Thread: "The Great Silence"

Originally Posted by Atmoscheer

Syme we are talking about hypothetical infinite distances and hypothetical infinitely collimated signals. Just the same as we're turning miniscule probabilities into measurable fact because we're approaching limits, if you have infinite objects randomly distributed throughout infinite space, eventually there will be a finite distance after which all signal has been obscured.

Obviously there's no way to know where that line gets drawn or how many life forms could exist within it at this point, but its worth acknowledging that we aren't dealing with a truly unlimited system. There is a limit to which even an everlasting signal emitted from Earth can actually travel.

Right, I'm definitely not saying that electromagnetic radiation can travel for an infinite distance through anything less than a perfect vacuum (which even the intergalactic medium isn't). The SETI question is generally limited to the Milky Way galaxy anyhow, though. Which is the context in which I've been considering it ITT so far. And within that context, barring occultation of certain regions by the hub and dusty areas, you can consider the range of signals more or less unlimited (although again, the range at which they can be detected may be much less based on signal strength and receiver sensitivity).

EDIT: I've seen SETI FAQs claim that the Arecibo dish can detect narrowband signals from a range of many thousands of light years, though I can't remember what was said about power, if anything. Presumably gigawatts at least. Arecibo is not the best radio telescope on Earth, either. Some multi-dish arrays are more sensitive. At any rate, again, that's only detection range, which is not the same as propagation range.