I put forward a view, on another thread, involving the uniform
acceleration of a rod of length d, to a constant velocity, v, in the
direction of its length, alongside two stationary observers, a
distance d apart, by applying an identical acceleration to every
part of the rod, in order to preserve the space-like length of the rod,
relative to the observers, which would not, then, immediately appear
to be foreshortened. This is because both observers retain identical
relationships to their respective ends of the rod. An argument against
this was put forward to the effect that the rod did not appear to be
foreshortened because this manner of acceleration had stretched the
rod so that it really was foreshortened and only appeared not to be.

If the rod is replaced by two separate posts, a distance d apart,
identically accelerated in the same manner as the ends of the rod, the
same argument would suggest that the distance between the posts had
been stretched in the same way.

With regard to this, one may ask, how are the posts to be accelerated
in a manner that would avoid stretching? According to the argument, it
would have to involve non-identical acceleration of the posts. This,
however,
creates a problem from the viewpoint of an observer accelerated with one
of the posts. Any difference in the acceleration of the posts will be
detected
by the moving observer, and will produce a change in their distance apart
in
the moving frame. But if identical acceleration causes stretching, and
non-identical
acceleration causes changes in the moving frame, and no kind of
acceleration will do, it appears that creating an inertial frame,
consistent
with its original dimensions, to examine SR effects, becomes impossible.
This, of course, cannot be accepted.

The form of accelerated frame that is identical to an inertial frame is a
freely falling frame. This is a perfectly accelerated frame, in that
acceleration
is uniformly applied to every part of the contents of the frame. A freely
falling
frame can be seen as accelerated relative to another freely falling frame
at a
slightly different elevation in a gravitational field. It can, therefore,
be called
'accelerated'.

Thus, in the above example, it would appear that an identical acceleration
of the posts is necessary to preserve their distance apart in the view of
the
moving observer, and an inertial frame, with original dimensions, cannot be
established without this. It thus appears that this will establish an
inertial frame
at velocity, v, which will not display a foreshortened space-like
separation to
the two stationary observers. This does not overthrow SR, however, because
travelling photons will generate a foreshortening effect. The 'stretching'
argument, however, does not appear to me to be a convincing
way out of the problem.

Alen

"alen" wrote in message news:01c37df1$3f454340$167ea6cb@default...
I put forward a view, on another thread, involving the uniform
acceleration of a rod of length d, ...

My bigger brother would be able to answer this one
he will be along soon.

Martin Hogbin

"Martin Hogbin" wrote in message ...

"alen" wrote in message news:01c37df1$3f454340$167ea6cb@default...
I put forward a view, on another thread, involving the uniform
acceleration of a rod of length d, ...

My bigger brother would be able to answer this one
he will be along soon.

:-))

Dirk Vdm

"alen" wrote in message news:01c37df1$3f454340$167ea6cb@default...

[snip]

Your error is in assuming that the accelerations of two spatially
separated objects can the identical both frames, when, in fact, they
can only be indentical in one frame.

Paul Cardinale

The great accelerator Cern has proven objects get shorter in the
direction they are going(noticably close to "C") I have a theory that
space contracts in front of an object going close to "C". That means a
space ship going at 94% 0f "C" to a star that is 25 LY away will get
there in 25 years. Bert

Dear alen:

"alen" wrote in message
news:01c37df1$3f454340$167ea6cb@default...
I put forward a view, on another thread, involving the uniform
acceleration of a rod of length d, to a constant velocity, v, in the
direction of its length, alongside two stationary observers, a
distance d apart, by applying an identical acceleration to every
part of the rod, in order to preserve the space-like length of the rod,
relative to the observers, which would not, then, immediately appear
to be foreshortened.

The problem is, you need no constraints on accelerating the rod, if it is
observed to be at constant velocity by the two observers.

"Length contraction" is not a compression problem, but a problem in
perspective. If you look out your window, and look between your thumb and
finger, you can usually find some really large object which can be viewed
in its entirety through the space found in your hand.

Length contraction is similar, in that distances in space (and time, for
time dilation) are a function of the differences in *velocity* (as opposed
to *distance* in my simile) between the observer and the observed.

David A. Smith

Paul Cardinale wrote:

Your error is in assuming that the accelerations of two spatially
separated objects can the identical both frames, when, in fact, they
can only be indentical in one frame.

If they are identical in one frame, can you describe which one is in some
way 'preferred' in the other frame?

I can see that the posts would not be identical in the view of either of
the
stationary observers alone. If they are viewed by only one observer, a
photon must travel to him from the other post, which makes the other post
different. But I don't see that they would be different in the views of
their
respective observers. That is, there appears to be no difference between
them in a space-like sense?

Alen

G=EMC^2 Glazier wrote:

The great accelerator Cern has proven objects get shorter in the
direction they are going(noticably close to "C") I have a theory that
space contracts in front of an object going close to "C".

I am not calling into question the existence of foreshortening. The
question is, is it 'space-like'? That is, is a frame moving at velocity,
v, foreshortened, in only one way, from minus infinity to plus infinity,
in an instantaneous, space-like manner, rather than due to photon
travel?

Alen

(formerly) wrote:

"Length contraction" is not a compression problem, but a problem in
perspective. If you look out your window, and look between your thumb
and
finger, you can usually find some really large object which can be viewed
in its entirety through the space found in your hand.

Length contraction is similar, in that distances in space (and time, for
time dilation) are a function of the differences in *velocity* (as
opposed
to *distance* in my simile) between the observer and the observed.

The perspective idea is quite good, but not without problems. You have
to see velocity as the equivalent of 'distance', which is not easy. Also,
it must not have the properties of distance. That is, a foreshortened
object can collide with an object in the stationary frame, which is not
possible in the case of perspective due to distance.

Alen

Alen Going at "C" and going into the event horizon of a BH will change
the shape of the object. This helps prove Einstein's equivalent
principle. Light speed and the event horizon are two sides to the same
coin. Bert