Question about Quantum Eraser

[bennyboy]

Nope, because observation of matter by beings means that the matter necessarily needs to interact with the matter the beings are made of. That it then behaves differently is not magic. The extent to which it behaves differently may be surprising, but not magic.

Quantum level physics is not something I really know anything about.  But if my basic understanding is right, observing things at the quantum level changes things at the quantum because we observe things by watching things bounce off things.  This isn't a problem if you are observing light bounce off an elephant or even a single  cell observed through a microscope because light has little immediate effect on the object observed. But to "see" a subatomic thing you must bounce something close to its own mass off of it because there isn't anything smaller to throw at it. It's like if you could only see elephants by bouncing cars off of them or hitting them with fire hoses.

(Edit) Or if we could only see elephants by seeing the effects of elephants running into largish thins like six foot fences.  Sort of like the way we see wind.  But of course the wind is affected by moving other things around.

Is that roughly right?  If not, please explain.

This isn't so much about the detection as about the nature of the photons under different observational conditions.  You are talking about the uncertainty principle I think.  Or I'm wrong.  One of those.

[LastPoet]

It has something to do with cats and attaching bombs with quantum detonators to them. I for one disaprove of this method.

[Anomalocaris]

Okay, if what you suspect is right, then that means you could, at least sometimes, infer whether a photon was acting as a particle or a wave from the resultant spread pattern.  But I guess that's true anyway-- if you are engaged in an experiment, and I walk into the room after it's done, I assume I will be able to see a 2-stripe pattern, and say, "Aha!  I know you were detecting activity at the slits!"  If certain apparatus could also do this, then the results themselves might actually be useful.

My problem is that if you could do this experiment at very long range, it seems you could actually send information at a speed faster than light.  You could, for example, send a burst of photons from the moon, and then use their entanglement with the transmitting apparatus to set their state just before they arrive at a receptor.  Isn't this "illegal"?

If you want to trip me out, show me a 4-state superposition (essentially a uniform distribution, right?), that only resolves itself to me when I look up my random symbols in a book.

I think what you are trying to ask is, can you affect the state of one of the two entangled particle in such a way as to instantly sets the state of the other some distance away.  If you do this you are communicating faster than speed of light.    I believe the answer is no.  You can only observe the state of one so as to collapse the probabilities of the state of the other.   But no new information that is predicated upon the outcome of your observation can possibly influence any event at the location of the other particle before light had time to travel from one particle to another.

(Looking nervously in fear of contradiction at Alex)

[bennyboy]

No, I'm not asking that, actually. I'm asking if you collapse one of an entangled pair, is the other collapsed likewise? Let's say I have an entangled pair of photons, and one goes off to chamber A, which has detectors in front of a double slit, and one goes to chamber B, which doesn't have detectors, will chamber A show a dual stripe and chamber B show an interference pattern? Or will one photon's "waviness" or "particleness," which result from the observation or lack of it, automatically force the other particle either to act as a particle or a wave as well, with regards to the interference pattern that results?

Okay, it's kind of like what you said. But what I'm really asking is whether the collapse of one wave function of an entangled pair auto-collapses its entangled partner.

[Anomalocaris]

I think the answer would be yes if the wave functions in question describes local measurable properties which are governed together by some physical law.  So for example, if you have two particles that observe Pauli's exclusion principle, and they have the same quantum numbers in all other respects except spin state, then you know if you determine the spin state of one, then you also collapse the spin state of the other.

But I am not sure the properties you ascribe to the two particles are governed by some law that would necessarily force one particle to behave in someway relative to the know property of the other.

Btw, this is from someone who took his last physics class 20 years ago and has been in industrial and management consulting during the last 17 years. So don't get on my case too hard if I am wrong.

[Anomalocaris]

Delete duplicate

[bennyboy]

I think the answer would be yes if the wave functions in question describes local measurable properties which are governed together by some physical law.  So for example, if you have two particles that observe Pauli's exclusion principle, and they have the same quantum numbers in all other respects except spin state, then you know if you determine the spin state of one, then you also collapse the spin state of the other.

But I am not sure the properties you ascribe to the two particles are governed by some law that would necessarily force one particle to behave in someway relative to the know property of the other.

Btw, this is from someone who took his last physics class 20 years ago and has been in industrial and management consulting during the last 17 years.   So don't get on my case too hard if I am wrong.

I just parrot what I see in youtube videos, which are very interesting but not a substitute for an actual education in physics.

I think in the last 20 years, a LOT of new double-slit experiments have been done, and I believe Quantum Erasing might be one of them, not sure though.

[Anomalocaris]

But I don't think any quantum mechanics experiment in the last 20 years have suggested information could be generated and propagated faster than speed of light.

[bennyboy]

But I don't think any quantum mechanics experiment in the last 20 years have suggested information could be generated and propagated faster than speed of light.

I dunno.  "Backward in time" is pretty fast.