Siva

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	1,476 reputation	bio	website	sivaramakrishnan.wikidot.com	visits	member for	1 year, 11 months
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28m	answered	How to directly calculate the infinitesimal generator of SU(2)
1d	comment	Scalar-fermion bound state How about baryons, which consists of 3 quarks and lots of gluons... Is that a satisfactory example?
1d	comment	Can we measure “wavefunction” of quantum particles? Another example: You could start out with N copies of a known state and time-evolve each under the same unknown Hamiltonian. That would give you N copies of the same unknown state. You could then proceed to measure the heck out of that ensemble and try to estimate the Hamiltonian.
1d	comment	Special conformal transformations and locality You might want to have a look at Section 1.1 of Ginsparg's notes. arxiv.org/abs/hep-th/9108028
1d	comment	Some questions about the BCFW reduction @user6818: Shouldn't you have two negative helicity gluons for an MHV amplitude?
1d	answered	How does an earthen pot keep water cool?
1d	comment	How does an earthen pot keep water cool? @Tariq: Usually, heat from a hotter to a colder body since that is statistically/thermodynamically preferred. I think that in this case, the evaporating water can't get heat from the atmosphere (since it's probably not interacting much with the environment before it evaporates) and hence, must get heat from the pot.
1d	answered	Uncertainty Principle on System of particles
1d	comment	Special conformal transformations and locality @Trimok, I'm confused as to what you mean. I think all conformal transformations (not just scale transformations) affect the metric by a local scale factor $e^{2 \phi(x)}$.
2d	comment	Symmetry of the stress tensor In some cases, the idea is that even if the stress-energy tensor you get by the definition $\frac{\delta S}{\delta g_{\mu\nu}}$ is not symmetric, you can add another piece to make it symmetric and still satisfy the necessary properties. eg: en.wikipedia.org/wiki/…
2d	comment	How can it be seen that ST unifies GR and QM as the quantum gravity scale is not directly accessible (...contd) You could either ask how it works in theory, or what observational consequences it might have. But the consistency of the theory has pretty much nothing to do with what we are (or are not) able to observe today.
2d	comment	How can it be seen that ST unifies GR and QM as the quantum gravity scale is not directly accessible @user14154: String theory gives a "reasonable" theoretical framework for how gravity might emerge from a consistent quantum theory (of stringy degrees of freedom, as it turns out). The theoretical validity of that framework doesn't have anything to do with the "current situation" (observational, I presume). The theoretical framework seems sensible; whether it is a correct description of nature at high energies remains to be seen. So I don't understand what you mean by "how then do ST unify GR and quantum theory at current situation?" (contd...)
2d	comment	Estimating the Kolmogorov Complexity of the Standard Model That's a good point, especially when a dumb loop can decrease the Kolmogorov complexity but increase the computational complexity. But how do you account for the complexity in the various keywords... Could I make up arbitrarily complicated ones? I wonder if it's okay to give a small (Kolmogorov complexity) weight to the for/while operator which runs a loop.
May 18	comment	Periodic boundary condition on a Wave Function of a Particle in a Box Hint (which might be obvious): Think of it as a particle on a "ring". That gives you a natural coordinate to talk about and things might be easier.
May 18	comment	How do we know that time and distance are not discrete? @Manishearth: Sure... theories assert very interesting things, but we really don't know if that's correct. For eg: Aristotle asserted that everything in the world could be made up of 5 elements (earth, fire, air, water, aether), and that was the leading theory of his time :-)
May 18	comment	How do we know that time and distance are not discrete? @Manishearth, Planck length is just a quantity/scale we came up with by dimensional analysis. We think something must happen at that length scale but to be honest, we don't know what that might be. One wacky possibility would be if spacetime is a field theory, but smoothed over a width of Planck length (like a moving time average) rather than an actual discretization. That would presumably give a length scale without any discreteness. But don't take that idea very seriously; I just made it up to illustrate my point.
May 18	comment	Estimating the Kolmogorov Complexity of the Standard Model Right, but afaik that's the first (only?) paper considering any kind of complexity in field theories. At least naively, I would expect an algorithm (corresponding to an output) which has a large Kolmogorov complexity to also have a large computational complexity -- because to actually compute the answer, you have to implement the algorithm which happens to have large Kolmogorov complexity.
May 18	answered	How do we know that time and distance are not discrete?
May 18	comment	Estimating the Kolmogorov Complexity of the Standard Model This paper might be of interest: Quantum Computation of Scattering in Scalar Quantum Field Theories
May 18	comment	Estimating the Kolmogorov Complexity of the Standard Model I'm not talking about the exact value. Any handle on an estimate of complexity would be very interesting. Maybe I'm making it out to be more complicated than it is, but I think we're some way from understanding such a characterization of QFTs, especially since they have "many" degrees off freedom.