The Weeping Angels are a group of psychopathic hunters featured in the Doctor Who episode "Blink". Because their physiology is quantum-locked (see Schrödinger's Cat), they turn to stone when observed, covering their eyes with their hands and arms to prevent themselves looking at each other: this gives the impression that they are 'weeping'. This acts as a defence mechanism; they cannot be killed while petrified (though equally they cannot kill). They can move with great speed, being fast enough to move across a street in a single blink of the eye.
According to the Doctor, the Angels are as old as the universe (or very nearly) but no one really knows where they come from. He also describes them as "creatures of the abstract", "the lonely assassins", and "the only psychopaths in the universe to kill you nicely", because their method of "killing" doesn't do anything of the sort: a touch sends their victims into the past to live out their lives before they were even born; the Angels then feed on the "potential energy" of the lives their victims would have lived in the present.
In "Blink", a quartet of Weeping Angels strand the Doctor and his companion Martha Jones in the year 1969, and attempt to feed off the vast potential energy reserves of the TARDIS. Despite dispatching the Doctor, the Angels fail to get into the TARDIS; though they get the key, they can't find the machine itself. Sally Sparrow takes the key from one of them while it is in stone form, leading them to stalk Sally to regain it. During their pursuit, Sally inadvertently leads them to the TARDIS. Eventually the four Angels, having surrounded the TARDIS, are tricked into looking at each other when the box disappears, leaving them permanently locked in their stone forms.
In a poll conducted by BBC, taking votes from 2,000 readers of the Doctor Who Adventures magazine, the Weeping Angels were voted the scariest monsters of 2007 with 55% of the vote; the Master and the Daleks took second and third place, with 15% and 4% of the vote, respectively. The Daleks usually come out on top in such polls. Moray Laing, Editor of Doctor Who Adventures, praised the concept of escaping a monster by not blinking, something both simple and difficult to do.
The science of it:
Schrödinger's cat, often described as a paradox, is a thought experiment devised by German physicist Erwin Schrödinger around 1935. It attempts to illustrate what he saw as the problems of the Copenhagen interpretation of quantum mechanics when it is applied beyond just atomic or subatomic systems.
The concept of superposition, one of the strangest in quantum mechanics, helped provoke Schrödinger's conjecture. Broadly stated, the superposition is the combination of all the possible positions of a subatomic particle. The Copenhagen interpretation implies that the superposition only undergoes collapse into a definite state at the exact moment of quantum measurement.
Schrödinger's mind-game was meant to criticize the strangeness of this. Influenced by a suggestion of Albert Einstein, Schrödinger extrapolated the concept to a larger scale. He proposed a scenario with a cat in a sealed box, where the cat's life or death was dependent on the state of a subatomic particle. According to Schrödinger, the Copenhagen interpretation implies that the cat remains both alive and dead until the box is opened.
Schrödinger did not wish to promote the idea of dead-and-alive cats as a serious possibility; quite the reverse: the thought experiment serves to illustrate the bizarreness of quantum mechanics and the mathematics necessary to describe quantum states. Several interpretations of quantum mechanics have been put forward in an attempt to resolve the paradox. How they treat it is often used as a way of illustrating and comparing their particular features, strengths and weaknesses.wiki wiki ha ha ha