Cafe Scientifique: Is time travel possible?

Tuesday night saw the return of Cafe Scientifique to Portsmouth, with a presentation title that predictably stirred up the science fiction reader in me – “Is time travel possible?” So naturally I was there half an hour early (because the Cafe Parisien where it is held does rather excellent continental-style snacks, and I like to get a good seat in the smoking area).

The speaker was Jim Al-Khalili, who is both Professor of Physics and Professor of the Public Engagement in Science based at the University of Surrey, as well as author of a number of popular science books – I can particularly recommend Quantum – A Guide for the Perplexed, but you’re not borrowing my copy because it is now adorned with an autograph (the science fan-boy strikes again). As his Public Engagement chair implies, he’s a great speaker, energetic and humorous, and gets across the tricky concepts of relativity in a way that a reasonably smart layman can visualise – if not necessarily comprehend! I’ll attempt to sum up his introductory talk, as follows:


2005 was designated as ‘International Year of Physics’ by the UN, in recognition of the centenary of Einstein’s Theory of Special Relativity. That means that a scientifically grounded idea of time travel is about the same age; Special Relativity opened the door to the idea that we could control the flow of time (albeit by incredibly inaccessible methods); the theory allowed for time to be slowed down.

Einstein stated that the speed of light (c) is the absolute maximum velocity possible in our universe, and that as the velocity of an object approaches c, strange things start to happen. For example, c is always a constant to any observer, no matter what velocity the observer is travelling at relative to the object whose velocity is being assessed. An easier way to explain that is to say that a clock on a spaceship approaching the speed of light appears to an outside observer to be running more slowly, despite the fact that an observer on the ship sees it running normally. This is time dilation, and it is one way we can control the flow of time. The twin paradox explains the relative passage of time by saying that if one of a pair of identical twins travels at speeds approaching c for some time, and then returns to their sibling who has stayed relatively motionless, they will find that their planet-bound sibling has experienced a much longer subjective period of time.

The majority consensus was that the future, having not actually come into existence yet, could not be travelled to (though there are theoretical objections to this notion; see later). However, the possibility of travelling backwards in time received some vindication from Einstein’s Theory of General Relativity in 1915, which includes the idea that gravity can also slow down time. Thanks to extrapolations of Einstein’s equations by Kurt Godel, it was demonstrated that it was theoretically possible to create loops of space-time that would deposit a traveller at a point in their relative past.

Of course, equations aren’t the whole story, especially not when causality becomes a factor – which in time travel, it certainly does. A whole slew of similar thought experiments (or paradoxes) were thought up to demonstrate that travelling in time would (or could) create fundamental discontinuities in reality itself; recursive logical loops that could never be escaped. Say you go back in time and accidentally kill your father as a young man; that means he could never have sired you; which means that you wouldn’t have existed to be able to time travel; which means that your father wouldn’t have been killed by you; which means you would exist to time travel; which means you’d be able to go back and kill your father; which means you’d never have been born … an infinite loop. The universe (it is assumed) will not permit such a thing – hence time travel gets a ‘thumbs’ down for possibility.

Physicists being physicists (and science fiction authors being science fiction authors), plenty of smart people came up with new explanations and theories that lent a new credence to the notion of time travel. Possibly the best known is the ‘multiple universes’ theory, which posits an infinite number of different versions of existence itself, some near identical to ours but for slight details, some wildly dissimilar, perhaps even to the point of having completely different fundamental constant values of nature. In this ‘multiverse’, you could theoretically go back in time by linking to a similar universe, and therein retain the power of agency that you possessed in your own. Then there are the mysterious properties of black holes, and those of wormholes – these and other undiscovered properties of the universe could perhaps offer some way of ‘folding’ space time, either within our own universe or between different ones.

As science-fictional as it may all sound, there are many highly intelligent and studious people investigating ideas like this, although they tend to talk of creating ‘closed time-like curves’ rather than claiming to be trying to build time machines. In the absence of hard evidence either for or against time travel, the debate is largely an intellectual exercise in testing theories to see how well they hold up to examination. Many of the arguments (both for and against) are logical or philosophical in origin: some claim that allowing time travel to exist means that free will cannot exist, allowing determinism free reign; others counter that quantum mechanics still hasn’t been fully reconciled with relativity, which allows for randomness outside of the causal system; and then there are cosmic strings


It’s easy to see why time travel has been such a rich lode for science fiction authors, being employed as everything from a simple plot device to a tool for serious philosophical and sociological enquiry. I am of the opinion that unless we transcend our physical existence entirely, our species will always be fascinated by the potential possibility of travelling outside the flow of the dimension that most defines our experience of the world.

If all that makes your head hurt, it’s no surprise – it’s a subject that baffles and fascinates some of the most intelligent people on the planet. Prof. Al-Khalili personally believes that time travel is an impossibility, but like any good scientist, he’s willing to be proved wrong! But as Stephen Hawking once said, echoing the Fermi Paradox, if people in the future have discovered time travel, why have we not been inundated with temporal tourists? There was much lively discussion and good-humoured debate after Prof Al-Khalili’s talk, and as always the atmosphere was very convivial – I’d recommend attending a similar event to almost anyone, be they layman, scientist or science fiction reader!

Hopefully I’ll be able to provide more detail on these matters, as Prof. Al-Khalili agreed to do an interview with me via email at some point in the future. I’m not going to state it as a certainty – he’s a busy man, and probably has many more important demands on his time than talking far-fetched theory with a science fiction blogger – but we can hope for the best.

The next Portsmouth Cafe Scientifique is on Tuesday January 23rd, on the subject of ‘Caffeine and Addiction’.

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