Re: There is no physical length contraction

Bruce Richmond wrote:
On Jul 22, 10:16 pm, "Whoever" <no...@xxxxxxxxxxx> wrote:
"Bruce Richmond" <bsr3...@xxxxxxxxxxx> wrote in message

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On Jul 22, 9:11 am, "Whoever" <no...@xxxxxxxxxxx> wrote:
"Bruce Richmond" <bsr3...@xxxxxxxxxxx> wrote in message
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On Jul 21, 7:13 pm, "Whoever" <no...@xxxxxxxxxxx> wrote:
"harry" <harald.vanlin...@xxxxxxx> wrote in message
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On Jul 21, 10:44 am, "Whoever" <no...@xxxxxxxxxxx> wrote:
"harry" <harald.vanlin...@xxxxxxx> wrote in message
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On Jul 20, 9:26 pm, stevendaryl3...@xxxxxxxxx (Daryl McCullough)
wrote:
Uncle Ben says...
Paul, that part is obvious. What is not obvious is how to use
the
rotation analogy to accomodate the essential parts of the
spaeship/
string phenomenon: the constraint of constant length and the
acceleration, leading to string breaking.
Okay, here's a math-free analogy:
If you take a stick in ordinary Euclidean space that is
initially horizontal, and you rotate it, the horizontal
extent (projection of the stick's length on the horizontal
axis) becomes smaller. Now, imagine rotating a stick in
a way that keeps the horizontal extent *constant*. How
can we do that? Well, imagine starting with a horizontal
stick, and pulling straight up on one end while pulling
straight down on the other end. If you manage to keep
the horizontal projection of the stick's length constant,
then the stick will break.
I agree with PD that the rotation through rapidity only shows you
where spacetime events marking events are in either frame (what I
call
a mapping),
Given that our reality is our experience of that mapping, that is
also
'physical'
but you seem to disagree with that. As far as I understand
your earlier words in this thread, you agree that the physical
world
is 3D but you also appear to claim that a rotation in Minkowski
space
represents physical reality (and not just a map of events). Then,
can
you explain how, taking your above analogy, an accelerating
spaceship
physically rotates so that we only see a "projection" of it? Into
what
does it rotate?
Time .. hence Relativity of simultaneity
No object can rotate into "time" (if you can do that, you're better
than David Copperfield!)
Unfortunately (or maybe not) you cannot dictate to nature what it can
do.
That's what SR says happens (well, in a lose sense). When an object
is
moving things that are simultaneous for it (eg the position of its end
points) are not simultaneous in the observers frame. Thats why you
the
front end of the moving object is behind in time and the back end
ahead
..
its 'rotated' slightly in time. And that what makes it contract
A few days ago Uncle Ben asked me about the contraction of an
accelerating rod as measured in the frame where the rod started out at
rest. I responded that the rod would be measured to contract, but
that the contraction was an artifact of how we measure things.
http://groups.google.com/group/sci.physics.relativity/msg/44809c25d2a...
I was aware of the interpertation of it rotating in time, but I didn't
see how that could apply since all the measurements are made using the
same coordinate system. If you look at the clocks of the moving
system they will be out of sync compared to the stationary system.
That is what I have always considered to be the rotation of time,
relative simultanity. But if all the measurements are made in the
stationary system the moving clocks have nothing to do with it.
If the ends of the rod are at x=0 and x=1 at t=0 and the rod is
accelerated, both ends of the rod start accelerating at the same
instant as measured in the stationary system. If both ends are
accelerating at the same rate they should cover the same distance in
the same time, leaving the rod the same length.
In the observers frame .. but stretched in the frame of the rod. Look up
Born Rigidity
How can we get the
predicted contraction using just the stationary coordinate system?
See above
Looked up "Born Rigidity". "The defining property of Born rigidity is
locally constant distance in the co-moving frame for all points of the
body in question." So it is not working in the frame I asked about.
Born rigidity isn't a frame.

The definition includes, "in the co-moving frame". I asked the
question, "How can we get the predicted contraction using just the
stationary coordinate system?" If you use "the co-moving frame" you
are not answering the question asked.

But it is the property you gave of the I-beam.
Do some more reading on it. In particular accelerated motion of born-rigid
objects. That is what you are saying happens to the I-Beam which
accelerated but does not stretch.

Put a bit differently, have a rocket at x=0 and a second one at x=1.
Have them both accelerate at t=0. Without referring to another frame,
what would cause the rockets to be closer together after accelerating?
Who says they are closer together? Which circumstance are you talking
about? Is it with the I-Beam, where the I-beam stops the ships from moving
further apart (in their own frames) as they accelerate?

SR says that we would measure the space between the rockets to be
contracted. If you accelerate a rod one unit long along with the
rockets, but not attached to them, the rod will be measured to be
contracted. That rod is made up of atoms with spaces between them.
For that rod to contract as predicted the space between the atoms must
contract as well as the atoms themselves. Do you see the space
between the atoms as having different properties than the space
between the rockets?

Without the rockets being attached the changed distance in the moving
frame can be explained because the rockets did not take off at the
same time in that frame.
They were both initially at rest,

I wrote, "in the moving frame". The rockets were initially at rest in
the stationary frame. That would mean they were moving in the moving
frame.

so they did take off at the same time in
their frames at that time of launch

Again, read what I wrote, "in the moving frame". The rockets started
moving at the same time in the stationary frame. The LT tells us that
they started moving at different times when measured using moving
frame coordinates. If you don't believe me try plugging t=0 into the
LT and calculate t' for x=0 and x=1.

BTW, I mentioned that the contraction in SR was not considered to be
the same type of contraction as that described by LET.
A given rod moving relative to us may 'really' be either expanded or
contracted compared to out own rod, in LET. And we have no way of
knowing
what it is really doing in LET. But our measurements will show it is
contracted but to our rulers and clocks being distorted by their movement
through the ether, though we cannot tell how much.
LET uses the exact same math as SR so the predictions are the same. I
explained to someone last week how a clock accelerated in the
direction which causes it to move slower WRT the ether still is
measured to slow down despite the fact that it speeds up in the ether
frame. It is due to the sync of the clocks it is being compared to.
Yes .. but that does not disagree with what I said above.


The tone you used above was that LET makes silly predictions that can
be interperted in contradictory ways. I was just pointing out that
the predictions of SR and LET are identical. If you poke fun at the
predictions of LET you are also making fun of SR.



I should have
said it is not the same kind of contraction you would get by cooling
the rod. That would make the rod shorter in both coordinate systems.
Yes. An LET contraction is like that though .. a 'real' contraction of
the
rod and slowing of processes for everything moving in the ether frame ..
though we cannot tell what that frame is or by how much a rod has shrunk,
or
if two identical (but differently moving) rods are 'really' the same
length,
or which one is 'really' longer (in the 'real' sense of LET).- Hide
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The LET contraction is the same as the SR contraction.
It would be observed as the same, yes.

The only
difference is the explaination of why it is happening.
In SR, the contraction is due to the nature of spacetime itself ,regardless
of frame of reference

In LET, the contraction is due to rulers and clocks changing when they move
in an absolute ether that we cannot detect, and due to the possibly
differing absolute lengths. of course, in LET, the moving rod may be
absolutely longer than the one at rest in the observers frame, but the
distortions of the clocks and rulers means you'll measure it as shorter.

Whether we are talking SR or LET, the cold ruler will measure shorter
than a standard ruler in its rest frame. That is not the same as a
contracted measurement due to motion.

The
contraction due to cooling is different. It takes place while at rest
and all frames agree that the rod contracted.
The point is, in the aether frame, it is a real physical contraction, like
cooling is. But in all other frames we are mistaken about what we measure
due to clocks and rulers being wrong due to absolute motion. So our
measured (and effective) reality is not what is really reality in LET. For
some reason, some people think that is a simple concept :):)-

For some reason, some people choose to willfully ignore the facts which make LET a simple concept.


And all this continues to divert attention from the question I asked
you, "How can we get the predicted contraction using just the
stationary coordinate system?"

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