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You may think that when the sun goes down and Earth slips into darkness, the magic of the beach comes to an end. For me, it’s the perfect setup for contemplating the night sky and its stars. With feet tucked in cool sand and a pointer in hand, I ask my partner – also an astrophysicist – to name the stars and constellations.

Spellbound by the heavens, I always end up talking of what may – or may not – lie beyond.

On a pitch-black night, our eyes can see up to 5000 stars (Elon Musk, please don’t ruin this!) But there are many more that we can’t see because they’re too faint or too far.

Our galaxy hosts hundreds of billions of stars; and as far as telescopes can see, there are about 100 billion galaxies in our Universe. That means that there are at least a 1 followed by 22 zeros stars in the Universe. Of these, about 10% are stars similar to our Sun. That’s more stars than the sand grains on our beaches and deserts combined.

We don’t know how many of these stars have the right conditions to host a planet like ours, with the right temperature and environment to harbour life. A recent study suggests that about one in four stars similar to our Sun can host a planet the size of Earth. This means that in our galaxy alone there should be about 1 billion stars with planets similar to Earth and many of these are older than our solar system. So if the conditions are met, intelligent life should have already developed. How many extraterrestrial civilisations are out there?

We can only speculate.

There’s a formula that tries to put a number on it called Drake’s equation, but there’s a catch. The equation depends on several unknowns such as the number of stars born each year and the fraction of those that have planets. So it doesn’t have one solution, but rather many possible solutions that range from “we are alone in the galaxy” to “there are millions of such civilisations”.

If there are millions indeed, these civilisations should have more advanced technologies than ours. So we should have already met them or at least heard from them, but we haven’t.

Where is everybody?

This question is called the Fermi paradox, named after Italian physicist Enrico Fermi, and has been nagging scientists for a long time. More than 75 theories have tried to answer it, three of the most acknowledged ones are:

1. Intelligent extraterrestrial life is very rare and only a few civilisations ever arise

2. The lifetime of intelligent civilisations is very short (which urges us to use our time more wisely!)

3. Civilisations exist, but we do not see the evidence.

Scientists are looking for answers using radio waves. The idea behind this is simple: our civilisation uses radio waves to communicate, from listening to the radio to calling our granny by mobile phone and checking social media. If intelligent civilisations exist, they may also have a technology that emits radio waves. On the other hand, celestial objects like stars and galaxies also produce radio waves and astrophysicists use huge radio telescopes to detect them. So why not use our telescopes to pick up signals coming from extraterrestrial civilisations?

SETI, which stands for “Searching for ExtraTerrestrial Intelligence” is a nonprofit organisation that has been looking for such signals with radio telescopes for more than 30 years. However, none have ever been detected. This may not be too surprising. A study that just came out in June suggests that in our galaxy there should be at least 36 civilisations that can communicate via radio signals but they are so far away that it is impossible for our current technology to spot them.

Perhaps we’ll find intelligent life one day, perhaps we won’t. Maybe we are the aliens on this beautiful planet, or we live in a simulation and don’t realise it. Until we find out (if ever), the notion of how small and insignificant we are compared to the vastness of the Universe will continue to amaze me. But, what if the theory that we haven’t heard of any such civilisations because they destroyed themselves before developing cutting-edge technologies, is true?

This is terrifying and it urges us to prove our intelligence and take responsibility for our actions. We must take care of our planet and every precious life on it instead of wasting time and resources on wars, violence, racism, xenophobia or misogyny. As intelligent beings, it is our duty to preserve not only our own species but others on our planet, the only place in the Universe where life exists and can be sustained as far as we know…

Illustration is by Martha Rosas Vilchis.

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