Symbol f

The passage around this formula

A processor held at fixed altitude near a black hole’s horizon runs slow. Not metaphorically: its proper time $\tau$ , the time its own internal clock and its own quantum gates actually tick through, elapses more slowly than the coordinate time t used by a bookkeeper stationed far away, by the ordinary gravitational redshift factor $\sqrt{f(r)}$ . A distant observer watching that processor through a telescope sees every one of its gates run in slow motion. Turn the statement around, though, and something more interesting appears to fall out. If the processor’s own clock is the one that is running normally — and by the equivalence principle, locally it is — then from the processor’s point of view…

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