Bryan Caplan desperately wants there to be more to life than arguing with Robin Hanson over population growth, so he believes in the existence of aliens (Martian, not Hispanic) despite serious evidence against it. Part of Bryan’s case was this claim:
Our powers of detection are bad enough to overlook hundreds of billions of planets. Detecting intelligent life will be vastly harder than detecting planets – maybe prohibitively harder.
That sounded like a bogus claim to me, so in the comments I asked if anyone could justify it. One guy said:
Non-directional electromagnetic communications (radio, TV, etc) follows an inverse cube law (I think, though it might be inverse square) meaning we can’t detect anything at what we would consider realistic power levels from more than a light year or so away. So, in order for us to detect intelligent life, they would either have to come here or send a coherent beam communication directly at us, one of 100 billion stars in the galaxy. Furthermore, it’s entirely possible that their communication isn’t even something we would recognize as a signal, like a stream of neutrinos using muon neutrinos as 0 and tau neutrinos as 1 the way we use high/low current for digital communications today. Not to mention that they might not be as outgoing as we are.
So detecting extrasolar life is hard because a.) they have to be intentionally trying to talk to us (among the 100 billion other possible stars) and b.) we would have to recognize that they are trying to do so.
We wouldn’t be able to detect ourselves from any of the planets we’ve found so far.
Does that sound right to people? Haven’t we been deliberately sending out probes and broadcasting messages for decades, with the express purpose of demonstrating our intelligence in things that would (we hope) be universally recognizable? Did all of the scientists working on those projects fail to consider that a guy could blow up their efforts in 5 seconds in an EconLog comment?