W.D.Clinger
Philosopher
And yet, during all those years, you never understood expectation values. As seen below, your mistakes demonstrate that you don't even understand the concept of average in the sense of an arithmetic mean.My students are and were far from imaginary: For years I taught them quantum mechanics
Okay, I'll explain.I did not ask the questions because I do not know the standard dogma, but in the hope that you would know the standard dogma and be willing to explain it from your viewpoints.
Close enough for now, although the concept of a wave function is not limited to electrons and their position.Now, according to Born, the intensity of the wave function is the probability distribution of where one will find an electron when one makes a measurement. Do you agree with this? This is what I have consistently read in text books and also taught my students.
No, because that's ridiculous.Thus the expectation value for position of an electron must be the position at which one expects to observe the electron most of the time when doing many measurements on an ensemble of identical electron waves. Do you agree with this?
Consider a two-person game of coin flipping. You and I flip a coin. If it comes up heads, I give you a dollar. If it comes up tails, you give me a dollar. For each of us, the expected value of that game is zero, because that's the average profit that each of us can expect if the game is repeated many times. That expected value is obviously not a possible outcome of any one game.
Similarly, the expectation value of an observable does not have to be a possible outcome of any one experiment.
As explained above, the expected value of a game or experiment or observable is not at all the same as the value you expect most of the time. As explained above, the expected value does not even have to be a possible outcome of the game or experiment or observable.Now calculate the expectation value for position for different wave intensities which satisfy Schroedinger's equation: What do you find? You find that for most calculations the expectation value for the position of the electron, is at a position where the intensity of the wave is zero and nothing more than zero. So for all these waves you expect to find an electron most of the time at a position where Born's probability distribution tells you that the electron can never be.
The question has been asked and answered for centuries.So this is why asked you what do you expect to find at the "expectation position". I think the question is very reasonable. It is just strange that nobody has asked it for nearly 100 years. Probably since one must not question "the book".
First you have to understand the concept of an average, or arithmetic mean, of a set of numbers. For example, the arithmetic mean of {1, 2, 4, 5} is 3, even though 3 is not one of the numbers being averaged.
Once you understand how that can happen with the arithmetic mean, you should know how that can happen when the arithmetic mean is generalized to a weighted average.
Once you understand how that can happen with a weighted average, you should know how that can happen when the weighted average is generalized to an expected value ∫ x P(x) dx.
Once you understand how that can happen with the expected value of a random variable, you should know how that can happen when the expected value is specialized to the expectation value of an operator on a Hilbert space.
Once you know how that can happen with the expectation value of an operator on a Hilbert space, you should know how that can happen with a quantum observable.
But you never knew that, even though you were teaching quantum mechanics at both undergraduate and graduate levels. That's sad.
. Please read a VERY elementary text book on electrostatics. It is clear that you do not know elementary physics at all.