Today, in
the remote northeast corner of California,
technology innovator and Microsoft co-founder Paul Allen will hit the big red
button.
No, he won't
be throwing heavy-duty machinery into an emergency shutdown, nor will he be
sending ICBMs screaming from their silos (traditional functions for ruddy
buttons). Instead, he'll be christening a new telescope that, in its
significance, could eventually outpace the Nina, Pinta,
and Santa Maria.
The famous
technologist will be inaugurating the initial 42 antennas of his namesake, the Allen
Telescope Array (ATA) – the first major radio telescope designed from the
pedestal up to efficiently (which is to say, rapidly) chew its way
through long lists of stars in a search for alien signals. Within two decades,
it will increase the number of stellar systems examined for artificial
emissions by a thousand-fold. The ATA will shift SETI into third gear.
This
telescope is truly a geek's barn-burner. In the last two decades, high-performance
radio amplifiers have gotten smaller and, more importantly, much cheaper. This
has changed the recipe for building radio telescopes, and the ATA is taking
advantage of the new formula.
Consider:
the single most consequential characteristic of a radio telescope (at least,
for SETI) is its collecting area: the number of square meters boasted by its "mirror."
There are two ways to increase this area: either build a bigger antenna, or
build lots of smaller ones and hook them together. As an example of the former
strategy, imagine doubling the diameter of the antenna's "dish",
thereby increasing the collecting area by a factor of four. A
good thing, surely. But since an antenna is a three-dimensional device,
the amount of aluminum and steel necessary for the larger antenna has gone up
by a factor of eight. Expensive. It's cheaper by half
to build four of the original-size antennas.
This is a
simple scaling argument, but it boils down to this: it's always more economical
to assemble a large collecting area by constructing small antennas, rather than
large ones.
In past
practice, this elementary fact of antenna life was routinely diluted by the
high cost of the receiver equipment. Check out the cryo-cooled,
quiet-as-death receivers at the focus of any other radio telescope, and you're
looking at a million dollars' worth of electronics. That's why the Very
Large Array – the iconic radio telescope in New Mexico that you've seen in a raft of
sci-fi films – has only 27 antennas. That number was a compromise between
structural and electronic costs.
Today, you
can festoon the focus of your antenna with high-grade receivers for about one
percent of the old price. So the paradigm has changed, and today it's better to
build a large number of small antennas, rather than a small number of large
antennas.
The
individual dishes of the ATA are 6 m in diameter, small enough that you can't
see them from California
state route 89, even though they're barely a mile
beyond its eastern berm. Like slow-growing lotus
blossoms, these antennas have methodically erupted on a lava-littered heath 300
miles northeast of San Francisco
during the last four years. Eventually, 350 dishes will grace the Hat Creek
Observatory site. But the 42 now up and running are equivalent in collecting
area to a 40 m single-dish antenna – and that's large enough to start doing
some serious science.
What it can do
A lot of
that science will be vanguard
radio astronomy. Thanks to the ATA's small
individual antennas, the instrument has a wide field of view. That is to say,
like wide-angle sports binoculars, it sees a big chunk of sky all at once. (In
contrast, most radio telescopes look at the heavens with a field of view
comparable to what you'd see through the tiniest of soda straws.) The University of California radio astronomers, who – together with the SETI Institute – are building the ATA, will fill that large
field of view with pixels to produce high-resolution radio photos of large
tracts of cosmic real estate.
The combination
of wide-angle view and high resolution allows rapid surveys of our local chunk
of the cosmos. And it's a hallowed axiom of astronomy that surveys nearly
always pay off with unexpected, major discoveries.
In
addition, by looking at lots of the sky, and looking at it often, radio
astronomers can find transient phenomena: things that go burp in the night, and that otherwise would never be seen.
The new
possibilities might best be understood by analogy. Consider making a time
exposure photo of Manhattan from the Empire State
Building. That's
comparable to what astronomers do now – collecting data with their radio
telescopes for hours, while staring at one patch of space. A time exposure
reveals lots of subtle detail – cars parked on the streets, the filigreed
facades of the skyscrapers, and so forth. But anything that changes – the
taxis, the pedestrians, or even the stoplights – gets blurred or lost by the
long exposure. Well, with the ATA's snappy radio
picture mode, things in the universe that change will finally be seen. Prepare
to be surprised.
For SETI,
the ATA will be as revolutionary as a Parisian mob. Most folks, indoctrinated
by Hollywood's
sleek, blue-lit view of science – with its immaculate laboratories and
aimlessly wandering engineers – imagine that SETI researchers spend their days
with earphones on their heads, straining to pick out ET's transmissions from
the fuzzy din of cosmic static. It isn't that way, and if it were, SETI
scientists would have long ago checked into the funny farm.
The reality
is more complex. Even the ATA-42, the first incarnation of this new instrument,
will be able to simultaneously observe several star systems at once, while
monitoring at least 40 million radio channels. You can't analyze all that data
with earphones, and so a sophisticated, custom software system carefully
screens all incoming static for the tell-tale whistle of an extraterrestrial
transmitter.
For its
first foray into SETI, the ATA-42 will be used to scan 20 square degrees of sky
in the direction of the center of our Galaxy. It will spend several months
looking for signals coming from the direction of the Milky Way's star-clotted,
inner realms. Eventually, the ATA will start a massive campaign to examine
approximately a million nearby star systems. That's a thousand times more than
all those carefully scrutinized in the past.
Today, when
Paul Allen hits the big button, 42 radio ears will pivot toward the sky like
synchronized swimmers, and the first official observations with the ATA will
begin. There'll be applause and smiles all around.
But the
true excitement is yet to come. It's hard to imagine that such a modest
collection of small metal contrivances, pinned to the earth, and each no bigger
than a delivery truck, could somehow reveal the activities of unknown, unseen
beings on a planet a thousand trillion miles away. But a simple calculation on
a small sheet of paper shows this to be true. And perhaps someday soon, that
discovery will be made.
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