Recent content by Jip

Hi, If I consider for instance N non interacting particles in a box, I can compute the energy spectrum quantum mechanically, and thus the number of (quantum) microstates corresponding to a total energy between $E_0$ and $E_0 + \delta E$. In the limit of large quantum numbers, the result is well...

Yup, I think I found it http://en.wikipedia.org/wiki/Nuclear_photonic_rocket Is it a correct intuition to say that it produces such a low acceleration because you emit pure momentum/energy but no mass (compared to standard fuel)? Is that the main reason?

Hi, I got this fun idea. Has anyone ever consider that heat radiation could be an efficient propellant for a spaceship? Imagine a spherical spaceship, half of which is hot and with a large emissivity coefficient (say almost 1), and the other half is cold and with low emmisivity. A naive...

Sure! Don't misunderstand me, I was talking about the symmetries of deformed Quantum Mechanics according to the Generalized uncertainty principle, not standard QM :)

Thanks for your replies! Aleazk, this is a great, great answer. First time I hear about this stuff. I see there is quite a lot to learn, indeed. And now I can come to my real business: deformation of Heisenberg algebra vs deformation of symmetries. The physics litterature has come up with a...

Hello, I have some troubles understanding Hilbert representations for the standard free quantum particle On the one hand, we can represent Heisenberg algebra [Xi,Pj]= i delta ij on the space of square integrable functions on, say, R^3, with the X operator represented as multiplication and P...

Thanks! And when 1/f is measurable, is it also true for f?

Hi, Let's say I consider the real numbers and some function real function f, nowhere zero, and positive. My question is, what are the conditions on f for dx/f(x) to be a valid measure on this space? (I have to consider a Hilbert space L^2(R, dx/f(x)) with scalar product a.b = \int a^*(x)...

Hi, My question is the following: As well known, the interference pattern disappears when one determines which slit the photon has gone through. This also holds for atoms and molecules. Now I understand how the actual experiment works for eg. an atom: They send excited atoms that can decay in...

Hi, I'm working the following paper ""Plane waves viewed from an accelerated frame, K Srinivasan, L Sriramkumar, T Padmanabhan - Physical Review D, 1997" and there's this integral: \int_{-\infty}^{+\infty} e^{- i \Omega t} \cos \left( \beta - e^{a(\phi/\Omega-t)}\right) dt whose result...

Yes, I'am aware of this, but I'm rather talking about mathematical description of large scale structure formation! I have found that details can be found in peeble's book, 1980. But I don't have it. Any other ref is welcome! :)

Hi, I have troubles understanding the difference between linear and non linear matter power spectrum. These words are commonly used in the litterature, but I have found no definitions yet. My understanding is that there is one definition of the power spectrum for matter distribution...

Hi, I read in Padmanabhan's book that \nabla_a J^a=0 implies that there exists an antisymetric tensor P such that J^a= \nabla_b P^{ba}. What's the name of the theorem? Any reference? Thanks

Ok I just saw quickly the references you gave me. I want to stress that my question is not about the cosmological constant or Dark Energy modeling, etc, but about the thermodynamical (or satistical physics) interpretation of the pressure and density as defined in GR through the perfect stress...

Well, some comment on your post. 1. I assume cosmological background in order to set the spatial derivatives to zero, indeed. 2. Then you get the two equations you gave for rho and p of the scalar field. By the way, you jut prove my claim (it is well known): take V(phi)=0, and see how your...