Ayanendu Dutta

An ordinary proton consists of three quarks, like a three-legged stool. But nature does not forbid assembling a 'chair' from four quarks, if two of them are heavy beauty quarks and two are light. Such particles are called tetraquarks, and until now they have been studied mainly at large accelerators, by colliding particles and sifting through the debris.

An eardrum at the very edge of a waterfall. Sound behaves strangely here: echoes don't multiply: they fade. That's exactly what gravitational waves look like at the horizon of a black hole — the boundary beyond which even light disappears.