/sci/ - Science & Math » Thread #13713747

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Anonymous Mon 04 Oct 07:55:24 2021 No.13713747 View Reply Original Report

Quoted By: >>13716876 >>13716970

Why does observation collapse the wave function of a particle? Are you telling me particles are aware of humans?

Anonymous

Anonymous Tue 05 Oct 2021 02:43:41 No.13716702 Report

Quoted By: >>13716712 >>13716744

>>13716696
>QM itself prevents local hidden variables.
OK, then how do the entangled photons "keep track" of the (apparently predestined?) spin?

Again, not disagreeing, just genuinely ignorant.

Anonymous

Anonymous Tue 05 Oct 2021 02:48:43 No.13716712 Report

Quoted By: >>13716728

>>13716702
>the entangled photons "keep track" of the (apparently predestined?) spin?
It would only 'keep track' if the entanglement isn't destroyed by some other process. For that to happen, these photons would have to be very isolated from the environment so as to prevent any decoherence. But really, you can't make statements like 'the electron keeps track' etc. in the copenhagen interpretation. In CI, the wavefunction is just a way the observer keeps track of information, it's not something real.

Anonymous

Anonymous Tue 05 Oct 2021 02:55:54 No.13716728 Report

Quoted By: >>13716744 >>13716761

>>13716712
>it's not something real.
OK, then why do they have complementary spin?
I'm not hearing an answer to this basic question, and I guess I'm really not expecting one.
I kind of assume there's no ready reconciliation between a lack of local hidden variables and the consistently complementary spins, which (I guess) is why people keep calling it "spooky".
Unless, of course, you _are_ arguing for action at a distance?

Anonymous

Anonymous Tue 05 Oct 2021 02:56:20 No.13716731 Report

Quoted By: >>13716797

Anons, help a libarts fag out: What does 'information' mean in the quantum context? I only understand it in the Shannon sense with regards to a channel carrying capacity which is dictated by the 'maximal entropy' possible in that channel.
>>13715138
This is how I always understood it. It's sort of like if I ask my friend "hey, we still on for Saturday night?" the mere act of asking could change their answer "Oh shit, I forgot, yeah of course! Good thing you reminded me I was about to organize a different thing."
>inb4 someone says "sounds like a shit friend" instead of just accepting it as a naive analogy for my understanding of what's happening

Anonymous

Anonymous Tue 05 Oct 2021 03:01:41 No.13716744 Report

Quoted By: >>13716755

>>13716702
In all honesty we don't know. CI doesn't claim to answer that, but it isn't falsified by its existence either. It cares about what we can measure, the results.
What we do know is that there is some character to quantum systems that cannot be explained by classical/"local" approaches.

>>13716728
>Unless, of course, you _are_ arguing for action at a distance?
Not him but it's not exactly something we can claim doesn't exist.
"Action" may be pushing it though.

Anonymous

Anonymous Tue 05 Oct 2021 03:05:41 No.13716755 Report

Quoted By: >>13716797

>>13716744
>we don't know.
Case closed, but it sure took a long time for us to get there, huh?
Ctrl-F4.

Anonymous

Anonymous Tue 05 Oct 2021 03:08:42 No.13716761 Report

Quoted By:

>>13716728
>>13716728
>OK, then why do they have complementary spin?
For you to know that they have complementary spin, you need to measure both the spins in the first place. If the observer knows that the photons are entangled in the first place, then his initial knowledge of the unmeasured system would be represented by a wave function of the form $\frac{|1 \rangle |0 \rangle + |0 \rangle |1 \rangle}{\sqrt{2}}$ (assume that both the spins are in the x-direction). Once the obsever measures the spins of both the electrons in the x-direction, the only results he can get are either 0,1 or 1,0 - that is just the definition of what it means to be entangled. If instead of measuring both the particles, suppose the observer only measures one particle and gets the result 0. Then even without measuring the other particle, he could conclude that IF he did measure the other particle, he would get a 1. That's all there is to it. In the copenhagen interpretation, you simply don't talk about what is 'really going on' or things like that because if you do, you be lead to make wrong conclusions (conclusions inconsistent with experimental evidence). That is what things like the double-slit experiment are meant to show.

Anonymous

Anonymous Tue 05 Oct 2021 03:25:31 No.13716797 Report

Quoted By: >>13716814 >>13716843

>>13716731
"Information" in the quantum sense is not terribly different, it's just that things are done in "quantum bits" instead of bits. This means that the storage states can be superpositions of 1 and 0 instead of just one or the other and they can be entangled with other qubits.
One important takeaway from quantum information theory is that a communication over a quantum channel by wave function collapse (teleported, as it were) cannot be decoded without a corresponding signal over a classical channel to convey what the sender got from their measurements. Information is thus still limited by the speed of light.

>>13716755
Sure, but it's not incompatible with CI which is where I hopped in.

Anonymous

Anonymous Tue 05 Oct 2021 03:36:43 No.13716814 Report

Quoted By: >>13716849 >>13716850

>>13716797
you lost poor brainlet me at "can be entangled with other qubits", kek so please excuse me if what I ask next is infuriating either in it's ignorance or just plain being wrong...
Superimposition is the state of not being a 1 or a 0 right? I remember some Suskind lecture where he giving the example of if you put a single particle in a magnetic field to influence the 'spin' that the particle would give off a photon and the power of that photon would tell you what the spin of the particle was before you exerted a magnetic field on it to 'observe it'. So lets say a 'left' spin could be 1, and a 'right' spin could be 0? Am I on the right track?
Now, in that example, the photon is part of measuring it through a 'classical channel' right?
Anyway, I still don't understand how they can get 'entangled' with other qubits...

Anonymous

Anonymous Tue 05 Oct 2021 03:53:14 No.13716843 Report

Quoted By: >>13716860

>>13716797
>Sure, but it's not incompatible with CI which is where I hopped in.
Then why did Einstein use it as a critique of CI?

Anonymous

Anonymous Tue 05 Oct 2021 03:59:05 No.13716849 Report

Quoted By: >>13717100

>>13716814
>Anyway, I still don't understand how they can get 'entangled' with other qubits...
Ultimately, you get entanglement because of the existence of superpositions. In turn, you get superpositions because the observables in Quantum mechanics are matrices instead of numbers and hence don't necessarily commute i.e. if the observables are the matrices A and B, then AB is not necessarily equal to BA (the Heisenberg uncertainty principle for example states that the position and momentum observables don't commute). As a consequence of this non-commutativity, when you have a state where the value of one observable is sharp, i.e. if you have a state which is an eigenvector of one of the observables, it need not be an eigenvector of some other observable - instead, it will be a linear combination of eigenvectors, which is what a superposition is.

Anonymous

Anonymous Tue 05 Oct 2021 03:59:24 No.13716850 Report

Quoted By: >>13717100

>>13716814
Superposition is a state of being some combination of basis states. "0" and "1" states of spin are the simplest to deal with (and what most quantum computing is based around) but you can get more complex systems. You're on the right track with your example, yeah.
The "how" of entangling is complicated, but it usually comes down to getting two particles produced from one event/interaction (and then NOT TOUCHING THEM or they'll collapse (decoherence)). I'm not actually sure how they even use them in quantum computing, I just know that they do.

The classical channel thing comes into play with communication by entangled particles. Say person A and person B each take one particle of an entangled pair. A can take a qubit and combine it with their particle to influence B's particle as well, but the "sent" qubit can only be determined by B after A tells them what they measured on their particle.

Anonymous

Anonymous Tue 05 Oct 2021 04:02:37 No.13716860 Report

Quoted By:

>>13716843
Because he felt it was insufficient.
While CI pretty much says "look we get results we don't care HOW this works under the hood," Einstein wasn't satisfied with that. Especially since the non-local character of the phenomenon flew in the face of how he believed reality should operate.

Anonymous

Anonymous Tue 05 Oct 2021 04:07:02 No.13716867 Report

Quoted By: >>13716868

>>13716677
>This is just a preservation of correlation as a I said earlier.
pseud.

Anonymous

Anonymous Tue 05 Oct 2021 04:09:08 No.13716868 Report

Quoted By: >>13716871

>>13716867
??? That is the prevalent explanation of the 'non-locality' of entanglement. That it is just the preservation of correlations. If you think I'm wrong, explain why.

Anonymous

Anonymous Tue 05 Oct 2021 04:10:46 No.13716871 Report

Quoted By: >>13716885

>>13716868
>??? That is the prevalent explanation of the 'non-locality' of entanglement.
no. its not. i read Nature. One electron sees what happened to the other and changes its state accordingly over any distance at infinite speed.

Anonymous

Anonymous Tue 05 Oct 2021 04:12:10 No.13716876 Report

Quoted By:

>>13713747
>Why does observation collapse the wave function of a particle? Are you telling me particles are aware of humans?
because particles dont really exist, they are just detection events. only the wave exists.

Waves can have energy put into or taken out of them only in discrete quantities. When you 'see' a particle what you are seeing is that wave emit energy. Inside the wave all the energy of all the particles is homoginous. A single particle makes a wave existing in all places along that waves path, untill it is detected, the detection event then makes 'the particle exist in the observed location'.

This is the truth the quantum memers dont want you to know.

Anonymous

Anonymous Tue 05 Oct 2021 04:15:16 No.13716885 Report

Quoted By: >>13716903 >>13716930 >>13716983

>>13716871
Ok, I think you're trolling but anyway, there is no real 'state' in the copenhagen interpretation it is just a way of quantifying an observer's information of the system. So there is no superluminal collapse either because the 'collapse' is just what happens when the observer updates their information.

Anonymous

Anonymous Tue 05 Oct 2021 04:23:19 No.13716903 Report

Quoted By: >>13716907

>>13716885
>there is no superluminal collapse
read Nature.

Anonymous

Anonymous Tue 05 Oct 2021 04:25:25 No.13716907 Report

Quoted By: >>13716951

>>13716903
Read a textbook on quantum mechanics first.

Anonymous

Anonymous Tue 05 Oct 2021 04:32:44 No.13716930 Report

Quoted By: >>13716936

>>13716885
i think you know very well that he's trolling but some deep insecurity is preventing you from committing to a position that you know is perfectly safe, because the mere logical possibility of being wrong about anon poses enough threat to give you reservation. this is a sickness

Anonymous

Anonymous Tue 05 Oct 2021 04:34:24 No.13716936 Report

Quoted By: >>13716956 >>13716976

>>13716930
Take your meds lmao

Anonymous

Anonymous Tue 05 Oct 2021 04:39:01 No.13716951 Report

Quoted By:

>>13716907
>Read a textbook on quantum mechanics first.
listen, your interpretation is contrary to Copenhagen, Einstein, and Nature. You can insist all you want, but your interpretation is pseud bullshit.

Anonymous

Anonymous Tue 05 Oct 2021 04:39:48 No.13716956 Report

Quoted By:

>>13716936
please respond

Anonymous

Anonymous Tue 05 Oct 2021 04:43:28 No.13716970 Report

Quoted By:

>>13713747
You're brain takes time to process stuff so things seem shorter. Like if a horse did the double slit experiment and can't measure things the electrons would probably still be chaotic too.

Anonymous

Anonymous Tue 05 Oct 2021 04:45:58 No.13716976 Report

Quoted By:

>>13716936
please respond

Anonymous

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Anonymous Tue 05 Oct 2021 04:53:31 No.13716983 Report

Quoted By: >>13716990 >>13717028

>>13716885
>there is no real 'state' in the copenhagen interpretation it is just a way of quantifying an observer's information of the system
Alright.
>So there is no superluminal collapse either because the 'collapse' is just what happens when the observer updates their information.
Not quite. Getting the information necessitates interaction with the system, and that interaction does affect the other end. Call it collapse, update, or donut, it happens all the same.
See Bell's Inequality for proof that the information cannot simply be embedded in the particle.

Anonymous

Anonymous Tue 05 Oct 2021 04:59:23 No.13716990 Report

Quoted By: >>13716994

>>13716983
"Getting the information necessitates interaction with the system, and that interaction does affect the other end."
ok i'm not him but it sounds like you're saying it's impossible to read the output of a light sensor without interacting with a laser beam? aren't you supposed to design the experiment so that doesn't happen? like the laser should be in a dark room with no humans breathing on it

Anonymous

Anonymous Tue 05 Oct 2021 05:01:22 No.13716994 Report

Quoted By: >>13717012

>>13716990
The light sensor itself has interacted with the laser beam, or it couldn't determine anything about the beam.

Anonymous

Anonymous Tue 05 Oct 2021 05:08:08 No.13717012 Report

Quoted By: >>13717019

>>13716994
i see so you can never see how light behaves when there's nothing to absorb it unless you have some ESP eye of god

Anonymous

Anonymous Tue 05 Oct 2021 05:14:27 No.13717019 Report

Quoted By: >>13717037

>>13717012
More or less. You can make very accurate predictions, but you can't know every property of a system all at the same time.
On the macroscopic scale we see things at in day to day life the effects of observation are vanishingly small, but on the quantum level the effects are dramatic and unavoidable.

Anonymous

Anonymous Tue 05 Oct 2021 05:21:09 No.13717028 Report

Quoted By: >>13717031

>>13716983
>Getting the information necessitates interaction with the system, and that interaction does affect the other end.
It does not 'affect' anything distant because that would violate relativity. Whatever you measure is just guaranteed to be correlated with what the person who measures the distant particle observes. You can see this by considering a third observer who observes the entire system consisting of the two distanct observers and the particles which they perform the experiments on.

Anonymous

Anonymous Tue 05 Oct 2021 05:21:55 No.13717031 Report

Quoted By:

>>13717028
*distant observers

Anonymous

Anonymous Tue 05 Oct 2021 05:24:10 No.13717032 Report

Quoted By:

>>13713770
Basically this. Its like trying to Smell your own nose, or see your own Eyeball. You cannot do it because you require your eyeball to be able to see. You are entangled with the Eyeball

Anonymous

Anonymous Tue 05 Oct 2021 05:30:23 No.13717037 Report

Quoted By: >>13717055

>>13717019
this makes me worry like there's an unresolved problem with my way of thinking because i don't see the world around me (with sense organs that require interaction) in the same way i see things in my internal model of the world (with my imagination). this asymmetry bothers me

Anonymous

Anonymous Tue 05 Oct 2021 05:31:41 No.13717039 Report

Quoted By: >>13717052

>>13715685
The why does it still take time for light to travel. Like it still takes years for us to see the light from a nearby star. Why wouldn’t we see it instantly?>>13715685

Anonymous

Anonymous Tue 05 Oct 2021 05:36:43 No.13717052 Report

Quoted By: >>13717059

>>13717039
The time to travel as "observed" by the light itself, and as seen by observers in other reference frames, are two very different things.
From our point of view, it is the light itself that is contracted to a length of zero. A point. Kinda like a photon.

Anonymous

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Anonymous Tue 05 Oct 2021 05:37:17 No.13717055 Report

Quoted By:

>>13717037
>this makes me worry like there's an unresolved problem with my way of thinking
this is precisely the intended effect, most of quantum physics is gatekeeping and copenhagen interpretation garbage like the OP is literally misinformation.

Yes they literally just made you go though a whole roundabout to say that no we can't observe light without it hitting something. The best part is that its all a ruse because this has NOTHING to do with the actual uses of QM. look its pictures of electron orbitals, surely this should be impossible right!?! fucking quacks the majority of them, they dont care about science they care about the gay mysticism with muh observation causes wave-function collapse

Anonymous

Anonymous Tue 05 Oct 2021 05:39:17 No.13717059 Report

Quoted By:

>>13717052
>zero
+- the quantum uncertainty (position spectrum)

Anonymous

Anonymous Tue 05 Oct 2021 06:01:47 No.13717099 Report

Quoted By: >>13717106

Honestly, the only people who complain about the copenhagen interpretation are those who have understood incorrectly due to some bad explanation of it - symptoms of this misunderstanding include thinking that wavefunctions are real things and collapse is some physical process. What the copenhagen interpretation does imply is that the idea of a classical reality where things definitely happen and have precise values is only an approximation/emergent concept. Once you accept that, it's all completely logical and sensible.

Anonymous

Anonymous Tue 05 Oct 2021 06:01:47 No.13717100 Report

Quoted By: >>13717150

>>13716849
>if the observables are the matrices A and B, then AB is not necessarily equal to BA (the Heisenberg uncertainty principle for example states that the position and momentum observables don't commute)
That bit actually helps a lot! Remembering they are matrices!
>>13716850
>but you can get more complex systems.
Let's just stick with the simple example for now, but good to know that there can be more complicated systems that can be in superimposed states
>The "how" of entangling is complicated, but it usually comes down to getting two particles produced from one event/interaction
I'm having a hard time understanding this, but it does make it a little more clearer.
> A can take a qubit and combine it with their particle to influence B's particle as well, but the "sent" qubit can only be determined by B after A tells them what they measured on their particle.
I'm worried, because this sounds rather understandable because it resembles just any causality: person B can only know the state after person A sends the bit. And I fear I've missed out on something if it seems so simple
Thanks anons for your responses, they're actually enlightening.

Anonymous

Anonymous Tue 05 Oct 2021 06:07:16 No.13717106 Report

Quoted By: >>13717134 >>13717143

>>13717099
"...the idea of a classical reality where things definitely happen and have precise values is only an approximation/emergent concept"
an approximation of what? this seems like a huge caveat

Anonymous

Anonymous Tue 05 Oct 2021 06:35:35 No.13717134 Report

Quoted By: >>13717143 >>13717159

>>13717106
I call it an approximation because ultimately, when you say that things happen, what that means in quantum mechanical terms is that you performed some experiment on some object and as a result, you were entangled with that object. Now because you are a macroscopic object, decoherence implies that it's safe for some other observer who is modeling your time evolution to assume (even without performing any measurement on you) that you obtained some specific result (but not exactly which result) once you performed the experiment - technically, this means that this observer can now model the result of your experiment as a mixed state instead of a pure state, and a mixed state is basically just a classical probability distribution. This assumption which allows the other observer to say that things happen even without them directly measuring it (this is the basis of the classical view of reality), while typically valid, is an approximation because decoherence is not perfect, so the transition from a pure state to a mixed state is also only approximately valid. So essentially, this approximate picture of a classical reality arises through entanglement (which are just quantum correlations) and decoherence.

Anonymous

Anonymous Tue 05 Oct 2021 06:45:10 No.13717143 Report

Quoted By:

>>13717106
>>13717134
I should add there is also a view where you can assume that there really is a thing such as a wavefunction which is not just a way of representing the information available to the observer. But this would, imo, clearly imply that you would also have to adopt some sort of many-worlds view. This would be a more realist (as opposed to instrumentalist) view of quantum mechanics and is probably a consistent view to hold but it requires some extra work to define in what sense exactly these many-worlds are real.

Anonymous

Anonymous Tue 05 Oct 2021 06:49:43 No.13717150 Report

Quoted By:

>>13717100
>I'm worried, because this sounds rather understandable because it resembles just any causality
If it sounds mundane... it kinda is. With entanglement and the sender's measurements, the receiver can produce the sent quantum states. The no-communication theorem holds that a quantum measurement/"collapse" alone cannot transfer information, as that would violate causality.
It's a neat experiment though.

In a mostly unrelated topic I found while looking up this stuff to make sure I wasn't spouting bullshit, there's been experiments that have been able to produce rudimentary photos of objects using photons that never encountered the object, but were entangled with photons that did.

Anonymous

Anonymous Tue 05 Oct 2021 06:53:39 No.13717159 Report

Quoted By: >>13717205

>>13717134
i'm having difficulty following you, please slow down. i'm guessing you're probably not a realist about things and i wonder if this is warranted by the copenhagen interpretation.

Anonymous

Anonymous Tue 05 Oct 2021 07:23:31 No.13717205 Report

Quoted By:

>>13717159
Well, I don't particularly subscribe to any philosophy regarding qm, but I would say that in the copenhagen interpretation (by which I mean mainly that the wavefunction is not accepted to be a real thing), things like particles and so on exist and interact with each other but assigning truth values to statements like 'A measured the property X of object B and found the value x' are ultimately done out of convenience.

> i wonder if this is warranted by the copenhagen interpretation.
I think this is the view Bohr more or less had. Einstein and Schrodinger disagreed with him however and Heisenberg had his own views which were not entirely consistent with the ones Bohr held, so copenhagen interpretation could mean lots of (sometimes inconsistent) things. You can read some article like https://plato.stanford.edu/entries/qm-copenhagen/#IntQua

Anonymous

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Anonymous Tue 05 Oct 2021 16:13:28 No.13718757 Report

Quoted By: >>13719651

I never studied QM beyond introductory course and this thread made me very insecure. Is everything I've learned from Griffiths a lie?

Anonymous

Anonymous Tue 05 Oct 2021 20:36:22 No.13719651 Report

Quoted By:

>>13718757
>I never studied QM beyond introductory course and this thread made me very insecure. Is everything I've learned from Griffiths a lie?
no. electrons are omnipresent and omniscient. Whats so hard to understand about that?

Anonymous

Anonymous Tue 05 Oct 2021 21:21:17 No.13719777 Report

Quoted By:

>>13715887
you are confusing acidity with oxidation/redox. to be fair oxidation is a bit of misnomer since the first oxidation reactions were rusting of iron with oxygen so all reactions where total number of electrons decreases is called oxidation. also oxidation isn't a household word like energy and work are

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