Why are we not already receiving alien transmissions?

[MeteorWayne]

I also find that highly unlikely. About 99% of earth's transmissions are (relatively) low intensity omnidirectional broadcasts. They would fall below the noise level before reaching even the closest star, in fact most wouldn't even make it to the transNeptunian scattered disk objects. A few high power focused beams (such as planetary radar) are sent out, but are not aimed at any stellar system, don't last very long, and would still only exceed the noise level for a few seconds anywhere else within 20 ly, and would be swamped beyond that.

 

[a_lost_packet_]

Well no, we shouldn't expect to be "pinged", but we musn't underestimate "leakage" either.. 1-70 ly's out from earth, the brightest radio object in the sky is,... well,.. Earth!

Are you sure about that? I was pretty certain the sun put out quite a bit more radio waves than the earth, and I thought that jupiter put out much more radio waves than the earth.

Look at it this way:

"Radio" (EM radiation) is the means of trade of the Universe. It's it's calling card of just about everything, the primary means of information exchange, the "Big Kahuna." If you're anything of any importance in the Universe, you're an emitter. Our Galaxy is like a huge, unregulated internet made up of all WI-Fi transmitters with absolutely nothing like the FCC to keep frequencies clear and neat. Instead of things getting sent off to specific locations in nice, neat, bundled up packages, the emissions sort of go everywhere, all which-way. A few specific types of transmitters tend to produce more directional signals. But, in the end, most of the traffic in the Galaxy is like picking up a huge party-line - Everyone is talking at once. In order to be heard, you have to shout. If you want someone specific to hear you then you need to find a way to shout directly at them.

In between all those transmitters are.. lots of other transmitters. There are also lots of particles like dust, gas and other debris that radio signals just don't like. They tend to bounce off, get absorbed or otherwise get mangled some way. They follow the lay of the land, being influenced by gravitational distortions and being "lensed" this way and that. In short, it's a rat's nest of EM spectra out there.

In order for Earth to be heard, a series of very complex actions must take place. All of them rely on one thing: Someone has to be listening in the right spot at the right time and they specifically have to listening for Earth to shout. An alien spaceship isn't going to be crusing by Alpha Centari and end up missing the end of the Galactic Snarf Playoffs because some stray Earth radio station broadcast jammed the frequency. They'd have to be specifically listening for us.*

*Note: This is all considering our current state of understanding and technology (As I know it right now.. which is a limited source of info by any stretch of the imagination.) It could, for instance, be possible for some ETI to have seeded this end of the Galaxy with scanners/sniffers that scanned more frequencies, more rapidly with more precision and more sensitivity than we could have ever imagined. AI could attempt recombinations of all sorts of gathered stray signals in an attempt to reconstruct them to determine intelligent origin. There could be other means of detecting EM spectrum besides radio that yield a much cleaner picture. We simply don't know. But, from what we do know, it's not likely our radio leakage is going to be picked up by accident by anyone. They would have to be looking for it. There is a very slight change very strong, focused military-grade radars used in planetary science/detection, as Meteor Wayne suggested, could be picked up and identified as an "artificial" signal. But, the area of sky we have covered with those is very, very, very small and not frequently revisited so there wouldn't be many "second confirmation" chances by alien radio-astronomers.

 

[Couerl]

Hi gentlemen,

I am not an expert on radio or EM, but I recall a few things from college and perhaps someone with more expertise will elucidate upon this further. The overwhelming majority of natural EM noise occurs at 300 ghz or less and this is our "swamp" from what I understand. Of course Jupiter and the Sun are brighter than we are on those bands and drown us out, but there is no interference with AM radio broadcast for instance. If there was then it makes sense that we would be listening to Jupiter and the sun instead of Buddy Holly in our cars etc.. To the best of my knowledge (without researching any of this) a theoretical person in a spaceship say, 65 ly's away from Earth could turn on his AM radio and listen to The Glenn Miller band without a problem.

 

[BurgerB75]

I thought I had read somewhere that in order to hear an AM broadcast from the 40's or 50's, from even the nearest stars, you would need a huge receiving antenna. If I remember right it is because the radio transmissions were omnidirectional and dissipated rapidly over those vast distances. In addition, those early transmitters were rather low powered.

As for Jupiter!

http://www.spacetoday.org/SolSys/Jupite ... Radio.html

 

[SANCHI]

well there could be many reasons:
1.they may be residing in a distant galaxy from where their signals can't reach us. or maybe they dont wanna interact!!!!
2.maybe the life forms/aliens with human like intelligence level have not yet evolved anywhere else. They may be in very primitive stages.
3.or the life forms which are much advanced than ours might have found us and are trying to interact with other form of communication which we are not aware of or not looking for!!!!!!!! :?:
4. considering the fact that the multiverse theory is true, they maybe present in any other universe and are not able to communicate from that universe!
5. maybe only earth has intelligent species(the probability of this fact is very bleak !!!!!! as it is almost impossible that evolution took place only on our planet) :!: