Free Astronomy Magazine January-February 2022

11 JANUARY-FEBRUARY 2022 ASTRO PUBLISHING T he BLC1 signal. Each panel in the plot is an observation towards Proxima Centauri (‘ON source’), or towards a reference source (‘OFF source’). BLC1 is the yellow drifting line and is only present when the telescope is pointed at Proxima Cen- tauri. [Smith et al., Nature Astronomy] the same technological level might exist simultaneously around two stars so close to each other. With our civilization as our only example, we cannot imagine how long other civ- ilizations can and will produce tech- nosignatures in the radio domain. However, we know that our galaxy is at least 13 billion years old (al- though at the beginning it was very different from how we perceive it today) and that humanity has been able to produce radio signals for only about a century. If we use the length of an Earth year to compare the age of the Milky Way to the time we’ve been able to produce radio signals, we see that we started producing radio signals just 0.2 sec- onds from the end of that year. Is it reasonable to assume that another technological civilization could be our contemporary, and that it is lo- cated on the nearest habitable zone exoplanet? From that probabilistic standpoint, this hypothesis is not reasonable, not even considering that having originated from distinct protostellar clouds, the Sun and Proxima Centauri were in the past certainly more distant than they are in our time. The timing of the coex- istence of the two “radio civiliza- tions” would nevertheless remain unlikely unless millions of techno- logical civilizations exist in the Milky Way. If there were so many, it is likely that some of them would have already contacted us. Not having done so, however, it could also be the demonstration that truly intelli- gent life exists nowhere else in the universe... The lesson that we can learn from the story of BLC1 is that we can cer- tainly pick up sufficiently powerful alien radio signals with today’s tech- nology, although it does not seem so easy to recognize them in the ocean of interference that we ourselves produce. What is certain is that we use radio frequencies, and it is all our belief that any alien technological civilization must necessarily make the same choice to communicate with other worlds. To get an idea of how the main SETI programs are set up today, let’s imagine that we are in a large stadium filled with fans who all support the home team at the top of their lungs, with the exception (perhaps) of one fan who supports the opposing team. What we try to do now is isolate the latter’s voice without even knowing what he is saying and where he is sitting. Might there not be a more distinguishing aspect to the person we’re trying to detect? Wouldn’t it be less random to look for a different colored flag in the areas reserved for guests? !