I thought the most surprising thing about wave/particle duality is that the act of observation itself is what causes the waveform of particles to collapse. Do we know of a mechanism for that? Are we not still surprised that you change the outcome of events by changing where you look?
No one (today) really believes that it is the observation that 'causes' a change in the experiment. What is happening is that the observer is becoming entangled with the experiment.
I don't really understand the difference. It sounds like you're saying the act of observation entangles you, and the entanglement is the cause of the collapse. It's just adding one more link in the causal chain.
The difference is that there is no special thing called 'collapse'; when you write down the laws of physics, it doesn't exist. It's an emergent phenomenon, and it's not surprising that it happens, although it's very counterintuitive _if_ you are starting in the naive model of treating quantum waves like classical ones.
As I understand it, collapse is an artifact of the necessity to derive classical results from an experiment. You can think of it as "at a certain scale, calculating this as a quantum system as opposed to classical is no longer worth it." But it's of course still a quantum system, because everything is quantum all the time.
I don't think so. The double-slit experiment demonstrates light acting as a wave in some circumstances and as individual photons in others [1].
> the basic version of this experiment, a coherent light source, such as a laser beam, illuminates a plate pierced by two parallel slits, and the light passing through the slits is observed on a screen behind the plate.[5][6] The wave nature of light causes the light waves passing through the two slits to interfere, producing bright and dark bands on the screen – a result that would not be expected if light consisted of classical particles.[5][7] However, the light is always found to be absorbed at the screen at discrete points, as individual particles (not waves); the interference pattern appears via the varying density of these particle hits on the screen.[8] Furthermore, versions of the experiment that include detectors at the slits find that each detected photon passes through one slit (as would a classical particle), and not through both slits (as would a wave).[9][10][11][12][13] However, such experiments demonstrate that particles do not form the interference pattern if one detects which slit they pass through. These results demonstrate the principle of wave–particle duality.[14][15]
This is the part I'm talking about, mainly.
> However, such experiments demonstrate that particles do not form the interference pattern if one detects which slit they pass through.
Once they are measured, you know where they are and they stop acting like a wave.
Well, as I understand it the problem is if you measure the slit the photon passes through, then the superposition is no longer "left slit or right slit", it's "left slit and sensor or right slit and not sensor", and the slit/sensor paired configuration can't interfere with itself anymore because the sensor state is different. In other words, this is what you'd expect to see collapse or no collapse.
For instance, consider https://en.wikipedia.org/wiki/Delayed-choice_quantum_eraser which demonstrates that the sensor state has to be part of the superposition instead of causing an irreversible collapse: if you store the detected slit until the photon hits the back wall, then delete it, an interference pattern emerges once again.
