The Fermi Paradox: Where Is Everybody?

Where is everybody? Nobody knows yet. The Fermi paradox is the puzzle that the universe seems to offer countless places where life could begin, yet we have found no clear sign of anyone else. That silence could mean intelligent life is very rare. It could also mean that others are far away, short-lived, hard to spot, or that we have barely started looking. Today’s evidence cannot tell these possibilities apart.

Here is what we can say with confidence. Planets are common. No confirmed alien signal has ever been found. And our searches so far have covered only a tiny slice of the sky, the radio dial and time. The silence is real, but it is not yet strong evidence either way.

Where did the question come from?

In the summer of 1950, the physicist Enrico Fermi was at lunch with three colleagues: Emil Konopinski, Edward Teller and Herbert York. According to a history written for Los Alamos National Laboratory in 1985, Fermi’s famous question, often remembered as “Where is everybody?”, came out of that conversation.

The reasoning behind it goes like this. Our galaxy is very old and full of stars. If even one civilization learned to travel between stars, or to send machines to do it, it could in principle spread widely long before now. So why don’t we see any trace of them? It is called a paradox, but it is really a mismatch between what we might expect and what we actually observe.

Picture yourself in a huge, dark forest at night. You hear nothing. Maybe the forest is empty. Maybe the animals are quiet, or far away, or making sounds your ears can’t pick up. Or maybe you have only been listening for a few seconds.

What does the Drake equation tell us?

In 1961, the astronomer Frank Drake wrote an equation to serve as the agenda for the first scientific meeting on SETI, the search for extraterrestrial intelligence. The meeting took place that November at what is now the Green Bank Observatory in West Virginia. The Drake equation multiplies seven factors: how fast stars form, what fraction have planets, how many planets per system could support life, the fraction where life actually starts, the fraction where intelligence evolves, the fraction that develops detectable technology, and how long such civilizations keep sending signals.

It works best as a checklist of what we would need to know. In 1961, according to the SETI Institute, essentially only the first factor, the rate at which stars form, was known. Since then, astronomers have made real progress on the planet factors. NASA reports that our galaxy has more planets than stars, and more than 6,000 planets around other stars have now been confirmed. The biological factors are still guesses. Published estimates for the number of communicating civilizations in our galaxy range from one to several million.

In 2018, Anders Sandberg, Eric Drexler and Toby Ord took that uncertainty seriously. Instead of plugging in single best guesses, they used the full range of what scientists think each factor could be. For some factors, our uncertainty spans many powers of ten. Think of not knowing whether a number is closer to 10 or to 10,000. After also accounting for the silence we observe, they estimated a substantial chance, somewhere between 53 and 99.6 percent depending on which evidence they counted, that there is no other intelligent life in our galaxy. That is one careful analysis, not a final verdict. But it shows the silence may not be so surprising after all.

What are the leading explanations?

Complex life may be rare

In their 2000 book Rare Earth, scientists Peter Ward and Donald Brownlee argued that simple microbes might be common in the universe, while complex animal life could be very rare. Many lucky conditions may have had to line up on Earth.

There may be a “Great Filter”

In 1998, Robin Hanson proposed the Great Filter. Somewhere on the path from lifeless chemistry to a galaxy-spanning civilization, he argued, there must be at least one step that is extremely unlikely. If that step is behind us, such as the origin of life, we may be rare. If it lies ahead, it is a sobering thought about our own future.

They may be too far away, or out of step in time

Radio signals travel at the speed of light, and humans have been broadcasting by radio for only about a century. The last factor in Drake’s equation, how long a technological civilization lasts, is almost unknown. Two civilizations could miss each other like fireflies blinking in a field at different moments.

We may not have looked enough

In 2018, researchers Jason Wright, Shubham Kanodia and Emily Lubar estimated how much of the possible search space major radio searches had covered. Their answer: about as much as a large hot tub compared with all of Earth’s oceans. If you scooped one hot tub of seawater and found no fish, you would not conclude the ocean is empty.

How are scientists searching now?

Researchers now look for technosignatures: signs of technology that could be detected from far away. NASA lists examples such as radio or laser signals, industrial gases like chlorofluorocarbons in a planet’s air, city lights on a planet’s night side, and giant structures around stars. NASA held a technosignatures workshop in 2018. So far, no technosignature has been confirmed.

The Breakthrough Listen project committed $100 million over ten years to survey about a million nearby stars and the 100 closest galaxies. The SETI Institute’s Allen Telescope Array in northern California was the first radio telescope designed specifically for SETI.

The search has also taught hard lessons. A signal called BLC1, recorded by the Parkes “Murriyang” telescope in Australia while it pointed toward our nearest neighbor star, Proxima Centauri, at first looked promising. After careful checks, the Berkeley SETI Research Center concluded it appears to be interference from human technology. Thirty-nine hours of follow-up listening found no repeat.

What don’t we know yet?

Almost everything that matters most. We do not know how easily life begins; that is the subject of how life on Earth began. We do not know whether intelligence is a common outcome of evolution or a rare accident. We do not know how long technological societies usually last, including our own. And we do not know what signs a truly advanced civilization would leave. For now, “we don’t know” is the most honest answer. That is also why the broader question of whether we are alone remains open.

What would change the answer?

• A confirmed technosignature. It would need to repeat, be seen by independent telescopes, stay fixed among the stars, and survive every test for human interference. BLC1 shows why those checks matter. Our guide to what would count as evidence explains the standard.
• Life found elsewhere, even microbes. A second, separate origin of life in our own solar system would suggest life starts easily. That would push any “filter” later in the story.
• Much bigger searches that still find nothing. As the searched share grows from a hot tub toward a lake, continued silence would start to carry real weight.

Note that an unexplained light in the sky is a different question. An unidentified object is not, by itself, evidence of visitors.

Fermi’s lunch-table question has lasted over 75 years because it is honest about what we don’t know. If it stirs something in you, keep asking: What would you need to see to change your mind? And what would it mean for us if the silence turns out to be real?