Faster than light travel is Dangerous with a capital D.

The main reason for this is because by the time you see something, you've already smashed into it and vaporised yourself, the target and any unfortunates in the general vicinity, as well as releasing all those crazy science particles inside the fuel tanks which could react in new and devastating ways depending on what you hit.

Smart aliens let computers work out the timing and control the engines to make sure this doesn't happen, but the Dum-d'uums have just bought their first FTL engine from some passing space merchants, and unfortunately they aren't patient enough to configure the computer before trying out their new toy.

The nearest inhabited planet to the Dum-d'uums' is called Switzerland (it's just a coincidence) and they are a ridiculously peaceful and scientifically advanced race who heard about the deal and just know that the Dum-d'uums are going to mess up their space lawn.

How would the Swiss protect themselves from a FTL impact without breaking their moral code and resorting to the obvious (to us evil non-Swiss, anyway) answers of 'sabotage their space program' or 'force field protection grid so the crash isn't near our stuff'?

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    $\begingroup$ I've always thought stupidity is man's unique trait since when did it pass on to "Swiss"? no worry if they don't understand the manual they can't bypass the safety override or can they?then that means the alien also contracted this trait hence their workmanship. Either way thats how man leave their mark in the universe so be proud it can't be erased. $\endgroup$
    – user6760
    Apr 19, 2015 at 4:36
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    $\begingroup$ @user6760 The Swiss are the peaceful ones and the Dum-d'uums are the dumb ones. $\endgroup$
    – MrLore
    May 6, 2017 at 18:33

5 Answers 5


Give the Dum-d'uums the computer tech they need, for free.

That might seem like a bad move at first, but on the cost/risk scale it's orders of magnitude cheaper to give away some computer tech than to replace a planet and all the people.

If they're unconvinced of the reasoning, take Fhnuzoag's idea and use an FTL drone to blow up a convenient nearby moon as a demonstration. Don't threaten them directly, but let them find out with their laughable intelligence service that most intelligent races keep MAD-type systems in place so that weaponizing FTL is a Bad Idea.

If despite all of the above they still refuse to play intelligently, infiltrate their FTL/space program. Don't sabotage it though - instead, modify the FTL engines they're building by adding in the necessary computers, pre-programming in the exclusion zones. When they try FTL, they'll find that it just "stops working" whenever they try to do anything dangerous. To keep them from figuring things out, you should use a specific gravity well gradient to define the exclusion zone, so they think it's some sort of natural limitation instead of a technical one. Have your scientists pick something that seems logical-like to further confuse them.

If they ask you how your FTL manages to go deeper into gravity wells, act mysterious and play your Elder Race Technology card.

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    $\begingroup$ Me chief dum-dumm engineer just sheared off the computer controls and flys the FTL by counting thousands. $\endgroup$
    – Joshua
    Nov 11, 2015 at 16:32

Provide an object lesson. Have a very carefully controlled accident take place near the Dum Dum's planet, causing massive but miraculously non-lethal damage, and leaving lots of evidence as to what exactly went wrong and why it is very very unwise to mess with stuff you don't understand.


If they can put aside their moral objections, the most obvious answer is to annihilate the Dum-d'uums' race with a pre-emptive strike.

I highly recommend reading The Killing Star.


Assuming your flavour of FTL drive is still susceptible to normal collision physics, a simple dust cloud around things you want to protect would do. Magical means of deflecting particles in the interstellar void seems to be unnecessary since, as far as we can tell, there really isn't much for dust out there in most places, so your odds of hitting a dust particle are probably lower than the odds of your drive system malfunctioning (especially if you're a Dum-d'uum.)

Which means that "Swiss" ships' computers will have them stop and cruise through the dust cloud at low speed in perfect safety, while the Dum-d'uums' ships will plow into the dust cloud at FTL speeds and be reduced to one blinding flash in the sky, followed by a few months of extra-pretty meteor showers. Since the composition of the dust doesn't matter much, the cloud can double as a convenient garbage-disposal area for anything not worth recycling.

The pieces of ship will still be going pretty fast, but as long as your protective sphere is large enough, they should spread out over a wide enough area to be handled by your planet's atmosphere and your satellites' anti-meteor measures.

What you need to do to protect yourself from the crystallized magic in the ship's fuel tanks depends on what it is and how it reacts when the ship goes up. I'd expect something volatile enough to push a ship to supraluminal velocities to just react and end up being no more dangerous than normal ship exhaust. But you might need some kind of network of collector satellites to sift it out of the passing debris somehow. Determining what to do really requires more information on what it is. They quite likely have most of the system already in place for dealing with fuel leakages and accidents though, it'll just need a bit of expansion/tweaking to work on the remains of visitors.

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    $\begingroup$ Why not put the dust cloud around the dum-dum system to keep them in? $\endgroup$
    – user535733
    Mar 16, 2017 at 12:58
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    $\begingroup$ @user535733 That could potentially work too, except it will cost roughly the same amount, and will only protect you from the Dum-d'umms, whereas putting it around your own system protects you from any other idiots plus malfunctioning computers. $\endgroup$
    – Perkins
    Mar 21, 2017 at 23:17

Idiots with FTL pose much bigger problems than flying blindly into your planet (although some theoretical ideas of FTL would suggest you are not even in normal space-time, so ideas like collisions would be moot.)

The huge problem is that FTL can affect causality, since FTL is essentially identical to time travel. If you arrive at the planet before the starlight from your home star arrives, you can effectively engage in all kinds of mind bending time travel games before reality catches up (overly simplified, I know). This means the "idiots with FTL" can effectively change the history of their planet, your planet and indeed the entire timeline of the Universe, either by accident (most likely outcome) or on purpose (although I suspect they will find it very hard to "fine tune" their changes to the existing time line.)

Even very smart people will fall prey to this, so FTL is effectively banned in the really real universe we live in. There are some possible hand waves with artificial wormholes (the wormhole line layer needs to be moving at a large fraction of the speed of light, but from your view looking through the wormhole it arrives at the destination at "ship time" rather than the hundreds or thousands of years later that you would expect from your frame of reference.) However, it is thought that anyone trying to create a closed timeline curve by clever arrangements of wormholes is in for a big surprise, as the wormholes consume themselves in a burst of radiation when the ends are brought close to each other to make the time machine...

  • $\begingroup$ I know this is world building not physics SE. But I've never heard a convincing argument as to why FTL is the same as real time travel (as opposed to technically time travel). I only see it allowing you to be somewhere earlier than you really should be (technical time travel) rather than being able to see an event and then prevent it (real time travel) $\endgroup$ Apr 19, 2015 at 20:46
  • $\begingroup$ @RichardTingle: I was in the same boat, but finally figured out a convincing scenario (to me) as to why. It's a bit long for a comment, but the key is relativity causes symmetrical time dilation. The way that worked best to me was to imagine people communicating back-and-forth using FTL, both experiencing time 10x faster than the other from their perspective. After I diagrammed a few messages back and forth, it became clear why FTL equals time travel. $\endgroup$ Apr 20, 2015 at 20:16
  • $\begingroup$ Experiments demonstrate the speed of the ligth is fixed and independent observer. The standard way to explain this is with relativity: When you are moving, your clock slows down so that I and you agree on the speed of light. A side-effect of Einstein equations is that light speed is the speed of the causality. It is embedded in the math. Has to do on how the space-time is modelled. However, relativity is not the whole history. A lot of research is going on in more complete models. The real underlying model may not have this limitation or allow workarrounds that allows FTL. $\endgroup$
    – Lucas
    Mar 4, 2017 at 2:46

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