Modern Physics is Computer Intensive

© Fernando Caracena, 2017

Physics, a fascinating study, aims to discover the basic patterns behind the operations and structures of nature. It uses mathematics as a language; pursues that mathematical logic to its limits; explores the nature of physical reality; and tries to reach the highest understanding of it all. Computers and the Internet have been part of the physicist's tools for decades.

Modern physicists use computers extensively. They often face a huge load of data processing, such as in the Large Hadron Collider (LHC). The post, "Particle Manifestation of Quantum States Part 1", describes the big data handling problem of the LHC. Automation solves a lot of big-science data collecting problems and its processing. In both these activities, computers and networks of computers are powerful tools. The science itself remains a very human activity. In trying to study every possible corner of physical reality, physicists have motivated a great deal of innovation and development of technology, often forming the cutting edge of technology.

The ATLAS, which is part of the LHC, is " the largest detector ever built at a particle collider". It furnishes data that is used to image events as digital clusters of pixels in three dimensions [voxels]. The various geometries of the different particle tracks identify their physical characteristics. For example, charged particle tracks are turned along the arc of a circle at right angles to an applied magnetic field, positively charged ones turn in on direction, and negatively charged ones, in the opposite direction. The component of motion in the direction of the magnetic field feels no force from it, so remains unaltered. A variety of energy and momentum characteristics are computed from the geometry of particle tracks together with calorimetry data. The pieces of the puzzle are further assembled using conservation principles.

To quote from a Wikipedia article describing the ATLAS particle detector:

"The Pixel Detector,..[its] innermost part..., contains three concentric layers and three disks on each end-cap, with a total of 1,744 modules, each measuring 2 centimetres by 6 centimetres. The detecting material is 250 µm thick silicon. Each module contains 16 readout chips and other electronic components. The smallest unit that can be read out is a pixel (50 by 400 micrometres); there are roughly 47,000 pixels per module. The minute pixel size is designed for extremely precise tracking very close to the interaction point. In total, the Pixel Detector has over 80 million readout channels, which is about 50% of the total readout channels of the whole experiment.


"The [Atlas] detector generates ... large amounts of raw data: about 25 megabytes per event ([compresed] to 1.6 MB), for 40 million [events] per second .... , a total of 1 petabyte ... per second. [Only the]... most interesting events [are] retain[ed] for ... analysis [based on] three trigger levels. ...[The remaining] amount of data still requires over 100 megabytes of disk space per second – at least a petabyte each year.[24]"

Pattern recognition software narrows the data archive stream to 100 megabytes  per second (108 bytes per second) from an initial data stream of petabytes per second (1015 bytes per second).

The Atlas forms the basis for a large number of scientific collaborations involving over 3000 scientists from 182 institutions around the world. Ironically, it has taken big science to probe the smallest aspects of nature, and to ddo it all, requires massive use of computers.




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