Originally posted by humy
but, assuming they haven't been deliberately sending signals specifically to Earth for millions of years hoping to get a response thus assuming any signals we can receive from them are stay accidental signals; for there own domestic purposes they might be using fibre optic broadband with no need for ever using radio. Or if they do use some radio, the stray radi ...[text shortened]... ing or colonising out planet) thus didn't inadvertently prevent us from evolving into existence?
Of course we wouldn't know at this point in time considering our level of tech, it may have actually happened cosiderimg the neandertal V homo sap thing. The lessening of the use of RF is already happening to humans, like 40 years ago there was a thriving short wave broadcast industry since around 1925 or so and all that RF has established a wavefront about 100 light years radius, so a 200 light year bubble of our radiation is already on its way into the galaxy but in human terms, a very slow growth of the wavefront, a hundred years from now it will still only be three or four hundred year wide bubble and if some alien was listening for a long term the would notice our reduced dependence on radio. My guess is the same thing would happen to any high tech civilization, they would arrive at our state at some point in time, maybe inventing the first transmitters, spark gap things, then proceeding to modulated narrow bandwidth signals and then transit to say IR transmissions and listeners would just find an end to radio waves.
But the idea of aliens being around in some kind of high tech existence to me seems impossible.
It already seems our brains are about as big as they can get as far as percentage of total body energy needed to run it, right now about 20% of all of our energy just to run the brain.
Maybe we could evolve to have 25% brains but the body would begin to suffer energy wise, like not being able to run for long distances and such, less stamina maybe less total body strength to compensate for brains using up such a massive amount of the total energy available for the human body.
My guess is brains would develop along similar lines anywhere in the galaxy and that would mean alien brains would probably not be much more native intelligence than we have right now.
And that would mean there would be the usual political strife leading to the downfall of civilizations after some time, say 2000 years max, then a fall and a new one starting up but looking at the end of the Roman empire and the long term effects of Europe, it is easy to see the loss of a major civilization could leave outliers like Ireland, Scotland and such to slide back centuries in quality of life and like it happened in Britain, a thousand years goes by before they have anything like the old Roman state tech wise.
The rules of physics are the same here and anywhere else in the galaxy and most likely anywhere else in the universe so life based on carbon would likely have the same limitations as us Terrans.
That said, it would indicate the civilizations extant in our galaxy stands a good chance of already being extinct, even if we give them a 10,000 year lifespan that would be at best a 10,000 light year radius and the radius of the galaxy is like 5 times that so room for 20 such civilizations to have spread in our galaxy.
But radio being rather slow on a galactic scale, signals may come and go and we wouldn't even know since our antennas would not see them in time or only be present 10,000 years later, way too late for us.
With all that in mind I think it is going to be a long long time before we find anything artificial.