Re: TOM ROBERTS - Dono is confused, please help him out (was SR cannot determine Contraction)

On Feb 26, 3:53 pm, Dono <sa...@xxxxxxxxxxx> wrote:
On Feb 26, 12:30 pm, PD <TheDraperFam...@xxxxxxxxx> wrote:



2. can you send me the original paper, I would highly appreciate it.

I'll have to hunt for it. It's a paper comparing ISR (collider)
rapidity distributions with those at FNAL (fixed target), if I
remember right. I think I remember seeing some references in Don
Perkins' book on particle physics, too.

Would be nice to have a look at it, I bet that Tom would like to see
it as well.

Tom and I have talked about it. He doesn't view as direct enough a
test to put it into the FAQ. I disagree, but it's not my FAQ. I
respect Tom a ton, but I don't always go to him as the authority on
relativity either.


Because there should be no difference between rest and uniform
relative motion, I thought that this should be self-evident.

And there isn't. If you have an object that is in motion in a
particular reference frame and you want to change its length without
changing its motion in that frame, then you have to compress the
lattice by introducing a stress. However, this does not mean that the
change that is observed in going from frame to frame has to be
attributed to the same process.

But this is not a valid proof, you realize that? A valid proof would
be to show that:

-while in the proper frame S_0 :    \ Sigma (F_internal) = 0

-in a frame moving with v wrt S_0  \Sigma (F'_internal)=0 (where F'_i
is the Lorentz transformation of F_i) and that , somehow, magically,
the atom sizes have Lorentz contracted. I think Lorentz spent a good
10 years of his life trying to prove that and it amounted to nothing.



It just isn't. And in fact, collisions of nuclei on nuclei
demonstrate just this fact, that the physical density of that nuclear matter is *higher* when the nucleus is in relative motion.

Are these experiments related to rigid lattices or to free atoms?

Yes, in the sense that those nuclei are lattices of quarks and gluons,
and that the introduction of additional stress would have experimental
implications that are not seen.

Is there any acceleration involved in the above?

Not in the region being probed.

Is there ANY acceleration involved? You know why I am asking, we've
been thru this before.

There is acceleration *before* the secondaries emerge from the
collision, yes. After the collision, they are in uniform motion as
much as the atoms in a steel rod are in uniform motion. There is no
difference in the process that produced the secondaries in both cases.
This is verified by several things: a) The cross-section's theoretical
dependence on only the center of mass energy is experimentally
confirmed, b) the other variables of the distributions, which would be
sensitive to any dynamic differences, are identical, c) rewriting the
angular distribution in terms of a kinematic variable that should be
Lorentz-invariant (viz., rapidity) shows that all distributions are
indeed *identical* in the two cases.

If you have a steel rod flying at a barn, you do not worry so much
about what accelerations were involved in getting the rod assembled,
nor too much about what's involved in getting it up to that speed. If
you *are* concerned about that, then all you need to do is to
decelerate by a different way than you accelerated it and see if there
was some stress-related hysteresis in the length of the rod. If the
effect is not due to some physical compression, you shouldn't see any
hysteresis.

PD
.

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