MEASURED EDGE TO EDGE,
the universe as we know it stretches some 93 billion light-
years across. That unfathomable expanse contains 2 trillion
galaxies, each shining with millions of stars and dotted with
more planets than you can imagine. Given all that real estate,
it seems unlikely we’re alone. Yet in all of human history,
we’ve found nothing to suggest otherwise.
Scientists who have spent their careers searching for any
sign of an otherworldly civilization concede it’s possible
we’ve got the cosmos to ourselves. Still, they highly doubt
that’s the case. “To say this is the only place where there’s
any intelligence is hubris of a very high order,” says astro-
physicist Seth Shostak of the SETI Institute. (The acronym
stands for “search for extraterrestrial intelligence.”) Statisti-
cally speaking, there are too many locations where life could
thrive for humanity to be an anomaly.
Astronomer Frank Drake suggested as much in 1961.
He posited that the number of technologically advanced
civilizations in our galaxy would be the product of seven
variables. They include the number of stars throughout the
Milky Way, how many of those bright, burning gas balls illu-
minate planets, and what percentage of those worlds could
support life. His eponymous equation was a thought exer-
cise meant to start a discussion among colleagues, but it has
helped frame the topic in the years since he wrote it.
Many of Drake’s variables are speculative, making his
math little more than conjecture. But astronomers now know
for certain that exoplanets, many of which could harbor life,
form throughout the Milky Way like dust bunnies under your
couch. In the past two decades, researchers have confirmed
the existence of more than 4,000 planets in our galaxy, a
finding that suggests the cosmos all but brims with them.
Astrophysicist Christopher Conselice of the University of
Nottingham puts the number at 100 quintillion. That’s a one
with 20 zeros. Some think there may be far more than that.
Scientists debate just how many of those planets could host
life, but a common estimate suggests 20 percent of the 250
billion or so stars in the Milky Way may shine on rocky worlds
temperate enough to allow liquid water. Do the math, and
you’re looking at tens of billions of Goldilocks planets in our
neighborhood alone where the gears of life could start grinding.
Could does not mean did, of course. Yet many astrono-
mers say the complex biochemistry that created intelligent
beings on Earth surely occurred more than once in 13.7 bil-
lion years, given the tens of billions of opportunities to do so
in just one galaxy out of trillions. To suggest otherwise de-
fies physics and the mediocrity principle, which states that,
from a probability standpoint, our solar system is more likely
a common event than a rare beast. “I think the universe is
teeming with life,” says Sara Seager, an astrophysicist and
planetary scientist at Massachusetts Institute of Technology.
So where is everybody?
Italian physicist Enrico Fermi posed that question in 1950,
and many scientists have riffed on it. They argue that there
must be planets older than Earth, and that at least one so-
ciety of extraterrestrial beings would be advanced enough
to possess technology that would alert us to its presence—
which is what astronomers mean by “intelligent life.”
That assumes anyone beyond our solar system wants to
make contact. Alien beings might lay low to avoid attracting
interstellar bullies. They could lack the technology to greet
us, or we may not yet have the means to hear them calling
(or understand the message). Anyone out there could be so
far away that we haven’t received their signal. It’s possible
that this big blue marble is an astronomical backwater no
one else finds interesting enough to bother checking out. It’s
also conceivable that other civilizations have already come
and gone, wiped out by some cosmic event, catastrophes of
their own making, or simply the passing of time. In that case,
perhaps we’ll one day find evidence of their existence.
But many astronomers believe there is a far more logical
reason we haven’t found anyone: Space is too spacious. For
all our searching, we haven’t looked much beyond our own
neighborhood. Retired astronomer Jill Tarter, a 40-year
veteran of the search for extraterrestrial intelligence and
emeritus chair for research at the SETI Institute, likes to use
an analogy: If you imagine all the places where we could look
for life and all the ways we could do so as the world’s oceans,
we’ve examined just one cup of water. Others in her field are
more generous; they say we’ve filled a small swimming pool.
It is about to get a bit deeper. On a high, arid plain about
400 miles northeast of Cape Town, South Africa, an array
of 64 white antenna dishes called MeerKAT peers deep into
space. That kind of research generates staggering quantities
of data. Beginning this fall, a supercomputer will begin an-
alyzing it for even the faintest electronic signal suggesting
that someone’s out there. Astronomers hope to survey 1 mil-
lion stars within five years, about 1,000 times more than any
project before it. “There’s some chance we’re going to see a
signal, that we’re going to make a detection,” says University
of California at Berkeley astronomer Andrew Siemion, who
leads the project. He and his colleagues may yet find the evi-
dence that they’re sure is out there, waiting to be discovered.BY ROB VERGERFALL 2019P. 4 3