Are We Alone In The Universe?

Are these guys hiding at the bottom of your garden?

Today, in a rather long blog post, I'd like to speculate a little about the possibility of life existing elsewhere in the Universe. Since I get asked about this topic just about every time I walk into a room, I’d like to tell you what science currently has to say about life in the Universe and what we’re doing to investigate the possibility.

The belief that we are not alone in the Universe is of course as old as humankind itself. The idea that there are other worlds populated by other-worldly creatures is a common and natural trait of our species. I think it was an inevitable idea once we had conceived of our own self-identity. But, the concept of life-forms existing elsewhere in the Universe, in the modern scientific sense that we all understand today, is also not new. Many ancient Greek philosophers, including Leucippus, Democritus, Epicurus and Plutarch, were of the firm belief that other worlds existed and some even speculated that the Moon harbored life.

There were similar ideas during the Renaissance. In 1440, Nicolas of Cusa, Bishop of Brixen, published a book entitled Of Learned Ignorance in which he advocated not only the plurality of worlds but also the existence of life on the Moon and the Sun.

But really, the floodgates to this kind of speculation were opened by the famous astronomer Nicolas Copernicus with his publication, in 1543, of the heliocentric model of the Universe, in which the Sun, not the Earth, was at the center. Although Copernicus himself never speculated on the issue, the demotion of the Earth to a mere planet led many others to advocate the existence of other habitable worlds. The most enthusiastic of these was probably Giordano Bruno who championed the existence of extraterrestrials until he was burned at the stake in 1584, although it must be said, not for that particular belief. Some other notable figures in the history of science have also speculated on the existence of extraterrestrials. These include Galileo, Kepler, Huygens, Descartes, Kant and William Herschel.

The difference today, of course, is that modern science is now in a position to attempt a serious investigation of the issues. With the advances in our understanding during the past century or so, with the development of new observational techniques, of telecommunications, of the biosciences and space technology, for the first time in our history are we able to look for an answer to this ancient question.

Let’s be clear at the outset; this blog post is not going to be primarily about Unidentified Flying Objects, or UFOs, nor about the mysterious aliens that pilot them, nor about the countless conspiracy theories or tales of abduction surrounding them. However, this is such an emotive and popular part of modern culture that we can’t simply ignore it. So, let’s begin with an assessment of the facts concerning the possibility that we are being, or have been in the past, visited by aliens from other worlds.

Many people have pointed out the apparent existence of mysterious flying objects or phenomena in the art, literature and mythology of the human race. They have also been quick to declare ancient archaeological sites or manuscripts as evidence for alien visitation. This whole area could easily take several blog posts alone, but I’d like to mention just one example.

Relief of Maya ruler 'Pakal'.

There is an image sculpted on the lid of a stone sarcophagus deep within the Temple of Inscriptions situated at the site of Palenque, Mexico, that depicts the Maya ruler 'Pakal'. It dates from around 690 AD. Now, some observers believe that Pakal is sat at the controls of a space craft, and that this is clear evidence that Mayan culture had contact with alien civilizations. But Mayan experts agree that Pakal is depicted as entering the road to the Underworld in typical Mayan fashion. In fact, it turns out the inscriptions on the sculpture actually say that!


Other examples often cited for evidence of ancient communication with extraterrestrials include the Giza Pyramids, The Nazca lines, the Easter Island Moai statues, Atlantis, Stonehenge, as well as scores of religious or mythological texts. The argument goes something like this – ancient humans couldn’t possibly have constructed these mysterious sites without modern science and technology. Therefore they were guided by a higher intelligence from outer space. And these aliens, and their craft, are manifest in the art, mythological and religious texts of these ancient people.

This is, of course, denying these people an intrinsic part of what it is to be human. It is a failure to concede the inventiveness of ancient peoples. Couldn’t they too have imaginations, fantasies, speculations, dreams of alien beings? Couldn’t they too be inspired to great and complex tasks and to invent methods and strategies to enable them? I think they could and I don’t think we have to invent an external influence to account for these great mysteries. These things deserve our respect and admiration, as well as pride, not our disparagement.

Masolino da Panicale's UFO portrait?

Let’s move on from prehistory to art. Now, many artworks have been put forward as evidence that UFOs, for example, have been around for a long time. Many of these examples are from Medieval or Renaissance artwork with a religious theme. The interpretation by some is that these strange objects in the sky, many of them saucer-shaped of course, are depictions of alien spacecraft, clear evidence that we have been visited regularly in the past. But all of these examples can just as easily be explained as depictions of the supreme Deity, of angels, halos, representations of the Holy Spirit, even a bishop’s hat hanging on a peg! Now, I know very little about art, but even I can accept that. The point is that there’s no need to interpret them as evidence of alien visitation. There’s already a much more plausible explanation which doesn’t require a fantastical leap-of-faith.

And finally, let’s talk about the modern UFO phenomenon. Now, this is a huge subject and one that I really don’t have to introduce to you. It all really began in 1947 when a pilot called Kenneth Arnold made what is widely regarded as the first report of a modern UFO sighting. Arnold saw nine objects flying erratically over Mount Rainier near Seattle and described their motion as ‘like saucers skimming off water’. It’s from this report that the term ‘flying saucer’ came. Within a few weeks of the Arnold sighting there were several hundred similar reports from all over the world. Since then there have been many witness testimonies, photographs or video evidence put forward in support of the belief that aliens are visiting our planet.

Now, certainly, many UFO sightings can be explained, and certainly some can’t. Explanations have included lenticular clouds, noctilucent clouds, mirages, ball lightning, weather balloons, rocket launches, searchlight reflections, meteors, aurorae, artificial satellites, stars, planets, aeroplanes, flocks of birds, and perhaps the strangest, luminous fungi.

Of course, there will always remain some percentage of UFO sightings that remain ‘unidentified’. But this doesn’t mean we should instantly conclude they are the vessels of interstellar travelers. Extraordinary claims require extraordinary evidence and there simply isn’t the evidence there. At least, it doesn’t convince me, but perhaps you disagree. I am not saying that all the witnesses are mistaken, that there are no strange objects in the skies, that abductees imagined everything, and that science can explain it all away, but until there is irrefutable proof of any of these things, science must be cautious. If there were the evidence available, you can bet your life there’d be a queue of scientists trying to get their hands on it. And I’d be at the front of the queue.

Kenneth Arnold: it's all his fault!

So, putting aside what science finds difficult to accept, let’s talk about what science does have to say about life in the Universe. I’d like to start by discussing what life is. How do we define life? Would we always recognize it if we found it? Most of us may think we have a pretty good idea what constitutes a living organism. Clearly, a giraffe is a living organism, as is a dolphin, or a human. But is a virus a living organism or is it just a bunch of replicating chemicals?

In fact, it turns out that biologists themselves can’t even agree on a definition of life. However, we know that all life on Earth has a set of common characteristics, which we generally understand, and I think we should assume that we’d recognize those characteristics even in the absence of a working definition of life. Most biologists agree that these characteristics are organization (being composed of one or more cells, the basic units of life), metabolism (the consumption of energy), adaptation (the ability to change over time in response to an environment), response to stimuli (such as light, heat and so on) and reproduction (the ability to replicate). If we come across something with these characteristics, particularly together, we’d have a good case for claiming it to be life.

Did life here on Earth develop spontaneously? Or is it an inevitable consequence of the Universe? At present, we can’t answer that directly, but we can pose an easier question. Do we know under what conditions life could develop?

Well, based on what we know of life on Earth, it seems that water is perhaps the most fundamental requirement. We all know that we’d very soon cease to be alive if we had no water! But, scientifically speaking, this requirement seems to be because water is a liquid over a wide range of temperatures (over which organic molecules are also stable) and because water molecules are what we call ‘polar’. The electric charge of the water molecule is not symmetrical. This means that molecules which are electrically symmetrical will not dissolve in water. This allows complex organic molecules, the building blocks of life, to be very stable in water, allowing them to interact. Water is the medium through which life’s chemistry acts.

In addition to water, life also needs the presence of the elements which participate in biochemical reactions. Surprisingly, out of the 92 naturally-occurring elements, only 11 play a major role in terrestrial life, and only 4 make up 99% of organic matter. Only another 18 are known to form part of some form of life. We all know that life on Earth is carbon-based. Carbon seems to be a unique element in that it very easily forms complex, stable molecules, forms long chains or ring structures and is able to bond with many other elements in a variety of ways. The other major components of life are hydrogen, oxygen, nitrogen, sulphur, phosphorus, sodium, potassium, magnesium, calcium and chlorine. Perhaps even more surprisingly, these are not the most abundant elements in the Universe, or even in the Earth, so life has clearly chosen those elements that are most advantageous, rather than those that are most available.

Finally, all life requires a source of energy. This energy is used to drive the biochemical reactions which constitute the organism. Life on Earth utilizes mainly sunlight for its energy source, either directly or indirectly, but life is also known to use hydrothermal, geothermal or chemical energy too.

Clearly then, our planet has provided an environment in which these conditions for life have been met. So, what is special about the Earth? What do we know about the origins of life here and can this tell us what kind of planetary environments may harbor other life-forms?

Firstly, we have to be careful here. We have decided that the presence of water, the use of carbon as the basis for life, and a readily-available energy source are required for life to develop. But we shouldn’t assume that these are the only set of necessary conditions. Because we only have one example of life, here on Earth, we are naturally inclined to define things in those terms. But, life elsewhere in the Universe may be very different to that on Earth. It’s unlikely, but it could be based on silicon rather than carbon. It could extract energy from a source completely unknown to us. Of course, these possibilities only increase the chance that we’re not alone, rather than diminish it, although of course it’s much more difficult to find something when you don’t know what you’re looking for! So, just as science has done and will continue to do, I am assuming that ‘life’ is something akin to ‘life on Earth’.

DNA: miracle chemical blueprint.

The origins of life on Earth are not at all understood. It is generally assumed that the primitive Earth had many of the basic components of biochemistry, that is, amino acids and/or nucleotides, and the right conditions for the formation of more complex molecules such as ribonucleic acid, or RNA. All life on Earth is based on a much more complex molecule called deoxyribonucleic acid, or DNA. How RNA could evolve into DNA and then the first single-cell organisms is still a mystery. It appears that a random process of chemical interaction is extremely unlikely to produce the complex molecules such as proteins that allow DNA to replicate itself.

However, it has been demonstrated experimentally that simple organic compounds, such as nucleotides, can form spontaneously under conditions like those of the primitive Earth. This area of science it must be said is still in its infancy and the process of kick-starting life on this planet is currently unknown. But clearly the process must have started somehow, otherwise I wouldn't be here writing this blog!

In this context I’d just like to quote Carl Sagan, who said of the complexity of life, ‘these are some of the things that hydrogen atoms do, given fifteen billion years of cosmic evolution.’ There’s no scientific law or reason why life could not have started spontaneously, however improbable it may seem.

Putting aside the problems with the origin of life, it is assumed that all life on Earth has descended from a single common microbial ancestry that developed on the primitive Earth. Every living organism has evolved from a single origin. The rich diversity of life, from microbes, through to humans, uses the same basic tools of biochemistry. This diversity and beauty are due to the complexity of the DNA molecule and the enormous time-span available for its metamorphosis into different forms.

There is very good evidence that life began on Earth surprisingly early in its history. The Earth is about 4.55 billion years old. It is known that the oceans were formed by about 3.8 to 4.0 billion years ago. The first evidence of life on Earth is found in rocks about 3.6 billion years old. This evidence comes in the form of fossilized ‘stromatolites’. These are layered structures formed by colonies of bacteria in shallow water. Although rare, stromatolites still exist today, but the Earth’s oldest rocks contain structures identical in nature. Evidence also comes from the fossilized remains of single-celled organisms in some rocks.

An ancient stromatolite shows evidence of very early life on Earth.

So, clearly, the development of life in the oceans was a rapid process on the geological scale, perhaps only requiring 200 million years, although by comparison it took until about 1.7 billion years ago for multi-cellular life to make an appearance. But this leaves us with an interesting conclusion – that for life to have appeared and then evolved to such a sophisticated state so quickly, it must be very robust. It must be capable of forming easily in the right conditions. And this conclusion drives us to believe that life might have formed and might exist today elsewhere in the Universe. So, the next question must surely be ‘how common are those conditions in the Universe?’

Our planet is just about the right distance from the Sun so that it is neither too hot nor too cold for life to develop. Our oceans don’t evaporate, nor are they permanently frozen. In fact, conditions here are just about perfect. That’s hardly surprising, of course, because we are the result of that perfection.

Scientists call this area around a parent star where planets would have liquid water the ‘Habitable Zone’. It’s also known as the ‘Goldilocks Zone’ because it implies the ‘temperature is just right’. But a planet suitable for life must have more than just the right temperature. Its environment must be stable, geologically and climatically, giving life the chance of survival. In addition, the parent star must also be stable over billions of years, and many stars are not stable. Finally, the planet probably also needs some mechanism of protecting its developing life from harmful radiation from the parent star. On Earth, it is the ozone layer which protects us from harmful UV radiation, or at least, it’s supposed to!

We should next consider whether any of these conditions can be found on the planets of our own neighborhood, the Solar System. Now, the belief in life on Mars has been around for some time. In the late 19th century an American businessman and astronomer called Percival Lowell began popularizing the belief that Mars was inhabited by intelligent life. This is probably the result of the mistranslation of the Italian word ‘canali’, meaning channels, in the detailed maps of Mars drawn by the astronomer Giovanni Schiaparelli. This fascination with Mars was heightened by H. G. Well’s classic War of the Worlds published in 1898, which even forty years later, in the hands or Orson Welles, was sending people into the streets in terror.

Although the Martian ‘canals’ have since been found to hold no water, both metaphorically and literally, this in fact hasn’t always been the case. It turns out that Mars’ climate has changed significantly since its formation and in its early history liquid water was present in abundance on the Martian surface. In fact, many of the geological features on Mars can only be explained by water erosion. There are large flood channels and ancient shorelines visible on Mars. Even today, we know that water exists in large quantities on Mars, locked up in the polar ice caps, the subsurface permafrost and the Martian clouds. The conditions on the young red planet were not too different to those of the young Earth.

So has life ever existed on Mars? Could it have survived in some ecological niche up to the present day? We have sent many probes to Mars looking for signs of life. Recently, NASA’s Phoenix Lander scooped up Martian soil at the planet’s north-pole and confirmed the presence of water on Mars. It’s pretty much accepted now that Mars has certainly had the temperature and geology in the past that were conducive to life, but that it is now too dry and cold to support life. However, it is possible that microbial life could once have existed on Mars, and could still survive in the Martian subsurface.

Perhaps the most striking claim concerning Martian life in recent decades was the Martian meteorite controversy. Now, we have for some time been aware that some meteorites, chunks of rock falling to Earth from space, have their origins on Mars. At some time in the past, large impacts have sent chunks of Mars’ surface floating off into space and at least 57 of these have been found on Earth. They are the only samples we have of Martian rock. One of these chunks, called ALH84001, made its way into headlines worldwide in 1996 when scientists announced that it may contain evidence for microscopic fossils of Martian bacteria. But these structures were much smaller than even the smallest bacteria found on Earth and have since been shown to resemble mineral deposits without a biological mechanism. The debate is still ranging over ALH84001, although most scientists now discount it as proof of life on Mars.

ALH840001; the most famous lump of rock ever?

Is there anywhere else in the Solar System that could harbor life? Well, Saturn’s moon Titan, despite being far out of the habitable zone, is ranked among the most likely worlds in the Solar System to support single-celled organisms. Titan is extremely cold, and shows evidence for frozen water, but has vast oceans of liquid ethane and methane. It is just possible that some primitive life could exist there, in the vast methane oceans, but personally I think the chances are slim.

So, as far as we know, the Solar System is occupied by only one planet that has produced life – Earth. If, as we continue to explore the Solar System, this turns out to be the case, then I wouldn’t be surprised.

But what are the possibilities for life outside the Solar System? In the last two decades modern astronomy has achieved one of its long-dreamt-of goals, that of discovering planets around other stars. We call these objects ‘exoplanets’ and to date we know of more than 1800 of them.

Why did it take us so long to discover exoplanets? Well, it’s not easy to detect something the size of a planet at the distance of the stars. Planets don’t give off any light of their own, and what light they reflect is tiny in comparison to their parent stars. In fact, the only way we can find them is using an indirect technique. There are several methods used to find exoplanets, but the most successful one is the analysis of the tiny wobble that a planet would induce on its parent star. We can see this wobbling effect in the spectrum of the star’s light, and the technique is sophisticated enough for us to be able to determine the size of exoplanets and their distance from their parent stars. This gives us an idea of whether they are Earth-like, or terrestrial planets, or more like Jupiter and Saturn, the gas giants, and also whether they orbit in the habitable zone of the parent star.

Although we have so far only discovered 1800 exoplanets, we can easily deduce how common they must be around other stars. According to the latest work, about one star in 14 may have gas giant planets, while one in three probably has rocky planets of below 30 Earth masses. Currently, we are a bit uncertain as to what fraction of those Earth-like planets reside in the parent star’s habitable zone. However, I hope you can see from this that modern science is beginning to conclude that, far from being unique or rare, planets like the Earth are probably extremely common in the Universe.

To give you some confidence that there are Earth-like planets out there, I’d like to briefly mention one of them. The star called Gliese 581, in the constellation of Libra, is a red dwarf star of about a third the mass of the Sun and at a distance of about 20.3 light years from Earth. The star is actually the 87th nearest star to the Sun. In other words, this star really is on our doorstep.

At least three planets are known to be orbiting this star. The first is very close to Gliese 581 and is about the size of Neptune. The second is believed to be a rocky planet orbiting just inside the habitable zone. However, it’s very likely that any atmosphere of this planet has raised its temperature to well above the boiling point of water. But the third planet orbits just outside the habitable zone. But because of the possibility of an insulating atmosphere, this planet could have just about the right temperature for liquid water. This planet, called Gliese 581 d, is, so far, science’s best bet for a habitable planet outside the Solar System. You can’t yet book it as a holiday destination though!

Perhaps the most crucial point here is that such a planet has been found within a volume about 40 light years across, whereas the Milky Way galaxy has a volume about 1000 billion times that. And of course, there are upward of 500 billion galaxies in the Universe. I’m not a betting man, but with those odds even I’d be willing to put a few dollars down on there being other Earth’s out there.

Gliese 581d: holiday destination for the 3214 season?

So, let’s stop for a moment and consider what we’ve discussed so far. It appears that life began on Earth very soon after our planet’s formation, that the basic chemical components of life can be synthesized in a primitive Earth environment and that Earth-like planets may well be common in the Universe. Although there is a huge amount needed to fill in the gaps, the implication must already be that life itself should be common in the Universe. If this is the case, is the Universe teeming with algae and microbes? What about intelligent life? Should that be common too?

Of course, there’s a big difference between a microbe and a human – possibly! How big is the difference between a chimp and a human? Not much, some might say. We distinguish ourselves from the rest of the organic world with this term ‘intelligent’. But what is ‘intelligence’? That’s probably more difficult to define than life itself. But again, I think we all have a common intuitive idea of what ‘intelligence’ is, as applied to a life-form. It is probably the ability to communicate complex concepts, to understand abstract ideas, to fashion complex tools and so on. But is all life destined to produce creatures like us with the ability to question and explore the Universe around us? Or is this what actually makes us unique and in fact we really are a lone voice in the cosmos?

We are used to thinking of intelligent life as an inevitable consequence of evolution. But this may not be the case. Intelligent beings may only be one of the possible outcomes, and a rare one at that. It took 2.5 billion years for multi-cellular organisms to evolve from single-celled bacteria and another billion years to evolve through to mammals. It only took another 100 million years for the earliest mammals to develop into us. Does the speed at which intelligent life developed on Earth actually imply it’s easy to achieve? I don’t think science can yet offer any firm conclusions over this issue of ‘intelligent life’ and how common it may be.

So, at this point I’d like to draw a line between ‘life’ and ‘intelligent life’. In answer to the question ‘is there life elsewhere in the Universe’, modern science would answer ‘yes, probably.’ The question of whether there is ‘intelligent’ life elsewhere in the Universe is an entirely different proposition.

We can approach this proposition by firstly pointing out that, contrary to what some people believe, we don’t see any signs of intelligent life elsewhere in the Universe. So then, if they really are common, why haven’t we made contact with them already?

This apparent paradox was first pointed out by the famous physicist Enrico Fermi. Fermi asked whether this lack of evidence already tells us that extraterrestrial life doesn’t exist, or exists so rarely or sparsely that we will never find evidence for it. Some people have countered this paradox by suggesting we haven’t really looked yet, or simply that such life could exist without our knowledge.

So, have we looked for signs of alien intelligence? Well, yes we have, many times. In 1960, a radio astronomer called Frank Drake used a radio telescope at Green Bank, West Virginia, to examine the stars Tau Ceti and Epsilon Eridani for radio signals from extraterrestrials. He found nothing of great interest but started a whole new field of astronomy.

Frank Drake, alien hunter extraordinaire!

This kind of work is known as SETI, or the Search for Extraterrestrial Intelligence. If we imagine that ET is trying to contact us, we assume it will be with radio. Radio waves are almost unaffected by the material through which they pass and so can travel great distances through the Universe and still be detectable. It is easy and economical to build radio transmitters. Radio waves travel at the speed of light. The problem is to know where to look in the electromagnetic spectrum and precisely what it is we’re looking for.

Nature itself has provided us with some of the answers to these questions. The most abundant element in the Universe, hydrogen, happens to emit radio waves at 1.42 GHz. Another common molecule in space, hydroxyl, emits at 1.66 GHz. Conveniently, the Earth’s atmosphere is pretty transparent to these frequencies. Now, hydrogen and hydroxyl together make water, presumably a basic requirement for life, so this region of the spectrum is often called ‘the water hole.’ Where would you expect water-based intelligent civilizations to meet? Around the water hole, of course! This would be the most natural choice to make.

But what kind of signals should we look for? The most obvious way for an alien civilization to get noticed would be to concentrate all of their radio energy in a very narrow frequency channel. Nature tends not to do that. Another way would be to change the signal in a way which signifies it is not natural. For example, you could make it count from one to ten using pulses. In fact, in 1967, astronomers thought they had detected aliens, when a radio telescope in Cambridge, UK, found an extremely fast and regular radio pulse in the sky. They named the phenomenon LGM1 for ‘Little Green Men’. But it turned out they had discovered a previously unknown kind of star, which we now call ‘pulsars’.

Since Frank Drake first attempted a SETI experiment, there have been many others attempts at finding ET. In 1977, the Big Ear radio telescope in Ohio found a very narrow-band signal with all the hallmarks of potential non-terrestrial and non-solar system origin. It so impressed the astronomer who was observing that he wrote ‘WOW’ on the computer printout. The ‘WOW’ signal lasted for 72 seconds, but despite numerous searches of that area of sky since, it has not been seen again. So far, nothing conclusive has been found and the only result of note is the inspiration for the movie Contact starring Jodie Foster.

When Frank Drake was trying to justify his SETI experiment in the 1960s, he wrote down an equation, now known as the Drake Equation. It estimates the number of extraterrestrial civilizations in the Milky Way galaxy with which there is the potential for communication. It includes all the possible influences on that number. These are the average rate of star formation in our galaxy, the fraction of those stars that have planets, the average number of planets that can potentially support life per star that has planets, the fraction of the those that actually go on to develop life at some point, the fraction of those that actually go on to develop intelligent life, the fraction of civilizations that develop a technology that releases detectable signs of their existence into space, and the length of time such civilizations release detectable signals into space.

What does the Drake Equation tell us? Actually, not much, because the estimates of some of those numbers are guesses at best. The answer we get for the number of civilizations out there with which we could communicate, is anything between 0 and 5000. So, you can see we still don’t really have an answer. However, just because we don’t know the numbers doesn’t mean we should throw the equation away. Astronomers, or in fact, people called ‘astrobiologists’ are working on these problems as we speak, and just as with all of science, we make steps towards a better understanding and a better representation of the truth. One day, we may know the numbers sufficiently well to prove the Drake Equation does not equal ‘0’. Alternatively, astrobiologists may conclude that we really are alone.

Of course, the Drake equation only applies to our galaxy, and only to intelligent life with radio technology. But, as we’ve already discussed, the Universe is so big, and so full of stuff, that the weight of numbers must make it almost a certainty that we’re not alone. Even if the kind of fractions in the Drake equation are tiny, and remember, we’ve already begun to prove some of them aren’t, then you still get a very big number when you do the maths. You’ve heard this argument before I’m sure. It’s not exactly scientific, but it’s a compelling argument nevertheless.

If intelligent life does exist elsewhere in the Universe, what would it be like? Unfortunately, we have no real way of knowing. The factors that have resulted in us being shaped and constructed like we are, are too numerous and complicated for us to make any predictions on how other life-forms will have developed. In this area, we are simply into science fiction. Perhaps these ‘aliens’ are gratuitous monsters with acid for blood (c.f. Alien), perhaps they look exactly like us but with Spandex suits (c.f. The Day The Earth Stood Still), or perhaps they are gas-filled beach-balls (c.f. Darkstar). Until we meet with them, and I don’t believe we already have, we will not know.

In the future, there are many planned experiments hoping to increase our knowledge of life in the Universe. There are several space-borne instruments hoping to find Earth-like planets. The SETI Institute, a privately funded organization based in California, is currently building a very powerful radio telescope northeast of San Francisco. The instrument will be used for dedicated SETI experiments, searching for those allusive signals. The instrument is called the Allen Telescope after Paul Allen, co-founder of Microsoft, who donated many millions of dollars to the project. Today, this whole area is a very respectable part of astronomy.

How would you feel if alien intelligence was discovered?

What about the philosophical implications of the question of life in the Universe? I’d just like you to consider for a moment, given the discovery of alien life, even extraterrestrial intelligence, how you would feel. Would you be fearful? Would you be hopeful for our own future? Would it be a threat to your own beliefs or would you embrace the news? I think you’ll agree it would probably be the most monumental discovery of all time. People have considered the implications of such a discovery. Studies suggest the announcement would lead to confusion and excitement, with a desire by individuals to know more, but little panic or hysteria. We are an adaptable species and we’d learn to live with it.

I've posed many questions in this blog post. How did life develop on Earth? Is there evidence for life on Mars? How common is life in the Universe? But, you will have noticed, I haven't definitively answered many of those questions. But I hope you didn’t expect me to give you any definitive answers. If I could answer the question that forms the title of this blog, I wouldn’t be here writing it – I’d be at a Nobel Awards Ceremony! But I do hope you’ve got a slightly better understanding of where science currently stands on the issue.

We’ve made progress, even in the last decade, but this most ancient of questions is not an easy one to answer and we’re still a long way from doing so. But like most of science, the journey towards that answer is as important as our arrival. I’m certain I will no longer be here when this question is finally answered, and that saddens me, but I live in hope that one day the question will indeed be answered. And I think the answer will be a clear ‘no, we are not alone’.

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If the subject of aliens fascinates you, you're bound to like my novel The Bergamese Sect. Check it out!