/sci/ - Science & Math

The cat is alive.

Let's talk about quantum mechanics and the role of the observer.

If the cat had consciousness, would it think Schrödinger is in superposition?

One of the axioms of quantum mechanics states that a collapsed wave function will yield the same eigenvalue when the same observable is applied again and no other observable was applied inbetween.

Let's apply this to Schrodinger's cat! You put the cat in the box. Clearly at this point the cat is alive. So you know the eigenvalue of the "dead or alive" operator. After closing the box, no measurement is made. We don't interact with the cat. Therefore opening the box again should alway yield the result "cat is alive".

Doesn't this invalidate Schrodinger's paradox? The cat cannot be in superposition of dead and alive because we always know it is alive!

What is /sci/'s opinion on the von-Neumann-Wigner interpretation?

Together with the "Wigner's friend" extension of the Schrodinger cat paradox it appears more plausible than Copenhagen interpretation.

http://en.wikipedia.org/wiki/Von_Neumann%E2%80%93Wigner_interpretation
http://en.wikipedia.org/wiki/Wigner%27s_friend#Consciousness_and_measurement

Thought?

In the double slit experimet, in quantum physics, it shows that a conscious being is necessary to collapse the wave function and become some'thing'.

My question is:
Are we sure that ONLY a conscious observer can collapse the wave function?
Can an animal other than a human?
If only humans can collapse the wave function, how did the universe become what it is without a conscious being observing it and collapsing the wave function?!?

To not jump automatically to concluding that there IS a consciousness above humans', I wonder then what are the alternate explainations.

What are the alternate explainations?

Any theoretical physicists here today? I have questions about multiverse theory.

What is the conceptual difference between a multiverse with finitely many universes vs a multiverse with infinitely many universes? Which one is scientifically more likely? How does the multiverse theory explain the big bang? Or does it make the question more complicated? What is the difference between a multiverse and a collection of parallel universes? In which theory is travelling between different universes possible in theory and how is it done practically?

Pop sci fan with a few questions here. Quantum mechanics.

Is superposition a different state of matter? I'm curious. What does it physically mean for a particle to be in superposition? How does a particle in superposition look differently from a particle not in superposition? What evidence is there for the superposition theory? Can superposition be iterated infinitely to get infinitely superposed particles?

Help me understand the Schrodinger cat experiment, /sci/.

Schrodinger says the cat is in superposition of being dead and alive until we open the box. But how do I have to think of superposition? Biology tells us that dead vs alive is binary and mutually exclusive. So the cat cannot really be dead and alive at the same time.

What is the right interpretation of superposition? What would the cat look like if we opened the box and observed the superposition state before collapsing its wave function?

What if actually the particles in QM are determinstic and only their trajectories are probabilistic?

Instead of a wavefunction the particle is just a particle in a definite state. The stochasticity emerges from random transitions of states. The time evolution operator is the truly probabilistic element acting on definite states. No collapse of wave function is needed anymore.

What do you think of my theory /sci/?

In the cat analogy: The cat is never in superposition. It is either dead or alive but inbetween - before opening the box - it has been transitioned randomly from dead to alive and from alive to dead possibly infinite times.

Is it possible to reconstruct the history of a wave function?

For example in the Schrodinger cat experiment. Let's say quantum mechanic X puts the cat in the box and leaves the room. A few hours later X comes back to his lab and opens the box, finding the cat alive. Can X know that it was him who collapsed the wave function? If for example his colleague Y opened the box before him and collapsed the cat's wave function, will X ever find out?

Imagine the standard Schrodinger's cat (let's call it AliceCat). It exists in a quantum superposition of both alive and dead until it is observed. But what if the observer is another Schrodinger's cat (let's call it BobCat)? A one way mirror lets BobCat observe AliceCat, but as BobCat is both alive and dead he is both observing and not observing AliceCat. What would happen? I don't think BobCat could simultaneously cause and not cause AliceCat's position to collapse into dead or alive.

And what if the mirror were replaced by glass so that AliceCat and BobCat were observing (and not observing) each other?

Am I right in thinking that only an observer that is not in a superposition can cause a superposition to collapse? If so, what would happen if a weapon big enough to destroy the universe were hooked up to a Schrodinger mechanism, putting the entire universe into a superposition (Schrodinger's universe if you will)? If there can be no observer outside the universe, presumably the whole universe and everything in it would remain in a superposition indefinitely - and no observer in the universe could cause superpositions to collapse?

If so, does that prove, from the fact that we can cause superpositions to collapse, that the universe is not in a superposition?

Put a particle in a box. The box is at rest, so you know the exact position of its center. Shrink the box. The particle will remain in the box. The smaller the box becomes, the less movement is possible for the particle. In the end the box will perfectly fit the particle. The particle cannot move anymore and has therefore zero momentum. We then know the exact position and the exact momentum of the particle.

Did I just disproved Heisenburg's uncertainty principal?

I'm trying to understand Schrodinger's cat and I need your help, /sci/.

The cat's wavefunction is 3 dimensional ("dead", "alive" and "superposition"). The reality surrounding the cat box is 3 dimensional as well ("length", "width", "depth").

How are the dimensions related? What does "dimension" even mean in physics?

So I was watching this documentary on quantum mechanics ( http://www.youtube.com/watch?v=TNAZlhewURA ) and a question came to my mind.

What is the physical/ontological nature of entanglement? We can write down the kets of an entangled state, but what does it mean physically/ontologically? What makes an entangled wave function different from a non-entangled wave function to allow instantaneous transmission of informatoin all acrosss the universe?

I like to think in analogies, so here's the Schrodinger cat picture: Imagine two entangled Schrodinger cats, each in its own box. One box is carried billions of lightyears away to the other end of the universe. Upon opening one box, the wave function of the _other_ cat is instantly collapsed. The information travelled faster than light, even faster than the expansion of the universe.

In the non-entangled case the cat's wavefunction is confined to the box. How does entanglement make the wavefunction universal and spatially unbounded?

Is it possible to reconstruct the history or the dimensionality of a wave function after it has been collapsed?

For example in the Schrodinger cat experiment. Imagine someone found a dead cat in the box. Can the observer reconstruct that the cat was in superpositiong before its wave function collapsed? Can he reconstruct that "dead" and "alive" were the only possible states? Or does he have to see the cat's state space as one dimensional? In the latter case, how can we know that general particles in quantum mechanics didn't have a higher or lower dimensional state space prior to collapsing their wave function?

Imagine two entangled particles A and B. For the sake of simplicity let's talk about Schrodinger cats. Collapsing the wave function of A causes the wave function of B to collapse and conversely collapsing the wave function of B causes the wave function of A to collapse.

Both A and B are being observed.
Observer X first receives the message "A is die" and infers "observing A caused the death of B".
Observer Y first receives the message "B is die" and infers "observing B caused the death of A".

Who is right? How can we reconstruct the correct causality?
Or is causality merely a construct of the mind and not a physical thing?

Is quantum mechanics applicable to the real world or does it only work in theory?

http://en.wikipedia.org/wiki/Schr%C3%B6dinger%27s_cat
someone explain this to someone who does not understand this.

I don't get it. How is the cat DEAD AND ALIVE AT THE SAME TIME?

Yeah, I just wanted to check with you guys-
Have ANY of you come up with your own solutions to Schrodinger's cat?

Why is it wrong to treat time like a spatial dimension?
I mean the mathematical notion of dimension doesn't care about physical interpretation.

There's one thing I don't understand about Schrodinger's cat experiment.

The cat being dead or alive depends on the state of a particle that decayed or didn't decay. The particle is a quantum particle to be viewed under the laws of quantum mechanics. In quantum mechanics state space of wave functions is infinite dimensional. How can then the cat be only dead or alive? Why do infinite states reduce to two states without loss of information?

Does Schrodinger's cat experiment account for quantum entanglement? Or can it be modified to account for quantum entanglement?

If the cat was entangled with a particle outside the box, we could infer the cat being dead or alive without opening the box. But this requires a particle which can only have two states. Does such a particle exist or is it purely hypothetical?

/b/ told me to come here.

I don't understand Schrodinger's cat. I know a little bit of cuantum mechanics but I don't get how the cat is dead AND alive at the same time.

Pls someone explain.