The Strange Science of Schrödinger’s Cat and Quantum Superposition

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The famous “Schrödinger’s cat” is more than a joke about the unknown. It’s a hypothetical way of understanding an idea in quantum mechanics known as superposition. This week on Wondrium, philosophy meets physics.

This video is lecture 10 from the series The Great Questions of Philosophy and Physics, presented by Steven Gimbel

00:00 Where Physics Meets Philosophy
02:53 “Schrödinger’s Cat” and Quantum Mechanics
08:12 Quantum Mechanics Interpretations
13:18 Perspectives on the Copenhagen Interpretation
18:25 Eugene Wigner and Observation Phases
20:50 Descartes and Metaphysical Dualism
23:11 Many-Worlds Interpretation
27:12 How Observations Create Superimpositions

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#physics #schrödinger #ThatDarnCat

[kevincronk]

people talk about Schrödinger’s cat so much as something he came up with to illustrate how weird quantum physics is, but that's not the case. he came up with it to rebut the Copenhagen interpretation which states that the cat would be both alive and dead, as that is clearly absurd and not how the real world works. He and other very famous physicists like Einstein were evangelists of just about anything that wasn't the Copenhagen interpretation.

[wmstuckey]

Hey Steven, I'm a physics professor just down the road from you at Elizabethtown College. Let me add an explanation of quantum superposition via Schrodinger's Cat using quantum information theory.

What people fail to mention when talking about quantum superposition using Schrodinger's Cat is the difference between a classical bit of information (like a computer bit being on or off) and a quantum bit of information (a qubit). Both bits produce one of two outcomes when queried (measured), but a classical bit has only one measurement possible while a qubit can be measured in many different ways (infinitely many, actually), each with two possible outcomes.

For example, when you pass an electron through an inhomogeneous magnetic field, the electron is either deflected towards the North magnetic pole ("up") or towards the South magnetic pole ("down"). You can orient the N-S magnetic field in any direction you like and the electrons will still give one of those two outcomes, so electron spin is a qubit with two outcomes of spin "up" and spin "down" relative the the N-S magnetic field. Now suppose you pass electrons through a N-S magnetic field oriented vertically and then send those that were deflected "up" (literally up in this case) to a N-S magnetic field oriented horizontally. What do you expect to find?

Well since the electrons have vertical spin up and spin is a vector (picture an arrow pointing upward here), then you probably expect the electron to pass straight through the horizontal magnetic field, i.e., they won't be deflected left or right at all ("up" or "down" relative to the horizontal N-S field). That's because the electron's spin vector (arrow) points up which means it doesn't point side-to-side (left of right) at all, so your horizontal spin measurement of a vertical spin up electron should seemingly yield a result of zero horizontal spin. But what you find instead is that 50% of the vertical spin up electrons are deflected left ("up" towards North pole) and 50% are deflected right ("down" towards South pole). True, 50% left plus 50% right *averages* to zero, but that's not what you expect from the measurement of a vector quantity in ordinary classical mechanics. [Aside: Quantum mechanics gives the classically expected results on average over the discrete or quantum measurement outcomes.] This is quantum superposition, a vertical spin up electron is a quantum superposition of 50% horizontal spin left and 50% horizontal spin right and we write that as |V+> = |H+> + |H-> (divided by root 2 for normalization, but I don't need that to make my point).

The point here is the horizontal spin measurement of the quantum state |V+> produces each of its two "up"-"down" (left-right) results in 50-50 fashion. This is exactly what you hear people say about Schrodinger's Cat, i.e., you open the box and find the cat is dead with 50% probability or find the cat is alive with 50% probability. With that information alone, Schrodinger's Cat could be a classical bit or a qubit. If Schrodinger's Cat is a qubit, then there must be a measurement of the cat-box system like the vertical spin measurement of the state |V+> that produces |V+>, i.e., |H+> + |H->, with 100% certainty. We know the measurement "open the box" producing "Live Cat"-"Dead Cat" results in 50-50 fashion is analogous to the horizontal spin measurement of |V+>, so what is the measurement of the cat-box system corresponding to |Live Cat> + |Dead Cat> with 100% certainty in analogy with the vertical spin measurement of the state |V+> that produces |V+> with 100% certainty? And what does its outcome mean physically? If you can't articulate that measurement and outcome of the cat-box system, and every possible measurement between that measurement and the "open the box" measurement, then the cat-box system is just a classical bit ... like opening a box to find a ball or no ball. No quantum superposition there 🙂

To read more about the quantum information approach to entanglement for the "general reader, " see "Einstein's Entanglement: Bell Inequalities, Relativity, and the Qubit" due out in June 2024 with Oxford UP.

Steven, Dr. Silberstein (coauthor and philosophy professor at Elizabethtown College) and I will gladly give a talk at Gettysburg College whenever it suits.

[DocSeville]

Bravo! Very well done and the ending was

[va]

Very good explanation of the interpretations.

[gregorynicholls]

We are also a part of nature, our observation of the object is also nature interacting with nature, why be surprised by an effect/change ? I think most great minds forget that we are also nature quantomly generated to interact with the rest of nature the way we do.

[jamestagge]

one more one more conditions of the Schroedinger’s Cat thought experiment remain exactly the same but for the poison in the vile which would be replaced with an acid, the fumes of which would still be lethal to the cat, and a mechanism on the floor of the box which were the cat to lie/fall down for having died from the acid fumes, would cause the vile to tip over. If broken, its contents would spill onto the floor of the box and eat through to the outside. In this then, there would be no observer opening the box but rather a chain of interdependent, deterministic events which would at their end, in effect, be “reaching out” to the observer after the fact. In other words, the acid leaking from the box would only be possible were the cat dead and only dead. No dead cat, no leaking acid, no odor to alarm the observer that he might turn to see. To illuminate further, that necessary for the Schroedinger version of this scheme is that there be no consequence of events of the cat’s state as either alive or dead or even potentially one or the other. The cat’s state as alive or dead is the end of the sequence of events contained within the box. In my version in which the cat’s state is nested within a line of other deterministic events, those subsequent to the cat’s state cannot be realized materially unless the cat were dead and only dead. The observer would not have looked to see the acid on the ground at all but for the process having in a sense “reached out” to alert him to its presence (the odor of the acid). If, as might be claimed that his observation of the dripping acid would cause the wave form to collapse and the condition of the acid dripping to manifest then how could it have been manifest already that it might capture his attention that he might turn to observe it to then cause the wave form to collapse so that it could be dripping to alert him which it was and had to be in the first place? This argument makes no sense and defies the same brand or current of logic by which the experiment was initially defined. Here the acid on the ground (the cat being dead) is the cause of the observation and not the effect as the state of the cat in the box (Schroedinger’s version) after it is opened that the cat might be observed. Additionally, it might be claimed that during the time the acid was eating through the bottom of the box that the cat would be in superposition and dead and alive at once and that the subsequent hole created by the acid would cause the wave form to collapse and the cat to then be dead or alive. However, this would then demonstrate that the original proposition as per Schroedinger was in error in the manner those of the Copenhagen school accepted it as a means of understanding superposition (of composite entities). It should be clear that there could not be the acid on the ground “and” the acid not having eaten through the box in the same manner that the hammer in the box in the original Schroedinger version had both fallen to break the vile and not. I would think that there is no reason to expound on that understanding.
As stated above, the means by which the wave form would collapse in the original version of the thought experiment was solely that the box was opened and the cat observed. This other claim then that the wave form would collapse merely because a hole was burned into the bottom of the box by the acid such that it could escape but insufficient for the observer to see the cat inside via this hole could not be true without contradicting the original understanding. It cannot be both. Were the experiment to take place, rather than in a box, under an open bottom dome which blocked the observation of the cat until it was lifted, would the cat be in superposition? Resolving this would answer the questions posed above. If observation is required to collapse the wave form then anyone trying to refute my scenario must compose some work-around this possible logical contradiction.

[kevincronk]

the description of quantum mechanics as a placeholder (despite Einstein being wrong about that particular alternative) seems very fitting, as quantum mechanics started as simply something that somehow worked to explain how the color of light emitted by an oven at different temperatures changed, after other methods failed. the guy who came up with it was certain it couldn't be inherently true, and thought it was just a mathematical hack and the true mechanisms would be eventually discovered. the theory has come a long way since then though.

[SampleroftheMultiverse]

It’s all about time and the propagation of time out from ever central point of a field and how long it takes for it to get to where we are. We are all living and seeing everything in the relative recent past. When you get so small and down close to that central point which is “absolute current” moment in time, things start behaving like they’re in the future that’s why quantum properties are highly probabilistic and weird to us because we’re seeing and responding to events in the past which are fixed. 29:41

[vinceypma]

Schrödinger's daughter (supposedly) said, "He hated cats."

[mickmccrory]

If you put that cat in the death box 1 more time,
there is a probability I may or may not call the animal control people.

[franciscojose]

Always unique channel pure information

[MrGiovannisassano]

9:40 even on or if the measurable quantities that is still available "information" to the just the plank scale thought of the interaction of the existence of the thought experiment. Not just a standard measurement by itself. Fixing the main reason for the math is the paradox to the equation!

[JamesWylde]

I was really enjoying this video, then after 4 rounds of mid roll ads and then it just cuts off at the end I ended up having to downvote it.

[MrGiovannisassano]

23:09 or the statement of "I see I see said the blind man to the flea" but only knowing that the flea was there cuz it bit the blind man.

[MrGiovannisassano]

21:00 finally got the understanding of what I mean. Cuz it's information ove substance of the existence of form to function.

[jamestagge]

I thought I would try this one more time after having had a kind of debate with someone, very intelligent but in my estimation, a bit prejudiced against any contradictions proposed of the conventional notions about superposition. I have adjusted my proposition a little to include what I thought were successful counters to his critique of my idea. So, here goes……..

A quick recap of the original argument and my proposition…Schroedings cat thought experiment modified slightly to show that there is no superposition of composite entities such as the cat. There is the box, the emitter, the collector, the hammer and the vile which would normally contain the poison but in my version, acid. So, the collector would at some time release the hammer and break the vile which would release the acid whose fumes would kill the cat. He would fall to the floor and a mechanism would cause the vile to tip over and release the acid to fall to the floor and begin to eat through it. The potential observer would be paying no attention to the box, it sitting on a nearby table perhaps. Suddenly, he would be alarmed by the odor of the acid and turn to observe it on the ground. Several relevant points;
 The observer’s attention was the “effect” of the experiment concluding, not the cause as in the original version, i.e., of his detecting the odor of the acid (outside the box), that being the consequence of the cat having to be only dead.
 The observer never looked into the box.
 The acid could only be outside the box if the cat were dead and only dead, not dead and alive at the same time. Some have tried to claim that by looking at the acid, the wave form would have collapsed and the cat then would have become dead. But this is a contradiction of the experiment as originally defined. The acid could not have been there to alert the observer so he would turn to it at which the wave form would collapse and cause the cat to die and fall over that the acid would eat through the box to alert him to look which it already had to begin with. This would make no sense. The cat had to have been dead already before the observer turned to see the acid which meant that the cat was never in superposition.
 The cat’s death was an event nested in a string of other deterministic events, those subsequent, impossible unless he were dead and only dead.
 The observer did not need to look in the box to see the cat for its state was fixed, that known to be true by the presence of the acid on the ground.
Now I debated the above and certain counterpoints were made by my opponent that didn’t stand additional scrutiny.
 My opponent claimed that the cat was both dead and alive until the acid leaked (created a hole) through the box at which point the wave form collapsed. This would have meant that the original definition of the experiment to which he subscribed was in error. It was the unpredictability of the decaying matter in the emitter which created the condition of superposition, that the shedding of particles was random. So said Schroedinger. By definition then, it could only be that it was the observer’s observation of the cat by opening the box which caused the wave form to collapse. So be it. But then that the acid created a hole in the box which did “not” allow the observer to see the cat could not have cause the wave form to collapse. How then could the acid have eaten through the box, the reality of which was directly observed and whose effect in its presence alarmed the observer to turn to see “it”?
 If the claim that the mere presence of a hole in the box from the acid which did “not” allow the observation of the cat’s state was sufficient to cause the wave form to collapse were true then the original version of the thought experiment was in error in that the cat’s state was said to be a product of it having been observed by the opening of the box. When I suggested that my opponent might inform me whether or not the experiment would have worked as originally defined by Schroedinger had it taken place under an open bottom dome which though open would not permit the observer to see the cat unless it was lifted, he ran from the question. In any case, if any analysis of the reality of superposition does not require the observation of the cat to cause the wave form to collapse, it cannot be thought to be correct in its conclusions, “if” we are to remain true to the Copenhagen school’s claims as to how these wave forms function in materiality. One cannot have it both ways. Either the cat’s state is the product of direct observation or not. If the former is true then my version of the experiment shows superposition to be untrue. If the latter then I am in error.
 I have seen toys which are constructed around the double slit experiment in which the interference pattern is created. However, the observation of the open mechanism by the user does “not” cause the collapse/termination of the phenomenon. Why not?
I do believe that “if” one were to truly and honestly deconstruct my argument in the context of the definitions of the reality of superposition by all scientists and most who study this kind of thing in some measure, he will find that there is no such phenomenon. If any of you think me arrogant and wrong, it should be a very simple matter to demonstrate how and why that is the case. To date, no one can including a few graduate students in physics. I find that astonishing. I also think that whomever posted this video would only have a great deal of fun discussion my proposition and if I am wrong, proving me so. This stuff is a blast to debate. I find it odd and troubling that most people take the challenge of it as such a personal affront. Why? The proposition of superposition is not theirs.

So, what do you think? On the off chance I am correct in this (and I am “if” we are to respect the original author’s formulation), consider the physics that would fall away as a consequence such as all that nonsense about multiverses, etc.

[oremazz]

See this revolutionary new approach: From intuitive thoughts, the universe can be simplified as “stuff in a media” where “stuff” is all the particles resumed by the Standard Model, and the “media” is the 3D space. The first entity is circumscribed inside the quantum system as compact, i.e., particle, and the second entity is the quantum system space that oscillates between 3D and its 4th longitudinal dimension. So, the universe will be the coexistence of particles with its wavy space; this particle will exist aleatorily in 3D meanwhile its space is in 3D. These two entities solve the wave-particle duality, not one entity that assumes two rolls in a weird-convenient way, but a wavy space that can split or join or interfere with itself given to the compact particle's characteristics of wave behavior.
On each new cycle, the particle will assume aleatorily a new eigenvalue so that only one eigenvalue exists in a given ephemeral moment, completely following the observations known as collapse. The oscillation frequency is so fast that it allows the particle to develop all its eigenstates in an apparent superposition form, accomplishing this way with all the math of Quantum Theory without the weirdness of multiple-superposition versus unique-collapse existence. Now, the issue that the quantum system space is temporarily out of the 3D longitudinal dimensions explains how particles can change from one eigenstate to another eigenstate without the conflict of the transition between them. Besides, this passage to its 4th longitudinal dimension explains how entangled particles interchange information without the relativistic speed limit at 3D. It also provides the zone where particle interaction (creation and destruction) occurs, accomplishing the conservation laws of momentum, energy, charge, etc.

[MrGiovannisassano]

16:27 and then not becoming the operator change that system is not interacting but interacting with that system while being the operator change the system so the uptown and the crossing to the cat is dead. Anytime you don't know if the cat hits the button itself that is in this system while being alive. The operating Observer then can statement of its alive and died otherwise no.

[johnathanfindlay]

The measurement problem of physics in space is the point between quantum physics and relativity with the emergence of time and space at a Planck length. The cat is not the only one in the Box... You are in the box we call the universe where from the view of sub Planck (quantum physics) perspective. It's not a philosophical result it's a literal one that is confused by a bad interpretation of the physical, not mathematical properties of the universe. But if people prefer the current interpretation I am easy.

[jeffnolan]

This guy has no idea what Schrodinger was trying to illustrate. There is no spin detector. There is only a cat and poison, and in thought, the cat is both alive and dead until you measure, or open the box, and expose the truth.

It is to illustrate you don't and can't understand quantum states until you measure. They are unpredictable. Heisenberg threw a rock through the glass when he showed you change characteristics of particles when you measure them since the only way to measure them is through the application of magnetic fields or electromagnetic detection, so you can never actually know any quantum state you measure.

This guy should either go back to school or mention that he's presenting his own views, not academic views.