/sci/ - Science & Math

[Anonymous No.3155442]

When two electrons are entangled, when observed, one will have a certain spin, the other will always be the opposite.

It's also said that before they're observed, the electron is in a state of flux, it's both a -1/2 and 1/2 spin. (Rather like the cat is both alive and dead).

But how do we know it's in this flux? What tells us?

Also, what are the effects of an electron in this state? As opposed to the effects of an electron that definitively has either a 1/2 or -1/2 spin?

[Anonymous No.3155454]

It has no effect. The effect would be a discrete observation, and it would cease to exist in such a state.

[Anonymous No.3155465]

>>3155454
Then if it has no effects, how have we determined that an entangled electron has both a positive and negative spin?

[Anonymous No.3155473]

... double slit experiment.

[Anonymous No.3155483]

>>3155454
It absolutely has effects, but it is simpler to give experiments demonstrating the probabilistic nature of location than spin. As the poster above me noted, experiments from the early 20th century definitively show that electrons (like all elementary particles) are waves when (relatively) undisturbed, creating interference patterns and so on.

[Anonymous No.3155504]

>>3155465
That's an <span class="math">\mathbf{interpretation}[/spoiler] of the wavefunction in quantum mechanics. Look up the goddamn Born rule and l2 differentiate between ontology and face-value mechanics.

[Anonymous No.3155522]

>>3155504
No need to be so aggressive, it was just a question.

[Anonymous No.3155540]

it can't be BOTH states. That's fucking retarded, like saying we live in a poetic universe. Things are objective, not magical. If anything, the electrons should rather be viewed as an elemental region within space in which the overall effect is an electrical charge. the standard model is a little outdated in that regard, depicting everything as perfectly spherical mental balls.

[Anonymous No.3155554]

>>3155522
I've heard it enough to be extremely annoyed by it and the soundbite science behind it. So I am a bit grumpy on the topic.

[Anonymous No.3155558]

>>3155540
So a wave can't be spread out in more than one location? Your rebuttal is kindergarten. Ho hum.

[Anonymous No.3155568]

>>3155442
Do you even understand quantized angular mometum?

You ask all these concepts that are way over your head. YOU NEED TO UNDERSTAND THE BASICS of quantized angular mometum to understand spin and the enganglment shit.

[Anonymous No.3155573]

>>3155558
ok, basically the electrons are constantly flickering around the general vacinity of the atom at discrete levels. Each is attracted by the other opposite and repulsed by the charge of its neighbours. It's possible that, travelling at such high speeds, the two intermingle at times giving the illusion of wave-like properties.

[sage No.3155586]

>>3155568


REPORTED AND SAGING FOR EMINEM FAGGOTRY

[Anonymous No.3155590]

>>3155573
>It's possible that, travelling at such high speeds, the two intermingle at times giving the illusion of wave-like properties

NO.
LMFAO
Where do you come up with such garbage?

[Anonymous No.3155597]

>>3155586
>Refuses to answer question

Do you understand quntized angular mometum of not?

[Anonymous No.3155598]

>>3155573
And you seriously think that lofty speculation designed as an alternative to wave-particle duality in a highly contrived and specific situation is viable to topple quantum theory with repeated measurements in all scores of setups and scenarios testing various bizarre effects and phenomena from all feasible angles? I realize I'm being a party-pooper and all but I think your attitude about this is a little... odd.

[Anonymous No.3155605]

>>3155597
op here, not the guy that fails at saging, nope, I don't understand quantized angular "mometum".

Or Quantized angular Momentum.

[Anonymous No.3155612]

>>3155590
creativity. the ability to think around the proposals of a few, admittedly confused men of the 20th century.

[Anonymous No.3155614]

>>3155442
>Rather like the cat is both alive and dead

Doesn't understand schodinger's cat. The cat is not alive and dead, that is bullshit. The thought experiment actually proves that it is bullshit to think that way. It actually proves that you cannot apply quantum rules to large scale phenomina (in general).

[Anonymous No.3155620]

>>3155614
Of course the cat is not both alive and dead.

The cat was just an analogy.

No one actually put a cat in a box with poison.

[Krakengineer !!5XY+x7grkpt No.3155626]

>>3155614
Nope.

That cat's life is controlled by the outcome of a quantum event: The decaying radioisotope which triggers the release of poison. Size matters not in this case. It was intended by Schrödinger to show the absurdity of QM to common sense, but something being absurd to common sense is irrelevant on these scales. It backfired on him.

[Anonymous No.3155640]

Probably the best way to view Schrodinger's cat is as an analogy to the quantum scale, or perhaps as a demonstration of decoherence. Obviously no macroscopic phenomena actually exist in a superposition of quantum states.

The idea that a cat could literally be both dead and alive is almost as annoying as the idea that particles do whatever they want as soon as we turn away from them (apparently human eyes are magic) or that Einstein proved that "everything is relative."

[Anonymous No.3155642]

>>3155612
It's a cool ability but when you have only a shallow understanding of the sensational version of QM it won't do you any good really.

>>3155614
>It actually proves that you cannot apply quantum rules to large scale phenomina (in general).

That was the intention behind the thought experiment, but it does not "prove" that in actuality. Only highlights the apparent absurdity (counterintuitiveness) of it. It plays off the naive assumption that reality is always in a single, definitive state, whereas many-worlds or other interpretations are actually able to handle the situation epistemologically.

[Scientist !!ThFjnJh4EkH No.3155647]

>>3155626
I'd like to pipe in something Dawkins once said to Lawrence Krauss. It was something like "Well, but don't you need an absurd interpretation to make sense of quantum theory?". Krauss was surprised, but ended up agreeing.

There is no sane interpretation of quantum mechanics. They're all crazy.

[Anonymous No.3155649]

>>3155640
>Obviously no macroscopic phenomena actually exist in a superposition of quantum states.

And yet again I hear this stupid self-assuring meme. Sigh.

[Anonymous No.3155668]

>>3155642
Things don't exist in many states. Probability wave is an attempt to predict what may happen. The events in the future have already happened along the axis of time. Determinism, including feynman's very own model in which particles spontaneously arise and disappear relies on the future being in a predetermined state. Double slit and many world theory are imo just pseudoscience.

[Scientist !!ThFjnJh4EkH No.3155670]

>>3155668
What is this "double slit" theory you speak of? "Double slit" is an experiment, not a theory.

[Anonymous No.3155683]

>>3155670
why, the interpretation of it! as per thread discussion

[Anonymous No.3155682]

ITT: Quantum mechanics doesn't agree with my world view so I want to disregard it.

[Anonymous No.3155677]

>>3155642
>epistemologically
The actual issue at stake here is ontology. MWI addresses the question of whether the cat IS dead, not whether we can know it.

[Anonymous No.3155679]

>>3155605
In classical mech, we have angular mometum. It can have values is any direction. We can say we have an x,y, and z components of angular mometum. We are able to measure all three componets (at the same time). Additionally, we can measure the total magnitude of the angular momentum.

In Quantum Mech, we are not able to measure all three componets of angular mometum at the same time, it if fucking impossible. This is because if we measure one component it will fuck up the values of the other two components. Hence, we can only measure the one component, we usually call this the "z" component (as we set the z-axis along the direction of our measurement). Additionally we can still measure the "magnitude".

Some reltionships between the magnitude and the z-component, are obvious. The z-component cant be greater then the maginidue, nor can the negative of the z-component be less then the negative of the magnitude. Essentially, the magintude will gives us "bounds" for the z-component.

[Anonymous No.3155678]

Spin isn't actually clockwise/anti-clockwise, is it?

It's an abstract concept like frequency in QM.

[Anonymous No.3155684]

>>3155679


The magnitude and z-componet are also quantized. The magnitude is always a positive integer, 0, or a positive integer +.5 (it is a magntidue after all). The z-componenet, goes from unit steps of the magnitude to -magnitude.

The quantization essentailly comes from the fact the the certain "wave properties" of quantum systems have to overlap perfectly around the system. Example, If you take a vibrating string, and curve it on itself, The "ends" have properties that have to synch up. This limits the types of waves I could place on the string.

Spin, is the exact same thing as angular momemtum, except it is an intresntic property of a particle, it doesnt actually involve anything orbiting anything. It is a particles "self" angular momentum.

Anyway, so when you speak of spin 1/2 (like an electron). 1/2 is the "magnitude", the z-component can either be 1/2 or -1/2. Any we don't (it isnt helpful) to measure the x,y, componets (as already mentioned).

Now you know the very basics. Questions?

[Scientist !!ThFjnJh4EkH No.3155688]

>>3155683
There is no such thing as the "double slit" interpretation of the double slit experiment. The hell are you trying to say?

[Anonymous No.3155689]

>>3155649
Cogsci fag here. Don't know any of this physics/math stuff. However, have taken for granted determinism at non-tiny (microscopic?) levels. Are there any actual examples of "macroscopic phenomena existing in a superposition of quantum states" ? Also, not entirely sure what that means. It doesn't simply mean two opposing things happening at the same time, does it?

[Anonymous No.3155694]

>>3155682
there are many interpretations that can work in QM and we're discussing them.

[Anonymous No.3155696]

>>3155668
You've stated your beliefs but apparently providing any sort of reason to believe you've put any thought into the matter slipped your mind while writing. Did you think you'd persuade me or anyone else to any extent when you have written no supporting arguments at all?

Where's your basis for assuming reality has a single, definitive branch? How do you explain what the wavefunction is and how it applies to our reality? How do you account for the probabilistic predictions of quantum mechanics? How do you explain the otherwise completely arbitrary definition of an "observation" which is completely fundamental to wavefunction collapse and therefore how our equations relate to our experimental results? A lot of thought has been put into these questions and it doesn't look to me like you've read or pondered anything substantive on this shit. No offense, but seriously.

[Scientist !!ThFjnJh4EkH No.3155701]

>>3155689
>Also, not entirely sure what that means. It doesn't simply mean two opposing things happening at the same time, does it?

It means that the cat is neither alive nor dead. It's in an inbetween state, until you measure it.

Because of QM, I've given up scientific realism. As long as it makes useful falsifiable predictions.

[Anonymous No.3155703]

>>3155688
see
>>3155442
and
>>3155483
and
>>3155504

[Anonymous No.3155704]

>>3155649
This is fucking true. Different quantum states decohere very quickly at large scales and cannot interact with eachother. Perhaps in some vague metaphysical way multiple states are "real," but only one can possibly have any effect on me, which is all I care about. MWI is one way of addressing this but it is by no means the only one.

What you are proposing is basically that the moon goes away when you stop looking at it.

[Anonymous No.3155727]

>>3155701
Thanks. While I admit that all of this seems rather difficult, I would like a small bit of closure:

Is it incorrect then, to seek causality and determinism in a relatively straightforward way in the other sciences? I sort of get your point about scientific realism, but I'm not sure it would apply to work done, in say, neuroscience.

[Anonymous No.3155729]

>>3155677
Yes but the interpretations in comparison to each other have varying levels of explanatory power and presumptuousness, making the task of sifting through them an epistemological one.

>>3155689
>Are there any actual examples of "macroscopic phenomena existing in a superposition of quantum states"?

Experimental verification: No, not really. Biggest things we've confirmed is buckyballs IIRC, but bizarre quantum phenomena become incredibly improbable on macroscopic scales because of the number of entities involved. Imagine flipping a coin 10 times for every particle in your body, and if 99% of them come up heads you can telescope straight through a "solid" wall.

In theory: Depends on your interpretation. Look up the Universal Wavefunction; our "reality" may simply be a single branch of every possible one made available by the equations of QM.

>It doesn't simply mean two opposing things happening at the same time, does it?

That's the lay concept, but mathematically the story is that the wavefunction assigns numbers to all the possible states of a system and only collapses to a definitive one after an "observation" is made (and the wavefunction quickly spreads out again like a wave after the collapse, as if it's a drop in a pool ripples outwards). Which state it collapses to is probabilistically determined by the wavefunction's spread at the time of collapsing.

[Anonymous No.3155747]

>>3155704
>What you are proposing is basically that the moon goes away when you stop looking at it.

That's both an off portrait of the theory and an attempt to evaluate physics with personal prejudices.

>>3155727
>Is it incorrect then, to seek causality and determinism in a relatively straightforward way in the other sciences?

Deviations from classical physics on macroscopic levels are negligible due to astronomically^astronomically low probability.

[Anonymous No.3155749]

>>3155729
I've heard that stuff about going through walls before.
I know this is a much more elementary question, but what prevents one from going through walls anyway? I thought it was some sort of force that repelled all the electrons away from each other (or some such thing). What sort of state would actually be needed (i.e. what states are the heads on your coins) on 99% of your body's particles that would enable you to go through the wall?

[Anonymous No.3155758]

>>3155729
>>3155729
Look up super fluids you gotta know your shit man before you post bose-einstein condensate ring a bell

[Anonymous No.3155764]

>>3155668
>Double slit just pseudoscience

Calls actual scientific experiment, pseudoscience? WTF? U HIGH? RETARDED?You sound as dumb as a christian!

[Anonymous No.3155765]

>>3155749
Classically I think it was that electrons in the outer shells of every atom repel each other (if they aren't bonded to each other because of their nuclei), but I'm not really into chemistry.

With the coin scenario I was just trying to convey the fact that the more particles you want to deviate largely from classical predictions in tandem, the more the possibility is compounded lower in likelihood. Essentially, the "state" of heads is the scenario of a particle spontaneously tunneling to the other side of a wall, which isn't really a "state".

[Anonymous No.3155770]

>>3155758
Ah you're right. Good thing I put the IIRC qualifier in there, knew I was a bit uninformed on that point.

[Anonymous No.3155772]

>>3155764
How dare you call me a christian. FUCK OFF

[Anonymous No.3155774]

>>3155765
Sure, thanks. I'd love to stay an pick everyone's brains a bit more, but I have to leave. I guess you guys are mainly physics grad students/post-docs working labs? Good luck with the issues of the day.

[Anonymous No.3155787]

>>3155747
>That's both an off portrait of the theory and an attempt to evaluate physics with personal prejudices.
wat
1) WTF is an "off portrait?"
2) What "prejudice" is indicated by the obviously true statement that decoherence prevents (to a very high degree of accuracy) quantum effects from appearing in macroscopic phenomena?

>>3155749
>I know this is a much more elementary question, but what prevents one from going through walls anyway? I thought it was some sort of force that repelled all the electrons away from each other (or some such thing).
The normal force the wall exerts on you is basically due to electrical repulsion of the electrons on the surface of you and on the wall.

>What sort of state would actually be needed (i.e. what states are the heads on your coins) on 99% of your body's particles that would enable you to go through the wall?
That was more of an analogy than a real statement of what is involved.

Quantum tunneling technically involves particles being able to pass barriers that would require more energy than they have in classical mechanics. But in quantum mechanics there is a very small probability that the particle does indeed tunnel to the other side. If every particle in your body tunneled across a wall in just the right way, you could say that you yourself tunneled.

Note that the probability of any individual particle tunneling more than a few nanometers is already incredibly small and that there are something like 10^29s of particles in your body.

[Anonymous No.3155789]

>>3155770
>>3155770
It's all good buddy


>>3155668
And you, fuck you man

[Anonymous No.3155794]

>Question about definite states in QM
>50 replies
>Ctrl-F bell
>only match: "hit a bell"
>mfw I have no reaction image
Seriously, Bell's inequality - end of thread.

[Anonymous No.3155806]

>>3155787
- Look up "define: off" and "define: portrait" on Google. I'm using def (1) or (5) [adj] for off and def (2) for portrait.

- I believe I misread your post, as it originally sounded like you were using the "moon goes away" idea against quantum theory, which would amount to evaluating physics with a prejudice (apparent objects are definitive and absolute). Apparently you were just describing a popular train of thought and I mischaracterized your comment.

- Nice clarification of my coin-flipping imagery.

>>3155774
Everything I know about QM I learned on my own. I'm a heavy mathfag so it opens up better when you know the language of Hilbert spaces, operators, eigenstuff, waves and so forth. And some general critical reasoning skills come into play on the "meta" level I guess.

[Grothendieck !Topos4qCwc No.3155809]

I really have to wonder if people understand the dangers of giving up ontological realism. Epistemological completeness I can live without.

>>3155794
I have some bad news for you. Setting aside the myriad other ways around Bell's inequalities the case is far from open-and-shut.

http://en.wikipedia.org/wiki/Superdeterminism

[Anonymous No.3155836]

>>3155809
Superdeterminism is a retarded way around Bell's Inequality that as far as I can tell no serious physicist advocates*. Even supposing it is true that the universe is superdeterministic, it's still incredibly unlikely that this would resolve the thesis of the Bell experiments since it would basically imply that the choice of state of an entangled pair is somehow determined by the same thing as the choices of the experimenter himself.

[Anonymous No.3155839]

>>3155809
>Setting aside the myriad other ways around Bell's inequalities
Such as what? Non-local hidden variable theories? Because these are in no sense ways "around" Bell's inequalities.

They are solid.

[Grothendieck !Topos4qCwc No.3155855]

>>3155836
1) The ideas main proponent is Gerard t'Hooft who I think meets the criterion of being a serious physicist.

2) Bell himself admitted (this is quoted in the Wiki article as well) that Superdeterminism was a way to get around the setup of his theorem he just didn't agree with it in principle because he associates it with 'free will.'

I'm not saying I necessarily agree with t'Hooft on this, but I certainly dislike the popular idea that Bell's inequality offers some kind of ironclad law that ends all discussion on the matter.

[Grothendieck !Topos4qCwc No.3155890]

>>3155839
None of the experiments used to confirm it avoid all of the difficulties inherent in the approach. Which some could take as sufficient refutation when the experiment is being used to prove that something is actually impossible.

Saying something is probabilistically unlikely is not the same as saying it's impossible.

[Anonymous No.3155934]

>>3155890
Bohoo, no matter what the fuck you do there will always be probabilities involved. We haven't proven anything with a 100% probability. Popper realized this and its why falsifiability is what we want in science. Bells inequalitites are very much falsifiable, and since noone has managed to falsify them (and not cause a lack of trying either) we should hold them as true.

Superdeterminism might hold logically, but I don't really like it and I think it got some problems cosmologically. Why not accept the probabilistic nature of QM and move on?