[Nesti (Mark)]

Thanks for clarifying my Metric; much appreciated.

Originally Posted by sjastro

The worldline of a photon is a null geodesic irrespective of the topology.

Surely that can only be so from the reference frame of the photon?! Because from any other frame it must traverse all topology along its geodesic pathway, ie light getting bent as it moves along its geodesic within a gravitational field, true? (I'm assuming we don't have two convenient sets of rules out there for how a photon behaves...like in QM)

So, if the photon must traverse its geodesic path, then surely gravity waves must get affected also (assuming that there are many local gravitational fields), otherwise we could easily get a situation where a gravity wave arrives ahead of the photon...which just isn't possible.

The metric of the perturbed space doesn't change.

Again, are you talking purely from the photon's frame of reference?

That's because even though the wave is moving the "shape" of the wave remains the same...Unless of course if you consider space-time in front of the wave being flat and the metric assuming the perturbed space as the wave passes through.

I agree with that.

In the real world however it is impossible to measure a metric as it is a mathematical equation not a value.

The universe itself might as well be a mathematical equation. I do realise that the entire Metric is purely for our understanding, and that the universe itself just 'does it'.

Gravitational waves will hopefully be detected by the forces they exert.

Dare I say the word 'Apparent'...again.


Cheers
Mark