Re: Is charge conserved between frames?

From: J.J. Simplicio (abc_at_nospam.com)
Date: 10/30/04 

Date: Sat, 30 Oct 2004 14:04:21 GMT

"sal" <pragmatist@nospam.org> wrote in message
news:pan.2004.10.30.02.53.08.511654@nospam.org...
> On Fri, 29 Oct 2004 21:47:11 +0000, J.J. Simplicio wrote:
>
>>>
>> Just wondering. Would it be OK to describe my age, weight, and height by
>> a
>> 4-vector? I simply take those three numbers and use them as the spatial
>> components of a 4-vector as measured in my own inertial reference frame.
>> For the time-component I just stick in a zero (my IQ?). Now I define the
>> components of this vector in any other inertial frame according to the
>> standard rule of how components of a 4-vector should transform. There! I
>> now have a 4-vector that I'll call 'JJ's-personal-characteristics
>> 4-vector'. Any objections?
>
> :-)
>
> Any string of 4 numbers which is known in some frame can be made into a
> 4-vector, but in this case I'm afraid it won't actually be good for much.
> One problem is that your age will now vary depending on how fast you're
> going. But your age is the proper interval you've traveled in your own
> rest frame since you were born, so it should be invariant.
>
> To put it another way, if someone alongside you in your car takes your
> picture, and someone standing beside the road takes a picture of you at
> the same instant as you zoom by a few inches from them (a shared event),
> you should look the same age in both photographs!
>

Yes, that's the point. If we demand that the components of a 4-vector have
the same 'physical meaning' in all coordinate systems, then JJ's 4-vector is
no good. But it seems to me that the electric field 4-vector is just as
lousy for the same reason. What is the meaning of a component of the
electric field 4-vector in some arbitrarily chosen coordinate system?

JJ

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