Computation vs Theory vs Experiment in Physics


Both experimental and theoretical physics are incomplete without the option to compute whenever it is neccessary.

The goal of computational physics is not to replace theory or experiment, but to enhance our understanding of physical processes.

Four different numerical techniques:

  1. simulation,
  2. enumeration,
  3. algebraic manipulations,
  4. solution of equations.

The numerical techniques listed here link into the lectures for the graduate course ``Computational Physics'', which is also open to undergraduates in their final semester.

Areas of physics where computational techniques are widely implemented include my own areas of condensed matter/statistical physics, astrophysics, nuclear physics, particle physics etc etc

In the Physics Department at the Technion ( Italics for professors giving talks in this course)

  • Condensed matter/statistical physics (J. Adler and students in association with the experimental groups of E. Polturak, E. Ribak and R. Kalish ). Students have done many projects with all three, remind me to talk about them later!)
  • Astrophysics (N. Soker, H. Peretz and A. Nusser)
  • Experimental particle physics (Yoram Rozen and Shomit Tarem)
    have been among the most active areas using computers in physics research.

    In the last years computational physics class there were 3 students who did projects that potentially lead to a new track of computations in their research groups. These involve ``big'' codes - EPOCH for plasma physics, QUANTUM ESPRESSO for energy bands and LAMMPS for Molecular Dynamics in models of quantum dots. More about this later....

    All the above and other fields of physics (and all the areas of Chemistry, Engineering, Economics etc) can benefit from computational methodology. Using computers in a specific field like physics is quite distinct from Computer Science, since in a specific field the emphasis is on solving problems of that field. Other computational scientists at the Technion include Simon Brandon in Chemical Engineering and Dan Mordehai in Mechanical Engineering.

    The use of computers in physics often leads to advances in computers, for example:

    1. John Hammersley writes about the early days of simulation of models in statistical physics on computers. These simulations were requested by AT&T Bell to test their ``newest'' machines in 1956! View extracts. See also pages about the theory of percolation here and of a new interactive percolation site here.

    2. Scott Kirkpatrick, formerly vice president of IBM and now a faculty member at the Hebrew University, introduced ``simulated annealing'' into the design of computer chips. Simulated annealing mimics the annealing process whereby a real crystal is cooled into its crystalline groundstate. It was developed to find the groundstate of ``spin glasses'' and can be used to find the lowest ``energy'' of e.g.
      a travelling salesman (lowest energy here corresponds to the shortest no. of miles he has to drive,)
      a computer chip (least amount of wires connecting the devices.)
      An introduction to simulated annealing suited to physics undergraduates is given in ``A Walk in Phase Space''

    3. The Wold Wide Web protocols originated from the internal communication needs of CERN in Geneva, Switzerland.

      Some general guidelines for Computational Physics are:

      1. ALWAYS compare with exact solutions for limiting cases, to validate your programming and algorithms. Do this with each calculation as a powerful way to find the ``trivial'' mistakes.
      2. If possible use more than one approach; in particular each of the four classes of approaches listed above is based on different (implicit) assumptions and so use of more than one is a powerful way to cross-check.
      3. There is no intrinsic value in calculating on a computer.
      4. There is intrinsic value in understanding the physics of complex systems which usually involves use of computers.
      5. Visualization is a very important tool for both research and presentation. This is usually, but not always done today on computers. See the discussion in my lecture notes from the Oporto Summer School, 1998.

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