# Looking to nature for precision? **URL:** \ **Category:** Factual Questions\ **Created:** [June 18, 2014, 4:23pm UTC](https://boards.straightdope.com/t/looking-to-nature-for-precision/691077 "2014-06-18T16:23:32Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [June 18, 2014, 7:11pm UTC](https://boards.straightdope.com/t/looking-to-nature-for-precision/691077/21 "2014-06-18T19:11:14Z")
The [plaque on the Pioneer spacecraft](http://en.wikipedia.org/wiki/Pioneer_plaque#Hyperfine_transition_of_neutral_hydrogen) used a feature of the hydrogen atom to define a unit of length and a unit of time. A mass unit could be defined in a manner similar to the kilogram, i.e. an arbitrary volume of a reference substance (with the volume defined in terms of the aforementioned hydrogen atom feature). A temperature scale is easily devised base on the behavior of a reference substance, just as it is now: ice thaws at X temperature, and water boils at Y temperature. Pick whatever units you like, e.g. ice thaws at 0 Honeybadger, and water boils at 1 Honeybadger. You don’t even have to use water. You can use the melting/boiling points of iridium if you want to, although that will be considerably less convenient. As it turns out, there is a proposal in the works to revamp the SI system so it is defined entirely in terms of natural constants: > **[2019 revision of the SI](https://en.wikipedia.org/wiki/Proposed_redefinition_of_SI_base_units)** > > In 2019, four of the seven SI base units specified in the International System of Quantities were redefined in terms of natural physical constants, rather than human artefacts such as the standard kilogram. Effective 20 May 2019, the 144th anniversary of the Metre Convention, the kilogram, ampere, kelvin, and mole are now defined by setting exact numerical values, when expressed in SI units, for the Planck constant (h), the elementary electric charge (e), the Boltzmann constant (kB), and th Th... > [@Wikipedia](#): > > A committee of the International Committee for Weights and Measures (CIPM) has proposed revised formal definitions of the SI base units, which are being examined by the CIPM and which may be considered by the 25th ‘General Conference on Weights and Measures’, in 2014. The metric system was originally conceived as a system of measurement that was derivable from nature. When the metric system was first introduced in France in 1799 technical problems necessitated the use of artifacts as the prototype metre and kilogram. In 1960 the metre was redefined in terms of the wavelength of light from a specified source, making it derivable from nature, but the kilogram has been defined by an artifact ever since its introduction. If the proposed redefinition is accepted, the metric system (SI) will, for the first time, be wholly derivable from nature. ---
**Author:** ![MikeS](https://avatars.discourse-cdn.com/v4/letter/m/919ad9/32.png) [@MikeS](https://boards.straightdope.com/u/MikeS)\ **Post date:** [June 18, 2014, 7:12pm UTC](https://boards.straightdope.com/t/looking-to-nature-for-precision/691077/22 "2014-06-18T19:12:01Z")
> [@somepumpkin](#): > > Kilogram: The gram was originally defined in 1795 as the mass of one cubic centimeter of water at 4 °C, making the kilogram equal to the mass of one liter of water. [wikiP] > > … > > That quoted reference of the kilogram sounds “natural” enough to me. It’s natural, but it’s not nearly as precise as scientists want. For starters, water isn’t perfectly incompressible, so you have to specify the pressure is measured at. But your units of pressure themselves depend on the kilogram (pressure is force per area, and how you define a unit of force is dependent on how you define a unit of mass.) So there’s a bit of a circularity problem there. The current definition of the kilogram is based on a platinum-iridium bar in a vault in France instead. But, as alluded to above, there are currently attempts afoot to define the kilogram more precisely. There’s a conference later this year to discuss whether these experiments are precise enough to warrant redefining the kilogram. ---
**Author:** ![sbunny8](https://avatars.discourse-cdn.com/v4/letter/s/c77e96/32.png) [@sbunny8](https://boards.straightdope.com/u/sbunny8)\ **Post date:** [June 18, 2014, 7:29pm UTC](https://boards.straightdope.com/t/looking-to-nature-for-precision/691077/23 "2014-06-18T19:29:04Z")
If you want to make it **easy** , define a meter as 1/10,000,000th the distance from the north pole to the equator. Then define a kilogram as the mass of a cube of water 1/10th of a meter on each side. Then define a second as 1/86,400th of the average time from one noon to the next, where “noon” means the point in time at the middle of the day when a pole sticking out 90 degrees from a wall casts a shadow which points straight down. A hundred years ago, that’s pretty much what we had, and it’s pretty darn easy to reconstruct it, if you’re on Earth. If you want to make it hard, or if you’re not on Earth, you could use vibrations of Cesium atoms and Planck masses, et cetera, but that’s not what I gathered the OP was asking for. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [June 18, 2014, 7:30pm UTC](https://boards.straightdope.com/t/looking-to-nature-for-precision/691077/24 "2014-06-18T19:30:53Z")
The problem with using Planck units as the standard isn’t their extreme size: Something like the oscillation period of a cesium atom is already small enough that defining the second in terms of it requires numbers best expressed in scientific notation. And you only need those big awkward numbers once to define convenient units like seconds and meters, and then you measure everything else in the convenient units. The problem with the Planck units is that they depend on the gravitational constant, which, practically speaking, is really hard to measure precisely. Most fundamental constants are known to ten or more decimal places; the gravitational constant is known to only about four. Units really need to be defined in terms of the most precise experiments possible, not the least. ---
**Author:** ![here\_and\_there](https://avatars.discourse-cdn.com/v4/letter/h/f07891/32.png) [@here\_and\_there](https://boards.straightdope.com/u/here_and_there)\ **Post date:** [June 18, 2014, 7:32pm UTC](https://boards.straightdope.com/t/looking-to-nature-for-precision/691077/25 "2014-06-18T19:32:57Z")
Gravity is a good standard. We could throw some cannon balls from a tower that we liked and measure the time it took them to hit the ground. Then we would call that “the new second”. Then we would compare that, to a quartz crystal (?), and define “the new second” as “that many times, point something” the time “circles” of the quartz crystal. - And why not go straight for the time circles of the quartz crystal, right from the start? Because it would be more “steampunk” my way… 😃 ---
**Author:** ![CurtC](https://avatars.discourse-cdn.com/v4/letter/c/ce73a5/32.png) [@CurtC](https://boards.straightdope.com/u/CurtC)\ **Post date:** [June 18, 2014, 9:11pm UTC](https://boards.straightdope.com/t/looking-to-nature-for-precision/691077/26 "2014-06-18T21:11:47Z")
> [@MikeS](#): > > The current definition of the kilogram is based on a platinum-iridium bar in a vault in France instead. But, as alluded to above, there are currently attempts afoot to define the kilogram more precisely. But it would be easy enough conceptually - the mass of 6.02 x 10[sup]26[/sup] atoms of H[sub]1[/sub] ---
**Author:** ![nate](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/nate/32/13085_2.png) [@nate](https://boards.straightdope.com/u/nate)\ **Post date:** [June 18, 2014, 9:24pm UTC](https://boards.straightdope.com/t/looking-to-nature-for-precision/691077/27 "2014-06-18T21:24:12Z")
> [@CurtC](#): > > But it would be easy enough conceptually - the mass of 6.02 x 10[sup]26[/sup] atoms of H[sub]1[/sub] That’s what I think not a lot of people understand… it may be trivial to define a standard, but the true value of a standard is how accurately you can measure it and disseminate it throughout the world and how stable it remains over time. The attempts to replace the kg include the [electronic kg](http://www.nist.gov/pml/div684/grp05/kilogram.cfm), but it seems like that effort has been going on for decades. So it may be easy to define a standard or a unit, but actually realizing that unit as accurately as possible is a whole 'nother animal. ---
**Author:** ![Dr.Strangelove](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr.strangelove/32/6613_2.png) [@Dr.Strangelove](https://boards.straightdope.com/u/Dr.Strangelove)\ **Post date:** [June 18, 2014, 10:27pm UTC](https://boards.straightdope.com/t/looking-to-nature-for-precision/691077/28 "2014-06-18T22:27:17Z")
> [@CurtC](#): > > But it would be easy enough conceptually - the mass of 6.02 x 10[sup]26[/sup] atoms of H[sub]1[/sub] It’s hard to count atoms of hydrogen precisely, but relatively easy for silicon, since (due to the semiconductor industry) it’s now straightforward to produce large, perfect crystals of the stuff. Hence, one of the current kilogram redefinition efforts involves a [sphere of silicon](http://www.wired.com/2010/10/platinum-silicon-kilogram-standard/). ---
**Author:** ![MikeS](https://avatars.discourse-cdn.com/v4/letter/m/919ad9/32.png) [@MikeS](https://boards.straightdope.com/u/MikeS)\ **Post date:** [June 19, 2014, 1:05pm UTC](https://boards.straightdope.com/t/looking-to-nature-for-precision/691077/29 "2014-06-19T13:05:29Z")
> [@here\_and\_there](#): > > Gravity is a good standard. > > We could throw some cannon balls from a tower that we liked > and measure the time it took them to hit the ground. > Then we would call that “the new second”. As noted above, gravity is an awful standard. The acceleration due to gravity (“little _g_”) varies between different locations on the Earth by as much as 5 parts per thousand. The current standard for the second, on the other hand, is precise to within one part in one hundred billion. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [June 19, 2014, 2:36pm UTC](https://boards.straightdope.com/t/looking-to-nature-for-precision/691077/30 "2014-06-19T14:36:25Z")
Not to mention that the tower might settle, or change height with thermal expansion and contraction, and that it’d be really inconvenient for all of the scientists and engineers in the world to have to travel to that tower to calibrate their instruments. ---
**Author:** ![here\_and\_there](https://avatars.discourse-cdn.com/v4/letter/h/f07891/32.png) [@here\_and\_there](https://boards.straightdope.com/u/here_and_there)\ **Post date:** [June 20, 2014, 2:05pm UTC](https://boards.straightdope.com/t/looking-to-nature-for-precision/691077/31 "2014-06-20T14:05:28Z")
> [@MikeS](#): > > As noted above, gravity is an awful standard. The acceleration due to gravity (“little _g_”) varies between different locations on the Earth by as much as 5 parts per thousand. The current standard for the second, on the other hand, is precise to within one part in one hundred billion. Does gravity change over time, in the same place? If not, I can’t see why this wouldn’t work. … and the new standards don’t have to be better than the old standards. They just have to be good enough. [QUOTE=Chronos] Not to mention that the tower might settle, or change height with thermal expansion and contraction, and that it’d be really inconvenient for all of the scientists and engineers in the world to have to travel to that tower to calibrate their instruments. [/QUOTE] Ok… maybe the tower of Pizza was a bad choice :rolleyes:. I am sure there are ways to double check a towers height, and record its change over time. And I don’t think that, nowadays, scientist have to travel to Paris or wherever that kilo is… unless, of course, they can justify the expenses 🆒 . * * * The point here is, that it’s relatively easy to create standards. ---
**Author:** ![HoneyBadgerDC](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/honeybadgerdc/32/1033_2.png) [@HoneyBadgerDC](https://boards.straightdope.com/u/HoneyBadgerDC)\ **Post date:** [June 20, 2014, 3:19pm UTC](https://boards.straightdope.com/t/looking-to-nature-for-precision/691077/32 "2014-06-20T15:19:22Z")
Let me slighty change the question. Using a natural substance or phenomina along with the naked eye and somewhat primitive tecniques what are some of the most consistent or constant things in nature that could be used as some kind of standard and how close could they get, Lets use accurate to within .01 of an inch to be the highest allowable tolerance. One more question to with that. Suppose you found a seed or a mineral grain that fell with in the .01 tolerance range and you lined up 1000 of them, how far would you expect to be off assuming they were roughly equally distrubuted in tolerance. ---
**Author:** ![Dewey\_Finn](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dewey_finn/32/4222_2.png) [@Dewey\_Finn](https://boards.straightdope.com/u/Dewey_Finn)\ **Post date:** [June 20, 2014, 3:26pm UTC](https://boards.straightdope.com/t/looking-to-nature-for-precision/691077/33 "2014-06-20T15:26:22Z")
Again, I’d suggest a crystalline substance. ---
**Author:** ![HoneyBadgerDC](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/honeybadgerdc/32/1033_2.png) [@HoneyBadgerDC](https://boards.straightdope.com/u/HoneyBadgerDC)\ **Post date:** [June 20, 2014, 3:34pm UTC](https://boards.straightdope.com/t/looking-to-nature-for-precision/691077/34 "2014-06-20T15:34:21Z")
> [@Dewey\_Finn](#): > > Again, I’d suggest a crystalline substance. That was my first thought even though I know little to nothing about them. ---
**Author:** ![Furious\_Marmot](https://avatars.discourse-cdn.com/v4/letter/f/dfb087/32.png) [@Furious\_Marmot](https://boards.straightdope.com/u/Furious_Marmot)\ **Post date:** [June 20, 2014, 3:39pm UTC](https://boards.straightdope.com/t/looking-to-nature-for-precision/691077/35 "2014-06-20T15:39:17Z")
I am unaware of any naturally occurring crystals of a single, uniform size. What mineral do you propose using? ---
**Author:** ![Dewey\_Finn](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dewey_finn/32/4222_2.png) [@Dewey\_Finn](https://boards.straightdope.com/u/Dewey_Finn)\ **Post date:** [June 20, 2014, 3:54pm UTC](https://boards.straightdope.com/t/looking-to-nature-for-precision/691077/36 "2014-06-20T15:54:07Z")
No, you’re probably not going to find multiple examples of a crystal that are all the same size. But you might find one crystal that might be measured to a very high tolerance. ---
**Author:** ![SmartAlecCat](https://avatars.discourse-cdn.com/v4/letter/s/67e7ee/32.png) [@SmartAlecCat](https://boards.straightdope.com/u/SmartAlecCat)\ **Post date:** [June 20, 2014, 3:57pm UTC](https://boards.straightdope.com/t/looking-to-nature-for-precision/691077/37 "2014-06-20T15:57:12Z")
> [@here\_and\_there](#): > > Does gravity change over time, in the same place? Yes. Consider [GRACE](http://www.nasa.gov/mission_pages/Grace/overview/index.html): > [@](#): > > GRACE consists of two identical spacecraft that fly about 220 kilometers (137 miles) apart in a polar orbit 500 kilometers (310 miles) above Earth. GRACE maps Earth’s gravity field by making accurate measurements of the distance between the two satellites, using GPS and a microwave ranging system. It is providing scientists from all over the world with an efficient and cost-effective way to map Earth’s gravity field with unprecedented accuracy. The results from this mission are yielding crucial information about the distribution and flow of mass within Earth and its surroundings. > > The gravity variations studied by GRACE include: changes due to surface and deep currents in the ocean; runoff and ground water storage on land masses; exchanges between ice sheets or glaciers and the ocean; and variations of mass within Earth. ---
**Author:** ![Furious\_Marmot](https://avatars.discourse-cdn.com/v4/letter/f/dfb087/32.png) [@Furious\_Marmot](https://boards.straightdope.com/u/Furious_Marmot)\ **Post date:** [June 20, 2014, 4:22pm UTC](https://boards.straightdope.com/t/looking-to-nature-for-precision/691077/38 "2014-06-20T16:22:54Z")
> [@Dewey\_Finn](#): > > No, you’re probably not going to find multiple examples of a crystal that are all the same size. But you might find one crystal that might be measured to a very high tolerance. How can we measure something to a high tolerance using only primitive techniques, as describe by the OP? Or do you mean we should find a crystal that had been measured before the rulers all disappeared and use that as the basis for a sytem of measurement? In that case, why should it be a crystal? ---
**Author:** ![Dewey\_Finn](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dewey_finn/32/4222_2.png) [@Dewey\_Finn](https://boards.straightdope.com/u/Dewey_Finn)\ **Post date:** [June 20, 2014, 4:31pm UTC](https://boards.straightdope.com/t/looking-to-nature-for-precision/691077/39 "2014-06-20T16:31:29Z")
The OP modified the question [here](http://boards.straightdope.com/sdmb/showthread.php?p=17479000#post17479000), so that we are now seeking “some of the most consistent or constant things in nature that could be used as some kind of standard.” Presumably this revised situation means that the rulers are still available to be used for measurement. ---
**Author:** ![HoneyBadgerDC](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/honeybadgerdc/32/1033_2.png) [@HoneyBadgerDC](https://boards.straightdope.com/u/HoneyBadgerDC)\ **Post date:** [June 20, 2014, 4:40pm UTC](https://boards.straightdope.com/t/looking-to-nature-for-precision/691077/40 "2014-06-20T16:40:37Z")
> [@Furious\_Marmot](#): > > How can we measure something to a high tolerance using only primitive techniques, as describe by the OP? > > Or do you mean we should find a crystal that had been measured before the rulers all disappeared and use that as the basis for a sytem of measurement? In that case, why should it be a crystal? That came back to bite me in the ass. By primitve I would say something like a calipers with a capacity for tolerance of .001 even though a measurement standard has not been established yet. [Previous page](https://boards.straightdope.com/t/looking-to-nature-for-precision/691077.md?page=1) [Next page](https://boards.straightdope.com/t/looking-to-nature-for-precision/691077.md?page=3)