Schmelzer
Valued Senior Member
And you think this helps you to avoid to answer the questions?
1.) Given that $\eta_{mn}$ is a trivial vacuum solution of GR, do you agree that the metric computed above from this using the coordinate transformation $x^m \to x^m + f^m(x,t)$ is also a vacuum solution of GR?
2.) Do you agree that above have curvature tensor 0?
3.) Do you agree that the $h_{mn}(x,t)$ computed above look (approximately) like waves, once the $f^m(x,t)$ are solutions of the wave equation $\square f^m(x,t)=0$, thus, like gravitational waves?
4.) Do you agree that these four types of gravitational waves are the four types of waves which, according to the Living Review article, are not present in GR?
All these solutions obtained in this way are valid vacuum solutions of the GR equations, as valid as $\eta_{mn}$ itself. They are indistinguishable from the vacuum by observation? Ok, big deal. They are, anyway, solutions of the equations. Which is what matters.
And this is the whole problem of your argument: They are all legal and legitimate solutions of the Einstein equations. Even if they have longitudinal components. They are not forbidden.
I have to admit that I have not checked if the TT gauge is a global one. I would guess it is, but I'm not sure, and I'm too lazy to check. If not, then, indeed, it could be possible that for such a global solution there will be always, somewhere, a place where it has some longitudinal component. Would this matter? Not. Because even without the TT gauge the solution would be a valid GR solution.
1.) Given that $\eta_{mn}$ is a trivial vacuum solution of GR, do you agree that the metric computed above from this using the coordinate transformation $x^m \to x^m + f^m(x,t)$ is also a vacuum solution of GR?
2.) Do you agree that above have curvature tensor 0?
3.) Do you agree that the $h_{mn}(x,t)$ computed above look (approximately) like waves, once the $f^m(x,t)$ are solutions of the wave equation $\square f^m(x,t)=0$, thus, like gravitational waves?
4.) Do you agree that these four types of gravitational waves are the four types of waves which, according to the Living Review article, are not present in GR?
All these solutions obtained in this way are valid vacuum solutions of the GR equations, as valid as $\eta_{mn}$ itself. They are indistinguishable from the vacuum by observation? Ok, big deal. They are, anyway, solutions of the equations. Which is what matters.
And this is the whole problem of your argument: They are all legal and legitimate solutions of the Einstein equations. Even if they have longitudinal components. They are not forbidden.
I have to admit that I have not checked if the TT gauge is a global one. I would guess it is, but I'm not sure, and I'm too lazy to check. If not, then, indeed, it could be possible that for such a global solution there will be always, somewhere, a place where it has some longitudinal component. Would this matter? Not. Because even without the TT gauge the solution would be a valid GR solution.