I'm currently doing a coursework in A2 Physics, on Zero Point Energy, and Casimir effect, and why doesn't Helium freeze at atmospheric pressure within micro-degrees of absolute zero. I've researched and I found out that only ZPE can account for the source of energy that prevents helium from freezing at atmospheric pressure. I know that absolute zero can never be reached due to the third law of thermodynamics, (basically absolute zero can never be reached within a finite number of steps), but I'm unsure of the Casimir effect has anything to do with that. I've read on Quantum Harmonic Oscillator and how it has been predicted and modelled due to experimental evidence and theory that, if you had an electron on a frictionless spring suspended in a total vacuum, it would continue to vibrate even if the temperature of the vacuum was reduced to absolute zero. (Tom Valone.) However, I am unsure if that effect is caused by the Casimir effect. Could it be that, within micro-degrees of absolute zero, the source of the ZPE is the Casimir Effect? My understanding of the Casimir effect isn't complete; I have tried to read and understand many sources; but after a few attempts, due to the density of information and depth (that my coursework does not require, as my teacher has told me), I could not completely understand what the Casimir Effect is. I would appreciate it if my doubts were clarified, and since I'm doing physics at A-Levels, I would very much appreciate a simplified, yet explained version of the Casimir Effect.