On Dec 27, 10:15 pm, "bergeron" <badd_...@yahoo.com> wrote:
> Koobee Wublee wrote:

> > > > > For a scalar field phi with mass m, the usual Lagrangian (density) is:
> > > > > L = g^uv (d_u phi) (d_v phi) - m^2 phi^2
> > >
> > > > > General knowledge of modern physics. You can look it up.
> > >
> > > > I did, and I did not find anything you have claimed.
> > > 
> > > Then, you did not try very hard, since the Lagrangian above
> > > is the relativistic wave equation, also know as the Klein-Gordon
> > > equation.
> > 
> > I don't see any resemblance to the following.
> > 
> > http://en.wikipedia.org/wiki/Klein-Gordon_equation
>
> Please tell me that you are kidding. Even if you didn't know how
> to get from the Lagrangian to the Hamiltonian shown throughout most
> of the Wikipedia page, the expression at the bottom of the page
> under ``Action'' minus the integral sign is the same as the one above.

I am sorry to disappoint you.  I am not kidding.  You are off on a
tangent.  <shrug>

In the meantime, we are still discussing the Lagrangians and the
Euler-Lagrange equations.

> >  What justifies it to be a Lagrangian?
> >
> > WTF?
>
> WTF?
>
> > WTF?
>
> It appears that you are rather unfamiliar with the concept
> of a Lagrangian.
>
> > Wrong.
>
>  Your comments above contradict any claim of understanding the concept
> that you could make.

Come on.  It is not fair to call me ignorant if I do not understand
your 'WTF'.  <shrug>  I don't find that resemble anything in the
terminologies in physics.  So, please explain.

> > Just because the classical Lagrangian is (L = K + U)
>
> The classical Lagrangian is L = T - U (T is the standard symbol for
> kinetic energy).

A symbol is only an expression of a physical quantity or whatever.  If
you want to discuss what I have addressed you need to use my
terminology.  On the other hand, I have no problem to read your
language.

> Really, if you want to argue about something, at
> least learn enough about it to be credible.

I have defined what I am talking about.  There should be no more
misunderstanding.  I am credible, and I have my own reasons of defining
these variables.  I have reasons to do so.  You just need to get over
with that.  <shrug>

In the meantime, you still have not addressed why you are allowed to
proceed to the checkout counter and freely tossing the Euler-Lagrange
equations around without any justification for the validity of the
Lagrangian you have chosen to embrace.  Are you still in the
kindergarten or something?  If not, please act like a responsible
adult.  <shrug>

You don't know why the Lagrangian is valid, do you?  You don't
understand the very gut details of the Lagrangian method, do you?
<sigh>

 See also

https://home.deds.nl/~dvdm/dirk/Physics/Fumbles/NewLagrangian.html