It takes two to tango, so to speak. No matter how peaceable we are as a race, if the other guy has bigger weapons and is itching to use them, it might not make any difference.
Theoretically, it isn't possible to stop an advanced alien race that has mastered ftl travel from being able to destroy earth. There is this concept called relativistic bombardment - your "artillary" is set to travel so fast, that the light that comes off it only arrives moments before the actual shell, and thus, there is little to no warning. The only way to stop this sort of attack is a shield that is impenatrable. However, such a thing cannot exist, since the attacker has all the time they need to devise a shell that can penetrate the specific shield you intend to use.
Hence, the only safety you can guarentee is if you know your enemy don't know where you are, and thus can't aim the weapon. Otherwise, its impossible to stop an attack.
Now, conversely, humans knows this too, so it makes rational sense to attack first. Its MAD on a galactic scale!
If my (admittedly rough) understanding of relativity is correct, there's a problem with this weapon: From the recipient's perspective, the shell would never arrive.
Basically, as the shell accelerates to C relative to the target, time in the target's reference frame expands relative to time in the shell's reference frame. A shell traveling at C would instantaneously travel from origin to destination (from the shell's perspective) but would take infinite time (from the target's perspective).
Of course, an impact at 1% C would still make one hell of a bang.
> would take infinite time (from the target's perspective).
this doesn't sound right - the shell does arrive, and arrives exactly X light years after being launched, as measured by the alien. Its just that from the perspective of the people in the shell, heaps of time has passed on the outside.
But my knowledge of relativity is cursory at best, so im not sure if i m right.
