Real physics is just weird sometimes. Like, totally.

One of my pet irks as a reader of science fiction is the way some authors play fast and loose with science. Sometimes it works. But usually, for me at least, the suspension of disbelief in SF is carried by the science as well as by story and characters. Goes with this particular genre.But that doesn’t preclude imagination. Physics sometimes gets very weird. Especially where our friend Albert Einstein is involved.

Albert Einstein lecturing in 1921 - after he'd published both the Special and General Theories of Relativity. Public domain, via Wikimedia Commons.
Albert Einstein lecturing in 1921 – after he’d published both the Special and General Theories of Relativity. Public domain, via Wikimedia Commons.

One of his principles was that nothing can travel faster than light. The end. And that’s been proven over and over and over. Of course, this spoils interstellar SF plots, so finding plausible ways around this annoying limit has been a focus for SF authors ever since Einstein came up with it. But very few have explored the weirder consequences of FTL travel.

Try this. Imagine you’ve got the most powerful telescope ever made. You can see spaceships with an instant faster-than-light (FTL) hyperdrive around nearby stars. The drive, using the Principles of Handwavium, allows them to jump from any star system to any other in zero time. That means they are moving way faster than light.

One day, your friends arrive at your house fizzing about their recent FTL journey from Earth to the nearby star 61 Cygni A, then to Proxima Centauri, then home.

Four and a bit years later, you’ve got your friends over for dinner, and your telescope pointed at Proxima Centauri. You see their ship appear around that star.

Seven years and a few weeks later, your friends are again over for dinner. Through the telescope, you see their ship disappear from around 61 Cygni A, departing on its instant journey to Proxima – where you saw them arrive all that time before, from your viewpoint

In short, you can watch your faster-than-light friends departing after they arrived, even though the trip was in normal sequence for them.

How does it work? Well, it’s all relative. 61 Cygni is 11.4 light years away, so light from that star takes that length of time to reach us on Earth. If you watch stuff going on there, from Earth, you’re looking back in time to the tune of 11.4 years.

Proxima Centauri is 4.3 light years away. Same deal for time – 4.3 years.

So what’s happening? The ship moves instantly. But light doesn’t. The light from Proxima, showing the ship arriving there, only takes 4.3 years to reach Earth, so it arrives before light from 61 Cygni showing it departing. And the ship reaches Earth before the light from either star arrives. So from Earth, you see the journey in reverse order.

See what I mean about weird? I’m put in mind of a piece of doggerel which, I’m told, has an unusual provenance of its own:

There once was a woman named Bright
Who could travel much faster than light
She departed one day,
In an Einsteinian way
And returned the previous night.

It’s not something sci-fi writers often consider. But there’s probably a story in it.

Copyright © Matthew Wright 2014


9 thoughts on “Real physics is just weird sometimes. Like, totally.

  1. And that’s why I’m sticking to fantasy 😀 (and if I ever do dip my toe into Sci-Fi I’ll keep it firmly grounded on Terra Firma – there’s enough incredible technology down here to play with – or go full-on space opera, where the science doesn’t matter all that much).

    1. Yes, space opera’s probably the only pure SF genre where the ‘science’ bends to suit the plot. One of my favourites was Doc Smith’s ‘Spacehounds of IPC’ – free from Project Gutenberg – a cracking yarn with a good deal of ‘refulgence’ from ‘ravening rays’ throughout. Smith wrote it as a serial around 1930, and the whole lot has a kind of deco-Flash Gordon feel to it. Fun & adventure? Absolutely. Science – uh, not so much…

  2. WhooHoo. A limerick!!! Can I add it to my collection? It’s cleaner than most, but still…I like it.

    As for science as it relates to sci-fi, I think some liberties are definitely acceptable. As long as there is an explanation of sorts. As you have stated, science was once magic before it was proven by theory.

    1. Please do. I didn’t write it. The provenance is a bit murky. A good one though, despite being disastrously clean. I still have a copy of Asimov’s collection of dirty limericks. Couldn’t stop laughing. 🙂

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