SETI –
Search for Extra-Terrestrial Intelligence
SETI, the branch of the astronomy that is dedicated to the search of
extra-terrestrial intelligence, proposes 3 basic hypotheses:
- Life on Earth is the result of a natural evolution
that occurred through physical processes that are applicable to the
entire Universe;
- What happened on Earth could have
happened in many other places;
- The human intelligence is not the most ingenious
thing that the Universe can produce.
The Drake Equation
The equation that expresses the chance of finding extra-terrestrial
intelligence in our galaxy is called "equation of Drake" and it is
formulated in the following way:
N = Ns x Fs x Fp x Ne x Fl x Fi x Fc x L, where:
- Ns is the number of stars in our galaxy (200 billion);
- Fs is the percentage of solar type stars;
- Fp is the percentage of solar type stars
that are surrounded by planetary systems;
- Ne is the number of planets in an adequate position for harbouring life, inside each planetary system
(assuming that it requires liquid water);
- Fl is the percentage of these planets
where life actually emerges;
- Fi is the percentage of those planets
where intelligent life emerges;
- Fc is the percentage of intelligent life
that develops the capacity to communicate with other civilizations;
- L is the average life expectancy of such
a civilization, divided by the age of the galaxy.
The number of civilizations of our galaxy with which we could
communicate is estimated to be between nearly zero and hundreds of millions.
Passive Search
There are 4 ways through which a contact with an extra-terrestrial
civilization could be achieved:
- The aliens come to Earth and expose their
culture to us;
- We receive a signal proceeding from an
alien emission;
- We discover some trace or object left by
an alien civilization;
- We start to explore the galaxy and we
discover life somewhere else.
Hypothesis 1
The first hypothesis, whenever the idea is appreciated or not, hints the
UFO phenomena. The hypothesis that the UFOs are alien transportation vehicles
can’t be dismissed outright. However, it doesn’t seem that until today there
were collected conclusive evidences that such aliens actually visit the Earth.
Although there were reports about close encounters’ with UFO-type objects for
centuries, it was in 1947 that the modern exploration of this phenomenon began,
when the interest about the issue increased a lot. The vast majority of the
reports are about distant sights and it is explainable through conventional arguments.
For that motive, only a small percentage of those phenomena offer a high enough
quality, for the detail and consistence that characterize the reports and for
the reliability of their sources.
Sight of an UFO (UFO BBS
Graphics)
Hypothesis 2
The second hypothesis is identified with the form of search that has
prevailed on SETI during the last decades. The research has been essentially
concentrated in the segment of radio
waves, which travel at the speed
of light.
If a civilization wants to transmit a high quantity of information then
it shall use low frequencies (like the radio waves), in which each photon
carries a weak quantity of energy. That way it’s possible, using the same
quantity of energy, to emit a higher number of photons, each one carrying one "bit" (unit) of information.
On the other hand, at the lowest frequencies, the sky is extremely
bright, because every kind of objects – nebulae, radiogalaxies, quasars, pulsars, supernovae, etc – emits quite strongly at those
frequencies. To search for a signal proceeding from an alien civilization would
become so complicated as it is to try to take a picture of a star under the
daylight.
During the last years there has been an increasing interest over the
detection of alien signals emitted in optical frequencies (under the form of
laser), with a wavelength much shorter than the radio signals. This trend is
due to the fact that optical rays can be transmitted under very concentrated
forms and because, when compared with the radio waves, they are far less
exposed to dispersion and to the consequent degradation caused by the ionized
hydrogen present in the interstellar space.
The main challenges faced by this kind of research are the vastness of
the space that needs to be studied (given the huge quantity of stars capable of
harbouring life) and the ignorance about the frequency at which the
hypothetical aliens are emitting.
Looking for SETI laser
signals in the visible and infrared segments of the spectrum, alternative to
the search of radio signals (Dr. Stuart A Kingsley)
Hypothesis 3
The third hypothesis could be materialized through the discovery of an
artifact on an object of easy access for the humanity and subject to an almost
inexistent activity across a period of many million years.
In bodies like Europa, Io or even Mars, any extraterrestrial
trace could gave been easily erased or covered by the processes occurring
there. On the other hand, Callisto presents the perfect
conditions under which such an artifact would be kept almost untouched during several
million or billion years.
It’s probable that an extraterrestrial object found on Callisto would
unveil secrets about the civilization that would have left it there and,
eventually, it would reveal entirely new knowledge about the cosmos and the
reality.
Hypothesis 4
In order to search for intelligent life through the direct exploration
of the galaxy, it would be required propulsion systems far more advanced than
those that humanity already managed to produce.
The Voyager 1, one of the fastest probes that humanity sent to the
interstellar space, only will reach an equivalent distance to the closest star’s
in a time lapse of 63 570 years. It travels at only 7 / 100 000 times the speed
of light. The system that has been used until today is the chemical propulsion,
or in other words, the reaction between a combustible and an oxidizing agent.
One of the Voyager probes
(Calvin J. Hamilton)
Other possible systems are the electrical propulsion (whose results
haven’t been encouraging) and the plasma propulsion (acceleration
of ionized gas along a magnetic field).
A system that would allow the accomplishment of inter-stellar voyages
would be the antimatter propulsion,
which is very difficult to be materialized. This system is based in the fact
that matter and antimatter annihilate themselves when they make contact with
each other, producing an enormous quantity of energy (since that all the mass
present in the matter and the antimatter is converted into energy). In order to
reach a reasonable acceleration it would be necessary a considerable amount of
antimatter, which would have to be stored. These two assumptions almost make
impossible the materialization of the idea of such a propulsion system, because
until today only tiny quantities of antimatter were successfully produced by
humans and it hasn’t been conceived any technique that allows the storing of
antimatter avoiding the explosive phenomenon of the annihilation. A vehicle
fuelled by antimatter would reach Alpha Centauri (the closest star) in 21 years
and Epsilon Eridani (which along with Epsilon Indi and Tau Ceti is one the 3 solar-type stars that
are closest to the Earth) in 53 years.
Active Search
Along with the passive search for extra-terrestrial intelligence, there
is also an active search, which is done constantly and most of the times is not
voluntary. The radio and TV transmissions sent into space may reveal our
existence to a distant civilization.
Another kind of active search is the sending of images or messages on
board of probes like Voyager. The direct exploration of the galaxy by
terrestrial vehicles, which was already mentioned, can also be faced as a form
of active search (since it would reveal us to the aliens), but it was never
tried and it’s not foreseen that it will be in a close future.
Traffic in India: one of
the images sent on board of the Voyager probes (United Nations)
And If Nobody Answers?
If no contact is achieved, this may mean that at least of the following
statements shall be true:
- We are the most advanced civilization in
our sector of the Universe: therefore, it’s up to us to look for another
hypothetical civilizations;
- They try to contact us, but we couldn’t
yet decode their messages;
- The surrounding civilizations aren’t
interested in ours, maybe because we are still in a primitive stage;
- The aliens leave as alone, as members of
some natural reserve or as objects for study.
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