Alexander Selkirk, the real life privateer whose solitary exploits on a tiny and remote South Pacific island were later served up in the fictional guise of Robinson Crusoe, by all accounts struggled to adapt to life back on home soil. He struggled so much to resettle, in fact, that he chose to cast himself out again from the land of his birth. He sailed for Africa with the Royal Navy where he contracted fever. Selkirk, the outcast, would never see home again.

There has to come a point where removing yourself from the society you once thought you knew so well becomes a journey of no return. How many roads must a man walk down before you can call him a hobo? Does it take a year in Provence to come up smelling of lavender? When does the exiled stop being a person and start existing as a memory?

There is a scene in the film Interstellar when Matthew McConaughey’s Cooper floats amid an infinite library of bookcases like those he left back home in the spare room. In this extra-dimensional projection of his mind, an acid-trip nightmare the likes of Escher’s famous staircase to nowhere confronts a brave Cooper. By now he has been away for decades and his beloved young daughter, Murph, is a grown woman. Nothing matters more to him than finding her again across trillions of black, empty miles. From shelf to shelf he spacewalks until through reality’s answer to a junk shop he finds a way to communicate through dimensional spacetime. It is then, at the sticking of the little hand of the watch on the bookshelf, his gifted daughter realises her father has found a way to reach out to her from a place she can scarcely conceive of. Suddenly Cooper ceases to be a memory and re-institutes himself as a living father in the mind of his daughter. He has spoken to her for the first time since she was a child across the arc of space and time using good old Morse code. The symbolic value of the watch is huge, coming to reify what had been an abstraction for Murph, a memory of abandonment lodged in her mind.

Living in a desert is not quite so extreme as falling into a wormhole off the coast of Saturn, but it might as well be an extra-dimension. Here where the sky turns milk blue every morning and burns in the west most evenings, where the treeless landscape never undergoes seasonal transformation, the feeling is cosmic. On this barren planet that lies on the event horizon – dangerously close to the black hole that is the Middle East with its information irretrievably lost in a Hawking paradox and its physical states tipping into one of infinite Daesh blackness – here a month might as well be a year and a year a lifetime, as far those back in the home quadrant of Eurospace are concerned. Time’s elasticity really does get to stretch itself in the mind of the exile. While he is busy hopscotching from past to future, skipping the bit they refer to as the now, he imagines that the world he left behind is one that spins at the right tempo and all who reside in it are likewise living in that blissful state they refer to as the now – a state the exile struggled to get to grips with. Maybe it does rotate in temporal stasis, or maybe it doesn’t in any mathematical sense, but who cares when all he feels is the pull of another planet.

The past is another country and the future another still. When the present tricks you with its mental mirages, it is to the two countries either side that the attention moves. The past is Nepal, where once is never enough. The future is that big trip around South America you keep telling yourself you are going to do. The present, that is wherever it is, but not where you always want it to be.

‘For who would bear the whips and scorns of time?‘ mused Hamlet. Well, not Shakespeare himself as history would have it. Far from whipping and scorning him, time has stroked him tenderly.  So, is there a way back for the time-travelling exile? Can that exile retrace his steps back to square one without it being a homecoming worthy of a weighed-down Christ looking miserable on the Via Dolorosa? How far can a man walk before it is too far to walk back? Would anyone care to guess without sending smug responses in on a postcard from some remote Tahitian isle, where they are currently having the time of their lives intending not to return home any time soon? Some sensitivity, please.

Dead men walking the earth, dead women, too. Leave for a while on your peregrinations and those you left behind will keep your grave. They’ll soothe you with words and questions as if expecting an answer. When leave they must, they’ll whisper into your granite ear, ‘back soon.’ Naturally, the visits will grow more infrequent until they cease altogether. For the best way ultimately to remember someone is not to pretend they are right there. It’s to accept they have gone, that being gone is as good as being gone for good. It’s to make peace with oneself in the way that the departed could never with himself. That’s the price we pay for going away. That was the price that Selkirk paid for being a castaway on that island for four long years.