Here from Star Talk, Neil deGrasse Tyson explains why we can never attain the temperature of absolute zero (−273.15 °C or −459.67 °F). It’s the theoretical temperature in which an ideal gas at constant pressure reaches a volume of zero.
His first explanation, while delivered with enthusiasm, doesn’t make a lot of sense to me, for it’s along the lines of “we need to put something a bit colder than the ambient temperature at the place where we want to obtain absolute zero so that it will suck away the heat (molecular motion) of the target. But as we approach absolute zero, we can’t GET anything whose temperature is just a tad above absolute zero to suck away that last bit of heat. But this seems to me begging the question, for it assumes what you’re trying to prove: there’s a low temperature that we can’t obtain because it becomes impossible to get anything just a wee bit warmer than that temperature.
His second explanation, is that there is always quantum vibration, that this vibration cannot be prevented completely, and therefore we cannot go below the temperature where the quantum energy is the only energy we have. That is, quantum mechanics gives us the limit of the lowest amount of kinetic energy possible. (I wonder if the magnitude of absolute zero can be predicted from quantum mechanics alone.)
The third explanation, based on the theory of the canceled physicist Erwin S———r, explains the phenomenon as somehow connected to the Bose-Einstein condensate, but doesn’t tell me, at least, why absolute zero is unattainable (the Wikipedia article explains why this is basically the same thing as the second explanation).
So we have an entertaining video that gives three explanations for why zero degrees Kelvin is unattainable, but only the second makes a lot of sense to me. On the other hand, I’m not a physicist. But on the third hand, this video isn’t intended for physicists, but for folks like me.