Are We Alone in the Universe ?

 I first published this blog in February 2022, just before Putin's invasion of Ukraine.

 A  report last year of  the possibility of life existing on another planet also presented a good opportunity for a fresh look at the question, which seems even more relevant now, given the increasingly fragile state of our planet's ecosystem and our own continuing descent into resource-driven conflict. All in all, perhaps a fitting time to consider whether there might be a possibility of alternative accommodation for humans elsewhere in the universe....

The combination of dimethyl sulphide (DMS), CO2 and methane in the atmosphere of  exoplanet K2-18b is seen as a 'biomarker' - although it does not by any means confirm the presence of life there, it is certainly intriguing. At a distance of 124 light years, however, the possibility of our ever venturing there are slim, to say the least. 

Read on to find out why....

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Are We Alone in the Universe ?

Introduction

Having myself already reached ‘a certain age’, and being mindful of the one certainty we have – that of our own mortality, I wanted to take the opportunity this blog platform presents to look ahead at some of the more profound questions we face as a species….

First a disclaimer - these thoughts are to an extent speculative, and are my own personal views; they are not intended to represent the views of others, some of whom may have very different ideas. Hopefully they will provoke some thought on our current situation and our future prospects as an ‘intelligent’ species.

I thought I’d start with two questions which have inspired and worried us in equal measure over the centuries, but to which, as yet, we have no definitive answers…

1)      Are we alone in the Universe ?

2)      Will we ever ‘reach the stars’ ?

Question 1: Are we alone in the Universe ?

Let’s look at this question first, as it leads logically to question 2). This question actually has two answers – Yes and No. Let me explain....

With the technology we have available, we have already discovered many solar systems in our own galactic ‘back yard’, and inferred the presence of planets with comparable size to our own and located within the so-called ‘goldilocks’ zones of some of these systems. The new James Webb space telescope, which so far seems to have avoided the teething troubles which beset Hubble in its early days, will no doubt continue to throw up many more examples in its working lifetime, and even bigger telescopes are planned within the next decade. Given the vastness of the universe, and the unimaginable number of star systems it must hold, it seems inconceivable that life has not evolved within at least a few of them. So the first answer to 1) is almost certainly ‘No’.

But the mere presence of life elsewhere does not mean we aren’t effectively alone. The vastness of space and the finite velocity of light (c) (faster than which we believe nothing can travel), both suggest that a single human being will never be able to make the journey  between earth and even the nearest potentially life-bearing planet in one lifetime. So from that point of view, the answer to question 1) would be ‘Yes’, as individual humans we are effectively alone in the universe, since we will, in all likelihood, never actually meet or even communicate with intelligent beings from another world. This is probably just as well - see later for a discussion of why this is the case.

It is possible that at some stage we may be able to engineer self-sustaining space ‘colonies’ able to travel between the stars, which would at least expand the possibilities – I’ll say more about this later.

Let’s turn our attention to question 2), and look at the practicalities of space travel in an attempt to answer it….

Question 2: Will we ever ‘reach the stars’ ?

Before we look at this question in detail, we should first consider the sheer scale of space. Even the nearest star to earth is still around 4 light-years distant from us. This equates to a mind-boggling 5.87 x 10¹² miles (i.e ca 10,000,000 times further from earth than any human has yet travelled; the Voyager probe, the farthest-travelled human invention, is still only a mere 0.025 light years from us, having taken over 40 years to get there). 

Humans have a finite lifetime (ca 70-100 years for the majority of those who manage to reach their 'natural' span). Assuming we could find a way of achieving even 50% of the velocity of light and survive the journey, a round trip to Proxima Centauri would take at least 20 years. There is a problem with this initial assumption, though – in order to make most of the journey at 50% of the speed of light, we would need to reach it first - and then perhaps more importantly, slow down again at the end.

As some of us may remember from our school physics lessons, the laws of motion dictate that acceleration places an additional force on the body which is being accelerated or decelerated. We feel these forces ourselves in small measure every day when we drive or use public transport. The human body is limited in the extent to which it can survive these forces. We have all been designed by evolution to exist in gravity of 1g. Fighter pilots and astronauts in training can survive up to 5-10g for short periods without losing consciousness – you may yourself have experienced 2-3g on a fairground ride at some point in your youth, and like me, probably felt quite uncomfortable. If we assume a maximum reasonable survivable long-term g value ‘exposure’ as ca 1.5g, how long would it take to reach 0.5 c ? 

The answer I come up with, assuming c=186,000 miles/sec and 1g=32ft/sec² is ca 118 days. This would imply spending at least 4 months continuously at 1.5 g (i.e weighing 50% more than we do on earth) at both ends of the journey, given the need to slow sufficiently to achieve orbit around a new planet. Possible, but not particularly pleasant. However, the sheer quantity of fuel we would need for the two ‘burns’ required to accelerate and decelerate the spacecraft during these events would be vast using present rocket technology, hence ruling out this type of long-haul space travel until we find alternative fuels with much higher power to mass ratios. Wholly ion-based propulsion is effectively a non-starter, since slowing from 0.5c to a speed compatible with orbital insertion would take literally centuries to achieve.

Even if we did manage to overcome the 'g' force and fuel questions, there’s an even more worrying one – that of space debris en route, which would definitely be a show-stopper for me if I were young and fit enough to consider a job as a potential long-range astronaut.

We've already cluttered up our planet's near-earth orbital area to such an extent that it is already becoming quite hazardous. This is because of the plethora of space ‘bits’ which have accumulated up there since we started firing rockets into orbit in the 1960s. It’s frankly amazing to me that the International Space Station (ISS) hasn’t yet had a serious accident - it has had significant alarms related to showers of satellite fragments intersecting its orbit on several occasions already. Micrometeorite hits to working earth satellites including ISS resulting from sand-grain size particles are quite common, and serious damage could be done by a collision with a even a pebble-sized object at a combined orbital speeds of up to 36,000 miles/h. This is due to the vast amount of kinetic energy that would need to be dissipated during any collision. 

Although interstellar space is of course a lot less crowded than near-earth orbit, you would still have to get there, and there’s plenty of assorted interplanetary debris in parts of our own solar system to negotiate before you did so. This implies that there would need to be a strict 'speed limit' within the inner solar system, and acceleration up to our suggested figure of 0.5c could only occur beyond notable known danger zones such as the asteroid belt. This would add significantly more time to the journey.

Almost any collision in interstellar space at 0.5c would of course be virtually certain to result in the destruction of some or all of the spacecraft – not a pleasant thought for anyone hoping to survive the long-term exposure to this risk during a 20+ year round trip….and of course even if you manage to avoid catastrophic accidents, there’s the question of what to do about long-term cosmic radiation exposure, regenerating oxygen and water, maintaining food supplies, psychological health, muscle atrophy in zero gravity, etc, etc……

Another interesting question that arises is: would travelling at speeds this high mean our intrepid travellers aged more slowly during the journey ? If so, this could be useful in reducing the effects of ageing and reduce the need for some kind of suspended animation during the journey. Unfortunately, if you accept Einstein's General Theory, the 'slow down factor' (i.e. the fold-reduction in the apparent passage of time) only becomes significant and speeds close to c:

0.1c: 1.005; 0.5c:1.15; 0.9c:2.3; 0.99c:7.1

Thus to get even a halving of your rate of ageing, you would need to travel at ca 90% of the speed of light for most of the journey - way beyond the 'safe' speed limit we've already considered.

I think the take home message at present, based on the evidence we have, has to be that the human anatomy and physiology were never designed for space travel, and we would need to think very carefully before hurling ourselves into such an inhospitable unknown for extended periods. 

While I’m all in favour of more local exploration of our own solar system, and I am quite excited by the prospect of a manned mission to Mars (possibly even within my own lifetime), I suspect we won’t get much farther out than this in the foreseeable future.

So will we ever 'reach the stars' ? I suspect probably not ‘in person’, at least with anything resembling current technology and assumptions. 

The sci-fi writers, and some of the more adventurous cosmologists, have raised the possibility of so-called 'wormholes' being used to jump directly between physically distant regions of space-time. Even if we did find a way to utilise these putative cosmic phenomena, it’s unlikely we would survive the forces involved in passing through them. According to current thinking, they can only occur when two adjacent and sufficiently massive objects (i.e. black holes) converge sufficiently closely to 'squeeze' space-time into a wormhole. Even if we put aside concerns about the risk of being sucked in to either black hole, we would likely be unable to control where we ended up; more to the point we would  be unable to navigate back to our starting point once we got there. Even if we did return to the same space, how far into the future would we arrive ? And what would we find when we got there ? 

This question opens up yet another 'can of worms' (or should it be wormholes!) which is not generally appreciated. What we see on earth never represents what is actually happening at the observed object's location. This is because the velocity of light is finite. Even messages sent from our nearest celestial neighbour, the moon, take about 1.5 secs to reach us, as those of us who were around then will have confirmed during the moon landings of the 1960s and 70s. The farthest galaxies we can see with the new James Webb telescope are around 13.6 billion light years away. The lifetime of most stars is only of the order of a few billion years, so identifying a potentially habitable planet more than a few hundred million light years distant (even if we could at that distance) would be pretty futile, as we could not guarantee it would still be there at all, if and when we ever reached it. Identifying an alien species through its radio signals and hoping to connect with it would be even more problematical, given that the 'technological' lifetime of most intelligent species (including in all probability, sadly, our own), is only likely to be a few hundred years at most, and they would probably already have died out long before we got there (see below for more detail on the likelihood of meeting aliens).

Sending robotic probes would probably also be useless unless they could be retrieved intact with a record of their travels, given that conventional direct electronic communication would not be possible through wormholes in space-time.

The idea of travelling faster than light to cover the vast distances of space has also cropped up frequently in sci-fi offerings. Star 'Trekkies' will be familiar with Kirk's frequent request for 'Warp factor 3' when setting off on another of his celestial perambulations. Even if it were possible to achieve speeds greater than c, the known universal laws would produce more than a few questions. The first is: what would happen to the traveller's local time ? 

Einstein's theories predict that time slows down as your speed approaches c. We've already considered how this would affect 'sub-c' travel. Would time actually reverse when you got beyond it ? Even if it didn't, your reaction time and hence your 'stopping distance' in response to an oncoming object would presumably tend to infinity as your local time passage slowed to nothing. There would also be an extreme Doppler effect resulting in a blue shift well into the UV range for any light emitted by the object, so that human eyes could not see anything coming without some form of ultra high frequency detector.

So the answer to 2) is: Probably not, but who can tell…..

All this speculation throws up a related question which I’ll designate as 3):

3)  If you still subscribe to the 'Big Bang' theory following some of the recent developments in cosmological thinking, the likelihood is that intelligent life will almost certainly have developed elsewhere in the ca 13.5 billion years since it happened. If (as I suspect is more likely - see related blog) the universe is actually  in continuous 'steady state' or cycling between contraction and expansion phases, it may have had even longer to get going. But are we ever likely to communicate with, or even actually meet, an alien species ? 

Question 3: Will We Ever Encounter Alien Life ?

To answer this one, we first need to define what we mean by ‘alien’.

We're all familiar with the concept of bug-eyed monsters with completely alien physiologies sailing in from distant galaxies to wipe us all out and take over earth, as represented in countless sci-fi offerings. However, the term ‘alien’ could apply to other forms of life yet to be discovered within our own solar system e.g. those which may exist in the upper-level clouds of Venus or the depths of the liquid water oceans we now know exist beneath the surface ice on Jupiter’s moon Europa and Saturn's satellites Enceladus and Mimas (The very recent discovery of Mimas's subsurface ocean has revealed this is a realtively 'young' feature which could be in the early stages of the development of life). It could even be applied to organisms yet to be discovered here on earth – our knowledge of the ocean deeps and the physiologies of the strange creatures that inhabit them is still in its infancy, and will doubtless throw up plenty more surprises.

There is even some doubt as to whether life actually originated on earth at all, (which would make us all ‘aliens’) – some theories suggest it could have reached us intact via ‘natural’ means using meteorites and then established itself on earth – this is doubtful, given the aeons it would have taken to get here, the destructively high temperatures involved in atmospheric re-entry, and the unshielded radiation exposure that would be experienced as such an object would have experienced as it neared our sun. The only other possibility would be an artificial ‘implant’ using protective technology – I’ll let the reader (and the theologists !) decide on the likelihood of that one, since it would have involved 'quasi-divine' intervention…

If we go with a more restricted definition of an alien as ‘an intelligent life form originating outside the solar system and capable of developing technology sufficiently sophisticated to convey them to earth intact and functional’, then we have something more useful to work with.

Firstly, do we have any ‘hard’ evidence that aliens have already reached earth ? There are plenty of UFO reports and accounts of supposed alien life forms of which the Roswell chronicles are perhaps the most celebrated. Most of these reports can be explained away as being of terrestrial origin, but some admittedly can’t. For the purposes of the discussion, let’s assume for now that there is no ‘definitive’ proof of aliens (as we’ve defined them above) existing in our midst, or even hidden away in one of the few remote corners of our planet's surface that we haven't yet explored.

We now need to consider why there is no hard evidence for a physical alien presence. Two likely causative factors immediately spring to mind – distance and time.

We’ve already considered the vastness of space and its implications for limiting our own interstellar travel options. The same physiological constraints would probably apply to any sentient carbon-based life form originating elsewhere, thus limiting maximum lifespans to a few hundred years at most. It is unlikely that any other life-form which might able to achieve much longer lifespans would have been able to develop technology advanced enough to escape the gravity of their own planet, let alone survive the rigours of space for the thousands of years needed to get here at 'survivable' speeds from even the closest stars. Let alone other galaxies.... 

We do of course have some types of organisms on earth that can survive for thousands of years - English oak trees being one...but they don’t seem to have got round to building any space ships (as yet !).

We’re therefore limited to the 'self-sustaining human colony’ concept, probably with some form of suspended animation built-in to extend survival time and reduce on-board consumption of resources. Given the potential for catastrophic space accidents already considered, the chances of completing a successful passage even under these conditions would seem to be quite low.

The other factor that isn’t as obvious, but probably best explains our lack of any contact with sentient life outside our system so far, is….time. Why is this important ?

We can best explain this by looking at the age of the universe and comparing this with our own ‘record’ as an intelligent and technologically competent species. If you still subscribe to the ‘Big Bang’ theory, the universe as we know it originated ca 13.5 billion (13,500,000,000) years ago. We have been capable of emitting signals in the radio spectrum at sufficient power to be received outside the solar system for only around 100 years (i.e. 1/135 millionth of the presumed age of the universe). Due to the finite value of c, the earliest signals we’ve produced will so far only have reached a distance of ca 100 light years beyond the solar system. To put this in context, the star system named Algol (Beta Persei) which contains planets in orbits which we think could make them habitable for carbon-based life, lies ca 92 light years from us. An observer based there would theoretically have been able to detect our broadcasts for only the last 8 years. If their receiving apparatus were sufficiently sensitive and capable of decoding our early broadcasts, they would already have had the opportunity to follow news of the Great Depression of the 1920s & early 1930s, with the 'spectacle' of the late 1930s and 1940s still to come (I suspect this experience in itself might not give them much encouragement to visit us…)

Any sentient life form elsewhere in the galaxy looking for a habitable planet to colonise would thus need to be located within this radius and have technology available to receive and our signals and distinguish them from background space ‘noise’. A positive indication would be essential from their point of view before embarking. 

What is the likelihood of intelligent life elsewhere having already 'spotted' us ?

If we assume life did actually originate on earth, and the ca 4 billion years it took to do so is 'par for the course', it is highly likely that life will probably have evolved elsewhere in the universe many times in the 9 billion years between the ‘Big Bang’ and the earth's formation. But the true nature of what I would call the 'awareness' problem becomes apparent when we think about the effective lifespans of intelligent societies. As discussed, homo sapiens has been technologically ‘competent’ enough to generate receivable messages for only 100 years or so, and we have yet to develop the ability to achieve viable interplanetary, let alone interstellar, space travel. 

We should also remember that there is an inherent problem associated with becoming technologically competent – it is likely to lead sooner or later to the ability to harness atomic fission and fusion, thus presenting the option of wholesale self-destruction if the technology is mishandled. We have survived this risk without major incident so far, (although apparently we came within a few minutes of accidental full-scale nuclear war in 1985, and uncomfortably close to it in 1962). Current events alone should convince us that this is no longer assured. If we assume we do actually manage survive as a society capable of sending out messages for, say,  another 100 years before either dying out, or losing the technical ability to radiate effectively in the electromagnetic spectrum, that would mean a ‘window’  of only 200 years during which an alien habitable planet-seeker could ever have been able to detect our presence.

For contact of this sort to be made both they and we would need to coexist over the same brief ‘cosmic microsecond’ for mutual or even one-way awareness to be possible. 

Theological considerations apart, this implies an almost miraculous coincidence in time and space, given the relative vastness of both dimensions. Even if this ‘miracle’ actually did occur, and our visitors set off as soon as they received our signals, they would probably reach earth long after our species' demise, (and might well be faced with a highly radioactive and uninhabitable biosphere resulting from our species' decent into wholesale nuclear conflict.)

Of course, an intelligent species looking for habitable real estate could take the 'scatter-gun' approach in the absence of positive evidence of intelligent life elsewhere and simply look at  planets within the 'Goldilocks' zone of their stars as exploration targets. This would however far from guarantee a positive result, and a negative one would ensure that the colony would eventually fail its mission and die out, given the distance to the next planetary candidate on their list. So it's likely that aliens would only choose to visit planets with positive evidence of intelligent life - i.e. ones emitting characteristic 'biomarker' radiation in the radio frequency spectrum.

Looking at it from another perspective, why have we not yet detected any signals unambiguously indicative of alien life elsewhere ? The SETI initiative has been looking for may years now and is still diligently scanning the radio and visible spectra for signs of life. The answer almost certainly lies in the same two directions - space and time. 

In order to generate a signal sufficiently strong to be received and decoded at even a few light years' distance, the source would have to be many times more powerful than anything ever produced on earth to date. This is because the inverse square law would in itself reduce its intensity to an infinitesimal fraction of its original strength over this vast distance, and the cumulative effect of dust and gas in the intervening space would be likely to mask it even further. The universe is actually quite a noisy place, particularly when it comes to the radio frequency portion of the spectrum, and signal to noise ratios will also have a major bearing. Short of actually finding a way to modulate their own star's output, it's difficult to see how an alien species would be able to render themselves detectable in this way. The time aspect is equally applicable here - our aliens would need to be capable of radiating over the same period that we were alive and both we and they would have to survive long enough to exchange messages and then physically traverse the distance between us. 

Yet another question arises from this: given the potential risks of detection, however slight, should we continue to advertise our presence at all ? As a biological scientist, I have to admit I used to be quite concerned about this. The experience of the recent pandemic, and a more in depth look at the possibilities have, however, allayed my own fears somewhat.

One of the reasons for this is that, as we’ve all realised more acutely recently, we are all surrounded by a ‘sea’ of opportunistic pathogens, and we breathe in literally millions of them every minute. Our immune systems have evolved to cope with this, and allow us to survive their continuous onslaught. Even the 'innate' elements of our immune responses are capable of dealing effectively with most attempts at colonisation, and this ability is greatly enhanced by our acquired immune memory of exposure to any pathogen we do fall prey to. 

Any alien carbon-based life-form reaching earth’s surface would be subject to the same opportunistic attacks, and would presumably have no acquired immunity to any of our local pathogens. The chances of survival for them once exposed would therefore be low – as indeed it would be for any of us arriving on an alien life-bearing planet. Any species intelligent and resourceful enough to be capable of making the trip would presumably realise this, but could only take limited action to avoid it.

Given the poor prognosis for any ‘invaders’ who managed to get here, and the infinitesimal likelihood of them being alerted to our presence and actually doing so in the first place, we can probably rest easy, and not feel the need to shut down all our communications and observe ‘global radio silence’ (at least not before the next major solar storm arranges it for us !). In short, the greatest danger we face as a species is probably - ourselves...

Final Thoughts

I’ve suggested it’s unlikely that, as humans in our present incarnation, we’ll ever physically  travel beyond the confines of our own solar system. 

So far we have made considerable strides in exploring the planets robotically, and it’s pretty clear already that there are no other places in the solar system where a human could exist without complete environmental support. We may eventually manage to set up and sustain limited colonies on the moon and possibly Mars - if we survive long enough as a ‘technologically competent’ species, and can summon up the extensive and highly-specialised resources required to do so. 

As I write this, some pundits are floating the possibility that the Ukraine conflict may turn out to have been the prequel to World War 3, which could start in earnest following an invasion of Taiwan by China. Hence any assumptions I've made on our continued 'technical competence' for long range communication, let alone space exploration, may already be somewhat optimistic. See "Modern Warfare -the Future?" for a more in-depth discussion of the possibilities facing us in the next couple of decades….

Given the likelihood that there really isn't anywhere else to go, and focusing on our options on our own planet, we know that humans can survive unsupported at the earth's surface only on land (ca 20% of the globe’s surface area), and a significant proportion of the available land area is too cold or otherwise inhospitable for survival. Our respiratory systems and relatively high oxygen demand means that we’re also limited to a very small range of altitude above mean sea level (MSL) – in practice the ‘death zone’ beyond which supplementary oxygen and atmospheric pressure are essential for survival for more than a few days, starts at only ca 20,000 feet (i.e. ca 4 miles) above MSL.

To help put all this in context, I'll leave you to ponder the attached NASA image (Figure 1) which shows our atmosphere as a tiny sliver of light just above the planetary surface before the blackness of space begins – the boundary of the visible layer in this picture is ca 100 miles high, but the human body can only exist unsupported in the bottom 2-3% of it. This rather beautiful, but stark, image should convince most of the real fragility of our existence, and the need to avoid losing what we have – if only because it’s likely to be all we’ll ever get.

How do we avoid losing it, given the current state of world politics and man's predilection for self-destruction ? I’ll leave that thorny question to a future blog…..

Viv

Version Date: 13.12.23

        Figure 1: NASA photo showing Earth's atmosphere at sunset, with Earth silhouetted