Re: If


"Spoonfed" <jonathan.doolin@xxxxxxxxxxxxxxxxxxxxxx> wrote in message
news:1117656174.831113.198080@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
| *** rD wrote:
|
| > > > Thank you but I don't subscribe to the view that simple
observational
| > > > limitations and mathematical perspective are of any interest but
academic
| > > > and I am more interested in the *actual* contraction and dilation of
matter
| > > > under acceleration, deceleration, velocity near c and gravitational
| > > > variation.
|
| ====================
| > "Spoonfed" <jonathan.doolin@xxxxxxxxxxxxxxxxxxxxxx> wrote in message
| > news:1117602139.784098.127510@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
| > |
| > | > | All right. There is no actual contraction and dilation of matter
at
| > | > | velocity near c.
| >
| > I did not pick this up on the previous reads but are you sure and for
what
| > reasons ?
| >
| >
|
| I think I may have misunderstood what you meant by "actual."
|
| By actual length contraction, you meant something like "What fits in a
| box simultaneously in the observer's frame" and I took it to mean "What
| feels uncomfortable and squished to the object itself."

My definition of actual would be something that an experimenters who were as
close as practical to an event under observation would measure as best they
could taking into consideration any effects that they should be aware of.
I'm a bit uncertain of frames as they tend to go round made up pictures in
my mind, mainly because they usually fail to adequately define the
environment they are defining and boxes can change in size due to humidity
{:-)

snip
|
| The observational questions you were wanting me to avoid were
| superluminal motion and other doppler related effects.
|

Not at all it was just heavy SR explanations that failed to explain {:-)


| This is the sort of thing where, though the moving object CAN fit in a
| small box in our reference frame, we don't observe it to have fit in
| the box because doppler effects cause the object to appear greatly
| elongated.

Doppler or observational transforms. Yes that that's the type I see as
academic

|
| We can nearly eliminate this from our observations by thinking of our
| observer as a camera, and restricting our field of view to a small
| region as shown here:
|
| http://www.spoonfedrelativity.com/files/ninephotons.swf (Start the
| demo and click "show filmed region")
|
| In this case, the observer (camera) will see the actual length
| contraction, and I am changing my meaning of actual leangth here, to
| mean what the observer can fit in a box.

Carefull with the boxes as they can be contracted as well.

|
| > There is actual contraction for accelerated bodies,
| > | > | which is very clear from watching people's faces under hi G. Also
| > | > | there is an actual time dilation of an object in a gravitational
| > field.
| > | > | The clock on top goes faster than the clock on the bottom, and on
an
| > | > | accelerated body,
| > | >
| > | > Not so sure of this last explain why the clock in front going at the
| > same
| > | > velocity as the one in front should show a different rate ?
| > | >
| > | > the clock in front goes faster than the clock in back.
| > | > |
| >
| > Due to compression\contraction\velocity state at rear being higher than
at
| > front due to finite propagation of thrust\velocity through the rod ?
| >
|
| Since the length is changes as the rod accelerates, the front and back
| cannot be going at the same speed.

Initials yes, but as the rod accommodates its length to the force of
acceleration and if this is constant the force at the front is the same as
at the rear although it may not be the same quantum of force as the force is
being propagated up the rod at up to c.

|I think you might be able to define
| the length contraction at the front and the back of the rod and perhaps
| they are different,

Only initially.

|but we are only concerned with the length
| contraction between the two clocks--

Why.

it would be a good approximation to
| use the velocity of the center of the rod...

After the initial contraction period the velocity at the front is the same
as the rear.

|
| > | > --
| > | > *** rD Vacuum Energy = 4 pi duration+length ^3 perhaps
| > | > http://home.freeuk.com/paulps/
| > | > Maybe updates. The spuds, beans and onions are coming up nicely.
Ooh
| > | > ah.{:-)
| > |
| > | If a solid object is accelerated, the internal forces (chemical
| > | bonding, nuclear bonding, etc.) will cause the object to maintain its
| > | shape, as long as the acceleration forces do not overpower the
internal
| > | forces.
| >
| > I disagree with that as it assumes an absolute rigid structure. Their is
| > always some effect as no structure is absolutely rigid. So a structure
is
| > *always* modified by acceleration or deceleration.?
| >
|
| All I meant to assume was that the structure does not break because of
| the acceleration. For instance, if someone tried to push a
| space-shuttle with a toothpick the structures would probably break.
| However, if you push softly enough, you WOULD be able to accelerate the
| space shuttle by pushing it with a toothpick.
|
| > |
| > | If it maintains it's shape in its own reference frame, then as it
| > | accelerates it will appear to contract (or as it decelerates, it will
| > | appear to uncontract) in any inertial frame.
| >
| > This contraction and
| > | decontraction occurs over a period of time so it has its own velocity
| > | which can be added to or subtracted from the velocity of whatever
| > | portion of the object is receiving the force of acceleration.
| >
| > Yes, the thrust\velocity effect can propagate through the object upto c.
?
|
| Up to c, yes. But that does not mean that we have to stop
| accelerating. It means we should switch to thinking of rapidity
| v/sqrt(1-(v/c)^2) (which is proportional to momentum, p) instead of
| velocity, which is proportional to p/(p^2+1). The rapidity of an
| object can continue to increase towards infinity, though the velocity
| is limited to the speed of light.
|

Hmm... I have reservations about this but need to think about it


| >
| > |
| > | Thus the front and back of the object are moving at different
| > | velocities, and thus the clocks are going at different speeds.
| > |

No I can only agree with that initially. The rod may be vibrating along its
length due to oscillations in the thrust input but this evens out the
velocity as far as the front and the rear of the rod are concerned. You can
only say that the rods velocity increases at the rear first.


| >
| > Good explanation, I hadn't thought of that, as the acceleration takes a
| > finite time to arrive at the front the back is moving faster than the
front
| > under acceleration assuming the acceleration is being applied at the
back.
| > Nice one {:-). This would also apply to deceleration in that the front
would
| > be moving slower than the back assuming the deceleration was being
applied
| > at the front.
|
| Originally, I thought as you did that the bottom and top of the
| structure should be moving at the same speed. So when I programmed the
| simulation I just used the velocity of the bottom of the structure.
| Then it produced this demonstration...
|
| http://www.spoonfedrelativity.com/files/myGravity-p-change-constant.swf


Haven't had a look yet but will come back to it latter perhaps.

|
| Worse, I had it programmed so that the dots would disappear if they got
| above the top or below the bottom of the platform--so they simply
| disappeared instead of rising above the platform top--It took me a
| while to figure out what was going on, that I needed to include the
| change in length as part of the velocity of the top of the platform!
|
| > This would apply only during the period it took for the rod to
| > stabilise in its contracted\decontracted condition due to constant
| > acceleration or deceleration. To make the change in this effect occur
over a
| > longer period the acceleration rate would also have to be accelerating
or
| > v.v..
| >
|
| As long as it keeps accelerating there is always a force coming up from
| the bottom of the structure to the top... as long as there are more
| phonons coming up the structure, the top and bottome will always be
| moving at different rates. It doesn't require a change in
| acceleration.
|

Disagree as long as the phonons are of the same strength and constant then
the velocity at the front of the rod will be, on average the same.


| >
| > | Only an accelerated observer on the object would say that the front
and
| > | back were moving at the same velocity. They would not observe the
| > | change in length contraction over time,
| >
| > Interesting question that raises, could you observer the contraction of
a
| > rod if you were sitting in the middle of it.
|
| That is my eventual goal to predict what sort of contraction would be
| seen by such an observer. The demo I've made is as yet incomplete,
| because the events happen at a constant rate according to the top or
| bottom of the structure, but that constant rate should be affected by
| time dilation when observed from outside. Also, we could set up two
| versions of the problem, one where (A) the force of acceleration came
| from a rocket on the platform, and one where (B) the force comes from
| the frame of reference of the outside observer. I've been running into
| trouble assuming (B), but perhaps assuming (A) will give me a usable
| solution. (This might be exactly what I needed for my writer's block
| :)
|
| > How about mirrors at front and back you shining coherent light to the
front
| > and back. This rod is inside a spaceship just to clarify the local
| > environment. You would notice a change in phase between the back and
front
| > as you accelerated from zero but this change in phase shift would
stabilise
| > as the rods contraction became stabilised unless your rate of
acceleration
| > was increasing.
|
| I think of a constant acceleration being a series of pulses. For
| instance a rocket appears to be a continuous stream of gas, but is
| actually individual explosions of very tiny atoms--each explosion can
| be considered to be an acceleration event, which sends energy upward in
| a teeny compression wave called (if I might steal a term from solid
| state phyisics and bastardize it for my own uses) a phonon, which moves
| toward the top of the ship.
|
| So it is not the change in acceleration which produces the difference
| in velocity between the top and bottom of the structure, but the
| production of a phonon which has accelerated the lower structure but
| has not yet accelerated the upper structure. As long as these are
| flowing, the bottom of the structure will be moving at a different
| speed from the top.

No, if the flow is constant the velocity at front will be the same as at the
back, on average.

|
| > So the rod would be shorter from the middle to the back than
| > from the middle to the front under continuos constant acceleration ? and
the
| > observer in the middle should be able to measure it as an actual fact. ?
Its
| > even more interesting under continues accelerating acceleration.
| >
| >
| > but they would see that the
| > | upper clock was going faster than the lower clock.
| > |
|
| You have question marks and I also have question marks. It is clear
| from the demo as-is that the wavelength of the light gets shorter
| toward the bottom, and the distance between falling objects becomes
| longer toward the bottom. Of course, a person standing on the platform
| would agree and outside observer (traffic cop) would also agree.
|
| Also, any uniform distortion in the structure would also affect any
| physical devices used to measure the structure (assuming that the
| structure and measuring devices had the same tensile strength.)
|
| The bottom has sped up toward the center since the light left. The top
| has sped up away from the center since the light left, so the bottom is
| closer than it appears, and the top is further than it appears. But if
| the engines are at the bottom, then more phonons have passed through
| the bottom than the top. For me, right now, there seem too many
| variables to get my mind around. I'll try to focus on what I need for
| the next demo.
|

--
rD *** E-field = Electric field, M-field =Magnetic field, two unbound
field effects
http://home.freeuk.com/paulps/
Maybe updates. The spuds, beans and onions are coming up nicely. Ooh
ah.{:-)


.

Quantcast