Special Relativity, whether we like it or not, imposes an ultimate speed limit for everything in the Universe. According to the laws of physics, nothing in the Universe can travel faster than light. And as any Star Trek fan should be able to tell you, you can’t change the laws of physics! All the same, this trope is quite ubiquitous. Faster than light travel and communications are a mainstay in sci fi. Mostly because without them, all of that boldly going would be rather less exciting. But just supposing you could actually travel faster than light and somehow avoid all of the time dilation effects which relativity imposes. What would that actually mean? What are the implications? Ignoring the question of how exactly it might be possible, the full effects of faster than light travel are largely ignored by science fiction. Possibly because thinking about them for too long can make your brain hurt.
For instance, here’s a fun set of facts. Earth orbits the Sun at around 150 million kilometres, while Saturn orbits the Sun at 1.4 billion kilometres. This means that even when the two planets are at their closest to each other, it would take light over 70 minutes to get from Earth to Saturn. In other words, if your space ship were to leave Earth right now and arrive at Saturn, you could look back with a sufficiently large telescope – and see yourself before you left. And you wouldn’t see yourself leave for over an hour. You could sit in orbit around Saturn and watch your space ship doing whatever it had previously been doing a second time over. This has some interesting implications which could actually be woven into key plot points.
For one, in those sci fi plot lines where some catastrophe occurs and the protagonists escape at superluminal speeds, they could quite readily travel to a suitable distance and then watch the events which happened as they left, to figure out what had happened. In fact, they could do so multiple times from different angles if they wanted to.
Or more interestingly, consider a scenario where the heroes are about to have their ship boarded and their computers scanned for some vital piece of information. They could take careful aim with a well focussed laser beam (of the non-lethal variety) and transmit that information out into space, before erasing it from their ship’s computer. This could trigger a whole story arc in which this vital piece of information only exists as a set of light pulses travelling through space, and a race would ensue to locate and receive this information before the signal attenuates too badly to be of use. Remember, it would take about a day to reach interstellar space, but at least a year till it reached the edge of the Oort cloud.
Things get messy if you consider faster than light communication as well. This would give the bizarre effect that, depending on where you’re looking from, a signal would appear to be received before it had been sent. Imagine we’re back at the Earth-Saturn distance gap again. You could travel to Saturn, have a conversation with someone back on Earth, and then go back, all before someone watching from Mars would even know you’d left Earth. Or you could travel and/or communicate with someone to warn them about an event which they haven’t seen happen yet. It has happened already, of course. It’s just that the light from that event hasn’t yet reached them.
This is all a bit mindbending, so have a look at this video, which might help explain things.
This isn’t an explosion, even thought it might look like it. It’s actually a light echo. The central star in this video, V838 Monocerotis, underwent a sudden bright flare up (believed by some to be a luminous red nova) in 2002 – or more accurately, that’s when we saw it here on Earth. The expanding “cloud” of material is actually light reflecting off interstellar dust. That dust was already there. What you’re seeing is an expanding sphere of light, and as the light spreads outwards and illuminates that dust, some of it gets bounced towards us here on Earth.
After staring blankly into space for at least 10 minutes while thinking about this, I don’t think I’ve thought up any way to truly violate causality in a universe where faster than light technology exists… yet. But somehow I have a feeling I’m going to be thinking about this during idle moments for quite some time.
A trope is a recurring theme in any narrative which conveys information to the audience. These are snippets of information which have somehow ended up in our collective subconscious as ways in which storytellers have gotten their points across. Overused tropes end up as clichés.
Images: Screencaptures from Star Wars Episode IV © Lucasfilm and Spaceballs © Metro-Goldwyn-Meyer – used here in accordance with fair use policies.