# In a nutshell: getting some perspective on invariance

1. Nov 17, 2012

### DrClapeyron

My understanding of the S&G relativity is that one theory deals with reference frames at speeds near the speed of light while the other deals with reference frames that are approaching the speed of light. There are variances in observation between the two reference frames arising from their relative states.

In order to explain the variance, it is necessary to find a coordinate system in which there is no variance - a variance becomes invariance. In order to find such a coordinate system, the coordinate system has to be based in units of light time, and a transformation from the Newtonian world of Cartesian coordinates to the Relativistic world of light-time coordinates has to take place.

To switch coordinate systems, a Lorentz transformation is used to create a coordinate system in which coordinates are described by light-time (i.e., a light meter, a light second). Now, as an observer approaches the speed of light she is essentially remaining in an indefinite state of acceleration - though a diminishing one at that.

For such an observer - in a continuous noninertial reference frame - she is like an asymptote. Can't assymptotes be explained without having to use transformations and tensors? Or is there some kind of irrationality involved like expressing 1/3 as an imperfect .333?

2. Nov 17, 2012

### robphy

Special and General Relativity are actually about all frames of reference.
Usually, one focuses on inertial reference frames in Special Relativity.. but one doesn't have to... although it is more difficult.