4 ms·
So there was a definition of a kilogram based on an actual physical thing with an arbitrary amount of mass. Does this new definition essentially try to approxi
by turdnagel 8y ago
So there was a definition of a kilogram based on an actual physical thing with an arbitrary amount of mass.
Does this new definition essentially try to approximate that mass as close as possible? What is the margin of error there?
I would love to know this for a second as well, although I don't know what we used to measure a second before we locked it to the vibrations of a cesium atom.
- bcoates 8y agoThe Earth?
- tialaramex 8y agoYes. In two ways. First, the assumption was that the Earth's rotational period was 86400 seconds. Mechanical clocks had given us no reason to doubt this was so. By the mid-20th century quartz timers were able to discern that the Earth has longer and shorter days, as numerous factors cause the spin to speed up or slow down. Instead of a single day the second was taken to be one 86400th part of an average day over the whole year. A few decades later the availability of atomic clocks made this seem silly and we uncoupled the second from the variably spinning Earth. The completely arbitrary seeming atomic clock definition of a second was basically chosen to be indistinguishable from our last guess at the "averaged over a year" second.