It is safe to say that the universe is teaming with life even though we are not aware of it off of earth. Here is a simple thought experiment: assume that there was a civilization that stagnated on our exact level of technology and interest in other life - when would they have detected us at various distances?
As we can see by this announcement they wouldn't have detected the first primal soup that formed life (we don't have any probes), but given enough time they would have sent a probe to our planet and detected single celled life, and they would have seen evidence of life.
At 5 light years (the closest start is just less than that) they wouldn't have had a chance before about 1900, and they might needed until 1960 (I give a range because there is room for debate on exactly what would be proof, they might have not been sure) to detect out radio transmissions. We would probably have made contact with them in the 1970s.
At up to 100 light years the above applies with more of a timeshift. After 200 we don't have the ability to detect ourselves (the technology of 1820 didn't give any emissions to go on.) I'm not sure if they would know there is a planet with water where we are (There has been great progress in detecting small planets but I don't know what their abilities are).
The farther out you go the harder it gets. Eventually they are still seeing the big bang form our galaxy and so have no idea life will eventually happen here (or where we will be as the universe is moving all along in directions that they cannot predict)
If you go just be what's detectable by radio emissions, there seems to be another problem.
Back when we started broadcasting radio, we needed very powerful transmitters since the receivers were pretty primitive - you could make receivers with no power source at all (Galena radios).
Then we started using them for other purposes. Powerful radars appeared. TV was invented. Later on we added digital signals and most traffic shifted to binary for computer to computer communication.
Now we have things like WIFI and 5g. The problem is that the technology has advanced so much that cellular antennas can talk to puny transmitters from miles away, while the transmitters are only outputting milliwatts. We can also electronically 'steer' transmissions so they will 'point' at the other party (beamforming).
Long range communication is shifting to satellites and fiber optic cables. Those are pretty directional and not very strong signals, by comparison (and fiber optic of course has none). We have been slowly shutting down TV stations in favor of internet streams.
Civilian radars still exist but they are relatively weak. They are also slowly being phased out in favor of technologies like ADS-B, which broadcast a fraction of the power. GPS signals are very weak.
Military radars are also more sensitive than before - and increasingly look like background noise. Given the high emphasis on stealth, they are also more directional and lower power than before. And may not even be on all the time.
Given this, it is possible that, if you are taking a SETI approach, there's only a very small window before a civilization switches to more efficient and less noisy RF comms.
> At up to 100 light year
At 100 light years you'll have very faint, possibly undetectable signals, as the strength decreases with distance squared. Unless they are pointing at us.
Advanced civilization, sure. But wouldn't a sufficiently designed spectroscopy telescope from afar have been able to detect the presence of oxygen on our exoplanet for hundreds of millions of years?
As we can see by this announcement they wouldn't have detected the first primal soup that formed life (we don't have any probes), but given enough time they would have sent a probe to our planet and detected single celled life, and they would have seen evidence of life.
At 5 light years (the closest start is just less than that) they wouldn't have had a chance before about 1900, and they might needed until 1960 (I give a range because there is room for debate on exactly what would be proof, they might have not been sure) to detect out radio transmissions. We would probably have made contact with them in the 1970s.
At up to 100 light years the above applies with more of a timeshift. After 200 we don't have the ability to detect ourselves (the technology of 1820 didn't give any emissions to go on.) I'm not sure if they would know there is a planet with water where we are (There has been great progress in detecting small planets but I don't know what their abilities are).
The farther out you go the harder it gets. Eventually they are still seeing the big bang form our galaxy and so have no idea life will eventually happen here (or where we will be as the universe is moving all along in directions that they cannot predict)