
Relativistic kill vehicle - lelf
https://en.wikipedia.org/wiki/Relativistic_kill_vehicle
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kmm
Interestingly, RKV's travel at speeds that are apparently faster than light,
because they immediately follow the light they emit. If an RKV was launched
towards us from Sirius at 99% of the speed of light, the news of that launch
would reach us 10 years later, with the missile following merely a month
later. Thus, if we could track the missile, it would appear to cross 10 light
years of distance in that month, at an apparent speed of almost 100c. We can
see a related effect in real life with jets coming from black holes and other
sources ejecting material at high speeds[1]. This is of course not true
superluminal motion, but an optical illusion.

1:
[http://en.wikipedia.org/wiki/Superluminal_motion](http://en.wikipedia.org/wiki/Superluminal_motion)

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darkmighty
Also interestingly, this accumulation of energy in front of the vehicle is the
cause of Sonic booms. Acoustic waves, and pressure dispersion in general, get
accumulated in front of the craft, momentarily creating enormous resistance
and temperatures as it passes the speed of sound. Of course the accumulation
of light is different in that it can't affect the vehicles themselves due to
the principle of relativity (constant speed of light for all inertial
observers).

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jakeogh
(Caution; dont click unless you have atleast an hour to kill)

[http://www.projectrho.com/public_html/rocket/spacegunexotic....](http://www.projectrho.com/public_html/rocket/spacegunexotic.php#id
--Relativistic_Weapons)

~~~
deeviant
Sigh, I should have heeded your warning. My productivity is not looking too
good today.

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lotsofmangos
It is also referred to in 'The Algebraist' by Ian M. Banks.

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.

~~~
theoh
I suspect the initial post was a response to Charlie Stross's remarks about
existential risks: [http://www.antipope.org/charlie/blog-static/2015/04/on-
the-g...](http://www.antipope.org/charlie/blog-static/2015/04/on-the-great-
filter-existentia.html)

Since we live in the twitteresque dark ages there's no way to know. Vannevar
Bush would be turning in his grave.

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dougk16
Question: The article mentions that a 1kg projectile travelling at 99% of the
speed of light would have such and such more explosive energy than the most
powerful nuclear bob ever detonated. I don't doubt the math, but would the
destructive effects (e.g. to a city) of such a projectile weapon actually
equal those of a nuclear bomb? I'm not talking about the radiation and such in
the aftermath, just the explosion itself. Wouldn't the projectile basically go
straight through a planet?

Edit: I suppose the shockwave from entering the atmosphere would cause a bit
of a rucus too...still interested in any responses.

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blackstache
This might give the beginnings of an idea of what would happen:

[https://what-if.xkcd.com/1/](https://what-if.xkcd.com/1/)

~~~
dougk16
Interesting, thanks for the link. Intuitively it still seems like much of the
energy from the projectile would be absorbed deep in the Earth as it traveled
through. For sure it would cause some damage, but it still seems like a
nuclear bomb would have a higher _effective_ energy, as far as the tactical
goal of taking out a city or something.

~~~
TheLoneWolfling
You can adjust effective penetration depth by the "density" (read, mass per
unit cross-sectional area) of the projectile.

You could go anywhere from an osmium needle through to a Mylar disk.

Another relevant XKCD: [https://what-if.xkcd.com/20/](https://what-
if.xkcd.com/20/)

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svachalek
The recent articles on Artificial Superintelligence have got me thinking about
interstellar MAD. It seems that once you have ASI you really have the
capability to do anything within the laws of physics because if there's
anything you don't know how to do, you just add intelligence until you do. If
so, it seems that primitive civilizations can become enormous, exponentially
expanding threats to established civilizations in relatively no time at all,
and in fact they are extremely vulnerable if they choose not to, not only to
established players but to any new ones that come along.

~~~
api
A little off topic but...

"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.

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RickHull
An analogy might be made in terms of escape velocity. For the longest time, we
hurled stones at targets in trees and towers. However, in the times leading up
to WWII, we (Germans, mostly) began to sense that we could launch objects at
the Moon or Mars with plausibly incremental improvements. A tipping or
inflection point is reached where things go all zoomy and nonlinear.

70 years later, we might be entering that era for intelligence. These sorts of
things are not easily rejected by looking at historical trajectories.

~~~
darkmighty
You are using the historical trajectory of rockets in a way to prove your
point :)

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.

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quanticle
Gwern has a a good write-up about various "realistic" scenarios for
interstellar war:
[http://www.gwern.net/Colder%20Wars](http://www.gwern.net/Colder%20Wars)

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t0mas88
The page mentions accelerating over a longer distance, but wouldn't that
defeat the undetectability of the whole thing?

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jjaredsimpson
If I accelerate 1000 1kg masses to .99c 1ly away from your planet you can't
detect them, and I've just destroyed your entire species (sterilized the
planet) with a metric ton of rocks.

It doesn't matter how long I take to accelerate them, once they are going fast
you are destroyed in 1 year.

~~~
TheLoneWolfling
Why are you saying we couldn't detect them? There's enough interstellar medium
to make any such impactor detectable.

(Rough calculation: 67kw/m^2. And that's not even talking about dust grains
(which ends up with much brighter instantaneous flashes))

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letstryagain
By the time you see it, it will be too late to respond.

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TheLoneWolfling
Why?

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.

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InclinedPlane
.99c means that you have 1/100th as much time to respond relative to the
detection distance. Let's say you spot the impactors an entire light-year
away. The light will only reach you less than 4 days before impact. Can you
put together an effective response plan in 4 days? If instead you spotted them
out in the oort cloud (say, 1000 AU away) you would have less than 2 hours to
respond.

~~~
TheLoneWolfling
Right, but that is compensated by the fact that that same time compression
also applies to any energy released by the impactor. It'd be putting out
>3.5*10^7 watts / m^2 at 0.99c, from our perspective. And a single sand grain
hitting it would release 27GJ.

Not to mention... How on earth are you managing to keep something together
when its being bombarded by hydrogen / helium at 0.99c?

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EarthLaunch
A more interesting idea would be accelerating someone to the point where they
meet the end of the universe.

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ringshall
Carl Sagan discussed this in episode 8 of Cosmos. This segment of video[1]
progresses from Leonardo DaVinci's flying machines to a relativistic space
craft in about 7 minutes.

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...](https://www.youtube.com/watch?v=abp3q7aYOss&feature=youtu.be&t=1600)

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compsciphd
federation couldn't have used these against the Borg? might have saved picard
a lot of trouble :)

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delecti
The Borg don't really stay stationed on planets, the Star Trek universe has
FTL scanning technology, and as a general rule, physical projectiles are
handwaved to be unable to penetrate shields on ships, and even if they didn't,
that's exactly what the deflector is for.

Sorry you got downvoted though.

