First published by surefish.co.uk in April 2008.


This recent article, looking at some of the better-known speculations of science fiction (SF) and dividing them into different classes of ‘impossibility’, confused me. And not just by doing so fairly respectfully, with just the one obligatory arch reference to Captain Kirk.

My issue is with how the piece – or rather the book that inspired it – seems to view time-travel. While time-travel proper is classed as a ‘Type 2’ impossibility (not necessarily contrary to the laws of physics, but unlikely to happen in the short term), precognition (true knowledge of future events, as featured in the film Minority Report) somehow merits being a ‘Type 3’, categorically outlawed by our current understanding of physics.

As an SF writer and general-purpose geek, I feel the overwhelming urge to highlight the contradiction. Precognition is just a special case of time-travel, where information rather than a physical object ‘travels’ from the future into the present.

Father Time

On reflection, though, I can see what Dr Kaku’s book is – presumably – getting at. Many philosophers (and not a few SF authors) believe we live in a ‘non-deterministic’ universe. Interfering with the past will change the present in unpredictable ways, creating a new history which incorporates that interference. This means, among other things, that a traveller to the past can never return to the same present that they left.

Similarly, information from the future would influence our actions in the present, changing the future it came from and immediately rendering itself unreliable. Since the entire point of precognition is its reliability, this does make the whole thing a tad problematic.

SF takes great delight in jumping around in this philosophical minefield. Some of the same difficulties also face theologians, in attempting to reconcile omniscience with free will.

A God who sees the whole of history from the perspective of eternity must know, for instance, what I’ll write in my Surefish column next month. But if my moral choices mean anything at all, I must also be free to choose whether or not I write a column (say) abjuring all God’s works and pledging my soul to the Devil.

So long as God’s perspective remains ‘outside time’, we can resolve this. God doesn’t know what I’m going to do ‘before’ I do it, because ‘before’ just isn’t a concept which applies to God.

The problem re-emerges, however, if God starts irresponsibly handing out prophecies. Either human beings can work to avert a prophecy, which compromises divine omniscience – or else God’s predictions are infallible, compromising human free will.

Prophets and Losses

A few columns ago I made a distinction between prophecy and futurology, suggesting that SF warns us of the potential consequences of our actions, rather than prognosticating events which will definitely come to pass. This type of foretelling, potentially changing the hearts and minds of one’s audience, makes imagining the invention of tanks look like a parlour-trick.

Nonetheless, an SF reader might view the Biblical prophets as precognitives in a non-deterministic universe – granted accurate foreknowledge of a future which, once foretold, may never come to pass.

This would make Jesus – an omniscient God incarnate in history as a human being – the equivalent of a time-traveller, changing the future he ‘knows’ by his mere presence. Would it be pushing speculative theology too far to point out that Jesus’s one unambiguous prophecy – of certain fairly specific events happening in the lifetimes of his contemporaries – never came to pass?

Perhaps it would. Perhaps this passage is indeed, as many commentators believe, an exaggerated account of the fall of Jerusalem.

Or perhaps, despite what Captain Jack Harkness might claim, it’s actually the first century when everything changes.

Read Philip Purser-Hallard’s blog.

© Philip Purser-Hallard 2008

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