Are We Alone in the Universe? SETI’s Search for Alien Life

Where is Everyone?

The Search for Extraterrestrial Intelligence (SETI) has captivated scientists and the cosmic-curious alike. Since the mid-20th century, astronomers have scanned the cosmos for whispers of alien civilisations, yet silence still echoes back. With so many brilliant minds on the case, why haven’t we found a single definitive sign of life beyond Earth?

To unravel this conundrum, we’re going to dive into the heart of the search:

1. Habitable worlds: Where do we look for planets where life could thrive?
2. The hunt: What methods are scientists using right now to detect intelligent life?
3. The odds: How likely is it that intelligent life actually exists?

But first, let’s rewind the cosmic clock and take a brief look of the history of SETI.

The Birth of Modern SETI: How the Alien-Hunting era Began

The Dawn of Discovery (1959-60)

The Search for Extraterrestrial Intelligence took its first significant step in late 1959 and early 1960 when physicists Giuseppe Cocconi and Philip Morrison published their groundbreaking paper proposing radio searches for signals from alien civilisations. Around the same time, Cornell University astronomer Frank Drake independently launched the first modern SETI experiment. Known as Project Ozma, Drake’s pioneering effort used the Green Bank radio telescope to scan the skies for potential extraterrestrial communications.

NASA’s Cautious Foray (1960s-70s)

During the following decades, NASA began showing interest in SETI, offering modest support to the initiative. However, this involvement remained limited, with no major institutional commitment.

The Birth of the SETI Institute (1984-85)

A major milestone arrived in 1984 when the SETI Institute was formally established as a non-profit organisation. With Thomas Pierson as CEO and Jill Tarter as the lead scientist, the institute officially commenced operations on February 1, 1985, marking a significant step forward in the structured search for extraterrestrial intelligence.

With SETI’s foundations in place, all attention was turned to the critical question: Where should we even look? The hunt for alien signals begins with finding the right cosmic real estate – planets in the ‘Goldilocks Zone’.

SETI Institute, Source: SETI Institute

The Search for Life’s Perfect Neighbourhood

Imagine a place where water flows freely, where temperatures are just perfect so that oceans are not so hot that they boil away, and not so cold that they freeze solid – a true cosmic real estate gem. This is known as the habitable zone, or what astronomers poetically call the “Goldilocks Zone”: the narrow orbital band around a star where conditions might be just right for life as we know it.

Earth, of course, is the poster child for this perfect positioning. But with 200 billion trillion stars lighting up the universe, nearly all of them hosting exoplanets, logic suggests that there must be countless other worlds lounging in their own stellar sweet spots.

The Catch? Not all Goldilocks Zones are created equal. Take red giants: these bloated stars offer sprawling habitable zones, but their “prime time” lasts only about 1 billion years – far shorter than the 4 billion years it took intelligent life to emerge on Earth. That’s why SETI scientists keep their telescopes posed on Sun-like stars, where stable conditions might give life enough time to appear. In fact, about 22% of Sun-like stars are estimated to have an Earth-sized planet parked comfortably in their habitable zone.

While we’ve discovered plenty of Earth-sized planets, most orbit feisty red dwarf stars known for deadly radiation flares. The real prizes – Earth twins circling Sun-like stars- are frustratingly harder to spot.  So the hunt continues – not just for planets in habitable zones, but for those rare worlds where everything aligns: the right size, distance and atmosphere, the right star, and enough time for life to carve its name into the cosmos.

Eavesdropping on the Cosmos: The Three Main Ways we Hunt for Alien Life

The search for extraterrestrial life is like tuning a universal radio – we’re scanning through static, hoping to catch a whisper of something not random. It can also be compared to searching for a needle in a haystack, except we don’t know whether the needle or the haystack exist. Hopeful scientists currently pursue three main distinct paths to detect our cosmic neighbours:

The Hands-On Approach: In-Situ Sampling

Imagine scooping up Martian soil or drilling into Europa’s icy crust – this is in-situ sampling in action. While NASA’s rovers and sample-return missions push these boundaries, the method has a hard limit: we’re stuck within our solar system. As thrilling as it would be to find microbes on Mars, this approach won’t help us detect life orbiting distant stars.

Reading Life’s Chemical Signature

Biosignatures offer a workaround. By analysing starlight filtered through a planet’s atmosphere – a technique called spectroscopy – we can hunt for molecules like oxygen, methane, or anything else that hints at biological activity. Though, distinguishing between “life” and “weird geology” still remains a challenge.

Technosignatures

Here’s where things get exciting. Technosignatures – evidence of intelligent life – could range from accidental radio leaks (like our own TV broadcasts) to deliberate attempts at communication. Humanity has already sent physical messages into the cosmos, most famously the Voyager Missions’ Golden Record – a time capsule of Earth’s sounds, images, and music, now drifting beyond our solar system for any spacefarers that may find them in the future. But for practical SETI work, radio waves remain the prime focus because they:

• Travel unaffected by cosmic dust
• Can carry complex information
• Might be universal “hailing frequencies” for civilisations

The Golden Record, Source: NASA Science

Facilities like Ireland’s I-LOFAR radio telescope now scour these frequencies, listening for patterns that scream “This isn’t natural!”

I-LOFAR Radio Telescope Array, Source: Astronomical Society of Ireland

Fun fact: This picture was taken by hot air balloon!

The Bottom Line

While biosignatures could reveal life, technosignatures might reveal minds, and that’s why SETI’s radio searches, though needle-in-a-possibly-imaginary-haystack hard, remain our best shot at finding life beyond Earth.

Playing the Numbers: The Drake Equation and What it Really Says About our Chances of Finding Life

In 1961, Frank Drake formulated an equation that would permanently alter how scientists explore the question of humanity’s solitude in the universe. The Drake Equation didn’t promise answers – it offered something more valuable: a way to frame our ignorance in scientific terms.

Drake’s interesting formula estimates the number of detectable civilisations in our galaxy through seven critical factors:

N = R* × fp × ne × fl × fi × fc × L

where:

N: Number of technologically advanced civilisations in the Milky Way galaxy

R*: Rate of formation of stars in the galaxy

fp: Fraction of those stars with planetary systems

ne: Number of planets per solar system with an environment suitable for life

fl: Fraction of suitable planets on which life actually appears

fi: Fraction of life-bearing planets on which intelligent life emerges

fc: Fraction of civilisations that develop a technology that releases detectable signs of their existence into space

L: Length of time such civilisations release detectable signals into space

At its core, the Drake Equation is not about finding a definitive answer – it’s about structuring the debate. Some variables, like R* and fp, now have well-supported estimates thanks to modern astronomy. Others, like fl and L, remain profound unknowns.

Here’s the kicker: Plug in optimistic numbers (say, fl=1, L=1 million years), and you get thousands of civilisations. Use pessimistic values (fl=0.0001, L=300 years), and N might be less than 1. That’s the equation’s dirty secret – it can “prove” we’re either swimming in company or utterly alone – optimistic assumptions suggest a galaxy buzzing with life; pessimistic ones paint a lonelier picture.

So, What’s the Answer?

The Search for Extraterrestrial Intelligence is humanity’s quiet love letter to the universe. Every silent scan, every unanswered signal, isn’t just data – it’s us reaching out, hoping the universe might reach back. We don’t know if we’re alone, if we’re the first, or if we’re simply not listening the right way. But there’s something beautiful in the trying.

So we’ll keep listening. Not just because we might find answers, but because the act of searching connects us – to each other, to the stars, and to the possibility that somewhere out there, another voice is waiting to be heard. Until then, the silence isn’t empty; it’s full of potential. And that’s enough to keep looking up.

So, perhaps the only way to solve the conundrum is to keep searching. After all, as American astronomer Carl Sagan said, “Absence of evidence is not evidence of absence.”  We won’t know if we don’t look!