Are We Alone in the Universe?

Arthur C. Clarke, a science writer and futurist, once said, “The idea that we are the only intelligent creatures in a cosmos of a hundred million galaxies is so preposterous that there are very few astronomers today who would take it seriously. It is safest to assume, therefore, that they are out there and to consider the manner in which this fact may impinge upon human society.” The universe is approximately 93 billion light-years in diameter and is expanding at roughly 1.96 million km/s [1]. In other words, when travelling at the speed of light (approximately 3 x 108 m/s), it would take an individual 93 billion years to travel across the universe. Many people are curious as to why we still have not encountered extraterrestrial (ET) life, despite the boundless possibilities that exist within the vast expense of the universe. This is also known as the Fermi paradox, which describes the conflict between expecting a high probability of the existence of intelligent life elsewhere in the universe compared to the ‘empty’ universe we observe [2]. Another term used to describe this silence and loneliness we are experiencing is the ‘Great Silence’ [3].

Image by StockSnap from Pixabay

Scientists have pondered the existence of ET life for centuries. In 1961, astrophysicist Frank Drake developed an equation — the Drake equation — that seeks to determine the potential number of intelligent civilisations in our galaxy (Table 1) [4]. However, many sceptics claim that the equation relies on too many assumptions and that the actual number of intelligent civilisations will more likely than not vastly differ from our predictions. Furthermore, scientists have proposed modifications and novel approaches to the original equation in recent years [5-7]. This article explores a few of the many proposed theories as to why we have yet to encounter ET life.

The Great Filter

Despite the universe being incredibly ancient, we do not have any solid evidence of ET intelligence colonising our solar system or nearby systems. R. Hanson [7] suggests that a ‘Great Filter’ stands between ordinary dead matter and advanced life that flourishes. For humans to thrive as a species like we are now, the appropriate conditions had to be present at the right time. It has been an arduous journey from the formation of our star system to the first ribonucleic acid (RNA). This subsequently led to the establishment of single and multicellular life and to the birth of complex organisms that utilise tools. Between each ‘checkpoint’, there are multiple ways in which the suitable conditions could have been absent, leading to our inexistence. Evolution is a complex biological process that — until the publication of Charles Darwin’s On the Origin of Species — we did not comprehensively understand [8]. Perhaps there are microorganisms somewhere out in the universe, but the probability of such organisms evolving into intelligent sentient beings is infinitesimal.

Another suggestion that has been made concerning the Great Filter is that sufficiently developed civilisations eventually eliminate themselves, rendering the species extinct with no traces of them left behind. Kardashev, N. S. [9] introduced a scale to classify technologically advanced civilisations according to the amount of energy they consume. Decades since, extended versions of the Kardashev have been suggested (Table 2) [10]. A Type I civilization is able to fully harness the energy that reaches its home planet from its parent star [9]. Basalla G. [11] claims that we are not a Type I civilization yet as we are unable to capture all the radiant energy streaming down on Earth. Our present civilization is closer to a Type 0.7, and scientists have predicted that we will attain Type I status by 2347 [12,13]. As a Type 0.7 civilisation, we already possess weapons of mass destruction that can destroy the Earth multiple times over. A moment of selfishness and carelessness could send us down a rabbit hole. As a species, we are also battling climate change. A new report generated by the United Nations (UN) mentioned that we must act now and reduce carbon emissions before we tread on an irreversible path toward climate disaster [14]. Climate change can lead to detrimental health outcomes; worse still, due to the unprecedented rate at which glacial ice is melting, thousands of microbes are now being released and reactivated into terrestrial and aquatic environments, which can lead to epidemics or even pandemics [15,16]. The Great Filter is a fantastic hypothesis for why we may not have encountered ET life. Recklessness and ignorance could have led to the fall of once glorious civilisations, preventing us from ever discovering their existence.

The Zoo Hypothesis

In 1973, John A. Ball proposed the Zoo hypothesis [17]. The hypothesis posits that intelligent life avoids interacting with us on purpose and that — like how we keep animals in enclosures and view them from a distance — they view the areas we reside in like a zoo. As a result, we will never discover ET life as they want to remain hidden from us, and they possess the technological capabilities to ensure it remains so [17]. The Zoo hypothesis is somewhat similar to the ‘Prime Directive’ — the belief that every society has the right to unimpeded and natural development — in the famous series Star Trek [18]. Much of the Zoo hypothesis is about respecting the autonomy of other civilisations, allowing infant civilisations to pursue their own destiny without interference. There is a possibility that advanced civilisations millions or billions of years older than us are watching us from the sidelines, waiting for us to achieve what they would consider intellectual, social and technological maturity. However, the concept that incredibly advanced beings are interested in the natural evolution of life on Earth sounds a little self-centred [19]. From an anthropocentric standpoint, we have never been great at non-interference with populations of other lands and differing cultures. Why should we assume that, unlike us, other civilisations are peaceful and altruistic? The Zoo hypothesis assumes that other civilisations care about our natural development. The contrasting proposal to this is that we are simply not worth contacting.

We Are Not Worth Contacting

When considering the age of the universe, we are an extremely young civilisation. To put this into perspective, scientists use the Cosmic Calendar, which compresses the timeline of the universe’s birth to our current time of technological development and globalisation. Based on this framework, with the Big Bang occurring on the exact first second of New Year’s Day, the first humans only appeared on December 31, at approximately 22:30. Agriculture was only invented by humans on December 31, at 23:59:20 [20]. The cosmic calendar demonstrates how insignificant our species is on a grand scale. Over the billion years in which the universe has come into existence, there could have been civilizations that are more than a thousand-fold more advanced than us. Like how we would not teach bacteria calculus, ET life may not find contacting us worthwhile. It is undeniable that we have made great strides in many aspects ranging from technological developments like smartphones and aeroplanes to scientific breakthroughs like the ability to edit our genes, amongst others. However, one must acknowledge that many social and scientific problems still exist. There are more than 20 ongoing military conflicts worldwide due to civil wars, territorial disputes and transnational terrorism [21]. Furthermore, there have been increasing inequalities in areas such as health and wealth, and many debilitating diseases still plague the population worldwide with no cure. As a species, we have much to learn and discover. Our lack of knowledge and wisdom, compared to potential ancient ET civilisations, may be why we have yet to encounter ET life.

Communication Differences

There are approximately 7,151 human languages spoken today [22]. When considering methods of communication the millions of species of animals worldwide use, we end up with a manifold of communication methods. The dolphin, for example, communicates through three known types of acoustic signals: burst-pulsed sounds, echolocation, and frequency modulated whistles [23]. Life on Earth alone communicates through a multitude of modalities. While we have sent and received many signals to and from space, we still have never directly interacted with ET intelligence. Current scientists involved in the Search for Extraterrestrial Intelligence (SETI) attempt to communicate with ET life by relying on the assumption that the basic principles of chemistry, mathematics and physics hold true throughout the universe [24]. This assumption may be wrong, and other scientific principles could govern the environment in which ET life thrives. Another challenge to communicating with ET life is the time it takes for civilisations to receive signals from other life forms. For example, a radio signal we have received from 12 million light-years away would mean that an ET civilization sent the signal toward us 12 million years ago. By now, the civilisation that sent said signal could have destroyed themselves or would have become so advanced that they have decided not to contact us. Similarly, we could send a signal into space now, and if a civilization one million light-years away receives it far into the future, we may have been long gone. Another interesting thought experiment is that ET life who look through a telescope — that must be technologically capable beyond human comprehension — would not see the technological progress we have made. If an ET species from 65 million light-years away looked at Earth through their telescope, they would see dinosaurs roaming around. There would then be no incentive in exhausting resources to travel to Earth and interact with life here.

To conclude, there are many suggestions made as to why we have not encountered ET life, most of which are plausible. Could we indeed be alone, or are the technological barriers to cross for interstellar interaction simply too high for us now? Even if we discover ET life over the next few centuries, there are multiple implications to consider. Fundamentally, our worldview will evolve. ET life will probably be vastly different from what most people expect them to be — green figures with large round eyes, or other cinematic representations of ETs. Whether the vast universe we reside in has other life forms remains to be seen.