As far as I know, Erwin Schrodinger used this thought experiment to show the absurdity of the interpretation of the quantum mechanics.

But many times I encounter on web even famous physicists say things like "When we observe this happens and we do not observe this does not happen ..."

But in the experiment there is a box and a cat inside. What is meant by "observing" here?

Does that mean looking at the box just by opening our eyes? Or does that mean opening the box? What if a blind person opens the box? What interaction causes here to collapse the wave function? What does that to do with "looking"? I don't understand what they mean by "looking" and "observing" in this context...

I'm asking this because some relate this experiment to consciousnesses.


marked as duplicate by StephenG, Kyle Kanos, Thomas Fritsch, Jon Custer, stafusa Jun 21 at 16:35

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    $\begingroup$ In my opinion it is a bad "experiment" because it replaces by a live animal a Geiger counter. The actual quantum mechanical uncertainty come on whether a particle has decayed or not, and that is the only quantum mechanical statement. $\endgroup$ – anna v Jun 21 at 9:40

Observation is measurement. We have a theoretically accepted interaction that qualifies as measurement if :

  1. you are using real particles

  2. virtual particles do not collapse the wavefunction, nor do they count as measurement

Now the wavefunction is the probability distribution of the particle's (or macro system in this case the cat) characteristics (like position or energy) in all of space (or spacetime).

The distribution is something that you can reveal with repeated experiments (measurements). One measurement will not show you the whole distribution (that is described by the whole wavefunction), but only one value of it.

It is like the double slit experiment, you will only see the pattern if you repeat shooting the electrons (or photons) at the screen.

Shooting one single electron will not give you a visible pattern of the probability distribution but just one single value in the distribution.

When you do a measurement (with real particles), you interact with the QM system. In reality, we do not know what happens to the wavefunction. There is the CI and the MWI, but these are just theories for describing a phenomenon that we really do not know. We make experiments, and see the results, and they fit the best the theories of QM. But whether CI or MWI is correct, nobody really knows.


In the thought experiment, the Schrodinger wave equation ascribes a wave-like character to the contents of the box. There is neither a live cat nor a dead one in there, but a dead/alive cat defined by a wave function. An observer is required to collapse the wave function by the act of observing. A blind observer would be sufficient, as he could observe in a tactile manner. If all this seems to defy common sense, don't worry. Famous pre-war physicist Max Born, along with many others, said that the wave function does not describe a physical system but merely describes our knowledge of it. This resolves the paradox of Schrodinger's cat. I don't think Schrodinger was serious about the dead/alive cat, and agreed with Max Born, but he is not on record as having said so..


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