Other civilisations in the Galaxy - are they really that likely?

I agree and would think there should be more radio signals if the galaxy was filled with intelligent civilizations, (i.e. at or above our level of technology).OTOH, our signals have only ventured out 50 light years. Considering the galaxy diameter at approximately 100,000 light years, then our signals have not traveled very far at all. Considering the time for a return signal, then only civilizations within a 25 light year envelope would have had a chance to return the call such that we could now hear them.This, of course, assumes: 1)They want to answer, 2)their technology is sufficiently advanced to pick up our puny signal strength, 3)they developed radio technology in the first place, 4)are currently using it, and 5)are looking at the right frequency/direction. Then on the return call, we would need to be looking at the right frequency/direction. That's a lot of "ifs". There may be many, (millions?) out there, it's just that all favorable conditions for contact have not been met.Given all of these "if's", I think it much more likely that if we detect a signal it will be an accident and a signal that is not intended specifically for us.

We didn't use compression for the first 50 years or so? Those signals are still out there travelling in an ever greater envelope around the Earth, its origin. So there was a period of time before we developed compression technology where signals were sent out uncompressed.If a given period of time is the normal and expected evolution in the development of the technology, and if that is a similar path other civilizations take, then there should be similar uncompressed signals out there that we might detect before their similar advancement with compression technology.Those signals would not be directed at or intended specifically for us. Of course, that is a very small window of opportunity.

Hi Omni Very true. One of my conditional "ifs" in Message 14 was that "they" would want to contact us. You've given a few good reasons why they may not want to. It's a big assumption to attribute motivations of aliens as being similar to our own. We can only hope that there is at least one alien civilation that was as careless with their signal generation as we have been over the last 50 years so that we might hear their carelessness.

As time marches on, is it reasonable to assume that our signal detection technology would improve? Is there an upper physical limit to the range of detection? Hold that thought and consider the following scenarios:

1. An advanced civilization has detected our existence and sends a message that we can detect.
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2. An advanced civilization maturing technologically along similar paths sends out uncompressed signals such that we can detect those signals without their knowledge.
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3. An advanced civilization, exploring the galaxy, stumbles upon our existence and decides to visit.

All are extremely unlikely, but how would they rank in order of probability of success?