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:
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.
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.
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.
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?
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, 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.
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.
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.
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.
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.
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.
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?
The OP modified the question here, 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.
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.
.