How would we recognise other life in the universe?
Even if primitive life and vegetation were ubiquitous, ‘advanced’ life may not be. Our emergence on Earth may have depended on many contingencies, such as the phases of glaciation, the planet’s tectonic history, the presence of the Moon and so forth. But searches are surely worthwhile. Instruments are searching for non-natural radio transmissions from nearby and distant stars, from the plane of the Milky Way, from the galactic centre and from nearby galaxies. But even if the search succeeded, it would still be unlikely that the ‘signal’ would be a decodable message.
A radio engineer familiar only with amplitude modulation might have a hard time decoding modern wireless communications. Indeed, compression techniques aim to make the signal as close to noise as possible – insofar as a signal is predictable, there’s scope for more compression. And the signal could just be ‘leakage’ anyway, rather than any kind of message.
Then again, many of us think that ‘organic’ human-level intelligence is just a brief interlude before the machines take over – before ‘organics’ are overtaken or transcended by inorganic intelligence, which will then persist, continuing to evolve for billions of years. This suggests that if we were to detect extraterrestrials, it would be far more likely to be inorganic: we would be most unlikely to ‘catch’ alien intelligence in the brief sliver of time when it was still in organic form.