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Perfect Silicon Sphere to Redefine the Kilogram
MrCreosote writes "The Age reports optical specialists at CSIRO are helping create a new standard for the kilogram, based on a precise number of atoms in a perfect sphere of silicon. This will replace the International Prototype, a lump of metal alloy in a vault in Paris."
No, it's impossible. What they -really- mean is that it'll be perfect as far as we are able to measure it. And it has absolutely nothing to do with what is really important here: They are counting the atoms of silicon in a kilogram and will use that measurement as the basis for the kilogram, instead of some lump of metal in a vault.
The kilogram will not change, only a proposed scientific definition of it.
The sphere doesn't mean -anything- except that it'll weight exactly a kilogram and be amazingly round.
There's either a lot of media spin, or someone's attempt to get his work recognized and used. From what I can see, there's not a single soul that has dedicated to USING this new scientific definition, other than those directly involved with the project.
"If you make people think they're thinking, they'll love you; But if you really make them think, they'll hate you." - DM
The point of having a physical object is that it can be used as a root for calibrating devices. From there you can calibrate more devices on each other. The further you get, the less likely you are to be precise, but the chances are pretty good that little deviations up and down will cancel out overall. But it's absolutely important to have an exact starting point, and a physical object is the only way to do that.
It's a lot easier to measure a large object than a small one and multiply it, since a small error will also multiply out. What I don't get is how they intend to build an exact number of atoms into the sphere. You would need some other exact measurement, like number of electrons for calculating precise electrolysis procedures.
Sam ty sig.
This method works along essentially the same principles as the Watt Balance. In it, a superconductor of a known mass is placed within a superconducting coil.
If you have a lump of anything of a known mass, why bother with the rest?
Trust the Computer. The Computer is your friend.
You are confusing mass and weight.
;-)
Mass = how much matter there is in an object.
Weight = how much pull does a particular gravity (like Earth's g) has on that quantity of matter.
That's why you could be floating (weightless) in a space ship without having lost any of your fingers or other parts of your body (mass)
Ok, people are giving snarky answers here, but I'll try to give you a more straight answer.
The only way we have to keep a standard unit is to have an object with that unit and call that the standard. Let's say you were building some sort of a scale that would measure weight in kilograms; you'd have to calibrate it first. This means that you'd have to find an existing weight that was one kilogram, put it on the scale, and mark that this weight is a kilogram. But then how do you find a 1 kilogram weight? You have to measure it on some scale that's already calibrated correctly. This chain continues, and has to end somewhere.
So the two questions I anticipate are:
To answer the first question, a scale would be harder to maintain accurately. It could break, and calibrations don't hold forever. You'd have to re-calibrate it every so often, and how do you do that without an object known to be exactly 1kg?
The answer to the second question (which I imagine might have been your question all along) is a little more complicated. Let's imagine that we have no exact 1kg object stored anywhere that we use as the standard. So one guy in a lab is using an iron ball as his 1kg weight, calibrating scales with it, and selling scales to others. The iron ball slowly rusts over time, and the weight of the ball changes a little. Someone takes one of the scales calibrated with the rusty balls and does the same thing, but this time with his own hunk of iron, but the environmental conditions in this guy's lab aren't as controlled, and he tends to get water condensation on his iron ball, meaning it rusts faster and each calibration varies depending on how much water has collected.
Now, imagine it keeps on like this for 75 years, with different guys selling scales, getting their original measure from someone else, and then using their less-than-perfect means to continue calibrating and making scales. After 75 years, there are some drastically different "kilograms" floating around I buy a scale, measure out 1 kilogram, take it to a different scale and get 1.5 kilograms, while another says .75 kilograms. In this case, who's kilogram is "correct"? When the issue was raised, people would say, "Oh, if only we had a standard "kilogram" to compare them to!"
And so we have someone keep a physical reference object under very controlled conditions and of materials that will prevent corrosion or other corruption to the material.