$ Tom's point-ROD mass.!!
Yes, but *ONLY* in the REAL WORLD; NOT in GR, at all, dimwit.!!
BECAUSE ..the GR gtr Tivity TEST-mass is a POiNT-mass *ONLY*.!!
So, ONLY "when LOOKed AT" simultaneously it STRETCHES, right.?!!
There is NO "DiFFERENCE in SiMULTANEiTY" ..numb-skull.!!

<> >><> >><> >><> >><>

Tom Roberts wrote:

schoenfeld1@gmail.com wrote:

#1 - the acceleration applies to all points on the rod
simultaneously relative to the stationary frame.

it would violate elastic laws if it DIDN'T STRETCH.

Yes. So you agree that the rod has stretched in its own frame.
As I said.

That rod is quite clearly stretched.
And the rockets quite clearly did it. <shrug>

There are no "mystical forces" here, there are rockets that pull on the
rod and stretch it. <shrug>

No, it just that you cannot read what you yourself have written above.
The rod stretches in its own frame. YOU SHOWED THAT. The only "*****"
is what you write.

It is you who does not understand. You showed the math above,
The rod _DOES_ stretch when you accelerate it in this manner.

Nonsense. The acceleration had the characteristic that it was

simultaneous everywhere relative to stationary frame --

NECESSARILY differ when looked at simultaneously in the rod's frame.
And that is what stretches the rod in its own frame.

So, ONLY "when LOOKed AT" simultaneously it STRETCHES, right.?!!

As I said before, at base this stretching is due to the
difference in simultaneity between moving frames.

-- one end of a 1.000000000000 meter steel ruler, do you really
believe it measures exactly 1.000000000000 meters while --

ends accelerate "just so", which requires more stretch than --

If I yank hard on --

".."just so", which REQUiREs more STRETCH than ..would naturally..",

-- from one end.

Tom Roberts

Tom Roberts wrote:

schoenfeld1@gmail.com wrote:

The physical mechanism for the
acceleration is immaterial, and Daryll was right to neglect it. The
TYPE of acceleration has the characteristic:
#1 - the acceleration applies to all points on the rod simultaneously
relative to the stationary frame.

OK.

This directly implies that in the rod's instantaneously-comoving
inertial frame the acceleration at different points along the rod is
different when looked at simultaneously in that frame. Work it out, and
you'll find that the proper acceleration of the front must be larger
than the proper acceleration of the rear -- that means that in order to
acomplish what you said above you must "pull harder" on the front than
on the back, and this "pulling" will stretch the rod. In my example I
used rockets, but as you say the mechanism is immaterial -- no matter
what you do, in order to accelerate the rod as described above it MUST
stretch in its own frame.

Now, you acknowledged yourself that this type of acceleration would
cause the rod to stretch in it's own frame. It boggles the mind that
you still don't see how this violates all the known physical laws.

What "physical laws"??? When you pull harder on one end of the rod than
the other, it is no violation of any physical law if the rod stretches;
it would violate elastic laws if it DIDN'T STRETCH.

The
simple fact that the proper length stretched in the rod's frame means
that rod observes a physical change in it's length and can only account
for this with mystical forces - how else can it account for the
stretching?

Whatever is pulling on its ends accounts for the stretching. This isn't
"mystical", this is simple and obvious, once you realize that in the
rod's instantaneously-comoving frame the pull on the front is larger
than the pull on the rear.

Here's the rod at rest relative to stationary frame A.


======================= <--- 1 meter rod
R R R R R R R R R R R R <--- rocket engines on rod


Now, it's at rest so you can synchronize all the clocks on those
rockets. You program the rockets to activate at time t = 0. (SYSTEM HAS
CHARACTERISTIC #1)

At t = 0, all the points on the rod simultaneously accelerate relative
to A.

At t > 0, all the rockets simultaneously run out of fuel relative to A.

At t = x, the rod simultaneously stops relative to A.

At t > x, the rod's velocity is v = 0.8666c relative to A.

At t > x, the rod's length is L_A = 1m relative to A.

So let's do a calculation to see the length of the rod from the rod's
frame after it stops accelerating (i.e. the proper length L).

L = L_A / gamma
= 1 / sqrt(1 - v^2/c^2)
= 2.

So, the previous 1 meter long rod is now 2 meters long in the rod's
frame! If you were that rod, you would look like in your own frame

= = = = = = = = = = = = = = = = = = = = = = =
R R R R R R R R R R R R R R R

Yes. So you agree that the rod has stretched in its own frame. As I
said. And it ought to be clear that the this stretching is not
"mystical" at all, it's due to all those rockets.

But before you accelerated, you looked like this in your own frame:
=======================
R R R R R R R R R R R R

Sure. But not after the rockets burn out. Then, as you showed above, the
rod looks like this in its own frame:

= = = = = = = = = = = = = = = = = = = = = = =
R R R R R R R R R R R R R R R

That rod is quite clearly stretched. And the rockets quite clearly did
it. <shrug>

Hey Roberts, you see how the rod is broken?

I see no broken rod here, I see a stretched rod.

Hey Roberts, you see how
mystical forces must've arised to break the rod?

There are no "mystical forces" here, there are rockets that pull on the
rod and stretch it. <shrug>

Hey Roberts, you see
how SR, in this instance, predicts a ***** result and thus fails as
a general description of noninertial frames?

No, it just that you cannot read what you yourself have written above.
The rod stretches in its own frame. YOU SHOWED THAT. The only "*****"
is what you write.

At base this is due to the unrealistic assumption that the
accelerations are equal in the initial frame, rather than
the more reasonable assumption of Born rigid motion. For
that of course the rod does not stretch. <shrug>

I understand Robert's that the Rod "must stretch". What you don't
understand is that this prediction goes in the face of the laws of
physics.

No, it doesn't. In the rod's frame the different rockets pull
differently on the rod, and it must stretch to maintain the condition of
the gedanken: that the ends accelerate identically in the initial
inertial frame.

Yes, that is a wierd condition. Yes, it's quite difficult to make this
happen. Yes, in the real world rods do not behave this way (because we
do not accelerate them this way). But the rod stretching _IS_ a
consequence of this condition. YOU SHOWED THAT ABOVE. <shrug>

It demonstrates why SR fails as a general description of
noninertial frames. That's my point, you keep proving it for me, but
you don't seem to understand it.

It is you who does not understand. You showed the math above, but
clearly do not understand how it relates to the physics. The rod _DOES_
stretch when you accelerate it in this manner.

[And there are other ways to accelerate the rod such that
it does not stretch. Those other ways correspond MUCH more
closely to how we normally think of accelerating rods.]

Nonsense. The acceleration had the characteristic that it was
simultaneous everywhere relative to stationary frame - this
characteristic alone predicts the complete destruction of the ruler in
the ruler's frame (and transitively all frames, due to causality)

As you showed above, the rod stretches. There is no "breaks" here at
all, except in your imagination. But yes, an observer in any frame at
all would agree that the rod's proper length increases when subject to
this particular type of acceleration.

which
is a bogus, absurd and a perverse result from SR.

No, this stretching is neither "bogus" nor "perverse" -- it is REQUIRED,
due to the way the acceleration was specified.

It is a perfect
example why SR fails a general description of noninertial frames.

It's merely an example of your failure to understand. <shrug>

the rod was initially at rest relative to A. At the instant the
acceleration began relative to A, it occured simultaneously everywhere
on the rod, relative to A. But since the rod is initially and
synchronized at rest relative to A it must be be simultaneous
everywhere in the rod's frame too.

Only at startup, not during the acceleration, nor at burnout.

Thus the proper accelerations are
the same on both ends of the rod,

Not true. The accelerations relative to the initial frame are equal for
the two ends at all times, but once the rod moves at all that is no
longer its proper acceleration. In order to maintain identical
accelerations in the initial frame, the proper accelerations must
NECESSARILY differ when looked at simultaneously in the rod's frame. And
that is what stretches the rod in its own frame.

As I said before, at base this stretching is due to the
difference in simultaneity between moving frames.

I added the word "break" to help you understand why this scenario is
nonsense.

But you have never shown it to be "nonsense", you have only shown that
you don't understand it. <shrug>

Hey Robert's, don't you think if you stretch a 1m ruler to 2m
that it breaks.

That was YOUR example, not mine, and it includes the highly-improbable
assumption that you can connect a bunch of rockets to that 1m ruler and
accelerate it to 0.866 c. When you make outrageous assumptions like that
you can get outrageous conclusions. I remark that if made out of a
suitable material, it could indeed stretch to double its initial length.

If I yank hard on one end of a 1.000000000000 meter steel ruler, do you
really believe it measures exactly 1.000000000000 meters while being
accelerated? The situation being discussed is similar, just with larger
accelerations over longer periods of time, and the requirement that the
ends accelerate "just so", which requires more stretch than the ruler
would naturally have if accelerated from one end.

Tom Roberts