Not even close encounters: If UFOs really exist, why would intelligent life forms use 1950s earth technology to travel here?

When people hear that I am a professional astronomer, they often ask "Do you believe in UFOs?" Sometimes they say, "I have seen a UFO…" and then proceed to describe their incredible encounter. Quite often they say they saw a bright light in the sky; some describe it moving at high speed and following them.

These types of stories are quite common among UFO believers. In 1967, police officers in 11 counties in the US state of Georgia chased after a reported UFO for several days - until someone told them they were chasing the planet Venus.

Venus is the brightest celestial object in the sky after the sun and moon. Since many city folk are not accustomed to viewing the sky, they are often astonished when they suddenly catch a glimpse of Venus. It can at times be very bright, even in early morning or late afternoon light. When the observer is in a moving vehicle, he often has the illusion that Venus is chasing after him. When I hear reports of UFOs, my first response is usually, "Which direction was it?" If the person says west, I then ask, "What time of day did you see it?" If they answer, "In the evening," I reply, "It is quite likely you saw Venus".

Casual observers have been known to confuse planes, balloons, meteors, fireballs, clouds and optical atmospheric phenomena with UFOs. Our skies are crowded with artificial satellites that move quickly across the sky. When sunlight reflects on them, they may be perceived as UFOs.

UFO believers may accuse me of being narrow-minded or conservative. But I would argue that it is they who are conservative. If an alien civilisation was capable of space travel and came hundreds of light years to reach us, why would they travel in a primitive mechanical device? Why would their spacecraft emit visible light, when they have the entire electromagnetic spectrum available? We forget that visible light is only a very narrow part of the spectrum, and our eyes are tuned to this narrow part to take maximum advantage of sunlight.

READ MORE: As Nasa discovers ‘Earth 2.0’, China nears completion of giant telescope designed to find signs of alien life

Our galaxy is 10 billion years old and has 100 billion stars. There are probably more than 100 billion planets in it. It is therefore not unreasonable to think that it contains other intelligent life forms, and we are not alone. We must, however, remember that we are a very young and primitive civilisation. Humans have been around for only 100,000 years, and we have been capable of distant communication for only about 100 years. Given the age of our galaxy, probability suggests that if there are alien civilisations in it, they will be millions of years older and technologically far more advanced.

We cannot imagine technologies 100 years from now, let alone 1,000 years. I am sure, however, that visiting aliens won't be using 1950s earth technology, which is what a light-emitting flying saucer is. If extraterrestrials visit our planet, they will travel in forms that are entirely unknown and invisible to us. They may actually be here already.

If you dropped a thumb drive onto a street in Paris or London 100 years ago and someone picked it up, would they know that it contained thousands of songs, hours of movies and volumes of books? Would they have any idea what it was? Almost certainly not. This is what technological progress can do - and that is only a few decades, not thousands of years.

READ MORE: Why 'anti-science' idiocy may have far-reaching consequences for us all

UFO believers are often adamant about what they have seen and describe their encounters as emotional or even spiritual experiences. They can be highly educated. It is very difficult to convince them that they are probably wrong.

I think the physicist Richard Feynman said it very well: "It is much more likely that the reports of flying saucers are the results of the known irrational characteristics of terrestrial intelligence than of the unknown rational efforts of extraterrestrial intelligence." Along this line of thought, I suggest that UFO studies should be pursued as a branch of psychological research. There are more mysteries in the human mind than bright lights in the sky.

Sun Kwok is a professional astronomer and president of the Astrobiology Commission of the International Astronomical Union. He serves as dean of science and chair professor of physics at the University of Hong Kong