Entanglement is the strangest feature of quantum theory, which Einstein dubbed "spooky action at a distance". Quantum entanglement can occur on a large scale with millions of electrons, leading to "strange metals" and novel superconductors which can conduct electricity without resistance even at relatively high temperatures. Remarkably, related entanglement structures also arise across the horizon of a black hole, and give rise to Hawking’s black hole entropy. I will describe a simple model of many particle quantum entanglement which has shed light on long-standing problems in these distinct physical systems.