Why We Will Never Meet Aliens

Scale and probability suggest that intelligent life should be common throughout the Universe, so why is it that we will never meet aliens?

A couple of weeks ago, I discussed the reasons why we’re extremely close to finding definitive evidence of extraterrestrial life and will most likely do so in in the next two or three decades. However, although such a discovery would still be one of the most profound in human history, we’re unlikely to find anything beyond microbial life, although it will be extremely difficult and, perhaps, impossible to tell exactly what sort of life it is. Intelligent aliens (herein after referred to simply as ‘aliens’) are another matter entirely.

Many respected scientists take the notion of actually encountering an extraterrestrial intelligence about as seriously as they do astrology. SETI might seem hopeful, and I wouldn’t want to discourage their search, but the chances of ever meeting a sapient extraterrestrial lifeform or, for that matter, even finding direct evidence that such a thing exists, is vanishingly small. Does that mean we’re the only intelligent species in the Universe? Absolutely not, but that’s more a matter for philosophers than scientists.

Our Fleeting Existence

Pyramid of GizaWikimedia Commons

We tend to think of the 4,500-year-old Pyramid of Giza as ancient, but its existence has been incredibly brief when compared to that of modern humans.

Let’s talk first about the possibility (or, more likely, the impossibility) of encountering an alien intelligence that we can meaningfully communicate with or even notice. Aside from the unimaginably immense distances involved, there’s also our own fleeting existence to consider. I also find it hard to imagine that it will be anything more than fleeting. Are we really going to exist for long enough, at least in a form that we ourselves could currently relate to, to encounter aliens?

To put everything into perspective, let’s briefly consider the history of life on Earth. As far as we know, life has existed in our little corner of the Universe for at least 3.8 billion years. Multicellular life has existed for around half that amount of time, and the first known animals, which were sea sponges, appeared around 670 million years ago during the Cryogenian Period. Our own genus, homo, has existed for a mere 2.86 million years, although the oldest civilisations only date about 8,000 back. We’ve been capable of broadcasting into outer space for less than a century.

Additionally, around 5 billion species have ever lived on Earth, and we’re just one of them. Over 99% of every animal, plant, fungus or microorganism that has ever lived is now extinct, and almost all of them disappeared long before our own ancestors started walking on two legs. We’re a geologically young species, and the existence of animals, including the humble sea sponge, also spans a relatively small portion of the Universe’s near 14-billion-year history.

English Professor Brian Cox has, in my opinion, one of the best explanations for the so-called Fermi Paradox. The paradox refers to the apparent contradiction between the high probability that aliens exist and the fact that we have absolutely no evidence that they do. Unfortunately, it isn’t too optimistic. Cox claims that a civilisation capable of interstellar travel is extremely unlikely to be sustainable. With such great power, a civilisation would also have the power to wipe itself out at the touch of a button.

While things like political turmoil, artificially induced environmental hazards and other potentially civilisation-destroying threats might not necessarily be universal, accidents can also happen. Ultimately, the incredible amount of power and resources required for a civilisation to last long enough to make a meaningful impact on the wider universe appears to be extremely volatile. That’s not to say we shouldn’t be trying our best, but it does seem that our long-term survival is rather unlikely.

Letters to the Universe

Voyager Golden RecordNASA/J

Both of the Voyager spacecraft, launched in 1977, were equipped with phonograph records containing sounds and images from our homeworld.

The first message intentionally broadcasted into outer space was the Arecibo message in 1974. Conventional radio broadcasts, however, have long had a hard time breaching the Earth’s ionosphere. The first message to do so may have, rather disturbingly, been the televised opening ceremony of the 1936 Berlin Olympics, in which Adolf Hitler featured prominently.

Once a radio signal has breached the Earth’s ionosphere, in most cases losing a great deal of clarity in the process, there’s little stopping it from reaching its destination. Considering the Arecibo message was the first intentional interstellar radio signal sent out from Earth, that gives us 43 years and, consequently, 43 light years of coverage. Nonetheless, it will still take another 25,000 years, travelling at the speed of light, to reach its destination – the Messier 13 cluster of stars.

Unless there’s a way to communicate faster than light, which the known laws of physics clearly contradict, there is no meaningful way to communicate over distances much further than a few hundred light years. Even if an obliging alien picks up the Arecibo signal on a planet 100 light years away, and decides to respond immediately, we can’t expect a reply before the year 2174.

The Voyager Golden Record, which was included aboard two of the most successful space exploration missions to date, also contains a letter to the Universe that’s meant to portray our species, life and culture to anyone who finds it. However, despite being by far the furthest manmade object from Earth (almost 12 billion miles or 19 billion km), its chances of being discovered are vanishingly small.

Should aliens ever discover our radio signals or our long-lost probes, which is theoretically possible, it’s likely that our civilisation will be long gone by then. In fact, the Voyager probes, as well as other missions we’ve sent out into space over the last half a century, will almost certainly be among the last relics of our existence. It’s a sobering thought that these machines will still be continuing their eternal journeys for millions, if not billions, of years after our own world has been swallowed by a dying sun.

While we should always have hope (and I myself support the efforts of organisations like SETI), the chances of our letters to the Universe being read, at least in the lifespan of human civilisation, are so tiny as to be practically non-existent.

Are We Special?

Ammonia WorldIttiz

An alien ecosystem may use ammonia, rather than water, as a solvent. This artist’s impression illustrates what such a world might look like.

As far as we know, humans are unique, which gives us all the more reason to do everything we can to protect our species, our planet and our legacy. The Rare Earth Hypothesis pretty much suggests that life is a miracle of circumstances, but it’s also built on entirely anthropic reasoning whereby we assume that everyone is just like us and that life needs the same very specific set of conditions to evolve. To name just a few:

  • A suitably large moon to influence the tides and keep the planet’s rotational period in check, thus stabilising its climate over a long enough period.
  • A comfortable stellar and galactic habitable zone where life-bearing surface temperatures and comfortable radiation levels can persist respectively.
  • A geologically active planet with a powerful enough magnetosphere to keep out harmful stellar radiation and help form a life-bearing atmosphere.
  • The right elemental composition and conditions for those elements to form life-giving molecules, such as DNA and RNA, common to all life on Earth.
  • A suitable arrangement of planets to ensure orbital stability over a long enough period for complex life to evolve.

As you probably guessed, the above requirements are extremely Earth-centric, and there really doesn’t seem to be any reason why alien ecosystems couldn’t follow their own rules. From alternative biochemistries to life that uses methane (rather than water) as a solvent, breathes a mix of nitrogen and carbon dioxide or doesn’t rely on photosynthesis, the possibilities are numerous.

In fact, for at least a billion years, microbial life managed just fine on Earth without there being any photosynthesis or free oxygen in the atmosphere. In other words, the last universal common ancestor to all life currently on Earth lived about 3.5 to 3.8 billion years ago in a world that would be deadly to almost all organisms that exist today.

Fortunately, the Universe is still big enough for plenty of other truly earthlike planets to exist, including civilisations much like our own that we could relate to. Although a multitude of aliens speaking English, as they do in Star Trek, might be a tad far-fetched, alien life on a planet that’s very like our own could just be remarkably similar, thanks to the effects of convergent evolution. But does that mean we’ll ever find them?

Not likely, given that we are special and that we are, almost certainly, alone in our region of the Universe. Our fleeting existence, combined with the vastness of space, makes it exceedingly likely that we are indeed the only sapient species in our galaxy, if not in an ever further radius. If aliens exist, the chances are that they’re millions, if not billions of light years away and forever out of our reach.

Technology Outlives All

Artificial IntelligencePixabay

Advancement in technology suggests that artificial intelligence will inevitably supersede biological sentience.

Given all the evidence we have and everything we know about the evolution of technology, it seems far more likely that technology will inevitably outlive the civilisation that created it. The Voyager space probes are a perfect example of this. However, we’re also closer than ever towards uploading the entire human consciousness into a machine or even creating a completely artificial intelligence from scratch. In other words, the chances of the human race (or any other technologically advanced civilisations) surviving are if they transition to purely machine-based intelligences. It sounds dystopian, but it does overcome the limitations of biological life.

Artificial intelligence has the potential to become vastly more intelligent than us mere biological creatures could ever dream of. Using an analogy, it would be like trying to explain the theory of relativity to a peanut. Such an intelligence would be unhindered by the bounds of biological mortality, while logical thinking would help to ensure that it didn’t wipe itself out. As an avid gamer, I’m reminded of the Reapers in the Mass Effect series, a machine intelligence that systematically purges all technologically advanced civilisations every 50,000 years to prevent them from destroying each other and thus wiping out all biological life in the galaxy.

While the Reapers might sound far-fetched, they exemplify an increasingly popular theory that makes more sense the more our own technology advances. It also makes sense, however, that if aliens are machines, they would likely be uninterested in us to the extent they might purposefully be avoiding us or even not notice us at all. Indeed, we might be about as irrelevant to them as the irritating fly you just swatted.

There’s also the possibility that aliens, machine or otherwise, wouldn’t even communicate using radio waves. In 2012, US physicists successfully managed to conduct the first communication using neutrinos, an elementary particle that interacts only with gravity and the weak nuclear force. Perhaps, empowered with neutrino communication, SETI might have better chances of achieving its goal, but I wouldn’t hold your breath.


While I do believe ours isn’t literally the only civilisation in the vastness of the Universe, actually encountering sapient aliens belongs squarely in the realm of science fiction. Nonetheless, I also think it’s important to keep an open mind, since the exploration of space yields an endless stream of incredible surprises. Perhaps one day, us sceptics will be proven wrong, but I’m not sure that would necessarily be a good thing. What do you think we’re going to find out there? I’d love to hear your opinions on this fascinating topic, so feel free to leave a comment!

Further Reading

4 Responses

  1. T. Douglas

    Whatever intelligence we ever do encounter through its own or our initiative will then almost certainly have to be artificial.

    • Charles

      Thanks for your comment T! Indeed, that seems to be the most realistic hypothesis. On the other hand, an alien intelligence could be naturally evolved enough to such an extent that it doesn’t need to rely on artificial intelligence.

  2. James C.

    “We tend to think of the 2,500-year-old Pyramid of Giza as ancient, but its existence has been incredibly brief when compared to that of modern humans.”

    It’s a little older than that – 4,500 years old, give or take a century or two. Though the point made is still valid.

    • Charles

      Thanks for pointing that out James! I had meant to say 2500 BC. Anyway, it’s corrected now 🙂


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