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/sci/ - Science & Math

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9314933 No.9314933 [Reply] [Original]

What does observer mean in quantum mechanics speak? I always hear about about things possibly existing in multiple places but being forced to take a position when observed but what exactly is an observer in this case?

>> No.9314936

>>9314933
usually a machine taking a measurement of a value of some property of whatever it's looking at.

>> No.9314939

>>9314936
Typically that measurement is made by bouncing a photon off the particle theyre measuring

>> No.9315773

"Observer" means taking a measurement which pins down the measured property. Bouncing a photon off a particle and registering the result on a dial is a measurement.
A human (or a cat) is not a necessary part of the process.
In the Copenhagen Interpretation of quantum mechanics (which is the most popular, though not universally accepted) the particle doesn't _have_ a defined position or momentum until the measurement. At which point the wave-function "collapses".
This is called "decoherence". Any interaction with the rest of the universe will do it -- not just intentional ones. This is why building a "quantum computer" is so difficult.

Physicists are usually vague when asked exactly when and how decoherence happens.
Hence the mantra "Shut up and calculate!"

>> No.9315775

:)