Ray McCarthy
Sentient Marmite: The Truth may make you fret.
Spectroscopic Analysis works at MASSIVE distances as it uses starlight as the "transmitter" and detects the dips caused by different compounds in the atmosphere of planet in transit.hen again, perhaps the natural weakening of our own broadcasts is process enough - that no one would necessarily know we are here - and conversely, we'd struggled to detect similar from other civilisations.
O2 CO2, signatures indicate possible life. Industrialisation causes "signatures" not plausible from any known natural source such as volcanoes, sunlight on atmosphere or under sea vents.
We have only started with Spectroscopic Analysis and need bigger telescopes in space. This will see a huge jump in our knowledge in the coming years just with the planned telescopes. Computer analysis of the existing recent data (over last 20 years) is improving too.