or antimatter-matter annihilation as a
power source might produce such rays.
But standard SETI strategy does not
embrace such “speculative” scenarios.
“We are very conservative at SETI,”
Drake says. “We assume in our searches
the existence of only things we ourselves
have and know how to make.”
0 Digital Predigital
Digital switch when sutro tower in san
Francisco converted to digital broadcasts in
2009, its radiated power dropped by more than
half —a sobering sign for setI researchers.
no human-produced light could have
been detected at interstellar distances.
“In the ’50s, if you wanted a bright
search light, you’d go to GE,” Horowitz
says; the brightest light came from bulbs.
“We couldn’t have predicted the laser.”
Today, powerful lasers can create light
pulses that would outshine their nearest
stars for a billionth of a second. Astrono-
mers observing a momentary burst of
extra light from a distant star could infer
that it came from ET, since most light
from natural sources lasts much longer.
Though such searches are ongoing,
Horowitz says optical SETI programs
should really look at infrared frequencies, just lower than those of visible light.
“Stars are darker in the infrared and
lasers are brighter and the smog goes
away,” Horowitz says. Infrared allows
astronomers to see into the galactic center, where dust scatters visible light.
For the most part, infrared channels
have been off-limits, but technologies
from other fields may soon make these
searches possible. The communications
industry, for example, has developed
detectors sensitive enough to spot just a
few photons of high-frequency infrared
light. And solid-state photodetectors are
sensitive at all infrared wavelengths.
Other scientists, and SETI enthusiasts,
have proposed hunting in different electromagnetic realms — like gamma rays.
Spacecraft that rely on nuclear fusion
Detectable and recognizable
There are people, however, who try to
imagine what life could be like thousands
of years from now. They’re called science
fiction writers, and in their worlds a roving researcher can travel the galaxy, interstellar civilizations can chitchat via music
and light shows and, yes, antimatter-matter annihilation can fuel the Enterprise.
SETI researchers, some say, should
also contemplate what technologies
supersmart aliens might possess and seek
out the corresponding signals. In a paper
posted at arXiv.org in 2008, John Learned
of the University of Hawaii at Manoa suggested that ET could be sending beams of
neutrinos Earth’s way. These elementary
particles travel close to the speed of light
and pass through ordinary matter undisturbed. Energy requirements for such a
beam make that scenario seem implausible, but not necessarily impossible.
Detectors currently under construc-
tion—such as IceCube at the South
Pole — could spot unexpected stray neu-
trinos. If a few with the same energy came
from the same direction, astronomers
would know something screwy was up.
Unheard channels major radio searches for extraterrestrial intelligence conducted in the
past 50 years have covered just a small portion of possible radio frequencies, mostly focusing on
the range between 1 and 3 gigahertz. ongoing and future searches conducted with the Allen telescope Array will cover more channels by simultaneously searching the 0.5 to 11 gigahertz range.
researchers also hope to scan more sky, and improve sensitivity, to search deeper into space.
SETI frequency coverage so far
fraction of sky negligible
SETI@HOME II (ALFA)
Fraction of sky covered (%)
source: dAn werthImer/uc berkeley
bottom: t. dubÉ