# Planetary Scale Artworks

A highly advanced civilization has developed and is about to ascend to become beings of pure energy in a hyper-dimensional universe. Before leaving they restore our universe to a reasonably pristine state so that new life can evolve and explore it. For the most part they remove all trace of their existence, however they want to leave something behind. This could either be out of a sense of fun (they still have practical jokers) or just to leave a signature behind to show that they existed.

What sort of things could they leave behind that would be stable for millions or even billions of years, clearly the work of sentient beings, and possible to spot from a distance of many light-years. In other words it must be on at least a planetary scale.

There must be no doubt at all to anyone detecting it that this is something unusual, and that it's an artificial construction. However it is a signature, not a library or anything else. It contains nothing of meaning and certainly no intelligence. This includes technology that could be salvaged (for example maintenance robots). It's just a huge "we were here" in the sky that needs to last for billions of years with no maintenance.

• in this universe, we will make "pi" infinitely long number, just for joke ;) – Pavel Janicek Dec 16 '14 at 13:01
• Obscene graffiti in the Cosmic Microwave Background! – Serban Tanasa Dec 16 '14 at 14:03
• What are you looking for, for your story? Are you planning a story where spacefaring humans chance upon this, or a present-time story where astronomers discover it through their telescopes? What kind of reaction do you want to elicit? – Abulafia Dec 16 '14 at 14:28
• Something to be discovered by spacefaring explorers who have basic FTL travel but no capabilities on anything like this scale. Desired reaction: Disbelief and Wonder... – Tim B Dec 16 '14 at 14:44
• In Diaspora by Greg Egan, an advanced civilization that leaves our universe leaves a planet with life, which has normal elemental composition, but all elements have non-standard isotopes with one more neutron in nucleus. This is definitely recognizable as an artificial product. – Irigi Dec 17 '14 at 7:26

How about creating a large planet made purely from one element, or better yet a couple dozen from different elements each, Iron, gold, silver, carbon etc. then set them to spinning around a giant star that will eventually collapse into a black hole, between the two stages it could be many (100?) billions of years before the planets are destroyed.

EDT: To go beyond a planet with exactly one element, maybe even the most singe most stable isotope as well. or maybe not? pick an isotope that can act as a clock is the planets formation?

EDT2: On top of the suggestions above, having the mass of the planets being a mathematical relationship to each other and maybe to their element could add more to the monument, maybe integrate the golden ratio, pi or the Fibonacci sequence?

EDT3: Could the gravity well (the "star") be made from dark matter? (do we really know that it exists?)

• The mention of a pure-carbon planet made me think of a diamond planet. Then I thought: how about a planet with a crystalline surface, where the entire surface is a single crystalline structure? – KSmarts Dec 16 '14 at 21:25
• Well making the Carbon planet one big diamond would certainly stand out as a 'look what we did!' – bowlturner Dec 16 '14 at 21:28
• @FreeConsulting Actually that's not true. The star needs a strong enough gravity well to keep a firm grip on its planets, and the planets need to not interfere with each others orbits, etc. – Tim B Dec 17 '14 at 15:34
• @HenryKeiter Actually I think the orbital period would be a good place for the Fibonacci sequence – bowlturner Dec 17 '14 at 16:36
• Rather than single elements, I'd suggest making them single fluorescent crystals. That should mean you can pick up the artificial spectral lines from waaaaay away. And you can put the spectral lines into a pattern. – Aesin Dec 17 '14 at 17:19

Dyson spheres may be a good idea, since they

1: cannot form naturally using non-exotic matter (in the shell around a star form)

2: can be detected from millions of light years away by their size and spectral signature

The most likely habitat for such beings would be a dark object, having a size comparable with the Earth's orbit, and a surface temperature of 200 deg. to 300 deg. K. Such a dark object would be radiating as copiously as the star which is hidden inside it, but the radiation would be in the far infrared, around 10 microns wavelength.

If the Dyson sphere is left unmanned and only rudimentary maintenance robots are left to prevent it from collapsing, it could act as a good piece of interplanetary art.

• Unfortunately maintenance robots would cross the line as they would contain technology, I'll clarify the question. – Tim B Dec 16 '14 at 16:05
• Aren't Dyson spheres unstable? Or is that what you meant by "collapsing"? – KSmarts Dec 17 '14 at 19:56
• Which is why robots were needed. The question was answered prior to OP specifying no technology. – March Ho Dec 17 '14 at 19:57

Some unusual planetary configuration, like torus planet? Or planet orbiting two suns in orbit in shape of infinity? Pair of planet in tidal lock, sharing atmosphere? We had few of these physically possible but really unprobable planetary configurations in last few days.

Or if 6-sided cube is way off from sphere and would collapse under own gravity, maybe 20-sided dice would be doable and epic.

• "We had a few of these .. in the last few days" Can you recommend a reading source for this? – agweber Dec 16 '14 at 15:16
• Ah, I've seen things like the links you've added in. I thought you were mentioning recent discoveries. Silly me. – agweber Dec 16 '14 at 15:28
• It's an interesting idea, unfortunately the cube and torus planets are both unstable (and unlikely to hold up under their own gravity) although I guess special materialize might fix that. A planet-sized torus made out of diamond for example would be pretty epic.... – Tim B Dec 16 '14 at 16:06
• Torus planet – Brian S Dec 16 '14 at 18:33

## Define recognizable

Take look at this picture from Hubble from instance: Image source

"Eye of the God!" some will say. "Great work of nature!" say the others. And both are (subjectively) right

For instance, our brain evolved around "uncertainty" so we tend to see "signal inside noise". Another example:

Was it Jesus? Or is it just burned bread?

Maybe the Earth is the sign (we created you to explore). Maybe the color green is the sign, because in previous version of the Universe, no such color existed. Maybe the life itself is the message.

We do not know and there is no specific metric to say on purpose.

And even creating something like this: Image source

Might get misunderstood...

• Still, if you found a perfectly cube-shaped planet, with the rest of the Universe remaining as we know it, I'm sure every rational human would accept that it's artificial. – vsz Dec 18 '14 at 20:46
• We are on different side of barricade regarding this. Because, knowing humans (being one of them helps), I can assure you that finding such planet could be also understood as "God is real and this proves it" – Pavel Janicek Dec 19 '14 at 7:07
• Ahhh, you said "rational". Now I have to admit, that we do not have issue here. I agree :) – Pavel Janicek Dec 19 '14 at 7:08
• I can believe in God (a transcendental one who designed the laws of the universe, not the "Grandpa God" sitting on a cloud which actually very few people believe in) but can still accept such a planet as a work of an intelligent alien species. If I travel to a different country and see a marvelous piece of architecture I didn't see before, my first thoughts will be that humans built it, and not divine intervention. If you think that all or most religious people would just say it's a "work of God" then you have a serious sampling bias :) – vsz Dec 19 '14 at 7:20

These are beings of incredible power! They'd not settle for any ordinary monolith - how about a planet, solar or galactic scale Escher work - art that bends space time in impossible ways!

http://en.wikipedia.org/wiki/File:Escher%27s_Relativity.jpg

If i was a hyper-being, with almost limitless power, and wanted to leave a sign that an intelligent civilisation had been here, i would make a "lighthouse star" - that is, something which emits radiation in a way which strongly suggests it's artificial, eg a sequence of prime numbers.

I would harness the energy of something already in existence which is already pumping out huge amounts of radiation, and i would achieve the sequencing by building a dyson sphere around it with large holes cut in it, then set the sphere spinning.

It's tempting to choose a quasar for this, since they are the biggest emitters - it could be visible across billions of light years. But, since they are black holes that might introduce too many engineering issues to do with stability. So, a pulsar might be a good choice - the fact that they are already emitting a pulsed signal might help draw attention to my extra layer of information.

EDIT - it just occurred to me that this is kind of a cruel trick: the sign of intelligence might cause many species to launch expensive, long-lasting missions to travel to the source of the signal, hoping to meet some powerful and intelligent aliens, only to discover that they've all gone and the lighthouse is all that's left. If i was the captain of that ship i'd be pissed.

• Excellent point. I was also thinking of pulsars, put somewhere far away from moving galaxies in some un-natural (or at least statistically highly unlikely) configuration. But the issue of luring other species there to no end is really cruel. – Ghanima Dec 19 '14 at 9:34
• They should probably put some kind of 'prize' there to reward species who made the trip. Some kind of advanced technology or something to help them join the transcendence party. – IndigoFenix Mar 7 '16 at 12:18

## We apologize for the inconvenience.

For those who are not familiar with the reference (Hitchiker's Guide to the Galaxy spoiler):

In the Hitchiker's Guide to the Galaxy series (specifically the 4th book, So Long and Thanks for All the Fish), there was a planet which contained God's Final Message to His Creation, written in giant gold letters. You could buy a post-card, but they always blurred out the words. When you visited, you could see them, in person, larger than life: "We apologize for the inconvenience."

• We'll miss you Mr. Adams! – Cort Ammon - Reinstate Monica Dec 17 '14 at 15:31
• Cort Ammon, you might want to explain the Hitchhiker's references. – HDE 226868 Dec 17 '14 at 16:00
• Explain the reference please...it's a good humour answer, but it's flagged – Twelfth Dec 17 '14 at 17:26
• I have added a spoiler for those who are not familiar with why it is a relevant answer. – Cort Ammon - Reinstate Monica Dec 17 '14 at 17:48

Klemperer rosette made up of stars

http://en.wikipedia.org/wiki/Klemperer_rosette

• Unfortunately Klemperer Rosette's are unstable, otherwise they'd be perfect :( – Tim B Dec 16 '14 at 16:04

Really? For humor, but also seriously, something like this then:

# A planetary sized (element/alloy of your choosing) baby fitting toy

(Sorry, couldnt think of anything else after this popped in my mind)

It definetly needed highly advanced technology to be made and couldnt have happened naturally. Maybe the pieces are made from different materials.

No message of significance, just a statement about how much we have to learn to be able to build something like this.

Maybe the aliens have such devices, or puzzles. Perhaps the pieces can only be fitted using an specific method, not only about the correct shape.

But I really like your vision about making it more like art than a test or such.

• "This would be the perfect present for my toddler," alien. – TheNumberOne Dec 17 '14 at 22:18

I can't stop thinking about the idea I've got from the misconception in the comments.

# An artificial black dwarf

A black dwarf is substellar object composed of everlasting electron-degenerate matter which can last for indefinite period of time and can be produced from regular white dwarf stellar remnant by artificial cooling it toward background temperature. There are no natural black dwarfs in the current Universe.

Pros:

• It lasts virtually forever
• It remains "a wonder" for at least 1014 (1,000,000,000,000,000) years

Cons:

• The "sender" party has be more advanced than as per original question, achieve a substantial progress in astroengineering to cool down a white dwarf
• The "recipient" party have to achieve at least orbital optical telescope stage to detect the dwarf's microlensing effect

And on the pedestal these words appear:

'My name is Ozymandias, king of kings:

Look on my works, ye Mighty, and despair!'

Nothing beside remains.

The issue that I struggle with here is the stability over time..I get the feeling it'd be easier to find it in mathematics or something to that extent, but by the way you've written the question, it almost seems like you're wanting people to look out a spaceship window and see it. When it comes to it, anything that exists on a planetary scale is eventually going to be reorganized by gravity as you extend the time line into the billions of years.

Art is ultimately beauty in the eye of the beholder. I've seen mention that a dog differentiates smells. They will smell peas, carrots, potatoes, meats, water, flour, and butters...we smell the full stew (can a dog appreciate the stew?). In artwork, you can stare at the individual brushstrokes, or you can appreciate the full painting. Following these lines, perhaps a series of spinning nuetron stars that produce background xray radiation thats relatively meaningless on its own becomes a song when listened to together. Though thats hard as over a billion year time scale, these eventually rearrange...but song left in background radiation that can only be heard/appreciated when taken as a symphony not individual 'sounds' would be one way of leaving this timeless.

Perhaps it can be found in the really massive...2 super massive black holes oribiting each other in a binary method at the center of the universe who's combined momentum is truly 0 for eternity. Perfection is a way of conveying intelligence afterall, however it's easy for any of this not to be interpreted correctly.

Perhaps it can be found as a hidden message in time...In the Planck epoch of the big bang (between 0 and 10^-43 seconds), the particles suddenly rearrange to flip us off.

Maybe we've seen it just haven't care to notice it. 1-8-1, the configuration of protons in water, is their symbol for joy?

Or we can get to silly…A higgs boson particle has a smiley face drawn on it?

Edit:

If you are looking for something a ship could accidentally stumble upon, it would be (theoretically) possible to have a location where the interference of background radiation with itself produces a 'song' to be heard. A single pinpoint (or reoccurring pinpoints) where background radiation from all directions uniquely combines to create something in it's interference...gives it something that cannot be found in the parts, only in the appreciated whole (which is a common place within art). Would definitely give that awe and disbelief feeling you are looking for, whether or not they attribute it to that race of ascending beings is hard to tell...and probably quite disputable.

Starting to feel like a 'proof of the existance of god' style question...everywhere yet no where.

How about a nebula that when viewed from certain angles resembles an impossible cube? That would be quite unmistakably the work of intelligent species, and, a nice joke as well.

• I like this, but it's not so obviously artificial – ArtOfCode Dec 16 '14 at 22:43
• It's also restricted to certain viewing angles. – Tim B Dec 17 '14 at 9:12
• @TimB I thought that was part of the fun. In every viewing angle you can tell this is something different, even interpolate that at certain angles it looks like an impossible cube. And then at a certain special angle... – Dhara Dec 17 '14 at 12:25

A perfectly spherical planet as the only object orbiting a sun in a perfect circular orbit. The planet being made of one, and only one pure element. No moons, asteroids, or other trash or solar system debris - just the sun and the perfectly spherical, single element planet. It should last quite some time before other objects enter it, and the majority of them should pass through without impacting the planet.

The perfection in the planet and orbit, and the utter lack of other solar system objects (except those small ones captured over billions of years) should set off alarm bells for any new organism sensing the planet.

I know this isn't to the massive scale as some answers, but, wouldn't rearranging mountain ranges qualify...think Nazca Lines on a huge scale. (We can't read them...but it's obvious they were written by somebody to somebody in orbit)

I mean, putting them in some non-random pattern, maybe, of uncommon materials. Something that is OBVIOUSLY non-normal and not within the expected parameters of the planet -- the reader might not get the message or the joke, but, it's been left as a message

• The timeline of how long that it lasts might not last long enough. Our continents move significantly over a billion years – bowlturner Dec 17 '14 at 17:15

Hmm. How about a nebula? Pavel Janicek mentioned it briefly in his answer, but I want to elaborate on it a little.

You have a bunch of choices if you want to pick a nebula:

• Dark nebula: As you can imagine, dark nebulae are - well, dark! They block light from objects behind them. They're made of dust particles. A dark nebula in itself wouldn't look like artowrk, but you could use it to blot out select regions of the sky, letting only certain light sources through. You don't have to create any light, only block the light you don't want! Here's a picture of one, Lupus 4:

• Emission nebula: An emission nebula - guess what - emits light. A typical emission nebula is a cloud of gas filled with ions. The source of the cloud may be a star throwing off its outer layers, or a place where stars are born. In both scenarios, hot gas - or stars inside, but typically gas - emits light. Here's the Ring Nebula, my favorite:

• Reflection nebula: A reflection nebula reflects the light of nearby stars or other light sources. Like the other types of nebulae, they span interstellar space and may contain many stars. You need a central source of light. Here's the Witch Head Nebula:

Create any of these and you're going to have some pretty nice artwork. But to make any watchers know that they're artificial, make sure that they follow patterns that Nature alone could not produce.

• A nice idea, and it's certainly got the scale part covered. My worry with a Nebula is that as I understand it they are not very stable? Wouldn't they change shape over time? – Tim B Dec 16 '14 at 19:17
• @TimB Over long periods of time, definitely. Many are short-lived, although Barnard's Loop is an excellent example of an exception. The shape of the nebula might not matter though. For example, if you have several large seemingly-planetary nebulae in an area where there aren't any stars - or, better yet, that have their centers arranged in some pattern - a watching civilization might understand that they're artificial. – HDE 226868 Dec 16 '14 at 19:23
• Also, it would be easy to rationalise away strangely shaped nebulae as pareidolia, so they are insufficiently clear. See Pavel Janicek's post for more details. – March Ho Dec 16 '14 at 19:41
• @MarchHo No, it's exactly the opposite. The concentric rings in that nebula are easily explained, and quite common in some types of nebulae. The things I'm talking about would not have simple strange shapes - they would be shapes that could not form by purely natural processes. Foe example, an extremely asymmetrical nebula that's half missing. – HDE 226868 Dec 16 '14 at 19:49
• I still don't think nebulae are a good way to leave behind a legacy. Other than being rather temporary, there is very little one can do to make a pattern that "cannot form naturally", considering chaotic gravity patterns. – March Ho Dec 16 '14 at 19:52

The problem with this is that whatever the signature is, a new civilization will consider it to be normal. It is like if I grew up always being told that 2+2=5, I would consider this normal. Or, how would we know if Earth has a moon because an ancient civilization put it there?

That said, the best kind of sign would likely be a direct statement. Maybe they have technology to predict the language that will grow in the new civilization. Otherwise, you could use a picture, since they are not as likely to be misunderstood as part of nature and more likely to be understood as what the picture represents. This is similar to cave drawings--we don't interpret them as natural phenomenon; rather, we interpret them as drawings. But we still consider them to be normal.

\                  |   __
| o  o  o      o  |  (  )
|                 |  (__)  (O)  O       O
/                  |                          *


But something like this would likely be interpreted as (comment if you know what it is before looking, I would like to see how obvious it is)...

The solar system

So there's a starting point, we can tell them we know about the solar system. You might use that to tell a time, say, the last time the planets lined up in a certain way or something.

Why stop at a mere planetary scale? If these beings are truly all powerful, perhaps they can retroactively construct an entire multiverse that acts out all possible permutations of experience purely to prove the entirety of what was possible. Such an art piece would encompass all possible art and would be a fitting legacy (pre-gacy?) for a species that has truly transcended reality. The only trouble would be whether the inhabitants would actually notice and appreciate the magnitude of the art while caught up in being it. If not, it might be more of a cruel joke.

A few billion years is about the lifespan of a decent-sized star so we can do something interesting with that. However, a lot can happen in that time, so let's make sure we're thorough. We pick out 16 bright stars, all within 32 light years of each other. If necessary, we, near-ascended beings that we are, can always shuffle a few stars closer to each other to make the construction more obvious.

Once we've figured out our little star cluster, it's time to build ourselves some artificial celestial objects. They don't really have to be much in terms of materials, though preferably we'll use a less valuable material so the beings that come after don't strip-mine our piece of modern space-art. As for building materials, we should probably strip the local space for this: empty out the kuyper belt, scavenge the gas-giants and asteroid belt, make sure the orbits around this planet are nice and clear. Fuse the whole lot together to something fairly simple and not terribly dense. Carbon is probably fine.

Then we'll push our newly produced celestial objects into a trajectory around our stars, in pairs of two (redundancy, you see). We calculate our orbits so the planets eclipse the star at regular patterns. The first two stars get a fairly heavy dose of newly created planets, such that, as long as you're looking at the star from the ecliptical, half of the time, it's obscured or dimmed by the passing planets. I imagine the timing for this to be in the scale of a few months.
The second set of stars gets a similar treatment, but with only half the material, ensuring it's clearly visible 3/4ths of the time and obscured the other quarter of the time. Apply the same process to the rest of the stars, halving the amount of time they're obscured each time. If desired, you may switch materials between steps, increasing in density as you go, to further prove the point.

Voila. You've now built an 8-bit incrementing counter at a celestial scale. Sure, it rolls over every 256 cycles, but any civilisation advanced enough to build a proper telescope is going to see your piece of galactic art and think "huh, that doesn't seem terribly natural"

If you want too, you can leave a snarky message on the artificial planets for bonus points, but I don't think that's neccesary.

In Arthur C Clarke's "Space Odyssey" series an unknown race of advanced beings left a series of monoliths. These were not immediately apparent but were discovered as the human civilisation advanced. These monoliths played a role in advancing the human civilisation, but in your story you could have them as just "easter eggs" for future civilisations to find.

http://en.wikipedia.org/wiki/Monolith_%28Space_Odyssey%29

• Nice idea but lacking the scale, you would only find the monoliths once you start exploring the planet that contains them. – Tim B Dec 18 '14 at 12:17
• You could design the monoliths so that they were detectable once suitable technology was discovered. For eg the one on the Moon had a very strong magnetic field thus was discovered even though it was buried under the surface. It could for eg emit radio bursts on specific wavelenths or with a specific period which had mathematical significance. – Qwerky Dec 18 '14 at 14:14

Why does it have to be huge to be visible to intelligent beings? I like Carl Sagan's idea in "Contact" where PI is calculated to millions of decimal places. Eventually the numbers become a series of 0s and 1s that form a perfect circle. This would be true eternally.

• I don't, because pi is not something that can be changed. It is thought to contain all possible finite sequences, so it is impressive that an advanced civilization could locate an interesting long sequence; not that the somehow caused it to happen. – JDługosz Dec 19 '14 at 7:11

In Strata from Terry Pratchett, a 24000 km flat disk world, complete with mechanically animated celestial sphere is planted in our universe (something like the Earth as it was seen in medieval age, i.e. flat, and you could actually fall off if you came too close from the edge).

Also some peoples make jokes like planting dinosaurs fossils wearing wristwatches, or holding a "No to nuclear power" signs.

If I was doing it, I'd plant a huge perfectly black monolith (something like the 2001 one, but bigger) with on the middle of one of its faces a small push button and a "Do not press" sign.

• A diskworld, when inserted into our universe, would be crushed by its own gravity forming a spherical planet. – slebetman Dec 18 '14 at 6:52
• @slebetman, don't tell me, tell Terry Pratchett :o). Anyways, I would think a civilization developed enough to ascend to become beings of pure energy in a hyper-dimensional universe could find a workaround to this issue. i.e. they could manipulate not only our universe but the meta-universe, allowing them to suspend locally physics laws in our universe. – LeFauve Dec 18 '14 at 10:38
• That would break the "no technology (science?) that could be slavaged" clause. A location in this universe with its laws changed or connected to a metaverse would allow engineers to use it to extract energy or violate conservation laws (which wold allow you to extract energy). Note that unlike physicists or mathematicians, engineers don't need to "understand" something in order to use it. We just need to characterize/observe it. We use technologies everyday that we don't really understand - glue for example. – slebetman Dec 19 '14 at 2:58
• That doesn't have to break the "no technology (science?) that could be salvaged" clause because it doesn't have to be "high-tech". The whole mechanically animated celestial sphere could be just a big clockwork machine. A little like the antikythera mechanism. It can looks like a very advanced technology if you consider it can predict eclipses but the technology is just cogs and gears. But I do agree about the problem that it would allow engineers to hijack it in order to cheat with the universe laws. – LeFauve Dec 19 '14 at 7:35