Maybe we don’t see aliens because they’re waiting to hear a signal from us first


Maybe we don't see aliens because they're waiting to hear a signal from us first

Illustration of some of the planets in our solar system. Source: NASA/JPL-Caltech/Lizbeth B. De La Torre

We have a long running series here at UT about potential solutions to the Fermi paradox – why can’t we detect any alien life out there in the universe? But more possible solutions are being developed all the time. Now, another paper adds a few more theories to one of the more popular solutions – that aliens are too busy to care about us.

paper, issued in arXivWritten by Amri Wandel of the Ratch Institute of Physics at the Hebrew University of Jerusalem. He makes two basic assumptions. First, the aliens don’t really care planets with life on them. Second, they’d be interested if they could spot intelligent life on one of them.

For the first assumption to be true, the prevalence of “biotic” (that is, having a biology) planets would be useful. In this case, even advanced civilizations may not have enough resources to devote to fully exploring those planets, especially in the form of an actual probe. Sending messages consumes much less power than sending a file tangible thingIt doesn’t make sense if it’s all of those radio waves Just washing a form of primitive unicellular organism.

Scientists recently put more stock to this theory, given how many exoplanets reside in the habitable zones of their stars. Suppose each of these developed life at some point in their evolution. In this case, the galaxy might be so swarming with them that it wouldn’t be worth the time of advanced civilizations to check out every vital planet before they developed intelligence.

UT has a lot of discussions about Fermi Paradox.

However, once a planet develops intelligence, it may actually be very interesting to them. The basis of Fermi’s paradox is that intelligent life is not easy to identify. So it’s likely to be relatively rare in the galaxy so far. So any example of this would be interesting even to an advanced civilization. To detect intelligent life from afar, the easiest thing for an advanced civilization to do is to look for artificial radio signals or other signals, similar to what we do with the Search for Extraterrestrial Intelligence (SETI) project.

What would that look like if the situation was reversed, and aliens could detect signs of intelligence on Earth? The most obvious answer would be the radio signals that the Earth began transmitting about 100 years ago. In those 100 years, the signals would have theoretically reached the nearest 15,000 stars, but only those within 50 light-years were able to send back anything we would have seen.

This beam includes 1300 star systems In total, from 100 billion to 400 billion star systems in the Milky Way. Not much by Hungarian standards, but still a non-zero number. However, the SETI scientists believe that the radio signals we sent back, which were more akin to a TV broadcast incident rather than any intended signaling mechanism, are indistinguishable from background noise after about a light-year of travel.

There are many solutions to Fermi’s paradox similar to those presented here. Credit: Isaac Arthur YouTube channel

So, even in those 1,300 star systems that could have responded, there is a very good chance that they wouldn’t even be able to detect our unintentional technological footprint and might still be ignorant of intelligent life on the planet. And if not –smart life plentiful, so why would they bother spending any resources trying to contact a potentially unintelligent scientist? Hence, a solution to the Fermi paradox is that the aliens have been silent so far because they have seen no indication that we are intelligent.

It is certainly an elegant solution and has been introduced in other variations previously. However, the argument is well explained in Wandel’s paper, which is well worth a read for anyone interested in finding solutions to the potentially biggest question of our time.

more information:
Amri Wandell, Revisiting the Fermi Paradox: Technological Signatures and the Age of Communication, arXiv (2022). doi: 10.48550/arxiv.2211.16505

Journal information:

Introduction of
the universe today

the quote: Maybe we don’t see aliens because they’re waiting to hear a signal from us first (2022, December 6) Retrieved December 7, 2022 from

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