Relativistic kill vehicle
en.wikipedia.org
en.wikipedia.org
http://www.projectrho.com/public_html/rocket/spacegunexotic....
It is mentioned that the Dweller species have a habit of taking a very long revenge against any other species stupid enough to wipe a community of them out. So a few generations after a species has completely forgotten about the load of strange jellyfish they killed off in their local gas giant, a shit-ton of sand and gravel comes through their system at a significant fraction of the speed of light.
Since we live in the twitteresque dark ages there's no way to know. Vannevar Bush would be turning in his grave.
Edit: I suppose the shockwave from entering the atmosphere would cause a bit of a rucus too...still interested in any responses.
You could go anywhere from an osmium needle through to a Mylar disk.
Another relevant XKCD: https://what-if.xkcd.com/20/
"you just add intelligence until you do"
So many assumptions. I'd challenge everyone to look deeply into learning theory and combinatorics. We have no reason to believe that intelligence is something you can just scale up without bound, and many reasons to believe otherwise.
For starters: nature "invented" intelligence hundreds of millions of years ago with the evolution of neural nets, and it's a powerful adaptation that confers significant advantage. Why are we the only intelligence with our level of analytical capability on Earth? If it were so easy to "just add intelligence," almost every large animal in nature should be capable of language, mathematics, and logic by now.
As someone who spent many years studying AI, machine learning, combinatorics, evolutionary theory, and related topics, some of the stuff that's been flying around about AI recently is making me itch.
Lots of animals seem to lack the ability to use fine tools and have limited vocal ranges that would make communication far more difficult. I'm inclined to question the 'significant advantage' part in its unqualified form.
Better yet, I really wish someone far more up to date than I am who is actually working today in the field would take up the cause of airing out some of this silliness. I considered it harmless up to the point I started reading actual calls to regulate or even ban basic CS research. If I see any more of that stuff there is one person I know that I might email and try to convince to do it. The last thing we need is to shut down one of our most productive areas of innovation with baseless fear mongering built on towers of wobbly assumptions and cheesy sci fi scenarios.
We don't know what the returns on computational power are in regards to intelligence levels, it may actually be non-linear (one way or the other). Or it may be mostly uncorrelated.
70 years later, we might be entering that era for intelligence. These sorts of things are not easily rejected by looking at historical trajectories.
But looking precisely at rockets, there was a boom in technology where the distances and velocities we could go increased exponentially until the tech matured, and now it's settled and still pretty expensive to go up there.
In fact, this trend seems common with technologies (rapid growth until a wall is reached). I wish I had a link to the graphs I have in mind that make this argument.
Of those assumptions, the one that seems most common around here is that intelligence is one thing.
Also, there are other animals that approach our intelligence and are probably sentient. They are just a bit behind us, but enough so that we dont recognize them as so (the pack of communication is also an issue).
Essentially, imagine trying to pick something the size of a telephone pole, angled end-on at you, from 20 miles away out of the entire night sky. By the time it gets close enough to spot easily, it's too late to do much about it.
Edit: jjaredsimpson's comment makes a very good point about velocities much closer to 1c. My comment mostly relates to the more immediately practical kinetic bombardment[0], which works on the same idea.
It doesn't matter how long I take to accelerate them, once they are going fast you are destroyed in 1 year.
Of course, if you're thinking of a scenario where aliens at that tech level launch such an attack against us 21st-century humans, yes, we'd be toast.
(Rough calculation: 67kw/m^2. And that's not even talking about dust grains (which ends up with much brighter instantaneous flashes))
Sure, there's time dilation effects, but they are largely cancelled out. We have less notice for a given distance, but we also can see it coming from farther away.
Not to mention... How on earth are you managing to keep something together when its being bombarded by hydrogen / helium at 0.99c?
Imagine a spacecraft using a standard inertial propulsion system. It shoots mass one way and it goes in the opposite direction. If it had something like a thrust signature, it would be in exactly the wrong direction for the intended target to see, add in a shroud and it would impossible to detect unless the target had sensors in other systems perpendicular and in between the launch site and target site.
Even if detected, what could be done? A planet is not going to change it's trajectory, and even if they fry it with some sort of energy weapon, it would still maintain it's velocity and the associated energy.
Truly, in a universe with advanced and aggressive space faring species, a planet would be about the most unsafe place you could be, it would be ridiculous easy for said advanced space faring species to destroy/make uninhabitable a planet. And you would hardly even need a RKV to do it.
A large-scale Whipple Shield, maybe? (http://en.wikipedia.org/wiki/Whipple_shield)
Throw a small moon into its path and engage it from as far away as possible. You'll end up with a lot of smaller slower pieces over a wider area.
Just coordinate trajectories. Throw a bunch of chaff at it from different trajectories, so that it passes through them in stages.
You need to throw enough at it that a large chunk of the nuclei in the impactor are hit by nuclei of the atoms you are throwing at it - not an insignificant feat. Small moon may work.
Anything less and yes, it's rapidly expanding into a cloud of gas, but nowhere near fast enough. It'll hit the target well before it dissipates significantly if you're not careful.
This cannot be solved by a shroud, as you'd then see the interstellar medium hitting the shroud instead.
The best response to something like this would be a whipple shield. Except you don't need an actual shield. Just drop a couple stages of a bunch of chaff in its trajectory, or a bunch of spin-stabilized mylar disks. Even ball bearings would be too much. You don't need to stop it, "just" diffuse it enough so that the atmosphere can handle it.
[1]: http://www.wolframalpha.com/input/?i=%28%281+-+0.9^2%29^-0.5..., Assuming ~1 atom/cc, 90% hydrogen 10% helium
1000 tons at .1c is 9818 megatons, which would be roughly the size of a US air craft carrier. The bow shock would be much less and the I'm assuming it would be using some sort of magnetic scoop ramjet would would channel interstellar medium to the propulsion system rather than striking the bow.
With a stealthy design, the thing would be very difficult if not impossible to detect, barring some sort of entirely need detection method.
And even at 0.1c, you encounter a grain of sand, that's, what, ~23MJ of energy released.
Your 1000 tons at 0.1c is going to have a whole lot more cross-sectional area than, say, 4 tons at 0.9c. At least the cube root of 250 times, or ~6.3x.
You'll also have, what, 11x more time to react to it at a given distance.
Neither of these compensate entirely, but both of these are compensatory effects.
(I was intending to assume constant density and shape, but forgot to turn that into cross-sectional area as opposed to radius.)
A spacecraft accelerating at 1 g, closer and closer to c, accelerating halfway and decelerating halfway, could travel to Barnard's Star in 8 years ship time; center of the Milky Way Galaxy in 21 years ship time, the Andromeda galaxy in 28 years ship time.
"In principle such a journey, mounting the decimal points closer and closer to the speed of light, would even permit us to circumnavigate the known universe in 56 years ship time. We would return tens of billions of years in the far future, with the Earth a charred cinder, and the Sun, dead. Relativistic space flight makes the universe accessible to advanced civilizations, but only to those who go on the journey, not to those who stay home."
https://www.youtube.com/watch?v=abp3q7aYOss&feature=youtu.be...
Sorry you got downvoted though.