cat in a box paradox

shaun_o_kane

I'm afraid cesiumfrog is wrong. Copenhagen does not say QM waveform "collapses" as a result of the interaction with a macroscopic system. Copenhagen say that you can choose the quantum-classical boundary anyway you want, typically at the interaction with macroscopic measurement devices. Hence the paradox. Two views are possible: the cat is the measurement device (classical-quantum boundary) and the waveform "collapses" (not a Copenhagen term) at the cat, or the external observer is the measurement device (classical-quantum boundary).

Copenhagen is simply applying the equations differently but equally validly.

cesiumfrog

I'd like to see you give an example of an irreversible process.

cesiumfrog

Perhaps you could specify where, since for this interpretation you seem both to have agreed with my representation of one "view" (your term; I used "take") and also agreed about the presence of a contradictory view?

Demystifier

Environment induced decoherence.
Of course, not true irreversible, but effectively (FAPP) irreversible. Just like "irreversible" processes in classical mechanics.

lightarrow

When I asked "Are you saying that QM can't describe irreversible processes?" I intended that as a question and nothing else, because I still don't know much about it; I'm aware that you know QM physics much better than me.
Or you intended to ask me a practical physical example?

shaun_o_kane

The Copenhagen Interpretation does not say that "collapse" occur when a quantum system interacts with a macroscopic system (how big does it have to be to be macroscopic?). Instead Bohr talked about a quantum-classic boundary - which can be chosen to be anywhere. Hence the Schrodinger's Cat Paradox.

One of goals of the Copenhagen school was to destroy the idea that somehow QM are described by a "real" waveform that evolves according to Schrodinger's equation. It seems in recent years that "real" waveforms have made a comeback (decoherence etc). There is no "paradox" if the waveform is not real. Each observer has different information, and therefore describes the situation using a different waveform.

Rade

If I place a coin in a box, and shake, is the coin: (1) alive (heads) or dead (tails) or (2) alive (heads) and dead (tails) ? imo, the correct answer is both (1) and (2) at the same moment of time and space. When you open the box you observe either heads or tails facing you, thus # 1 answer is correct. But at all times, whether observed or not, the coin has both head and tail aspects, thus # 2 answer is also equally correct at any time, including the time you observe when you open the box. I view this what Schrödinger was trying to say with the cat problem--that is, at the very same moment of time and space, the cat is a dialectic superposition of two opposite states (1) it is alive or dead and (2) it is alive and dead, thus [or state + and state ] = quantum reality.

lightarrow

Isnt'it a contradiction? It's real what you measure, not what you write down in a notebook.

mn4j

In Logic 101
by definition:
dead = not(alive)
alive = not(dead)

not(not(alive)) = alive

neither alive = dead
nor dead = alive
therefore the following statements are identically nonsensical:
- The cat is both alive and dead . ( The cat is not(dead) and dead )
- The can is neither alive nor dead. (The cat is dead and not(dead)


It follows therefore that the two statements have exactly identical meaning. They are not even false, they are illogical or nonsensical.

mn4j

The problem with a lot of these discussions is a confusion between epistemological issues and physical issues. Bohr's approach is epistemic rather than physical. And that's why Einstein had problems following it. To illustrate using your example

First, by definition if the coin is showing heads, it MUST not be showing tails.
ie. heads = not(tails) and not(heads) = tails. heads and tails are mutually exclusive PHYSICAL STATES. However, heads and tails are not mutually exclusive EPISTEMIC states.

Within the box, only one state can exist. Within the mind however, without adequate information (the box has not been opened), both states can have a certain probability adding up to 1. With absolutely no extra information, each physical state, will have an epistemic probability within the mind of 0.5 (heads=0.5, tails=0.5). Thus the "wavefunction" has two superposed states. The moment you open the box, you now have complete information "heads" for example, and the wave function collapses to a single point (heads=1, tails=0). Nothing is happening in the system, but a lot is happening in your mind.

The moment you start confusing epistemic states with physical states, you start contradicting yourself. Fortunately, or rather unfortunately, if you had a million coins in the box, you will notice that the physical state matches very closely the epistemic state of and opening the box does not give you any significant extra information.

This is fortunate in the sense that most quantum phenomena to date have been studied using ensembles of large numbers of individual entities. And this is the only reason the faulty copenhagen interpretation has appeared to work to date.

It is unfortunate because to date, QM continues to be paradoxical and unclear when explaining phenomena involving individual particles.

ZapperZ

If you are looking for someone and asked me where this person is, and I answered "he is neither in that room, nor in the other room", do you still go looking for this person in those 2 rooms?

The response given clearly stated that this person is not in that room, and this person is also not in the other room. Try it. Ask someone and see what it means.

This is still besides the point since I had clearly cited a reputable article by a respectable physicist who unambiguously used the same identical phrase that I had used in saying in English the Schrodinger Cat-state wavefunction. We could continue with this on and on with out own preferences, but I have seen no one else providing me with exact references where these other forms of describing this situation has been used.

Zz.

mn4j

This is a straw man. The question has to do with DEAD and ALIVE. There is a relationship between those two states, which your 2 rooms do not have. If by definition, not being in one room meant the person was in the other, the same as the relationship between dead and alive , then I would think you were smoking something by asserting the person was in neither room. And in that case, it would mean exactly the same thing as saying the person is in both rooms.

Read my logic again. The relationship between "dead" and "alive" can not be ignored in your analysis. If the OP had been about two rooms, the issue will be different. But so long as "not dead" IS "alive" and "not alive" is "dead", the phrases "neither dead nor alive" and "both dead and alive" mean exactly the same thing. This is logic 101, no need for a reference.

f95toli

But there has also been a LOT of work done on systems consisting of single objects that STILL can be put in a superposition; solid state qubits are a good example (single ions in ion traps is another). Superpositions are as " real" as any other state; if they were just due to "classical probability" quantum computers would not work (not to mention the fact that much of atomic and molecular physics would also not work).

ZapperZ

It isn't a straw man. The ONLY time we need to actually talk about something like this is when we communicate to the general public who has no clue on the mathematical description! We seldom have to use such words when we communicate among physicists, and certainly this issue is completely irrelevant when we make use of it.

Thus, it is with that audience in mind that such phrases are used. You are saying that the cat is "not dead" and also "not alive". It means that there are no alive property and there are no dead properties associated with that system. You can no longer force this into a binary system where by if it is not 1, it MUST be zero, because now, not 1 no longer means it is 0. That's the whole point of having a QUBIT where the states in between these two binaries are allowed before a measurement!

In the Stony Brook/Delft experiment, in fact, these two orthorgonal states oscillate between these two states! So now if you think things don't make sense, try figuring out that a cat can in fact oscillate not only from dead to alive and back to dead, but also transition in between those two states! These are not "strawman", they are experimental observations!

Zz.

f95toli

This is a nice paper for people who still think that superpositions in QM are only due to probabilistic effects.

http://www.arxiv.org/abs/0709.2135

Note that this system is EXACTLY analogous to a cavity-QED (QED=Quantum electrodynamics) experiment in the dispersive regime (this field is called circuit-QED). The difference is that in cavity-QED experiments microscopic systems like atoms and ions are used; here the two-state systems are superconducting qubits that are so large that you can easily see them an optical microscope. Despite this you still can see all the "usual" QM effects.

OOO

Let me ask several interconnected questions. Maybe they have already been answered and I haven't noticed. Maybe this is at the heart of my misunderstanding of the cat in a box paradox.

If we have a quantum system that is in a superposition of two states that decide between dead or alive:

1) Isn't the mechanism (the gun) that reads out this quantum system in order to make its decision a measuring device ?
2) Doesn't this measurement put the two-state system into one of the eigenstates such that the system isn't in a superposition anymore after the measurement ?
3) Aren't we obliged to press a red button in order to decide when the measurement ought to take place ?
4) Doesn't our pressing the red button decide about dead or alive unequivocally ?

So where is the paradox ?

f95toli

In my view the main problem with this paradox (or at least with the way it is often interpreted) is that there is a mysterios "observer" involved which performs the measurement. This observer is usually assumed to be a human (e.g. Schrödinger himself), meaning there is an implied assumption that the "collapse" must happen because a human is looking at the cat.

Now, obviously this is unphysical (unless one belives that humans are for some reason "special" in QM).
One could e.g. imagine replacing the cat with a Ph.D student; with the exception for the fact that the student is somewhat bigger than the cat (but not by orders magnitude) we have NOT changed the experimental conditions in any way. Hence, we must draw the conclusion that a Ph.D student can also be put in a superpostion of dead and alive.
In my view this shows quite clearly that there is something wrong with this gedanken experiment, and presumably the error comes from the fact that it is also implied that the cat is is not subject do decoherence due to interaction with the enviroment which ultmately will put it in a pointer state whether or not someone is looking or not.