The idea that "Earth has a special place in the Universe." lost its validity after Copernicus. With scientific discoveries and developing technology, this idea has left its place in our current understanding of space. Is there life outside of Earth in the Universe? Astronomers are looking for answers to this question.
Hydrogen is the Universe's simplest atomic structure that we are aware of. A neutral hydrogen atom has only one electron. This electron's spin-flip motion results in a frequency of 1420 MHz. 1/sec is equivalent to 1 Hz. If we divide the speed of light by this frequency, we get a wavelength of 21 cm.
Since the message at a wavelength of 21 cm could be distinguished from random interstellar noise, an intelligent society would be aware that they should get in touch with us on this frequency if they wish to communicate. In addition, radiation with a wavelength of 21, which corresponds to the microwave region in the electromagnetic spectrum, can continue without undergoing any significant deterioration, despite the gas and dust on its path. As a matter of fact microwaves from 1 GHz to 10 GHz are particularly good for extraterrestrial intelligence studies.
SETI (Search for Extra-Terrestrial Intelligence) is a well-reputed research group for the extraterrestrial life search. SETI records and analyzes the signal with the frequency range between 1 and 10 GHz for signs of extraterrestrial intelligence. The Drake Equation, which states that there is a chance even in the Milky Way Galaxy, can be used to calculate the likelihood of real life existing somewhere other than Earth in the Milky Way. Let’s have look at the Drake equation:
N = R*x fpx nex flx fix fcx L.
Here,
R* = The rate of formation of stars suitable for the development of intelligent life (number per year).
fp= The fraction of those stars with planetary systems.
ne= The number of planets, per solar system, with an environment suitable for life.
fl= The fraction of suitable planets on which life actually appears.
fi = The fraction of life bearing planets on which intelligent life emerges.
fc= The fraction of civilizations that develop a technology that produces detectable signs of their existence.
L = The average length of time such civilizations produce such signs (years).
N= The number of civilizations in the Milky Way galaxy whose electromagnetic emissions are detectable.
When the minimum and maximum numbers are entered into this equation, N equals a number between 20 and 50.000.000, respectively. As a result, the probability of Earth being the only planet with an intelligent life force is very low.
Even if our civilization gets destroyed, we have messages that will be on the way to interstellar intelligent species that are also waiting for it. Take, for instance, the gold plaque on Voyager 1. This plaque has messages engraved on it, as well as audio and video files. Besides that, the binary message sent by the Arecibo telescope contains information such as the position of our planet, our living form, our number system, and our DNA form. The Pioneer plaque also contains a message for extraterrestrial intelligence. All of this work was done with the understanding that we are not alone. As Carl Sagan said; “The Universe is a pretty big place. If it's just us, it seems like an awful waste of space.”
Resources;
https://academic.oup.com/mnras/article/402/4/2617/1747855?login=false
https://www.seti.org/drake-equation-index
https://voyager.jpl.nasa.gov/golden-record/golden-record-cover/