So Vile a Sin

'Now, there's a frightening thought.' He smiled. 'Once upon a
time… that's a good way to start the story. Once upon a time,
there were unicorns and bread-and-butterflies, planets like giant
apples and suns like red balloons. But since no sentient life had
yet evolved, there was no one to notice they were impossible, so
no one minded. And then along came the Time Lords.'

...

And then Rassilon made his decision.'

...

'The world solidified around us, like water turning to ice.
Squeezing out the magick. But, like an ice cube, there were little
cracks and bubbles. Psi was the last magick to survive, perhaps
because it was the least impossible, the closest to science. The
residue of psi became a network of ley lines, stretching through
the universe in improbable directions.

...

The Doctor nodded. 'The Time Lords were aware of the ley
lines before the Wars began. We'd chosen to make the universe
rational. Its irrational citizens objected. So we turned the psi lines
into weapons. A Distant Early Warning line that stretched
through the galaxy, studded with receivers the size of mountains
or even small moons, parabolic dishes disguised as craters.
Listening for eruptions of psi power beyond Gallifrey.'