Quantum uncertainty, and Schrodinger's cat

[untermensche]

I have to disagree.

When we take a measurement, it's not the scientist that is the observer, it's the measuring device. The measuring device is interacting with whatever it is you're measuring, and that's what causes the collapse of the wave function. The scientist reading the dial is not what causes the collapse of the wave function. So in the Schrodinger's cat example, once a quantum state starts a chemical reaction in the petri dish, then the damn petri dish is the measuring device that causes the collapse of the wave function. By the time the chemical reaction starts, the chain of events has entered the macroscopic world. The person opening the box is the equivalent of a scientist looking at a dial on a measuring device.

I would love to know what exactly can be an "observer", and how it makes it's "observations".

How does something observe when it has no eyes?

Are we twisting the definition of "observer"?

 

[skepticalbip]

The Copenhagen interpretation has nothing to do with cats or entanglement. It is an interpretation of the meaning of quantum uncertainty. It takes Schrodinger's wave function literally as meaning that all possible states exist simultaneously while Schrodinger meant it as a mathematical tool to calculate the probability of the state.

Schrodinger’s thought experiment was intended to show the absurdity of that interpretation. However, the supporters of the interpretation said that, since the state of the cat was solely dependent on the state of the decay process, the state of the cat was entangled with it. If the quantum uncertainty says that the state of the decay process exists in all possible states (superposition) then, since the cat’s state is entangled with it, the cat’s state is in all possible states, a state of entangled superposition.

ETA:
It is a thought experiment that can not be actually carried out. It is like Einstein's thought experiment of riding on a photon to see what the universe looks like from that perspective. Such experiments allow us to mentally test ideas to see where they take us. Einstein's led to the theory of relativity. Whether this one will lead anywhere is, as yet, not known.

I have to disagree.

When we take a measurement, it's not the scientist that is the observer, it's the measuring device. The measuring device is interacting with whatever it is you're measuring, and that's what causes the collapse of the wave function. The scientist reading the dial is not what causes the collapse of the wave function. So in the Schrodinger's cat example, once a quantum state starts a chemical reaction in the petri dish, then the damn petri dish is the measuring device that causes the collapse of the wave function. By the time the chemical reaction starts, the chain of events has entered the macroscopic world. The person opening the box is the equivalent of a scientist looking at a dial on a measuring device.

You don't seem to have understood my post or thought experiments in general. Your response has nothing to do with what I wrote or with the argument made by those who support the Copenhagen interpretation.

 

[ryan]

I have to disagree.

When we take a measurement, it's not the scientist that is the observer, it's the measuring device. The measuring device is interacting with whatever it is you're measuring, and that's what causes the collapse of the wave function. The scientist reading the dial is not what causes the collapse of the wave function. So in the Schrodinger's cat example, once a quantum state starts a chemical reaction in the petri dish, then the damn petri dish is the measuring device that causes the collapse of the wave function. By the time the chemical reaction starts, the chain of events has entered the macroscopic world. The person opening the box is the equivalent of a scientist looking at a dial on a measuring device.

You don't seem to have understood my post or thought experiments in general. Your response has nothing to do with what I wrote or with the argument made by those who support the Copenhagen interpretation.

* I should add that this probably should have been posted for Underseer to read.

I think I know what the main issue is here. The controversy seems to come down to whether the cat is alive and dead in a superposition or if it just seems that way because of our limited ability to predict its actual state.

But from what I have read, it seems like the crazier notion of a superposition is winning the philosophical argument. This seems to be because the probability of certain simple experiments continues to be consistently random within the wave function's expected values.

 

[ryan]

I have to disagree.

When we take a measurement, it's not the scientist that is the observer, it's the measuring device. The measuring device is interacting with whatever it is you're measuring, and that's what causes the collapse of the wave function. The scientist reading the dial is not what causes the collapse of the wave function. So in the Schrodinger's cat example, once a quantum state starts a chemical reaction in the petri dish, then the damn petri dish is the measuring device that causes the collapse of the wave function. By the time the chemical reaction starts, the chain of events has entered the macroscopic world. The person opening the box is the equivalent of a scientist looking at a dial on a measuring device.

I would love to know what exactly can be an "observer", and how it makes it's "observations".

How does something observe when it has no eyes?

Are we twisting the definition of "observer"?

I think it makes sense just to think of a measurement or an observation as decoherence or interference of a quantum system.

 

[Bomb#20]

I have to disagree.

When we take a measurement, it's not the scientist that is the observer, it's the measuring device. The measuring device is interacting with whatever it is you're measuring, and that's what causes the collapse of the wave function. The scientist reading the dial is not what causes the collapse of the wave function. So in the Schrodinger's cat example, once a quantum state starts a chemical reaction in the petri dish, then the damn petri dish is the measuring device that causes the collapse of the wave function. By the time the chemical reaction starts, the chain of events has entered the macroscopic world. The person opening the box is the equivalent of a scientist looking at a dial on a measuring device.

I would love to know what exactly can be an "observer", and how it makes it's "observations".

How does something observe when it has no eyes?

Are we twisting the definition of "observer"?

The problem is we don't have a definition of "observer". Physicists have been arguing with one another about this since the 1920s without ever resolving it. The issue is called the Heisenberg Cut. Oversimplifying (but not by much), Quantum Mechanics consists of two laws, the Schroedinger Equation and the Born Rule. To predict any experimental outcome, first you apply the Schroedinger Equation to the initial conditions, which gives you the "amplitude" of each possible outcome. Then you apply the Born Rule to the amplitudes, which gives you the probability of each outcome. So the question is, at what point in the physical process we're modeling does Nature actually switch from following Schroedinger to following Born? That's the Cut. Nobody knows the answer -- all we can tell is it's sometime after all the crazy quantum weirdness but before we mentally recognize that the Geiger-counter clicked. Some people think the Cut is at the last possible moment, the changing of a conscious human mind -- and say "Observation" collapses the wave function; other people say it's much earlier than that, at the Geiger-counter itself, and say "Measurement" collapses the wave function; other people say it's even earlier than that -- the wave function is intrinsically slightly unstable and collapses all by itself; still other people say there simply is no Cut, and have various explanations for how Nature makes it look like there is one.

 

[ryan]

I would love to know what exactly can be an "observer", and how it makes it's "observations".

How does something observe when it has no eyes?

Are we twisting the definition of "observer"?

The problem is we don't have a definition of "observer". Physicists have been arguing with one another about this since the 1920s without ever resolving it. The issue is called the Heisenberg Cut. Oversimplifying (but not by much), Quantum Mechanics consists of two laws, the Schroedinger Equation and the Born Rule. To predict any experimental outcome, first you apply the Schroedinger Equation to the initial conditions, which gives you the "amplitude" of each possible outcome. Then you apply the Born Rule to the amplitudes, which gives you the probability of each outcome. So the question is, at what point in the physical process we're modeling does Nature actually switch from following Schroedinger to following Born? That's the Cut. Nobody knows the answer -- all we can tell is it's sometime after all the crazy quantum weirdness but before we mentally recognize that the Geiger-counter clicked. Some people think the Cut is at the last possible moment, the changing of a conscious human mind -- and say "Observation" collapses the wave function; other people say it's much earlier than that, at the Geiger-counter itself, and say "Measurement" collapses the wave function; other people say it's even earlier than that -- the wave function is intrinsically slightly unstable and collapses all by itself; still other people say there simply is no Cut, and have various explanations for how Nature makes it look like there is one.

I think Untermensche doesn't understand what the observation is. I think it is just the point where the state is "revealed". However, the observation seems relative only to the observer. The first observer is still in a superposition to a second would-be observer who hasn't observed the first observer yet. It seems like a chain of uncertainties linked together by observers living or nonliving.

 

[Juma]

The problem is we don't have a definition of "observer". Physicists have been arguing with one another about this since the 1920s without ever resolving it. The issue is called the Heisenberg Cut. Oversimplifying (but not by much), Quantum Mechanics consists of two laws, the Schroedinger Equation and the Born Rule. To predict any experimental outcome, first you apply the Schroedinger Equation to the initial conditions, which gives you the "amplitude" of each possible outcome. Then you apply the Born Rule to the amplitudes, which gives you the probability of each outcome. So the question is, at what point in the physical process we're modeling does Nature actually switch from following Schroedinger to following Born? That's the Cut. Nobody knows the answer -- all we can tell is it's sometime after all the crazy quantum weirdness but before we mentally recognize that the Geiger-counter clicked. Some people think the Cut is at the last possible moment, the changing of a conscious human mind -- and say "Observation" collapses the wave function; other people say it's much earlier than that, at the Geiger-counter itself, and say "Measurement" collapses the wave function; other people say it's even earlier than that -- the wave function is intrinsically slightly unstable and collapses all by itself; still other people say there simply is no Cut, and have various explanations for how Nature makes it look like there is one.

I think Untermensche doesn't understand what the observation is. I think it is just the point where the state is "revealed". However, the observation seems relative only to the observer. The first observer is still in a superposition to a second would-be observer who hasn't observed the first observer yet. It seems like a chain of uncertainties linked together by observers living or nonliving.

No. It isnt. When the wave has collapsed, it has done so for all observers.

 

[Bomb#20]

I think Untermensche doesn't understand what the observation is. I think it is just the point where the state is "revealed". However, the observation seems relative only to the observer. The first observer is still in a superposition to a second would-be observer who hasn't observed the first observer yet. It seems like a chain of uncertainties linked together by observers living or nonliving.

No. It isnt. When the wave has collapsed, it has done so for all observers.

This is a long-standing question, not yet settled. It's called Wigner's Friend.

 

[ryan]

I think Untermensche doesn't understand what the observation is. I think it is just the point where the state is "revealed". However, the observation seems relative only to the observer. The first observer is still in a superposition to a second would-be observer who hasn't observed the first observer yet. It seems like a chain of uncertainties linked together by observers living or nonliving.

No. It isnt. When the wave has collapsed, it has done so for all observers.

Okay, but then you are taking the side of a wave function that collapses. From what I understand, that is still in debate.

Then there is the many worlds interpretation as you are probably well aware of. The first observer knows the state, say, the cat is alive in his "world". But the cat might still be alive for a different person. But in the "world" with the cat alive, they might both agree that the cat died.

 

[DBT]

MMI says that the world splits at each point of probability, in one world the cat is alive, in another world the cat is dead. An observer in the former only sees the cat as alive, the latter observer only sees the cat as being dead, there is no contact between observers and worlds, the cat is in a definite state in both worlds, dead in one, alive in the other.

 

[Underseer]

I have to disagree.

When we take a measurement, it's not the scientist that is the observer, it's the measuring device. The measuring device is interacting with whatever it is you're measuring, and that's what causes the collapse of the wave function. The scientist reading the dial is not what causes the collapse of the wave function. So in the Schrodinger's cat example, once a quantum state starts a chemical reaction in the petri dish, then the damn petri dish is the measuring device that causes the collapse of the wave function. By the time the chemical reaction starts, the chain of events has entered the macroscopic world. The person opening the box is the equivalent of a scientist looking at a dial on a measuring device.

I would love to know what exactly can be an "observer", and how it makes it's "observations".

How does something observe when it has no eyes?

Are we twisting the definition of "observer"?

No, I'm not.

Heisenberg's Uncertainty principle exists because any attempt to measure the position and velocity/direction of a particle necessarily involves bouncing another particle off of it or having it pass through a field. In either case, your measuring device is causing a significant change in the thing you're trying to measure, so simply by measuring it, you are changing it enough that your measurements are no longer valid.

This is caused by the part of the measuring device that interacts with the particle in question and is not caused by the scientist looking at a dial on a machine. Similarly, the collapse of the wave function is caused by the business end of the measuring device, not the part of the device that sets the position of a needle on a dial.

 

[Bomb#20]

Are we twisting the definition of "observer"?

No, I'm not.

Heisenberg's Uncertainty principle exists because any attempt to measure the position and velocity/direction of a particle necessarily involves bouncing another particle off of it or having it pass through a field. In either case, your measuring device is causing a significant change in the thing you're trying to measure, so simply by measuring it, you are changing it enough that your measurements are no longer valid.

That's a widespread misconception perpetuated by many bad popularizations of QM.

"... the uncertainty principle is inherent in the properties of all wave-like systems, and that it arises in quantum mechanics simply due to the matter wave nature of all quantum objects. ...
Mathematically, in wave mechanics, the uncertainty relation between position and momentum arises because the expressions of the wavefunction in the two corresponding orthonormal bases in Hilbert space are Fourier transforms of one another (i.e., position and momentum are conjugate variables). A nonzero function and its Fourier transform cannot both be sharply localized."

(Source)

ETA: It's straightforward to measure a particle's position or momentum or spin or whatever without bouncing anything off it or doing anything at all to it that can change it. You just have to generate two particles in an entangled state, such that the sum of their properties of interest is known based on a conservation law. Then you bounce something off the other particle from the one you want to measure without affecting.

 

[bilby]

No, I'm not.

Heisenberg's Uncertainty principle exists because any attempt to measure the position and velocity/direction of a particle necessarily involves bouncing another particle off of it or having it pass through a field. In either case, your measuring device is causing a significant change in the thing you're trying to measure, so simply by measuring it, you are changing it enough that your measurements are no longer valid.

That's a widespread misconception perpetuated by many bad popularizations of QM.

"... the uncertainty principle is inherent in the properties of all wave-like systems, and that it arises in quantum mechanics simply due to the matter wave nature of all quantum objects. ...
Mathematically, in wave mechanics, the uncertainty relation between position and momentum arises because the expressions of the wavefunction in the two corresponding orthonormal bases in Hilbert space are Fourier transforms of one another (i.e., position and momentum are conjugate variables). A nonzero function and its Fourier transform cannot both be sharply localized."

(Source)

ETA: It's straightforward to measure a particle's position or momentum or spin or whatever without bouncing anything off it or doing anything at all to it that can change it. You just have to generate two particles in an entangled state, such that the sum of their properties of interest is known based on a conservation law. Then you bounce something off the other particle from the one you want to measure without affecting.

A cop pulled Werner Heisenberg over on the freeway. "Excuse me sir," says the cop, "Did you know you that I just recorded your speed at exactly 98 miles per hour?"

"Oh great," says Heisenberg. "Now I'm lost".

 

[Juma]

No. It isnt. When the wave has collapsed, it has done so for all observers.

This is a long-standing question, not yet settled. It's called Wigner's Friend.

No. There really is no question. You have "interpreters" arguing over nothing. When you have a measurement then the wave has collapsed.

 

[untermensche]

I would love to know what exactly can be an "observer", and how it makes it's "observations".

How does something observe when it has no eyes?

Are we twisting the definition of "observer"?

No, I'm not.

Heisenberg's Uncertainty principle exists because any attempt to measure the position and velocity/direction of a particle necessarily involves bouncing another particle off of it or having it pass through a field. In either case, your measuring device is causing a significant change in the thing you're trying to measure, so simply by measuring it, you are changing it enough that your measurements are no longer valid.

This is caused by the part of the measuring device that interacts with the particle in question and is not caused by the scientist looking at a dial on a machine. Similarly, the collapse of the wave function is caused by the business end of the measuring device, not the part of the device that sets the position of a needle on a dial.

Are you saying that "observing" and "detecting" are the same thing?

Because one is an act of consciousness and one is not.

But if we have some kind of "detection" does it have to be man-made "detection"? Is this whole theory consciousness-centric?

Because all matter can "detect" the gravitational fields of other matter. If some lethal gas has been emitted the air molecules in the box can "detect" that, even the box itself can "detect" it.

- - - Updated - - -

This is a long-standing question, not yet settled. It's called Wigner's Friend.

No. There really is no question. You have "interpreters" arguing over nothing. When you have a measurement then the wave has collapsed.

What counts as a measurement?

An oxygen molecule will react to the gravitational field of any gas molecules emitted in the box. And it will react in accordance to the strength of that field.

Is that a measurement?

 

[Bomb#20]

This is a long-standing question, not yet settled. It's called Wigner's Friend.

No. There really is no question. You have "interpreters" arguing over nothing. When you have a measurement then the wave has collapsed.

That isn't how this works. If you say

No. There really is no question. You have "interpreters" arguing over nothing. Shut up and calculate.​

then you have a case; but if you say

No. There really is no question. You have "interpreters" arguing over nothing. When you have a measurement then the wave has collapsed.​

then that just makes you one of the interpreters arguing over the question.

 

[ryan]

This is a long-standing question, not yet settled. It's called Wigner's Friend.

No. There really is no question. You have "interpreters" arguing over nothing. When you have a measurement then the wave has collapsed.

How do you know that you are not suspended in a superposition relative to someone who hasn't observed you or the experimental outcome yet?

 

[Juma]

No. There really is no question. You have "interpreters" arguing over nothing. When you have a measurement then the wave has collapsed.

How do you know that you are not suspended in a superposition relative to someone who hasn't observed you or the experimental outcome yet?

Because i am at a specific position doing specific things. How could another observer observe anything else?

 

[ryan]

How do you know that you are not suspended in a superposition relative to someone who hasn't observed you or the experimental outcome yet?

Because i am at a specific position doing specific things. How could another observer observe anything else?

Oh, so you do you not believe that the cat is in a superposition of being alive and dead?

 

[Juma]

Because i am at a specific position doing specific things. How could another observer observe anything else?

Oh, so you do you not believe that the cat is in a superposition of being alive and dead?

What cat?