Now
supposing there are other civilizations in the Galaxy, can we detect them by
their Technosignatures? If they are of our technological level, we can start by
imagining what unusual feature about our own planet might reveal our presence
to a distant observer. One is the nightglow seen from space. The side of the
earth facing away from the Sun is illuminated by millions of lights. But this
is very faint and our instruments would not be able to detect it from a
distance in light years. So this is not something that is very tell tale with
our current set of instruments.
Industrial
pollution in the atmosphere is a giveaway and is a techno signature. In this
CFC’s or Chlorofluorocarbons are not produced by any natural process and hence
can be detected if they are present. Our own James Webb space Telescope put
into orbit last year has the capacity to do that if they are present in any
other planets.
Now,
there may be civilizations that may be millions of years ahead of us and
therefore have far more advanced instruments than us and they may allow them to
get over this problem of finding as to which planet is housing intelligent
life. But, then again, if the speed of light is insurmountable and is a barrier
that cannot be breached, then however advanced the civilization maybe, they
cannot pierce through the barrier and therefore space travel seeking
intelligent beings may technically prove to be impossible. Our movies fancifully
show aircraft cruising over the speed of light.
If anything can travel at the speed of light
or over it, then Einstein’s mathematical deductions which hitherto stand unquestioned
would fall apart. As per Einstein’s deductions, the mass of an object
travelling at the speed of its light becomes infinite. Similarly it would
shrink infinitely in the direction of its travel. With these two parameters in
mind it is an impossibility to travel at the speed of light.
Accelerating
the spacecraft to the speed of light is one thing, but then you have to deal
with infinite mass and infinite shrinkage which is much more difficult than
achieving the speed. Apart from that, at the speed of light time too stands
still without any movement. Unless Einstein’s mathematical deductions are
proved wrong, there is no way any civilization; however advanced it may be would
be able to travel at the speed of light. If that is the case then none of the
civilizations of one star can visit another star despite being highly advanced.
Despite
that, they can certainly communicate with each other through radio waves. But
then, space is too vast. For that both the civilizations: the transmitter and
the receiver have to be at least as advanced as us. Now communicating through
radio waves is possible only for the nearer planets say 15 light years from
each other. Otherwise the communication takes too long to get received.
There
are 2000 stars within a distance of up to 50 light years. We have so far
discovered 34 exoplanets (planets outside our solar system) of which 11 are
considered to be in the inhabitable zone. Again, of these only 3 planets seem
good for life.
They
are
1)
Gilsec 832c orbiting the star Gilsec 832 with a mass of over 5 times that of
earth and an average surface temperature of -22 degrees C, lying 16 light years
away from us.
2)
Gilsec 667Cc orbiting the star Gilsec 667 with about 4 times the earth’s mass with
a temperature of 29 degrees C at a distance of 22 light years.
3)
GJ180b orbiting the star GJ180 with about 2 times the earths mass with a temperature of 39 degrees C, and is 38
light years away from us.
If
any civilization manages to accelerate their spacecraft up to the speed of
light, they require an enormous amount of thrust to do so. However efficient
their fuel systems are, still there would be some loss of energy and this is
the thing that is detectable. The spacecraft would generate radiation ranging
from radio waves all the way up to gamma rays which can be detected at long
distances. The problem is, such radiation is also emitted from natural sources.
So to decipher it as intelligence made we have to look for orderly bursts
unlike natural radiation.
The
writer Erich Van Daniken in his book “The Chariots of the Gods” postulates that
aliens had been visiting us throughout earth’s history and are also helping us
to shape the history. However, he quotes several examples to buttress his theory
which do not seem plausible and do not offer any such proof as he claims. I
remember reading his books in fascination when I was at college, but even then
it did not strike me as plausible.
Well
the idea that aliens may have visited us during the millions of years of the
evolution of life may well be likely, but what visited us would have been robot
probes rather than aliens themselves. Today we explore the solar system the
same way. The advantage of robot probes is that they can travel endlessly for
thousands of years while the living beings cannot do that. The probes may
travel at less than the speed of light and yet can explore many star systems
given the time. Of course their communication back to their home planets would
take an immense amount of time so the viability of such probes is limited by
the distance. We possibly cannot send a probe to the stars and wait for 100
years for them to communicate back.
A
physicist Von Neumann suggested the idea of probes when they reach a certain
planet can replicate themselves using the material available there. That would
multiply their number continuously enabling them to explore more area of space.
Such probes are known as Von Neumann probes. Of course that is only theory so
far.
Based
on this theory Robert Freitas and Engineer published a paper study of such a
probes viability in 1980. The result is very complex and it required many sub
systems. Considering all that Freitas estimated that the weight of such probe
to be 10 million tons at the minimum and it would take 1000 years to fabricate
it. Anyways what would be the thrust needed to put that into space? So it is just
a purely imaginary concept for us. However, the same cannot be said for a
civilization which is far ahead of us in technology. They may be able to
fabricate such probes far faster and would be capable of giving it a thrust to
fly to the stars.
That
being the case, it is probable that such a probe has visited earth at some point
of time and not necessarily during the 300,000 years our species came into
being. Even if one such probe landed on the earth in the millions of years when
life evolved and became inert here after replicating other probes it would be
impossible for us to even know the existence of that mother probe because it
would be inert now.
Even
if there is a small alien robotic probe in our solar system today, it would be
impossible for us to detect unless it sends us radio signals. Otherwise
considering its minuscule size its discovery can only made by chance rather than
methodical research.
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