We have only been sending radio signals out into space for something like 80 years, and we have only been looking for extraterrestrial signals for a good few years less. The way we’re going with planetary destruction, the threat of nuclear war, the threat of lethal pandemics – I give us maybe another 120 years if we’re lucky. So if we take this 200-year span as also the time over which we are able to detect alien signals – I think you can see the problem looming.
If the aliens follow a similar technological timescale with all the accompanying possibilities for extinction, plus adding a few like asteroid impact or loss of planetary magnetic field, then you might come up with a similar timescale for transmitting/detecting signals. Let’s be even more generous and give the aliens a 500-year span over which they can emit/detect signals.
Now if the aliens are to be aware of our existence, or us of theirs, then our emitting/detecting time periods obviously have to overlap. Also, if these aliens are say 10,000 light years away, then their emitting/detecting capability would have had to have been active 10,000 years ago if we were to pick their signals up. You should now be able to see that however you cut it, the overlap time is pretty much going to be zero.
What does the famous Drake Equation have to say about this? Well if you look at the Drake Equation the only thing he includes (time-wise for signal production/detection) is the length of time (in years) that the aliens transmit for. In other words he assumes that there is someone out there listening ALL THE TIME, which clearly there isn’t. Combine the Drake Equation with the Overlap Time and you get something pretty indistinguishable from zero. And that explains Fermi’s Paradox.
And what’s the biggest thing I left out in the above? You also have to be pointing your detector in the right direction during the overlap time as well. Makes the whole thing even less likely!
