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Do you think quantum rules apply at large scales?


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I’m torn. On one hand, it seems pretty obvious that humans can’t be in 2 places at the same time like atoms can. Otherwise, we should observe this in our daily lives without needing a microscope. 
 

On the other hand, humans are made of atoms, which are in turn made of subatomic particles. This kind of begs the question of how big an object has to be before quantum rules stop applying.

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11 minutes ago, Don410 said:

On the other hand, humans are made of atoms, which are in turn made of subatomic particles. This kind of begs the question of how big an object has to be before quantum rules stop applying.

In order for a multi-particle system to be in a state of superposition, the various parts of the overall wave-function need to be coherent. And here's the problem, because the larger a system becomes, the more it will interact with itself and its environment, and the more quickly it will undergo decoherence. There is in principle nothing stopping a human from being in a state of superposition, but in practice there are so many interactions taking place that the superposition would break down essentially immediately, meaning decoherence time is so short (almost instantaneous) that superposition can never be observed on classical scales. There is no sharp boundary between quantum and classical, it's a sliding (but not necessarily linear) scale.

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I always thought that was the point or "Shrodinger's cat"- that quantum actions, a nucleus ejecting a subatomic particle, can have macro consequences, a cat dying or living.   As for the human body, or any large collection of quantum  objects, the quantum effects will tend to average out.

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This dual nature of reality isn’t just restricted to light, either, but has been observed to apply to all quantum particles: electrons, protons, neutrons, even significantly large collections of atoms. In fact, if we can define it, we can quantify just how “wave-like” a particle or set of particles is. Even an entire human being, under the right conditions, can act like a quantum wave. 

https://www.forbes.com/sites/startswithabang/2020/08/19/in-quantum-physics-even-humans-act-as-waves/

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They can apply but be irrelevant. Consider the act of walking through a doorway. Will anyone notice how much you diffract? Your deBroglie wavelength is of order 10^-36m, which is similar to the deflection you would have with the first diffraction order through a 1m doorway, 1m after you walked through.

Similarly, you are in a (gravitationally) bound state — do you notice the quantized energy levels?  In the basic 1D particle-in-a-box problem, the energy levels are proportional to h^2 and scale with the inverse of mass. So perhaps the steps are of order 10^-70J. Are you going to notice the difference between settling in on different energy levels as you take a step up the stairs?

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On 8/11/2020 at 7:11 PM, Don410 said:

humans are made of atoms, which are in turn made of subatomic particles.

Nature supports our childish game of assembling/disassembling things - so we are ever so easily jumping to the conclusion that everything is "made of" some elementary particles.

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42 minutes ago, Alex Caledin said:

Nature supports our childish game of assembling/disassembling things - so we are ever so easily jumping to the conclusion that everything is "made of" some elementary particles.

Why do you think this is “jumping to a conclusion” rather than, say, examining the evidence?

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