Re: [Phys-l] relativity misconception #437

["Rauber, Joel" <Joel.Rauber@SDSTATE.EDU>]

This may or may not be helpful.

Moe certainly has a world-line; how is it drawn?

In the "MOE" reference frame Moe's world-line is a vertical straight line using the standard space-time axes of x->horizontal and t->vertical.

Joel

_________________________

Joel Rauber, Ph.D 
Professor and Head of Physics
Department of Physics
South Dakota State University
Brookings, SD 57007
Joel.Rauber@sdstate.edu 
605.688.5428 (w)
605.688.5878 (fax) 

> -----Original Message-----
> From: phys-l-bounces@carnot.physics.buffalo.edu [mailto:phys-l-
> bounces@carnot.physics.buffalo.edu] On Behalf Of Bill Nettles
> Sent: Wednesday, October 12, 2011 9:46 AM
> To: Forum for Physics Educators
> Subject: Re: [Phys-l] relativity misconception #437
>
> I don't deal with 4-vectors on a regular basis, and haven't taught the
> Modern section in quite a while. SO...be gentle. I'm trying to
> understand this.
>
> JD said:" What we care about is the coordinate system.  Moe himself is
> moving toward the future at the rate of 60 minutes per hour, in
> accordance with answer (B), but his coordinate system is not.  In
> particular the contours of constant time in his coordinate system are
> not moving, and those are what we normally use to measure spacetime
> positions, velocities, et cetera."
>
> Does this mean that there are continually "new" coordinate systems that
> are instantaneous with Moe, but that we have chosen a coordinate system
> at a fixed space-time point with which to measure all other space-time
> action?  I haven't thought of coordinate systems in this way, at least
> not recently (maybe I did while as a grad student in survey class of
> GR). I've always thought of Moe actually BEING the coordinate system so
> that the answer to (B) would be (0,0,0,0).  But if "the contours of
> constant time ... not moving," is it really "his coordinate system?"
> Isn't it a coordinate system that we chose at a single time which has
> no special velocity relative to him?  And what is a real problem in
> which this makes a difference in what we would measure? Not playing
> devil's advocate here; really looking to understand the nuances of this
> 4-vector coordinate system definition.
>
> Thanks,
>
> BillN
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