How do I expand gamma matrices without adding a unity matrix?

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Discussion Overview

The discussion revolves around the expansion of the gamma matrix, specifically i\hbar \gamma^0, within the context of quantum mechanics and spinor space. Participants seek clarification on how to express this matrix without resorting to a unity matrix, exploring various representations and definitions of the gamma matrices.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant expresses confusion about how to expand i\hbar \gamma^0 and requests assistance.
  • Another participant suggests that the expansion is simply i\hbar \gamma^0 itself and mentions using Mathematica.
  • There is a discussion about the gamma matrices being 4x4 matrices that depend on the chosen representation in spinor space, with a reference to Wikipedia for further details.
  • Some participants challenge the clarity of the Wikipedia article and express the need for a more straightforward explanation of the expansion.
  • A participant provides the explicit form of \gamma^0 in the Dirac representation and shows how to compute i \hbar \gamma^0 using that matrix.
  • Another participant questions why \gamma^{0}^2 equals the unity matrix, prompting further clarification on the concept of the unity matrix.
  • One participant acknowledges their earlier misunderstanding regarding the unity matrix after receiving clarification.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the meaning of "expand" in this context, leading to multiple interpretations and ongoing confusion regarding the expansion of the gamma matrix.

Contextual Notes

There are unresolved assumptions about the definitions and representations of the gamma matrices, as well as the specific nature of the requested expansion.

help1please
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\pi = \frac{\partial \mathcal{L}}{\partial \dot{q}} = i \hbar \gamma^0

How do I expand

i\hbar \gamma^0

the matrix in this term, I am a bit lost. All the help would be appreciated!
 
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help1please said:
\pi = \frac{\partial \mathcal{L}}{\partial \dot{q}} = i \hbar \gamma^0

How do I expand

i\hbar \gamma^0

the matrix in this term, I am a bit lost. All the help would be appreciated!

It's itself.Using Mathematica.
 
Expanding that, gives back that?

What is mathematica??
 
The gamma matrices are 4 x 4 matrices whose values depend on the basis ("representation") you decide to use in spinor space. For a list of possibilities, see "gamma matrix" in Wikipedia.
 
so you don't know how to expand the terms I asked of?
 
so you don't know how to expand the terms I asked of?
I thought the Wikipedia article explained it pretty clearly. It gives the explicit form of γ0 in the Dirac, Weyl and Majorana representations. Isn't that what you want?

But if that's not what you mean by "expanding" it, the only other thing to do is this...

iħγ0
 
Bill_K said:
I thought the Wikipedia article explained it pretty clearly. It gives the explicit form of γ0 in the Dirac, Weyl and Majorana representations. Isn't that what you want?

But if that's not what you mean by "expanding" it, the only other thing to do is this...

iħγ0

Why have that when I started off with that... my equation I really thought was simple. HOW do you expand i \hbar \gamma^0

The answer I was looking for was not a go to wiki one! And no wiki does not explain it well for me, I am new at this stuff.
 
Can you show me, in plane mathematical language, in an equation, how to expand it please.
 
You will have to define what you mean by "expand". So far we have only been able to guess, and apparently this was not what you intended. So define "expand" please.
 
  • #10
Do you mean this? \qquad \gamma^0 = <br /> \begin{pmatrix}<br /> 1 &amp; 0 &amp; 0 &amp; 0\\<br /> 0 &amp; 1 &amp; 0 &amp; 0\\<br /> 0 &amp; 0 &amp; -1 &amp; 0\\<br /> 0 &amp; 0 &amp; 0 &amp; -1<br /> \end{pmatrix} \qquad \qquad <br /> (which is the Dirac representation)

so that \ \ \qquad \qquad i \hbar \gamma^0 = <br /> \begin{pmatrix}<br /> i \hbar &amp; 0 &amp; 0 &amp; 0\\<br /> 0 &amp; i \hbar &amp; 0 &amp; 0\\<br /> 0 &amp; 0 &amp; -i \hbar &amp; 0\\<br /> 0 &amp; 0 &amp; 0 &amp; -i \hbar<br /> \end{pmatrix} \qquad \qquad <br />
 
Last edited:
  • #11
PhilDSP said:
Do you mean this? \qquad \gamma^0 = <br /> \begin{pmatrix}<br /> 1 &amp; 0 &amp; 0 &amp; 0\\<br /> 0 &amp; 1 &amp; 0 &amp; 0\\<br /> 0 &amp; 0 &amp; -1 &amp; 0\\<br /> 0 &amp; 0 &amp; 0 &amp; -1<br /> \end{pmatrix} \qquad \qquad <br /> (which is the Dirac representation)

so that \ \ \qquad \qquad i \hbar \gamma^0 = <br /> \begin{pmatrix}<br /> i \hbar &amp; 0 &amp; 0 &amp; 0\\<br /> 0 &amp; i \hbar &amp; 0 &amp; 0\\<br /> 0 &amp; 0 &amp; -i \hbar &amp; 0\\<br /> 0 &amp; 0 &amp; 0 &amp; -i \hbar<br /> \end{pmatrix} \qquad \qquad <br />

Why is then when \gamma^{0}^2 is equal to 1?
 
  • #12
\qquad (\gamma^0)^2 = <br /> \begin{pmatrix}<br /> 1 &amp; 0 &amp; 0 &amp; 0\\<br /> 0 &amp; 1 &amp; 0 &amp; 0\\<br /> 0 &amp; 0 &amp; -1 &amp; 0\\<br /> 0 &amp; 0 &amp; 0 &amp; -1<br /> \end{pmatrix}<br /> \begin{pmatrix}<br /> 1 &amp; 0 &amp; 0 &amp; 0\\<br /> 0 &amp; 1 &amp; 0 &amp; 0\\<br /> 0 &amp; 0 &amp; -1 &amp; 0\\<br /> 0 &amp; 0 &amp; 0 &amp; -1<br /> \end{pmatrix} =<br /> \begin{pmatrix}<br /> 1 &amp; 0 &amp; 0 &amp; 0\\<br /> 0 &amp; 1 &amp; 0 &amp; 0\\<br /> 0 &amp; 0 &amp; 1 &amp; 0\\<br /> 0 &amp; 0 &amp; 0 &amp; 1<br /> \end{pmatrix}<br />
 
  • #13
Ah sorry, unity matrix.I don't know what I read earlier but this didn't immediately pop out to me! ty
 

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