[Richard Honea]

Richard Honea  asked the Naked Scientists:

Hi,

love the show - I listen in Los Angeles via the podcast.

I heard on another science podcast that our radio signals emitted from Earth only get out to about the edge of our own solar system and then they basically become background noise of the universe.

My question is why are groups like SETI listening for signals from some other world, supposedly outside of our own solar system? It seems that it would be a useless search since the radio signals from such great distances would seem to never make it to us. There could be worlds teaming with life communicating all over but we'll never know given the current technology.

thanks!

Richard

What do you think?

[lyner]

Yes they do.
But it is, surprisingly, not as bad as you might think.
The Inverse Square Law applies (however narrow the beam of your transmitting antenna is) so that every time you double your distance, the received power (over a given area of receive antenna) will go down to 1/4.  That sounds pretty dire except when you realise that signals from a distant galaxy would only be four times stronger than from a galaxy TWICE as far away - think how many billions of miles that would represent.
The Radio Telescope which SETI use is very sensitive and can receive extremely weak signals (the numbers are almost irrelevant) so, if  'someone'  within a pretty huge radius were to be beaming a powerful transmitter in this general direction, they reckon there is a fair chance of picking it up.
Of course, there is the issue of where they are pointing it and what state their technology is in at the present time (or rather when they sent it - could be millions of years ago!). It isn't a hugely expensive project and, as we don't know of the actual likelihood of a suitable civilisation exisiting, it's worth a go.
I think it's an incredibly romantic idea.

[syhprum]

I have seen the figure quoted that the range of communication between two communities with Arecibo like equipment if they deliberately targeted each other would be 1000 light years with a bandwidth of 1 Hz.

[Madidus_Scientia]

An advanced alien civilisation might have detected that our solar system might have life before any complex life even evolved on earth, and commenced sending focused signals with their crazy super high powered transmitters, we might begin recieving the signals tomorrow!

[lyner]

The shame is that we are so unlikely to be able to have an actual conversation because any likely life form would be so far away and the time delay would be hundreds of generations.