There might be a very good reason why aliens have not, or maybe will never, made contact with us on Earth.
It's one of the longest on-going conspiracies in the human race, with clues to extraterrestrial life seemingly littered around evidence left over from Ancient Greece, Ancient Rome, and Ancient Egypt and its mysterious pyramids.
It seems as though speculation around the subject will never end, but the bottom line is we don't have any hard evidence proving that we've ever come into contact with aliens.
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Of course, there is the belief that we are the only species in the universe on this level of intelligence, however, one scientist claims they have a more likely theory - that alien civilisations were destroyed by one thing in particular.
Astronomy professor Dr Frederick Walter believes that gamma-ray bursts (GRBs) have destroyed alien civilisations.
GRBs are extremely energetic explosions that have luckily only been observed in distant galaxies. They occur when the core of a huge star runs out of nuclear fuel and collapses under its own weight, which emits a colossal 'super nova' of radiation.
The professor spoke to DailyMail.com, describing it as a 'tightly focused beam', and that if it were to be directed through the plane of the galaxy, 'it could basically sterilise about 10 percent of the planets in the galaxy'.
"It's just one of many possible explanations, sort of morbid, I suppose," he highlighted.
Gamma-ray bursts are no joke, with NASA calling them 'the most powerful class of explosions in the universe'.
A typical GRB will deliver a bright beam of directed energy, and by bright, it means one quintillion (one followed by 19 zeros) times the brightness of our own Sun.
Believe it or not, that is apparently enough to burn an alien civilisation off the face of its galaxy.
You'll be relieved to hear though, that according to research from NASA's orbital Compton Gamma-Ray Observatory, these bursts are quite rare in our own Milky Way galaxy.
Following the observatory's opening in 1991, scientists thought they would see more GRBs coming from our galaxy, but it was discovered that these events are more common in younger galaxies that are still in the process of forming new stars, or transforming collapsed stars into black holes.
Dr Walter further added: "It's estimated that there is a gamma-ray burst every 100 million years or so, in any galaxy.
"Over a billion years, on average, you might expect a significant number of civilisations to be eradicated, should they exist."
The expert highlighted that this is just one hypothesis for why we haven't discovered signs of extraterrestrial civilisation, as he estimates there may have been 45 to 450 GRB events in the 4.5 billion year history of our planet.
However, others have theorised the Earth's Ordovician mass extinction approximately 359 million years ago, or its Devonian mass extinction, were a result of a GRB or a black-hole event.
Dr Walter said that despite its apocalyptic capabilities, a GRB is 'not worth worrying about for humanity as they're 'rare' and 'directed', making them less likely to hit our planet.
And also, we literally can't prepare for one, so if it happens, we're all done for - fun.
He also pointed out that aliens could be aquatic species for example, and wouldn't be able to develop technology for space travel, despite possibly having large brains and developed social skills.
Another theory is that other civilisations have followed our trajectory of polluting our atmosphere, with technology exceeding wisdom and eventually leading to their species being wiped out by their own doing.
Dr Walter stated: "I would guess that's the leading theory, but, look, it's all speculation.
"We have one example: That's us."
But at the same time, he mentioned that humanity's first leap into the rank of technologically advanced species happened during the 19th Century Industrial Revolution, so we've only been 150 years as an 'advanced species'.
"There's always a risk we're not going to make it through another one or 150 years," Dr Walter concluded.
Topics: Science, Space, Aliens, Technology
Joshua Nair