- #1
binbagsss
- 1,265
- 11
Homework Statement
The question is to find ##A## and ##B## such that the specified curve (we are given a certain parameterisation , see below) is a timelike geodesic , where we have ##|s| < 1 ##
I am just stuck on the last bit really.
So since the geodesic is affinely paramterised ##dL/ds=0## and so I can set ##L=constant##, ##L ## the Lagrangian of a freely-falling particle.
Let ## L ## be this constant.
And with the specified metric and parameterised curve, which are all given to us, this gives:
##B^2(\frac{A^2-s^2}{1-s^2}) = L ##
This is all fine.
MY QUESTION IS...
2. Homework Equations
see above
The Attempt at a Solution
MY QUESTION IS...
From this I conclude that (since a null curve is given by ##L=0##, a space-like by ## L < 0 ## and a time-like by ##L>0##, since the metric signature in the question is ( +, - ) ) that we require ##|A|<1## since we have ##|s| < 1 ## , and ##B\neq 0 ##, however the solution gives:
we need ##A=\pm 1 ## and ##B\neq 0 ##.
I don't understand where ##A=\pm 1 ## comes from, I thought we just need it such that ##L > 0## and ##A=\pm 1 ## does this
Many thanks in advance