Ampere Could Be Redefined After Experiments Track Single Electrons Crossing Chip

ananyo writes "Physicists have tracked electrons crossing a semiconductor chip one at a time — an experiment that should at last enable a rational definition of the ampere, the unit of electrical current. At present, an ampere is defined as the amount of charge flowing per second through two infinitely long wires one meter apart, such that the wires attract each other with a force of 2×10^-7 newtons per meter of length. That definition, adopted in 1948 and based on a thought experiment that can at best be approximated in the laboratory, is clumsy — almost as much of an embarrassment as the definition of the kilogram, which relies on the fluctuating mass of a 125-year-old platinum-and-iridium cylinder stored at the International Bureau of Weights and Measures in Paris. The new approach, described in a paper posted onto the arXiv server on 19 December, would redefine the amp on the basis of e, a physical constant representing the charge of an electron."

Comments

Re:Gravity is not constant...

[Immerman]

Sure, the same way they "weigh" things in freefall - measuring the radial forces necessary to keep it moving in a fixed circular path at a given speed. You can even vary the speed to get multiple measurements to reduce error. That may be as simple as a scale in a centrifuge, but does not depend on any way on potentially fluctuating gravitational field. It also incidentally directly measures inertial mass, rather than gravitational mass, which *apparently* is always present in precisely proportional amounts, but which we currently have no accepted theoretical reason to believe is a fundamental equivalence.