Conundrum

You’d think there would be a neat equation for how
when travelling by train the view from the window
and in the mirror opposite make clear we are hurtling
away from the past, and into our future, at precisely
the same speed. Simple you say, stating the obvious.
But it doesn’t explain how images, as they recede,
may enlarge in the memory; tunnels ahead shorten
or lengthen in accordance with changes of mood.
Even more how an intrusive cell or invisible speck
between sets of nerves can have an impact more
catastrophic than a rock fissure in a mountain ravine;
the tremor of an eyelid, cataclysmic as any fault-line.