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Re: [Phys-l] velocity-dependent mass (or not)



Hi all-
Time dilatation is a corpse? Measure the lifetimes of some of the muons that are bombarding you in cosmic rays. The answer you get will be greater than the value in the Particle Data Book, and will depend upon the velocity of the muon. Time dilation is a real observable.
Regards,
Jack

On Sun, 28 Jun 2009, Moses Fayngold wrote:

--- On Sun, 6/28/09, John Denker <jsd@av8n.com> wrote:
"It doesn't "come from" anywhere.  You shouldn't assume it needs to
"come from" anywhere.  Asking where it comes from has no physical
significance, because mass is not conserved.  There is no reason
why it should be."


   It comes from the past. If an isolated system (e.g. positronium) had a certain rest mass before reaction (e.g., annihilation), it has the same rest mass after reaction. In case of annihilation, the system of emerging two photons has the rest mass exactly equal to the initial mas of positronium. The system has changed beyond recognition, but its rest mass remains as before. The rest mass of the new state comes from the rest mass of the initial state.This is what conservation means.
.

  " Energy is conserved.  Rest energy (by
  itself) is not conserved.  There is no reason why it should be".

The reason is that the rest energy is also energy. Would you deny this?

 I don't have a problem with non-conserved mass.  If you have a
problem with it, then, well, that's /your/ problem, and Henny
Youngman has the only solution.  There is plenty of evidence
(including the "extreme" example cited above) to tell us that
mass is not in fact conserved.

Mass is Lorentz invariant.  That means it is invariant with respect
to Lorentz transformations.  That does *not* mean it is invariant
with respect to all imaginable transformations (such as annihilation
reactions).

I apologize to the list members who think I am belaboring the obvious.

Also:  Let's keep in mind that velocity-dependent mass is not the only
dead idea that is haunting us.  In the same category are the Fitzgerald-
Lorentz contraction and time dilatation, i.e. rulers that cannot be
trusted and clocks that cannot be trusted.  All three of these stinking
corpses need to be buried once and for all.

Relativity is not weird or paradoxical.  It is just the geometry and
trigonometry of spacetime.  The smart way to handle this has been known
since 1908, i.e. for 101 of the 104 years that relativity has existed.

Maybe in a few more decades, textbook writers will get a clue.

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_______________________________________________
Forum for Physics Educators
Phys-l@carnot.physics.buffalo.edu
https://carnot.physics.buffalo.edu/mailman/listinfo/phys-l


--
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General Custer's unremembered message to his men,
just before leading them into the Little Big Horn Valley