Soul Bound

1        Soul Bound

1.2      Taking Control

1.2.5    An Idiosyncratic Interlude

1.2.5.20 Fermi paradox

Nadine: “If it’s that important, why did you return?”

Heather: “I spent 5 years up there and, yes, I was tempted to remain. But I decided there was more I could do to affect the answers to those two questions back on Earth than I could in space. Partially because of one man: Enrico Fermi.”

Nadine: “The physicist who created the first nuclear reactor? Bulgaria mentioned him when teaching us about tipping points. He’s dead, isn’t he?”

Heather: “He is. But he had good instincts when it came to numbers, and he was good at estimating things. He estimated that there ought to be intelligent alien species alive out there around other stars and he wondered why, if that were the case, were we unaware of receiving any communication from them?”

Nadine: “Interesting question. But I don’t see the connection to whether we manage to spread to other stars, nor to whether that should be an immediate priority for the Wombles.”

Heather: “Oh, it’s connected alright. Let me walk you through it, step by step, then we’ll head back, and I’ll give the other part of my answer tomorrow when we’ve got more time. But I warn ye, it may jus’ involve a wee number or twa.” Heather let a little bit of her native Scottish accent show through, which was something she reserved for special occasions.

Nadine: “Lay on MacQuarrie, and damn’d be she, that first cries ‘Hold! Enough.’”

Nadine lay back, gazing at the stars and learning their stories, while Heather spent a few minutes immersed with her expert system Tink, programming bees and double-checking numbers.

A buzz warned her before the bees rose up to block her view of the skies, forming a rotating model of the Milky Way galaxy above her head. In one corner of her goggles an infodot popped up, shaped like the head of a winking cat. She opened it.

YEARS   EVENT

-13.8 billion : Universe starts with a big bang

-13.5 billion : First stars in the milky way formed

-13.4 billion : Biggest stars go supernova

-8.51 billion : End of supernovae cascade

-4.57 billion : Our star formed (The Sun)

-4.54 billion : Our planet formed (The Earth)

-4.38 billion : Earth cools enough to form oceans

-3.77 billion : First life on earth

-2.70 billion : Eukaryotes

-1.56 billion : Multicellular life

-850 million : Land photosynthesis

-500 million : Land plants

-412 million : Insects

-370 million : Land animals

-2.75 million : Emergence of the genus Homo

-109 : Radio coverage of the 1936 Berlin Olympics

First Earth broadcast to reach other stars

+1.00 billion : Sun gets 10% hotter

+1.01 billion : Sea and surface water gone

Earth no longer able to support the

creation of complex new water-using

species via natural evolution

Heather: “There may be many forms of life, but the only one we know can evolve unaided is based upon complex chains of carbon molecules floating in liquid water, so let’s restrict ourselves to that. And, further, let’s stick to considering just the Milky Way and assume that the 5.5 billion year long window of opportunity between the Earth becoming cool enough for oceans and it becoming too hot for them again is the maximum that any candidate planet gets.”

Heather: “It took Earth 4.5 out of those 5.5 to go from a lifeless ocean to a sentient species. It isn’t stretching things too far to assume we’re nothing special, and that some do it as quickly as 3.5 billion years, while others are slow-coaches who take 5.5 billion, with most somewhere in the middle. Of those that manage it at all. We’ll return to that assumption later, but let’s stick with that for now, and see what it predicts.”

Heather: “Immediately we can eliminate 98% of the stars in our galaxy. Either they don’t contain carbon, or they are less than 3.5 billion years old. The bigger the star, the faster it burns out.”

Most of the bees in the disk above their heads turned a dim blue, leaving only a thin ring of bees still lit yellow, about ⅔ of the way from the center.

Heather: “That’s the Galactic Habitable Zone, 10 kiloparsecs from Sagittarius A* .”

Heather: “We can eliminate 90% of those, by further restricting ourselves to stars between 0.9 and 1.1 times the mass of the Sun, and to those hotter than 5,000 kelvin and cooler than 7,600 kelvin. So, primarily, G-type stars in the main sequence.”

The number of bees still lit reduced further.

Heather: “Furthermore, if we look inside a solar system, a candidate planet needs more than having the right size, composition and orbit to have liquid water and an atmosphere. It has to stay in that Circumstellar Habitable Zone continuously for billions of years, not occasionally wandering out on an overly elliptical orbit.”

Most of the remaining bees went out, leaving just 10 illuminated.

Nadine: “Just 10 candidates?”

Heather: “Ah, well, I don’t have enough bees to allocate one for every star in the milky way. Each bee still lit represents 1 million solar systems containing a candidate planet. If we take the rest of the physical and chemical factors into account, we’re reduced to just one bee. A million planets the size of the Earth, with a magnetosphere to protect them from radiation, oceans, a moon to create tidal effects in the crust, and enough gas giant planets in the system to suck up asteroids and reduce the frequency of species-killing meteor impacts.”

Nadine: “So 1,000,000 candidates then?”

Heather: “At least. If even just 1 in every 1000 of those produces sentient life, we’d expect the nearest civilisation to be on average 160 light years away from Earth. So where are they? Why can’t we hear their TV stations broadcasting alien sitcoms? Why can’t we see the chatter between their space stations or the spectral shift of their stars due to Dyson Bubbles?”

Nadine: “Sentient, like chimps?”

Heather: “I’m not a biologist. Maybe I’m using the wrong word. I mean a species that’s capable of discovering science and space technology. One that’s good at thinking, learning, and passing its discoveries onto its children.”

Nadine: “Sentient is fine. Ok, I see the puzzle. What’s the answer?”

Heather: “The puzzle is called the ‘Fermi paradox’ and nobody knows the answer for certain. But many answers have been suggested, some more likely than others, and they fall into four main categories.”

Nadine: “Which are?”

Heather: “Aliens are out there, perhaps they’ve even visited our planet and are still here, but for some reason we’re not aware of them. Or maybe they just sit at home writing poems, because this urge to build big stuff is just a weird personality quirk only humans have.”

Heather: “Aliens have never been out there. We are wrong about the chances of sentient species evolving. We’re the first, and may be the only ones who’ll ever evolve unaided.”

Heather: “Aliens were out there, but there’s a Great Filter - some intrinsic reason why sentient species don’t survive for long once they start down the route of science. It could be something we’ve already met and got past, it could be something we’ve already met which hasn’t yet wiped us out but likely will, it could be something we haven’t met yet.”

Heather: “Lastly, there’s ‘other’ category. For example, we understand the maths and all the factors, and it’s just a coincidence that we’ve not received a ‘Hello Humans’ signal, but one will arrive Any-Day-Now.”

Nadine: “What’s your favourite answer?”

Heather: “Sentient cat Aliens visited us and decapitated us, but then uploaded our brains into a simulation of what the planet was like before they arrived. Because they’re cats and we are toys to play with.”

Nadine: “Let me rephrase that. Which answer do you think is mostly likely?”

Heather: “The least likely is ‘Aliens have never been out there’. The ability to run accurate chemistry simulations at the molecular level has made the mechanics of abiogenesis very well understood. Similarly, we’re really confident about the physics factors involved during the creation of solar systems and planets. The only people remaining who think sentient life doesn’t evolve, are those who believe that for political or religious reasons.”

Heather: “The next least likely is the ‘other’ category. You can never eliminate coincidence, but the odds are fantastically against it.”

Heather: “The ‘Aliens are out there’ category is hard to estimate, because it contains a wide range of answers, from Star-Trek-like prime directives to everyone hiding from Berserkers.”

Nadine: “You dragged me to enough Star Trek marathons that I remember the don’t-talk-to-non-spacefaring-cultures-so-you-don’t-contaminate-them-with-your-ideas plot line. But what have hairy Norse warriors got to do with it?”

Heather: “Old science fiction book by Fred Saberhagen. They never made a film about it. Pity really, I’d love to work on the special effects.”

Nadine: “Heather!”

Heather: “Oh, right. Berserkers are what Saberhagen called his baddies. They were interstellar drones, controlled by expert systems unswervingly dedicated to destroying all life in a solar system, using the solar system’s resources to replicate multiple times, then heading off to all the other nearby systems and repeating the process.”

Nadine: “Nasty. Is that a possibility?”

Heather: “Either some species escape them, in which case you’d think that at least one of the escapees would send out a warning signal to alert other species to the danger. It wouldn’t be hard to leave long-term evidence that others would find hard to cover-up. Or the Berserkers are perfect at what they do, in which case we might as well ignore the possibility because there’s nothing we can do about it. A lot of the answers in the ‘Aliens are out there’ category face a similar problem. They rely upon perfect compliance by thousands of different species.”

Nadine: “So you’re saying that, in the Star Trek universe, at least one species who didn’t care about The Federation would have done something that astronomers with the Earth’s current level of technology could have detected?”

Heather: “Exactly. An insane Ferengi starting a pirate radio station that broadcast from millions of relays in interstellar space, just 1 hour per relay before switching then having the previous relay move. A god-like race blowing up stars in a pretty geometric pattern. Or just building Dyson Bubbles. We have actually seen a few stars which could have been Bubbles.”

Nadine: “Oh?”

Heather: “They were only faintly likely. Even when first detected we could tell it was more probable that they were just being dimmed by a dust cloud. But that didn’t stop the Gorilla Signal being sent.”

Nadine: “I used to have a stuffed toy shaped like a gorilla when I was a child; I called him Mr. Grumpy. I cried so much when the last one died during the Bad Years. Silly thing for an adult to do, wasn’t it? What’s the signal?”

Heather: “You weren’t the only one to feel that way, like humans had received a final failing grade in an exam. Back in 2034, a billionaire paid the Arecibo II observatory in the state of Puerto Rico to send out a message to every potential Dyson Bubble star we’d found, containing the DNA sequence of the gorilla species, and instructions on how to interpret it. They tried to refuse, but he had influence with the governor, and it was sent.”

Nadine: “I take your point. You’d need total conformity not just of every species but every member of every species, in order to hide. If just one group decides to send out a self-replicating messenger, then it doesn’t matter what the others did - there would be messengers. So, what does that leave?”