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Here is a good analysis of the technical matters involved with extra terrestrial communicationhttp://home.fnal.gov/~carrigan/SETI/SETI%20Hacker_AC-03-IAA-8-3-06.doc
'Journey into space; the Red Planet' by Charles Chiltern. Andrew Faulds played Jet Morgan, the leader of the crew.I was allowed to stay up for that one!
next step further out is zero
Can't see it. My watch is a tiny tiny fleapower transmitter at 32.768 KHz barely detectable with a receiver right next to it. Is it going to be stimulating electrons in a bit of copper 1000 lt years away? Can't see it somehow. What if I put it 100 metres under water (assuming it survives. Would it still be stimulating electrons at a great distance. Of course not. There MUST be a limit. If want you to talk photons then they are speading out covering a greater and greater area the further they travel so at some point the density beacome so low that they miss the bit of copper by millions of km.
Some figures.....A broadcast FM receiver might work down to 10E-15 Watts (including a bit of aerial gain).. A tiny signal. A transmitter might be 100 kW.ERP (Effective power with transmit aerial gain).. 10E5 Watts. So the signal path loss maximum is 10E20 times (diff between power transmitted and that received) . A very big number. There are on-line calculators to work at the path loss at different frequencies.. At 100 MHz 10E20 (200 dB) occurs at a distance of 2.5 Million Km..
===So, if an extraterrestrial civilization 100 light years away from us would send all the signal's power towards our solar system, we would have plenty of power to perceive it...===Eh? Only if they had transmitter powers of many Suns.
It is purely based on spreading out of the RF....Square law basically.So if 100 kW will reach 2.5 km... to reach 1 ltr year which is 4,000,000 times further then you need 4 million squared times more power. 16 x 10E12 x 10E5 Watts.. = 16 x 10E17 Watts. or 1,600,000,000. GW. I think the max ouput of all the UKs power stations is about 78 GW. All in all many times more than all the World's power stsions.
collimated ??We are talking about low frequencies here...very long wavelengths...not light. It will always be a diverging beam even if you had parabolic dishes of enormous size. If it is diverging then square law applies.
Home computers will always be used inefficiently and left idle for, at least, minutes on end, even if they are not left on overnight. Productive screensavers will always be justified for use in such circumstances.In addition to the 'long shot' of discovering alien intelligence, there is the other possibility of discovering other regular signals from, as yet, unknown and unexplained, natural phenomena. Seti can reveal these, too.There are many other things to have a more justifiable rant about. Give nerds a break.
Diffraction will always occur as waves go through an aperture. For a Maser, Laser or whatever, the 'divergence' of the beam will be affected by how wide it is. To get a Maser with low divergence, you would need a large diameter, in wavelengths. I'm not sure that a maser is of any benefit for a transmitting system; it is easy to produce high powers levels of coherent microwaves with other means, these days and Masers are hideously inefficient - as are lasers.Maser amplification may still be good value for low noise receivers (with noise temperatures of 10K).A large dish - many km across would give gain / directivity but we all (?) agree that there is divergence, whatever you do. Signal to noise ratio is the issue. You can get some information out of any signal as long as you are prepared to wait, using a narrow enough bandwidth. The receiver noise performance is also very relevant.