Circle and Ellipse


This is how Einstein's Lorentz boost works. If we label the horizontal and vertical axes as the longitudinal and time-like axes, the circle becomes an ellipse in a different Lorentz frame.

If you are not convinced, use Dirac's light-cone variables. According to special relativity,

It is matter of simple algebra to write this expression as

If the variable (t + z) becomes expanded, (t - z) must be contracted.

When I include this circle/ellipse picture, I am talking about Einstein, and also about Paul A. M. Dirac.