There are billions of galaxies in the observable universe, each with up to a trillion stars, meaning there are likely trillions and trillions of habitable planets in the cosmos.

But, if such worlds are so abundant, and life on Earth has been able to thrive, then why have we not found any aliens yet?

Known as the Fermi paradox, this is a question that continues to plague scientists - and in a video, experts have tried to tackle what's going on.

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Italian physicist Enrico Fermi posed a troubling question in 1950. He asked, if life was so abundant, why has no one made contact with us? No-one has been able to solve the Fermi Paradox to date. In a new video (still image shown), experts took at look at what the answer might be

Humanity has rapidly advanced in the last 100 years, but this is considered 'a blink of an eye' in history of the 13.82-billion-year-old universe.

So it’s not inconceivable to think we might start visiting other stars in the future.

But it seems unlikely that we would be the first civilisation to reach this stage, so surely we should have heard from someone by now?

This has led people to suggest that true interstellar travel may be impossible or, more dauntingly, perhaps no civilisation can last long enough to make contact.

WHAT IS THE FERMI PARADOX? The Fermi Paradox questions why have we not found aliens, despite the existence of hundreds of billions of exosolar systems in our galactic neighborhood in which life might evolve. Italian physicist Enrico Fermi devised it in 1950. He believed it was too extraordinary that not a single extraterrestrial signal or engineering project has yet been detected. He claimed there must be some kind of barrier that prevents the rise of intelligent, self-aware, technologically advanced, space-colonising civilisations. This barrier is sometimes referred to as a 'Great Filter'. The absence could be caused because either intelligent life is extremely rare or intelligent life has a tendency to go extinct. Advertisement

In a video created by YouTube channel Kurz Gesagt, they take a look at some of the factors that might have prevented us from making contact so far.

The first - and perhaps biggest - obstacle is space travel itself, which is extremely difficult, based on our current knowledge.

To colonise another planet with our current technologies, ‘a journey of maybe thousands of years needs to be survived by a population big enough to start from a scratch,' the narrator in the video explained.

Even if we could travel close to the speed of light, something inconceivable to us right now, it would take 100,000 years to cross the Milky Way.

So perhaps visiting another planet is out of the question.

It may also be a chance of cosmic circumstance that we have not yet made contact.

‘The universe is very old,’ the narrator in the video explained.

‘On Earth there's been life for at least 3.6 billion years. Intelligent human life for about 250,000 years.’

‘But only for about a century have we had the technology to communicate over great distances.

‘There might have been grand alien empires that stretched across thousands of systems and existed for millions of years, and we might just have missed them.’

Humanity has advanced in the last one hundred years, a blink of an eye in the 14.6 billion-year-old universe, so it’s not inconceivable to think that we might start visiting other stars in the future (artist's impression shown). But it seems unlikely that we would be the first civilisation to reach this stage, so where is everyone?

Another problem could be that, even if there are other alien civilisations alive right now, it might just be that our methods of communication are too primitive at the moment.

‘Imagine sitting in a house with a morse code transmitter, you'd keep sending messages but nobody would answer, and you would feel pretty lonely,' said the narrator.

‘Maybe we're still undetectable for intelligent species.’

Another interesting concept is the idea of a Matrioshka Brain.

This would essentially be a virtual reality within which a species that had no desire to progress further could live in paradise for eternity - not unlike The Matrix, although slightly less dystopian.

We have been searching in earnest for planets outside the solar system for decades using telescopes like Kepler (illustrated) but, so far, no sign of life has been found. In addition, we have been sending our own signals out for more than a century but, again, no one seems to have taken notice

One theory for an advanced alien race is that they might harness the power of an entire star, known as a Dyson Sphere (illustrated). However, if such a structure existed, it is theorised that we would be able to detect its infrared signature - but a recent study found no such evidence

HOW COULD ALIENS HARNESS THE POWER OF ENTIRE STARS? A proposed method for harnessing the power of an entire star is known as a Dyson sphere. First proposed by theoretical physicist Freeman Dyson in 1960, this would be a swarm of satellites that surrounds a star. They could be an enclosed shell, or spacecraft spread out to gather its energy - known as a Dyson swarm. If such structures do exist, they would emit huge amounts of noticeable infrared radiation back on Earth. But as of yet, such a structure has not been detected. Source: All About Space magazine Advertisement

A giant structure containing the collective consciousness of the species inside this virtual reality would harness the power of a star.

‘If built around a red dwarf [star], this computer could be powered for up to ten trillion years,’ said the narrator.

‘Who would want to conquer the galaxy or make contact with other life forms if this were an option?’

It has been theorised that such a structure - sometimes called a Dyson Sphere - would be noticeable if it did exist, owing to the huge amounts of infrared radiation it would give off.

But a study by Penn State University in Pennsylvania to find one of these structures in 100,000 galaxies proved unsuccessful, although further attempts are likely to be made.

‘All these solutions to the Fermi Paradox have one problem,’ said the narrator.

‘We don't know where the borders of technology are. We could be close to the limit or nowhere near it.

‘And super technology awaits us, granting us immortality, transporting us to other galaxies, elevating us to the level of gods.

‘One thing we do have to acknowledge is that we really don't know anything.’

We have now found planets beyond the solar system that could possibly support life, such as Kepler-186f (illustrated), but the chances of visiting one of these planets at the moment with our current forms of propulsion is out of the question - and perhaps true interstellar travel is simply not possible

The video concludes by saying that, although we might be ‘embryos’ on a galactic time scale, the only way to find out our true place in the universe, and discover if we are alone, is to continue our search, the advancement of our species and, ultimately, the colonisation of other worlds.

It could even be that we are, in fact, the most advanced race in the universe.