Fermi Paradox: Where Are The Aliens?

The Fermi paradox is a popularly cited argument against the existence of extraterrestrial civilizations in our galaxy or beyond.

It states that, if advanced alien civilizations are common in the universe, then we should have seen evidence of their presence by now. After all, they’ve had enough time to find us.

The universe is roughly 13.8 billions year old. Meanwhile, our solar system has only been around for about 4.5 billion years.

And in that time, we’ve been able to master travel to other planets and send our probes pretty far into the universe. If aliens are out there, and they’ve had more than twice as long as us to explore, why haven’t we seen evidence of their existence?

The Fermi paradox asks a question that’s difficult to answer, and scientists have been struggling to solve the problem for decades.

They’re likely to wrestle with it for a lot longer. Looking at the night sky, there appears to be numerous opportunities for life in outer space. So, where are the aliens?

What Is The Fermi Paradox?

So the story goes, the Fermi paradox was started by one simple question: “But where is everybody?” Italian-American physicist Enrico Fermi was enjoying a casual conversation with fellow physicists about the possibility of life in outer space, when he blurted out the awkward question.

If there’s so much potential for intelligent life on other planets, why have we found no evidence for it?

The Fermi Paradox (sometimes known as the Great Silence) describes the apparent contradiction: if scale and probability are in favor of the existence of intelligent life, why does the evidence suggest otherwise? 

Enrico Fermi was not the first person to pose the question, but perhaps the first to say it so succinctly. Fermi died in 1954, before humans made their first manned journeys into space. In the years since his death, the paradox has only become more pressing.

Humans have successfully sent probes beyond the reaches of our solar system. Technological advances mean we know more about the prevalence of exoplanets, and the potential habitats for intelligent life. And still, we see no signs of it. 

What Are The Chances Of Intelligent Life In Outer Space?

A simple way to consider this question is to look at how many habitable worlds there are in the Milky Way galaxy alone. According to NASA, there are between 100 billion and 1 trillion Earth-like planets orbiting stars like ours.

And while not all of them can support life, there could still be hundreds of millions, or even billions of habitable worlds in our own galaxy alone.

If only a small fraction of these have developed life, and a smaller fraction again hosts intelligent life, that’s still a good chance there are alien civilizations out there. And that’s just in one medium-sized galaxy. 

The Drake Equation, created by Frank Drake, was formulated in an attempt to evaluate the probability of life in the universe. Drake Equation is: N = R* • fp • ne • fl • fi • fc • L.

“N” represents the number of advanced civilizations within our galaxy.

“R*” represents the average rate of star formation in our galaxy.

“fp” represents the fraction of those stars that host planetary systems.

“ne” represents the number of such planets which can potentially sustain organic life.

“fl” represents the fraction of planets that develop life.

“fi” represents the fraction of life-bearing planets that evolve intelligence.

“fc” represents the fraction of technologically mature civilizations that can produce signals indicating their existence.

“L” represents the average lifespan of these civilizations. 

Using the Drake Equation, we should be able to calculate how many planets in the Milky Way host intelligent civilizations. But there’s one big issue: we don’t know these values with certainty.

The last four are completely unknown. Those who have used the Drake Equation have come up with both wildly optimistic (up to 100,000,000 civilizations), and incredibly pessimistic (much less than 1) estimates.

There might be life in outer space, but there’s also a chance that there isn’t. And many scientists have argued passionately one way or the other.

What Are Some Possible Answers To The Fermi Paradox?

Answers to the Fermi Paradox attempt to explain why we haven’t heard from any extraterrestrials (or seen evidence of their existence). 

Rare Earth Hypothesis

According to the Rare Earth hypothesis, we live on a planet unique in its ability to host and sustain life. The theory proposes that the conditions that led to life evolving on Earth are so rare that we only met them by circumstance.

A further theory suggests that although developing life may not be that unusual, intelligent life is. For example, of all the species on Earth, humans are the only ones to develop space travel.

Earth Developed Early

One theory suggests that rather than being a newcomer, Earth is actually further along the evolutionary journey than most. Life might be out there, but not intelligent life. If aliens are going to get in contact, we’re in for a long wait.

Earth’s Developed Late

It’s possible that aliens have communicated with us, but we missed the message. Humans have only been exploring space since the 1960s. If an alien civilization sent a message 500 years ago, we’d have had no way to receive it.

And as communication between planets could take thousands of years, we might be in for a long wait for the next one.

Intelligent Life Destroys Itself

Another explanation is that intelligent life ends up destroying itself. This theory proposes that the quest for knowledge is driven by a desire to rule, and the wish for an easy life. And the result of both of these might be annihilation.

A related theory suggests that intelligent life destroys others. This would suggest that civilizations destroy intelligent life as it appears. In which case, we might be glad they haven’t contacted us.

Aliens Are Too Alien

We assume life on other planets is different, but it might be more different than we realize. It’s possible that aliens would be just too alien for us to successfully communicate.

Perhaps they have gotten in contact, and we just didn’t notice because we weren’t watching for the right kinds of signals. 

In many cases, life may have evolved underwater. Beneath the waves, aliens might not even know there are other planets out there. And we would struggle to identify life underwater. 

They Don’t Want To Speak To Us

While humans are excited to find life on other planets, aliens might not feel the same way. There are numerous theories suggesting that intelligent civilizations are simply quiet.

It might be that they don’t want to talk to a planet still seen as primitive, nor affect our development. Or they might see communication as dangerous.

Alternatively, alien societies might be listening, rather than transmitting. That would mean that we were all sitting quietly, waiting for someone else to talk.

It’s Just Us

The Great Filter Theory suggests that numerous events occur to make the development of life to the point of space colonization impossible, or exceedingly rare.

The theory proposes that Earth has either passed through the filter (and is the only one so far), or that the filter lies ahead.

Final Thoughts

The Fermi Paradox suggests that we might be the only developed life in the entirety of the Universe, but responses propose numerous explanations for the silence of our cosmic neighbors. For many scientists, the quest for alien life continues.