Aliens haven't contacted Earth because there's no sign of intelligence here, new answer to the Fermi paradox suggests

milky way
Is the Milky Way home to intelligent aliens? (Image credit: NASA/Adler/U. Chicago/Wesleyan/JPL-Caltech)

Why haven't aliens gotten in touch? Maybe they think Earth is boring. 

A new preprint paper published to the arXiv database suggests that intelligent extraterrestrials might not find planets that host life particularly interesting. If life has evolved on many planets in the galaxy, then aliens are probably more interested in the ones where there are signs not just of biology but technology, study author Amri Wandel, an astrophysicist at The Hebrew University of Jerusalem, wrote in the paper. The paper is yet to be peer-reviewed.

The study explores the Fermi paradox, which holds that given the age of the universe, it's likely that intelligent aliens would have developed long-distance space travel by now, and thus it’s likely that they would have visited Earth. The fact that they haven't (as far as we know) may be evidence that there is no other intelligent life in the Milky Way galaxy. 

But experts have offered  other explanations for the missing aliens: Perhaps they visited Earth in the past, before humans evolved or were capable of recording the visit. Or maybe long-distance space travel is more difficult than believed. Perhaps aliens evolved advanced civilization too recently to make it to Earth. Or they've deliberately decided not to explore the cosmos. It’s even possible that they’ve killed themselves off.

Related: Why have aliens never visited Earth? Scientists have a disturbing answer.

In the new paper, Wandel offers another possible explanation: that life is actually really common in the Milky Way. If many of the rocky planets orbiting in the habitable zone of stars host life, aliens probably aren't going to waste their resources sending signals to every one — they'd likely end up trying to communicate with alien algae or amoebas. 

If life is common, intelligent aliens are likely much more interested in signs of technology. But tech signals may be tough to detect. Earth has only been beaming out signals detectable from space (in the form of radio waves) since the 1930s. In theory, these signals have now washed over about 15,000 stars and  their orbiting planets, but that is a tiny fraction of the up to 400 billion stars in the Milky Way. Furthermore, Wandel wrote, it takes time for any return message from aliens to travel back, so only stars within 50 light-years have had time to respond since Earth started broadcasting off-planet. 

Even worse, Earth's oldest radio signals weren't deliberately broadcast into space, so they're likely so garbled after about one light-year that aliens would be unable to distinguish them, according to Universe Today. (Earthlings sent out the first deliberate high-power broadcast to aliens with the Arecibo message in 1974, directed to the globular star cluster M13. Some scientists think it's time to send another.) 

Wandel found that unless intelligent civilizations are very abundant, with more than 100 million technologically advanced planets in the Milky Way, it's likely that Earth's signals haven't reached another form of intelligent life. However, with time, and as our planet beams out more and more radio chatter, it becomes more likely that Earth's technological signals will find intelligent listeners, Wandel wrote. 

The findings suggest that perhaps there are no intelligent civilizations within about 50 light-years of our planet, he wrote. But intelligent life could still be out there — they’re just waiting for our call.

Stephanie Pappas
Live Science Contributor

Stephanie Pappas is a contributing writer for Live Science, covering topics ranging from geoscience to archaeology to the human brain and behavior. She was previously a senior writer for Live Science but is now a freelancer based in Denver, Colorado, and regularly contributes to Scientific American and The Monitor, the monthly magazine of the American Psychological Association. Stephanie received a bachelor's degree in psychology from the University of South Carolina and a graduate certificate in science communication from the University of California, Santa Cruz. 

  • CodyJay
    signs of intelligence? Why,theres plenty here,the aliens just need to stop searching the old CSA states....
  • Dr.Alimantando
    Mostly harmless...
  • Snorrie
    Those purported extraterrestrial aliens might be monitoring our electromagnetic TV and Radio signals. As a consequence, those aliens may have come to the conclusion that Evolution has by sheer random luck isolated Homo Sapiens in some backwater of the Milky Way Galaxy. ...... Sort of like a Zoo.
  • papadave
    The probable answer which is mentioned only obliquely here is that based on current physics nothing can go faster then light. That means that at best it takes 4 years at light speed to reach our closest neighbor star. No matter how advanced the civilization and there is no high probability of life on any given star system.. Then you start to need longer and longer lengths of time to reach us. If your counting on worm holes to speed the process,, dont hold your breath
  • yossarian22
    Dr.Alimantando said:
    Mostly harmless...
    Needs to be removed for the new bypass
  • Merrall
    admin said:
    A new paper claims that intelligent aliens would only be interested in contacting the most technologically advanced planets, and Earth doesn't make the cut.

    Aliens haven't contacted Earth because there's no sign of intelligence here, new answer to the Fermi paradox suggests : Read more
    To travel to our solar system and the planet, the aliens would probably have to have some sort of vehicle able to exceed the speed of light by some multiple, have control of time (no dilation) and some form of gravity control (to stop the inhabitants being crushed in acceleration and stopping) . Since we have no idea what they would be using, we can't trace or track them, or importantly, contact them. And they can't notice us, however important we may think we are (even Donald Trump ;-)
  • yossarian22
    That's what we get for living in the unfashionable end of the Milky Way galaxy.
  • KMacK
    First off, due to the limits of free radiation in a vacuum, aliens on Proxima Centauri would still think that Trump was president and Russia hadn't invaded yet. Speed-of-Light data limitation.
    Second, supposing that they are here and observing from orbit (say the daylight terminator where both outbound radio and visual observation is very limited) they would see that we have poisoned our climate with carbonic gasses as well as industrial pollutants. If so, they would probably be watching to see what we do about it (if we do anything about it, that is). Scientific Method would suppose that they would watch rather than involve themselves in what is a purely local (planetary local) problem.
    Finally, assuming a possible "intent to invade and conquer" (the stuff and substance of most Sci-Fi stories) they would hold back because, honestly, "Is this planet and population WORTH conquering... or should we just wait and pick up the pieces later?"
    Lots of reasons for them to watch but not get involved...that's the basic Scientific Method, after all.
  • Francis_K
    Doesn't really seem logical.

    If there are so many technically advanced alien species in our area of the cosmos that we are irrelevant and uninteresting in comparison then why aren't we detecting any signs of their technology?

    If there are so many civilizations out there the evidence of them should be relatively easy to detect. Maybe some could be so advanced that we would not recognize the evidence but there should be a full spectrum from the most highly advanced to the lowest.

    There has to be other intelligent life but the argument described in the article seems unlikely to be accurate.
  • Rick From CT
    Lol, they haven't contacted Earth? Someone needs to let the military know that the exponential increase in UAP encounters they're experiencing is imaginary, even if they do show up on our sensor platforms. Articles like this are why people ignore the science community.