# Can a space-faring robot still function over a billion years?

This short story, which I've already written, is set in the FAR, FAR FUTURE, where a robotic space probe is exploring as much of the known universe as it can, despite its AI not knowing if its creators--humanity--still exists as a species. The exact number it has calculated to be slightly over a billion years since it first departed Earth.

Currently, could a robotic, humanoid space probe (a successor to the Voyager 1) be able to last 1 billion years or longer out in space, as long as it doesn't take on any external damage? If so, I'm curious what kind of materials don't deteriorate over time?

• Have you seen Star Trek: The Motion Picture? Even a 1970s probe can do it with a little help from his friends. – ShadoCat Mar 5 at 18:02
• @ShadoCat V-Ger was only a couple hundred years old. That's a far cry from "over a billion"... – Darrel Hoffman Mar 5 at 19:35
• @DarrelHoffman Oh ye of little time-displacement faith... – jeffronicus Mar 5 at 19:38
• Robots require maintenance. That's just a fact of the universe. NASA was still activating Voyager backup hardware systems at least as late as 2002, and has been carefully maintaining and modifying the instructions to control it throughout it's entire life. Without intending to disrespect your question, your robot needs to focus less on exotic materials and more on how it can perform maintenance and refueling tasks for itself. With sufficiently advanced self-maintenance systems, it can last indefinitely. – GrandOpener Mar 5 at 20:04
• Um, what's a "humanoid"space probe? – Spencer Mar 5 at 22:53

## Nope! (but you can still make this story work!)

So the short answer is no -

• the power source would run out
• the physical hardware of the computer, thrusters, etc. would degrade
• high energy particles and high-speed dust collisions would slowly convert the spacecraft into a ball of metal and rock

50 years is probably about the limit of what is achievable right now, and a billion years is just too, too much longer than that to be reasonable.

BUT

What if it doesn't have to "last" that long at all?

Von Neumann Probes have been the stuff of sci-fi for decades. Have your spaceship stop in various systems, harvest new materials, repair itself, and move on. It's basically a gigantic factory, flying through space stuffed to the gills with spare parts.

The nice bonus for a short story is that now your AI can ponder if it has become "life" given that it grows, experiences the universe, and perhaps even procreates. How does this affect its relationship with the long lost human race?

• on a similar vein to vonn neumann probes, you could have a limited number of probes that repair each other. The repairs might be so involved that not a single atom of the original remains, but hey – rtpax Mar 5 at 21:33
• A billion years might just be long enough that a single device is likely to end up in some unavoidable event big enough that nothing is left to be repaired. Like larger rocks or supernovas. – Sebastiaan van den Broek Mar 6 at 5:50
• @SebastiaanvandenBroek Nope. Unless it's moving at relativistic speeds, the expansion of the universe would outrun it fast enough that it would never reach far enough to have a significant chance of being next to a supernova. – forest Mar 6 at 6:39
• An AI would fast come to the point that it is much more efficient and safer to duplicate itself to fulfill the task. Would be a nice sub-story when two of these clones meet each other – Julian Egner Mar 6 at 8:52
• We Are Legion (We Are Bob), by Dennis E. Taylor. All that needs to be said. – Elliot Bonneville Mar 6 at 17:16

## Yes.

Relativity is on the robot's side. Using the Time Dilation Equation,

$$t = \cfrac{t_0}{\sqrt{1-\cfrac{v^2}{c^2}}}$$

where $$t$$ is time seen by stationary observer, $$v$$ is velocity, $$t_0$$ is time in rest frame, and $$c$$ is speed of light (≈ 2.998 × 108 m/s).

And if we apply the following values:

$$t = 1\,000\,000\,000$$
$$v = 0.999999999999999 c$$

We'll get a dilated distance of ~44.70.

So that means that if you make the robot accelerate to 99.9999999999999% of the speed of light and make it travel for 44.7 years (or 391570 hours) from its point of view, roughly a billion years will have passed for a stationary observer.

45 years seems to be a reasonable amount of time to keep a particularly sturdy robot operational.

(Disclaimer: The method to accelerate the robot to 0.999999999999999 c is left to the OP's discretion.)

Credits: Wolfram Alpha, Time Dilation Calculator

• Not so sure time dilation actually makes something last longer. Even in interstellar space, traveling at that speed would make it encounter hydrogen atoms that strike like nuclear bombs. Finding a cave on an airless moon and just sitting in place may be better in the long term – JollyJoker Mar 6 at 8:27
• @JollyJoker Time dilation itself is sufficient; see hyperphysics.phy-astr.gsu.edu/hbase/Relativ/muon.html. Surviving high-speed impact with interstellar gas is a separate issue :) – chepner Mar 6 at 16:06
• Does not work; the intragalactic medium erodes your probe. It will be a cloud of disorganized atoms before a day passes as observed by a stationary observer. – Joshua Mar 6 at 17:17
• If you've got the technology to accelerate a robot to that many nines of c, and you've got the power source to provide the ludicrous quantity of energy that it would require to do so, then finding some way to protect the robot from impacts is probably within your capabilities, and should really be at the top of your to-do list. – anaximander Mar 7 at 9:48
• @anaximander in fact, unless you're in the business of inventing very expensive fireworks, you probably should have thought of it before developing the propulsion system – JeffUK Mar 7 at 16:08

I have to agree with others: self-repair is your only hope. Everything wears out, given enough time.

You may want to see how other authors have addressed this. Robert Silverberg thought it could be done, in Across a Billion Years, but I don't recall that he specified how. James Hogan pointed out how self-repairing AIs might go wrong in Code of the Lifemaker.

Meanwhile, Robert Moore Williams wrote in "Robots' Return" of a future so far that Man had become a myth among the robots.

• Yep, what Mark said. Maybe have self-replicating repair nano-bots to automatically maintain the host? In theory that 'system state' only wears out if raw materials (or their fundamental properties) cease to be available. – Sid James Mar 6 at 1:37
• Stanisław Lem earlier explored the idea of robot evolution as well, in The Invincible. – Jacob C. Mar 6 at 20:42

The Centennial light is the world's longest-lasting light bulb, burning since 1901.

Electronic and/or electromechanical devices have been in use for less than that, but none of them has shown a lifetime longer than a few decades.

Currently, could a robotic, humanoid space probe (a successor to the Voyager 1) be able to last 1 billion years or longer out in space, as long as it doesn't take on any external damage?

Even if this device took no damage, which is already a far-fetched assumption, considering how "nice" space is (high energy photons and particles, strong magnetic fields), we have no power source which can supply energy at an appreciable level for such a long time span.

The only thing which has been able to self sustain for a billion years has been life as a whole, but it doesn't stand up in the environment of space.

• A) The Centennial light was a PR stunt by Edison, and they have (supposedly, can't be sure) been replacing that bulb for the sake of the PR. B) Uranium has a half-life of about 4.3 billion years, so power should be about OK (I don't know if the initial exceeds critical mass ;) ) – Varad Mahashabde Mar 7 at 5:17
• @VaradMahashabde - the linked Wikipedia article notes that this light bulb was first noted for its longevity in 1972, Could you cite some evidence for your claim that Edison concocted a PR stunt 41 years after his death? – Paul Sinclair Mar 7 at 18:21
• "Electronic and/or electromechanical devices have been in use for less than that, but none of them has shown a lifetime longer than a few decades." I own an electric motor manufactured some time in the early 1900s, or possibly even late 1800s (documentation of such things wasn't so good back then, but it's made in a way that the company in question stopped using in the early 1930s), and that motor still spins when power is applied to it. Mechanical devices can be made to last a very long time, if properly maintained, and these days, it's totally possible for machines to do so for themselves. – Matthew Najmon Mar 7 at 22:57
• @PaulSinclair Sorry, my bad. Centennial light is the legit one, the Edison one is called Eternal Light, never turned on but made to look like it is by automobile headlights beneath it – Varad Mahashabde Mar 30 at 13:17

Have your robot based on crystals.

A tiny 4.4-billion-year-old crystal has been confirmed as the oldest fragment of Earth's crust.

The zircon was found in sandstone in the Jack Hills region of Western Australia.

Scientists dated the crystal by studying its uranium and lead atoms. The former decays into the latter very slowly over time and can be used like a clock.

Your robot uses solid state electronics based on zircon crystals. These are durable on Earth for billions of years and so with a modicum of shielding should do for your spacefarer. Extremities, probes and other moving apparati will probably be manufactured new for each solar system visited but the main program of the robot and its memory will be as immortal crystals.

• I never really understood what "the oldest fragment of Earth's crust" really means. Am I not made of fragments of the Earth's crust too? – Mad Physicist Mar 5 at 21:30
• 'The former decays into the latter very slowly over time ' Aye and therein is the rub. Any memory or data that it encoded is now corrupt. It may still exist, but can it FUNCTION? – Justin Thyme the Second Mar 5 at 21:37
• @Mad Physicist - I think you will find those fragments of "Earth's crust" are only loosely adherent to you. They will wash off. Use soap. Possibly a loofah. – Willk Mar 5 at 22:06
• @JustinThymetheSecond - re decay - it is random. By having multiple copies and periodically checking against each other you can correct corruption due to decay, as random change will likely occur in only 1 iteration of your memory. When outvoted the different one is changed to match the others. – Willk Mar 5 at 22:08
• @JustinThymetheSecond That sentence applies to the elements uranium and lead, only. Those are just present in the form impurity traces, they are not a part of any importance, except for their usability as a long-time clock. A crystal based robot won't be fabricated to rely on radioactive materials. – cmaster Mar 5 at 22:14

Your biggest problem is going to be entropy and redundancy.

Entropy pretty much guarantees that anything, given enough time, will gp through molecular changes from the original. Atoms will migrate through the material, any exposed surface will diminish through vapor pressure, 'pure' substances will always become less pure, and after a billion years you will not have anything at the atomic level close to what you started with. So systems will have to be redundant to the extreme.

Then, you have quantum effects. Quantum tunneling and indeterminacy. How do you prevent this from happening in critical systems?

And, of course, there is radioactive decay. Elements change in physical properties as they go through such basic changes as emitting radiation.

So is a billion years enough time for all of these things to affect critical systems? With today's level of technology, absolutely a certainty. No robotic system that we build will last a billion years.

Consider recent history. As humans endeavored to reduce the size of computer chips, the first pentium processors began to suffer terminal illnesses. Turns out, the copper traces were so thin (atoms wide), that as high frequency electrons flowed through them and coursed around sharp corners, the electrons 'shortened' their path by rounding the corners into curved ones, and they began to short out on the traces beside them. Just the act of sending an electrical current through a copper wire is enough to cause it to change shape. So any computer chip microprocessor today is extremely unlikely to be operational in a billion years. It will be one huge mass of electrical shorts and cross signals. At most, it is extremely unlikely that any pentium processor in continuous use will last a hundred years without the circuits degrading enough to produce just random garbage in the data. Even twenty year old chips can no longer be relied upon in critical applications.

And yes, that means any ICBM made more than twenty years ago, the electronics of which have not been replaced, should no longer be considered reliable enough to target and perform properly. ('Dang, it hit New York? It was supposed to be aimed for Moscow!!!!')

• +1. It's a question of what elements have a half life of two billion years. – Mazura Mar 5 at 21:44
• And PLEASE don't tell me the Voyager spacecraft are still going strong. There are no pentium chips in these spacecraft. They were built using primitive chip technologies, using very wide traces. – Justin Thyme the Second Mar 5 at 21:46
• You don't need redundancy "in the extreme". What you need is a basic level of redundancy, combined with on-board automated systems for implementing repairs and producing the parts to supply those repairs, including for repairs of the on-board automated repair system, itself. – Matthew Najmon Mar 7 at 23:10
• @ Matthew Najmon In other words, you need a community of humans that self-replicate. Recall that the first human ancestors lived over seven million years ago, and life is about two billion years old. – Justin Thyme the Second Mar 7 at 23:42

We have no good evidence for or against the possibility of any kind of machine remaining operable on those time-scales. That said,

## Probably, but not by accident.

I'm going to ignore the various more creative options
(on the one extreme, a completely passive porous rock that "explores" by absorbing stellar ions as it passes near each star)
(on the other extreme, a dwarf-planet engineered to "naturally" evolve extremely specific kinds of life when warmed by a star)
and focus on machines that are recognizably analogous to probes humans have already launched into space.

### In general, simpler devices will function longer.

A probe designed for a 100-year mission, or even a 1k-year mission, would not still work after 1G-years, because its designers would have had no reason to make the kinds of compromises to the probes capabilities that would have been needed. For example, they would have wanted a smarter AI (requiring silicon transistors or similar electronics that degrade naturally on extreme timescales), more sensitive cameras (which would be more easily burnt out), or more powerful thrusters (which would have their own problems, and would add stress to all the other components).

### A machine that was still operating after 1Gy would be simple to the point of idiocy.

• A camera? How about a single directional photo-sensor. We'll just sweep it across the sky to build a picture. We can refract the input and adjust the lens a little to get color.
• On-board power? How about a 100m sphere of $$^{40}\mathsf{K}$$. This person's estimates suggest it might work
• Thrusters? How about we adjust a big electromagnet against the magnetic field of the nearest star. Might work if we plan our trajectory a millennia in advance and aren't too picky about where we're going.
• An AI? Willk's answer is ok, but the electronics will still need to be over-built by a factor of a thousand. "Solid state" electronics do have moving parts: The electrons move back and forth, smashing into atoms. The atomic lattice jiggles around; defects form, heal, and move. Dopants diffuse. I think you can have a computer, maybe even an "AI", but it will be physically large, dumb as bricks by it's maker's standards, and slow.
• Landing gear? Tools for making spare parts? NO! Absolutely not! This probe will never come within 30AU of a star, and will prioritize avoiding any close passes with any objects or phenomena.

Even in principal, is it possible for a machine to last a billion years? I still think it is. Consider the surface of Ultima Thule. As long as the probe stays well away from all the excitement of inner solar-systems, space is a nice relaxed place to pass the eons.

• You wouldn't be able to plan a trajectory that far into the future due to uncertainties that arise from Lyapunov time. – forest Mar 6 at 6:41
• @ShapeOfMatter Half-life of Potassium 40 is only 1251 years, that would cut down on the juice quickly. (Presumably banana juice) – Measure of despare. Mar 6 at 8:41
• @forest: I'm mostly working off Wikipedia here, which suggests that even within a solar system it should be feasible to plan a trajectory 1Ky in advance. – ShapeOfMatter Mar 6 at 15:51
• @Agrajag: No, you're off by six orders of magnitude! I picked K specifically because it's abundant and has a half-life of about a billion years. The down-side is that you'll need a lot of it to generate even a couple kilowatts. – ShapeOfMatter Mar 6 at 15:55
• You better vacuum seal the banannas otherwise they will go bad... – Efialtes Mar 6 at 22:24

Sure it can. Every critical system must exist in multiple copies and the robot must be capable of manufacturing replacement parts when it finds accessible raw material (say, an asteroid that it can land on.) You can make a robot with any desired mean time to failure by application of sufficient redundancy. In the extremes your "robot" is really a swarm, anyone of which can rebuild the whole swarm if need be. The robot spends a lot of time checking it's data for errors and repairing corruption from other copies or from error-correcting codes.

A swarm approach actually makes repair easier as it means you can go with total replacement on some suitable timescale, thus avoiding headaches caused by transmutation-induced weakening of parts and the slow evaporation that happens to everything.

• "You can make a robot with any desired mean time to failure by application of sufficient redundancy" That assumes that you can predict in advance every possible single-point failure scenario of your robot swarm for the next billion years. Who knows exactly what happens when two super-massive black holes collide, for example? The EMP pulse might effectively destroy an entire galaxy, for all we know. And since EM travels at the speed of light, you don't get any advance warning! – alephzero Mar 6 at 22:48
• @alephzero Look at the question--he's excluding external damage. Your black hole event would certainly class as external damage. (And it's not going to cause EMP anyway, although it might fry the swarm with radiation.) – Loren Pechtel Mar 7 at 3:39
• @LorenPechtel The collision of two super-massive black holes is probably not going to cause EMP. We don't really know if it would or not, because there's just too much we don't yet know about black holes for that to be determined theoretically with certainty, and because that particular outcome isn't one anyone has yet been able to thoroughly check for in any of the very few such collisions for which any data at all has ever been gained observationally – Matthew Najmon Mar 7 at 23:19
• @MatthewNajmon True, we can't absolutely say it won't, but it would be pretty hard. EMP is a very sudden burst in the radio spectrum, a supermassive black hole is a very energetic event, if energy comes off as photons they'll mostly be very short wavelength. You need something to convert them down--and whatever it is must be small so you get the very sharp spike. (With a nuke the conversion is done by the gradient of the atmosphere, something you're not going to find near a supermassive black hole.) – Loren Pechtel Mar 8 at 5:34

The chances for a modern day space probe to survive for 1 gyr and be anything but a metalrich asteroid are quite slim. How slim exactly depends on its speed and that it doesn't run into any big debris out there. While debris are rare and space is quite empty there is always a chance for bad luck. Speed and time are the factors here. If you plot a smart course with several solar flybys a few percent of lightspeed are on the table. Needless to say that this makes collisions way worse as Ekin = 0.5 * m * v^2. Even a few atoms might degrade the probe significantly at high speeds. Of course lower speeds could help, yet I assume you want the probe to get somewhere within 1 gyr.

I'm not an expert on radiation induced material fatigue. Your probe will most likely suffer mostly from cosmic rays, but especially during solar flybys charged particle radiation will be an issue. Assume that the material will wither away over the eons. Your worst issue on the radiation front will be the breakdown of computers though. Look up the design of computers on mars rovers like opportunity for example.

Less probable yet more intriguing story whise is data corruption. The mission (given more complex ai and some freedom to take decisions) statement might be "explore milky-way"; have some freak data corruption turn a r into a d and you have "explode milky-way". (Not very probable but an ai will do anything as long as it gets the reward circuit tickling).

So the answer is no. BUT there might be a solution, albeit one using slightly future technologies.

Don't aim for longevity, aim for maintenance. Pick a big (maybe 10 to 100 m diameter), metalrich asteroid and turn the whole thing into a probe. Reinforce it structurally to get meters of radiation and impact shielding. Have huge databanks and really smart or slavishly dumb, yet specialised AI. Most importantly you need manufactories capable of producing anything on the asteriod probe and redundancies for every system.

For power you could employ a number of technologies. Nuclear reactors, (fusion or antimatter if available), radioisotope generators with an isotpe with a long (the desired mission time) half live, or solar panels during stellar flybys (you want to keep doing those as they counteract drag or slow you down if the system is interesting) (keep in mind that you can manufacture solar panels once you approach a system so the won't degrade). Generally beeing really conservative about using power will be helpfull as well. Let the probe hibernate during inter system flights and let it do the repair and exploration near stars where there is free energy and something to do.

Now you might wonder how to move such a kiloton behemoth to interstellar velocities, yet thats not so hard. Huge lightsails, laser thermal rockets, nuclear rockets or even ion drives will move it eventually. Then you simply need to plot a very smart flyby course arround moons planets and suns and you might cruise of at a not insignificant portion of lightspeed. Astronomer Paul Birch once said that one could theoretically throw a pebble into the asteroid belt and end up crashing mars into the sun.

Now even such a maintenance probe will run out of some resource (energy, ejection mass or raw materials) eventually or might degrade from collisions. (Come to think of it manufacturing, a huge thin mirror arround the probe when in a system seems highly beneficial. Use it as a high resolution telescope to scout out the system and the route ahead and use it as a solar sail to save ejection mass to get into an optimal gravity assist.) It is very conceivable that such a probe might survive for a billion years.

PS:Check out this video, it deals with constructing a spaceship for similar ammounts of time. https://youtu.be/25ODAzr6Bbw

Currently, could a robotic, humanoid space probe (a successor to the Voyager 1) be able to last 1 billion years or longer out in space, as long as it doesn't take on any external damage?

If you want a "real science" answer: No

Most people won't know this, so publish your story anyway - I'd read it.
Many people know that "Transistors don't have moving parts,"
but then wrongly believe that implies: "so they never fail."

## If you're interested in the science:

Transistors built 50+ years ago are likely still working fine today if they were cared for properly, and may be expected to work without issue for 1,000 years in the future (maximum life approx 10,000 years).

Let's ignore the additional problems of traveling through space for even a century - as most of those (radiation/power/propulsion) are insurmountable given today's knowledge.

A probe that is 'smart' enough to be called AI would likely be based on current technologies.
Modern chips have very very small transistors with very very small connectors.

Part of the reason that integrated circuit voltages have gone down is that the smaller the "wires" the more troubles you have, like electromigration (as the device is used, current flowing through the circuit causes the metal to actually move around which can form opens or shorts in your circuit).
As transistors get smaller, you see problems that weren't even known recently such as Hot-carrier injection (where the switching characteristics of the transistor can be permanently changed).

A good read is "Transistor Aging" in IEEE. The article's focus is how to test transistors, but you'll learn some stuff related to your question if you read through it. It contains on of the better descriptions of Hot-carrier injection that I've encountered:

"Over time, charge carriers... with a little more energy than the average, will stray out of the conductive channel between the source and drain and get trapped in the insulating dielectric. This process, called hot-carrier injection, eventually builds up electric charge within the dielectric layer, increasing the voltage needed to turn the transistor on. As this threshold voltage increases, the transistor switches more and more slowly."

A slowing of switching (your probe's computer computes slower) and a need for increased voltage (your probe's power consumption increases over time) spell doom for a "real science" answer to a space probe that lasts a million years.

I will restate my opinion that your stories do not need to be completely based in 'real science' to be enjoyed.

• A good summary of the atom-level changes in 'unmoving' solid state devices. The 'unmoving' part is a misnomer, as there definitely ARE things (electrons) that are moving, and at very high speeds and frequencies. A minor issue, however, with your 10,000 year estimation. It is now known that transistors, and solid state devices in general, operate on quantum principles. Indeterminacy and quantum tunneling, for example. Since this is a relatively new field (as applied to solid sate devices) it is not absolutely known for how long these quantum effects may be sustained before breakdown. – Justin Thyme the Second Mar 7 at 17:39
• For example, it is not absolutely known that after thousands of years of the electron being on this side of the barrier, and then on the other side of the barrier, without going THROUGH the barrier, the process could eventually happen with such efficiency that it is as if the barrier were never there in the first place? That is, we do not know for certain if quantum tunnelling can exhibit some as yet unknown form of a memory effect, and 'remember' that it went by the barrier in the past. – Justin Thyme the Second Mar 7 at 17:51
• FYI everyone knows about the 'speed of light', and about how fast it is, and about how far it travels in one second. Interesting to note that, at today's processor cycle speeds, light would travel about 10 cm. on each cycle. – Justin Thyme the Second Mar 7 at 18:07
• And I notice the article you referenced was written in 2011, the field has progressed substantially since then, along with the problems. – Justin Thyme the Second Mar 7 at 18:17
• @JustinThymetheSecond Thanks for the feedback. The 10,000 year number was my Father's when he told me about them a long time ago, hardware isn't really my field but he was an EE and a PE. Do you have a more recent reference than my 2011 one that is, for lack of a better term, readable by an "average science field university grad"? – J. Chris Compton Mar 7 at 18:55

Interesting question; this timeline will probably cause your craft to encouter issues never before seen. You will need some sort of material that is not easily affected by radiation. Perhaps Tungsten would be a good material for your craft's shielding? Tungsten is the densest metal on the planet.

Also, we currently struggle with computer memory degradation for long term storage, our best and most stable storage devices currently are, oddly enough, clay pots and magnetic tape. Crystal based memory has shown good potentiality for overcoming those challenges.

Superman style crystal memory storage. Think of the Fortress of Solitude.

Researchers at the University of Southampton have discovered a way to store data in five dimensions on nanostructure glass that can survive for billions of years.

The storage method enables up to 360TB of capacity on a disc about one-inch in diameter that can withstand temperatures of up to 1,000 degrees Celsius and has a virtually unlimited lifetime at room temperature (13.8 billion years at 190 Celsius).

"As a very stable and safe form of portable memory, the technology could be highly useful for organizations with big archives, such as national archives, museums and libraries, to preserve their information and records," the researchers said.

The technology has already allowed major documents from human history such as the Universal Declaration of Human Rights (UDHR), Newton's Opticks, the Magna Carta and the Kings James Bible, to be saved as digital copies "that could survive the human race," the researchers said.