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# Relativity/Minkowsky diagram

Question
Good day sir,
i have problem to understand how work this applet
http://www.trell.org/div/minkowski.html
Can see that if you chose a <relative velocity as example 0.5 c)and write the coordinate of EVENT B and after press <calculate> ,the program give you the value of coordinate t' and d' in blu color.
You can see that in the blue coordinates the spaces between 1-2-3-4-5-6 is more than the spaces in the black coordinates.
Why there is this difference ?

Good question, Nello.

The distance between the points as you see them is not the "interval" between them.  What you see is the square root of the sum of the squares of the coordinate differences (I hope this concept is familiar to you).

That value is not important in relativity. It is normal that the result is different in the two coordinate systems.

What remains the same is rather the square root of the difference in the t-coordinate difference squared MINUS the d-coordinate difference squared. This is the so-called interval between the points and is the same before and after the transformation of coordinates.

For an obvious example. consider two events that lie on the light line. This may represent the start and end of a flash of light from one place to another. In units using c=1, the difference between the t-coordinates is equal to the difference in d-coordinates: d2 - d1 = t2 - t1, because c=1.  The interval between the start point and the end point is ZERO in all frames of reference.

This may seem mysterious, but you just have to study relativity more.

Ben

Relativity

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#### Uncle Ben

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I can answer questions regarding Einstein's Theory of Relativity, particularly in Special Relativity. I will not answer homework questions or mathematical problems that require special symbols.

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I have taught physics at the college level, undergraduate and graduate, for many years including Special Relativity. I have taught at Johns Hopkins, Case-Western, and MIT. I have also served as a staff member of the Commission on College Physics, which was supported by the National Science Foundation to recommend improvements in the curriculum of college physics departments in the US. I am also the author of a textbook titled Vector Calculus, which was used at MIT in the teaching of electromagnetic theory and relativity. My research interests were mainly in solid state physics, especially the properties of metals at low temperatures. I am listed in the publication known as American Men of Science.

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