Recent Posts - page 5

  • Introduction to special theory of relativity.

    Introduction to special theory of relativity: Michelson interferometer, first configuration. Photo Credit: mdashf.org

    Special Theory of Relativity:
    Galilean Transformations,. Newtonian Relativity.

    This was a lecture delivered to physics-elective class of a 3 year non-physics degree students on 10th April 2017. This is also a good exposition to honors students and anyone at an introductory level of the special theory of relativity, with requisite mathematical background. 

    Let us consider an inertial frame of reference S. The space and time coordinates of any event occurring in frame S are given by x, y, z, t.

    Now let us consider another frame of reference S’ which is inertial but moves wrt frame S at speed v, along +x direction.

    The coordinates of the same event in the S’ frame are given as: x’, y’, z’, t’. The relationship among the coordinates of any event in two different frames of reference both of which are inertial frames, is known as Galilean Coordinate Transformation or Galilean Transformation.

    If we assume that time passes by at the same rate in both S and S’ frames, the resulting laws satisfy Newtonian Relativity. We say time is an absolute quantity in an infinitude of equivalent inertial frames of references as the rate of time change is independent of the particular inertial frame of reference we have chosen. Consequently: t = t’.

    The above equation is known as velocity addition rule in Newtonian Relativity. This is valid only for classical mechanics in the sense of speed of objects and speed of frame of reference, which are quite insignificant with respect to the speed-of-light value.

    Velocity addition is nothing but a relation of velocities of objects in different frames among each other. So its exactly what we call “relative velocities” in elementary mechanics. Relative velocity, velocity addition and velocity transformation are the exact same thing. Read more about these here and here. The second link also expounds on what happens when speeds approach that of light.

  • My employment history.

    Interviewer: So where did you work last?
    Me: Sir previously I have been working at FB for many years.
    Interviewer: wow tell us more. 
    Me:

    1. I worked in the capacity of “s

  • My graduate student days.

    My graduate student days were fun — most of the times.

    I had 3 different professors — in 3 different semesters, when I was their teaching assistant (TA).

    None of them was any acerbic to me ever, even when I would be at fault.

    Professor 1:
    Guy Indebetow was the very first one. A cheerful person and very friendly. He would say — in spirit, not necessarily all the wording, “I would not interfere in how you grade the students, but wisdom says you give them a little lose marking, if anyone comes with any grievance though, I would redirect them to you.”

    It so happened that the only students that would come banging on my doors are the ones who would often just seek some more marks, than “deserve it”. — I am not speaking from their POV though, I wasn’t taking theirs — you see.

    I remember two cases.

    Case-1
    A student who was originally from Pune. He would come looking for some marks.

    Me: I am sorry you don’t deserve more here.

  • Can a black-hole be created on earth by LHC?

    This post belongs to the eschaton theme. Which means a small and swift blog post just to do justice to something that can’t be made comprehensively large by any reason, at the moment. 

    Read the linked news article which giving excerpts from a book by the famed Martin Rees which I haven’t read, nonetheless which sound very tenuous on the scientific merit its purported to be based on, claims that particle physics experiments can create black-hole catastrophes on earth in the very unfortunate event that something goes wrong.

    Here is my initial reaction to the article. 

    “apocalypse mongering”

    Earth’s Schwarzschild radius is less than 1 cm. What that means is earth needs to be compressed into a sphere of that radius with its current given mass, for it to turn into a black-hole.

  • Falling Masses, the Big Picture.

    This lecture note will make your life ten-fold easier in the scope of the problems it addresses. Consider it a talisman. I discovered this a couple of weeks ago when I was solving these problems for my own conceptual understanding. So I waited till I can completely enunciate the big picture. When I confirmed that its valid for all the following problems I made this note and sharing with you.