Hi guys! My question is kinda stupid and I'm new here so: At the border between the quantum and classics worlds how E=mc^2 works? Like in which states you'll have quantum tunnelling, in which just the classic classical way of not passing the barrier (I do not mean classic/quantum world) and when some kinda of other state in unnatural energy comparisons with the barrier and the particle? I would be glad to receive a mathematical fulfilled explanation. I hope for all kind of replies but hopefully from experienced people. I don't have any physics degree I'm just a student with passion. Thanks.