Uncertainty principle
From Tardis Wiki, the free Doctor Who reference
Heisenberg's uncertainty principle stated that the very act of measuring something changed its nature.
Professor Osric extrapolated from this that Heisenberg's revolutionary idea, that to observe something was also to change it, might also apply to time. He believed that using a clock to measure time, "merely by counting off the seconds, disturb[ed], change[d] time", such that time travel, or at least a view into other times, might be possible with sufficient clocks and mirrors. (AUDIO: The Time of the Daleks)
