Killing time

Paul Nigh’s ‘’ Back to the Future DeLorean Time Machine

I would love to own a classic car. A 65 Mustang, an E-Type Jag, maybe a DeLorean. If I had a DeLorean, I’d treat it gently, keep it in a secure garage, and only drive it from time to time.

I love time travel stories. The original Back to the Future movie presses my buttons. I especially love the over-the-top performance of Christopher Lloyd as Dr. Emmett “Doc” Brown.

But. Time travel stories always sidestep two major difficulties. The traditional method is to have the time-travellers disappear in one time and reappear in another. In the same place.

How is that even possible? Even if we take time travel as a given, our planet is rotating (at 834 km/h at the equator) and orbiting the Sun at 54 000 kilometres per hour. If your time travel is only from one second to the next (or previous), you’re still going to emerge 90 kilometres away, which could be high in the atmosphere, or (more likely) deep in the Earth’s crust.

But that’s only the start. The sun is orbiting the Milky Way at 828 000 km/h, and our galaxy is itself barreling through space, though it’s impossible to get a straight answer on the exact speed from those wild-eyed astronomer types. Add in a very large number, that’s the best I can get.

So if you go back fifty years to kill your grandfather as a child, that’s a distance of at least 362 664 000 000 000 kilometres you will have to travel through space. Forty thousand times the diameter of the Solar System, but even then that’s only 3% of a light year.

So time travel isn’t so much a matter of zapping from one time to another at the flick of a switch (or whatever – some of these tales merely require a bit of high intensity dreaming) as it is in moving immense distances through space. No matter how much you modify your DeLorean, that V6 engine ain’t up to the task.

I once raised this difficulty with an astrophysicist swimsuit model in a summer Sanskrit class and she said that if you were able to pick a precise point in time, why not pick a precise point in space as well?

Well, okay. If we’re waving a magic wand. But how do you get to the degree of precision required? Over an unimaginably long distance, you have to hit just the right spot. Get it wrong by a couple of metres and you end up sharing space with a time machine-sized hunk of granite. Try snorting that out of your lungs, mate!

The second difficulty is the germ load we carry with us. We have a vast cargo of viruses and bacteria, and short of sterilising our bodies to death, if we flick into a sufficiently distant time period, we are not only going to infect anybody we touch with a massive and lethal spectrum of germs, we are going to take the same hit from them.

Yes, I know it’s a delightful thought to go back and have some hot sex with a clan chieftain, try out Casanova or Cleopatra’s charms, or even get down and dirty with a dinosaur, as some erotica sub-genres do. But most likely a week later both participants would be dead.

Granted, we might possibly inoculate ourselves against smallpox and the bubonic plague and maybe whatever flu varieties were going around that century in the past – and you get those injections all at once, you might not survive yourself! – but those we might meet would have no such protection. Our first handshake would be the epicentre of a global pandemic of multiple diseases.

In Guns, Germs, and Steel, Jared Diamond describes the usual fate of native people encountered by European explorers. Their culture immediately collapses as most of the population succumbs to smallpox, venereal disease, and whatever else the intrepid sailors are carrying.

The Europeans also took some heavy hits from exotic disease, but with millennia of close contact with a wide range of domestic animals, they had immune systems boosted well above the levels of hunter-gatherer societies, and enough survived to take over whatever once healthy and thriving lands they cared to plant their flags on.

With the twin factors of a universe in rapid motion and multiple disease cargoes, there’s not one of the classic time travel stories that would survive. Sorry, Marty McFly, but it didn’t happen. Better luck next time.


Image credit: &, CC BY-SA 4.0,

philosophy, science, travel , ,

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