Everything in our universe has mass — from the smallest atom to the largest star. But the amount of mass has remained constant throughout existence even during the birth and death of stars, planets and you. How can the universe grow while maintaining its mass? Todd Ramsey answers that question by unravelling the law of conservation of mass.

One of the most amazing facts in physics is that everything in the universe, from light to electrons to atoms, behaves like both a particle and a wave at the same time. But how did physicists arrive at this mind-boggling conclusion? Chad Orzel recounts the string of scientists who built on each other’s discoveries to arrive at this ‘central mystery’ of quantum mechanics.

The classical physics that we encounter in our everyday, macroscopic world is very different from the quantum physics that governs systems on a much smaller scale (like atoms). One great example of quantum physics’ weirdness can be shown in the Schrödinger's cat thought experiment. Josh Samani walks us through this experiment in quantum entanglement. View the complete lesson at TED-Ed