I’ve been reading about the concept of invisibility in physics and am curious about its feasibility. We often see references to invisibility cloaks in science fiction, but what does physics say about it? Are there any existing theories or technologies based on real-world physics that might enable...

I am a university student preparing for a report on density functional theory (DFT). When reading a paper on the DFT for van der Waals forces$^\dagger$, I was led to an equation for the non-local correlation energy functional in terms of the Coulomb interaction potential and some dielectric funct...

Upon detection by an observer or measurement device, an isolated system changes (or collapses) from it's superposition of states to a single state. In decoherence, does an isolated system undergo the same kind of (or dare I say exact?) transition when decohered by it's environment?

Given any tensor $A \,\text{and}\, B$. (Not necessarily symmetric or anti-symmetric) $$A^{\mu}_{\,\,\,\nu}B_{\mu}^{\,\,\,\rho} = C_{\nu}^{\,\,\rho} \,\,\, \text{or} \,\,\, C^{\rho}_{\,\,\,\nu}\,\,\,?\tag1 $$ Which one is true? I've tried writing $A$ and $B$ as a sum of symmetric and anti-symmetr...

What I have studied in books is that "Work done by all the forces acting on a body is equal to the change in kinetic energy of the system" as the Work-Energy Theorem says. But for the derivation, it takes mass $m$ as constant, so if the mass is varying with time, will the law still be valid or no...