Our Radio and TV shows have already sold us to Aliens

Our reception to Worldly affairs inside this city-forest is more through diffusion by land, even in this Internet Information Transfer age. So, we got to discuss only the other day about Stephen Hawking's recent warning about aliens, the likelihood of a meeting with them could result in the certainty of us getting wiped out. Instead of SETI, SETI@home we better STFU.

I am not going to discuss here whether Hawking is right or wrong or how much of it is right. Many around the web and in the blogosphere have done it. Read here, here, here, here and here for a start. But read Brin if you need to pick one.

A lively discussion about aliens eventually gets us to Drake Equation, SETI, METI, Fermi Paradox, radio silence, and even Eerie Silence, a new book by Paul Davies. There now is even a SETI@home where our idle PCs computing power can be used in sifting radio signals for locating one that matters, if it exists.

But I refrain to elaborate these lofty ideals and actions. What I am going to mention is something trivial. A mere technicality.

At least one of the intelligent folks present in such discussions would throw up the argument in the title of this note, to dismiss with contempt whatever plans we propose in the future to prevent, preempt or promote alien encounter.

The argument goes like, since the rerun of I Love Lucy sixty years back, and thenceforth, we have transmitted all our cultural 'garbage' out to space as radio waves. The aliens could have picked up any of these signals by now. What is the point of doing something about it now... right?

Wrong.

Well, at least if such an argument is promulgated without the caveats...

Our radio or TV program signals don't matter very much. At least highly unlikely that they would be picked. Reason?

David Brin, who assessed all the existing alien theories in a classic peer-reviewed Great Silence review paper (which I haven't read, but have read some follow-up popular accounts by him - here is one), has provided a neat example for this I Love Lucy versus Arecibo type signals (see table below for difference) and their detection:

go to a lake with a rock and a laser pointer. Now drop the rock into the pond, making ripples. Then aim the laser pointer at the other shore. Which wave front will be detected on the opposite side? That is “I love Lucy” vs a high-power, collimated, coherent transmission from Arecibo.  Sure, in theory, advanced scientists on the other shore, who are passionately eager and who know where to look, might detect the rock-ripples. But Jesus, have some scale and some sense, before you blithely declare that everybody on all shores will always detect all ripples!

In which case, How far away could we detect radio transmissions? For instance,

a TV picture having 5 MHz of bandwidth and 5 MWatts of power could not be detected beyond the solar system even with a radio telescope with 100 times the sensitivity of the 305 meter diameter Arecibo telescope.

That is for broadband signals, which includes most of our AM/FM radio and UHF TV signals (see the table below). For narrow band, it is more promising and that is what Arecibo - at 305m, it is the largest we have - is designed to detect as one of its exercises. Arecibo radio telescope could detect narrow band signals coming from thousands of light-years away from us. A small amateur radio telescope could of course detect narrow-band signals from within 100 light years, provided the transmitting power at the source is in terra-watts. The detailed calculation for all of this is in the SET@home FAQ. The formula comes down to

where R is the signal detection range in Light Years (if Rl is in LY). Some of the other terms are: EIRP is the effective power at the source, is the effective area of the receiver (radio telescope), snr is the signal to noise ratio.

The take home point is for maximum detection range R, the transmitting power, the area of the receiving antenna and the time bandwidth product (twp) should be high. The snr, the receiver bandwidth (Br), and thus transmit signal bandwidth (Bt), and the receiver system temperature (Tsys) to be as small as possible.

Here is the data by doing such a calculation for some of our radio sources. The receiver is assumed to be as big as the Arecibo (305 m dia, efficiency 50%); snr = 25, twp = Br * Tr = 1.

The orange circled numbers are what we are capable of by our radio and TV shows. For reference, 1 AU is the distance between us and our Sun, 5 AU is about the distance from Sun to Jupiter and the next nearest star is about 4.2 light years away.

In short, we don't need to think we have irreversibly sinned by blaring our radio into space. It is highly unlikely it will be heard beyond our galaxy, is at all.

A radio telescope as big as the Arecibo should be at least 0.3 light years within us to detect our radio ga ga.

That is, if by sheer Providence (I presume an event with such infinitesimal likelihood of occurrence could require such an un-human impetus) a radio telescope is in the right place and is turned in the right direction at the right time (remember, our radio programs are intermittent).

It goes without saying, that radio telescope would be christened John McClane.

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