A View from Christopher Mims
Using Einstein's Relativity to Speed up Supercomputer Simulations 10,000%
Physicists realized it’s not the algorithm or the hardware, but the reference frame that needed an update.
Sometimes when you need to break a computational log-jam, what’s required isn’t more power, but a conceptual breakthrough. And sometimes that breakthrough comes directly from the work of Albert Einstein.
In this case, the problem at hand is the simulation of lasers hitting plasmas - which is one of those bleeding-edge areas of physics that could lead to, according to a 2008 summary of the field, “proton therapy for the treatment of cancers, materials characterization, radiation-driven chemistry, border security through the detection of explosives, narcotics and other dangerous substances, and of course high-energy particle physics.”
Or in other words, desktop particle accelerators.
But before we can build accelerators as capable as CERN’s Large Hadron Collider in the comfort of our underground lairs, we first have to use computers to model the behavior of these so-called “laser-plasma accelerators.”
Even on the world’s 17th fastest supercomputer, this turns out to be a Herculean task.
And here comes the breakthrough: Physicists realized that because the laser is accelerating electrons in its path to nearly the speed of light, Relativistic effects start to be a big deal - the same effects first discovered by Albert Einstein.
And if we remember anything from A Brief History of Time or even the original Planet of the Apes, it’s that at speeds approaching the speed of light, where the observer is standing has a huge impact on what they perceive - this is, for example, the reason that an astronaut traveling close to the speed of light would age much slower than the people he or she left behind on earth.
Previously, all simulations of laser-plasma accelerators were run from the perspective of a physicist standing somewhere in the vicinity of the experiment - in other words, someone who sees a super short laser pulse traveling at a near-stationary plasma. Mathematically, this is very hard to simulate - the laser is brief.
But what if, instead, we take the perspective of the plasma itself? Now, relative to the laser, it’s as if the plasma is traveling toward the beam of light at near-light speed. Because of relativistic effects, this stretches out the beam of the laser, making it longer and mathematically more tractable to simulate.