5 ms·

Or send a chunk of metal at near light speed. Things in space move very predictably for thousands of years, and as the projectile only barely trails the signal

by kmm 8y ago

Or send a chunk of metal at near light speed. Things in space move very predictably for thousands of years, and as the projectile only barely trails the signal of its departure, it would come as a total surprise even for very advanced civilizations. Let's say an advanced civilization around Sirius wants to take us out. A chunk of metal (or anything really) of about 1000 metric tonnes would be completely invisible until it were very close. Travelling at 99.99% of the speed of light, it would impact with the energy of 13 times the meteor that wiped out the dinosaurs. The light of the projectile being "fired" would reach us in 10 years, and the projectile itself would arrive just 8 hours later. There is no foreseeable way to defend ourselves against that. An overly cautious civilization with that kind of technology might just decide to start sterilizing all the planets in its surroundings without having to leave their solar system, just in case.

jandrese 8y ago
This is kind of like worrying that God might just decide to kill everyone some day. There's nothing you can do about it, so it's best to just forget about it and hope that by the time a civilization is advanced enough to build such technology they also have advanced ethics enough to not use it. This used to be a common SciFi staple, that a civilization advanced enough to travel the stars must have solved their social issues first or they would have destroyed themselves with their own technology. Basically as the cost of ending all life on the planet drops you need to advance your ethics fast enough to prevent it from happening. Eventually everybody is carrying around pocket antimatter batteries and either everybody is well adjusted or everybody is dead.
CharlesColeman 8y ago
The problem with that is that targeting may be much more difficult. A passive weapon could be thrown off target over long distances due to gravitational perturbations or survey inaccuracies, and would likely have been mistargeted in the first place due to civilizational changes at the target (kinda like the problem with aiming flak, your target can move unpredictably between when you fire your gun and when your shell arrives, see https://www.youtube.com/watch?v=eRJC2mkrZks https://www.youtube.com/watch?v=eRJC2mkrZks). An active weapon could be targeted at a solar system too far away for an accurate preparatory survey, then identify and target rocky planets and large artificial structures once it arrives. It could also perform course-corrections in transit, and remain substantially dormant for much of the trip for stealth and surprise.

by kmm 8y ago

jandrese 8y ago

This is kind of like worrying that God might just decide to kill everyone some day. There's nothing you can do about it, so it's best to just forget about it and hope that by the time a civilization is advanced enough to build such technology they also have advanced ethics enough to not use it. This used to be a common SciFi staple, that a civilization advanced enough to travel the stars must have solved their social issues first or they would have destroyed themselves with their own technology. Basically as the cost of ending all life on the planet drops you need to advance your ethics fast enough to prevent it from happening. Eventually everybody is carrying around pocket antimatter batteries and either everybody is well adjusted or everybody is dead.

CharlesColeman 8y ago

The problem with that is that targeting may be much more difficult. A passive weapon could be thrown off target over long distances due to gravitational perturbations or survey inaccuracies, and would likely have been mistargeted in the first place due to civilizational changes at the target (kinda like the problem with aiming flak, your target can move unpredictably between when you fire your gun and when your shell arrives, see https://www.youtube.com/watch?v=eRJC2mkrZks https://www.youtube.com/watch?v=eRJC2mkrZks). An active weapon could be targeted at a solar system too far away for an accurate preparatory survey, then identify and target rocky planets and large artificial structures once it arrives. It could also perform course-corrections in transit, and remain substantially dormant for much of the trip for stealth and surprise.