I’m not sure that Bob was after SETI in particular; Tyson’s article was about the electromagnetic spectrum generally. But you raise some interesting issues.
[quote author=“jimmiekeyes”]SETI is assumed by many of those who have heard of it to be looking for messages from outer space. In point of fact it is looking for any electromagnetic emissions of the kind you mention. The sort we are pumping out in huge quantities with our radio and television broadcasts.
A discovery of that sort is far more likely than a message aimed at us. The time travel restriction due to the distances involved makes the prospect of a message quite dim.
Yes, the problem with this is that our TV broadcasts are comparatively weak. I recall going to a talk many years ago with someone in the SETI program who said that basically our radio telescopes could only hope to pick up equivalent TV/radio traffic from very nearby stars ... (and even then it would be overwhelmed by our own TV/radio “noise” so it would be impossible to hear, unless we could build a radio telescope on the far side of the moon).
So I think our present SETI aim is to assume that the distant civilizations are beaming the messages in our precise direction with some sort of high-powered focused signal, like lasers or focused radio beams.
But is it really so likely that an alien civilization would beam out focused messages towards us? Remember, we have to assume they would be far enough away that our TV/radio traffic would have dissipated before reaching them ... or wouldn’t have had time to reach them at all.
Basically we have to assume they are sending out these beacons in all directions in the hopes of getting a response back.
Doesn’t sound too likely to me ...