The views of early Greek philosophers
The earliest recorded conjectures on extraterrestrial life began in ancient Greece during the 5th century B.C.
Formed by a small band of renegade Greek philosophers and mathematicians, there was a time when human curiosity and thinking were seen as mightier than the sword. New knowledge and the recording of such knowledge during this golden age became the valuable commodity and people could freely debate and argue the knowledge of the day and so help others at the time to see a different perspective and with it new ways of solving problems.
Among the great thinkers were Leucippus (approximately 480BC - 420BC), regarded by many today as the founder of atomic theory in physics. Another was Democritus (approximately 460BC - 370BC), a mathematician by nature focusing mainly on geometry but held a fervent interest in things relating to the real world around him. After much listening, thinking and debating, he too came to the same view and quickly became an avid supporter of Leucippus' view of the atomic world.
When Leucippus and Democritus turned their attention to the sky and asked whether life could exist, their careful thinking suggested to these men that the answer should be in the affirmative. They summed up their belief by saying the random collisions of atoms to form the Earth and everything in it could not be a singular event. There had to be other worlds like the Earth.
Another Greek philosopher to become an atomist philosopher was Epicurus. He too would give his support to Leucippus and Democritus.
Metrodurus of Chios, an Epicurean philosopher from the school of Democritus in the third and fourth century B.C., gave his staunch support for his mentor, Epicurus, by neatly summarizing the view in a romantic way for people to understand when he said:
"To consider the Earth the only populated world in infinite space is as absurd as to assert that in an entire field sown with millet, only one grain will grow." (1)
Or a more accurate translation as Metrodurus would have said in the Greek language:
"A single ear of corn in a large field is as strange as a single world in infinite space." (2)
Yet a romantic statement about corns in a field summarizing the thinking and ultimately the belief in extraterrestrial life was never going to convince the more rational members of society (i.e., the ones who need to see the evidence with their own eyes). Without direct evidence to observe with one's own eyes of a size that is going to be easy and beyond reasonable doubt, there would always be some rational thinking individuals who will disagree.
The views of Aristotle and Plato
Aristotle (384-322 BCE) and Plato were the principal thinkers against any belief in extraterrestrial life. With the issue of God firmly planted in their minds, they had other ideas of how people should see life in the universe. As there was no direct evidence for extraterrestrial life and with only the Earth to go by, the belief by these men became one of God creating man in his own unique image and no other creature could ever exist in the Universe to look like God or create another world like the Earth. The Earth has to be seen as a singular and significant event and no other worlds with living things could ever possibly exist.
The views of the Church
Apparently such an argument was considered more convincing to the Catholic Church than Greek philosophers talking about corns in a field. As a result, religious leaders in Europe came to embrace this view and for more than 2,000 years almost no soul was brave enough to take the opposing view on the grounds of heresy.
Indeed the consequences for anyone trying to challenge the church view were quite devastating. Take, for instance, the curious thinker named Giordano Bruno. His observations of the universe and careful thinking of the evidence suggested to him it was time to resurrect the idea of multiple worlds in his book titled On the Infinite Universe and Worlds, published in 1584. Unfortunately, once the Church found out, he was apprehended by the Inquisition on his return to Italy late in his life. He was asked to recant his belief. Bruno refused. Not good considering Bruno's punishment for disobedience and an unwillingness to accept the Church position was a fiery death on the stake in Rome.
The late 19th century views on extraterrestrial life
Fortunately, things have improved dramatically in the 19th and 20th century. People power eventually forced the Church (3) to accept the questioning mind of humans and to allow exploration of the heavens in a more scientific manner. It would begin among the educated and rich people of Europe asking themselves why God, with his immeasurable power, would create a single Earth in a grander infinite Universe? Surely there have to be other Earth-like worlds.
Astronomers at the time thought so too and soon began to train their telescopes towards the heavens for possible scientific proof of the idea.
The current views on extraterrestrial life
Today, enough astronomers believe there has to be a high probability we will find life outside of Earth. Among the indirect evidence they have found in support of this modern belief are the number of planets discovered outside our solar system, not to mention the vast numbers of sun-like stars in the Milky Way (and, by implications, for any other galaxy in the universe).. Add to this the availability of the right raw chemical elements and molecules for building life throughout the universe and it would be a very brave soul indeed to think ETs don't exist (don't worry, in the 21st century we won't burn you on the stake if you believe otherwise — people will probably just ignore you).
As we speak, astronomers have discovered more planets orbiting other suns than they can count on their fingers. Indeed we are talking conservatively in the hundreds with more being detected almost on a daily basis. As the instruments for detecting planets around other distant stars get more sensitive, astronomers are discovering some planets around other stars are about the size of our Earth. And it will not be long before instruments will detect the atmospheres of these planets to determine if oxygen (a tell-tale sign of life) exists in reasonable quantities.
Then the astronomers tell us our Earth orbits an ordinary medium-sized yellowish sun not unlike the hundreds of millions sauntering about within the Milky Way. And considering the Milky Way is just one of billions of galaxies rummaging through the universe, the same numbers game is employed today by scientists when we ask the likelihood of finding ETs..
There is considerable belief among many sensible and open-minded scientists in the 21st century in the likely existence of extraterrestrial life. Even among the public, the belief is growing steadily by the year. For example, the late Jean Cocteau (1889-1963), famous poet and member of the Acedèmie française, said prior to his death on 1 October 1963:
"The astonishing thing would be if they [ETs] did not exist." (4)
In the early 21st century, engineer Bill Stone of Stone Aerospace under contract by NASA in 2007 to build the space probe to find alien life gave his positive support when he said:
"If you want an experience at being humbled, go look at the NASA Hubble deep space image that looked into the darkest, darkest, little tiny segment of the sky. And what they saw back in that picture to me was the most devastating news of all for people who think we are important. What you saw were clusters of light that were not stars, they were galaxies. And there were thousands and thousands of galaxies in that little picture of the darkest part of the universe. If you think there is not other life out there, think again." (5)
But for those more rational members of society, discussions of shear numbers of stars and the growing numbers of plants around other stars is usually never enough to convince them that ETs should exist. More solid proof for the existence of extraterrestrial life is necessary.
NASA understands this point very well. Finding direct evidence for ETs remains a fundamental issue in this whole ET debate. Because if you can find just find one instance of ETs somewhere beyond the Earth, the great ET debate can be finally solved. As a result, NASA is sending probes to other planets and moons within our solar system to see if life might exist, or have existed. And the scientists are not expecting anything too complex or advanced. Just one bacteria thriving on another world is enough to convince them of the existence of ETs.
However, can we be sure that one single supposedly alien bacteria will be seen as enough evidence to convince every single rational person that ETs exist? Probably not. Of particular concern in this regard is how our innocent efforts to visit other worlds could already have carried, or soon will be carrying, inadvertently Earthly bugs to these places. These bugs have the potential to contaminate other worlds and affect our results to such a significant degree that questions would still be raised as to whether we have truly found ETs, especially if we start to wonder why the bacteria we may discover on neighbouring worlds look remarkably like those on our planet. And all it takes is one bacteria to contaminate another world no matter how hard we clean our scientific space probes.
Not even space is enough to stop a bacteria from surviving the journey. All it takes is a sufficiently protected spot on a spacecraft, stay in suspended animation in the coldness of space (apparently it can survive indefinitely like this) and by the time the spacecraft plunges into liquid water on another planet, that is enough to thaw out the little critter and help it to survive in its new environment. Then before you know it, the bacteria will thrive and multiply to such an extent that soon any analysis of the water will reveal countless numbers of the little lifeform.
How do we know for sure whether a bacteria on another world is truly alien? Or should we be looking for more advanced and complex life of a size that we can clearly observe with the naked eye and then we can say, "Hey! That's definitely alien"? and "No, there is no chance we could have created it". Because a primitive lifeform such as a bacteria must eventually grow and become advanced life given enough time to the point where we can observe and say with absolute certainty that it is alien. And if this is the case, could this advanced life be already quietly watching and studying us as we speak with their own technology and so making it harder for our scientists to detect them? In which case, where should we be looking to find this evidence of complex life?
This contamination issue could easily see the current search for ETs by way of alien bacteria become a waste of time and money. At some point, the goal posts will have to be pushed further back and efforts made to find larger and more intelligent forms of life in the universe, just to be absolutely certain. Furthermore, if aliens are hiding from us, there is a distinct risk scientists may not be looking in the right area for the evidence (especially if we put all our eggs in the "alien radio signal" or "alien bacteria" baskets in the hope we might find an alien civilisation sending signals to us, or anything looking remotely alien if it is found on another world).
Come to think of it, given how long the search for alien radio signals has taken, one would think the universe would have thrown at us at least one alien radio signal to keep us preoccupied and solve our problem of whether we are alone. Apparently none as we speak. Extraordinary. But what if the Australian CSIRO astronomer, Dr Kelvin Wellington, is true when he said:
"There's a joke around that everybody might be listening, nobody sending." (6)
Maybe ETs have a good reason for not sending radio signals into space?
Surely this quote reveals how important it is to expand the search to other areas where ETs might exist. How about UFO reports? A logical next step one would think. However, scientists are assuming nothing will eventuate from a study of UFOs.
A very poor decision as our research has uncovered.
However, since we already have the answer and know the importance of UFOs to the SETI situation, the remaining part of this discussion will now involve a look at the probability of finding life in the universe based on key aspects needed to build life in the universe and where such life are likely to be found and use this probability to estimate the number of planets with life in our Milky Way and how many of those are likely to become technically advanced alien civilizations. Then we will look at whether there is enough time to reach our planet by one of these alien civilizations, with or without an electromagnetic technology to make the journey much faster than we think. And finally, we will look at one reasonable explanation why alien civilizations may wish to keep quiet with us.
Of course, all this work to discuss the topic of ETs may not be necessary given what we know from the UFO reports. However, for now, and as a useful information service to the public, it is important that we at least give an indication of the probability of finding ETs without the help of UFO reports (and so make everyone aware of the general prevalent scientific views on the extraterrestrial life debate). Let us see just how likely we are alone based on observations of the Earth and the universe through our telescopes. Later, the testing of the electromagnetic technology will some come to help end the debate once and for all. And there will be no need to muck around any more.
So, for now, this section on ETs will present the current scientific situation regarding extraterrestrial life as we know it today.