If intelligent aliens exist, why haven't we seen them?

If intelligent aliens exist, why haven’t we seen them?
Briony Horgan is a Mars expert and co-investigator on the Mastcam-Z camera system for NASA’s Mars2020 rover mission. Credit: Purdue University photo

Thousands of planets have been discovered in the last few decades, although astronomers tell us there are probably billions. In such a large and diverse set of solar systems, it seems impossible that humans could be the only intelligent life.

This contradiction – between the high probability that life exists elsewhere in the and the lack of evidence for it – is known as Fermi's Paradox. Coined by physicist Enrico Fermi in the 1960s, it's a mystery that continues to invite consideration more than half a century later.

The first thing any planet needs to support life is liquid water – it's essential for living creatures. Researchers recently found signs of a lake on Mars, albeit buried beneath a thick layer of ice, near the planet's south pole. If there is liquid water down there, it could serve as a temporary home for organisms hiding out until conditions get more comfortable on the surface. Even if life on Mars exists, it's probably limited to simple, single-celled organisms – a far cry from the intelligent aliens of science fiction.

This is one potential solution to the paradox: life exists outside Earth, but it isn't intelligent. Or maybe intelligent life exists too, it's just quiet. Finally, it's possible (but unlikely) that we're the only life in the universe.

While any of these scenarios are possible, Briony Horgan, a professor of earth, atmospheric and planetary sciences at Purdue University, doesn't think we should give up hope.

"We've only been looking for communicating civilizations for the last 60 or 70 years. The universe is 13 billion years old, and 60 years is an extremely short period of that time," she said. "Perhaps isn't as common as we think and we're just looking at the wrong time."

The search for extraterrestrial life so far has relied primarily on radio signals, which could also be limiting our chances of communicating, Horgan said. Many radio frequencies are able to penetrate Earth's atmosphere, and they're easy to recognize as artificial because of their repetitive nature and narrow bandwidths. But this means if whatever civilization we're looking for isn't actively emitting signals for communication, we probably wouldn't see them.

Humans are getting better at detecting signals from space, though, and technological advancements like the Kepler Observatory have taught researchers a lot about the solar system. NASA has plans for a rover on Mars, a solar probe to touch the sun, a mission to Jupiter's moon and so much more – all in hopes of using space as a vantage point to uncover the mysteries of our own home planet.

"How does life evolve? How unique are we? How critical is it that humanity makes it off this planet? Our quest to find life outside Earth brings us back to those very fundamental questions," Horgan said. "I think life is the most incredible thing the universe has ever produced, so if we are the only in the universe, that to me is a huge motivating factor for moving beyond our Earth."


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Aug 02, 2018
"Space is big. You just won't believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it's a long way down the road to the chemist's, but that's just peanuts to space."

-- Douglas Adams, The Hitchhiker's Guide to the Galaxy

Aug 02, 2018
The vacuum is unlimited in its dimensions!

The same question people on other planets are asking, why if aliens exist on planet Earth in the Milkyway, why have they not visited us on our Andromeda planet, is our Andromeda planet the only planet in the universe with life – the eternal question of all planetary life
arcmetal> Space is big. You just won't believe how vastly, hugely, mind-bogglingly big it is

The speed of light moves at a snail's pace compared to the size of the vacuum and human life span is too short for the galactic size's and distance

Aug 02, 2018
Space is no place for flesh.

Aug 02, 2018
Perhaps the question should be: "why don't we believe it when we see aliens?"

Aug 02, 2018
"The first thing any planet needs to support life is liquid water – it's essential for living creatures. "

Open your mind. We don't know that. It may be that water is required for "life as we know it" - but what about "life as we DON'T know it"? Would we even RECOGNIZE it?

Beyond that .... we've been looking for what, 90 years? This is going to be a LONG search. We're on one planet. We've sent 12 men to the Moon, but none for the last 45 years. We've never been further. We haven't even been beyond LEO since then. And we have no firm plans to go beyond any time soon.

I'm confident that we'll eventually - EVENTUALLY - find life on other planets circling other stars. But not in my lifetime or yours. Don't be so impatient!

Aug 02, 2018
Claudius, you otto lay off drinking out of cast-ead goblets. The metal poisoning is detrimental to your mental health.

You see aliens. That guy over there sees angels, That woman sees ghosts. That trumpeting copperhead sees pink elephants flying around his head, when ever he can lift it out of the toilet.

Which of you am I suppose to believe?

This universe is still relatively young. Less than 14 billion years. If you say it real fast it sounds like a longtime.

However, in my opinion, it will be hundreds of billions of years before there will exist the density of Living Worlds old enough to evolve a multitude of sophont species. Such as is speculated in our fictions and fantasies.

Many of the deluded fear to confront what is in front of them. That there are a multitude of reasonably intelligent species extent on the only Known Living World. Most lack the physical ability to manipulate for using tools.

As Homo Anthropophagus busily consumes them.

Aug 02, 2018
There's a fourth possibility. Without sounding like the X-Files, what if intelligent aliens are on Earth peacefully observing us. Using sufficiently advanced technology, they could look and act human. Without giving everyone on Earth an MRI, how could we detect them?

Aug 02, 2018
The vacuum is unlimited in its dimensions!

The same question people on other planets are asking, why if aliens exist on planet Earth in the Milkyway, why have they not visited us on our Andromeda planet, is our Andromeda planet the only planet in the universe with life – the eternal question of all planetary life
arcmetal> Space is big. You just won't believe how vastly, hugely, mind-bogglingly big it is

The speed of light moves at a snail's pace compared to the size of the vacuum and human life span is too short for the galactic size's and distance

Or, it is like a fish living in the deep ocean of Europa wondering why they haven't discovered any extra-europians.

Aug 02, 2018
@SkyAbove
There's a fourth possibility. Without sounding like the X-Files, what if intelligent aliens are on Earth peacefully observing us. Using sufficiently advanced technology, they could look and act human. Without giving everyone on Earth an MRI, how could we detect them?

However, the (Earthling) scientist won't be interested because they can't test such an idea. As a layman I find it interesting to look at all the alternatives although extremes (David Icke for example) probably don't get a second thought by most, with good reason.
If aliens are among us now, then it's not worth worrying about is it and if they exist somewhere else then I'm sure we'll find out some time. If they land on some PM's/President's back garden lawn then that would be great, as evidence. Till then, I gonna enjoy my cuppa, Ha!

Aug 03, 2018
There's a fourth possibility. Without sounding like the X-Files, what if intelligent aliens are on Earth peacefully observing us. Using sufficiently advanced technology, they could look and act human. Without giving everyone on Earth an MRI, how could we detect them?

Just go out and meet people. Eventually you'll run into one or two. Well, they practically own South America. I mean, they taught the Incas everything they know. :P

Aug 03, 2018
First, I have to wonder why this article even came up. If there's anything new here to add to the discussion, I must have missed it.

As for radio signals, the model was built on 60s era communication. Since then we've moved from long range, strong, global radio communications to short range low power communications and long range over cables.

Has anyone checked how the Earth's radio signature has changed over time? I'm sure it's much harder to detect, moving from strong coherent signals at well defined frequencies to what is basically a lot of weak noise at a wide range of frequencies. If we're looking for those strong, coherent signals from space, would be even consider Earth as having intelligence? And what will happen 50 years from now, even if we continue to use radio waves?

I'm interested in whether anyone has done anything to see how detectable current communications are from space. Anyone knows?

Aug 03, 2018
The universe is so big - let alone the multiverse - and the speed limit is so slow. So much to read, so much to know, so little time for unfalsifiable nonsense non-science.

It is as conceivable that ETI existed at the time of Inflation and has been hurrying towards us ever since, "The faster I go, the behinder I get!"

Aug 03, 2018
Perhaps, like whales, the nature of their intelligence and intercommunication is beyond us. Maybe if we learned to communicate with marine mammals, we will be one step closer to communicating with extraterrestrials.

Aug 04, 2018
Perhaps, like whales, the nature of their intelligence and intercommunication is beyond us. Maybe if we learned to communicate with marine mammals, we will be one step closer to communicating with extraterrestrials.

So true. We do now know that dolphins are speaking a language that contains a transfer of information, via information theory. But what they are saying is anyone's guess.

Aug 06, 2018
Such a bogus Article on an otherwise useful website.

Aug 07, 2018
We have not seen any intelligent aliens because they are intelligent enough to stay away from us. The last thing we need is Trump starting an interstellar war on Twitter.

Aug 08, 2018
The last thing we need is Trump starting an interstellar war on Twitter.


Shhh... Don't spill the beans. He still doesn't know that Twitter is run by aliens.

Aug 08, 2018
"If intelligent aliens exist, why haven't we seen them?"

-Because theyre MACHINES, living very frugally, and they have absolutely no reason whatsoever to converse with us.

This is the inevitable end result of techno-dependent civilizations.

Sep 27, 2018
The probability of other live existing in the universe is a big number but the probability of live existing in our observable universe is not that big.
If you use the program Gaia Sky then you see how little we are actually able to observe, it's almost an embarrassing small part.

Like saying my lost keys are not in this solar system because I couldn't find them on my desk.

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