The Second Renaissance And Informationization
LOOP QUANTUM GRAVITY (LQG)
10 January 2009
LOOP QUANTUM GRAVITY (LQG), rival of string theory in the quest to unite quantum mechanics with general relativity, does not suffer from certain mathematical "infinities" (corresponding to ephemeral, but numerous, alternatives in the way that interactions take place in spacetime), a new study shows. This clears up some doubts as to the theory's usefulness. What is LQG, and why has it been so difficult to quantize gravity? To address this question, return to classical (pre-1900) physics, a regime in which space was fixed. Then the relativity and quantum revolutions changed everything utterly. With the advent of general relativity, space was combined with time in an integrated, but deformable, spacetime. Meanwhile, in quantum mechanics spacetime remains fixed but matter becomes fuzzy; the whereabouts of particles can only be expressed in terms of probability clouds. In a theory that would combine quantum and gravity features, spacetime would then have to be both deformable and fuzzy, and this has been difficult to do. In string theory, the merger is accomplished by imagining that matter ultimately consists of tiny strings. In loop theory, the merger is attempted by imagining that space itself consists of moveable tiny loops. Carlo Rovelli (Center for Theoretical Physics, Marseilles, rovelli@cpt.univ-mrs.fr, 33-0491-269644; also Univ Pittsburgh) argues that loop theory does not have to import the extra commodities (additional dimensions and particles) needed by string theory and that it offers, in principle, more testable predictions, such as the idea of quantized surface areas (that is, regions of space would come in discrete chunks and there would be a minimum possible size scale) and the notion that quantized spacetime might manifest itself as a minute difference in the speed of light for different colors. The new version of loop gravity studied by Rovelli and his colleagues pictures spacetime as being foamy: points in space sometimes grow into bubbles. The bubbles are not "in" space but constitute space itself. The infinities pondered in the present paper represent not difficulties posed by the reality of particles within particles (a necessary complexity dealt with in Richard Feynman's quantum electrodynamics theory) but rather, analogously, to those potentially corresponding to interactions occurring on spacetime loops within loops. (Crane et al., Physical Review Letters, 29 October 2001)
IMPLANTABLE BioMEMS. Microelectromechanical systems (MEMS), tiny devices crafted using microchip technology, have appeared in a number of settings; examples include micron-sized motors, gears, pumps, and detectors. One would also like to use MEMS in implantable medical applications, but bio-compatibility has been a problem. To address this obstacle Tejal Desai at the University of Illinois-Chicago (tdesai@uic.edu, 312-413-8723) has developed a capsule containing insulin-secreting cells. The capsule is covered with pores as small as 7 nm which allow the release of insulin while blocking the entrance of antibodies thrown up the immune system to counteract the transplanted cells. Desai, who has tested her capsules on mice and rats, will report her new results with nanopore capsules (including also compartmented 100-micron chips for drug delivery) at the AVS Science and Technology Society meeting in San Francisco, Oct 29-Nov 2 (http://www.avssymposium.org/Overview.asp. Desai's abstract at :http://www.avssymposium.org/paper.asp?abstractID=145; her university website: http://www.uic.edu/depts/bioe/faculty/tejal_desai/CML%20lab/res _lab.htm.)
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IMPLANTABLE BioMEMS. Microelectromechanical systems (MEMS), tiny devices crafted using microchip technology, have appeared in a number of settings; examples include micron-sized motors, gears, pumps, and detectors. One would also like to use MEMS in implantable medical applications, but bio-compatibility has been a problem. To address this obstacle Tejal Desai at the University of Illinois-Chicago (tdesai@uic.edu, 312-413-8723) has developed a capsule containing insulin-secreting cells. The capsule is covered with pores as small as 7 nm which allow the release of insulin while blocking the entrance of antibodies thrown up the immune system to counteract the transplanted cells. Desai, who has tested her capsules on mice and rats, will report her new results with nanopore capsules (including also compartmented 100-micron chips for drug delivery) at the AVS Science and Technology Society meeting in San Francisco, Oct 29-Nov 2 (http://www.avssymposium.org/Overview.asp. Desai's abstract at :http://www.avssymposium.org/paper.asp?abstractID=145; her university website: http://www.uic.edu/depts/bioe/faculty/tejal_desai/CML%20lab/res _lab.htm.)
PHYSICS NEWS UPDATE SUBSCRIPTION REMINDER: To put yourself on, or take yourself off, our list at your leisure, please send a message to listserv@aip.org and specify either "add physnews" or "delete physnews." You can view all past Updates and perform searches on specific physics terms at our website (http://www.aip.org/physnews/update/). Associated websites include Physics News Graphics (http://www.aip.org/mgr/png/ ) and Physics News Links (http://www.aip.org/physnews/links/).
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