Remember
studying the (heavy chords) Scientific Method in middle school?
According to your dour-faced science teacher, this was the secret formula by
which legions of clipboard-carrying, lab coat-attired researchers pushed back
the frontiers of knowledge. The scheme was simple: Scientists sat around
dreaming up hypotheses--possible new truths--which they torture-tested in the lab
or in the field. Experiment would arbitrate, either by validating the truth of
a hypothesis, or by sending the scientist back to the blackboard to think
again.
Indeed,
some research is done like that; investigations that proceed by testing a
falsifiable premise. But there's another way to learn about the world which
you might call "discovery" science. Consider X-rays or penicillin. They
weren't first hypothesized by tweedy academics; they were simply found, and
their nature and significance worked out after the fact. The same is true for
quasars, pulsars, dark matter, dark energy, and nearly every object you'll find
described in an astronomy textbook.
SETI is
akin to discovery science, despite its obvious presumption that the
extraterrestrials exist, because that hypothesis is not falsifiable. A failure
to receive a radio beacon from space doesn't say a whole lot about whether
aliens do, or do not inhabit the 'hood. But while we can't prove that aliens
are not there, we can prove they are. We just have to find a
signal.
Four
decades ago we might have imagined that tripping across an extraterrestrial
broadcast would be an easy matter, but all the searches since then tell us it's
not. The sky isn't cluttered with honking signals that anyone with a backyard
satellite dish, a crystal set, and abundant spare time can find. If we hope to
discover ET in the near future, we're going to need highly sensitive antenna
systems that can check out large expanses of cosmic real estate quickly. That's
simply the consequence of doing a discovery experiment with a universe of
possible search locales.
The need
for speed is a major impetus for the Allen Telescope Array (ATA), a specialized
radio telescope now under construction by the SETI Institute and the University of California Berkeley--and the first such instrument designed with SETI
in mind. Sure, making a search with someone else's telescope spares you the
bother of building one, and using a loaner instrument is a modus operandi that
has given SETI scientists access to some of the largest antennas in the world.
But frankly, it's mightily inefficient: comparable to doing medical research
with borrowed microscopes. Usually only a few weeks per year of a big
telescope's observing schedule will be devoted to SETI, and some of that
precious time is inevitably lost in the ritual of repeatedly setting up and
turning on specialized hardware that has been dormant for months.
The ATA,
however, will be available 24/7. That's a factor of ten more search time per
year than was available for the SETI Institute's Project Phoenix, which ran on
telescopes in Australia, West Virginia, and Puerto Rico.
In
addition, the ATA benefits from startling new developments in receiver design.
Most receivers used for radio telescopes can tune a band that's a few hundred
megahertz wide. That beats the heck out of your AM radio, but it's still a
pretty small chunk of the radio spectrum--which means that if you want to search
for ET's transmission, but don't know where on the dial to listen, then you
have to keep changing out receivers to cover different frequency ranges.
The Allen
Telescope Array's MMIC (Monolithic Microwave Integrated Circuit) receiver
simultaneously picks up all cosmic static between 0.5 and 11.2 gigahertz--a
spectral range equivalent to two thousand TV channels, side-by-side on the
dial. In its first incarnation, only four selected sections of that spectrum
will be examined. Nonetheless, that's a several-fold improvement over past SETI
experiments. In a decade or two, as digital electronics become cheaper and more
powerful, even these modest bandwidth limitations will seem quaint.
Finally,
and undoubtedly most importantly, the ATA is an imaging telescope. In contrast,
a single-dish instrument such as the Arecibo antenna in Puerto Rico is basically a one-pixel radio camera, its metal eye stares at a single spot on the heavens.
Yes, you can bolt multibeam receivers to the focus of such a scope and get a
dozen or so pixels in place of that one spot beam, but those dozen are tightly
clustered and in a fixed pattern. But an array of small antennas, such as the
ATA, is able to simultaneously create pixels at arbitrary positions over many
square degrees of sky. Again, the initial configuration of the ATA is modest:
three pixels will be its limit. Still, that's three times better than for
earlier SETI experiments, which had to look at star systems one at a time. But
as processing power becomes cheaper, those three pixels will eventually blossom
to ten, a hundred, a thousand, or more. The speed of the search will increase accordingly.
In sum,
when the ATA is completed, it will be about a hundred times faster than any
previous radio search. And that's just its opening gambit, since its speed
will only increase.
Of course,
if there's nothing to be found--if nowhere in the Galaxy are other beings
stabbing the darkness of space with their radio beacons--then the capabilities
of our telescopes won't matter. But if - as many think reasonable and likely--intelligent
life is a phenomenon that is something less than miraculous, then a discovery
experiment will benefit from the increased speed of new instrumentation. SETI
scientists are combing the cosmos for a signal, and the ATA will be the mother
of all combs.
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