Fungibility

TBoF 

p. 289

"...for any fungible collection of instances of a physical object, some of their attributes must be diverse. This is known as the 'Heisenberg uncertainty principle'

p. 291

"The term 'uncertainty principle' is misleading... The diversity of attributes... is a physical fact, independent of what anyone knows or feels."

"Thanks to string internal interference that it is continuously undergoing a typical electron is a irreducibly multiversal object, and not a collection of parallel-universe or parallel-histories objects... it has multiple positions and multiple speeds without being divisible into autonomous sub-entities eachof which has one speed and one position."

p. 297

Brilliant description of why, in a Mach-Zehnder interferometry experiment, the independent photon paths do not entangle with the photon that reflects, which depends on fungibility, and the indeterminacy of the original energy of the mirror. The difference in the momentum of the mirror, after the photon strikes, is tiny compared to the original indeterminacy of the momentum; the chance of entanglement is about the same a the tiny-ness of this difference.