Does the universe in fact contain almost no information?

At first sight, an accurate description of the state of the universe appears to require a mind-bogglingly large and perhaps even infinite amount of information, even if we restrict our attention to a small subsystem such as a rabbit. In this paper, it is suggested that most of this information is merely apparent, as seen from our subjective viewpoints, and that the algorithmic information content of the universe as a whole is close to zero. It is argued that if the Schr\"odinger equation is universally valid, then decoherence together with the standard chaotic behavior of certain non-linear systems will make the universe appear extremely complex to any self-aware subsets that happen to inhabit it now, even if it was in a quite simple state shortly after the big bang. For instance, gravitational instability would amplify the microscopic primordial density fluctuations that are required by the Heisenberg uncertainty principle into quite macroscopic inhomogeneities, forcing the current wavefunction of the universe to contain such Byzantine superpositions as our planet being in many macroscopically different places at once. Since decoherence bars us from experiencing more than one macroscopic reality, we would see seemingly complex constellations of stars etc, even if the initial wavefunction of the universe was perfectly homogeneous and isotropic.Comment: 17 pages, LATeX, no figures. Online with refs at http://astro.berkeley.edu/~max/nihilo.html (faster from the US), from http://www.mpa-garching.mpg.de/~max/nihilo.html (faster from Europe) or from [email protected]

Relative luminosity measurement of the LHC with the ATLAS forward calorimeter

In this paper it is shown that a measurement of the relative luminosity changes at the LHC may be obtained by analysing the currents drawn from the high voltage power supplies of the electromagnetic section of the forward calorimeter of the ATLAS detector. The method was verified with a reproduction of a small section of the ATLAS forward calorimeter using proton beams of known beam energies and variable intensities at the U-70 accelerator at IHEP in Protvino, Russia. The experimental setup and the data taking during a test beam run in April 2008 are described in detail. A comparison of the measured high voltage currents with reference measurements from beam intensity monitors shows a linear dependence on the beam intensity. The non-linearities are measured to be less than 0.5 % combining statistical and systematic uncertainties.Comment: 16 page

GEANT 4: an Object-Oriented toolkit for simulation in HEP

%RD44 %title\\ \\The GEANT4 software has been developed by a world-wide collaboration of about 100 scientists from over 40 institutions and laboratories participating in more than 10 experiments in Europe, Russia, Japan, Canada, and the United States. The GEANT4 detector simulation toolkit has been designed for the next generation of High Energy Physics (HEP) experiments, with primary requirements from the LHC, the CP violation, and the heavy ions experiments. In addition, GEANT4 also meets the requirements from the space and medical communities, thanks to very low energy extensions developed in a joint project with the European Space Agency (ESA). GEANT4 has exploited advanced software engineering techniques (for example PSS-05) and Object-Oriented technology to improve the validation process of the physics results, and in the same time to make possible the distributed software design and development in the world-wide collaboration. Fifteen specialised working groups have been responsible for fields as diverse as physics, geometric modelling, visualisation, event generation, and user interfaces. The geometric modelling is CAD compliant via the STEP ISO standard. The tranport in electromagnetic and other types of fields is performed via several optional mathematical techniques for integration of the equation of motion. Virtually any graphics system can be used for visualisation purposes, including VRML for detectors and physics events. The widest energy range for electromagnetic interactions for gammas (including optical photons and x-rays), electrons, protons, and ions is covered via implementations from the eV region to the TeV energy regime. Muon physics extends beyond the PeV energies for cosmic rays experiments. The full set of hadronic physics interactions is implemented via alternative or complementary physics models, ranging from theoretical models, to parameterisations, and to data-driven models. Neutrons physics is modelled down to thermal and cold energies for radiation background studies (including a wide set of biasing options), offering a choice and a combination of neutron data from all existing databases in the world. These features make GEANT4 the most powerful integrated simulation tool developed to date. The GEANT4 project was proposed to and approved by the CERN Detector Research Development Committee (DRDC) at the end of 1994 as the R\&D project RD44. From 1995 to its completion at the end of 1998 the project has reported to the CERN Large Hadron Collider Committee (LHCC). It has met all the required milestones. A first prototype was delivered at the end of 1995, the first alpha version was released in Spring 1997, and the first beta version at mid-1998. The first production version has been released in December 1998. With the release of the first production version the RD44 project has met its goals and has terminated. A formal collaboration, based on a Memorandum Of Understanding signed by CERN, major HEP laboratories and experiments, and by the European Space Agency, has been created to address the production phase of the software. Thus it should be possible for GEANT4 to take the inheritance of the GEANT3.21 (the de-facto standard simulation program which has been used to simulate the LEP, DESY, FNAL, SLAC detectors and many fixed target experiments, and to model all the four LHC detectors, as referenced in their relative Technical Proposals and Technical Design Reports) application domains and beyond. In less than one year from the first production release, GEANT4 has in facts already been successfully applied to test-beams studies for LHC in HEP, to astronomy-related space detectors, and to critical medical studies

The WASA detector at CELSIUS

The assembly of the WASA 4 pi detector at the The Svedberg Laboratory in Uppsala is now completed. The superconducting solenoid, the vacuum chambers and all of the sensitive parts of the detector have been installed at the CELSIUS accelerator and storage ring. The pellet generator, providing internal hydrogen (and deuterium)targets, has been installed on top of WASA. The first test run together with the CELSIUS proton beam was carried through in May 1999