(July 12, 2020 at 12:14 pm)polymath257 Wrote: Sigh.
The problem is that people want to use classical notions, such as waves and particles, as opposed to the actual quantum description.
All *quantum* effects go forward in time. This is true even in the quantum eraser. But, if you insist on thinking of things classically, the results will appear paradoxical.
All paths of the quantum eraser need to be taken into account, including phase information. And, yes, if 'which path' information exists, then no interference pattern occurs. And if 'which path' information is not, then a pattern is seen. This is well modeled in QM and with only forward influences in time.
'particle' and 'wave' (classical) I agree they are metaphors which have properties that relate to tangible things we experience 'classically' - water wave, sound wave, projectile etc where the waves are in fact series of particles acting on each other. experimental results show that whatever the 'particles' are at a fundamental level they display properties that relate to things we can perceive and illustrate - eg. a photon, or electron, interacts with the back screen in the double slit experiment and leaves a mark such as that we would expect if we launched a tennis ball at it.
but the 'wave function' is a different beast. it dictates the range of potential properties of the particle which only becomes reality when it is 'measured' ie interacts with the environment. where we see interference, we also see that photons arrived as quantized energy chunks, but their distribution is dictated by the wave function in the absence of the which-path information.
