Heretical thoughts about science and society: Frederick S. Pardee distinguished lecture, November 1, 2005

A version of this essay was delivered in November 1, 2005 as the Frederick S. Pardee Distinguished Lecture at Boston University.Freeman Dyson illuminates the importance of having heretics to challenge assumptions, and gives six heretical predictions of his own. The first is that American hegemony will not last until the next century. The second is that global warming is not the enormous problem that people make it out to be, primarily because increasing topsoil can counteract the excess of carbon dioxide and also, our knowledge is still too limited to diagnose the situation. His third heresy is that the increase in carbon dioxide may take us back to that wettest and warmest point in the interglacial period when the Sahara Desert was wet, and that this may be a better climate overall, driving at the critical juncture between naturalists and humanists. The fourth heresy makes an analogy between the transition that computers made to become small and ubiquitous, and the direction that biotechnology perhaps ought to go. Number five elaborates on communal sharing of genes and a completely new path for biology and evolution, and his sixth is that rural poverty should be solved by increasing the productivity of rural activities using “green technology,” (based on biology) such that people are not forced to migrate to urban centers

An Afternoon with Dr. Freeman Dyson

Dyson will speak with IMSA students and faculty on a variety of topics including space, origins of the universe, and how science and technology change society. Learn how three burgeoning technologies – solar energy, genetic engineering and the Internet could narrow the gap between rich and poor in this century. Dyson’s visions for the future include forests of genetically enhanced trees oozing high-octane fuel from their roots and laser-launched earthlings colonizing the comets of the Kuiper Belt. Are his visions convincing? You can decide by joining us at IMSA’s website

Phase Transitions in the Quantum Heisenberg Model

We rigorously prove that in three or more dimensions, the nearest-neighbor, simple-cubic, ferromagnetic, quantum Heisenberg model of spin S(= 1/2, 1, …) has a phase transition at nonzero temperature

The Oklo bound on the time variation of the fine-structure constant revisited

It has been pointed out by Shlyakhter that data from the natural fission reactors which operated about two billion years ago at Oklo (Gabon) had the potential of providing an extremely tight bound on the variability of the fine-structure constant alpha. We revisit the derivation of such a bound by: (i) reanalyzing a large selection of published rare-earth data from Oklo, (ii) critically taking into account the very large uncertainty of the temperature at which the reactors operated, and (iii) connecting in a new way (using isotope shift measurements) the Oklo-derived constraint on a possible shift of thermal neutron-capture resonances with a bound on the time variation of alpha. Our final (95% C.L.) results are: -0.9 \times 10^{-7} <(alpha^{Oklo} - alpha^{now})/alpha <1.2\times 10^{-7} and -6.7 \times 10^{-17} {yr}^{-1} < {\dot alpha}^{averaged}/alpha <5.0\times10^{-17} {yr}^{-1}$.Comment: 23 pages, Latex, submitted to Nucl.Phys.

Feynman's interpretation of quantum theory

A historically important but little known debate regarding the necessity and meaning of macroscopic superpositions, in particular those containing different gravitational fields, is discussed from a modern perspective.Comment: Published version for Eur.Phys.J. H. 15 pages pdf. Final version available at http://www.springerlink.com/openurl.asp?genre=article&id=doi:10.1140/epjh/e2011-10035-

One-sided versus two-sided stochastic descriptions

It is well-known that discrete-time finite-state Markov Chains, which are described by one-sided conditional probabilities which describe a dependence on the past as only dependent on the present, can also be described as one-dimensional Markov Fields, that is, nearest-neighbour Gibbs measures for finite-spin models, which are described by two-sided conditional probabilities. In such Markov Fields the time interpretation of past and future is being replaced by the space interpretation of an interior volume, surrounded by an exterior to the left and to the right. If we relax the Markov requirement to weak dependence, that is, continuous dependence, either on the past (generalising the Markov-Chain description) or on the external configuration (generalising the Markov-Field description), it turns out this equivalence breaks down, and neither class contains the other. In one direction this result has been known for a few years, in the opposite direction a counterexample was found recently. Our counterexample is based on the phenomenon of entropic repulsion in long-range Ising (or "Dyson") models.Comment: 13 pages, Contribution for "Statistical Mechanics of Classical and Disordered Systems

Exoplanets and SETI

The discovery of exoplanets has both focused and expanded the search for extraterrestrial intelligence. The consideration of Earth as an exoplanet, the knowledge of the orbital parameters of individual exoplanets, and our new understanding of the prevalence of exoplanets throughout the galaxy have all altered the search strategies of communication SETI efforts, by inspiring new "Schelling points" (i.e. optimal search strategies for beacons). Future efforts to characterize individual planets photometrically and spectroscopically, with imaging and via transit, will also allow for searches for a variety of technosignatures on their surfaces, in their atmospheres, and in orbit around them. In the near-term, searches for new planetary systems might even turn up free-floating megastructures.Comment: 9 page invited review. v2 adds some references and v3 has other minor additions and modification

A Road Map for the Exploration of Neighboring Planetary Systems (ExNPS)

A brown dwarf star having only 20-50 times the mass of Jupiter is located below and to the left of the bright star GL 229 in this image from the Hubble Space Telescope. At the 19 light year distance to GL 229, the 7.7-arcsec separation between the star and the brown dwarf corresponds to roughly the separation between Pluto and the Sun in our Solar System. The goal of the program described in this report is to detect and characterize Earth-like planets around nearby stars where conditions suitable for life might be found. For a star like the Sun located 30 light years away, the appropriate star-planet separation would be almost 100 times closer than seen here for GL 229B

Expressions 1990

https://openspace.dmacc.edu/expressions/1012/thumbnail.jp