What is the Unit 'a.u.' and How to Convert it to SI?

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Discussion Overview

The discussion centers around the meaning of the unit "a.u." as encountered in graphs representing the unit of |E|^2, where E denotes the electromagnetic field. Participants explore its significance and conversion to SI units, addressing potential ambiguities associated with the term.

Discussion Character

  • Exploratory
  • Debate/contested

Main Points Raised

  • Some participants propose that "a.u." refers to "arbitrary units," indicating a lack of specific measurement and suggesting that the graphs display relative values of E^2.
  • Others argue that "a.u." could refer to the Astronomical Unit, a measure of distance, although this interpretation may not align with the context of electromagnetic field measurements.
  • A participant notes that many journals have moved away from using "a.u." to prevent confusion, advocating for clearer terminology like "arb. units" or "arbitrary units."

Areas of Agreement / Disagreement

Participants express differing interpretations of "a.u." with no consensus reached on its meaning. Some support the idea of it being "arbitrary units," while others suggest it could be confused with the Astronomical Unit.

Contextual Notes

The discussion highlights potential confusion surrounding the term "a.u." and its application in scientific literature, particularly in relation to electromagnetic field measurements.

El Flea
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Does anyone knows what this unit "a.u" means? I found it on many graphs, where "a.u" represents the unit of |E|^2 (E represents electromagnetic field). How do I convert "a.u" to SI unit?
 
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El Flea said:
Does anyone knows what this unit "a.u" means? I found it on many graphs, where "a.u" represents the unit of |E|^2 (E represents electromagnetic field). How do I convert "a.u" to SI unit?
Are you sure that you have that right? a.u. usually refers to the Astronomical Unit, which is a measure of distance (I can't remember the exact conversion factor, but I'm sure its of the order of 109m).
 
I suspect it means "arbitrary unit", that is, no particular unit at all. In this case those graphs are intended to show only the relative values of E^2 at different points on the graph, without regard for the overall scale.
 
jtbell said:
I suspect it means "arbitrary unit", that is, no particular unit at all. In this case those graphs are intended to show only the relative values of E^2 at different points on the graph, without regard for the overall scale.
Well I never knew that! You learn something new every day, thanks jtbell.
 
In many journals, such as the Phys. Rev. journals, they no longer permit the use of "a.u." abbreviation. They want those figures to at least say "arb. units" or even "arbitrary units", to avoid the confusion with Astronomical Unit.

Zz.
 
I see. That makes sense now, thank you very much.
 

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