Re: the real cosmic filter..

From: Charlie Stross (
Date: Fri May 26 2000 - 02:58:00 MDT

On Thu, May 25, 2000 at 03:29:22PM -0400, Michael S. Lorrey wrote:
> Don't know if anyone has thought of this, but it occured to me that the cosmic
> filter may really be a real filter that we imposed on ourselves. The idea is our
> continuous broadcasting of radio and video feeds out into the universe is seen
> by the galactic civilization as the equivalent of spam, and that they imposed a
> filter on our solar system to eliminate interference from our signals. Then
> again, maybe we just aren't subbed to the right lists... ;)

Unlikely without causality violation.

Reason: radio transmissions began around 1900 and propagate outwards at
the speed of light. Radio astronomy first begins around 1940 (Karl Jansky
may have been working a few years before that, but it was the development
and military utility of radar that really got the ball rolling).
Transmissions powerful enough to pick up at a range of light years didn't
really start until the 1930's.

Assuming that people out there are talking, but sent us to coventry because
of our incessant spamming, there'd be a real-time lag of about a decade
between our first signals loud enough to be picked up, and our first
chance to pick up _their_ signals. That means the galactic civilization
is entirely concentrated within about five light years of us, or their
descendants in the 21st-30000th centuries sent them back a tachyon-gram
(directed to the 20th century AD through 29900th century BC) to say
"there's a bunch of offensive loud-mouthed primates on the third planet
orbiting that G2 star -- don't broadcast in their direction!"

-- Charlie

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