Fermi asked the question, referring to the lack of contact
from other, inter-galactic civilizations. He asked “If there are intelligent
people out there, where are they? Why have they not made contact with us?”
Of course, the question ignores numerous factors, such as
the time it would require to travel to us, if that is what he expected them to
do. A spacecraft, traveling at 20% of the speed of light, a speed well in
excess of what we, as a supposedly advanced civilization, could hope to achieve
with our present state of knowledge, would require more than six hundred years
from a star system only 120 light years away, given the time required to
accelerate to that speed and then to slow down on arrival. And that would imply
that such a civilization would have a valid reason to visit us, a civilization
that only managed to start using radio more than 450 years after they would
have had to leave home!
Perhaps the answer lies in some simple calculations.
Assume that humans on Earth have been able to send and
receive radio messages for about 120 years. That’s not long, considering our
2 000 000 year development as sentient beings, the Earth’s
3 600 000 000 year existence, and the
13 600 000 000 year life of the Universe. Assume that other
civilizations have followed more or less the same path. That seems to be not
unreasonable.
Now consider that radio waves travel at about the speed of
light. That means that a radio message, a flashing light signal or other
similar form of communication that was sent by a civilization somewhere in the
Universe, let’s say 120 light years from Earth, on the day they first developed
radio communication 120 years ago, would reach Earth today. To receive that
message, we would have to aim a large radio antenna (large, in order to collect
the faint signal sent by an early-stage technology) at exactly that point in
the heavens that the transmitter would have occupied, adjusted for their
movement and ours (because all celestial objects are in relative motion, at
high speeds, so an antenna aimed at a star system we see in the sky today would
miss the actual point it now is by many millions of miles if we were to reply
immediately) in order to receive the signal. If our aim were even one degree
off, there is a high probability that we would not receive the message. And, to
top it all, we would have to be ready to receive the message at exactly the
time it passed us. One minute too early or too late, and we would miss the
signal, because it comes, not as a long beam, but as a single block.
If our radio antenna is able to scan an area of one degree
by one degree at a distance of 120 light years, it would have to scan 42 253
such areas! If such a scan requires one day each, to be meaningful at the
lowest level, about 365 blocks per year, the scan would require about 190
years! Alternatively, we would need about two hundred antennae continuously working
for a full year to receive the signal from our celestial neighbors, to allow us
to have a reasonable chance to receive the signal.
Of course, that neighbor might be further than 120 light
years away, say 200 light years, in which case we would have to wait another
eighty years to receive that message. They might have developed earlier, or
more quickly, than we did. If so, two hundred years ago, they might have tried
to make contact with us by radio, perhaps for fifty years, and then given up
hope that there were other sentient beings out there, and reverted to other
methods of communication, such as using the opportunities offered by quantum
entanglement. The radio signals would have zipped on by us, leaving us ignorant
of our neighbors. On the other hand, their development might have lagged ours,
leaving us to wait another hundred years, or a thousand, to hear from them. A
thousand years is an insignificant fraction of the period of existence of
sentient life on Earth.
It is an enormous arrogance on our part to base our belief
that there are no other sentient beings in the Universe entirely on our own
example. We are, in effect, demanding that life on another planet developed in
the same timescale as it did on ours! The factors that might influence when we
receive a radio signal from another civilization are legion – their distance,
the date of origin of the other civilizations, their rate of development to
create radio signals, our ability and preparedness to receive a radio signal as
it zips past our location at the speed of light, even the question of whether
they use radio as a means of communication. While looking for such signals is a
whole lot better than doing nothing, it is very far short of a valid test for
the non-existence of sentient beings out in the Universe. Asking that another
civilization should have developed both long-distance spaceflight capability,
and then decided to look for intelligent life in our isolated nook of the
Universe, at all and long enough ago to have reached us within the tiny portion
of our existence when we would have the scientific development and religious
permission to receive and understand such a visit is even more preposterous.
On any basis of science and logic, the answer to Fermi’s
question, “Where are they?” is “Wait and see.”
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