5 ms·

>because it assumes that projecting power over interstellar distances is easier than defending yourself This seems really obviously true to me. Accelerating a

>because it assumes that projecting power over interstellar distances is easier than defending yourself This seems really obviously true to me. Accelerating a rock to relativistic speeds is pretty easy, defending against a rock potentially coming from anywhere in space traveling at relativistic speeds is extremely difficult.

evrydayhustling 5y ago
IANAAstrophysicist but it seems like targeting that rock gets proportionally hard with the speed and distance. Throwing a dart and hitting an ant on the other side of the world, etc. And the other side of that equation is: does the species who can do that have anything to fear from us? Or does the same technology make them likely able to stay ahead on defense, making it uninteresting to destroy us? Three Body Problem introduces all this dimension folding tech that makes being the first to strike totally dominate. But the closest equivalent on Earth hasn't (yet) led to nuclear holocaust, because preventing others from getting the tech and establishing mutual detente with those who do has been better for each actor.
- Retric 5y ago
  We can already hit tiny (Ed: planet sized) targets at interstellar distances. Planets are relatively speaking quite large targets especially if you’re tossing several rocks. This stuff doesn’t need sci-fi style new physics, just the kind of infrastructure we could actually build.
  - AnIdiotOnTheNet 5y ago
    ....we have never hit anything at interstellar distances, which are several orders of magnitude farther than interplanetary distances.
    - Retric 5y ago
      I didn’t say we have, just that we can. The closest Star is ~268,770 AU where voyager 1 is only 152.6 AU. However, being able to target a probe within 50 feet at 150AU, means hitting a planet sized target at 4.25 light years. Building a probe large enough and fast enough to do significant damage at the other side is the hard part, not targeting. Calculating where a planet sized object would be by the time our probe got there is a different story.
      - edgyquant 5y ago
        Voyager is not traveling a relativistic speeds. We could definitely defend against someone sending voyager at us.
        Retric 5y ago
        That’s moving the goalposts. I said we could hit a planet at those distances not that we can create a relativistic impactor.
        edgyquant 5y ago
        No it isn’t since the whole topic here is that any civilization capable of accelerating an object to relativistic speeds and hitting a target from light years away is capable of defending against one. We can send voyager to target an object on the other side of the solar system but we are also perfectly able to defend against a potential voyager. Just because you now claim to not be addressing the actual goal at hand doesn’t mean I moved the goalpost; if anything you’re now implying you did.
        Retric 5y ago
        Voyager 1 isn’t a weapon so defending against it is kind of a meaningless argument. The Parker Soar probe is aiming for 0.064% the speed of light and covered in scientific instruments and shielding. So that’s arguably a solid baseline of what we could do in terms of speed. Even at those speeds we are still talking 8,000 years to the closest planet making it a poor weapon. Still, I doubt we could detect a barrage of incoming 0.0005c weapons designed for minimal levels of stealth in time to do anything about it.
  - evrydayhustling 5y ago
    What tech are you thinking of? Remember it's not just the distance but the speed. How would we course correct a relativistic object once the target was close enough to estimate the desired change?
    - marcosdumay 5y ago
      Well, you do that with the same kind of engines that propels them at relativistic speed. Anyway, it's not a target and forget situation, because relativistic ships get a (relatively) lot of drag in space.
      - gilbetron 5y ago
        > Well, you do that with the same kind of engines that propels them at relativistic speed. Which don't exist except as fantasy, and even most of the fantasy ones wouldn't work for targeting adjustments.
      - edgyquant 5y ago
        Right, if you have the tech to allow you to course correct an object traveling at relativistic speeds you have the tech to defend against on by moving it out of the way.
        marcosdumay 5y ago
        Yep, that's probably correct. Even more because you can just throw something into the projectile too, and destroy it... And they can throw something into your projectile, and etc. I don't think anybody can make any claim on what side is easier. But targeting the attack does not seem to be the hard part.
        Retric 5y ago
        The belief is that detecting the attack in time to do anything makes defense more difficult. Your warning is limited by light speed, so detecting something moving .99c at 100 AU and you get just over 7 minutes to respond. Worse, it doesn’t need to be some solid object. A loose field of debris 1,000 miles wide could sterilize a planet with enough mass and enough velocity.
AnIdiotOnTheNet 5y ago
1) I think you're underestimating the difficulty of accelerating any massive object to relativistic speeds, 2) doing so with enough accuracy to hit a relatively small moving target many light-years away is not exactly trivial, 3) a civilization with the capability to accelerate a massive object to relativistic speeds is probably also capable of building self-sufficient artificial habitats around its star, which is a lot of targets you'd have to take out for complete obliteration. So in summation, I think defending against an incoming relativistic rock is at least as easy as using relativistic rocks to obliterate a distant civilization.
- riffraff 5y ago
  another thing: I believe at relativistic speeds hitting any debris in your path would cause a pretty large BOOM, and for a multi-lightyear route that seems somewhat risky.
- ping_pong 5y ago
  You're definitely not thinking creatively enough. You don't need to hit the planet directly with anything, all you need to do is destabilize the orbit of all the planets or even just the Earth itself. You could send a gravity wave for example, that would cause the Earth's near circular orbit to shift to a very eliptical orbit. The vast change in temperatures would kill all life on the planet, and then you could come and mine all the resources that you needed and leave.
  - AnIdiotOnTheNet 5y ago
    If you have the capability of engineering such a gravity wave then Earth's resources aren't worth your time.
    - mentalpiracy 5y ago
      Resources not the point here, the point is removing the possibility that our civ could ever be a risk to them
roenxi 5y ago
Fortunately, it is possible to imagine other scenarios. For example; it would take relatively little energy to deflect such a missile and there is likely to be a lot of time to detect it's incoming presence assuming that some sort of planet-like mass is required to host all the technology to create a relativistic speed accelerating engine.
gilbetron 5y ago
> Accelerating a rock to relativistic speeds is pretty easy Huh? How? I haven't seen any proposal that doesn't start with the assumption that we can inject a rock with a preposterous amount of energy let alone hit (in astronomical scales) a ridiculously small target, not to mention navigate all the gravity wells in between.
- a1369209993 5y ago
  Multistage rocket using ion engines. Remember this is over interstellar distances (>4 lightyears), so you have multiple years, if not decades or centuries to accellerate. This does get back to the "Why didn't we RKKV it millions of years before intellegent life even existed, much less had a opportunity to hide, based on biosignatures in the atmosphere?", though.
  - gilbetron 5y ago
    Ok, that gets us to maybe 0.3% of the speed of light on something small, which isn't very interesting. https://space.stackexchange.com/questions/22140/what-is-the-maximum-speed-an-ion-engine-can-propel-a-spacecraft-at https://space.stackexchange.com/questions/22140/what-is-the-...
a1369209993 5y ago
> defending against a rock potentially coming from anywhere in space traveling at relativistic speeds is extremely difficult. Also, while 'proper' stealth is difficult, you can make the rock pretty close to invisible for practical purposes by coating it in vantablack and cooling it to liquid helium temperatures.

evrydayhustling 5y ago

IANAAstrophysicist but it seems like targeting that rock gets proportionally hard with the speed and distance. Throwing a dart and hitting an ant on the other side of the world, etc. And the other side of that equation is: does the species who can do that have anything to fear from us? Or does the same technology make them likely able to stay ahead on defense, making it uninteresting to destroy us? Three Body Problem introduces all this dimension folding tech that makes being the first to strike totally dominate. But the closest equivalent on Earth hasn't (yet) led to nuclear holocaust, because preventing others from getting the tech and establishing mutual detente with those who do has been better for each actor.

Retric 5y ago
We can already hit tiny (Ed: planet sized) targets at interstellar distances. Planets are relatively speaking quite large targets especially if you’re tossing several rocks. This stuff doesn’t need sci-fi style new physics, just the kind of infrastructure we could actually build.
- AnIdiotOnTheNet 5y ago
  ....we have never hit anything at interstellar distances, which are several orders of magnitude farther than interplanetary distances.
  - Retric 5y ago
    I didn’t say we have, just that we can. The closest Star is ~268,770 AU where voyager 1 is only 152.6 AU. However, being able to target a probe within 50 feet at 150AU, means hitting a planet sized target at 4.25 light years. Building a probe large enough and fast enough to do significant damage at the other side is the hard part, not targeting. Calculating where a planet sized object would be by the time our probe got there is a different story.
    - edgyquant 5y ago
      Voyager is not traveling a relativistic speeds. We could definitely defend against someone sending voyager at us.
      - Retric 5y ago
        That’s moving the goalposts. I said we could hit a planet at those distances not that we can create a relativistic impactor.
        edgyquant 5y ago
        No it isn’t since the whole topic here is that any civilization capable of accelerating an object to relativistic speeds and hitting a target from light years away is capable of defending against one. We can send voyager to target an object on the other side of the solar system but we are also perfectly able to defend against a potential voyager. Just because you now claim to not be addressing the actual goal at hand doesn’t mean I moved the goalpost; if anything you’re now implying you did.
        Retric 5y ago
        Voyager 1 isn’t a weapon so defending against it is kind of a meaningless argument. The Parker Soar probe is aiming for 0.064% the speed of light and covered in scientific instruments and shielding. So that’s arguably a solid baseline of what we could do in terms of speed. Even at those speeds we are still talking 8,000 years to the closest planet making it a poor weapon. Still, I doubt we could detect a barrage of incoming 0.0005c weapons designed for minimal levels of stealth in time to do anything about it.
- evrydayhustling 5y ago
  What tech are you thinking of? Remember it's not just the distance but the speed. How would we course correct a relativistic object once the target was close enough to estimate the desired change?
  - marcosdumay 5y ago
    Well, you do that with the same kind of engines that propels them at relativistic speed. Anyway, it's not a target and forget situation, because relativistic ships get a (relatively) lot of drag in space.
    - gilbetron 5y ago
      > Well, you do that with the same kind of engines that propels them at relativistic speed. Which don't exist except as fantasy, and even most of the fantasy ones wouldn't work for targeting adjustments.
    - edgyquant 5y ago
      Right, if you have the tech to allow you to course correct an object traveling at relativistic speeds you have the tech to defend against on by moving it out of the way.
      - marcosdumay 5y ago
        Yep, that's probably correct. Even more because you can just throw something into the projectile too, and destroy it... And they can throw something into your projectile, and etc. I don't think anybody can make any claim on what side is easier. But targeting the attack does not seem to be the hard part.
        Retric 5y ago
        The belief is that detecting the attack in time to do anything makes defense more difficult. Your warning is limited by light speed, so detecting something moving .99c at 100 AU and you get just over 7 minutes to respond. Worse, it doesn’t need to be some solid object. A loose field of debris 1,000 miles wide could sterilize a planet with enough mass and enough velocity.

AnIdiotOnTheNet 5y ago

1) I think you're underestimating the difficulty of accelerating any massive object to relativistic speeds, 2) doing so with enough accuracy to hit a relatively small moving target many light-years away is not exactly trivial, 3) a civilization with the capability to accelerate a massive object to relativistic speeds is probably also capable of building self-sufficient artificial habitats around its star, which is a lot of targets you'd have to take out for complete obliteration. So in summation, I think defending against an incoming relativistic rock is at least as easy as using relativistic rocks to obliterate a distant civilization.

riffraff 5y ago
another thing: I believe at relativistic speeds hitting any debris in your path would cause a pretty large BOOM, and for a multi-lightyear route that seems somewhat risky.
ping_pong 5y ago
You're definitely not thinking creatively enough. You don't need to hit the planet directly with anything, all you need to do is destabilize the orbit of all the planets or even just the Earth itself. You could send a gravity wave for example, that would cause the Earth's near circular orbit to shift to a very eliptical orbit. The vast change in temperatures would kill all life on the planet, and then you could come and mine all the resources that you needed and leave.
- AnIdiotOnTheNet 5y ago
  If you have the capability of engineering such a gravity wave then Earth's resources aren't worth your time.
  - mentalpiracy 5y ago
    Resources not the point here, the point is removing the possibility that our civ could ever be a risk to them

roenxi 5y ago

Fortunately, it is possible to imagine other scenarios. For example; it would take relatively little energy to deflect such a missile and there is likely to be a lot of time to detect it's incoming presence assuming that some sort of planet-like mass is required to host all the technology to create a relativistic speed accelerating engine.

gilbetron 5y ago

> Accelerating a rock to relativistic speeds is pretty easy Huh? How? I haven't seen any proposal that doesn't start with the assumption that we can inject a rock with a preposterous amount of energy let alone hit (in astronomical scales) a ridiculously small target, not to mention navigate all the gravity wells in between.

a1369209993 5y ago
Multistage rocket using ion engines. Remember this is over interstellar distances (>4 lightyears), so you have multiple years, if not decades or centuries to accellerate. This does get back to the "Why didn't we RKKV it millions of years before intellegent life even existed, much less had a opportunity to hide, based on biosignatures in the atmosphere?", though.
- gilbetron 5y ago
  Ok, that gets us to maybe 0.3% of the speed of light on something small, which isn't very interesting. https://space.stackexchange.com/questions/22140/what-is-the-maximum-speed-an-ion-engine-can-propel-a-spacecraft-at https://space.stackexchange.com/questions/22140/what-is-the-...

a1369209993 5y ago

> defending against a rock potentially coming from anywhere in space traveling at relativistic speeds is extremely difficult. Also, while 'proper' stealth is difficult, you can make the rock pretty close to invisible for practical purposes by coating it in vantablack and cooling it to liquid helium temperatures.