radio – UCLA SETI

Every week, we answer a question from our February 16, 2023 launch event Q&A session or from a Zooniverse participant. This week’s questions comes from Alejo Weyh: How much background noise is Earth sending out there? Do they have a better chance of finding our radio signals or do we have a better chance of finding them?

This week, we address an important question: do other civilizations know that we are here? It is not unusual to hear astronomers answer this question in the affirmative. However, apart from rather improbable conditions, the answer is almost certainly “No.” We have transmitted radio signals over distances approaching an Earth radius for approximately 120 years, and radio waves propagate at the speed of light. Our radio transmissions have reached a distance of 120 light years, illuminating a spherical bubble with a volume of 7.2 million cubic light years. Although this number may sound large, it represents only 1 millionth (0.0001%) of the volume of the Galaxy. The probability that another civilization resides in this tiny bubble is extraordinarily small, unless there are millions of civilizations in the Milky Way, which seems unlikely. Could another civilization have traveled to our local bubble and detected our transmissions? Perhaps, but even in that improbable situation, news of our existence would be confined to our bubble. Could another civilization further away have detected biosignatures in our atmosphere? Perhaps, but in that case they would not know whether terrestrial lifeforms are technological or even intelligent. The laws of physics lead us to conclude that no one knows about the existence of a technological civilization on Earth except for the improbable civilizations that would reside in our tiny, local bubble.

We answer this week’s second question unequivocally: we have a much better chance at detecting other technological civilizations than the other way around, a fact that motivates UCLA SETI searches. It is reasonable to assume that other civilizations have been technological much longer than we have been (see our webinar), perhaps preceding us by thousands or millions of years. Their detectability bubbles are therefore considerably greater than ours.

Electromagnetically yours,

UCLA SETI

Every week, we answer a question from our February 16, 2023 launch event Q&A session or from a Zooniverse participant. This week’s question comes from Clark Ramsey: Is it reasonable to believe that radio communication would be employed by more advanced civilizations?

This excellent question originates from the logical supposition that other civilizations are more advanced than we are (see our webinar). Therefore, it is reasonable to wonder whether “they” have abandoned radio technology and instead communicate by other means. Here is our take on this question. Even if most communications of advanced civilizations no longer rely on radio technology, it is possible that some of their communications still use radio signals. After all, radio waves are inexpensive to generate and propagate at the speed of light through habitable planetary atmospheres and the interstellar medium with little attenuation. Advanced civilizations are still bound by the laws of physics, and it is entirely conceivable that radio communications provide the best technological solution for some applications. The first part of our answer is a qualified yes. Our reasoning so far, however, is incomplete because it considers primarily signals that are not designed to be recognizable by other civilizations.

What if a civilization decided to intentionally announce its existence? What would be the most effective broadcast strategy, bearing in mind that other civilizations, like ours, might be in the early stages of development? In this scenario, radio technology becomes a compelling contender in the arsenal of communication technologies, not only because of the propagation advantages of radio waves, but also because the most abundant element in the universe – hydrogen – relentlessly emits a distinctive radio signal. This reasoning was first articulated in a 1959 Nature paper by Giuseppe Cocconi and Philip Morrison, who described “a unique, objective standard of frequency, which must be known to every observer in the universe: the outstanding radio emission line at 1,420 Mc./s. (λ=21 cm) of neutral hydrogen”. In other words, one of the best ways to announce one’s existence to other civilizations is to broadcast a powerful, attention-grabbing radio signal near 1420 MHz. The second part of our answer, in the context of intentional interstellar greetings, is a more decisive yes.

SETI is most likely to be successful if other civilizations operate powerful beacons. We cannot know a priori if other civilizations or radio beacons exist. Their existence is a scientific hypothesis that is testable with radio telescopes like the Green Bank Telescope (GBT). At UCLA SETI, we scrutinize the 1100–1900 MHz region of the spectrum, which includes the 1420 MHz hydrogen line, with the GBT. The probability of a detection may be low, but it is not zero, and the potential reward justifies the search.

We have been uploading our most interesting signals to http://arewealone.earth and have been enjoying the discussions of unusual signals on the Talk boards. We hope you will join us.

Electromagnetically yours,

UCLA SETI

Tag: radio

Question of the Week: Is humanity detectable by aliens?

Question of the Week: Do advanced civilizations use radio?