What did Schrodinger's Cat experiment prove? (2013) | Hacker News Reader

What did Schrodinger's Cat experiment prove? (2013)

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61 pointsslynn1244 comments

Nonsense. Under the Copenhagen interpretation (which I do not personally subscribe to, but it is a legitimate interpretation and it has its defenders), when one particle interacts with another particle that's in a superposition, the result is that both particles are in an entangled superposition. Cat, Geiger counter and gunpowder can thus all be in an entangled superposition; one can argue that this is absurd, but Einstein also thought that the EPR experiment showed that quantum mechanics was absurd, and actually that result has been experimentally verified.

That takes me back to a slide in my physics honours talk.

1935: Einstein, Podolsky and Rosen show that quantum mechanics doesn't make sense.

1982: Aspect shows that nature doesn't make sense either.

I recently worked through this essay: https://quantum.country/qm

Thanks to that i understand what "Aspect shows that nature doesn't make sense either" means. I can recommend the article (and the three others) but it takes a few hours to get through.

However, the article also explains it without quantum mechanics. Polarized photons are enough to understand why our universe is not "locally realistic". Read part 2.

Because nonlocality?

Which part are you saying is nonsense? You just repeated what the article was saying.

This part of the article is nonsense:

> Since that time, there has been ample evidence that wavefunction collapse is not driven by conscious observers alone. In fact, every interaction a quantum particle makes can collapse its state. Careful analysis reveals that the Schrodinger Cat "experiment" would play out in the real world as follows: as soon as the radioactive atom interacts with the Geiger counter, it collapses from its non-decayed/decayed state into one definite state. The Geiger counter gets definitely triggered and the Cat gets definitely killed. Or the Geiger counter gets definitely not triggered and the cat is definitely alive. But both don't happen.

I think the article is just saying in practise its impossible to have entanglement on such a macro scale, so in practise the geiger counter would collapse the wave function and thus the cat would not stay in a superposition state. I don't see anything contradictory in that.

But its been a very long time and my physics is pretty rusty

Yes. In practice the cat, box, posion and Geiger counter system is not a fully closed system, and it gets entangled with the observer through unavoidable interactions.

When the observer's state gets entangled with the cat's state (whether gradually or suddenly) it's still perfectly valid to say that the cat is in a superposition of being dead and alive, and so is the observer in the superposition of observing the cat dead and observing the cat alive. That doesn't mean that the observer ever can nor should observe the cat being both dead and alive.

> I think the article is just saying in practise its impossible to have entanglement on such a macro scale

That much is not true though. Of course an ordinary cardboard box does not thoroughly isolate its inside from its outside, but complete isolation is possible in other situations (e.g. two spatially separated labs making measurements at the exact same time, which has been done in tests of the Bell inequalities).

I prefer to replace Schrodinger's cat with Schrodinger's brother. Now you claim to have a human observer in a superposition of dead and alive states. He will not suddenly experience collapse when let out of the box to greet Schrodinger. The entire notion of "wave function collapse" is a fictional construct that can not be observed because it doesnt happen.

Schrödinger's brother is Wigner's friend

https://en.m.wikipedia.org/wiki/Wigner%27s_friend

> He will not suddenly experience collapse when let out of the box to greet Schrodinger.

How do you know? What would you expect to be different if that was what was happening?

I never thought of it as something to, uh, prove but more like yet another way to point out the limits of our understanding when it comes to our ability to measure something.

This exactly. The simplest explanation for quantum behavior is just that we’re unable to measure it. There are a lot of weird and magical explanations that people have come up with in order to write formulas that work.

In a base sense, I agree with you. But this way of looking at it will lead to a misinterpretation that it's just our inability to measure it that is behind the weirdness. I tend to think of it like this: nature, at it's core, is fundamentally weird. Our frame of understanding is based on definite postulates that "things" have a certain "position", they can be only be in one "place" at one "time" and our body of scientific logic and reasoning is built on it. At core of QM, there is the Broglie concept of matter waves. What we used to consider as elementary particles are fundamentally a wave which exhibits particle-like behavior in certain scenarios. If you accept that everything (the double slit, the beam, the screen, a bunch of grey cells postulating about it) is a combination of fields of probabilities of what we call as "elementary particles", it will become easier to digest. "observation" is nothing but an act of interaction of some of these fields that takes away the "coherent" nature of an observed weirdness ("collapse").

I believe experiments were conducted in a way measurement capacity is irrelevant. Either it's an effect of things being rendered (as in a real "simulation",much like pixels in a game depened on the "camera" to render) or there is an undiscovered quantum property that is confined to dimensions known or unknown that have yet to be discovered.

In QM you have the observer, in relativity you have the reference frame, I think physics is exploring fundamental properies of the reality we experience,that it is a subset of something else.

People talk about a quantum particles as being in many places at once. When you ask what that means, the explanation is that they aren’t in one place, their position is represented as a probability curve of the places that they might be right now, and then when an observer observes the particle, that curve flattens down to where the particle is.

That seems like a very anthropocentric view of the universe. Why would it matter whether a particle is “being observed”, UNLESS the act of observation has a side-effect. If “observation” is purely passive then it can’t affect anything, by definition.

A MUCH simpler explanation is that the way that we observe things (by looking at them) is by bouncing photos off of them. Quantum particles are small enough that bouncing a photon off of it can change its course.

Here’s an analogy : you’re blind, but you’re super good at throwing and catching basketballs. The way that you observe the world is by throwing a basketball and then timing how long it takes to come back to you and catch it, and by observing if it comes back at an angle or with some spin on it. Imagine you come across a pigeon. You throw the basketball at the pigeon. You observe strange behavior of the pigeon when you “observe” it vs when you don’t. You formulate the pigeon uncertainty principle. You describe pigeons as spooky. You just accept that pigeons follow different physics than school buses.

I believe the experiments were conductes in vaccum without light or photons. The double silt experiment I believe. From what I gather,they send particles in a controlled environment and see where they land AFTER it went through the silts, so interactions after the silt shouldn't affect which silt it goes through. That's why I said it could be some unknown interaction between the observer and the particles. Or unknown propery of a known interaction like gravitation.

To me, it sort of sounds like how time dilation works in relativity except for a different dimension.

My $0.02 exactly. I see this is everyday life. People think if you can't measure something it doesn't exist or isn't worthwhile. I would argue quite the contrary :)

I think of it as driven by thermodynamics - the state is "collapsed" when it's too informationally entangled with the rest of the universe. It's not really "collapse", just our good friend positive entropy.

This is indeed the case, this process is called decoherence. https://en.wikipedia.org/wiki/Quantum_decoherence

So does that mean the idea of a "multiverse" is in the same box?

Edit: I'll rephrase (I'm serious) - isn't the idea of the multiverse based on the schrodinger's cat in a box idea, and the need for an observer? Or is the whole multiverse idea just sci fi? Or is there another physical basis for the idea of a multiverse?

The paralell universe thingy or the "multiple worlds" interpretation (which is what i assume you mean) is one of the competing philosophical explanations for what is going on during quantum mechanics. Like most topics in metaphysics, there is no evidence either way, and there are competiting interpretations that are just as good (but don't capture the imagination in the same way). Its based off the cat experiment in that its trying to explain what is happening there metaphysically, but the parallel universe interpretation doesn't make any testable predictions beyond those made by quantum mechanics, so neither the experiment nor any other experiment, proves it.

Any sort of visiting paralell universes stuff is pure sf.

The Everett interpretation of quantum mechanics is not "metaphysics", the theory is principally testable and falsifiable by empirical data. The experiments needed to test it are just not yet feasible. Sean Caroll has written a nice blog post about this in 2015 [1].

[1] https://www.preposterousuniverse.com/blog/2015/02/19/the-wro...

yes, thanks, thats what I meant. While I'm here, something I've always wondered about the multiple worlds interpretation is where does the energy come from for all these parallel universes? Like if each possible event causes a split then haven't we just doubled the energy we started with? since we've created a whole new universe.

I don't think there's new energy: the 'new universe' is just a part of the evolving wavefunction, which conserves energy.

Yes, and there is billon of quantum events happening right now in each cubic inches of air around you. So billions of universe literally from thin air. Multiverse is fun but absurd.

You seem to argue from an economic point of view, as if it was too "expensive" or "wasteful" to have all those universes. But MWI doesn't add any postulates to QM, in fact it is the simplest of the interpretations and a direct translation of what the math of QM says. All those universes are as "expensive" as the quantum mechanical state superposition they represent, and the superposition is a central tenet of QM and thoroughly tested. Your conclusion could be rephrased as "quantum superposition is fun but absurd".

There are several different "multiverse" ideas, from the top of my head the many worlds interpretation of QM, the string landscape, the multiverse of general relativity, the multiple branes in Randall-Sudrum models.

Thing is, multiverse ideas are not testable and therefore not physics. Theorists like to entertain ourselves with them to a certain degree, but they are just that, a kind of Science Fiction. For that reason, theorists never bother to distinguish between the different kinds of multiverses, that is a tedious and ultimately not important task.

Now science writers love to write about the multiverse, because they are good entertainment, however they lack the technical sophistication to actually distinguish between the different kinds of multiverse.

https://en.wikipedia.org/wiki/Interpretations_of_quantum_mec...

Yes thanks, I've looked at all these from time to time, but the schrodinger's cat interpretation presented here (lets call it (1) and the many worlds interpretation (2) seems contradictory to me (or perhaps the same fallacy). So in (1) schrodinger's experiment says that you can't regard the observer as being some intelligent entity, the observer is just other particles - the wave form collapses in a small delta of time, and provides the continuity we see in the macroscopic world (a lot of my interpretation here I suppose). Now in (2) isn't this the same as the problem with (1)? the collapse happens near instantaneously and so these other worlds are fleeting possibilities that never really existed, its the same fallacy as the cat in the box never really being dead and alive.

>in (1)..., the observer is just other particles.

It has been proven that non-concious observers can trigger a wavefunction collapse through variations of the dual slit experiment. What we don't necessarily know is exactly how the chain of wavefunction collapse occurs from e.g. the "opening of the box" to e.g. the human eye. This is known as "the measurement problem".

Also, fwiw, in both the Copenhagen interpretation (1) and the Many Worlds Interpretation (2), the observer is simply any particle which measures the event. It may be more intuitive to say that as soon as particle/s depend on knowing the answer to the wavefunction collapse, it will collapse.

This may be "fuzzy" as well meaning that if the particles don't need a precise answer only the amount of wavefunction collapse needed to give that level of precision will occur.

>Now in (2) isn't this the same as the problem with (1)? the collapse happens near instantaneously and so these other worlds are fleeting possibilities that never really existed, its the same fallacy as the cat in the box never really being dead

Many Worlds Interpretation posits that the _all_ other worlds absolutely exist before and after the collapse. After wavefunction collapse, each possible outcome occurs in a separate world. The one that "we see" is merely one outcome being experienced. Indeed, the reason this may be confusing is that you have to realize that other versions of yourself will see the different outcomes, each one convinced that they're the only version.

It can sound kind of crazy and we have no way of proving the existence of these other worlds but the interpretation is still taken seriously by many in part due to it being the most literal interpretation of the Schrodinger Equations.

>the wave form collapses in a small delta of time, and provides the continuity we see in the macroscopic world

You refer to this as a "problem" i.e. that these collapses are vanishingly small and so we never encounter them. But we can in fact encounter them!

Imagine shooting thousands of bullets through two slits with some degree of known error in aiming. The wall on the other side of the two slits will likely have holes in two vertical lines.

    |    |

This is also what happens when we measure a photon before it enters the slits. It behaves as a particle would.

Now imagine you push liquid water through the slits instead. The water forms waves as it passes through the slits. The peaks of the waves when they hit the wall on the other side form something different that looks like this instead.

| | | | | | | |

This is what happens (after shooting multiple photons) when we make no such measurement of the photons.

Now, to us, each photon comes out in different spots instead of all at once like with the wave. The first might be

And then

   |.    |

But sure enough, with enough photons it will eventually appear as

| | | | | | | |

This means that either:

Copenhagen:

A pretty literal wave of possibilities travels through the slits. When it hits the wall, this so-called wavefunction collapses into a single point. That point will be statistically likely to land somewhere on the many-lined diffraction pattern.

Many Worlds:

Multiple worlds exist in which each of the single points follow the different trajectories we see. They still form a diffraction pattern because these worlds are defined by the same Schrodinger Equations that may also define the wavefunction collapse.

There's a lot more that I'm skipping over such as Pilot Wave Theory which posits that each particle was in fact always a particle that instead is guided by a "pilot wave" that can sort of see the future, or travel faster than light in order to determine where it should land. Ultimately what I'm trying to say though is that there is no way around quantum mechanics. Yes, the timeframes are tiny and the cat probably isn't alive and dead at the same time due to decoherence occuring well before you open the box; but reality is still very much quantum and there are ways to observe that.

It's weird af, but it's absolutely happening.

Many thanks, I don't doubt its how things are, almost thought I had a handle on it :-). Will have to take a year or two sometime and do some reading, don't think I really understand what a 'collapse' is, amongst many other things.

Edit: is a collapse a measurement? Before the measurement all the possible states are there, then a measurement occurs, and we then know the result (within uncertainty).

I believe it to be fundamentally at odds with how we evolved to understand the universe, so don't feel bad. Even Einstein was conflicted by some of it while he worked to prove it.

The collapse is a measurement. It is also the instantaneous moment that a particle such as a photon goes from being a wave-like to being particle-like. In many ways it is just a name given to the phenomenon that we know occurs - that particles act as waves until we need them to be more "real" so to speak.

In Copenhagen, the "wavefunction collapse" is when the particle "picks a spot to land" inside of its wave. The spots it is likely to land are defined by the peaks and valleys of the wave.

Imagine liquid waves in the ocean again. They go up and down with fairly predictable heights of waves. Wavefunction collapse is when those waves decide to collapse into a small rock instead. But where should the small rock wind up? Well the highest wave of course. The wavefunction collapse is when the decision occurs to _place_ the rock; when the universe says "throw a dart somewhere along this path of likely positions".

That's a bit more metaphorical and philosophical but maybe it puts it into perspective a bit better? To be honest, I don't understand it very well and certainly couldn't tell you why it happens from more basic principles. This is part of the reason there are competing interpretations which is that even Copenhagen style wavefunction collapse _feels_ weird.

Thanks again, there seems to be a lot of then thats what happens :-), hopefully some bright young fellow figures it out one day.

There is something and there is nothing. We think we are something, but in someone else's view we are nothing.

You are the cat inside the box. You exist as a person, live in a planet and the entire setup could and couldn't be real. The experiment prooves that something is uncertain and all these are nonsense.

> as soon as the radioactive atom interacts with the Geiger counter

Doesn't the paradox arise precisely because the time at which the atom will interact is probabilistic?

Pretty sure no one's ever actually done this experiment, have you ever tried to put a cat in a box?

They love boxes. Or taped rectangles.

It proved that it was and wasn't an experiment at the same time, and that the experiment's setup was and wasn't detailed enough and you could only know it when you read the teaching material.

I have been mislead about Schroedinger's cat, but now I get the absurdity. However, I also feel there might be a conceptual mistake in the experiment setup: there -is- a conscious observer present inside of the sealed box: the cat. Thus there is no super-position and therefore the cat will observe itself when it dies (or stays alive), matching later experiments' results. Science: it works! But Schrodinger's attempt at absurd comedy seems to have failed.

> there -is- a conscious observer present inside of the sealed box: the cat. Thus there is no super-position and therefore the cat will observe itself

I think you are misinterpreting what "observe" means in this context. Conciousness has nothing to do with it.

The article mentions "conscious observer" six times. Surely it must mean something involving consciousness?

This usage is misleading and surprisingly common because it helps to frame the problem well. To be clear, an "observer" in the quantum context is merely anything which is measuring the outcome of an event. It need not be conscious but it can be.

Having said that, I think you're actually correct to point this out! The cat will obviously have a look around inside the box and likely cause wavefunction collapse. I believe the cat is meant to be fundamentally unable to effect things though.

After all, it's mostly an interesting problem because it posits that anything that could be "alive" inside the box would be in a superposition of alive and dead which is something that's never been observed and probably can't happen due to the unstable nature of wavefunction collapse in the real world.

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