# Humans meet a distant alien species. How do they standardize? - Units of Measure

Humans meet some distant alien species. They are mutual first contacts. After learning the languages of each other, they begin to share scientific and engineering knowledge with one another, but here's the problem: given our separate lines of evolution and scientific development, we have different systems of units, computer architectures, character encodings, names for the same mathematical concepts, mathematical notation (including default numeric base), etc...

We have to standardize or coordinate- and this question will begin with units of measure. We can certainly use unit conversions, but this becomes a complicated matter when working on e.g. spacecraft, as past human experience has shown that bad things happen when engineers are using two different units of measure for different components.

The problem here is there are a lot of units and neither species can really strongarm their way into making the other conform to their units (assume both have a well-defined and self-consistent system like SI, so neither is objectively superior). They have to come to a compromise somehow.

How do two independent interstellar species come to agree on a system of units?

In all likelihood, there is no forcing one society to adopt the other's system, instead, people would likely adopt a local market approach to measurements. Let's say you are on Earth building spaceship parts that will be used to make ships on Farawaynos, you manufacture to the other society's system of measurements. If they want to sell parts to Earth, they need to manufacture to the metric system of measurements. This is basically the same way that we do things now with the Metric and Imperial systems.

The only way you will probably see a standardisation is if one society is much more influential than the other. If Humans have 20 billion people across 5 planets and the Farawayans have 20 trillion people across thousands of planets, the humans would likely be strong-armed into accepting that the alien societies unit of measurement is more reasonable for standardisation. Or, if one society conquered the other, you'd likely see the loser's system be replaced.

Another option would be for the societies to agree on a new "interstellar" standard that is different than both nation's customary systems. If we use a base-10 metric derived from our own planetary motions and properties of water, and they use a base-6 metric derived from their planetary motions and properties of methane, we might agree that both systems have their flaws and adopt a new base-16 standard derived from the properties of our galaxy's central black hole and hydrogen. Chances are, both societies would be slow to adopt this as THE standard, but if all interplanetary trade becomes based on this, eventually, societies would shift to accept it as the more useful metric.

Humans have already solved this problem.

There are many useful universal numbers that can be used. mostly atomic phenomenon such as the mass of X atoms of a particular isotope or natural atomic oscillation. You may want to checkout the current definitions of all SI units. which are defined in such as way as to make them universal. That is they are based on universal constants like the transition states of cesium atoms.

Second: The duration of 9192631770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom.

Meter: The distance travelled by light in vacuum in 1/299792458 second.

Kilogram: The kilogram is defined by setting the Planck constant h exactly to 6.62607015×1034 J⋅s (J = kg⋅m2⋅s2), given the definitions of the metre and the second.

Mole:The amount of substance of exactly 6.02214076×1023 elementary entities.

Kelvin: fixed numerical value of the Boltzmann constant k to 1.380649×1023 J/K, (J = kg⋅m2/s2), given the definition of the kilogram, the metre and the second.

Ampere:The flow of 1/1.602176634×1019 times the elementary charge e per second.

Candela: The luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 5.4×1014 hertz and that has a radiant intensity in that direction of 1/683 watt per steradian.

The individual numbers can be derived by any civilization you can communicate with. They will not have the same units but as long as you can communicate with them they can match the units using the universal constants used to define them and use them as common unit of measure. Alternatively the two species (them and us) can come up with a mutual set of units defined in similar ways, an interstellar system of units.

• @John -- All of these examples have arbitrary-seeming constants with many digits of precision. This means that it is very unlikely that another civilization would coincidentally come up with the same constants -- or even be willing to think that these particular values are particularly good choices. – Jasper May 28 '19 at 21:11
• @John -- If expressed using short (but still accurate) constants, the definitions are still within rounding error of 40,000,000 meters for the polar circumference of the Earth at sea level, 86,400 seconds in Earth's solar day, et cetera. These definitions show where (and when, on a geological timescale) they were developed. – Jasper May 28 '19 at 21:17
• @Jasper any civilization you are capable of communicating with across interstellar distances can match that precision. I never said they would come up with the same units, but the units are based on universal constants, so said civilization can use them with reliable accuracy. – John May 29 '19 at 0:12
• Thing is, even with that, we're not guaranteed to stick to decimal exponential notation because aliens might not have 5 fingers or may have chosen another numeric base for other reasons. They might think it's completely bananas that we use base 10 because dividing things into fives is not nearly as useful as dividing into threes. Maybe when base 10 and base 6 come together, we might compromise on base 12, binary, or hexadecimal. Meaning everyone has to change their units and exponential factor. – Beefster May 29 '19 at 19:55
• @Beefster they do not have to if you are communicating with them you can explain how our number system works. that is fairly easy. we convert our number system to binary and back on a regular basis with no issues. Also I never said they had to coincide, actually your are the second person to get this confused I am going to highlight the relevent section. – John May 29 '19 at 19:57

This isn't as hard as it might seem

It would be harder to work out the semiotics than the conversion and/or adoption. After that it's just software. Why?

Because a substantial amount of science involves relationships. For example, the value of 𝜋 is unitless (3.14159...) That relationship would be the same no matter what mathematical base was used, or what standard of length, or even what the alien's definition of base units like meters or "seconds" (base unit of time) are.

Consequently, once you've figured out how to represent 𝜋 in both languages (and every other unitless relationship number, like the proton-to-electron mass ratio or the Planck constant, (see more)), everything else is basically algebra.1

As for whose version of the math/semiotics wins out, that has more to do with who's the bigger gorilla. If we have an empire of ten worlds and they have an empire of 100, the odds are very good that their systems will win out. In other words, we may use our systems internally, but anything that touches both species will also have their system.

Like o.m. said, it's like the U.S. being metric. We hate it, but every can of soda has both ounces and liters printed on the can. Eventually a generation will be born who wonders what an ounce is.... But not today. 😆

1Or calculus. It's either going to be high-school trivial or PhD hard ... but it'll still just be an issue of software.

• This actually makes me think of writing software to handle datetimes. Dates and times are SUPER unstandardised, there are dozens ways to write the same datetime, sometimes you need it all the way down to microsecond, sometimes years will suffice. sometimes you write 5/28/2019, sometimes you write 2019-5-28. Sometimes you have Daylights savings time, sometimes you don't, but we write software to figure all that out. If we can write software to get around these incongruencies, then making our digital media automatically translate km to kellicam should be trivial. – Nosajimiki May 28 '19 at 20:45
• @Hoyle'sghost, the moment the OP said "units of measure" he opened up the discussion to every unitless mathematical constant in the universe. (Nice Hickam quote, BTW). To be fair, the OP could have a world/universe where it's impossible to actually draw a circle - but he did say "humans." Sounds like our universe to me, and I think it's a bit pedantic to argue, "that might not be true." – JBH May 28 '19 at 21:13
• Us: Wow, Your ships have really cool architecture, I really like the octagonal thrust exhaust ports. Them: Well, we would use circles, but we can't figure out how to compute those in our cad software. – Nosajimiki May 29 '19 at 4:46
• @Nosajimiki - Obviously datetime would need to become expressed in microseconds since the Big Bang. But now the question is "using who's clock" . . . – MrWonderful May 29 '19 at 8:47
• @Nosajimiki Just because you bring it up... we're just going to be continuously late for every meeting, just to make sure nobody has the impression we'll get date/time conversions ironed out. As long as we're late, nobody shoudl care! – Cort Ammon May 30 '19 at 0:03

Why do they need to standardize?

Humans haven't managed to do it amongst themselves. All they need is a conversion process like we already do for imperial to metric.

Currently, a second is 9 192 631 770 times a certain transition of a caesium 133 atom. One could make the time unit $$2^{32}$$ transitions of this or another atom.

• How are distances, weights, light intensity, etc. based on powers of two? Or what other common units do you mean? – Soan May 28 '19 at 19:39
• I think he means as what system would take precedent. We use base-10 because we have 10 fingers to count on. If the aliens had a base-2 or NoC system, then, thiers would be more logical as a universal standard since there will be shared logical reasons for these systems between races. – Nosajimiki May 28 '19 at 19:42
• We are not! We are not! WAAAAAH! We are not metric! Just because I have to have whole sets of metric wrenches and socket sets (It's because the cars aren't built in the U.S. anymore! Right? AmIRight? It's not our fault!) and people in hardware stores keep asking for metric wood screws! Say it ain't so! (*puts hands over ears*) We are not metric! We are not metric! (Where's a paper bag! quick!) – JBH May 28 '19 at 20:17
• @JBH -- My car was built in the U.S. to Japanese standards. And good luck with the hiccups:) – Jasper May 28 '19 at 20:23
• @AaronF, does everyone you know follow the speed limit? Or drunk driving laws? – o.m. May 30 '19 at 4:43

They would not "standardize" on a single set of units. Changing the tooling, measurement instruments, slang, intuition, and jargon of two advanced inter-stellar civilizations won't happen.

Instead, like the use of Metric components in Imperial countries, both would exist in parallel. Depending on the market dynamics, they may revolve around conversions of bulk materials (like shipments of grain and ore), or specific items may be made to the other's standards for export or replacement parts (like am M3x1.5-13 machine screw).

Among the few individuals on both sides who directly interact with the others, there will emerge an agreement to use common units. This will probably be determined by which side has more desire for interaction with the other and may not be driven by civilization size or level of economic activity. The emergent solution is unlikely to be the same among every group of mixing individuals.

It will be chaotic and opportunistic, and it will mostly work.

Or, the "civilizations" will struggle for dominance and either ignore each other or go to war.

They might simply choose to use Planck units, which are all ratios of various physical constants of nature (like the speed of light and planck's constant), which implies that if you express these constants of physics in terms of these units, they all have a numerical value of 1--for example, in these units the speed of light is 1 (planck length)/(planck time), and Planck's constant is 1 (planck mass)*(planck length^2)/(planck time).

The disadvantage of these units is that ordinary human-scale phenomena will have huge values, for example 10^35 planck lengths is about 1.6 meters and 10^44 planck times is about 5.4 seconds, but you could just invent special names for large multiples, for example 1 YGlengths could be defined as 10^33 plank lengths (where Y and G stand for yotta and giga) which would be about 1.6 centimeters, and 1 YZtimes (where Y and Z stand for yotta and zetta) could be defined as 10^45 planck times or about 54 seconds.

edit: Apparently Planck units are not the only possible system of units defined in terms of physical constants though, see various others on wikipedia's natural units page.

• Planck units are entirely theoretical. They predict some interesting situations (first moment of the big bang, distance scales much much smaller than elementary particles, etc.) which we have never observed and which may be impossible to ever observe. Therefore, the theory is not supported empirically. Even if we could observe a Planck unit, we may discover that we are off by some weird factor like 4pi. Thus, it's a bad choice of units. – DrSheldon May 29 '19 at 20:00
• Yes, but the idea of Planck units will almost certainly have occurred to whatever aliens we meet who are advanced enough for interstellar travel. We're not even that far along and we've calculated the values. They probably won't be using them for day-to-day work, but they will know what the values are, and we can use them as a basis for conversion. – EvilSnack May 30 '19 at 3:25
• @DrSheldon - The idea that Planck units have some important meaning in quantum gravity is theoretical (for example, the idea that space is in some sense quantized so the Planck length is the smallest physically meaningful distance), but the Planck units themselves don't require any specific physical interpretation, they're just based on finding the unique combination physical constants such that when you multiply/divide them (with certain exponents), the result will be something with the appropriate dimension, like length or charge. – Hypnosifl Jun 1 '19 at 0:59
• You both are missing the point. Dimensional analysis is not sufficient; there may be an underlying relationship which requires an additional factor that we don't yet understand, but the aliens do. Such a factor invalidates what we presume the Planck units are. – DrSheldon Jun 1 '19 at 2:43
• @DrSheldon - By "underlying relationship" do you mean a physical relationship (for example laws that would allow you to derive the value of some constants from others), or do you just mean additional new physical constants, such that there might be alternate combinations of constants that could be multiplied/divided together (with various exponents) that would produce something with dimensions of length (or time, or charge, etc.) – Hypnosifl Jun 1 '19 at 3:22

Basically, the bigger economy will win. (Usually. Exceptions apply.)

First, you get commercial exchange between the two markets, simply because that ramps up faster than any technological cooperation.
Now you don't have any strong-arming; it's just that the larger economy is usually not too interested in dealing with the specifics of the smaller economy, so the smaller economy will be faster to adopt standards and regulations.

When the high end of the power structure finally manage to start technological cooperation, the markets have already agreed. Without any strong-arming involved, actually - though strong-arming can speed up the process.

Obviously, there are exceptions.
An alien race may not have an economy like we know it, though that would be a pretty different story than "let's build a spaceship together".
Or the aliens may not have standardized something that the humans did, but now that they see the benefits, they want a standard as well - that's the situation where the flow of regulations is independent of market size, or military/political power (heck, the military people usually prefer standards simply because things get much cheaper for them).
One side may intentionally make life difficult for the other. E.g. when technology levels are to wildly different that the advanced side does not want to share anything at all. Sure we can do cooperation, but the warp drive will be sealed off, and we intentionally use our own, incompatible measurement systems (and standards! never forget the destructive power of incompatible standards!) so that your attempts as reverse engineering will be that much harder... er I meant to say, you are not yet mature enough to wield the power of Warp Flight.

This would actually happen before the language barrier is broken. Math is a universal language and regardless of bases, any creature that has developed language and mathmatical skill to be considered intelligent will also be able to recognize certain mathmatical constants. For example, First Contact is likely not to be an exchange of words, but numbers. One of the first messages used by SETI was a series of pulses that cycled over the first 20* prime numbers. This is because the prime numbers are a mathmatical constant. No matter what you call your number 7, it's a prime number... even if it's 10 because you use a base 6 counting system, it is still the 4th Prime Number in the cycle (2, 3, 5, 7...) and is still the number that is one greater than 6 and one less than 8. Similarly, Binary, which is a base 2 counting system, is still going to find it's value for the base 10 7 (0000 0111) and it is still greater than 6 (0000 0110) and less than 8 (0000 1000).

The other reason this was used is because the order does not naturally occur in any phenomena. An intelligent being would be able to pick up the signal as something more important that wasn't just randomly made, but intelligently constructed and transmitted. It's random enough that if you weren't looking at it it would disappear, but patterned enough that if you understood math, you would get it right away.

They keep their units. Just like the meter is based on the circumference of the earth they have a similar unit of measure based on their planet. So you use meters on earth and zeters (or whatever alien measurement) on their planet.

If you need to use units for interstellar travel or collaborative projects between the species you use fundamental constants like planck length, the only true units.

Its important to note that there is a human standard called the Gauge Block. This would be the basis of any communication of industrial measurements to said aliens if we wished them to produce goods to our specifications. Conversely it would be appropriate to assume that the aliens, being space faring, would have a similar system of their own. There it becomes the mere question of which system are you using, and then you can tool to that system.

Gauge blocks are the main means of length standardization used by industry.

https://en.wikipedia.org/wiki/Gauge_block

This is how humans can specify a certain length in one country and assume those in another will produce it exactly to specification. Both sides would own a gauge block, or a gauge.

The blocks are so flat, and precise that putting two of them together makes them almost inseparable by pulling, and must be slide apart.

An important feature of gauge blocks is that they can be joined together with very little dimensional uncertainty. The blocks are joined by a sliding process called wringing, which causes their ultra-flat surfaces to cling together.

The easiest way to do so is to standardize on universe-invariant measurements - for example, mass is standardized on the mass of the proton, length is standardized on the wavelength of the radiation emitted by a particular electron transition in an atomic orbital (or perhaps on Planck Length), and time is standardized on light travelling in vacuum across the length standard (or perhaps Planck Time), electrical charge is standardized on the charge of the proton/electron. Everything else can be derived from those measurements.