Finding general expression for probability current.

AI Thread Summary
The discussion focuses on deriving the probability current density \( J^{i}(\vec{r}) \) using the conservation of probability equation, which states that the time derivative of probability density plus the divergence of the probability current equals zero. Participants express confusion regarding the notation, particularly the meaning of the partial derivatives and the use of the Schrödinger equation. Clarifications are provided that \( x^0 = t \) and \( x^i \) corresponds to spatial coordinates, with repeated indices indicating summation. The conversation emphasizes the equivalence of the conservation of probability in traditional notation as \( \frac{\partial \rho}{\partial t} + \nabla \cdot \vec{j} = 0 \). Overall, the thread aims to guide understanding of the notation and its application in the context of quantum mechanics.
David Silva
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The conservation of probability says:

$$\partial_t J^{0} + \partial{i}J^{i} = 0$$

Use the Schrodinger equation to obtain$$ J^{i} (\vec r)$$.

I have no idea where to start this kind of problem because the notation makes no sense to me. I would appreciate a hint or nudge in the correct direction.
 
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What about the notation confuses you?
 
vela said:
What about the notation confuses you?
What do those partials mean? I am not used to seeing them this way? Also would I be using the general SE eq or the radial one since we are in r?
 
Typically ##x^0 = t##, ##x^1 = x##, ##x^2 = y##, and ##x^3 = z##, so ##\partial_1## would mean ##\partial_x##. The repeated index ##i## implies a summation from ##i=1## to ##i=3##.

You have ##J^\mu = (\rho,J_x, J_y, J_z)##, so in more traditional notation, conservation of probability is
$$\frac{\partial \rho}{\partial t} + \nabla \cdot \vec{j} = 0$$ where ##\vec{j} = (J_x, J_y, J_z)##.
 
vela said:
Typically ##x^0 = t##, ##x^1 = x##, ##x^2 = y##, and ##x^3 = z##, so ##\partial_1## would mean ##\partial_x##. The repeated index ##i## implies a summation from ##i=1## to ##i=3##.

You have ##J^\mu = (\rho,J_x, J_y, J_z)##, so in more traditional notation, conservation of probability is
$$\frac{\partial \rho}{\partial t} + \nabla \cdot \vec{j} = 0$$ where ##\vec{j} = (J_x, J_y, J_z)##.

Thanks, I will look at this later today and see if it helps!
 
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