carllacan
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 Feb 1 comment Light cones and reference frames Let me reword my question: what stops us from choosing a frame in which two events separated by a timelike interval have the same or reversed order? What is the constraint that forbids us to do so that does not apply on events separated by spacelike intervals? Jan 30 comment Converse of the Lagrangian form-invariance That last link is the most illuminating thing I read about mechanics in a month. I cannot thank you enough, is the first explicit definition of $\delta q$ I've seen. Jan 30 comment Converse of the Lagrangian form-invariance Simply perfect. Thank you. Just a detail: I've read somewhere that the function A could depend on velocities, but we would need to know the final velocities. I don't understand what this means. In the third step of your prove the two A functions cancel each other because the q coordinates don't change from tb to ta. But why shouldn't the velocities change? Jan 21 comment Light cones and reference frames Suposing a (2 + 1)-dimensional space we can draw a cone that delimits spacetime intervals and timelike intervals. I am curious about how these transformations would be represented on that (2 + 1)-dimensional space. Jan 21 comment Light cones and reference frames I know that. My question was how would these frames "look like". Jan 19 comment What causes different decays? I see. Which characteristics of the isotopes determine then (through Quantum Field Theory calculations) which decays are "available" for a specific nucleus? Jan 19 comment What causes different decays? Thank you, perfectly explained. However I don't think I understood the final part.Do you mean that the decay rates influence one another? Jan 18 comment Different kinds of the same isotope Thank you! I used google too and found nothing... weird. Jan 18 comment Origin of the names for the decay chains Ra226 has a half life of 1601 years, and an abundance of 100%, and Uranium 238 has a half life of billions of years and abundance of 99.3%... I don't know what can we conclude from this. Jan 7 comment Do eigenvectors of quantum operators span the whole Hilbert Space? I was taught that the columns of a diagonalised matrix are its eigenvectors. But now I feel like I'm confused about that. Jan 7 comment Do eigenvectors of quantum operators span the whole Hilbert Space? Oh, right, that's the whole problem, I didn't get the right eigenvectors. I just took them to be the coumns of the matrix. Aren't they supposed to be the eigenvectors? Jan 6 comment Do eigenvectors of quantum operators span the whole Hilbert Space? Well, the three Lx eigenvectors I get are (0, 0, 0), (1, 1, 1) and (1, -1, 1). How can you compose, say, the vector (0, 0, 1) out of them? Dec 2 comment General wavefunction and Schrödinger Equation Thanks for your answers. I didn't get this, though: " You can think of the first as doing an inner product with a momentum eigenstate in the position basis, and of the latter as doing an inner product with a position eigenstate in the momentum basis." Could you (or anyone else) explain that a little more? An inner product of what? PD: Trimok, may it be that you've written system instead of state? Jan 14 comment Entalpy and entropy role in freezing-point depression phenomena Yeah, I'm more interested in a "physical" explanation, rather than a mathematical one. But thanks, anyway. Jan 14 comment Eutectic systems behavior near 100%-0% composition and low temperature Thanks! That completely answers my question. However, what will happen if we were to lower even more the temperature of the almost-pure sample? According to the diagram it would turn into $\alpha$ + $\beta$, does it mean that the atoms of the low-concentration component would "get closer" until we could see some of them with the naked eye? How could this even happen at an atomic level if the high-concentration element particles have already organized into a solid body? Jan 14 comment Eutectic systems behavior near 100%-0% composition and low temperature Suppose we have a number of mixtures of $\alpha$ and $\beta$. If we pick one with a 99% concentration of, say $\alpha$ at a temperature above $\alpha$'s fusion point. When the temperature drops to below the L+$\alpha$ - Solid $\alpha$ equilibrium line, what happens? According to the diagram we have pure solid $\alpha$. Where does the other component go? Dec 30 comment How are constraint forces represented in Lagrangian mechanics? Did someone changed the title of the question? That is not what I'm asking, the original question was about the mathematical representation of these forces, the translation was a minor side question. Dec 21 comment Are Carnot engine efficieny and Fourier heat trasmission law related? I understand. However, they must both have a "cause" that explains them, don't them? Perhaps using statistical mechanics? My interest was if the causes or both phenomena could be traced back to a common one. Dec 19 comment Are Carnot theorem and Carnot Cycle related? Thanks, everything's clear now :-)