetic flux quantization in superconductors. London's fluxoid can also be viewed as a quantum vortex.
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Polariton superfluid is predicted to be a state of the exciton-polaritons system that combines the characteristics of lasers with those of excellent electrical conductors. Researchers look for this state in a solid state optical microcavity coupled with quantum well excitons. The idea is to create an ensemble of particles known as exciton-polaritons and trap them. Wave behavior in this state results in a light beam similar to that from a laser but possibly more energy efficient.
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In physics, the exciton–polariton is a type of polariton; a hybrid light and matter quasiparticle arising from the strong coupling of the electromagnetic dipolar oscillations of excitons and photons. Because light excitations are observed classically as photons, which are massless particles, they do not therefore have mass, like a physical particle. This property makes them a quasiparticle.
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