108 DECEMBER 2019|COMPUTER SHOPPER|ISSUE 382
leakage that wasn’t really intendedfor
us. The advantageof leakage,ofc ourse,
would be that you don’t count on the
aliens as having sufficient interest in us
to send anything our way. On the other
hand, atargeted signal would be much
easier to detect because theywould
make it intense and theywould put all
the information intoavery narrow
band to make it easierforustofind.”
However,beamed transmissions are
probably unlikely.“Forany star system
more than about 35 light years away
–and that’s the majorityof them –
there’s not been enough time since the
SecondWorld Warfor our strong
transmissions at high frequency,the
ones theycould pick up like radar,to
reach them, andforthem to have
decidedto send something back
relentlessly,” Shostak says.
It’s not onlyamatter or where
to look in the sky. The needle in a
haystack problem is compoundedby
the difficultyof knowing what
frequenciesto look at in the radio
spectrum. Shostak explains how they
look fornarrow signals because
they’re much easierto detect.
“Weassume that any signal will
have narrow band components.
Narrow band in this instance is about
one hertz, and these are much easier
to see than the broadband
componentsof the signal that carry
the information,”hes ays.
Even so,the broad-brush approach
still improves the likelihoodof finding
something out there.
Shostak adds: “Your receiver
swallows as much bandwidth as it
can, and you useaFourier Transform
to break this up intonarrow channels.
We observe with 72 million channels
at once .”
When asked how likely the SETI
approach isto providing answersto the
questionof whether we’re alone,
Shostak’s response was predictable.
“That’s like asking James Cook,
‘What are the chances you’re going
to find the NorthWest Passage?’.
He didn’t know.But the important
point is that SETI is the beneficiaryof
improvements intechnology known as
Moore’s Law,which means that the
searches are increasing relentlessly
in speed. Soby 2035, we’ll be able
to look at amillion star systems.
Is that enoughof asample to be able
to saythat now there’sachance of
success? I’d beteveryone acup of
Starbucks that it is.”
THECOMPUTINTHECOMPUTINGP OWERGPOWER
BEHIND SETIBEHIND SETI
Talk of Moore’s Law underlines the
need forsophisticated computer
hardware in SETI, but just what is the
processing requirement and what
hardware is usedto achieve it? Shostak
emphasised that, wherever possible,
the AllenTelescope Arraycaptures as
much data as possibleto improve the
likelihoodof finding thattell-tale signal.
However,having captured data from a
reasonably large areaof the sk yover a
broad rangeof frequencies, from 1GHz
to 3GHz, it’s necessaryto home in on
single areasof the sk yand searchfor
signals just one hertz wide from the
massive 140Gbit/s data stream. And
this is justforthe current 42 antennas,
let alone the 350 dishes that will be
present when the arrayisc omplete.
Selectingavery specific partof
the sk y–perhaps one withastar
THE WOW!
SIGNAL
At first sight, astronomer JerryREhman’s
task at OhioStateUniversity’s radio
observatory didn’t soundtooenthralling.
All that changed in August 1977.Asu sual,
he’d been analysing the huge volumesof line
printer paper from the observatory’s IBM
1130 computer,when something caught his
eye. This particular signal was so arresting
that Ehman circled it in red, writingWow!
against it.To this da y, it’s called theWow! Signal.
The radio observatory had been built as partof the University’s SETI programme.And that
signal looked nothing like anything anyone hadever seen before.The signal lasted 72 seconds,
it was 30 times stronger than the background noise,and it appearedto be asignal that couldn’t
have been generated on Earth.
Needlessto say, scientists have looked again and again on the same frequency,and in the
same direction, but nothing similar hasever been heard. Although natural causesof that
signal have more recently been putforward, it remains the most likely candidatefor an
extraterrestrial signal.
⬆Att he birthof
SETI, no exoplanets
(planets orbiting
other stars) were
known. The first
was found in 1992
and now,thanks
mainly to the Kepler
Space Telescope,
astronomers
know of 4,103
⬆It’s just possible that an extraterrestrial radio signal
was received back in 1977
