Metric sign

[Thrice]

Main Question or Discussion Point

I guess this is more of an anthropological post. Is there any pattern to which sign convention people prefer? Or is it just a matter of which you were exposed to first?

 

[robphy]

I think it really depends on which you and your research community uses, which is often influenced by the convention in the primary textbook for that community.

 

[neutrino]

Just wondering...isn't +++- more prominent than -+++?

 

[coalquay404]

Just wondering...isn't +++- more prominent than -+++?

No. It's much, much more usual to see the timelike coordinate placed first in the list. As someone else already said, the degree to which you use/prefer either (-+++) or (+---) depends on what field you work in. (+---) is ubiquitous in QFTs, while (-+++) is seen most often in GR, string theory (where it's actually (-+++...+)), and so on.

 

[cristo]

I think it even depends on what particular problem you are trying to solve within each field. There are some times when -+++ is more convenient, and others when +--- is. However, I would agree that the timelike coordinate is, in my experience, always placed first.

 

[George Jones]

I agree with cristo, but whenever possible, I use +---.

 

[pervect]

I think it mostly depends on what you read, I think. Most of what I've read (in GR) uses the Landau-Lifschitz spacelike convetion, i.e. -+++. I don't read much about string theory, QFT, etc.

However, if (for instance) I'm writing a post on how geodesic motion extremizes proper time, I'll usually use a +--- convention, it makes the problem easier.

 

[robphy]

IMHO, it's okay to switch signature conventions in private or among friends. However, for presentations (research or pedagogical), one should stick to one and be consistent. (I can't imagine switching sign conventions in [say] optics problems.) Let's not forget other sign-conventions associated with the index positions in Riemann, etc... (I can't imagine switching sign conventions there.)

 

[George Jones]

(I can't imagine switching sign conventions in [say] optics problems.)

I once taught an introductory optics course in which the text and lab manual used different sign conventions for geometric optics.

 

[Thrice]

(IMHO, it's okay to switch signature conventions in private or among friends. However, for presentations (research or pedagogical), one should stick to one and be consistent.)

Which is what puzzled me about metric sign switching. Physics guys are often sticklers about convention (& for good reasons, i think). It seems too pervasive given the amount of time its been around & I was curious why.

 

[AlphaNumeric]

Most of what I've read (in GR) uses the Landau-Lifschitz spacelike convetion, i.e. -+++. I don't read much about string theory, QFT, etc.

Green, Schwartz and Witten use -+++ (or rather -+++++++++ :tongue: ) in their book and that's Green's personal preference too.

I tend to use that for QFT and string stuff, though when I first learnt QFT the lecturer used +--- and then I couldn't work out, when it came to revision, why I kept getting unwanted factors of -1 in the places. Then I realised I'd adopted the string theory and black holes courses convention of -+++ and forgotten my QFT course used the other one

I never used to understand why they didn't just nail down a convention once and for all, but I suppose it's now past the point of no return, since there's so many textbooks and lecture courses using various conventions and plenty of researchers stuck in their ways. Too late to do much about it now which wouldn't just annoy loads of people.

 

[robphy]

I never used to understand why they didn't just nail down a convention once and for all, but I suppose it's now past the point of no return, since there's so many textbooks and lecture courses using various conventions and plenty of researchers stuck in their ways. Too late to do much about it now which wouldn't just annoy loads of people.

Sounds like an argument about the metric SYSTEM.

 

[Meir Achuz]

Green, Schwartz and Witten use -+++ (or rather -+++++++++ :tongue: ) in their book and that's Green's personal preference too.
do much about it now which wouldn't just annoy loads of people.

I always thought that -+++ was used by mathists, and +--- by physists
(so s=+m^2).
You have confirmed that, although Schwartz was a physist before he went to Princeton.

 

[AlphaNumeric]

I think when you get into the more indepth parts of string theory like Green, Witten and Schwartz do, the lines between mathematician, physicist and magician can blur a bit ;)

 

[lalbatros]

Anyway, physics is invariant with respect to sign conventions!

 

[Meir Achuz]

Anyway, physics is invariant with respect to sign conventions!

Yes, but some physicists don't like the equation p^2=-m^2.

 

[Demystifier]

Yes, but some physicists don't like the equation p^2=-m^2.

Especially particle physicists.
It seems to me that particle physicists prefer +---, while relativists prefer -+++. But the surprising thing then is that string theorists prefer -+++, inspite of the fact that they are more like particle physicists than relativists.

 

[Ahmes]

I use ++++ :surprised and the 4th component taken as a pure imaginary number. e.g. (x,y,z,ict)
But I don't know how well it can be applied to curved spaces etc. It works well in special relativity and you can forget all about covariance and contravariance.