# Maxwell's equations

ehrenfest
Are Maxwell's equations thought to be exact? I realize this question is very open-ended and loosely-phrased.

lzkelley
Yes they are. But keep in mind that each one of maxwell's equations inevitably contains some sort of fundamental constant (mu or epsilon usually; not to mention electric charge etc etc) which are measured quantities and therein not exact.

ehrenfest
Yes.

Phlogistonian
They're not exactly exact. QED makes slightly different predictions from classical electromagnetism.

tgt
Mathematically, correct hence exact. Physically, it's a good approximation and only an approximation to model phenomena. Hence not exact physically. Is anything exact physically? No.

rbj
Yes they are. But keep in mind that each one of maxwell's equations inevitably contains some sort of fundamental constant (mu or epsilon usually; not to mention electric charge etc etc) which are measured quantities and therein not exact.

lz, be careful.

which constant in Maxwell's equation is measured and not defined (to an exact value)?

Poop-Loops
Epsilon-not.

Mu-not is defined. At least, that's what my professor said.

rbj
Epsilon-not.

Mu-not is defined. At least, that's what my professor said.

you mean this epsilon-not ?

Staff Emeritus
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dst
Mathematically, correct hence exact. Physically, it's a good approximation and only an approximation to model phenomena. Hence not exact physically. Is anything exact physically? No.

I have one apple, I add another one, I have exactly two apples.

humanino
I have one apple, I add another one, I have exactly two apples.
Well, if you take into account the masses of the apples, which is what is physically relevant when you buy apples, then you have less mass when the two apples are together, right ?

dst
Well, if you take into account the masses of the apples, which is what is physically relevant when you buy apples, then you have less mass when the two apples are together, right ?

Pfft, technicalities. If truth be told, the error is in disguise - it's either present in the definition(s) or as a constant in whatever expression you're using.

On the other hand, there is no match for the physics of two cows™.

You have two communist cows.

Homework Helper
Gold Member
Epsilon-not.

Mu-not is defined. At least, that's what my professor said.

by the way, that's
epsilon-http://www.answers.com/naught&r=67" [Broken] (epsilon-zero) and similarly for mu-naught.

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rewebster
Well, if you take into account the masses of the apples, which is what is physically relevant when you buy apples, then you have less mass when the two apples are together, right ?

so, that applies, too, when two physicists get together?

ehrenfest
Well, if you take into account the masses of the apples, which is what is physically relevant when you buy apples, then you have less mass when the two apples are together, right ?

Umm--what? Are you using special relativity?

humanino
so, that applies, too, when two physicists get together?
I guess so :rofl:
edit
Actually, it depends. If they disagree on the status of "is string a theory ?", their interaction can be very exothermic.
Umm--what? Are you using special relativity?
They have gravitational biding energy, don't they ?