[thomassmith65]

There may be countless other planets with intelligent life right now, but... if it took them millions of years to evolve... and they're millions of lightyears away... we might have to wait millions of years for signals to reach Earth from the eldest civilizations in the closest galaxies.

[spartanatreyu]

Why would we have to wait? Why would you assume that they're only sending signals now? Why would you not assume that they had a head start on sending signals before us?

[thomassmith65]

My guess would be that there are millions of other intelligent species out there.

Maybe these species are distributed evenly throughout our 90-billion-lightyear-in-diameter universe.

Maybe half evolved to our current level of sophistication in less time than it took us.

So... what is the minimum duration of time, after the big bang, that some lineage of creatures might take to evolve from sludge into a life form capable of emitting data via radio waves? It cannot happen instantaneously... first conditions need to cool down enough to be amenable. Beyond that, it seems to require a little time for evolution to get to human-like level, it took us 13+ billion years.

So given the lack of meaningful signals we have detected so far, Occam's Razor says the nearest intelligent life that currently exists out there is too young and far away for its transmissions to have yet reached Earth.

[recursivecaveat]

Earth is 4.5 billion years old, but the milky way is only 105 thousand light years across. So even if you assume an earth like planet couldn't have formed any earlier than ours, other intelligent life in the galaxy only has to go through the geological processes and evolve a tiny tiny fraction of a percent faster to have tons of time to send all the signals they ever want. Nearest other galaxy is only a couple million LYA which ain't too bad either.

[thomassmith65]

My guess, again based on the lack of cosmic signals we have detected, is that intelligent life is rare enough - at this age of the universe, at least - that we have no company yet in the Milky Way. That leaves a lot of room though - there might already be simpler forms of life.

But I won't go to the mat arguing my impression; we only have evidence from one planet to go by, so any view here lacks empirical evidence.

[creativenolo]

Given the timescales involved and brevity planetary conditions perhaps life is unlikely to observed nearby a star system.

Perhaps instead it is to be observed in energy preserving vessels (i.e. emit nothing) in transit to the next fuel stop (a planetary system). Perhaps dark matter can be explained by the congested highway of these unobservable vessels.