First of all, I would like to state that I'm not a physicist in any sense of the word. I know only pre-calculus math so it's probably best to avoid equations when answering my question. Basically, I'm just a guy who enjoys reading articles and watching videos on quantum mechanics.

Let's get to the bulk of my question. I asked the following over at reddit:

Quantum randomness on a macro scale. We don't see it with our bare eyes. Why? I can think of two possible answers. Which one is correct? 1. Our eyes are not accurate enough to be considered detectors, thus the wave function is NOT being collapsed before our eyes - quantum randomness still happens but we don't see it because the spaces between the possible locations of particles are too small. 2. We collapse the wave function just by looking at an object with our bare eyes, hence the particles have (at the time of us looking) well-defined positions.

As an answer I was presented with this wikipedia entry. It seems that we don't observe superposition in every-day life because of quantum decoherence. That still doesn't fully answer my question, though.

  • Firstly, I don't see how the interference between two or more wave functions would lead to us seeing the lack of a superposition. Could someone elaborate on this in layman's terms?

  • Secondly, what exactly happens to a given wave function when it's interfered with by another wave function (when quantum coherence is lost)? My guess would be that it collpases. However, that collapse would be starnge knowing that MEASUREMENT is required in order to collapse a wave function - which is absent in our case.

  • $\begingroup$ this would need an elaboration on what is meant by a collapse. It is not very good to involve eyes in the problem, since they depend on a photon that comes from the experiment, and it is not a philosophical/mental thing- 'I've seen you - collapse now' $\endgroup$ – jaromrax Feb 10 '17 at 9:21
  • $\begingroup$ By 'collapse' I mean the same collapse you would observe in the double-slit experiment when measuring particles by means of detectors located right next to the slits. I have to involve eyes in this problem since the question at hand directly correlates to what we see. $\endgroup$ – DanteeChaos Feb 10 '17 at 9:28

Think of the two slit experiment. You have a coherent wave travelling towards the slits. At each slit you have the same coherent wave exiting. When the waves from each slit hits the screen and overlap because they are coherent with each other you get a nice interference pattern. But if you have detectors at the slits, this introduces a random phase shift at each slit. So when the two waves meet at the screen they are no longer coherent and so you don't get the interference pattern.

When the photons strikes the screen it's effect is amplified so that it can be observed by a classical instrument. At this stage the wave function is said to collapse in the Copenhagen interpretation. So the decoherence destroys the interference pattern and the measurement at the screen collapses the wave function.

  • $\begingroup$ I'm sorry but I fail to see the connection between the two-slit experiment and the loss of coherence. My understanding is that the collapse of the wave function (by means of measurement) is NOT the same as quantum decoherence. The way I understand 'collapse of the wave function' is that the wave function disappears altogether (it's replaced by a well-defined position of a particle) while 'quantum decoherence' is the nullification or constraint of the superposition of a particle. These two are not the same. Your answer implies that the are. Correct me if I misunderstood you. $\endgroup$ – DanteeChaos Feb 10 '17 at 10:10
  • $\begingroup$ OK I added on another paragraph. $\endgroup$ – Virgo Feb 11 '17 at 2:23

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