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 Aug 9 comment Why does nonlinearity in quantum mechanics lead to superluminal signaling? So linearity implies no cloning implies no signalling (if we assume that signalling with cloning is the only way one could potentially signal). This means that signalling implies nonlinearity. If I understand the question though, the OP wants to know how/why nonlinearity implies signalling. Jul 12 comment Difference between Eulerian and Lagrangian formulation of Fluid Dynamics Jul 12 comment Difference between Eulerian and Lagrangian formulation of Fluid Dynamics Force is not $\frac{\partial (m v)}{\partial t}$, it is $\frac{d(mv)}{d t}$. Expand the derivative in terms of partial derivatives and you will get the same equation in both cases. Jul 5 comment The derivation of fractional equations Forces proportional to velocity, such as friction for example, can be described by putting fractional derivatives in the Lagrangian. Jun 28 comment Can isotropic states have bound entanglement? The states you write here are called Werner states. There do exist Werner states that are single-copy undistillable and NPT in a certain region, but general distillability conditions are unknown as far as I know. See for example arxiv.org/abs/1003.4337. Somebody else might be able to tell you more. Jun 28 comment Can the entangelement of basis vectors increase under local operations? Everything you write here is true, but you may have misunderstood the question (maybe OP can clarify). He's not asking if $E(\rho') < E(\rho)$, but whether a single component of $\rho'$ can have a greater entanglement than a single component of $\rho$. Imagine that $\rho$ is pure and you are doing probabilistic single-copy entanglement distillation. You can write the output as a mixed state, with one of the components having greater $E$, but the output state as a whole having less entanglement, so satisfying the LOCC requirements. Jun 28 answered Can the entangelement of basis vectors increase under local operations? Jun 26 answered Do the states forming an orthonormal basis have the same amount of entanglement? Jun 22 comment Time dilation problem ($\gamma$ and $u$ are unknown) Express time for the passenger in terms of $\gamma$ and $u$. Express $\gamma$ in terms of $u$ and insert back into the time for passenger. Then solve for $u$. It shouldn't be too difficult from there on. Jun 22 comment Proof for the completeness of eigenfunctions of a self-adjoint operator Mathematicians have a proof for compact self-adjoint operators on Wikipedia: en.wikipedia.org/wiki/Compact_operator_on_Hilbert_space Jun 19 comment Is time continuous or discrete? I just mean that there exist quantum observables corresponding to position, and their outcomes in general form a continuum. Time is another issue. Jun 13 revised Limits of superdense coding added 275 characters in body Jun 13 comment Limits of superdense coding Notation: $\rho$ is the quantum state in question, $A$ refers to Alice's part of the state, $B$ to Bob's. So $\rho^A = Tr_B(\rho^{AB})$, ie. the state that Alice sees, having no access to Bob's part of the state. $S$ is entropy, $S(\rho) = -Tr[\rho \log_2(\rho)]$, $S(A|B)$ is the conditional entropy, ie $S(\rho^{AB}) - S(\rho^B)$ and $S(\rho || \sigma) = Tr[\rho(\log_2(\rho) - \log_2(\sigma))]$ is the relative entropy of states $\rho$ and $\sigma$. For $N$ I updated the answer as there is not enough space in this comment. Jun 12 answered Limits of superdense coding Jun 12 revised Quantum Collapse added 319 characters in body Jun 12 answered Quantum Collapse Jun 7 comment A question about quantum measurement and associating a linear self adjoint operator to it I don't quite follow what you are saying. In particular, I don't see how you can deduce a basis by being given a single vector. Jun 7 comment Are scientists missing the point with distant cosmic objects, or is it just me? Just one comment regarding the time light was created. Saying that light was created five billion years ago and has now reached us is the same as saying that it took five billion years to reach us. So it's logically impossible for light to have been created five billion years ago and it having reached us now, and yet having taken 13 billion years to reach us. Jun 6 answered A question about quantum measurement and associating a linear self adjoint operator to it Jun 6 comment Why does this state have a Schmidt rank of 1? @Trimok You probably mean the state is a separable (rather than pure) state if and only if $ad - bc = 0$. As it's written down, it's always pure...