“An Oasis For Aliens”

“An Oasis For Aliens” © Mark McAndrew

Aliens - you either believe in them or you don’t. Now, in all fairness, most people are quite content to accept ET exists ‘out there somewhere’, but until the little buggers land on the White House lawn (or the White House itself, with any luck) far less are prepared to say they are here. Fair point?

No, it isn’t. By the time you finish this article you will have evidence, beyond a reasonable doubt, that aliens really have discovered the Earth. How’s that for a promise? There are no photographs, bits of UFO or secret documents for you to believe or disbelieve - it’s just some simple logic and a couple of sums. All you have to do is follow the numbers. Numbers don’t lie.

“Don’t Believe The Truth”

The basic problem with space travel is the ridiculous distances involved. Astronomers don’t talk in miles, they talk in ‘light-years’. One light-year is the distance light travels in a year, and it is absolutely gigantic. We shine lasers at the Moon to measure how far away it is, the green beams bouncing back from reflectors left by the Apollo astronauts. The light gets to the Moon and back in less than three seconds. Tick… Leave the Earth, tock…hit the Moon, tick… back on Earth. How far light can go in a whole year is beyond comprehension, but that’s a light-year - almost six trillion miles. (Six trillion of anything is huge. If you imagine a clock ticking, one million seconds takes about 12 days. One billion seconds takes about 30 years. Six trillion seconds would take until the year 190,000 AD…)

A light-year may be an enormous distance to us, but to the Universe it is nothing. We can see galaxies that are billions of light-years away, unbelievable journeys even at light-speed itself. Of course, nothing we can make gets even close to light-speed. The fastest - and furthest - space probe we have out there is Voyager 1, which whipped past the planets of our solar system and was flung out into space at almost 40,000 mph (that’s 30 times faster than Concorde). At that speed a mushy pea can destroy a tank, yet it is still 18,000 times slower than light - it’s like comparing a snail to a rifle bullet. Voyager is now headed for a star ‘just’ nine light-years away and it will take 160,000 years to get there. No wonder astronomers don’t talk in miles.

When it comes to talk of aliens, such brain-squeezing figures certainly seem to ruin the chance of meaningful contact with the Cosmos. But they are not the only numbers we have to work with. As mentioned previously, the numbers suggest that not only should there be plenty of alien civilisations for us to find, some will have already found us first. How is this possible?

“Definitely Maybe”

In 1961, a certain Professor Frank Drake came up with a method for estimating how many alien civilisations the soon-to-be-formed SETI (Search for Extra-Terrestrial Intelligence) project might detect in our galaxy; the famous Drake Equation. It starts with an obvious truth: if you have a Sun-type star with an Earth-like planet around it, a civilisation can exist. After all, we do.

It is also true that before we discovered complete little ecosystems in boiling springs and under polar icecaps, we used to think life needed sunlight, oxygen and reasonable temperatures. Now we know bacteria can even survive the vacuum and radiation of outer space itself, munching asteroids until they hit somewhere more hospitable and get busy evolving.

Even so, we are not talking about bacteria; we are talking about intelligent civilisations. The only example we know of - us - lives on a pleasant, watery world orbiting a stable little star, so Drake’s equation usually assumes those conditions are required. Even if they aren’t, we know they work.

Drake only considered our own galaxy, the Milky Way, worthy of searching. There is a very good reason for this. Every star you can see with the naked eye is part of the Milky Way, a colossal spiral disc some 100,000 light-years across, an oasis of 100 billion stars. Fill an Olympic-sized swimming pool with sand and you have roughly that number of grains. There is plenty to look at on our cosmic doorstep.

Which is just as well, because even our closest galactic neighbour (Andromeda) is far beyond communication range - over two million light-years away. Send a signal, wait two million years, they get the signal and send a reply, wait another two million years… it just doesn’t work. The gap is 20 times the width of the Milky Way, with practically nothing in-between. To all intents and purposes humans will never reach another galaxy because, by then, we will be several stages of evolution past ‘human’. Unlike meandering from planet to planet and star to star, leaping from one galaxy to another really will require something like warp drive because there aren’t any pit stops for a long, long time. If there are intergalactic civilisations out there, we are ants in comparison.

“The Masterplan”

We are fortunate indeed to be part of a galaxy. These 100 billion stars are practically next-door compared to the rest of the Universe and roughly 10% of them are like the Sun. That’s ten billion (10,000,000,000) Suns. We also know that planets are pretty common around stars. If only one Sun in a thousand has an Earth-like planet (it could easily be more), that’s ten million Earths in the Milky Way.

Ten million Earths is a good start, but we are only interested in the number of civilisations. Alien plants, dinosaurs and cavemen might be fascinating, but they won’t be contacting us any time soon. Although astronomers’ estimations vary wildly, none think the answer to this part of Drake’s equation is zero - who could with those numbers? Even for just our own galaxy, those estimates vary from single figures to a nice, round million (the latter figure being Drake and Carl Sagan’s first answer). More recently, Prof Drake has revised his figure to 10,000.

Yet still the sky is silent. A decade before SETI began, the noted physicist Enrico Fermi made the point which became known as Fermi’s Paradox; the galaxy should be stuffed with aliens, so where is everyone? Drake’s equation makes allowances for that; it’s not a question of how many are out there, it’s how many we can detect.

Detecting them basically means picking up a radio signal. Okay, so ET has to be at least that advanced - that’s obvious. But what if they are too advanced? Aliens might use something more efficient than radio waves, something that we just don’t know about. Maybe civilisations tend to blow themselves up within a few years of discovering radio, a fate we cannot exclude for ourselves yet. Or maybe, just maybe, ET doesn’t want to be detected.

Even if thousands of ET civilisations are sending out signals, the odds are still stacked against SETI anyway. For a start, we can only detect a deliberate attempt to make contact. Picking up alien TV, for example, is far beyond our capabilities - ET must carefully aim a very big dish and direct a hugely-powerful radio beam right at us. Assuming they’ve done that, then at the exact time their signal hits the Earth many years later, our big dishes have to be pointing exactly at theirs - or we miss it. It will be a long time yet before SETI has ‘looked properly’.

Earth has been broadcasting for about 100 years, but fibre-optic cables are already reducing our reliance on radio and TV transmitters. We may stop using radio far sooner than we expect. Professor Freeman Dyson has calculated that by about the year 4000AD humanity could be constructing a sphere around the Sun (!) to capture all its energy, so one way or another the Earth won’t be wastefully blasting out radio waves in all directions for much longer. Let’s be ultra-conservative and say we will take a million years to find something more efficient - assuming we don’t self-destruct.

So, for the SETI project to discover an ET civilisation it has to be just the right age, transmitting radio - or something else we can pick up - right about now. Too young or too old, ET may as well be invisible. Even assuming a civilisation uses radio for a million years, the chances of ET being in that window of opportunity are tiny. The odds say ET will be either too young or too old to detect. You may as well hear it now; the odds say they’re too old - much too old.

“Heathen Chemistry”

Let us assume the answer to Drake’s equation is not tens or thousands, but just one; a single advanced civilisation in the Milky Way that we might conceivably contact. They must be at our level or better, but we grant them no favours and assume they took just as long to evolve as we did. So how old could they be? How old is Humanity anyway?

As a civilisation - especially using Drake’s restrictions - we are barely a cosmic embryo. People are still alive today who were born before the first radio signals were sent from our planet. Our species is fairly young, but seeing as Life on Earth actually dates back four billion years - and we are the result - you could argue that Humanity is ‘four billion years old, from scratch’. Not bad. Can ET be much older than that?

Yes, they can. The Milky Way is an astonishing 13 billion (13,000,000,000) years old. Knocking off a billion years (because the heavy elements needed for life are only made by dying stars) still leaves an enormous 12 billion years to play with. If we are saying ET evolved just like we did, they could still be eight billion years ahead of us, right now. Maybe it’s only four billion. Maybe it’s half a billion. Any way you look at it, such a civilisation would be unimaginably advanced.

“What’s the Story, Morning Glory?”

This is where things get really interesting. Remember, just because an advanced civilisation is no more detectable than a Stone Age one, it doesn’t mean they can’t detect us. In fact, for nearly four billion years anyone who has cared to look will have noticed that Earth’s blue-white colour shows the presence of water, oxygen and chlorophyll - the green chemical all plants use to absorb sunlight. Water means life might be there, but oxygen or chlorophyll mean life is definitely there. Only microbes and plants can make oxygen or chlorophyll, which is why we ourselves are looking for that tell-tale glow on other planets.

ET wouldn’t even need to ‘see’ the Earth to detect signs of life. Lightning storms give off a billion watts of radio clicks and whistles per second, all the time. Those radio clicks are ‘tuned’ by our oxygen-rich atmosphere, advertising to all and sundry that not only does the Earth have electrical storms, but they are in an atmosphere only life could have made. The detectable range isn’t massive, but it’s been merrily whistling away like that for - again - nearly four billion years. That’s a very long time to be noticed.

One other possible clue for ET is the planet Jupiter. Our civilisation owes as much to Jupiter as it does to Earth, because without it, dinosaur-style asteroid impacts would be so common that we would simply not be here. A giant planet at roughly that distance from the Sun takes all the hits and protects the inner solar system. Maybe every civilisation needs a Jupiter - ours certainly did - so you could look for them first. Gas giants are much easier to spot than an Earth and our Jupiter has been there for nearly five billion years. That’s an even longer time to be noticed.

From the first ships navigating the globe to sending Voyagers around our solar system has taken only a few centuries. How long before we’ve surveyed some local star systems? Another thousand years? What about a sizeable chunk of our galaxy - or the whole thing? Bear in mind that we are not talking about actually colonising it, rather just knowing what’s there - probably using unmanned space probes. Fortunately for us, other people have already done the maths.

“Standing On The Shoulder Of Giants”

John von Neumann was a genius mathematician and physicist, partly responsible for the H-bomb and the principles behind all computers. Amongst these stunning insights and discoveries, he also determined that self-replicating robotic machines would be the most efficient way to mine asteroids or other worlds. It didn’t matter if they were slow because their numbers would grow exponentially, spreading out like mould on a Petri dish. Before long they’d be everywhere.

Von Neumann himself didn’t take his work to the logical conclusion, but others soon did. How long it would take these machines to spread throughout the entire galaxy if they were tasked with exploration instead of mining? Limited to travelling at just one-tenth the speed of light (no big deal at all), the calculations led to a shocking answer. It could be done in just half a million years.

Let’s be ultra-conservative once again and say it will take us a hundred times longer than that, that’s fifty million years to fully explore the Milky Way. Now we have all the numbers in place. What do they tell us?

“Familiar To Millions”

Remember, this is assuming only one advanced ET civilisation that evolved no quicker than us. Everyone reckons there’s at least one out there - and one is all you need:

1. Maximum length of time a civilisation uses radio, in millions of years: 1.
2. Maximum length of time a civilisation needs to explore the galaxy, in millions of years: 50.
3. Maximum length of time a civilisation could be ahead of Humanity, in millions of years: 8,000.

By now you should see the conclusions - if ET is older than us by a paltry one million years, they’re not in the ‘detectable’ window. No wonder SETI is having trouble - the odds are 8,000/1 that ET’s civilisation is so young. The other 7,999 chances say they’re too advanced. But then the question is: just how advanced can they be?

Well, ET could be eight billion years ahead of us, right now. Maybe it’s four billion. Maybe it’s only half a billion. The thing is, with a possible head-start of up to 8000 million years, 50 million is chickenfeed - less than one percent. ET is 99% likely to be more than 50 million years in front of us and that’s ample time to completely explore this galaxy. So it’s 99% likely they know we are here.

That 99% chance we are on ET’s star-charts assumes just one advanced civilisation somewhere in the Milky Way, with all its millions of copycat Earths. If there are two, the odds we have been found are 99.997%. If there are three, it’s 99.999999998%. If there are 10,000…

With more realistic numbers plugged into Drake’s equation (say, 10,000 civilisations and galaxy-spanning by their equivalent of 500,000 AD, like we should be) the chance we haven’t been found is less than winning the National Lottery, every week, for your whole life. The scientific term for that is ‘not a hope in Hell’.

“Be Here Now”

There will be races in the Milky Way that really are billions of years older than the Earth itself - and that’s without even considering the other 100 billion galaxies out there with 100 billion stars in each of them. There are layers of cosmic civilisation we cannot possibly imagine. Despite its incredible size, our galaxy (let alone the Universe) is far, far too old to be able to think, ‘Just because aliens are out there doesn’t mean they’ve been here.’ Yes, it does. That’s exactly what it means. They’ve been everywhere.

Some civilisations could have mapped this galaxy hundreds of times over and Earth has glowed with life signs since before we were apes. They cannot have missed it. Numbers don’t lie: either we are the only civilisation that exists or somebody else found Earth a long time ago. The only question is whether or not they care.

If the Universe is teeming with life then maybe we are not interesting enough for study just yet. (By definition, that would mean there are aliens aplenty.) But if life is rare then Earth is a paradise planet, a Garden of Eden - and will have been watched continuously from the moment they found it.

We are alone or we are known. Take your pick.