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[Phys-L] variations on spacetime interval



Hi Folks --

Suppose we write
s^2 = t^2 - x^2 - y^2 - z^2

Some authorities say s^2 should be called "the interval".
Other authorities say s itself should be called "the interval".

Does anybody have a good reason why we should prefer one over the
other?

Considerations include:
-- s (not s^2) corresponds more closely to our prosaic non-relativistic
notion of "time interval"
-- s^2 (not s) is better behaved for most relativistic purposes, since
s^2 will be negative for a spacelike interval, and I would prefer to
deal with a negative s^2 than an imaginary s.

Neither of those considerations seems particularly stronger than the
other, so they pretty much cancel each other out, leaving me as
uncertain as before.

======

Would it help to call s^2 the squinterval (as in squared interval)?
Giving it a one-word name helps me to focus attention on s^2 which
is what I want.

Also coining a new name allows me to duck the question of what the
old name means.
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