
Observational Signatures of Self-Destructive Civilisations - gnocchi
http://arxiv.org/abs/1507.08530
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matt_morgan
This was not obvious to me from the title, but what they're talking about is
ways that with tomorrow's telescopes, we could infer via observation how a
technological civilization had destroyed itself, and therefore that an
advanced extra-terrestrial civilization had been on that planet.

They seem to say that given Fermi's paradox and the possibility that _most_
civilizations self-annihilate, this is actually a good way to do SETI. Makes
sense.

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jleahy
>> As a star’s gravitational well will likely be the deepest in the system, it
is also energetically efficient to launch material on a stellar­ intercept
trajectory.

Quite the opposite, that's one of the most delta-v expensive trajectories to
embark upon. In fact from earth it's about twice as expensive as leaving the
solar system.

~~~
3pt14159
Really? Why? Isn't the sun moving along some path in the milky way and can't
we use that to accelerate the launch of a spacecraft? It looks like Voyager 2
used the effect, at least according to this image:

[http://abyss.uoregon.edu/~js/images/voy_traj.jpg](http://abyss.uoregon.edu/~js/images/voy_traj.jpg)

~~~
demallien
Orbits are not intuitive. To head "downwards", you have to slow down your
orbital velocity, which reduces the radius of the orbit. In other words you
have to decelerate. When you do the maths, you actually have to decelerate
more from Earth orbit to get to the sun than you do to accelerate up to solar
escape velocity.

~~~
redcalx
Right, so an orbit implies an amount of kinetic energy which you need to lose
to lower your orbit; and losing kinetic energy in a frictionless environment
requires some kind of propulsion.

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ChuckMcM
I believe it was Vernor Vinge who made the comment that perhaps unexplained
gamma ray burst were the last gasp of a planet or star that had been
obliterated in anger by an adversary.

That said, if, for example, humans kill themselves off with a climate change
it would have very little external signature.

~~~
stcredzero
Vernor Vinge also made the observation, that if most civilizations undergo an
exponential increase in technological and societal progress, they're likely to
disappear within a dozen generations after inventing radio. I'm not so sure we
can reasonably imagine the signature of a civilization "subliming" to put it
in Iain M. Bank's "Culture" terms.

So if the likeliest outcomes of industrial civilization are environmental
self-destruct, self immolation in war, or "subliming" to something we can't
imagine, then this would handily explain the Fermi paradox.

~~~
trhway
we know that we can't "see" most of the Universe - the dark matter/energy.
That pretty much can happen to be the real Universe, and we're just living in
the part set aside for the non-intelligent species. It is like being an ant on
Earth - there is a planetary tech civilization being developed while you have
no idea what is going around. The only interaction you my have with the
civilization - if you're lucky, and you are some kind of special ants, then
your colony may get moved before dam valley to be flooded, otherwise - not
even that...

~~~
jerf
Given that A: dark matter has to have been around since the beginning to solve
the problems it is meant to solve and B: must not interact strongly with
anything, including itself, to solve the problems it is meant to solve, it
seems unlikely that it can be supporting any structures whatsoever, let alone
usefully living or computing ones.

~~~
AnimalMuppet
I don't think that's quite right. I think that it can't interact with anything
electromagnetically, and it can't strongly interact with even itself _at
larger distances_. But it could support something similar to the strong force
with itself, and could therefore have structure at smaller scales ("smaller"
means perhaps even at the scale of a planet).

Or have I missed something?

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landryraccoon
Dark matter is believed to be very weakly self interacting. If it had any type
of self interaction it is assumed that it would aggregate into large
structures (like stars) because it would lose momentum due to collisions or
"drag" interacting with other dark matter. We would expect to observe
structures like dark matter stars/galaxies/planets, but no such structures are
observed. Even if those large structures did not interact electromagnetically,
the gravitational effects of those objects would be felt on "ordinary matter"
like stars and galaxies that we could observe.

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nickhalfasleep
I don't think these can differentiate between Self-Destruction and Murder by
other parties?

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jerf
Under their assumptions, murder doesn't come up very often, because
civizilations rarely-to-never cross paths in the first place.

