At what point does a mechanical system—governed by classical dynamics—become a quantum system, or vice-versa? In 1920, Neils Bohr argued that quantum systems became describable with classical mechanics when the correspondence (or classical) limit had been reached. He described this as occurring "when the quantum numbers describing the system are large." The exact interpretation of "large" has been left to the reader as a 90-year-old take-home exercise.
The supermassive black hole is 40 million times as massive as the sun and powers a quasar that existed 700 million years after the Big Bang.
Vision Pro is here and it’s a surprisingly capable device. Apple has also loaded the headset with a ton of options and features that aren’t obvious at first glance.
Engineers expect to lose contact with the private US moon lander Odysseus on Tuesday, cutting short the mission after its sideways touchdown last week.
