One of the biggest questions, still unanswered, is posed by the Fermi Paradox.
This paradox asks the question why, considering the billions of stars and galaxies in the known universe, we haven’t heard from extraterrestrial civilizations. Where is everyone?
The SETI Institute estimates that there are 300 billion habitable planets in our Milky Way Galaxy. But there are approximately 200 trillion galaxies in the known universe, and the total number of planets is, well, just about anyone's guess.
The Drake Equation, beloved by mathematicians, attempts to provide answers, but the estimated values for several of its factors are so highly conjectural, that final numbers are unreiiable.
Overall, the uncertainty about planet numbers is largely because we're not sure about the size of the universe. For example, we can't see the edge of the universe, even if such a finite place exists. We can see only the part of the universe that is within the time frame that microwave radiation has been able to reach us. Astrophysicists describe this realm as 'the observable universe'.
But even within this (limited) realm, the observable universe is in a constant state of flux - galaxies collide and tear each other apart, some black holes swallow others, supernovae are catastrophic explosions of stars (and presumably planets) and other stars are being born. Finite numbers are therefore only guesswork.
And anyway, is there only one universe? There's a school of thought that our universe is only one in the multiverse.
But even only one universe, our own, challenges our imagination, and seems to stretch forever, without end.
But let's start with the nearest sun to ours, Proxima Centauri, in our own Milky Way Galaxy. This is one of a cluster of 3 red dwarf stars just under 4.5 light years away. Proxima Centauri is about an eighth of the mass of the sun. (1)
Travelling to Proxima Centauri with our present propulsion systems would take a very long time. For example, the Voyager 1 probe, which has now left our solar system, is travelling at 38,000mph (51,000km/h). (2) This is 1/18,000ththe speed of light, and at this rate, it would take Voyager 1 approximately 80,000 years to reach Proxima Centauri. (3)
Or, to look at this time frame in a different way, it would take Voyager 1 approximately 2,500 generations (4) to get there.
The fastest earth-manufactured object is now the Parker Probe, which travels at 192 kilometers per second. But this speed is still only one tenth of one per cent of light speed in interstellar terms, and even at this speed, it would take the Parker Probe 6000 years to get to Centauri A/B.
Intergalactic travel presents far greater problems. For example, the Andromeda Galaxy, the closest spiral galaxy to our Milky Way, is 2,480,000 light years distant, and with our current propulsion systems, would take billions of years to get there.
And if we could travel at the speed of light? Well, not so fast. According to our present knowledge of physics, it’s impossible for a physical object to travel at this speed. Cosmos Magazine tells us that the faster something travels, the more massive it becomes, and the more time slows – until at the speed of light itself, time stops altogether. (5)
Unless we find a place where the laws of physics don't apply, we can't even approach the speed of light without experiencing catastrophic changes. The Destiny Channel explains more about cosmic time and space, and looks at propulsion systems that could be possible contenders, although these are not yet viable.
In addition to the problem of speed, there’s obviously the problem of time. The thousands of years necessary for interstellar travel mean that the human beings who set out on an interstellar journey wouldn’t be the same species to arrive at the other end.
This is because we know that for even short periods of time in space, astronauts suffer physiological changes. NASA tells us (6) that without gravity, ‘bones lose minerals, with density dropping at over 1% per month'. By comparison, the rate of bone loss for elderly men and women is from 1% to 1.5% per year.
Also, muscles atrophy and cardiovascular changes affect the heart.
Obviously, interstellar space travel would take far longer, and the body changes over generations in space are unknown. We're not even sure if viviparity (bringing forth live young that have developed inside the body of the parent) is safe in outer space. We also don't know how well the microorganisms in the human body will be able to function, if at all, during prolonged periods in space. Although the biggest problem will probably be the prolonged exposure to space radiation and how to survive it.
At this stage, it's impossible to predict the physical and psychological changes that a (minimum) 6000 year space journey would have on a group confined in a single spaceship. And assuming that birth and generational succession would be possible, as it would need to be, how do you cope with the extra children (increase in numbers) born into this environment? How do you keep up with the advances in knowledge back on earth? So many problems... Would being put into some form of suspended animation at the beginning of your journey, and then woken up just before arrival, be a solution? Yes, but could you trust a 6000 year old computer to end up getting this right?
Aliens from advanced civilizations might overcome these problems by dispensing with physical limitations altogether, and uploading their consciousness into some version of a computer simulation. But a computer simulation isn't really life, is it? And what if this computer simulation was designed only to self-replicate in the interests of immortality? In similar circumstances, definitions of life, consciousness and intelligence would need to be redefined.
Artificial Intelligence here on earth, and the empowerment of artificial superintelligence, will force us to start answering such questions, or similar ones, sooner rather than later. So far, it's mainly science fictiion (e.g., A Space Odyssey 2001 and the Terminator movies) that has explored how AI might come to consider human beings a threat, although such problems are widely debated. The capacity to empower killer robots is already here. And apart from the question of ethics, there's now the question about what sort of intelligence we are creating, and how much autonomy we should allow it to have. Will we be able to control self-learning, and ultimately sentient, systems?
But back to space travel and another obstacle - sustainability. The Space Shuttle lasted for 'only' 30 years, until it was retired for a variety of reasons in 2011. Also, there were a total of 6 different space shuttles that were in use. So how could a single spacecraft and its on board systems possibly last for 80,000 years, or even 6000 years with no supply stations or upgrade systems along the way?
There are few models of anything humanity has created over the last, say, 100 years that are still working perfectly. Consider 100 year old cars and aeroplanes as examples. Even though early models may continue to work, they would lack the sophistication of subsequent models and advances in technology. Also, how long do our computers last, and how could we sustain their performance without upgrades and advances in chiip technology?
Human civilization began at least 5000 years ago, and none of these civilizations remain, apart from a few ruins. The few traces we do find are in the form of fragments that are preserved as precious relics.
Reliability, durability and self-sufficiency over many thousands of years are far from possible by our present standards. Also, the ability to sustain social and educational structures that could survive thousands of years in comparatively cramped spaceships would be a huge challenge.
In addition, it would be impossible to represent the diversity of humanity in a single space ship. Also, the cost of sending a swarm of colonies, in order to ensure the survival of at least one, would be insurmountable. There would be no possibility of representing humanity in all of its ethnic and cultural diversity in a single space ship. And then, how would this group evolve and change further during thousands of years in space?
So far, this discussion is about travel to our nearest star, 'only' 4.2 light years away. Travel across our own galaxy, or intergalectic travel, is far beyond us.
And what about fuel? Possible propulsion systems are still only a matter of conjecture.
An extraterrestrial civilization able to successfully cross interstellar or intergalactic space to get to us, and able to overcome the technical challenges of sustainability, light speed, biological survival and time, would need to be vastly superior to us. Here on earth, we haven't yet managed to accomplish an interplanetary mission with a human crew inside our own solar system.
Accordingly, such uncertainties and difficulties have led to theories that question the very existence of extraterrestrial life.
A comparatively recent attempt to explain the cosmic silence around us is the Rare Earth Hypothesis (REH). The REH argues that the evolution of biological complexity resulting in intelligent life is exceedingly rare, or perhaps even unique to earth. This is because our own evolution was the result of an improbable combination of fortuitous circumstances or accidents, often within a narrow zone of acceptability, many of which needed to occur within the right sequence.
For example, the best known event that accelerated our human evolution was a gigantic accident, called the Cretaceous Paleogene Extinction. This extinction event was caused by a meteorite estimated at 10-15 kilometers (6-9 miles) in diameter hitting the earth at Chicxulub on Mexico’s Yucatan Peninsula. The energy released by this impact was approximately the same as 100 tetratonnes of TNT, or more than a billion times the energy of the atomic bombings of Hiroshima and Nagasake. (7)
Another way of understanding this enormous amount of energy is that it would be enough to power our current civilization for the next 230 years. (8)
The Chicxulub impact not only caused catastrophic climate change, but it resulted in the extinction of the then dominant vertebrates, the dinosaurs, thereby creating a niche for smaller mammals to emerge and develop in directions that eventually led to human evolution.
Our ancestors were then able to evolve three times faster (8) in the ten million years after the extinction of the dinosaurs than they’d been able to accomplish in the preceding eighty million years. In evolutionary terms, this was an explosion of diversity. (9)
It's arguable that such a series of extinctions and accidents cleared the way to allow for human evolution. The creationists describe these same extinctions and accidents as miracles. And yes, whatever the cause, whether it was chance, divinity, or evolution, all of these events occurred in the right sequence, at the right time, for homo sapiens to emerge and dominate. Or, to put this the other way, if these extinctions and events hadn't happened in the same sequence and time frame, we wouldn't be here at all.
Unbelievably (or believably if you are religious), everything has been just right for us over billions of years.
Another fortuitous accident that allowed for life to develop on earth was an even more massive collision. This one, thought to have been caused by a Mars-sized object hitting earth during the formation of our planetary system, resulted in the expulsion of enough material to form the moon. This impact also caused the earth’s axis to tilt to 23 degrees of obliquity.
Earth’s axial tilt provides the different seasons essential for plant growth. Life on earth could not have developed the way it has without this seasonal cycle of growth and fertility. The moon has also acted as a balance to help earth resist the gravitational pull of Jupiter and has therefore limited axial wobbling that in turn, has preserved this obliquity over a long period of time. (10)
The Rare Earth Hypothesis argues that these two accidents, and the sequence of many other significant evolutionary events, have been essential for the development of our species. Another lucky break for earth is our location in the solar system in relation to the gas giant, Jupiter. Jupiter, and its massive gravitationnal system, has acted as a sort of planetary sweeper that has deflected, or swallowed up, otherwise dangerous intruders that might have smashed into earth.
There have been at least five major extinction events during our own evolution. All of these have been fortuitous in the sense that unsuitable ecological hierarchies were toppled to create a new environment in which surviving species emerged and prospered, and then, in turn, these surviving species later became extinct to provide the ‘right’ conditions for the next evolutionary step. Science reminds us that over the last 3.5 billion years, about 99 per cent of the estimated 4 billion species that ever evolved are now extinct.
This has proved to be a highly successful evolutionary refinement. Or, as seen by the creationists, a predestined journey plotted by the Great Navigator.
Oh, yes. And it wasn't just the impact of the asteroid hitting the Yukatan Peninsula that caused the extinction of the non-avian dinosaurs. It was the actual site of this impact that proved to be so destructive at the end of the Cretaceous Period. The underlying sediments in the Chicxulub area were oil rich and were what resulted in the necessary amount of soot to be ejected that was able to block out the sun for long enough to cause catastrophic changes in climate and biology. According to Scientific Reports, only 13 per cent of the earth's surface is comprised of rocks that could have burned off an equivalent amount of soot. These areas largely conform to the sources of our oil and gas supplies today.
Other big asteroids have hit earth in the past, leaving their mark, for example, in Chesapeake Bay and in western Baveria in Germany, but these caused no mass extinctions, probably because their impact sites didn't have the same volatile nature of underlying sediment.
It's interesting to speculate about whether or not homo sapiens would have been able to evolve if the so-called Chicxulub asteroid had hit in a different place, where the substrata was more inert. The dinosaurs might then have continued their domination, and mammals might never have been able to emerge and evolve as they did. But this is just conjecture, as we have ended up being the product of the geological and biological events (and accidents) that actually happened in the time frame and the sequence that history has recorded..
We tend to take this progress of remarkably precise and 'lucky' transformations in the 'right' time frame for granted, as though these are all normal. But considering the extinction of so many billions of preceding lifeforms, perhaps it was also our (unique?) ability to adapt to the kaleidoscopic, disasterous, and frequently toxic, changes in our environment that enabled us to survive and prosper.
Therefore, is it presumptious to believe that other, identical circumstances and timely transformations on similar planets would have resulted in another complex, 'lucky' species just like us? Mathematically speaking, there's a case to make that these odds would be just as probable as the mythical tale of a tribe of monkeys using word processors and eventually writing the works of Shakespeare.
A browse through other theories associated with the Fermi Paradox makes interesting reading. Some of these touch on the realm of science fiction and are highly speculative.
Do other forms of intelligent life exist in the cosmos? In all probability, yes, I think so. No alien civilizations anywhere would be just as amazing as finding one or many. Although the definition of 'intelligent life' assumes our anthropomorphic interpretation. Our human brains are the most complex structures that we know of, and we're not really sure how they work, or how they evolved. Trying to definie, or agree upon, intelligence in aliens is therefore maybe presumptuous.
But there is likely to be extraterrestrial life of some sort because there are just so many billions of galaxies and stars, and therefore planets. We know from life on earth that it emerges and prospers in an explosion of diversity, also that life is tenacious, and can prosper even in toxic environments. Extremophiles are amazing examples.
Also, many galaxies are older than our own and life within these galaxies, if it exists, would have had longer to evolve. Although this is still just guesswork.
But maybe, this supposition about extra-terrestrial life is also about hope. It’s a common human desire not to want to be alone. Like religion, the belief in life beyond our own world might be associated with our hope for immortality. Or at least, for more profound meaning beyond our comparatively short life spans. A single human life is considerably less than a blink in terms of the history of our cosmos. A single human life is also less than a miniscule speck in the swarm of time, set against the enormous scale of the universe.
But even though individual lives are so short, we'll be able to survive as a species, right? Well, maybe, but the caveat that questions such long term survival is the Great Filter Theory (GFT). This theory postulates, broadly speaking, that after a certain stage of technological development, civilizations self-destruct before they reach the level of interstellar communication and travel. It's not inconcievable that we will soon face such a threat ourselves.
But even if we can avoid the Great Filter, there’s the final question about what would happen if and when an advanced civilization actually did make contact with us. Our own history of colonization is a cautionary tale. Or are the traits of power, exploitation, greed, cruelty and genocide only human aberrations? And how could we expect aliens to respect human life when our own history is so bloody?
And anyway, such speculation begs the question about why advanced aliens would bother to make an expedition to earth in the first place. What could we possibly offer aliens who have solved the problems of interstellar or intergalectic travel and time? Presumably such aliens would already be harnessing the power of their own sun(s) and/or galaxies, as per their progress along the Kardashev Scale of civilizations. Plundering earth's resources would then be a puny and insignificant reward, not worth the enormous effort and cost involved in getting here and then returning with the spoils (what spoils?).
But it's a common human assumption that advanced forms of intelligent life would want to meet us, and thereby empower our own interstellar ambitions and solve all of those pesky puzzles posed by the limitations of physics. This (benign) assumption would involve visiting aliens unlocking our access to the universe to ensure our own long-term survival.
Yes, but these are very human assumptions about sharing knowledge, based on the belief that advanced beings would want to help us. But would they have crossed time and space for philanthropic or educational reasons? And would they help all of us, or only those whom they first choose to initiate into such superhuman powers? In this context, first contact and the human scramble to be at the head of the queue to access and control such god-like gifts, would likely tear our social structures apart.
Also, after first contact, it's unlikely we could remain as the same species. The changes and challenges would be sudden, huge, and possibly catastrophic. Global religions, for example, would be forced to do some quick readjustments about why mankind (humans) are made in the likeness of god, and why aliens are excluded, especially if the ones who arrive and check us out on earth are so clearly superior?
And anyway, does anyone seriously believe that advanced aliens (non-humans) would share human values, including altruism and philanthropy? And which human values? Whose? We can't even agree ourselves. The history of humanity is also the history of wars, many of which were, and are, caused by conflicting ideologies. Perhaps violence itself is our nature, irrespetive of race, religion, nationality or ideology. Could presumably superior beings comprehend or relate to what must appear to be such primitive brutality?
So many questions, and so many conflicting opinions. And yet, it would be fascinating to bridge the void and actually meet aliens, and then be able to ask, in addition to finding out where they are from, and about interstellar travel, more philosophical questions such as, is death the inevitable consequence of life? Have they transcended mortality? How do they propagate their species, if at all? To what extent are they biological and how much are they synthetic? What is their relationship to Artificial Superintelligence (ASI) and how did this develop? Do they have families? How does this question relate to immortality, if they have achieved such a state? What is their perception of time? Does alien philosophy consider the same questions as us? What about alien religion, if any? What about alien concepts of morality and right and wrong? Their concept of equality? Are there different alien ethnicities? Do they know of other alien species? If so, where are they located and what are they like? What about alien art, literature and music? Is creativity universal? Do they kill members of their own species, and if so, why? What about governance and power structures? Who is in control, and how does this management system work? What do they think of democracy? Do aliens comprehend compassion, and what are their highest aspirations? Do aliens dream, and if so, what are these dreams about? What about alien wisdom, and would we recognize it and be able to understand it? Is entertainment a familiar concept, and if so, how do they entertain themselves?
Another big question would be, to what extent is our consciousness limited by being human, and by our acceptance of the boundaries of physics as we know them? Or maybe an even bigger question - what have we got to teach aliens, and what can they learn from us?
But before rolling out the red carpet, perhaps we should consider the theory that advanced beings would want to destroy any other competition (advanced civilizations) in the interests of self preservation. This is the Dark Forest Theory, and is the most bleak answer to the Fermi Paradox.
Of course, all of this speculation is another reason why stargazing is so fascinating. It's not just about beauty and awe. Stargazing raises so many fundamental questions - scientific, philosophical and existential.
Currently, the answers to these questions, like the stars and the Fermi Paradox, are tantalisingly out of reach. We can only watch and wonder.
And wait, perhaps? Yes, but trying to answer the Fermi Pardox shouldn't distract us too much from looking after our own survival and progress here in our own galactic neighborhood.
Waiting for definitive answers to the Fermi Paradox, and/or waiting to be enlightened by aliens, will probably take a very long time. If we receive such answers at all.
Then, of course, there's always the possibility that we mightn't like the aliens we (eventually?) meet, and will choose, if possible, not to have anything to do with them. Non-humans, of course, won't be human, and it's difficult to believe that we might have anything in common at all. There's absolutely no guarantee that aliens would share, or even comprehend concepts such as generosity, compassion and (ahem) humanitarianism. Could there be higher realms that aliens might have attained? Who knows?
Maybe, just maybe, we are the ones with the best answers.
Really? Do we need to bow down to anyone? Or any thing? Is technological supremacy the only answer? Is the dream of immortality counterproductive to the human drive for progress?