" The real 'theory of everything' "

That would be thermodynamics. Yes, thermodynamics, not string theory or relativity or the standard model. At least, that's the claim of this recent book review in Science. Let me just pull some tantalizing quotes:

Thermodynamics ought to be the cornerstone of any scientist's understanding of nature. ...

The development of thermodynamics in the nineteenth century was the most wide-reaching and fundamental advance since Newton's mechanics.