In the Newtonian theory of relativity ,we measure the distance in two ways:
1- By using a meter scale.
2-By measuring the time taken by a massive particle moving with a constant velocity in a straight lines.
These two methods are equivalent provided we do not consider the time taken by the light ray to measure the distance.This type of the measurement of the distance has also been considered in the special theory of relativity besides the two methods mentioned above used in the theory of relativity.Here,we would like to point out that in the special relativity the measurement of distance by time taken by a massive particle moving with constant velocity in a straight line is quite different from the measurement of distance by the time taken by a light ray.Therefore, it would be necessary to be careful when using the two methods of measurements in a single system.
The measurements are the same as in Galilean system but the matter complicates when the same thing is measured by two different moving systems because their clocks are not simultaneously synchronised.
Dear A.wutke,
Our measurement is for study of a dynamical system therefore, we may reject the use of the measuring scale unless it necessary.In the Newtonian relativity then the constant velocity of massive particle in a straight line is suitable for the measurement.In the special relativity,there are to ways:either by the velocity of light ray or by the constant velocity of massive particle in straigt line but we should not mix the both types of measurements in a single dynamical system.Of course, it would be interesting to see the difference of the two types of the measurements when applied on a single dynamical system one by one.
Regards
In my opinion the relativistic Doppler effect is better to describe the wavelength shift of two events, caused by the relative motion of the source and the observer. We can calculate Doppler's wavelength shift (as a distance) if we have two relativistic distinguish events.
https://en.wikipedia.org/wiki/Relativistic_Doppler_effect
Dear Chanta
An event is determined when we define the measuring unit and hence,the relativity will dependent on the choice of the measuring unit.
Regards
Hi
Interesting question. I remember an old article related to the definition of intrinsic geometrical distances in general relativity:
Measurement of Distance in General Relativity
E. Newman and J. N. Goldberg
Phys. Rev. 114, 1391 – Published 15 June 1959
"An instrinsic geometrical definition of distance is presented in terms of the geodesic deviation of null rays. This definition is applied to the Schwarzschild solution and the homogeneous and isotropic cosmological solutions of the Einstein field equations. In the former case the distance is proportional to the radial coordinate of the standard metric and in the latter case it yields the usual cosmological distance. However, since the geodesic deviation is a scalar, the results are independent of the particular metric used. The relationship of this definition to observation is discussed and it is concluded that it agrees with the astronomical definition of luminosity distance."
Dear vasconcellos,
Thank you for your reply.I would like to explain my view about the measurement in the special theory of relativity as follows:
The use of measuring rod is not appropriate in the study of a dynamical system.The use clock and the knowledge of velocity and acceleration are sufficient to determine the distance.Hence,the definition of a constant velocity (i.e.the unit of velocity ) is more suitable in the study of the dynamical system.There no problem if we use the constant velosity as a unit of the measurement in the Newtonian relativity but,in the special relativity,there are two constant velocities.The constant velocity of a massive particle and the constant velosity of the light ray.My question is which one is more suitable or otherwise?
Regards
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