We have already explored the likelihood of intelligent life existing elsewhere in the universe on our Universal Life page and we arrived at the conclusion that it is quite credible to believe that intelligent extraterrestrial life probably does exist. The next question is whether extraterrestrial life is visiting the Earth.
Let's start with the easy question. Is it possible that low level extraterrestrial life like bacteria can travel to the Earth by hitch hiking on meteoroids? Believe it or not this is indeed a very real hypothesis called panspermia. No smoking guns have been found, but there does exist at least some weak or disputed evidence for panspermia. This Scientific American article details research on a meteorite that fell to Earth in the 1960's in which chemicals have been found that represent the basic building blocks of life. The researchers claim to have proven that the chemicals were present before the meteorite landed on Earth. Additionally the Allen Hills 84001 meteorite found in Antarctica has been shown to have originated on Mars around 15 million years ago, and researchers have shown the possibility that it contains fossilised nano-bacteria. This claim is not 100% proven. Further reading on this topic is available on Wikipedia.
But that's not what most people mean when they think of extraterrestrial life visiting the Earth. The more popular question, which itself opens up a veritable minefield of questions, accusations and speculation is whether intelligent extraterrestrial life is systematically visiting the Earth for any number of reasons, whether benevolent or nefarious.
593-571BC: The bible describes several visions of the prophet Ezekiel. One such vision, well known in the UFO community as 'Ezekiels Wheel' is often interpreted as a sighting of flying saucers. Unfortunately for those of us who would like nothing better than to have confirmation that aliens are visiting the Earth, the interpretation of flying saucers requires a great deal of imagination. A great analysis can be found on Ancient Aliens Debunked.
329BC: Sources across the internet say that Alexander The Great had UFO encounters, and that they have been chronicled in historical texts. However, you only need to dig a little further to find that there are no existing copies of these supposed historical texts, and that the whole episode seems to have been manufactured in modern times. Even if it had been chronicled, and there is no evidence to support this, it would still not be proof of anything other than something that Alexander couldn't identify. Some lively discussion can be found on Project Avalon.
On a search through the piles of data available on the topic of alien visitation it becomes painfully obvious that there are people who simply 'want to believe' and will attribute almost anything to alien visitation. There are thousands of "sightings" listed on internet forums, in books, and on Youtube videos.
1561. An alleged UFO battle over Nuremberg Germany. The original source of this story appears to be a 16th century woodcut. These woodcuts were an early version of a news article. Their purpose was to record events, tell stories and most likely to sway popular opinion on various matters. UFO enthusiasts see this particular woodcut as irrefutable proof of a 16th century battle between flying craft. The truth is more likely to be that it's either a fanciful story about religious rivalry, a recording of unusual (but not unheard of) atmospheric phenomena or a combination of these.
1676. Edmund Halley saw a UFO, or did he? This is another example that appears to be just a modern manufactured event. I found 14 sites referencing this on the internet. Each site told the same story and none of them provided a valid source. Several of the sites linked to each other as the source, and two of them linked to a site that was a simply an advertisement for hotels.
1930's. There is a photo alleged to have been taken in Alaska of an alien in the 1930's by an anonymous photographer. This photo surfaced around 2009 and can be viewed on many websites including Cool Interesting Stuff. Once again though, the authenticity of this photo is dubious and it does not contain a clear image that could undoubtedly be recognised as an alien. It actually looks more like a child’s toy staged for the photograph.
1947 Pilot Kenneth Arnold saw something from his cockpit that he described as moving "like saucers skipping over water". This was the beginning of the term flying saucer. We emphasise here that he probably did see something. We have no reason to doubt that. But is it any more likely that he saw alien craft, or that he saw something more mundane that looked unusual? Kenneth Arnold clarified his comment later, saying that the objects did not look like saucers, but they moved like saucers skipping.
The problem with eyewitness reports is that they are very unreliable. In most cases there is no doubt that the eyewitness saw "something unusual", but exactly what they saw can not be verified. Because it can not be verified, there is no reason to assign the phenomena with being extraterrestrial in origin.
1947 The Roswell Incident is an alleged cover up of a crash landing by an alien flying saucer in Roswell New Mexico. Wikipedia has a good page about this topic. The thing about the Roswell Incident is that the official version of events, that it was a weather balloon, was widely accepted until the late 1970's when UFO researchers found a few anomalies in the official story and decided that therefore "it must have been aliens". In the 1990's the Air Force released declassified information about the incident explaining that it wasn't actually an ordinary weather balloon. The secret nature about the actual situation, Project Mogul, goes a long way towards explaining the anomalies that the UFO researchers attributed to aliens. Of course, UFO enthusiasts will counter by arguing that the new information is just to cover up the actual events. Again there is no evidence for this accusation - just a desire to believe.
1961 Betty and Barney Hill are widely credited with being the first people abducted by aliens to gain worldwide attention. In searching through the literature on this case there seems to be much back and forth about the credibility of the couple. It's another minefield of information, but once again, the whole case is relying on nothing but human memory (or imagination). There is no hard evidence that anything occurred on the night in question.
Above are just some of the well known cases, and all involve the weakest possible 'evidence'. There seems to exist no hard evidence that intelligent extraterrestrials are visiting the Earth. All evidence is eyewitness, disputed or unverified. With such an abundance of reports, none of which can be verified as definitely Extraterrestrial. UFO enthusiasts will say that with so many reports, some of them must be extraterrestrials, but on the other side of that coin it could more correctly be argued that with so many reports, and the fact that not a single one is indisputably verified, it’s far more likely that aliens are not visiting the Earth.
We would love to know that interstellar travel is possible, and it would be fantastic to learn that intelligent extraterrestrials are visiting us, so long as they aren't here to kill or enslave us, but until real evidence surfaces we have to apply a measure of scepticism to all reports.
In recent times interest in the possibility of extraterrestrial visitors to the Earth has hit an all time high. Fuelling the interest has been a multitude of books, followed by movies, followed by television shows and more recently still, the internet. Now almost everyone has first hand access to the reports and videos that abound. The problem is that not one of these reports or videos undisputedly proves the existence of extraterrestrial visitors. If you can provide us with one we will gladly publish it here. Such a video or report that undeniably presents proof of extraterrestrials would be all over the National News media everywhere on the planet. Forget the conspiracy theories about an unimaginably huge cover up, if real proof ever becomes available it won't be sequestered to the dark corners of the internet. It will be big news everywhere. Some people "want to believe", and will continue to believe despite the lack of hard evidence, but nearly everybody on the planet really "wants to know".
Given that intelligent extraterrestrial life probably does exist, the real question is whether they could ever visit us.
Many people believe that the universe is simply too large and the distances involved preclude the possibility of travel between the stars within our own galaxy, let alone between galaxies. Whilst it is generally accepted that faster than light travel is not possible, this only takes into consideration our own limited understanding of everything. Can we really say that a civilisation that may have existed for 100,000 years or more would not be able to overcome some of the hurdles that we think are insurmountable? See this excellent article on the topic of interstellar travel by physicist and futurist Michio Kaku.
Another thing to consider is that if extraterrestrials are indeed visiting us, why are they being so damned secretive about it? It's an awfully long way for them to come if they are just going to hide out in the clouds or to only appear for blurry pictures by people with malfunctioning cameras or shaky hands.
Based on the available evidence, our opinion of the likelihood of space aliens or inter-dimensional beings visiting the Earth is next to nil. I only say 'next to nil' because it is impossible for anyone to prove that they aren't. You can't prove a negative.
There is definitely a lot of vague flying saucer and alien visitation 'evidence' available, but good hard evidence is impossible to find. So much 'evidence' can be proven flawed or manufactured that it becomes difficult to believe that any of it is valid. Believers in alien visitation will often state that "with so much evidence some of it has to be true" however I would counter that with so much incorrect, flawed, manufactured and disproved evidence there is a very good chance that none of it is true. Not a single piece of verifiable evidence has surfaced from the mountain with which we are presented.
There are definitely some very interesting reports, and I have seen a UFO myself, but a UFO is nothing more than something in the sky that is unidentified. The UFO I saw appeared to be a meteor entering the atmosphere, but to my knowledge meteors don't perform a zigzag across the sky. This encounter isn't documented anywhere other than emails I sent to two UFO research organisations after the encounter. I would be interested to know whether my current recollection of the event has changed from the report I sent to UFORQ. To my knowledge, UFORQ didn't publish it. It probably wasn't exciting enough. If anyone does have an explanation as to what could possibly look like a meteor tracing out a reversed letter "Z" I would be delighted to hear it.