If the wave function is complex and the measurement is real

[rasp]

Would not any real measurement taken on a complex state logically require that the results of the measurement have less information than the state? Although I’m just beginning in QM, it appears to me unsurpring that a real measurement on the complex wave function seems to collapse the wave function into a specific value. Where is the controversy that I’m missing?

 

[Nugatory]

Would not any real measurement taken on a complex state logically require that the results of the measurement have less information than the state?

There's no complex/real involved here. Of course a measurement provides less information than the state, and classical mechanics works the same way. For example, the state of a cannonball fired with a speed of 100 m/sec towards me from a cannon 100 meters to my right is clearly a different state than that of a cannonball fired towards me from a cannon 100 meters to my left. However, a position measurement performed one second after the cannon fires will not distinguish between the two states - the cannonball is in the same place either way.

Although I’m just beginning in QM, it appears to me unsurpring that a real measurement on the complex wave function seems to collapse the wave function into a specific value.

There's a very serious misunderstanding here. You do not perform a measurement on the wave function, you perform a measurement on the system described by the wave function. The measurement changes the state of the system and therefore the wave function that describes it changes with the measurement. However, the wave function does not change to "a specific value", and even though the measurement result is necessarily a real number the wave function after the measurement is still a complex function, as it was before the measurement. It's just a different one.

Where is the controversy that I’m missing?

Without more context, I'm not sure which controversy you're thinking about - there are several.

 

[rasp]

I was thinking that because the wave function encodes all we can know about the electron, then in a real sense it is equal to and the same as the electron. So when we go to perform a measurement on the electron we are just looking at the real components of the wave function.

 

[stevendaryl]

I was thinking that because the wave function encodes all we can know about the electron, then in a real sense it is equal to and the same as the electron. So when we go to perform a measurement on the electron we are just looking at the real components of the wave function.

No, what we measure about an electron is not the wave function, but various observables, such as position, energy, momentum, angular momentum, etc. The wave function tells us the probabilities associated with the various measurement results. You need both the real and imaginary parts of the wave function to compute these probabilities.

 

[rasp]

OK Thank-you..