patrick.net

Wait wasn't this topic already discussed ad nauseam in another thread?

Wasn't it just a "thought experiment" and not a real experiment?

See this old post.

Executive Summary

The Heisenberg Uncertainty Principle says that the value of any property of a quantum object cannot be know with zero error, i.e., there is always some uncertainty in in actual value. The Heisenberg Uncertainty Formulas are

Δx Δp > h / 2
Δx is the change in a particle's position or displacement.
Δp is the change in the particle's momentum.
h is the Planck constant, 6.62606957 x 10^-34 J s

All this formula says is that the product of the change in displacement and the change in momentum is greater than a certain constant value, which implies if you try to measure either the displacement or the momentum, you can only do so within a certain error.

The Copenhagen Interpretation is a philosophical, not physics, school of thought that says because the value of the property can only be estimated to within a range (the maximum error), the property actually assumes all values within that range.

The Schrödinger's Cat thought experiment refutes the Copenhagen Interpretation by showing how ridiculous it is when applied to the real world. It takes a binary property, whether or not a radioactive particle has decayed, and converts it into a macroscopic property, whether a cat is dead or alive. If the quantum property actually can take on both states at once, so two must the cat, but that's impossible and ridiculous and no one would believe it.

Advocates of the Copenhagen Interpretation tried to bullshit their way out of this by saying that as soon as the radioactive decay is observed by the sensor, the quantum property "collapses" to one specific value. But if that actually did happen in the physical world, the Copenhagen Interpretation would be meaningless anyway as it could never have any affect on anything.

freak80 says

Wasn't it just a "thought experiment" and not a real experiment?

Only because it would be unethical to run the experiment in real life. Newton's two bricks falling at the same time was a thought experiment as well. Thought experiments serve to show flows in logic and reasoning.

Dan Simmons' excellent "Hyperion" series uses a narrator who is stuck in a Schroedinger "cat box" and sentenced to die when a particle decays and the cyanide is released.

freak80 says

Wait wasn't this topic already discussed ad nauseam in another thread?

It was discussed in another thread. Heraclitusstudent proposed the subject, even though it was off topic, and seemed to disagree with Dan's comment:

Heraclitusstudent says

The MWI states there are 2 overlapping quantum states that encompass the entire cat, both have an objective reality, and that is what we are talking about: the quantum properties extend to macro objects... The only thing that is asserted and that can be empirically verified is that if you open the box, then, to you as an observer, it will appear like the dice is thrown and either the cat is alive or the cat is dead. What you think happened in-between (or after) is just interpretations not physics.

It is the topic of this thread, so as far as I'm concerned, others more knowledgeable than I can have at it. So far, I think Dan's interpretation more persuasive, i.e. the point of the thought experiment is to reduce to absurdity the Copenhagen Interpretation.

That a particle can exist in 2 states is the only way to explain certain observations.
But whether the cat can be in 2 states is just an interpretation that has no practical consequence. By the time it reaches someone's brain, the dice is cast one way or the other. This is just philosophy.

If you consider science an ever expanding reservoir of knowledge on the world around us - and consequently the remaining unknowns and superstitions an ever shrinking knowledge gap - it's very reassuring but it assumes that there is a tangible world around us that is independent of the observer. Unfortunately quantum mechanics puts you in the uncomfortable situation where the result of an experiment depends on what is measured. An observation 'collapses' a wave function. From there, some will jump to say human consciousness 'creates' the world, something that evokes Hindu mythology. That can't go very far because of the randomness of results, but in a way they have a right to raise the issue.

There is an interpretation that doesn't require a collapse of the wave function. If the 2 states exist in whatever is impacted. That extends to the observer's eyes and neurons. Then the observer's brain itself will exist in 2 states. And we are just one of these states and we observe only 1 branch. In some other state of the world the observer sees something else. So it sweeps under the carpet the uncomfortable notion of observer dependency.

It remains that science can only be based on observation and speculating on the existence of other states that we can't observe is not science. As far as science goes, observation causes collapse. And observation is always decided by a human being. You're left with a probability. And that's all there is to it.

Heraclitusstudent says

You're left with a probability. And that's all there is to it.

I hope there's more to it than that. As my statistics professor used to say: "Ultimately, all probabilities resolve to either zero or one, because something either happens or it doesn't." To posit a universe of macro-level uncertainty, or even a multi-verse, goes in the opposite direction of Occam's razor. I understand that the MWI can't currently be disproved, but I question whether things are in fact that complicated, with an infinite number of cats in an infinite number of boxes, and an infinite number of brains each embodying a slightly different collection of thoughts and every other possibility.

If you buy a lottery ticket, MWI would suggest that in an infinite number of universes you bought a losing ticket, yet in an infinite (and yet paradoxically smaller) number of universes you bought the winning ticket. Somehow, in this universe, most people find out within a few days that they lost, i.e. their probability of winning resolved from a small number to zero.

curious2 says

the MWI can't currently be disproved

Neither can the theory that we're all living in a computer simulation (like in The Matrix movie).

Such an idea is "not even wrong."

curious2 says

To posit a universe of macro-level uncertainty, or even a multi-verse, goes in the opposite direction of Occam's razor.

The uncertainty is there for sure for a particle decay. If you make the life of a cat depend on it, then you have the same uncertainty for the life of the cat. So there you have uncertainty at the macro level.
Logically that can't be avoided.

Heraclitusstudent says

From there, some will jump to say human consciousness 'creates' the world, something that evokes Hindu mythology.

Uh oh...I detect me some Quantum Woo...