Schrodinger Cell – aka “Paradox Box”, “Magic Box”. A Time Lord device capable of protecting its contents from the results of Temporal Paradoxes and the Blinovitch Limitation Effect. Anything placed within the box enters a “quantum null state” until the box is opened. So long as the box is closed, its contents are indeterminate, thus the box could contain any object. During and after the Time War, The Doctor carried a Schrodinger Cell bearing the Seal of Rassilon, given to him by The War King (WDA:The Ancestor Cell), which he planned to open only in his moment of greatest need (US:The Last Time Lord). He considered, but ultimately rejected opening the box when facing Varnax (US:The Mark of Varnax) and the Mothrai (US:Nothing at the End of the Lane). The War Doctor placed the Philosopher’s Stone into his box, allowing the tenth and ninth Doctors to create identical copies of it by removing the stone from their own boxes (US:War of the Doctor). Later, the War Doctor placed the sixth segment of the Key to Time into the box, allowing Alice Jones to remove it in the Guardians’ Domain to complete the key without sacrificing herself. Schrodinger Cells could also be used as a power source by extracting the temporal energy of unrealized potential universes (WDA:Sometime Never). Among its other features, the Pandorica was a Dimensionally Trancendental Schrodinger Cell (BF:The Pandorica Opens, BF:Other Wars).
He's everything you want; he's everything you need; he's everything indise of you that you wish you could be. He says all the right things, at exactly the right time, but he means nothing to you and you don't know why. -- Vertical Horizon, Everything You Want