Mass problem or something of a sort (E=mc^2)

[Nikola Kolev]

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.

 

[mfb]

E=mc² gives you the total energy of an object with mass m at rest, both in classical physics and in quantum mechanics. In many setups this energy is not relevant at all.

Quantum mechanics applies to all systems (at least no one ever found an exception), for large objects the classical description gives a very good approximation. There is no fixed boundary.

 

[Nikola Kolev]

Thanks