# What are the problems in trying to interpret the Klein-Gordon equation as a single particle equation?

What is the problem if we try to interpret KG equation as a single particle equation? Also I wish to know whether the born interpretation of wavefunction is applicable in relativistic quantum mechanics.

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If you try to construct the probablilty current for the KG equation, its zero component $j^0$ is not positive definite, even though you want to interpret it as a probability.