6k views

### Why aren't particles constantly “measured” by the whole universe?

Let's say we are doing the double slit experiment with electrons. We get an interference pattern, and if we put detectors at slits, then we get two piles pattern because we measure electrons' ...
1k views

### Why doesn't a typical beam splitter cause a photon to decohere?

In many experiments in quantum mechanics, a single photon is sent to a mirror which it passes through or bounces off with 50% probability, then the same for some more similar mirrors, and at the end ...
573 views

### Why doesn't superselection forbid almost every superposition?

A superselection rule is a rule that forbids superposition of quantum states. As stated by Lubos here, one cannot superpose states with different charges because of the conservation of charge: An ...
1k views

### When light reflects off a mirror, does the wave function collapse?

This question is specific to the Copenhagen interpretation, which states that the wave function collapses on interaction. If we have a beam of light reflected off a mirror, whether you see this light ...
173 views

### How do photons interact with a very fine edge?

Suppose you have some material which has a low reflectance and is opaque to an incomming photon when the angle of incidence is small. Now take that material and make a narrow (20:1 width:length ratio ...
124 views

### Are superpositions contagious?

Does quantum mechanics really predict that a particle prepared in a state of superposition of spin will result, after being measured by an appropriate instrument (Stern-Gerlach device), in a ...
160 views

### How do “many worlds” theorists explain particle double-slit interference patterns?

In the past couple of weeks I’ve re-watched Sidney Coleman’s wonderful 1994 lecture “Quantum Mechanics” in Your Face” and Sean Carroll’s 2019 Google talk “Something Deeply Hidden: Quantum Worlds & ...
298 views

### Is an atom's photon recoil on absorption affected by a beam splitter?

Consider a photon with momentum p approaching a half-reflective mirror. After encountering the mirror it is in a superposition of momentum +p and -p and the mirror (we presume) is in a superposition ...
214 views

### When does Quantum Mechanics Measurement lead to Mixed State

Consider the context of the Stern-Gerlach experiment. As is stated on numerous sources (e.g. Feynman Lectures, MIT Lecture), a silver atom in the state of $\vert+z\rangle$ that is put through a Stern-...
401 views

### Meaning of phase relationship for a superposition of states

I have studied an introductory course in quantum mechanics, and yet I still do not understand the significance of a phase difference between quantum states that a system is in a superposition of. In ...
303 views

### How does a reflected photon keep its entanglement [duplicate]

I'm curious how a photon from an entangled pair, travelling through say a delayed choice quantum eraser experiment, can bounce around between mirrors but remain entangled with its partner photon, when ...
140 views

### Why can’t macroscopic objects like apples be isolated but a photon can?

I read that the reason that macroscopic superpositions decohere is because it’s difficult/impossible to isolate macroscopic objects from the environment. Why is this so difficult/impossible and why ...
138 views

### In the double-slit experiment, why don't slits destroy interference pattern?

In the double-slit experiment with electrons, if a detector is placed in one of the paths to show where the electron is passing, the wave nature of the particle is lost and you have no interference. ...
109 views

### Double slit experiment: why does the barrier between the slits not collapse the wave function?

During the double slit experiment the electron passes through both slits, how come the material between the two slits does not collapse the wave function and we get an interference pattern? On the ...
96 views

### The wavefunction's knowledge of its surroundings

This seems to me it must be trivial, but I have not been able to grasp it. As I understand it, the wavefunction crucially depends on its immediate surroundings, whether it be a nucleus, a box, etc. ...

15 30 50 per page