First Contact

This is a prequel to a relativistic interstellar trade scheme I am currently building on.

An alien culture has sent a signal with design plans for solving an advanced anti-matter engine, allowing us to store large quantities of antimatter in a Minimum Magnetic Field Trap. This is first contact, no prior communication has happened—in either direction. They know nothing at all about Earth and sent the message out in the blind. It is a pulsing light message from a star, which simply repeats.

  • Earth noticed that the pulses had a pattern, and assumed it came from an intelligence.
  • The pattern had been repeating for years, we never looked that way. Now we found it.
  • The pattern begins with a basic alphabet, then relatable words like "star," "space," "person", etc., and then starts putting grammar together for us using basic words to teach connectors like "and", "the", "under", etc.
  • In the end, after lots of work, they teach us their language, building from the simplest common concepts up. Then they include plans for building an antimatter engine. That seems to be the point of the message.


They have no idea what an "inch" or a "second" or a "kilogram" is (how could they? It's first contact). They sent us a complete set of instructions to make this engine. But, it needs to be 18.85 gwelrits long, connected with 3 triamed diameter Zinc wire, and we must never exceed a temperature of 7,139 Wodnurbs for more than 32 dyups, or it will explode, Etc.Many more details like this are included.

Assuming we got a set of instructions to solve our space-travel limitations from an advanced civilization, how could we possibly build it? What could they also include in the instructions that would allow us to manufacture this engine?

  • The message came from many lightyears away. We cannot communicate with them, and they do not know about us at all.
  • $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$
    – L.Dutch
    Feb 18, 2022 at 16:32
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    $\begingroup$ Have you considered Planck units? $\endgroup$ Feb 18, 2022 at 20:12
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    $\begingroup$ Of course. They can tell you to build a tube 1.6E34 Planck lengths wide. Planck length is defined based on the speed of light, the gravitational constant and the reduced Planck constant, all of which are constants independent of the system of measurements used. $\endgroup$ Feb 19, 2022 at 0:30
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    $\begingroup$ Because of what you just pointed out-related to G- the plank length is only accurate to 7 digits. “ Planck length It is equal to 1.616255(18)×10−35 m, where the two digits enclosed by parentheses are the estimated standard error associated with the reported numerical value, or about 10−20 times the diameter of a proton.” Wiki. That can leave some sloppy engineering. $\endgroup$
    – Vogon Poet
    Feb 19, 2022 at 1:07
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    $\begingroup$ What I am seeing in the question and comments are a lot of excuses and rationalizations to avoid accepting what everyone is telling you: They would use Planck Units and we would initially assume that they were using Planck Units, so: No Problem. $\endgroup$ Feb 19, 2022 at 19:38

5 Answers 5


Universal constants

They would do the same thing we did in the Voyager record: put things in terms of universal constants that are based on universal physics. On the Voyager record, the way we indicate units is:

Time: expressed in time units of 0.70 billionths of a second, the time period associated with a fundamental transition of the hydrogen atom

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Distance: how far light travels in a vacuum in one of those time units

Mass: described in masses of hydrogen atoms

enter image description here

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    $\begingroup$ the Pioneer plaques came already 5 years before that. $\endgroup$
    – ths
    Feb 17, 2022 at 22:05
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    $\begingroup$ @ths sure, but the voyager records are likely better known, so I used them as the touch point. $\endgroup$
    – Daniel B
    Feb 17, 2022 at 22:25
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    $\begingroup$ It would be easier to teach us this than it would be to teach us their language. $\endgroup$
    – c1moore
    Feb 19, 2022 at 5:14
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    $\begingroup$ Starting point: 'wavelength this message was transmitted at' (which admittedly isn't perfect due to redshift). Then e.g. 'element with emission lines at X Y and Z wavelengths'. Then go from there. $\endgroup$
    – TLW
    Feb 19, 2022 at 19:17
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    $\begingroup$ @Vogon Math doesn't really require numbers or symbols. We've assigned those symbols to concepts. It's much easier to teach concepts than language. The people who are decoding this message are doing so using patterns. It'd be much easier to send universal constants and decode those than a language. We never would have been able to understand Ancient Egyptian if we didn't have a reference point with the Rosetta stone. What is going to be the reference language for this new language except the hunch that they started off simple to teach us the language? $\endgroup$
    – c1moore
    Feb 20, 2022 at 22:33

All our units of measurement for physical quantities have absolute definitions, which mean the exact same thing everywhere in the universe.

  • For example, a second is the duration of exactly 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the fundamental unperturbed ground-state of the caesium-133 atom. Numbers are numbers everywhere, and cesium-133 is cesium-133 everywhere.

  • A meter is the length of the path travelled by light in vacuum during a time interval of exactly 1/299,792,458 of a second.

  • A kilogram is the unit of mass so that the Planck constant comes up to exactly 6.626,070,15×10−34 kg⋅m2⋅s−1.

I would assume that long before going into the details of the antimatter engine they told us that a gwelrit is the length of the path travelled by light in a vacuum during a time interval of so many dyups, with a dyup being the duration of so many periods of the radiation corresponding to such and such hyperfine spectral line of such and such atom. And so on.

Basically, explaining the magnitude of the units of measurement referring to physical quantities is easy. It would be among the first things that a technical manual would include.

As it is the custom when translating novels from American into another language. The first time the word "inch" comes up in the original, the translator would translate to some archaic word denoting a local obsolete unit of measurement (for example, in Romanian it would be "țol" or "deget"), and put a footnote saying that this word translates the American word "inch" and one of those equals 2.54 centimeters. Same for gallon, ounce, furlong, firkin, hogshead etc.

The problem exists also in Earthling-to-Earthling communication; some physicists use a system of units of measurement where the speed of light has the numerical value 1, so that it disappears from formulas. In olden days, many physicists used any of a family of systems of units of measurement called CGS (for centimeter-gram-second), which are conceptually different from the common SI of our days -- even the basic formulas don't translate directly. But it is still not all that hard to explain what a statcoulomb is, and how it relates to a regular coulomb.

Now, some units of measurement refer to sensations, such as the phon for loudness, or the candela for luminous intensity, or our color models. All we can do is send the curves which relate those to physical quantities, and hope for the best.

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    $\begingroup$ @Matthew: Yes, we can transmit the empirical curves which define such human-centric units; the problem is that we cannot explain what they mean in terms of sensations. Is a phon loud of not loud? Is a candela dim or very bright? $\endgroup$
    – AlexP
    Feb 17, 2022 at 21:45
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    $\begingroup$ I honestly wouldn't expect their plans to be concerned with aesthetics, or even ergonomics (not human ergonomics, anyway!). In fact, figuring out how to adapt an engine designed for a ship that's a size we humans consider totally unreasonable, or emits radiation lethal to us but harmless to them, is fertile ground for... y'know, story 🙂. (Obligatory Freefall reference) $\endgroup$
    – Matthew
    Feb 17, 2022 at 21:54
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    $\begingroup$ Americans translating inch to a local obsolete unit of measure is the height of irony. We are going to be getting three quatlons to the warg on the intergalactic market and Merica will still be refusing to go metric. $\endgroup$
    – Skeith
    Feb 18, 2022 at 12:45
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    $\begingroup$ @AlexP if they have entirely different biology, what is loud to us or bright to us may not be loud or bright to them anyway, so the subjective impression of such measurements is largely irrelevant for this kind of communication. $\endgroup$ Feb 18, 2022 at 16:17
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    $\begingroup$ Maybe we should say that, whether it's with reference to the candela or the metre, that we cannot transmit qualia. There are more qualia associated with the candela than with the metre, since it's more complicated, but both ‘Does this seem bright?’ and ‘Does this seem long?’ are questions whose answers depend on qualia. (And as @Matthew said, this is where the story can happen, as the aliens give us a design that technically works, but is maybe cramped, itchy, full of distracting lights and sounds, or otherwise ugly and uncomfortable.) $\endgroup$ Feb 18, 2022 at 18:13

Units aren't the biggest problem — not by a long shot

I don't know what your aliens are like, or how much more advanced they are, but I can explore a different (and analogous) problem: could we teach a medieval society, circa 1450, to make an iPhone?

For starters, they wouldn't understand the operating principles. They don't know what electricity is, or a wire, or a semiconductor. They've never heard of a capacitive touchscreen because they've never heard of capacitance. How could they understand an OLED display when the discovery that white light is made of colours is still 200 years away?

You might ask "can't they just follow the instructions blindly?", but that won't work. They can't do quality control on the phone's components without understanding what each component is supposed to do — they'd just end up building a phone in which all the components look right, but don't work. To them, a functioning microchip and a useless flake of polished metal are identical.

What about materials? They need ultra-pure silicon for the chips, oil for the plastic parts, exotic metals like gallium and arsenic to dope the semiconductors, lithium for the battery... and just look at what you need to make an OLED panel. They don't know how to make any of those! And even if they could find the raw materials, how would they process them to the required purity? Remember: these are people who, if you handed them a lump of pure gallium, wouldn't even be able to identify it.

They don't have modern supply-chains in place. They don't have any relevant institutional knowledge. They'd need to build it all from scratch.

Manufacturing: iPhone chips contain components that are just 5nm wide — much smaller than the wavelength of visible light. We'd need to send instructions for building an electron microscope just for them to see those components, much less manufacture them independently! Of course, we'd first need to explain what an "electron" is...

Troubleshooting: Nothing works first time. According to Elon (who says dumb things, but in this case knows what he's talking about), "building a car factory is 100 times harder than building a car". Even if you know what the end result should look like, you still have to figure out how to get there. Our medieval friends will need to bootstrap a boatload of industries just to make the components they need: oil drilling, oil refining, organic chemistry, inorganic chemistry, rare-earth metal mining, silicon chip manufacture, battery production, etc.

And what if things don't work first time? The communication is one-way, so they can't ask us for help. They don't have the institutional knowledge they need to solve the inevitable problems.

Funding: it should be clear by now that this is a massive undertaking for the medievalists. For us, building a chip fabrication plant is a billion-dollar investment. For them, they need to boostrap multiple entire industries, from scratch, in a world that currently has no demand for those products. How the hell are they going to pay for it?

Workforce: the iPhone is manufactured in the modern world, by modern workers. It requires a skilled, literate, educated workforce. To build an iPhone, you need to teach an army of people about every step of the manufacturing process — all of which will be new to them!

In summary, the iPhone was designed with the assumption of a modern workforce, modern supply chains, a modern manufacturing base, and modern logistics. The design of the phone is inseparable from the civilisation it was designed for. Those medieval people would need to revolutionise every aspect of their society, just to make their first phone.

In fact, they couldn't even have built an iPhone in the 1950s, let alone the 1450s.

Medieval Europe is just 600 years behind us, and its inhabitants human, like us. How much greater will our difficulties be following blueprints written by aliens that could be thousands, or even millions, of years ahead of us?

Of course, we won't have any of the problems I've outlined above. But we will have new problems, even more difficult problems, trying to understand an alien design, thought up by alien science, and made using alien techniques.

The hard part is not the design, it's everything that feeds into that. If we were advanced enough to follow the aliens' blueprints, we'd be at most a few decades from figuring it out ourselves.

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    $\begingroup$ I disagree with this frame challenge. The question asked how the advanced species would attempt to communicate their design. It didn't ask how we would decode their message, or what we would be able to do with that info. For all we know, OP is writing a story that takes place over centuries, where the plans at first only give suggestions to Earth scientists where to focus their research. $\endgroup$
    – CPomerantz
    Feb 18, 2022 at 20:43
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    $\begingroup$ "What about materials?": a particular problem for an antimatter engine, as it's entirely possible we'll have all the materials and manufacturing capabilities needed to build it...but no antimatter to fuel it with. It's not exactly available at every corner drugstore... $\endgroup$ Feb 19, 2022 at 1:13
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    $\begingroup$ It's comparable to medieval humans building an iPhone only, if there are entirely new physics we don't understand. Like, if the aliens sent us a diagram of an antimatter reactor's atom-level meta-material structure to safely contain antimatter atoms, we could understand the diagram, even if we couldn't simulate how it works due to insufficient computers, or have technologies to construct the material (at least not more than hundreds or thousands of atoms worth of it), or produce the anti-matter atoms needed in the material. But if the tech went "beyond quarks" so to say, then it'd be hard. $\endgroup$
    – hyde
    Feb 19, 2022 at 8:15
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    $\begingroup$ Understanding is not the problem, if the aliens did their job correctly. Every human is born knowing absolutely nothing about the principles of physics, yet in 30 years (if they choose to study physics) they can be the world expert of their (sub)field. It's just a matter of explaining everything from first principles step by step. As the aliens don't know what our technical level of development is they will need to do that anyway. $\endgroup$
    – JanKanis
    Feb 19, 2022 at 13:31

Assuming we got a set of instructions to solve our space-travel limitations from an advanced civilization, how could we possibly build it? What could they also include in the instructions that would allow us to manufacture this engine?

Carl Sagan's novel Contact answers this specific question. In the book, the machine's technical manual is the message. But it is just as you say: we don't know their units or concepts, so it is mostly unintelligible at first. However when the characters investigate the phase modulation of the message they discover a primer - a key that explains all the concepts and units in the manual by extrapolating from empirical principles, such as the characteristics of a hydrogen atom etc. Mathematics is the same throughout the universe, so the primer soon teaches the Earth's scientists how to understand the message, and how to read the technical elements of the manual.

The message came from hundreds of lightyears away. We cannot communicate with them, and they do not know about us at all.

This is where we must deviate from the Contact story. In that story the aliens had received an early television broadcast (the first one powerful enough to breach the ionosphere, which was in 1939) and so had some grasp of our body shapes, and were able to determine the habitation requirements.

However in this case I would suggest that the machine's manual covers mainly the engine itself, perhaps at several scales (because they don't know the size of the creatures reading their message). The engine would then mount on a habitation of some sort, and that would be explained with plenty of examples at varying scales, but left up to us to design, as they have no idea of our body shape and composition. The manual can still help us here, explaining the expected compression and tensile forces, acceleration, and such. If the intention was to carry humans, we could easily add in the missing pieces - aerospace engineers do this all the time.

  • $\begingroup$ A broadcast from 1939, so a system no more than 35 light years away (round trip, spontaneous response) could detect our minute radio signal, decode it, and… oh, never mind. So I guess my question boils down to “what primer would they send” in Contact lingo. Food to know it has a word! $\endgroup$
    – Vogon Poet
    Feb 20, 2022 at 1:31
  • $\begingroup$ @VogonPoet - if I remember right, in the book it was local-ish relay that sent the message... something not too far from us. However the machine enabled FTL travel (through an Einstein-Rosenstein bridge) so they were able to travel a lot further. Great book, well worth a read. There's a movie too, but it leaves a lot out. $\endgroup$
    – gbe
    Feb 20, 2022 at 9:47

I'm going to say units are the least of issues but for a different reason: I think they will express everything in fundamental units. Length will be that hydrogen length from Voyager, mass will be protonium, time will be the time for one wave for the hydrogen length.

They'll send a periodic table so there's no question of what the units are.

And it's not Zinc wire, it's atom-30 wire. Remove names wherever possible.

It's still going to have to be followed by a whole bunch of this-is-how-you-make-the-tool-to-make-that instructions, repeat however many iterations needed until you can be confident that anyone who can receive the signal knows how to make the item--and then probably a bit more so the receivers of the message can compare the instructions to what they already know and see that they are instructions to build something that works.

Epic engineering issue but I don't see a language problem.


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