Is it possible...

[spurius]

Is it possible to detect transmission signals from several light years away? Given how faint the Voyagers signals must be, I wonder about the possibility of detecting alien signals, or aliens detecting signals from Earth or Mars.

[emadmoussa]

And that's the whole reason SETI was established

[spurius]

And that's the whole reason SETI was established

I was thinkin more about the detecting of life rather than of what that life might be. I also doubt hairy snowmen would be capable of sending any form of signal across space. But thats the fun of astrobiology, you can theorise literally any form of life and nobody can conclusively prove that such a life form doesnt exist somewhere out there. I mean look how strange sea life can get, some really weird stuff down there.

[Knight of Clear Skies]

This Ask xkcd column claims our TV signals would only be detectable from a few light years away. Some radar systems - especially those used in the Cold War - were more powerful, but the most powerful transmitter of all is the Arecibo dish. In theory there is nothing to stop us building an even bigger one.

[x6gas]

We've been broadcasting for 100 years so man-made radio signals are out to 100 light years away.  Need a pretty sensitive radio to pick it up though!

[Kropster]

If the aliens only have DAB radios, then there is no chance!

[x6gas]

A bit of high school maths:  We have broadcast radio fairly indiscriminately at powers as high as 500kW (500,000 watts).  By my reckoning at 100 light years away that signal strength would have dropped to around 5 thousandths of a yoctowatt - that 5 x 10^ -27 of a watt, assuming perfect transmission out of the atmosphere...

Arecibo can pump out 20 terawatts so a signal from that would be about 20 zeptowatts at 100 light-years.