Frankly, I'm very concerned about how much energy Earth is emitting into space. I think Hawking wrote about that subject too. Some things to consider:
-The nearest potentially habitable planet in another star system is
Tau Ceti e at 11.905 light years away.
-Even if they turned a light on 12 years ago, it would have to be very bright and pointing directly at Earth for us to see it.
-Even if they did turn on a light, it was sufficiently bright, and we happened to be looking directly at it, would we be able to distinguish that artificial light source from the power of the Tau Ceti sun?
-There are a countless number of potential planets out there that support life. When you put it into context of light years versus how long said light was being emitted, our visibility is quite limited unless the civilization is very old.
-Even if we received a signal for a planet, it's easy to forget how alien the signal would be. Remember everything on Earth comes from a common ancestory--this is why humans can form relationships with most mammals, for example. Even though modern man has removed himself from Earth's nature as much as possible, we all live a similar existence. That creates an understanding on a deep level. That's even more true of the different, isolated human cultures. For example, we can learn each other's words by referencing something we both know, like a bird. Now consider this as it relates to radios, telescopes, and other forms of wireless communication. Even if we saw their communications, would we know we were even looking at it? Case in point, and this a far-out-there-theory, what if the "
cosmic microwave background" noise isn't from the Big Bang at all but is, in fact, an encrypted or alien message that's constantly being broadcasted? How would we know the difference? How could we even begin to unravel it because it is so alien?
-Just look at humanity now: it's commuting less and less by analog means (you know, talking and listening to each other) and more by digital means. This happened over the period of just a few decades--what happens in 100 years? 1000?
-Our means of bursting transmissions (which end up in space) is inefficient. A species with far more years under their belt likely found a more efficient means to communicate, like through quantum entanglement, so there is no longer wasteful communication into space.
-Why does a species have to live on a planet at all? It is theoretically possible to build a space ship that is 100% sustainable, mining asteroids for raw materials. It's also possible to breed a species for living in a zero gravity environment.
-If there were aliens mining asteroids in the asteroid belt, would we even know?
-Even if a message were sent directly at us from 10+ light years away, would the message be clear by the time it arrived? Parts of it get lost due to hitting mass, parts of it get bent and misdirected because of the effect of mass on light, some of it gets jammed by background noise (e.g. a pulsor), and the list goes on.
I have every right to be a skeptic; we all do. To be certain of anything in this universe is to be ignorant of everything we don't know and understand.