Aliens picking up human radio and TV: how might it really happen?

In the Carl Sagan novel Contact and the 1997 film of the book, aliens from Vega have picked up TV pictures of Hitler opening the 1936 Olympics, which is depicted as the first TV signal powerful enough to reach the stars. The idea of aliens picking up our TV signals and learning human customs and languages from soap operas and commercials is well known enough to be a comedy trope.

1) How plausible is the basic idea that aliens might pick up Earth's TV or radio broadcasts in real life, assuming sentient technological aliens exist within the distance to which Earth's electromagnetic signals have penetrated? (That distance is a maximum of 79 light-years, if you agree with Sagan's view that the 1936 broadcasts were the first ones strong enough.)

2) Which types of broadcasts (in the sense of which frequency of EM radiation and type of signal modulation, amplitude or frequency) would pass through the atmosphere? My understanding is that TV and FM radio are the only realistic possibilities, as longwave radio is too weak and shortwave radio is bounced back by the ionosphere.

3) How powerful does the transmission have to be? This piece by Brian Koberlein expresses the view that a signal from earth would need a power of 110 MW to be picked up at the nearest star, Proxima Centauri, in order to be received about as well as we pick up the signals from Voyager I. UHF TV stations, he says, are limited to about 5MW, so the whole idea is unlikely. Do you agree?

4) Has humanity largely stopped sending signals that can be picked up by aliens? According to Frank Drake, the astronomer behind the Drake Equation, since nowadays "most TV and radio programmes are transmitted from satellites that typically use only 75 watts and have aerials pointing toward Earth, rather than into space" it is no longer feasible for aliens to pick up our signals. So they'll get The Twilight Zone but not Stargate.

5) If they do get Earth TV, whose TV will it mostly be? I had assumed that the US output was dominant in the early part of the peak period for broadcasting power, as the signals that are most likely to be picked up are from the late 1950s to early 1980s, when America, as the richest large country, had the largest ownership of TV sets and the largest TV industry. In the comments to this Worldbuilding SE answer Jorge Aldo disagrees. I have not been able to find good data about the historical spread of TV ownership and/or transmitter power across the world, so I might be wrong. And the answer might change if we look at FM radio rather than just TV. It is certain that latterly the amount of broadcasting in English has been equalled or surpassed by the amount in other languages such as Spanish and then Chinese. But would this be enough to counteract the effect in point (4)?

6) What other factors have I missed that might make aliens seeing our TV likely or unlikely?

posted over 9 years ago

Lostinfrance‭

1 reputation 4 0 0 0