Last year, we showed you the massive size of the universe (hint, it’s REALLY big). But in a universe that large — and given the Milky Way Galaxy itself is so expansive — why haven’t aliens contacted us? That’s the essence of the Fermi Paradox.

The idea is this: It shouldn’t be out of the question that there are many sophisticated civilizations across the galaxy. Given the age of the Milky Way itself (about 13.21 billion years), even a cosmically small sliver of time (like 10 million years) should be enough for some type of contact to occur.

Italian physicist Enrico Fermi is credited with bringing this question into the scientific forefront. According to stories, the genesis of the Fermi Paradox came during a 1950 lunchtime discussion with colleagues. They all thought it reasonable to speculate that we were not alone, and that we likely have a lot of company. But Fermi began to wonder, if that’s true then where is everyone?

Think about it in terms of humankind’s own space accomplishments. We’re on the cusp of interstellar space travel, and likely will send our first interstellar probes within the next few decades. That’s less than a century after mankind first sent a human being into space. In hundreds, thousands, if not millions of years, what could we do?

This point wasn’t lost on Fermi and his companions, even years before the first humans made it to space. An alien race should have no trouble colonizing the galaxy with a decent amount of rocket technology and some imperial wherewithal — especially in ten million years.

But scientists need proof though, and there’s little if any scientifically accepted evidence to back up the notion that we’re not alone in the universe. Even so, and using physics as an excuse for limiting speed of any alien spacecraft, it just doesn’t make sense.

Take Proxima Centauri, for example. Even going just a quarter of the speed of light, an alien craft could make it to Earth in 16 years. The planets around Gilese, 60 years. The slew of potentially habitable planets around TRAPPIST-1? About 160 years. That’s a long time, but nowhere near the 10 million year timeframe Fermi and his colleagues discussed, and a drop in the bucket when compared to the age of the Milky Way Galaxy itself.

The Drake Equation

Let’s shift gears to understand further why the Fermi Paradox gives astrophysicists fits. The Drake Equation is a simple mathematical formula first proposed by astronomer Frank Drake in 1961. Simply put, it tries to estimate the number of technologically advanced and communicating societies present in the galaxy. It looks like this:

Over the years, many astrophysicists have attempted to estimate each of the values, but here’s what they have come up with. R can also be thought of as the number of stars in the galaxy, which is currently estimated at 100 billion. Even on the low end, the fraction of good stars with planetary systems is thought to be about 20 percent, and those with “ecoshells” — life sustaining atmospheres — thought to be at least one per star. For the sake of argument, let’s say only 10 percent could actually develop lifeforms capable of human intelligence and communication. We’re eliminating quite a few possibilities, since that’s 10 percent of 10 percent of 10 percent.

Finally, “L” is a fraction of time the planet has borne communicable life. We’ll assume that they’ve been on their planet for as long as we have, so we make this 1/100,000,000. So, we’ve been awfully pessimistic. What is our result?

Two. So us, and somebody — or thing — else. It’s hard to believe that other civilizations haven’t been around longer than us. There are also other pre-technology civilizations that Drake’s Equation doesn’t even address. This leaves us with even more questions.

The Kardashev Scale

Adding to the debate is something called the Kardashev scale. Created by Soviet Russian astronomer Nikolai Kardashev, it classifies civilizations by the amount of usable energy they can harness. These classes are:

Type I. This civilization has the ability to use all energy available on their planet.

This civilization has the ability to use all energy available on their planet. Type II. This civilization can harness all the energy radiated by its star.

This civilization can harness all the energy radiated by its star. Type III. This civilization can harness the energy of the entire galaxy.

Carl Sagan put us about 70 percent of the way to Type I, and we should be able to achieve it within a century or two. Current calculations estimate we will reach Type II in a few thousand years, and to Type III within 100,000 to a million years.

At Type II or III, a civilization should be able to speed across the galaxy at close to the speed of light (or faster, if they’ve managed to discover ways to bend the current laws of physics). Things get even more mysterious.

So what gives?

The problem with the Fermi Paradox is that we might not ever be able to confirm or deny it, unless we either gain the technology to scan every planet in the galaxy, find aliens ourselves, or they find us. In the meantime, we’re left to speculate why we still haven’t heard from any galactic neighbors.

The Great Filter

One explanation is known as The Great Filter theory. In simplified terms, “The Great Filter” is an evolutionary step that is so difficult to surpass that most civilizations cannot surpass it. This prevents civilizations that could eventually gain spacefaring capabilities from doing so, simply because they destroy themselves first.

But there’s no consensus on where this Great Filter is located on the path from the origins of a civilization to a Type III on the Kardashev scale. Some even argue that we’ve already surpassed it, or that there are actually multiple ‘Great Filters.’ We also have no way of knowing how far we’ve come in the process, and we could simply be the most evolved species currently in existence.

Another version of the theory argues that we haven’t even made it to one of these Great Filters, and that we’re destined for destruction just like everybody else. The discovery of fossilized complex lifeforms on other planets could lend credence to this theory — but that hasn’t happened yet.

There’s a reason for the silence

Another line of reasoning speculates that it’s not necessarily the Great Filter, but a host of other reasons for why we haven’t heard from aliens yet. Here are a few possibilities:

They were already here. Aliens could have visited us thousands of years ago, and we’d have no way of knowing. Early humans had no way to describe what they were seeing in modern terms. In fact, they’d probably consider it a sign from God himself. But there is merit to this theory, in spite of that crazy-haired guy from Ancient Aliens. Some of the structures built by early man are so extraordinarily complex that they defy explanation even in our modern society.

They’re too advanced, and don’t care. Galactic snobbery may be at play. Spacefaring societies may already know about us, but believe Earth has nothing to offer. So they pass us by, and will continue to do so until we’re interesting to them.

We live in the Galactic version of the boondocks. Other portions of the galaxy may already be colonized, it’s just that Earth and the solar system are in a remote area. This would prevent them from getting to us easily, and vice-versa.

Safety reasons. interstellar chatter might attract the attention of aggressive species aimed at galactic domination — think Star Trek’s Borg. This species may have also wiped out other communicative species, which is actually a tad bit scary if you think about it. We could be next!

We’re too primitive. Maybe signals from other civilizations are already out there, and our current communications technologies are too primitive to either pick out those signals, or we’re listening the wrong way (applying our techniques for communication transmission to an alien society which might be doing things completely differently). Think of it like turning on the radio to the wrong station.

We live in The Matrix. Perhaps the most depressing explanation is that none of this reality is actually real, and it’s all just a simulation. The theory has gained some speed over the past decade or two, and it would indicate that we are alone, and an experiment for another, far more advanced civilization’s scientific curiosity.

As you can see, there’s a multitude of reasons — all of them even in the slightest bit plausible — for why the search for alien life has come up fruitless. But until we find concrete proof, the Fermi Paradox will continue to keep astrophysicists busy trying to explain the eerie galactic silence.

It might not be Fermi after all…

In the interest of complete accuracy, we should mention that Fermi was not the first scientist to speculate on this issue, and some accounts dispute he was even speaking of the lack of alien contact in terms of the actual existence of alien life during that lunch conversation. As early as 1933 astronautical theorist Konstantin Tsiolkovsky was speculating on many of the same issues that Fermi is credited for, although in unpublished manuscripts.

Fermi’s rumored discussions were the first to be extensively debated in the scientific community, and he’s received many of the accolades — fair or not.

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