Einstein Relatively Easy

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In our previous article Minkowski spacetime and time dilation calculation, we have explained how to visualise the time dilation effect among two inertial referentials Ziga and Ranja  in constant velocity v relative to each other via the Minkowski space time diagram.


However, we did not really explain how to show the second inertial frame Ranja belonging to a second observer O'. How do we draw the ct' and x' axis relative to Ranja referential?

Each possible event that can happen in frame Ranja when the spatial coordinate x' equals zero, joined together, will form the ct' axis. So we just have to consider the point x'=0 : this point is moving along the x axis with a velocity v (as the frame Ranja is moving at this velocity)

We could state that if an object is travelling with a constant velocity v then that velocity will equal distance travelled divided by time taken and is given by


 But we could have found this equation directly using the Lorentz transformations:


 Similarly, if we want to find the equation of the x' axis, which is the line where ct'=0, we deduce from Lorentz transformation applied to ct' transformation:

The figure belows shows the lines ct = (v/c) x  and ct = (c/v) x, which are the equations of the x' and ct' axes of a frame R' moving with speed v relative to S.

The angles  between ct' and ct and x' and x are equal and are defined as tan θ = v/c.





"The essence of my theory is precisely that no independent properties are attributed to space on its own. It can be put jokingly this way. If I allow all things to vanish from the world, then following Newton, the Galilean inertial space remains; following my interpretation, however, nothing remains.."
Letter from A.Einstein to Karl Schwarzschild - Berlin, 9 January 1916

"Quantum mechanics is certainly imposing. But an inner voice tells me that it is not yet the real thing. The theory says a lot, but does not really bring us any closer to the secret of the 'old one'. I, at any rate, am convinced that He is not playing at dice."
Einstein to Max Born, letter 52, 4th december 1926

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