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    Former Staff Senior Contributor Ironduke's Avatar
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    Relativistic Kill Vehicles and the Fermi Paradox

    A Wikipedia primer:
    https://en.wikipedia.org/wiki/Relativistic_kill_vehicle

    As a guy whose favorite genre of fiction is science fiction, and I've read a large number of books and have seen most of the sci-fi TV shows and films ever made, I got to thinking one day - what would occur if we were actually able to accomplish space travel at relativistic speeds? Meaning, space travel at significant fractions of the speed of light.

    In the books I've read, I eventually came across one in which relativistic kill vehicles are used as weapons in warfare. Quite interesting stuff.

    It sparked curiosity in me - if we were able to accelerate a space vehicle to relativistic speeds, and it were to impact an object, say, the Earth, what kind of destruction would it do?

    I took two figures - the first being a mass equal to that of the space shuttle (~2 million kg), and picked a speed, in this case, 50% of the speed of light (~150,000,000 meters per second), and plugged it into a kinetic energy calculator (http://www.1728.org/energy.htm).

    The result I came up with was 5.3776e+6 megatons (TNT equivalent).

    Or, converted from scientific notation to regular decimal, 5,377,600 megatons.

    By comparison, the Chicxulub Impact Event that occurred 65 million years ago is estimated to have had an impact equivalent to 130 million megatons. A 48.5 million kg mass traveling at 50% C, if the calculations are to hold true, would impact with the same energy. Obviously, greater masses traveling at these speeds, the magnitude of the impact would scale with mass.

    If we were to develop this technology that enabled us to travel at relativistic speeds - it seems likely it would result in our own extinction. A world-ender - all that may be left of the Earth is an asteroid belt circling the Sun at 93 million miles. Perhaps within months, or years/decades at the most. An impact might come about via pilot error, malfunction, or even a hijacking and intentional targeting of the planet - the end result would be just the same.

    Perhaps the final and ultimate occurrence of Murphy's Law - anything that can go wrong, will go wrong. I can't imagine something not going wrong if we were to have this technology at our disposal.

    Which leaves me wondering - have these factors at all been taken into consideration by scientists and engineers who theorize about these technologies, and wish to develop space travel at these sorts of speeds?

    It also left me wondering - maybe this is the answer to the Fermi Paradox? That the reason we've never been contacted is that every civilization that may have ever developed this technology, soon went extinct by their own hand shortly thereafter?
    Last edited by Ironduke; 04 Jun 17, at 16:36.

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    Not sure about this theorising... of course if one managed to speed up a vehicle - or only a lump of rock - to beyond light speed and direct it at a planet the result would be catastrophic for any life on that planet, and most likely any small to medium sized planet depending on the size of vehicle/rock. However the closer ones get's - theoretically - to the speed of light the smaller one becomes as it were. In 'special relativity' the innert mass of the object - as of say my wine glass on the table - does not become added to by it's momentum. Only it's 'relativistic mass' (that seen by outside 'stationary' observer) changes but they are not in the same 'time frame' so to speak but by special relativity mass and energy are the same. The energy preservation rule also applies I imagine - even in space; how hard one can hurl an object subject to 'solar winds' and gravitational forces - towards it's desired destination will effect both it's aim and impact. Of course one can also use gravitational forces to accelerate objects as we have been doing for some time.

    I used to read my Brother's sci fi books after he left home and gleaned some theoretical physics at Uni as well as my own reading (mostly learning how to do the quantum equations) and I do not think myself that the "relativistic speeds" (which I assume to mean near light speed) can be reached. As you probably know it would (theoretically) require the entire energy of the Universe to achieve light speed. This though does not mean we cannot travel far outside our own galaxy; time and space bend with gravitational and electro magnetic forces. If the universe can be bent - or even folded as it were - then distances between two points which are two dimensionally far away become far closer.

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    Senior Contributor Monash's Avatar
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    I've read speculative articles and SF on this issue myself. I think the key issue would be the distance between any two technically advanced civilizations. As far as we can tell there is there are no technically advanced (superior) civilizations within at least 100 LY of our solar system. This is based on the principal that we have the capacity to detect the emissions of such a superior, space based civilization out to around that distance and so far - Nada.

    That said humans have only been transmitting radio signals for about 100 years or so and the vast majority of those signals don't actually escape into outer space, at least I have read scientific articles to this effect. Apparently certain long wave radar emissions and spaced based telemetry broadcasts do escape the solar system but most TV and radio broadcasts don't so anyone listening with hostile intent won't 'hear' anything for decades yet if not centuries.

    So using your scenario and assuming we emitted a signal 20 years ago that is detected by a hostile civilization 120 LY away we still have 100 years to go before they even detect it. Then assuming they immediately launch your relativistic 'space shuttle' at .5C we have another 250 years or so before it arrives (allowing for acceleration time). In total then we would have something like 350 years before the attack arrives. And of course pushing the distance between us out even farther to the thousands of light years that some scientists believe must separate any two advanced civilizations in this galaxy makes the problem even worse for an attacker.

    I'm certainly in no position to predict human technical development out that far into the future but assuming we don't blow ourselves up first (thereby saving E.T the trouble) I would think by that time (350 years plus) humanity would at least in part be a spaced based culture having spread out across the solar system. We might even be contemplating if not yet attempting our own interstellar missions. This means two things, firstly we are no longer confined to one planet and secondly we have at least some capacity to interdict any attack with high velocity projectiles of our own. This should mean single shot attacks are unlikely to work.

    On the plus side for the defenders the important thing is not so much having drives capable of matching the speed of the incoming projectile as is having very good sensors that can detect the approaching missile while it is still several light weeks or months away - at least. You then have a chance to launch a swarm of low V interceptors, preferably from somewhere out past Jupiter with the intention of killing the vessel in the outer solar system - if not further out. You don't need speed to do this so much as accuracy because the incoming projectile will presumably have limited maneuverability itself - dodging incoming attacks at .5C will almost certainly throw it off its track. For that matter you could have a multi layered defense with a final line of defense around the earth/lunar gravity well.

    (I'm assuming for my argument that high C vessels have a distinct 'signature' in the form of EM emissions given off via interactions with the interstellar medium i.e. a 2 mil kg vessel striking hydrogen atoms in space at .5C is going to displace and accelerate those atoms and other particles out of the way - I think that process would generate 'noise' that could be detected by sophisticated, space based sensors.)

    So in summary I would guess that by this time this issue becomes a potential problem we will have the means of dealing with it. And any attacker is only going to get one chance before we return the favor - with interest.

    Cheers
    Last edited by Monash; 05 Jun 17, at 04:01.

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    Former Staff Senior Contributor Ironduke's Avatar
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    Quote Originally Posted by Monash View Post
    So using your scenario and assuming we emitted a signal 20 years ago that is detected by a hostile civilization 120 LY away we still have 100 years to go before they even detect it. Then assuming they immediately launch your relativistic 'space shuttle' at .5C we have another 250 years or so before it arrives (allowing for acceleration time). In total then we would have something like 350 years before the attack arrives. And of course pushing the distance between us out even farther to the thousands of light years that some scientists believe must separate any two advanced civilizations in this galaxy makes the problem even worse for an attacker.
    I'd love to address your post at greater length - about to head to bed here - but what I'm referring to is an "own goal" event.

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    Senior Contributor Monash's Avatar
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    Quote Originally Posted by Ironduke View Post
    I'd love to address your post at greater length - about to head to bed here - but what I'm referring to is an "own goal" event.
    I suppose an 'own goal' is possible but I also think it unlikely. Firstly as I observed before Earth wouldn't be in position to create extra solar colonies until long after it had expanded out into the solar system and become a space based culture - or at least it's machines had. So again a single relatavistic strike isn't going to do it.

    Secondly if/when we do start founding extra solar colonies there isn't any chance of a 'Terran Empire' springing up to control everything. The distances and time delays are simply too large to be manageable. You can't run an empire where the decision loop between HQ and the 'colonies' is measured in human lifetimes. So more than likely every colony you found is on its own from day one, master of its own fate. Assuming ideological or religious differences arose for instance between one colony and 'home' you are most likely too far apart to be a threat to each others ideas or beliefs. Hell you'd be too far apart to even exchange insults via radio effectively!

    There' also two ways the colonization program can go (I think). Plan (A) is you colonize most stars along a given 'string' via a chain of space habitats build orbiting each (or most) of the stars in that chain. This creates lots of mini colonies' but also makes it hard if not impossible for any one colony to take out or damage all the others. There could be hundreds of them busily mining the resources of the their respective systems to expand their habitats.

    Plan (B) involves you pushing on outwards until you find stars with habitable planets or more likely those with worlds that can be terraformed. Best we can tell at the moment truly earth type worlds are uber rare. There might not be more than a handful across the entire galaxy. Terraformable worlds would be much more common but would still widely spaced - they still have to be Goldilocks planets after all. This plan ends up with the same problem that an alien attacker would have. Your colonies are so far apart that 'attacks' would take centuries if not thousands of years to strike home. Maybe you do both (A) and (B). In that case you still end up with multiple targets that can strike back if you 'miss' plus a number of home worlds that are so far apart strikes are impracticable.

    Finally IMO Earth, located as it would be at the at the center of of a 'sphere of influence' would still be an important source of news and scientific and technical advances for all the colonies simply because it would be the oldest world in the 'human zone'. It would also possibly lie at the center of a network of high C space craft that act as messengers and/or transports taking high value payloads to the other worlds. As such Earth would have more value intact than destroyed. I suspect most colonies would probably not want to see it knocked out and would take retaliatory action against any colony that tried - assuming any attack was successful (and again given the fact that Earth is the oldest world in the network it would have or should have the most advanced and best developed defensive networks on the block.
    Last edited by Monash; 05 Jun 17, at 10:43.

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    Quote Originally Posted by Monash View Post
    I suppose an 'own goal' is possible but I also think it unlikely. Firstly as I observed before Earth wouldn't be in position to create extra solar colonies until long after it had expanded out into the solar system and become a space based culture - or at least it's machines had. So again a single relatavistic strike isn't going to do it.
    Not so sure, the Battle Tech universe uses fusion powered drop ships that accelerate inward from the nadir or zenith points of a star system. At a half way point they flip over and decelerate. A 10,000 ton ship accelerating at 1g for say 20 days they are travelling at near 38 million mph. If a stars gravitational zenith is say 30au away the drop ship would cross the distance in about 55 days. If they don't flip over and just keep accelerating by day 40 they are travelling more than 75 million mph... That is only about 25% of light speed but it is relativistic. I freely admit i don't know at what point moving 1 kilogram 1 meter goes from costing Y (non-relativistic) energy to an ever increasing X (relativistic) energy.

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    I think by "own goal" Iron Duke probably means accidents might happen with a lot of relativistic travel.

    But, there are ways to mitigate this. Travel in between established outposts, are likely to occur via laser powered lightsail. In that case you'd set the receiving station in a system well outside the core planets.

    Also you can set a speed limit of say .5c.

    Going heavily relativistic only makes sense for shortening the passenger's journey. You can try to do that for going to new worlds, but you'd still need to slow down well outside of solar systems as any dust strike would become increasingly catastrophic. To an incoming relativistic ship the space dust around a star system might look very dense.

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    Former Staff Senior Contributor Ironduke's Avatar
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    Quote Originally Posted by zraver View Post
    Not so sure, the Battle Tech universe uses fusion powered drop ships that accelerate inward from the nadir or zenith points of a star system. At a half way point they flip over and decelerate. A 10,000 ton ship accelerating at 1g for say 20 days they are travelling at near 38 million mph. If a stars gravitational zenith is say 30au away the drop ship would cross the distance in about 55 days. If they don't flip over and just keep accelerating by day 40 they are travelling more than 75 million mph... That is only about 25% of light speed but it is relativistic. I freely admit i don't know at what point moving 1 kilogram 1 meter goes from costing Y (non-relativistic) energy to an ever increasing X (relativistic) energy.
    Same concept as in The Expanse, btw. I've heard of Warhammer - I've read loads on the Warhammer Wikia but have never had the time or inclination to get into it.

    edit: completely misread your post, lol. But same concept as the show I mentioned. I'll have to look into Battle Tech.
    Last edited by Ironduke; 22 Mar 18, at 01:31.

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    Senior Contributor antimony's Avatar
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    Quote Originally Posted by Ironduke View Post
    A Wikipedia primer:
    https://en.wikipedia.org/wiki/Relativistic_kill_vehicle

    As a guy whose favorite genre of fiction is science fiction, and I've read a large number of books and have seen most of the sci-fi TV shows and films ever made, I got to thinking one day - what would occur if we were actually able to accomplish space travel at relativistic speeds? Meaning, space travel at significant fractions of the speed of light.

    In the books I've read, I eventually came across one in which relativistic kill vehicles are used as weapons in warfare. Quite interesting stuff.

    It sparked curiosity in me - if we were able to accelerate a space vehicle to relativistic speeds, and it were to impact an object, say, the Earth, what kind of destruction would it do?

    I took two figures - the first being a mass equal to that of the space shuttle (~2 million kg), and picked a speed, in this case, 50% of the speed of light (~150,000,000 meters per second), and plugged it into a kinetic energy calculator (http://www.1728.org/energy.htm).

    The result I came up with was 5.3776e+6 megatons (TNT equivalent).

    Or, converted from scientific notation to regular decimal, 5,377,600 megatons.

    By comparison, the Chicxulub Impact Event that occurred 65 million years ago is estimated to have had an impact equivalent to 130 million megatons. A 48.5 million kg mass traveling at 50% C, if the calculations are to hold true, would impact with the same energy. Obviously, greater masses traveling at these speeds, the magnitude of the impact would scale with mass.

    If we were to develop this technology that enabled us to travel at relativistic speeds - it seems likely it would result in our own extinction. A world-ender - all that may be left of the Earth is an asteroid belt circling the Sun at 93 million miles. Perhaps within months, or years/decades at the most. An impact might come about via pilot error, malfunction, or even a hijacking and intentional targeting of the planet - the end result would be just the same.

    Perhaps the final and ultimate occurrence of Murphy's Law - anything that can go wrong, will go wrong. I can't imagine something not going wrong if we were to have this technology at our disposal.

    Which leaves me wondering - have these factors at all been taken into consideration by scientists and engineers who theorize about these technologies, and wish to develop space travel at these sorts of speeds?

    It also left me wondering - maybe this is the answer to the Fermi Paradox? That the reason we've never been contacted is that every civilization that may have ever developed this technology, soon went extinct by their own hand shortly thereafter?
    To me, aiming to travel at relativistic speeds do not make any sense at all. First, it would not help with any kind of interstellar travel. Second, the time dilation effect.

    I would pin my hope on actually getting something like the Alcubierre Drive (https://en.wikipedia.org/wiki/Alcubierre_drive) working. Nasa's Eagleworks was working to test out the theory since 2011, have not heard from them for a while.

    https://ntrs.nasa.gov/archive/nasa/c...0130011213.pdf
    "Is God willing to prevent evil, but not able? Then he is not omnipotent. Is he able, but not willing? Then he is malevolent. Is he both able and willing? Then whence cometh evil? Is he neither able nor willing? Then why call him God?" ~ Epicurus

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