“Time is related to the space coordinates, but they are not equivalent. Pythagoras’s theorem treats all coordinates on an equal footing (see Euclidean space for more details). We can exchange two space coordinates without changing the length, but we can not simply exchange a space coordinate with time: they are fundamentally different.

It is an entirely different thing for two events to be separated in space and to be separated in time. Minkowski proposed that the formula for distance needed a change. He found that the correct formula was actually quite simple, differing only by a sign from Pythagoras’s theorem:

Where c is a constant and t is the time coordinate.[Note 2] Multiplication by c, which has the dimensions L T −1, converts the time to units of length and this constant has the same value as the speed of light.”

My question is: where does the negative sign come from ?”

why negative

Link: https://www.scienceforums.net/to

In this article of Wikipedia, about spacetime interval, from which I post some extract here below, it is said (in bold the part concerning my question): “After Einstein derived special relativity formally from the (at first sight counter-intuitive) assumption that the speed of light is the same t.... Read more