Jump to content

Ganesh Ujwal

Senior Members
 View Profile  See their activity

  • Posts

    74

  • Joined

  • Last visited

 Content Type 

Posts posted by Ganesh Ujwal

    What disease am i facing?

    in Medical Science

    Posted · Edited by Ganesh Ujwal

    What disease am i facing?

    when ever i see burned matchsticks or char coal etc, skin itching takes places all over body. is this allergy?

    & also I am not asking solution to my problem, i am just asking what disease am i facing?

    0

    will shop keeper replace Hard Disk for free if it has Bad Sectors?

    in Computer Science

    Posted · Edited by Ganesh Ujwal

    My Hard Disk has 5 Years warranty & but it has lots of bad sectors

    will shop keeper replace Hard Disk for free if it has Bad Sectors?

     

    Actual Problem:Yesterday i downloaded 700 MB file, Now I can't able to copy or move the file, it showing "Data error cyclic redundancy check file".

    My Whole Time got wasted, again i should download whole 700 MB again.

    0

    Does Human Body sustain light speed vehicles?

    in Physics

    Posted

    You are moving through the universe at 1 200 000mph WRT CMB; are you having a problem at this speed? If it feels like this at that speed, what will it feel like near the speed of light? At any constant speed, in a straight line, you will feel stationary.

    but i can feel the speed , while travel by train or bus.

    0

    Why quantum states are classified using only conserved quantities?

    in Quantum Theory

    Posted

    While studying quantum mechanics from standard textbooks I always felt some conceptual gap that was never mentioned or explained. In what follow I tried to formulate my question, please be patient with me.


    For a quantum particle in an infinite potential well the stationary states are labelled by the quantum number [latex]n[/latex] which labels the eigenenergies. An eigenenergy, that corresponds to a stationary state, does not change with time, hence is a conserved quantity.


    For a spinless electron in Coulomb potential, to model the hydrogen atom, again we have the same story, the stationary states are labeled by the quantum numbers [latex]n[/latex], [latex]l[/latex], [latex]m[/latex] which corresponds to conserved quantities.


    My question is rather general since I am trying to understand conceptually why only conserved quantities are used to label the quantum states.


    I mean how would someone think in advance that he has to look for conserved quantities, and then use such conserved quantities to label the states ?

    0

    Is general relativity holonomic?

    in Relativity

    Posted

    Is it meaningful to ask whether general relativity is holonomic or nonholonomic, and if so, which is it? If not, then does the question become meaningful if, rather than the full dynamics of the spacetime itself, we consider only the dynamics of test particles in a fixed globally hyperbolic spacetime?


    For the full problem, my immediate conceptual obstacle is that it's not obvious what the phase space is. In ordinary mechanics, we think of the phase space as a graph-paper grid superimposed on a fixed, Galilean space.


    The definitions of holonomic and nonholonomic systems that I've seen seem to assume that time has some special role and is absolute. This isn't the case in GR.


    There is a Hamiltonian formulation of GR, which would seem to suggest that it's holonomic.


    In classical GR, information can be hidden behind a horizon, but not lost. This suggests that some form of Liouville's theorem might be valid.


    The motivation for the question is that Liouville's theorem is sort of the classical analog of unitarity, and before worrying about whether quantum gravity is unitary, it might make sense to understand whether the corresponding classical property holds for GR.

    0

    How is the Horizon Problem really a problem?

    in Astronomy and Cosmology

    Posted

    The problem stemmed from having to deal with how such a vast region of space had such a fine tuned uniformity. Without inflation that same volume could not have maintained the same uniformity once you consider the mean free path between the particles. Thermal equilibrium requires not only a high temperature. It also requires a sufficient density to allow the reverse reactions to occur.

     

    Prior to inflation the temperature and density is sufficient. Then inflation occurs. That sudden volume change would normally cause a sudden cooling. If inflation has multiple waves or perturbations there would have been anistropies crop up. However the slow roll process at the end of inflation caused a significant reheating effectively wiping slate clean of any previous anistropies and previous particles that were not in equilibrium. This makes determing which inflation out of the 70+ inflation models more difficult.

     

    The latest Planck dataset favors an inflation model with a single scalar and low kinetic term. However this does not rule out multiscalar models.

    http://arxiv.org/pdf/hep-th/0503203.pdf"Particle Physics and Inflationary Cosmology" by Andrei Linde

    http://www.wiese.itp.unibe.ch/lectures/universe.pdf:"Particle Physics of the Early universe" by Uwe-Jens Wiese Thermodynamics, Big bang Nucleosynthesis

    These articles will help the finer details see chapter 3 of the second one.

    http://arxiv.org/abs/1303.3787

     

     

    That doesn't address the main point that the original conditions of the universe would favor uniformity, which already solves the Horizon Problem. No causal contact is necessary to maintain equilibrium if the system is already in equilibrium.

    0

    How is the Horizon Problem really a problem?

    in Astronomy and Cosmology

    Posted · Edited by Ganesh Ujwal

    I always thought the uniformity in the temperature of the CMB was supposed to be expected, since it's a much more probable initial condition for the universe, what I mean in much better words:

    Horizon problem isn't really a problem
    If we examine from statistical mechanics principles what thermal equilibrium really means, we see that it is the most probable macrostate for a system (in other words, the state with highest entropy). Systems evolve towards thermal equilibrium not because nature has any sort of preference for evening out energy among all degrees of freedom, but simply because having a roughly equal partition of energy among degrees of freedom is OVERWHELMINGLY probable.
    For exactly the same reason why it is overwhelmingly probable for a closed system to move toward thermal equilibrium, it is overwhelmingly probable for a completely randomly selected initial condition to be in thermal equilibrium. No causal contact is necessary.

     

     

    The only "counter-argument" I could find for that, ironically enough, comes from Jason Lisle (link):
    (...) in the early universe, the temperature of the CMB would have been very different at different places in space due to the random nature of the initial conditions.

     

     

    But if that "random nature of the initial conditions" is of the same order of magnitude as quantum fluctuations, wouldn't that apply to the early instants of inflation too? If so, how would thermal equilibrium be even possible under such quantum fluctuations during inflation?
    1
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.