The answer to this question was provided by the Fermi paradox. Enrico Fermi was an Italian physicist who worked on the Manhattan Project that developed the first nuclear weapons during World War II. He later became a professor at the University of Chicago, where he and his colleagues came up with a theory about alien life forms in our galaxy. If we ever detect signs of extraterrestrial life, they theorized, we might find out by "listening" for radio waves being transmitted from their home planet.
If the signals are being broadcast in all directions equally, then perhaps they are just emanating from a single civilization. But if the signal is loudest only in one direction, it would imply that there was someone else out there trying to communicate with us.
Fermi's colleagues were excited about this idea and started building radio telescopes to search for alien broadcasts. Fermi himself was much more skeptical. The paradox he articulated goes something like this: if there is intelligent life out there, why haven't humans detected any evidence of communication?
Traveling even at the speed of light which is one of the fastest objects we know is a radio signal from another civilization would take hundreds of years to reach us. So if we received a message, that would mean it had to be coming from a star system at least several hundred light-years away.
We now know that stars much farther than several hundred light-years away exist, including some stars with as many as one trillion planets. This means there are as many as 10 civilizations out there who might like to chat or might already be doing so and we simply can't hear them. We're not even sure how likely we are to detect an alien signal; astrophysicist Michael Garrett estimates that our closest intelligent neighbors may live as far 1,500 light-years away. But with the considerable amount of time it would take for a message to reach us, they might not be thinking about us anymore. Which is reassuring if you're looking for intelligent life but sobering if you're part of that civilization trying to get in touch.
Of course, this logic assumes that these aliens are using radio signals or similar technologies at all. Perhaps they're on their way here on spaceships like the ones we've seen in countless movies and TV shows (and which Fermi also considered unlikely, due to the enormous distances involved). Or perhaps they communicate via some other means, such as through artificial beams of light or gravitational waves , both of which our current technology might make it to detect one day. It's even possible that they're not out there at all, though given the number of galaxies in the universe , it's difficult to accept this alternative.
We don't know the answer, and there are very good reasons why we haven't heard from anyone yet. But until we do, this question will live on in the back of our minds—just like Fermi's paradox itself.
You can start by reading Fermi's original paper or watching a short presentation on YouTube.
Here are some other interesting reads:
I like your articles on science and scientists. Fermi was a great scientist. I now live in Kolkata (Calcutta), where the famous physicist Satyendranath Bose (S. N. Bose) lived. Fermi visited Kolkata, and Bose and Fermi were incidentally seated in different rows -- their scientist friends cracked jokes that Fermions and Bosons follow different physical rules!
I was a kid when S. N. Bose expired.