Linked Questions
30 questions linked to/from How general is the Lagrangian quantization approach to field theory?
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Can we derive most fundamental laws from the Action Principle? [duplicate]
It is said in the book Fearful Symmetry - The Search for Beauty in Modern Physics that we can derive all basic laws in physics from a simple principle called Least Action Principle (although it may be ...
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Why does Principle for least action hold for classical fields [duplicate]
Let $\mathscr L (\phi(\mathbf x), \partial \phi(\mathbf x))$ denote the Lagrangian density of field $\phi(\mathbf x)$. Then then actual value of the field $\phi(\mathbf x)$ can be computed from the ...
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Why are action principles so powerful and widely applicable? [duplicate]
I've been trying to wrap my head around Lagrangian mechanics and Lagrangians in general, and I've found it difficult. After some thinking, I believe that the issue I have is with action principles. ...
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Why does it seem like there is always a Lagrangian? [duplicate]
All the fundamental laws of physics can be written in terms of an action principle. This includes electromagnetism, general relativity, the standard model of particle physics, and attempts to go ...
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Which class of Dynamical Systems is governed by Lagrangian Dynamics? [duplicate]
Lagrangian formalism is a technique using which we can obtain the time evolution of a dynamical system. Given a dynamical system, can we say whether or not we can write down a Lagrangian (solving it ...
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Why should physical theories always have a Lagrangian formalism? [duplicate]
I've often heard that every physical theory has some kind of Lagrangian formalism, or a formalism in terms of a principle of stationary action. The Standard Model has one, General Relativity has one, ...
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Does the principle of stationary action always work? [duplicate]
Give some Lagrangian we use the principle of stationary action to find the desired euqations of motion for something (e.g. a field).
A lot of modern physics seems to be based on the principle of ...
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Is It Possible to Express all fundamental forces in the form of generalized potentials? [duplicate]
I have Started reading Hamilton's Principle or Principle of Least Action In first course of Undergraduate classical mechanics.
So, I think it becomes easier to apply the Variational principles if ...
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Why the Principle of Least Action?
I'll be generous and say it might be reasonable to assume that nature would tend to minimize, or maybe even maximize, the integral over time of $T-V$. Okay, fine. You write down the action ...
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Does a non-lagrangian field theory have a stress-energy tensor?
In classical field theory, the stress-energy tensor can be defined in terms of the variation of the action with respect to the metric field, or with respect to a frame field if spinors are involved. ...
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Is the Lagrangian approach essentially a 'theory of everything'?
From learning about the Lagrangian lately it seems that that it can underlie so many phenomena that it must be the unifying concept that underpins all physics. I often hear that physicists are ...
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Do "typical" QFT's lack a lagrangian description?
Sometimes as a result of learning new things you realize that you are incredibly confused about something you thought you understood very well, and that perhaps your intuition needs to be revised. ...
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QFT's that have no action
What does it mean to have a QFT that can not be encoded by an action. What is by far the most powerful approach of study in such a case. What is the best studied physical theory that falls into this ...
user37343
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Is there a valid Lagrangian formulation for all classical systems?
Can one use the Lagrangian formalism for all classical systems, i.e. systems with a set of trajectories $\vec{x}_i(t)$ describing paths?
On the wikipedia page of Lagrangian mechanics, there is an ...
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Is there any physics that cannot be expressed in terms of Lagrange equations?
A lot of physics, such as classical mechanics, General Relativity, Quantum Mechanics etc can be expressed in terms of Lagrangian Mechanics and Hamiltonian Principles. But sometimes I just can't help ...
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