In the 1960s, American radio astronomer Frank Drake (1930 ~) devised an equation that predicts the number of civilizations that could be intercommunicated within the galaxy.
Each factor of the equation cannot be estimated almost accurately, so when calculated, the result varies greatly from less than 1 to millions, depending on the estimate.
Nevertheless, it is not unreasonable to think that there are at least a few such civilizations in the galaxy.
To calculate the Drake equation, various factors (such as the percentage of stars with planets) need to be estimated.
Next, multiply all the factors.
In the example below, we are using only rather optimistic estimates. (There are also some guesswork).
Percentage of stellar births
A reasonable number of new stars born in the galaxy is 50 per year.
A star with a planet
Perhaps half of the new stars will have planets.
The average number of dwelling planets maybe only 0.4 per planetary system.
Planet with life
90% of the inhabitable planets will have life.
About 10% of newly uttered life may acquire intelligence.
Of intellectual life, at most 10% will develop interstellar communication technology.
Life of civilization
The average lifespan of civilization will be about 10,000 years.
Using the above estimates, the galactic system has an alien civilization that we can communicate with, theoretically about 50 × 0.5 × 0.4 × 0.9 × 0.1 × 0.1 × 10,000 = 900. Expected to be. However, some estimates may be off.