Register to reply

Volume element as n-form

Tags: element, nform, volume
Share this thread:
Nov11-10, 12:14 PM
P: 411

I'm reading Sean Carroll's text, ch2, and believe I understood most of the discussion on Integration in section 2.10. However in equation 2.96, he states that

[tex] \epsilon\equiv\epsilon_{\mu_1\mu_2...\mu_n}dx^{\mu_1}\otimes dx^{\mu_2}\otimes...\otimes dx^{\mu_n} =\frac{1}{n!}\epsilon_{\mu_1\mu_2...\mu_n}}dx^{\mu_1}\wedge dx^{\mu_2}\wedge...\wedge dx^{\mu_n}[/tex]

I don't quite understand this equality. For example just taking n=2, the LHS is [tex] dx^0\otimes dx^1-dx^1\otimes dx^0[/tex] (which isn't zero because tensor products don't commute). Where on the RHS one would have [tex] \frac{1}{2}\left(dx^0\wedge dx^1-dx^1\wedge dx^0\right)=dx^0\wedge dx^1[/tex], by the antisymmetry of the wedge product.

So I'm at a loss to understand this part of 2.96 despite understand the following lines.

Thanks alot for any replies.
Phys.Org News Partner Science news on
Apple to unveil 'iWatch' on September 9
NASA deep-space rocket, SLS, to launch in 2018
Study examines 13,000-year-old nanodiamonds from multiple locations across three continents
Nov12-10, 02:32 AM
P: 1,411
Formula (1.81) in Carroll's "Lecture Notes on General Relativity" (1997) tells you:

[tex]A\wedge B=A\otimes B-B\otimes A[/tex]

So, what is it that causes you the problem?
Nov12-10, 06:12 AM
P: 411
Oh I was unaware of this formula.

Do you mean (1.80) in this edition of Carroll? namely [tex] (A\wedge B)_{\mu\nu}=A_{\mu}B_{\nu}-A_{\nu}B_{\mu}[/tex]

Which I guess can be written [tex] (A\wedge B)_{\mu\nu} =(A\otimes B)_{\mu\nu}-(B\otimes A)_{\mu\nu}[/tex], leading to the equation you stated: [tex] (A\wedge B) =(A\otimes B)-(B\otimes A)[/tex]

Nov12-10, 06:21 AM
P: 1,411
Volume element as n-form

Yes - that is another way of writing it.

Register to reply

Related Discussions
How to pass array element form a subroutine to main function Programming & Computer Science 14
Divergence defined from volume element Differential Geometry 9
Volume element in phase space Advanced Physics Homework 0
Form of line element of a torus. General Math 8
Integrating with volume element (d^3)x Introductory Physics Homework 1