This may seem basic, but I am wondering if anyone has any input on this topic. It doesn't make any sense to me (I mean I don't need to use the Schrödinger equation to find my cell phone...). I just do not understand how things can appear to be highly statistical when observing the rudiments of matter, yet when observing the large scale result, very consistent (for all practical reasons). How can things with no position make up something with a position? Is it possible that our detection methods are flawed beyond what Heisenberg suggested? Is there some intuition here that I could be missing?

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    $\begingroup$ Here's a related concept that's even more mind blowing: by age 12, almost every single atom that constituted your body when you were born would no longer be there, your body would have been made of completely different atoms. So, how can you be "you"? $\endgroup$ – slebetman May 27 '14 at 3:34

Simply put, it averages out.

Ignoring quantum physics for a moment, consider the random movement of molecules in a gas. The number of particles bouncing against each wall per second is random, too. But the variation in this number is roughly proportional to the square root of collisions. Therefore, the relative variation is inversely proportional to the square root.

Thus, the more particles you have, the less variation you have.

  • $\begingroup$ That makes sense. I thought the explanation would be much less intuitive, thank you. $\endgroup$ – Gödel May 26 '14 at 19:01
  • $\begingroup$ "Therefore, the relative variation is inversely proportional to the square root" ... of a truly gigantic number, in macroscopic cases. $\endgroup$ – David Richerby May 26 '14 at 19:36
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    $\begingroup$ @NaturalPhilosopher This is far from a trivial question, and this doesn't really answer it ... see the Sachin's answer for the correct trail to follow. $\endgroup$ – Szabolcs May 26 '14 at 20:20
  • $\begingroup$ @Szabolcs To the contrary, the article notes "A total superposition of the global or universal wavefunction still exists (and remains coherent at the global level), but its ultimate fate remains an interpretational issue." Quantum decoherence is only the explanation in a subset of current interpretations. $\endgroup$ – SevenSidedDie May 26 '14 at 23:52

I've read an news article on NewScientist about this not so long ago, might be controversial but sure offers a much more intuitive way to look at the issue.


Basically, as far as I understand, they argue that there is nothing really uncertain about quantum state and that the issue really is that we think that we always can measure reality exactly, which might not be the case. So the "uncertainty" about quantum state is not in reality itself, but in our perception of it.

I hope a more educated physicist might be able to further expand on this answer and the credibility of the Quantum Bayesianism model if needed, but basically this model completely removes the intuitive gap between quantum physics and reality, since there really is no absolute objective uncertainty.

Picture taken from newscientist.com

  • $\begingroup$ Nice one, but I don't think it's officially accepted. $\endgroup$ – Schrödinger's Cat May 27 '14 at 7:35
  • $\begingroup$ @SachinShekhar That is true, but since this alternative model is very intuitive, does not suffer from any obvious lack of plausibility and have some decent support in the field considering it's position, I think it is worthy a mentioning for anyone that is thinking about how "quantum reality" maps to "classical reality". $\endgroup$ – Alex May 27 '14 at 7:57
  • $\begingroup$ Yeah, I liked it.. $\endgroup$ – Schrödinger's Cat May 27 '14 at 8:07
  • $\begingroup$ Who has the power to "officially accept" concepts/theories? $\endgroup$ – bright magus May 28 '14 at 6:51

This is called Quantum Decoherence which kills all quantum behaviours.

From the linked Wikipedia page:

In quantum mechanics, quantum decoherence is the loss of coherence or ordering of the phase angles between the components of a system in a quantum superposition. One consequence of this dephasing is classical or probabilistically additive behavior. Quantum decoherence gives the appearance of wave function collapse (the reduction of the physical possibilities into a single possibility as seen by an observer) and justifies the framework and intuition of classical physics as an acceptable approximation: decoherence is the mechanism by which the classical limit emerges from a quantum starting point and it determines the location of the quantum-classical boundary. Decoherence occurs when a system interacts with its environment in a thermodynamically irreversible way. This prevents different elements in the quantum superposition of the total scene's wavefunction from interfering with each other. Decoherence has been a subject of active research since the 1980s.

  • $\begingroup$ @Jim I think it's fine now. Yes, the link is the answer as the question shows lack of research. $\endgroup$ – Schrödinger's Cat May 27 '14 at 13:56

You ask:

How can things with no position make up something with a position?

That's a misunderstanding of the model. The particles are in all possible positions at the same time. Observation collapses these possibilities to only one position.

At no time do they have “no position”.


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