- #1
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I understand gravitational waves as ripples in spacetime. As PeterDonis said in an earlier post,
" The 4-d spacetime geometry does not have to "propagate" anything; it just is."
On the other hand, this is block-universe speak. In this language, verbs that imply change are forbidden. We might just as well say that radiation is present within the light cone of a supernova. In this language light does not propagate either.
When we detect gravitational waves coming from some event, we can say that our wordline intersects with a region of spacetime that contains ripples which are there because of some extreme event in another point of spacetime (a bit like experiencing bumps on the road).
Alternatively, we can express ourselves in a more natural way and just say that there is some passing wave that makes *space* (not spacetime) contract and expand for a few moments and then passes. Is this an acceptable way of expressing it?
I guess the problem of this way of talking is that prompts the question "a wave of what?". Which puts me in a substantivalist frame of mind...
" The 4-d spacetime geometry does not have to "propagate" anything; it just is."
On the other hand, this is block-universe speak. In this language, verbs that imply change are forbidden. We might just as well say that radiation is present within the light cone of a supernova. In this language light does not propagate either.
When we detect gravitational waves coming from some event, we can say that our wordline intersects with a region of spacetime that contains ripples which are there because of some extreme event in another point of spacetime (a bit like experiencing bumps on the road).
Alternatively, we can express ourselves in a more natural way and just say that there is some passing wave that makes *space* (not spacetime) contract and expand for a few moments and then passes. Is this an acceptable way of expressing it?
I guess the problem of this way of talking is that prompts the question "a wave of what?". Which puts me in a substantivalist frame of mind...