# Porbability Density?

## Main Question or Discussion Point

In quantum mechanics, given ψ, we calculate the probability density in a given space by (mod[ψ]^2)*dx*dy*dz (as given in any standard textbook). But my suggetion is that it should be (mod[ψ]^2)*dx*dy*dz*dt where dt is the differential time element. Its seems to me to be more fundamental. Then why dont we do that?
Thanks

## Answers and Replies

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mathman
The probability density is at a given instant, not per unit time.

HallsofIvy
Also we do NOT use $\Psi$ to calculate the probability density. $\Psi$ is the probability density. The integral, over a space interval, gives the probability that the object is in that space at the given instant.