> To the absolute limit of our ability to measure it — and our ability to measure it is really good, since we used electromagnets and lasers and other expensive science things — when an object is dropped, it begins falling instantaneously.
That's not true. Our ability to measure the "speed of gravity" gives us measurements that say "the speed of light":
> the actual measurement confirms that the speed of gravity is equal to the speed of light to within 1%.
I eliminated the cruft so it was more obvious. RobotRollCall's information is older than the linked article (that's from 1998).
>when an object is dropped, it begins falling instantaneously.
Is answering a different question than this:
>the actual measurement confirms that the speed of gravity is equal to the speed of light to within 1%.
It is true that things drop immediately when you let go of them. Because they're already in the gravitational field. It is not true that when I drop something, a gravity particle from the surface of the earth (say 1km away) comes up and gets my apple, and until that gravity particle reaches it, the apple magically is suspended in the air. RRC covered this in the post.
It is the changes in the gravitational field that propagate at the speed of light. So if the sun vanished, which it can't, we wouldn't be flung away for 8 minutes.
That's all true, but that's not what I quoted. RobotRollCall's comment said we can't measure the "speed" of gravity, but in the article linked, we do precisely that.
What? No - what you quoted is about measuring the delay between when I let go of something and when it starts to fall. That is what we've used lazers and rockets and microscopes to measure.
I get what is actually going on, what I'm saying is that RRC's comment does not go from A to B. It goes from A to A', then jumps ahead to B, without any reasoning why.
Or, as she puts it, "If you feel up to the challenging of following a lot of advanced mathematics, here's the best paper I know on the subject.".
What she writes is basically a long explanation of why the speed of light is not correct, right up until the end, where she hastily covers it up with what the actual science says.
What would be useful would be a dissection of the "best paper I know on the subject". The rest of it just says, "It's not the speed of light... actually yes it is. Don't look further unless you're smarter than I think you are."
You said the article disagrees with RRC's post, which it does not. It seems now you're just taking issue with the progression RRC made to get to the point? Or that you think she should have gone into the paper she cited? OK. But it doesn't make claims contrary to the OP. And the thing you quoted does not disagree with the other thing you quoted.
The part you quoted does disagree with the article, but not with the part you quoted: RRC said we can measure the delay, and it is 0. The article said we can derive the delay, and it is almost 0.
That aside, yes, RRC's comments are often lacking in one way or another. However, they're also solid attempts at explaining something ad hoc, a very valuable thing on Reddit.
"The net result is that the effect of propagation delay is almost exactly cancelled, and general relativity very nearly reproduces the newtonian result."
That's not true. Our ability to measure the "speed of gravity" gives us measurements that say "the speed of light":
> the actual measurement confirms that the speed of gravity is equal to the speed of light to within 1%.
I eliminated the cruft so it was more obvious. RobotRollCall's information is older than the linked article (that's from 1998).