5 articles
Motion crowds the waves in front of a source and stretches the ones behind. That single geometric fact explains sirens, sonic booms, weather radar, and the expanding universe.
Maxwell combined everything known about electricity and magnetism, found a self-sustaining wave hiding in the algebra, and computed its speed from two bench-top constants. The answer was the speed of light.
How escape velocity reaching the speed of light defines an event horizon, why the Sun would be 3 km across, and what a black hole would — and would not — do to Earth.
How accelerating masses shake spacetime, why the resulting strain is only ~10⁻²¹, and how LIGO's laser interferometers detect a ripple that stretches a 4 km arm by less than a thousandth of a proton's width.
How Einstein's special relativity predicts that time passes differently for observers in relative motion.