Is Anybody Out There? - The Search for Alien Life

A visualization of the various factors of the Drake Equation. Image Credit: NOIRLab/AURA/NSF/P. Marenfeld (CC BY 4.0)

Are we alone? It’s a question that humanity has long asked itself. Is the universe beyond this rock we call Earth teeming with life, or is biology a fluke never to be repeated? The only way to know the answers is to hunt for them ourselves.

The Search for Extraterrestrial Intelligence, also known as SETI, is a project with the sole purpose of hunting for intelligent alien life and answering the pressing question. Searches for extraterrestrial intelligence began in earnest largely in part due to Frank Drake, the physicist responsible for the eponymous Drake Equation. While structured as a mathematical equation, the Drake Equation is rather a thought experiment used to estimate the number of alien civilizations that could be detected right now based on various factors. These factors include the rate of star formation in our galaxy, the fraction of those stars with planets, the fraction of those planets suitable for life, the fraction of those planets that actually develop life, the fraction of planets with life that develop intelligent life, the fraction of civilizations that develop communication which could be detected by us, and finally the average length of time such a civilization would be broadcasting. Except for the first two factors, we have no real way of knowing what the factors of this equation would be. All we can do are plug in educated guesses. Plugging in the most pessimistic numbers yields an estimate of about 20 civilizations currently in the Milky Way galaxy, while the most optimistic can give upwards of 50 million. While only an estimate, it implies that life is out there. We only need to find it.

But how does one look for alien life when humans haven’t even traveled to another planet before? The answer is radio signals. SETI works under the assumption that any alien civilization at least advanced as us will be broadcasting radio signals. This could be messages meant specifically for us, or it could simply be their popular entertainment.

Ever since the radio became popular in the early 20^th century, humanity has been sending radio waves out into space in no small quantities. That’s not just the radio, but also television broadcasts, phone calls, and other wireless media. Even after the signals have done their job, they continue to travel outwards from our planet at the speed of light. Right now, humanity’s “radio bubble” extends out about a hundred lightyears in every direction from Earth. At the edge of that bubble is our earliest radio shows. At its center is last night’s news. As time goes on, this bubble grows larger as the first radio signals have a longer time to travel. At this moment, an alien civilization sixty lightyears from Earth could be tuning in to the premiere of the first episode of Star Trek.

Likewise, the goal of SETI is to find the equivalent broadcasts made by an alien civilization. More likely, this will be signals that are many hundreds of years old, or even thousands. The main issue is the signal strength. Signals degrade and get weaker over time. That means any transmission reaching Earth will be incredibly difficult to spot. The SETI program makes up for this with quantity. Massive arrays of radio telescopes, such as the Allen Array in Northern California, are the weapon of choice. A radio telescope is like a giant satellite dish. Essentially, it’s like a regular telescope, but made for radio waves instead of visible light. The array is an interferometer, which means its 42 large telescopes work in tandem to form what amounts to one massive telescope. The larger the telescope, the easier it is to detect a weak signal.

Despite over 60 years of nonstop searching, no confirmed signal of extraterrestrial origin has ever been found. Does that mean this is all a waste and that aliens don’t exist? Absolutely not. Space is big. Really big. The human radio bubble that stretches out for 100 lightyears in every direction may sound large, but it’s actually tiny. The Milky Way, our home galaxy, has a radius of nearly 53,000 lightyears. That means the area of our bubble is 0.0004% that of the Milky Way. That’s practically nothing. There very well could be an alien signal out there for us to find, but it just hasn’t reached us yet. Or, it has, but was rendered too weak by the mind-boggling distances it traveled to reach us. Either way, if we don’t keep our ears out, we’ll miss it altogether.