Unfortunately, the abbreviation, or term, "UFO" has become synonymous with so-called "extraterrestrial intelligence", with the result that many people uncritically and unquestioningly interpret anything unusual in the sky as being of extraterrestrial origin instead of seeking a rational explanation.

I first started giving public talks on astronomy in 1998, while living on a farm where I had set up a small open-air observatory. Groups of school children and adults would visit me for a short  presentation, followed by viewing of interesting objects in the sky through a telescope. I now live on a different farm, but I continue to give presentations to those who are interested in astronomy. The interesting fact about these presentations, from my perspective, is that there is always someone in the audience who asks me about "life out there" or about UFOs. I cannot recall a single evening when someone did not raise these subjects.
Read MoreThere is clearly a deep-rooted desire in most of us to know whether we are alone in the Universe, and I am no exception. But when it comes to finding out whether we are alone, I put my money on the scientific method, and not on pseudo-science or popular belief. Therefore, when people ask me whether I believe in UFOs or whether I believe that there is intelligent life elsewhere in the Universe, I try to give a polite, rational answer to their questions. Because I am usually asked whether I "believe" these things, I point out that belief does not come into the picture. I do not believe in either, because to believe something is one thing; to know for certain is quite another matter. Unfortunately, people in general, and adherents of pseudo-science in particular (whether it be UFOs, extraterrestrial intelligence, astrology or whatever), seldom bother to draw this distinction.

Closely related to these questions are accounts by people who claim to have seen UFOs. Of course, here I single out people who use the term "UFO" in its extraterrestrial context, and not those who (correctly) use it as a term to describe an unusual phenomenon in the sky. Well, I'm treading on dangerous ground, for how does one politely convince someone that what he or she saw possibly has a simple rational explanation, or may not even be what they thought they saw? Most accounts of UFO sightings are accepted and gain credence because they were sighted by "reliable witnesses".

There are several problems with eyewitness accounts. The legal profession may accept eyewitness accounts as evidence in a court case, but that's as far as it goes. An eyewitness account does not constitute scientific evidence, nor does it provide data that are open to scrutiny by anyone who wishes to test a hypothesis. A more difficult problem arises when the UFO was sighted by one person only. Most people would probably respond with indignation if I told them that they should not always trust their eyes! Well, it is true. What we sometimes believe we see, is not always what we really see. Our eyes (and brain) often play tricks on us under conditions of poor light, adverse atmospheric conditions, fatigue, stress, illness or when taking certain medication.

I wish to step off the eyewitness issue, but there is another line of reasoning worth mentioning. Consider this: astronomers, especially amateur astronomers, spend far more time watching the sky than the average person. When I say far more time, I mean thousands of hours. It follows that the number of UFO sightings by astronomers should be proportionately higher than the number of sightings by non-astronomers. If this is not the case, then it is probable that most UFOs reported are either unfamiliar (and hence, unidentified) objects, or optical illusions. Even if such objects are not of celestial origin, it is highly unlikely that an astronomer would turn a blind eye to an object supposedly moving rapidly around the sky, stopping suddenly, hovering, then taking off again in a different direction. Many amateur astronomers use photographic equipment as part of their observing set-up, and they know how to use it. If they saw something unusual in the sky while observing, the chances are they would know how to use their equipment under those circumstances. The photographic evidence from astronomers in favour of UFOs is absent.

At this point the believer in the UFO myth may jump up and remind me of all the photographic 'evidence' that has been published over the years. Well, let me point out that just about all the cases that were subsequently researched scientifically, were proven to be hoaxes. One of the best examples of this, was the vast body of reports of alien encounters that started with the Apollo 11 Moon landing in 1969. Over the years, literally dozens of stories have been written about purported UFO sightings and photographs made during that particular mission in July 1969. I have neither the time nor the space to elaborate on this, except to mention that subsequent research and investigation of the photographs and communications transcripts archived by NASA, proved that all these UFO stories were the result of an elaborate hoax. Unfortunately, the damage had been done, and I wonder how many UFO enthusiasts today owe their belief to that one particular hoax, using it as 'evidence' to substantiate their claims.

My intention with this article is to present some arguments against the popular UFO myth, and not to discuss the possibility of life elsewhere; that is the topic of another article. But because the UFO issue is inextricably tied to extraterrestrial intelligence, I must say a few words about this. I repeat, a "few" words, because this is a topic that requires some fairly laborious and complicated calculations in order to arrive at an answer against or in favour of extraterrestrial visitations.

Let's test the hypothesis that, of all the UFO sightings reported, say in one year, at least some of them are true extraterrestrial visitations. We can choose any number, so let's start with the assumption that one visitation per year is the real thing. Before we can continue, however, we need an idea of how many technical civilizations there might be in our Galaxy (we'll ignore other galaxies, because they are too far away). We will use the so-called Drake equation to determine this number. The Drake equation multiplies together several factors: the number of stars in the Milky Way Galaxy; the fraction of stars that have planetary systems (unknown, but we can guess); the number of planets in a given system that are suitable for life (as we know it); the fraction of otherwise suitable planets on which life actually arises; the fraction of inhabited planets on which an intelligent form of life evolves; the fraction of planets inhabited by intelligent beings on which a communicative technical civilization develops; and the average lifetime of such a civilization. As you can see, once we have entered the number of stars in the Galaxy, we have to rely on guesswork for the other values. But it doesn't matter—even very optimistic choices will not change the outcome.

To cut a long story short, for the values that I chose, we arrive at an answer of about one million (106) technical civilizations in the Galaxy, actively engaged in space exploration. Now, the question is, how many interstellar space vehicles does each of these civilizations launch per year? Suppose that each launch is successful. If only one space vehicle reaches the Earth every year, this would mean that each civilization has to launch many space vehicles per year, not all targeted at Earth (why should we be so important, anyway?). If these vehicles are launched with the purpose of visiting interesting places in the Galaxy, and we assume that only, say, 25% of the 4x1011 stars in the galaxy offer interesting places to visit, then the one million civilizations have 1011 interesting places to visit. This means that there are 1011/106 = 105 places per civilization to visit per year, which gives us the answer: each civilization has to launch 100000 space vehicles per year!  Think about the implications of this result: 105 space vehicles x 106 civilizations per year = 1011 space vehicles per year. The load on the extraterrestrials' resources would be astronomical, not leaving much for those civilizations to get on with in their daily lives. I am forced to conclude that our original assumption of one true visitation per year, is highly improbable.

Now, let's change the argument somewhat and assume that all those civilizations are interested only in us, and that each civilization sends out only one space vehicle per year, and not 105. This still leaves 106 space vehicles being sent to Earth every year. We should have extraterrestrial visitors flitting about the sky every day. Where are they?

Believing in UFOs and extraterrestrial visitations is akin to believing in Santa Claus—it is nothing but a myth.