Hey Guys. I'm having trouble wrapping my head around the idea of a particle being in a classically prohibited region. A particle is in a classically prohibited region if its total energy is less than the potential energy at that location. To me, this would seem to imply negative kinetic energy (and hence imaginary momentum), if we accept that total energy = kinetic energy + potential energy. I asked my instructor and he said, "I don't think you should think of total energy as kinetic energy plus potential when dealing with quantum." My TA said that the act of measurement would impart energy to the particle (changing the ψ in the process), thus allowing it to get over that barrier and be in the classically prohibited region and conserving energy in the process. This made sense to me but then if this is true, tunneling doesn't really seem as mysterious/mystifying as it was presented to be. When I googled my question, I saw some answers that said it comes down to the uncertainty principle: the more you know about the location of the particle, the less you know about the its momentum and hence kinetic energy so you can't really say anything about its kinetic energy if you measured its location in a classically prohibited region. I would really appreciate if you guys could help me understand this as I have gotten three different answers!