This question is related to a SE:WB question of mine. I shelved the project about a year ago and am now dusting it off. To sum the concept up: several hundred million years ago a rather impenetrable barrier was erected by an unknown actor to encase the Solar System; extrasolar objects may enter the cordoned volume, which spans a couple dozen thousand AUs in diameter, but anything attempting to leave is quietly voided. (This means that objects that are "deleted" produce no emissions as a result of deletion.)

I imagine that in the near future, perhaps in the 2060s, we'll get some real cosmic shots off, shooting away perhaps a thousand small nanocraft probes to a nearby candidate solar system, probably Proxima b, more or less as the Breakthrough Initiative envisions it. (As of yet, the team leading the initiative finds no "dealbreakers" in the concept; however, there remain challenges to be overcome.) Ultimately, the effort will fail as the ultra-velocity spacecraft ghost into the night, and we won't have any good idea why--or will we? This is essentially my dilemma. Could we explain the disappearances without invoking an alien presence? Or would the evidence against any unexpected nature of the interstellar medium/design flaw be too damning? Given the likely mission objectives of Starshot, what evidence could there even be?

(Let's work with the Breakthrough Initiative concept proposal linked above, assuming their listed hinderences have been nominally surpassed and following their proposed target and mission objectives.)

Knowing this will help me develop the, um, psychology of future space explorers/colonizers. Currently, I'm thinking that if the failure could be reasonably explained away without much woo-woo, I can put off/suppress the launch of further interstellar Starshot missions for the deployment of sophisticated space-based observatories and telescopes perhaps capable of directly-imaging exoplanet features, in effect making Starshot temporarily "obsolete" or out-competed. The Starshot arrays could then be relegated to intrasolar missions--at least for a while.
If the failure can't be rationalized without giving people shivers, I will have to follow a different chain of events that thus alters the worldbuilding. After enough of Starshot attempts, it will become quite clear to people that something out there is seriously suspect. If, however, I can put off future attempts as mentioned previously, then I can allow space-based infrastructure to develop under a more hopeful and optimistic mindset. If not, then I expect an attitude of near-nihilism or a nonbelief in the infinite potential of humanity--and an uptick in the Lovecraftian horror genres.
I don't expect the effect to be so great to produce super-radically different futures, but I do expect there to be a psychological difference among people should they learn this higher truth early on in spaceborne development.

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    $\begingroup$ There was a short story, I believe called "Crystal Spheres", that discuses something like this. $\endgroup$
    – NomadMaker
    Commented Aug 31, 2020 at 21:15
  • $\begingroup$ @NomadMaker Ah, I remember hearing about that a while back. Not sure how I forgot it, but bought it and am now reading it. Thanks! $\endgroup$
    – BMF
    Commented Aug 31, 2020 at 21:31
  • $\begingroup$ Is the "deletion" a simple matter of crossing an invisible barrier, or is it an intelligent agent removing objects that might originate from humans when they get "far enough"? One plausible way to deal with fallible machinery would be to send a swarm of independent probes that can monitor and coordinate with each other, possibly launched over a period of months or years...which means in the first scenario, those probes would see the leading members of the swarm disappear one by one as they reach the barrier. In the second scenario, the whole swarm might get deleted at once. $\endgroup$ Commented Aug 31, 2020 at 21:56
  • $\begingroup$ @ChristopherJamesHuff The barrier deletes indiscriminately. The idea I'm running with now is that most solar systems have an intelligent "watcher," and when a watcher discovers some stir of life that meets some criteria within its domain, it erects the barrier. The watcher itself is incredibly smart, but it isn't omniscient. The life it contains may try the long game of discreetly hiding artifacts inside natural bodies over obnoxious timescales--comets, asteroids, space dust, etc.--tampered bodies that may exit the watcher's influence should it not be so indiscriminate. $\endgroup$
    – BMF
    Commented Aug 31, 2020 at 22:18
  • $\begingroup$ The barrier defines a pretty hard and invariable volume. You can get right up snug near it, so long as you aren't too close, which I guess is on the order of millimeters. $\endgroup$
    – BMF
    Commented Aug 31, 2020 at 22:21

2 Answers 2


That would be a scary thing to discover, however I doubt the first serious explanations as to why involve the word "Aliens".

It will actually take us a while to realise they're all gone, and even longer to realise it occurred at the same distance from the sun, as they wont be in constant communication, they will just slowly start missing the weekly check-in. These probes aren't flying parallel to each other (they're scattered intentionally), nor would they be at the same distance from the sun as other probes, and there'd be a variation in speed. Depending on the launch timetables, the probes would just slowly miss check-ins and be written off, a few at a time, for months.

We'll pull our hair out debugging the satellites, our knowledge of the universe, and physics, before we even propose aliens.

Here's what I can think of:

  • Someone sabotaged the program. (Enter the FBI checking for people with radical anti-SETI beliefs or something).
  • Failure of earth based radio software. (It'll get debugged and rewritten).
  • Atomic clock failure, so were listening at the wrong time, or in the wrong place. (We will recalibrate all the clocks)
  • Simultaneous failure of all 3-5 earth based receivers hardware. (Its more likely than hundreds of transmitting antennas failing. The hardware will be checked. Bird poo will be swept out and itll be polished).
  • Dark matter / energy interacts with radio signals, reducing their strength over distance. What we previously thought was a weak radio signal was actually really strong. (Next batch will have stronger radios.).
  • These probes were mass produced, and the same manufacturing error seeped into all the designs. (eg tin whiskers, temperate stresses detach a solder joint, some part overheating or freezing). (Next batch will be better engineered)
  • A software glitch occurred. Eg they lost light calibration, can't find stars, and can't orient their antenna correctly. Or just bluescreened. (Next batch will have redundant computers)
  • The dispenser has a silently malfunction mode - probes are travelling with parts of their final stage / cover / case / still in their shipping racks / etc. Or the dispenser magnetised / or statically charged / or something else the probes, making them all fail prematurely (new dispenser will be designed).
  • A star was hidden behind a black object invisible to us, when the probes get far enough out they can see it, their internal star maps are wrong, and they can't get their bearings, so antennae isn't pointed in the right direction. (Next batch will be written to survive this)
  • Conversely, a star could only be visible through a narrow slit in a black object, so when the probes get a bit out from Earth, a key navigation star disappears.
  • There are planets / Dwarf planets going out a lot further than we know. We just sent thousands of interstellar probes to crash into a few giant balls of liquid helium (or some other crazy thing) that we didn't know existed. (Queue us rewriting how the solar system formed)
  • Our sun has a dust cloud around it, when you get far enough through it, you can't see our sun looking back as clearly as we thought. (Next batch will have a more powerful radio, and not visually search for the sun).
  • There is a galactic background noise interfering with our chosen radio frequency. (Next batch will use different radio technology)
  • There is a shell of abrasive particles out there, like diamond grid cloud, and they scratch the crap out of things to the point they don't work. (armour-plated probes next time)
  • There are a few high mass objects out there that haven't been detected, and they're refracting the radio signals, or changed the trajectory of the probes. (We panic search for Black Holes that aren't emitting Hawking radiation).
  • The solar wind is interfering with radio signals, refracting them or frequency shifting them. (Next batch might use laser communication, or some other tech)
  • Cosmic background radiation is more dangerous than we thought, our solar wind is pushing away cosmic rays that are EMPing our probes. (Next batch will have a stronger faraday cage)
  • Wandering "rogue" planets are out there in large numbers, and their gravity swung the probes. (Queue a mission to check for them)
  • We've made some catastrophic error in calculations of the universe (eg maybe the speed of light isn't a constant). (We'll try to rewrite physics to explain what's going on)

Not all these are "likely", but they'll be proposed to try to figure it out. You dont want to be the first NASA engineer to say "must be aliens!".

The process of Launch, Die, Analyse, Redesign would go on many times. Potentially dozens of times. We will be trying to disprove everything else we can think of before we go "Ok, it must be aliens." Those launches will be years, maybe decades apart, and it may be demoralising enough failing over and over and not knowing why that we stop trying for long periods.

Unless we see evidence in some other way (An asteroid with a unusual cut from partially intersecting the field, for example), we probably wouldn't suspect aliens until we see a video of the field eating matter. And it'll probably be the last few seconds of a live feed from a camera on a (sadly, probably manned) space craft sent there specifically with no purpose other than to investigate wtf is going on at about 10,000AU

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    $\begingroup$ I can't touch your list, well done and +1. However, wouldn't humanity figure out almost instantly (in reasonable terms) that the barrier is spherical? That's a pretty big coincidence to overlook. "The most exciting phrase to hear in science, the one that heralds new discoveries, is not 'Eureka' but 'That's funny...'" —Isaac Asimov. I guess the real question is how long the OP needs humanity to remain in the dark. The longer it must be, the less likely it's believable. $\endgroup$
    – JBH
    Commented Aug 31, 2020 at 7:14
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    $\begingroup$ @JBH At first I thought that, with the probes running on a radioisotope, they'd be weakly transmitting on their way out, but it turns out that the power required is too great and that the radioisotope would charge a capacitor that supplies the right kind of power. If the probes were transmitting back to Earth at the time of crossing the threshold (interstellar medium analysis?), which is likely, uh, unlikely, due to small transmit windows, we probably wouldn't know they all vanished until the next expected programmed transmition. $\endgroup$
    – BMF
    Commented Aug 31, 2020 at 10:41
  • $\begingroup$ I'm not sure about some of your points. For instance, we can receive low energy radio waves from the universe already. And a star hidden in a dust cloud is pretty unlikely due to its thermal emissions, which we certainly should've detected. Same goes for our sun being hidden in dust, the emissions from the dust would've long ago been detected. An error in production or software is probably the best of them. I suppose we'd settle for that uncertain explanation like we settle for the hypotheses of dark energy and dark matter, until some better explanation comes along. $\endgroup$
    – BMF
    Commented Aug 31, 2020 at 10:49
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    $\begingroup$ @BMF oh your totally right, some of these are a massive stretch. But we'd attempt all these crazy hypothesis, including rewriting physics, trying to explain it before we go "oh it must be aliens" $\endgroup$
    – Ash
    Commented Aug 31, 2020 at 11:39
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    $\begingroup$ @Ash basically they turn everything off and on again $\endgroup$
    – Topcode
    Commented Aug 31, 2020 at 15:34

The Second We Start Losing Multiple Probes at the Same Distance from the Sun the Jig is Up

It would take approximately 30 years of "design/build time" along with the travel time it takes probes to reach the barrier for the world to consider aliens the primary cause of probe loss.

Ash has a lovely list of all the things scientists would think when the first probe is lost. Space dust, random failure of receiver/emitter and so on. However you can rule out multiple problems per launch, and indeed scientists being scientists they probably would. Once you start losing multiple probes at the same range the suspicions are going to pile up pretty quickly. Especially once people start aiming for other parts of the sky and getting the same result.

You sent a probe to Alpha Centauri. The probe loses signal a Light-day out from the sun(122ish AU, roughly the distance from the sun to the edge of the solar system). So you boost the power and harden the systems and send out another probe, had to be something mechanical. If someone's real paranoid you'll also increase the frequency of reporting as you near the 122 AU limit. Second wave probe still goes dark a light-day out. At this point the head scratching increases. But still, can't be aliens, plenty of other things could go wrong! So you do it again, increasing the probe's ability to gather data about their trip, just in case. You lose the probe again.... exactly where the last ones were lost.

Paranoia in the scientific community is now REAL high. You fire off another two probes, of a simpler design, at slightly different patches of the sky because at this point you don't want to waste multi-billion dollar solar-system-scanning probes when what you REALLY want to know is Why Do The Probes Die at 122 AU. You have them continually broadcasting once they get close to The Limit. They go dark at the exact same distance as the last set.

Governments are now Very Concerned, and it wouldn't surprise me at all if the word aliens started getting thrown around. Another pair of probes are launched, this time in tandem, with one following in visual range of the lead probe. The lead probe hits 122 AU, and dissolves. The trailing probe sends back the intel, and is lost soon after. Everyone now must admit that we live in some sort of Galactic Zoo.

So that's 5 iterations from First Loss to cue hand gesture Aliens. You could shrink it to maybe 3 or increase it a few more times, but scientists are real smart and probes are build with every-conceivable-failsafe-and-variable in mind today, so it doesn't seem likely you could keep doing this ad-nauseam.

Where does that leave us? It can be a decade to design, build, and launch a probe, and 5 years seems like a pretty fast turnaround. Plus travel time, which is whatever you make of it. Even if you wanted to launch the same probe again you probably wouldn't, just because of how bureaucracy works. (When probes crash they tend to add on new tech to the next probe even though it's trying to do the exact same thing the lost one was, rather than just re-build the already designed probe. Usually because the new tech is miles better but it still takes redesign time.) So say 5 years between first loss and second launch. Then 10 years between the second and third wave (because at this point you're essentially designing new probes) Then 5 years again (because you're using third-wave design, more or less, just aimed at another spot) then 10 years for the final pair.

Once you start factoring in travel time though it could be a century or more (Space is BIG, takes a long time to get places) before your poor Terrans realize what's what though, and that seems like plenty of time for happy and hopeful colonies on Mars or Europa or wherever. If your travel times are more like a year or two between probes it wouldn't be too hard to imagine budget fights meaning that Starshot II takes 20 years to be approved because hey, the guys wanting to send a probe into Neptune's atmosphere have a REALLY great proposal, or Why Do Probes Die At 122AU Probe I never getting off the ground because Starshot I and II bankrupted the company and why should some OTHER company figure it out when mining the Asteroid Belt is a more lucrative idea? Conversely if you have some competing companies/nations and 3 different Starshot probes are launched at Alpha Centauri a month apart who then get into a Moon-Race-esq contest to figure out WHY they were lost you could come to the "Alien Zoo" conclusion within a decade, minus travel-time.

  • $\begingroup$ Yeah, this is more or less what I anticipate will happen in my story's future. I should note that the distance is not 122 AU, but ~12,000 AU, increasing the time between Starshots. (We're not going to send out many Starshots at once, not when they're so expensive to build and launch, and you've got to pay the "mission control" team during the years-long transit time.) $\endgroup$
    – BMF
    Commented Aug 31, 2020 at 18:14
  • $\begingroup$ Because the initial Starshot probes won't be broadcasting continuously--no, more likely they'll turn on and briefly transmit some data on the interstellar medium, then turn off when the capacitors are once again depleted--it might take more than a few tries before things get fishy. We'll know something went wrong eventually of course. We'll miss a collective data burst past 12,000 AU and immediately suspect something went wrong with the mission, which, consequently, might expedite the launch of the next batch of probes rather than waiting around for a potential response at Proxima. $\endgroup$
    – BMF
    Commented Aug 31, 2020 at 18:18
  • $\begingroup$ I think at first scientists will chalk it up to a software failure. The probes may be communicating via laser diodes, and misalignment would cause just that. However, I think the general public might by then already be talking of aliens. Think of how fast Tabby's Star went to "it's aliens!" Or basically any other unexplained phenomena. The thought that "it's aliens" would gradually rise to bas-relief, while scientific explanations become hairier and hairier. $\endgroup$
    – BMF
    Commented Aug 31, 2020 at 18:21
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    $\begingroup$ "Once is happenstance; twice is coincidence; three times is enemy action" -- Ian Fleming :) $\endgroup$ Commented Sep 1, 2020 at 4:04

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