“Infinity is a demented concept,” astrophysicist Janna Levin, who studies the finitude of the universe, wrote in her spectacular diary-turned-book about the universe. Infinity is also a dementing concept. Most of us find it oddly hard, impossible even, to actually wrap our minds around it and envisage a thing — for it can’t really be a number, can it? — to which we can’t simply add something else to produce infinity-plus-one, instantly rendering “infinity” finite.

To help ordinary humans tussle with this extraordinary concept, German mathematician David Hilbert conceived of what is now known as the Infinite Hotel Paradox — a brilliant and mind-bending specimen of that neat intersection of science and philosophy: the thought experiment. Hilbert came up with the Infinite Hotel Paradox in 1924, but it was popularized only after his death by Russian-American theoretical physicist George Gamow’s 1947 book One Two Three… Infinity: Facts and Speculations of Science (public library).

This illuminating short animation from TED-Ed, written by Jeff Dekofsky, brings the famous thought experiment to life — fasten your neurons:

For other stimulating TED-Ed animations, see how a dog actually “sees” the world through smell, why music benefits your brain more than any other activity, how to spot liars, and why bees build perfect hexagons.