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Suppose we knew of an extinction level event in a few decades, and through a large Manhattan Project-type effort humanity manages to construct a von Neumann probe with a copy of all human knowledge. Like with Voyager's record but more sophisticated. A self-replicating message in a bottle from a dying civilization.

Are there any plausible disasters that would provide the reason why such a probe should be sent to a different star system first instead of starting in our own system on, say, Mars or the asteroid belt or just hibernating on Earth for a few millennia?

Since everyone is (or will be soon) dead, time isn't really a factor, but the energy to get a spacecraft at solar escape velocity certainly is.

Bonus points the further you'd have to send the probe.

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  • $\begingroup$ The sun turning into a red giant would require the probe leaving but since that's not going to happen for ages I don't think it's that useful for your story. $\endgroup$
    – Bellerophon
    Commented Dec 10, 2019 at 18:34
  • $\begingroup$ @Bellerophon - yeah, the billions of years from now issue is mildly problematic. I could make it an alien civilization ala the TNG episode "inner light", but I'd prefer it to be Earth. $\endgroup$
    – Jay Lemmon
    Commented Dec 10, 2019 at 18:39
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    $\begingroup$ The whole point of a 'message in a bottle' is to be discovered. Assuming we don't have any intelligent alien life forms on our solar system (let's say Europans can exist, but intelligent to the level of Octupus at best), why delay the journey at all? $\endgroup$
    – Sach
    Commented Dec 10, 2019 at 18:46
  • $\begingroup$ @Sach I'm assuming we don't know of any particular aliens, as then we'd just send a regular probe or even just beam a message to them. I'm not sure what you mean by delay? $\endgroup$
    – Jay Lemmon
    Commented Dec 11, 2019 at 0:56

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The Solar System will soon be englobed

I'm basing this off my current story in progress, for which I've asked a supporting question here on SE:WB. My idea (not really my idea, the core element is about as old as antiquity) is that early on in our development, astronomers find tantalizing evidence of an astronomical structure surrounding the Solar System, and then, much, much later on, it is discovered that the structure is a barrier prohibiting us from leaving.

Perhaps in your story, humanity learns of a similar barrier soon to be thrown up; perhaps a message or visitation from the barrier creators warns us of it, for whatever reason they'd choose to do that.

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  • $\begingroup$ Getting a strong Deathworlders vibe going on here... $\endgroup$
    – Joe Bloggs
    Commented Dec 10, 2019 at 20:05
  • $\begingroup$ @JoeBloggs I haven't heard of it before, but now that I have it looks like a good read. I'm guessing somewhere in the chapters, a biiigg barrier is erected? $\endgroup$
    – BMF
    Commented Dec 10, 2019 at 20:46
  • $\begingroup$ Many big barriers. Also a Von-Neumann probe swarm. But mostly just humans being ridiculously overpowered by normal interstellar standards. $\endgroup$
    – Joe Bloggs
    Commented Dec 10, 2019 at 21:28
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Through sheer luck, a planet-hunting satellite has detected micro-lensing events that are eventually deduced to be due to a primordial black hole (one that masses less than our Sun). The hole is quiescent at discovery, because it's been in the low-density interstellar medium for millennia, but it's soon discovered that a) its heading relative to the galactic background is constant, and b) its distance (detected by additional lensing events) is reducing.

Anyone familiar with navigation knows that "constant bearing, closing range" is a more precise way of saying "collision course."

A tiny black hole passing through the Solar System would be disastrous, but not an immediate extinction event -- disrupting the orbits of the planets wouldn't kill everyone quickly, though there's reason to believe it would do so over a period of centuries (you think we have a climate change problem). However, every refinement of the measurements continues to indicate collision course -- in fact, if not a direct hit collision with the Sun, a miss so close that the black hole will draw gas from the Sun as it passes.

The very best possible outcome is a series of flares that will each sterilize the face of the Earth then in day, down to a depth of multiple meters in water and a few tens of centimeters in soil. There's enough error to believe there's also a possibility of a black hole induced supernova explosion (if the hole center-punches the Sun); such an event would melt the day side surfaces of the inner planets, sweep off their atmospheres -- well, further details are counter productive.

The good news is, we have a bit more than a century before the hole arrives. The bad news is that our message in a bottle needs to be well beyond the Kuiper Belt by that time, to be sure a supernova doesn't disrupt its systems enough to effectively destroy it.

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  • $\begingroup$ The Sun erupting as a supernova is a dubious proposition. Great flaring seems much more realistic. $\endgroup$
    – BMF
    Commented Dec 10, 2019 at 19:57
  • $\begingroup$ @BMFForMonica Sol is too small to supernova -- but there are new hypotheses that suggest too-small stars may supernova if they swallow a black hole. One less massive than the sun still might not do it, I'm not an astrophysicist by any stretch. $\endgroup$
    – Zeiss Ikon
    Commented Dec 10, 2019 at 20:22
  • $\begingroup$ I'm not an astrophysicist either, but here's what I think I know: For the PBH to enter the Sun (at realistically tens of km/s) and remain inside the Sun, it would have to interact with at least its own mass' worth of solar innards, imparting that needed opposing momentum. A PBH's cross-section would be small, because, well, they're supposed to be tiny. I think it is unlikely to encounter that much material on a journey through the Sun. $\endgroup$
    – BMF
    Commented Dec 10, 2019 at 20:37
  • $\begingroup$ Furthermore, upsetting the Sun's hydrostatic equilibrium, lending to any sort of explosion, would likely take considerable, astronomical time. That PBH's small cross-section doesn't do it any favors. It could take it billions to trillions of years to build up to any considerable size. As it grows larger, so does its accretion disk, which would lend to radiation pressure preventing further material from falling into it, stunting its own growth. $\endgroup$
    – BMF
    Commented Dec 10, 2019 at 20:41
  • $\begingroup$ As previously noted, I'm not an astrophysicist. I do recall, however, that if the hole has an event horizon even as big as a tennis ball it'll evaporate slowly enough to last a long time, and in in a high pressure gas/plasma environment, ought to collect matter pretty quickly. Also, the effect of gravity causing a density increase in the Sun's outer layers should be effectively immediate. $\endgroup$
    – Zeiss Ikon
    Commented Dec 11, 2019 at 12:25
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The probe is small, Earth is at risk. We are talking about current Earth. We don't have technology to move people off of Earth in any appreciable way at the moment, and we certainly couldn't sustain a colony on another planet if Earth is uninhabited. You'd need a suitably big asteroid to ensure total extinction of humanity, but such an asteroid wouldn't be that big. Maybe a rogue planet that we couldn't detect until it was too late (since it's so dark) whips into the solar system on a collision course. No one is surviving that and there is such a huge debris field that nothing is safe anywhere in the vicinity of Sol.

So, you only have the technology and resources to reliably launch a small-ish probe, replicating or not, and not any appreciable subset of humanity.

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  • $\begingroup$ Depending on what the "extinction-level event" prompting the von Neumann machine is, it may not matter that Earth is at risk from it. $\endgroup$
    – BMF
    Commented Dec 10, 2019 at 18:52
  • $\begingroup$ @BMFForMonica: Perhaps, but the question isn't why wouldn't we send people but why doesn't the probe start replicating in the Sol system. We need a plausible event to make the solar system itself a bad choice of location to store the probe for a while $\endgroup$
    – Michael Stachowsky
    Commented Dec 10, 2019 at 18:58
  • $\begingroup$ This reminds me of a sort of Kessler syndrome but on the scale of a whole system. I'm somewhat sceptical we wouldn't be better off sending the probe to, say, one of the moons of Uranus or Neptune, though. Space is a big place and I'm not sure even an Earth sized shrapnel bomb is going to make the entire solar system inhospitable to our probe. $\endgroup$
    – Jay Lemmon
    Commented Dec 11, 2019 at 1:09
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Does being wipedout by genocidal aliens count as a disaster?

Because that would be a good reason to send it far from home. Probably the most plausible reason to need to send it as far away from home as possible, and fast.

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  • $\begingroup$ The problem is it would have to be a very slow genocide, since I think even conservatively it would take humanity a few decades to build a self replicating probe. $\endgroup$
    – Jay Lemmon
    Commented Dec 12, 2019 at 12:53

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