There are probably thousands of alien civilisations living in the Milky Way, but our chances of ever meeting them are extremely low, an expert has said.
Michael Garrett, head of the Netherlands Institute for Radio Astronomy (Astron), made the comments at the International Astronomical Congress in Toronto.
Reported by Discovery News, the astronomer said data collected by Nasa and other space agencies suggests that Earth is one of 40 billion potentially habitable planets in our galaxy.
In addition, another habitable planet is believed to form every year, meaning the chance of alien civilisations existing is very high - there may be around 3,000 alien civilisations already out there according to the study.
However, Garrett said that with the sheer size of the Milky Way, sending out signals and receiving one back from a civilisation advanced enough to possess this technology is unlikely at the moment.
"On average, you'd expect the civilizations to be separated by at least 1,000 light-years in the Milky Way," he is quoted as saying. "That's a large distance, and for communication purposes you need to allow for twice the travel distance, so you're talking about civilizations that have to be around for at least a few thousand years in order to have the opportunity to talk to each other."
He pointed to Earth as an example of how life developed, with extremely simple life forms having been around for billions of years. Intelligent life only arrived much later, he said.
"We don't really know the time scales in which civilizations persist. [Intelligent life only developed] essentially in the last few minutes of the overall evolution of life on the planet. I don't want to be too negative about this, but... my basic conclusion is that Seti (search for extraterrestrial intelligence) signals will be rare in the Milky Way."
While Garrett does not expect to hear from aliens in the near future, experts at Seti are more hopeful.
In March, leading Seti astronomer Seth Shostak said he expects to make contact within the next 20 years thanks to advances in technology.
Speaking to Popular Mechanics, he said the search is still in its infancy, and is limited by equipment and money, but believes we are not far off: "My guess that we'll succeed in the next two decades is based on the fact that with improvements in digital electronics and computers – which are getting better and cheaper, following Moore's law – we will be continually sifting through the sky faster.
"And you can extrapolate how fast we'll be able to search, assuming we have the money, in the next decade or two."
It had better happen in the next twenty years -or before! Otherwise my final words will be "D'oh! I've wasted my life!"
That writ, people believe humans are not prepared for alien contact, nor should we be attempting such a thing: neuro-psychologist Gabriel G. de la Torre, professor at the University of Cádiz, has said scientists operating at organisations such as the SETI Institute (Search for Extraterrestrial Intelligence) should not be actively sending out messages to try to contact alien beings.
I think that, after a hundred plus years of science fiction literature, thousands of books and articles on aliens, UFOs and more -added to hundreds of movies and TV programmes about extra terrestrials, if de la Torre thinks humans cannot handle that concept then he is wrong. It is not the more naiive 1930s when the late great Orson Welles created panic with his War of the Worlds broadcast. This is 2015.
What humans will ask is the same they ask in any terrestrial meeting: "hostile or friendly?" THAT is what it comes down to. Hundreds of thousands -possibly millions- watch Ancient Astronaut and UFO documentaries each year and say "There has to be something in it!" But are they running around screaming in panic? No.
I once had a very "loud argument" with Carl Sagan. He was seen as the "arch debunker" of UFOs but he was, as I found out, far more open than seemed to be publicly known. Discussing people like Erich von Daniken and his Chariots of the Gods claims, which are about 99% sheer rubbish, Sagan actually stated that there was no proof aliens had visited Earth in the past -nor was there evidence that they had not.
And I have always been similar in my thinking. A great many Ancient Astronaut followers see 'evidence' everywhere and yet ignore a proper explanation. "Humans could not have built large ancient structures" such as the pyramids or even Stone Henge they declare. "Only" anti-gravitational devices from visitors to our planet could have achieved this.
In fact, back in the early 1980s I got so "steamed up" at someone giving a talk about "How aliens built the pyramids" because humans could not that I pointed out what we knew about pyramid construction back then -and we have learnt far more since then. "Well, that is what archaeologists want you to believe" I was told. You cannot argue with blinkered minds that will spit on the achievements of humankind because it spoils their theories. Humankind achieved a great deal and that needs to be acknowledged.
Nasa has released a new book that suggests ancient rock carvings found across the globe were may have been created by extraterrestrials.
As the search for life on planets other than our own continues, the space agency has suggested ways in which we might communicate with aliens from other worlds.
In one section, William Edmondson, from the University of Birmingham, considers the possibility that rock art on Earth is of extraterrestrial origin.
And many UFO believers will tell you matter-of-factly, "They" are already here so why bother looking and, oh, by-the-way, "there are thousands of them out there -and the governments know where they come from!"
Now let's not get into that here!