On the persistence of time dilation

Cool thought: Einstein's Special Theory of Relativity, which isn't so much a theory anymore for reasons I'll discuss later, tells us that increased speeds results in a slower clock rate for that object relative to a slower one (sorry, time isn't a fixed or constant thing across the Universe, get used to it). But Einstein didn't stop there. He also went on to describe his General Theory of Relativity in which he showed that gravity produces a similar time dilation effect; the heavier the gravity, the slower the clock.

So, as Einstein famously noted in his space-faring twin thought experiment, the returning twin, because he was moving faster relative to his Earth-bound sibling, will have aged less than his counterpart. Similarly, because of gravitational time dilation, a clock on Jupiter would run slower than a clock on Earth on account of its great size. I know it doesn't sound intuitive, but that's Relativity for you and why Einstein is considered such a genius for figuring this out.

Now, as messed as this sounds, this effect is becoming more perceptible to us, particularly as we travel faster and venture further into space. Gravitational time dilation has been experimentally measured using atomic clocks on airplanes and the effect is significant enough that the Global Positioning System's artificial satellites need to have their clocks corrected regularly. The International Space Station, because it is moving faster relative to Earth, and because it experiences less gravity, is subject to both effects; a faster speed means a slower clock, but less gravity means a faster clock! NASA's mathematicians must be having a blast trying to keep their clocks in synch with the ISS's.

And if you think that's complicated, we also have to deal with our robots on Mars where we need to account for the speed of Mars relative to Earth's and factor in the gravitational differences between the two planets. What blows my mind is that the Mars Rover is experiencing the passage of time at a slightly different rate than what we're experiencing on Earth.

Yikes. Problems like these remind me why I dropped out of high school math.

Speeding up supercomputer simulations using Einsteinian relativity

Writing in Technology Review, Christopher Mims is reporting on how physicists will soon be able to use Einstein's relativity to speed up supercomputer simulations by as much as 10,000%. He says it's not the algorithm or the hardware, but the reference frame that needed an update:

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.

Voila - the resulting algorithm is hundreds of times faster than previous attempts to simulate a laser-plasma accelerator.

Source.