When something floats, it is due to the buoyant force from the liquid onto the object, but what force does the object exert in response down on the liquid? I feel as if the object would have to exert a downward force on the liquid due to Newton's Third Law, but I haven't been able to figure out w...

As we know, water becomes ice at $0^°$C. After becoming ice, if we lower the temperature further ($<0^°$C), then does the density of ice increase further? If yes, in that case, does the volume decrease?

There's interesting statement about amplitude of Goldstone bosons: I wanna to understand simple argument for statement of vanishing of amplitudes in the single scalar soft limit. In principle, it is obvious that this have direct relation to symmetry of model. But technically I can't find argumen...

Looking at the QED-Lagrangian $$\mathcal L = -\bar\psi(\not\!p + e\not\!\!A + m)\psi -\frac14 F_{\mu\nu} F^{\mu\nu} $$ I was wondering: While $\bar\psi\not\!\!A\psi$ describes the interaction between the electron field (or rather generally, a charged fermion) and the photon field (a neutral boson...