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Computational capacity of the universe (and other physics news)

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  • wayne radinsky
    This first one is, I think, of particular interest to John Smart and our group: Computational capacity of the universe Seth Lloyd is at it again, calculating
    Message 1 of 1 , May 31, 2002
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      This first one is, I think, of particular interest to John Smart
      and our group:

      Computational capacity of the universe

      Seth Lloyd is at it again, calculating the limits of computation

      Two years ago, Seth Lloyd of MIT studied the properties of the
      "ultimate laptop," a hypothetical device whose speed and memory
      would be limited solely by physical laws. Now Lloyd has applied
      the same approach to the Universe as a whole.

      Full journal article:


      Here's an article for John :) And anyone else wondering how
      to build a computer out of a neutron star.

      Nuclear pasta

      The formation of neutron stars from collapsing supernovae
      are some of the most dramatic processes in stellar
      evolution. In a neutron star, high densities cause matter
      to form a uniform liquid but just before that happens,
      nuclei form rod-like and slab-like structures and bubbles,
      termed nuclear "pasta". The existence of pasta phases
      change the dynamics of neutron stars and how they behave
      astrophysically. New detailed simulations have shown how
      hot nucleic matter can form the various pasta phases as it
      cools. The matter seems to pass through a series of phases
      starting from uniform matter and heading through spherical,
      cylinder-like, slab-like phases and then as more uniform
      matter with holes that are cylindrical and then spherical
      before the whole lot becomes uniform again at a lower



      I think John will also find this one interesting. John says
      that the end result of singularity is a black hole, and
      I've been asking where the gravitational force to produce
      enough density would come from. This article says
      "microscopic" black holes can be created on earth. Sounds
      pretty strange to me. But hey, what do I know?

      Evaporating black holes to pin down the Higgs boson

      A number of authors have suggested that microscopic black
      holes may be produced in the next generation of particle
      colliders currently being planned and built. Now one
      physicist has claimed that among the residues as the
      microscopic black holes evaporate should be Higgs bosons
      and that only one month of running time of the Large Hadron
      Collider (LHC) should be sufficient to determine one
      property, the spin, of the Higgs boson.

      Background journal article


      Another article on black holes:

      Collapsing black holes ring loud

      Experiments are being constructed to "listen" to the
      universe through gravity waves. However, understanding what
      is heard depends on models of how various astronomical
      objects resonate. This paper investigates black hole
      collapse and collision and finds that after an initial loud
      gravity wave, there may be persistent loud ringing that can
      be detected.



      Patterns in food web structures

      Natural ecosystems are connected via intricate networks.
      Past modeling of these "food webs" involving small systems
      has not allowed discovery of significant universal factors
      across all webs. Now a larger study of seven sufficiently
      detailed webs has led researchers to discover that a single
      parameter, the linkage density, determines many important
      properties such as distribution of prey and number of
      predators. The advantage is that measuring the linkage
      density in real-life ecosystems is relatively easy and may
      allow a greater understanding of ecosystem interactions.

      Journal article: http://link.aps.org/abstract/PRL/v88/e228102
      (subscription required for the full article)


      Single photon LED
      Physics News Update/CLEO-QELS meeting

      A light-emitting diode that fires one photon at a time has
      been created. It is a potentially inexpensive, easily
      manufactured component for quantum cryptography and other
      applications. The researchers believe this is the first
      electrically driven single-photon source.



      Short pulses of entangled light for quantum communication

      Researchers have created pairs of entangled photons, the
      basic resource for quantum communication, in a form that is
      suitable for transmission over long-distance optical
      fibers. This will allow for realistic complex quantum
      communication protocols.



      3D high-density memory

      Researchers have experimentally shown that information can
      be written in three-dimensional crystals at densities of
      greater than 100 terabits/cm^3 (1 Terabit = 10^12 bits).
      The microfabrication works on a scale of 0.2 micrometers.
      The recording uses a combination of direct laser writing
      and a holographic technique that turns converts one
      ultrashort-pulsed laser beam into four beams, which
      interfere to create the desired pattern.



      Learning and predicting can be unrelated for neural networks

      (subscription required for full journal article)


      Particle physics probes of extra spacetime dimensions

      The possibility that spacetime is extended beyond the
      familiar four dimensions has intrigued physicists for a
      century. Indeed, the consequences of a dimensionally richer
      spacetime would be profound. Recently, new theories with
      higher dimensional spacetimes have been developed to
      resolve the hierarchy problem in particle physics. These
      scenarios make distinct predictions that allow for
      experiment to probe the existence of extra dimensions in
      new ways. The authors review the conceptual framework of
      these scenarios, their implications in collider and
      short-range gravity experiments, their astrophysical and
      cosmological effects, as well as the constraints placed on
      these models from present data.



      Neutrinos make for small extra dimensions

      Fundamental theories of particle physics and cosmology
      often require the use of extra dimensions that might be
      "curled up" to small scales. The existence of oscillating
      neutrinos (as recently confirmed by Sudbury Neutrino
      Observatory data) places constraints on how large any extra
      dimensions could be. Using the latest neutrino data, the
      authors� most conservative bound suggests that extra
      dimension should only be visible on a scale less than 0.82
      micrometers (approx. one millionth of a meter). Thus,
      currently planned gravitational experiments are unlikely to
      detect these dimensions if they exist.

      (again subscription required for full article)


      Physicists claim to have made a Bose-Einstein
      condensate of molecules

      Researchers in the US claim to have created a molecular
      Bose-Einstein condensate, a state of matter in which many
      molecules co-exist in the same quantum state. Elizabeth
      Donley and colleagues at the JILA laboratory in Boulder say
      that they have observed coherent oscillations between atoms
      and molecules in a sample of rubidium-85. The discovery
      could have important applications in molecular physics,
      chemistry and quantum computing (E Donley et al 2002 Nature
      417 529).



      Here's another article on the Bose-Einstein

      Stunning Demonstration Of Wavelike Behavior Of Atoms

      Now, in a BEC of lithium atoms, the Rice team has produced
      "bright" solitons, each representing a condensate of actual
      atoms extracted from the main BEC


      Anybody want to speculate on the use of the Bose-Einstein
      condensate for future computing or data storage devices?


      How fit are the surviving fittest?

      Darwin�s great idea of "survival of the fittest" is well
      accepted in evolutionary circles but how do you define
      fittest? A common way is in terms of the number of
      surviving offspring per organism. However, models have
      shown that it is possible for a species with high
      reproduction rates to dominate in the short term but die
      out over a longer timescale (~200 generations) due to
      depletion of resources. This paper looks at a new
      definition of long-term fitness by taking into account that
      descendents may have different reproductive success than
      their ancestors. One conclusion is that different species
      are adapted to survive over different time scales and that
      this leads to a different range of surviving species than
      if selection worked only at one time scale.

      (again subscription required for full article)


      Electron liquid crystals

      Electrons don't normally know one direction from another,
      so researchers were perplexed a few years ago when they
      found a cold plane of electrons suddenly choosing to
      conduct many times better in one direction than in the
      perpendicular one. Maybe they could acquire a preferred
      orientation by acting like liquid crystals, theorists
      proposed. Now a group reports it has worked this theory out
      well enough that experimenters may finally have some
      detailed signs to search for.



      Chromium atoms on demand

      A NIST group can now supply chromium atoms on demand, one
      at a time, the first time such control over neutral atom
      delivery has been achieved.

      Meeting abstract:


      Noisy signals strengthen human brainwaves

      Physicists have shown for the first time that electrical
      signals in the human brain are amplified by noise. This
      effect is called `stochastic resonance' and is well known
      in a wide range of systems, including living organisms. But
      the discovery by Toshio Mori and Shoichi Kai of the
      University of Kyushu in Japan is the first observation of
      stochastic resonance in the information processing part of
      the human central nervous system (T Mori and S Kai 2002
      Phys. Rev. Lett. 88 218101).


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