Delayed Choice Quantum Eraser Experiment Explained
In the Delayed Choice Quantum Eraser Experiment Explained video, respect your intellect explains how the delayed choice quantum eraser (DCQE) experiment shows that causality can travel faster than light. I placed a comment where I suggested this was not necessarily a violation of causality according to relativity. This is also covered in a more elaborate article: “Causality”
Check the lights perspective
My original respons is below and in the linked comment above that includes the whole conversation. I commented somewhere in August 2019 and in the mean time, I also created a somewhat more informed article on this issue, see “Causality”.
Let's look at the experiment from the light's perspective.
According to relativity, light does not experience time: its creation, the events on its way and its destruction happen simultaneously. This can be interpreted as the light's wave function "knowing how and where it will die (collapse) as soon as it comes into existence". If light knows it entire, timeless existence, that might explain why it eerily "knows" the scientist flipped the switch and changes its properties from, say, wave-like to particle-like.
The scientist does have mass and does experience time. For the scientist, creating the light happens before the scientist decides to alter part of the light's path and that happens before the eventual destruction on a sensor. But intervals between (and possibly ordering of) these events are only relevant for the scientist: not to the light.
If this all sounds spooky, it is because we don't give relatvitiy the weirdness-credit it deserves!
Though the timeless perspective of light could explain the link between the measurements from a relativistic point of view: it raises more questions than it answers and makes nature even weirder than I already thought it was... But I guess that's the fun of it.
The photons are massless, and thus can travel at C... The same thing happens not only with electrons, which have mass, but also with molecules like Buckminsterfullerene. Does your explanation still work?
@Aaron It depends on what is mean by "the same thing".
It is absolutely True that particles with mass also show interference patterns under the right conditions and that the experimenter can change these conditions to make the patterns disappear. That however, in my humble opinion, is not what this experiment is about. This experiment is designed to show that the observer can change conditions in a way that defies the classical senses of locality and causality. And it does: for photons. My argument is that the outcome does not necessarily contradict special relativity: for photons.
Most implementations of the Bell experiment use photons. 1 The quantum eraser combines a two split with a crystal that creates entangled particles from incoming particles and uses switchable split-mirrors and such. I have no information about setups that can do all this for, say, electrons.2 Until we come up with such an equivalent experiment, I have no idea if "the same thing" happens to particles with mass. The occurrence of interference patterns for a type of particle, does not imply that non-local behavior can be observed for those particles. These are separate aspects that need separate verification or falsification. This experiment correlates them, but only for photons.
If we do come up with an experiment using mass-particles, it could give us some interesting information. I am going to be wildly speculative here. Maybe the "fabric" of wave functions behaves somewhat like "light", in the sense that it does not experience time until the function collapses. This could remove the observed or perceived contradiction between quantum mechanics and relativity and open up interesting research.