Falling into a black hole

String theory tells us that quantum gravity has a dual description as a field theory (without gravity). We use the field theory dual to ask what happens to an object as it falls into the simplest black hole: the 2-charge extremal hole. In the field theory description the wavefunction of a particle is spread over a large number of ‘loops’, and the particle has a well-defined position in space only if it has the same ‘position’ on each loop. For the infalling particle we find one definition of ‘same position’ on each loop, but there is a different definition for outgoing particles and no canonical definition in general in the horizon region. Thus the meaning of ‘position’ becomes ill-defined inside the horizon. [email protected] When an object falls through a horizon, where does it go? This question leads to vexing paradoxes. But perhaps the situation is similar to the early days of quantum mechanics, when classical intuition gave questions with no resolution. In this essay we take a simple explicit model of a black hole in string theory. We note that gravitational systems have a dual description in terms of a field theory [1]. Using the field theory dual we find that the notion of spacetime itself breaks down behind the horizon.