Re: SR and Light from GR


"Kevin Donnelly" <kevin@xxxxxxxxxxxxx> wrote in message
news:49a3b691$1@xxxxxxxxxxxxxxxxxxxx
Bill Hobba wrote:
"Kevin Donnelly" <kevin@xxxxxxxxxxxxx> wrote in message
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GR implies a 5th Dimension that spacetime curves into.

No

GR in 5 dimensions gives Maxwell equations.

I presume you are talking of Kaluza Klein theories. It actually requires
more than just a 5 th dimension - it requires the metric to not depend on
that dimension, which basically imposes the symmetry of a circle ie the
symmetry of EM. Basically EM in - EM out. That does not mean its not
true - it may very well be true - but that the reason Kaluza Klein
theories work - not the fact it is 5 dimensional.

Thanks
Bill


So compactifaction is not just to explain why the additional dimensions
are not visible.
I thought Kaluza Klein produced the theory before compactifaction was
added.

Kaluza made the assumption the metric did not depend explicitly on the 5th
dimension. If you don't make that assumption the Kaluza- Klien miracle does
not work. Klein made that assumption explicit by assuming the 5th dimension
is curled up in a circle. This is the physical explanation of the 'ad hoc'
assumption Kaluza made. It allows one to see the explicit incorporation of
U(1) symmetry that is slightly obscured in Kaluza's original treatment that
so stunned Einstein. It is now known this is the reason Kaluza-Klein
works - EM is put in by assuming U(1) symmetry so it is not surprising EM
pops out.

Thanks
Bill


.

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