The Heisenberg Uncertainty Principle is derived for two operators $\hat A$ and $\hat B$ as- $$\Delta \hat A\ \Delta \hat B \geq \dfrac{1}{2}|\langle[\hat A, \hat B] \rangle|$$ where $\Delta$ denotes the standard deviation in a variable. Taking position and momentum as $\hat A$ and $\hat B$ respec...

Why does the internal energy of a ice- water system increase when a ice slab melts at 273K at atmospheric pressure? I don't understand how the internal energy tends to change when there is no change in the temperature at the melting point. Can someone clear my doubt?

I have been reading about how gravity has 2 equivalents descriptions: General Relativity. Explained by the graviton. How are these two things compatible? How can it be that gravity is explained perfectly through curving spacetime, and at the same time we want to understand it by thinking of a p...

Can we use sound energy to move a car? What if, instead of an engine, we put something near the tires which make tires move with the help of sound energy? Is this possible?

I am reading about tetrads in a GR textbook and a question occured to me. It seems natural to assume that the Levi Civita tensor in tetrad/vielbein basis is the Levi Civita symbol in the flat indices, i.e. in 2D: $$\sqrt{g} \ \epsilon_{\mu \nu}=\epsilon_{ab} e^{a}_\mu e^b_\nu$$ and $$\frac{1}{\sq...