5 ms·

The linked article directly disagrees with this post (except the last paragraph, which itself disagrees with the rest of the post), however: > The fact that gr

The linked article directly disagrees with this post (except the last paragraph, which itself disagrees with the rest of the post), however: > The fact that gravitational damping is measured at all is a strong indication that the propagation speed of gravity is not infinite. If the calculational framework of general relativity is accepted, the damping can be used to calculate the speed, and the actual measurement confirms that the speed of gravity is equal to the speed of light to within 1%. (Measurements of at least one other binary pulsar system, PSR B1534+12, confirm this result, although so far with less precision.) This was always my problem with RobotRollCall on Reddit - no one could challenge anything she wrote lest they be downvoted into oblivion. Furthermore, she never took criticism very well, and would assert authoritative dominance over the topic of knowledge (how dare you disagree with me, I read research papers!). Her explanations were good, but they weren't ever very complete and while they were well written, they weren't always accurate.

prawn 13y ago
I think she pulled up stumps and left at some point over issues with how some of the community was responding to her? Something like that. Real shame because she inspired strong interest in so many who read her explanations.
- InclinedPlane 13y ago
  She probably just got tired of being treated the way highly visible women often are on the internet. This is not always visible to everyone else since there are private messages on reddit. It's possible things are better now, it's hard to say. I tried to perform an experiment on reddit a while ago by posting under a handle that was obviously feminine but I had to cancel the experiment because it didn't really work due to my posting style being too abnormal.
  - prawn 13y ago
    I never noticed gender come into it on the public side, at least. A good number of people wouldn't have even been aware she was female. (Think of the Groklaw thread the other day and many assuming PJ is male.) There was an abrasive way RRC responded to some that fired up discussions and I got the impression that this ultimately frustrated her into ending her participation. I've seen that abrasive style/response feedback loop develop with males just the same.
vehementi 13y ago
That... doesn't contradict anything.
- diminoten 13y ago
  > 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).
  - vehementi 13y ago
    This: >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.
    - diminoten 13y ago
      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.
      - vehementi 13y ago
        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.
pdonis 13y ago
The linked article directly disagrees with this post (except the last paragraph, which itself disagrees with the rest of the post) Actually, Baez's article disagrees with the last paragraph of RRC's post; in so far as it talks about what's in the rest of RRC's post, it basically agrees with it (the part at the beginning about the Wile E. Coyote stuff isn't really talked about in Baez' article, except in so far as it's supposed to illustrate that a static gravity field doesn't have to "propagate" at all). Baez' article, and the paper by Carlip that is referenced in it (and by RRC) basically say that measurements like the binary pulsar show that this statement from RRC's post is, strictly speaking, false: all the aberrations you might expect because of a finite speed of light end up canceling out, so gravity acts like it's instantaneous The cancellation is not exact; that's why binary pulsar systems can lose energy by emitting gravitational waves. But it's very close to being exact, closer than the analogous cancellations for electromagnetism; that's why we don't observe "aberration" in the direction of the gravitational force to the same extent that we do for the electromagnetic force.

prawn 13y ago

I think she pulled up stumps and left at some point over issues with how some of the community was responding to her? Something like that. Real shame because she inspired strong interest in so many who read her explanations.

InclinedPlane 13y ago
She probably just got tired of being treated the way highly visible women often are on the internet. This is not always visible to everyone else since there are private messages on reddit. It's possible things are better now, it's hard to say. I tried to perform an experiment on reddit a while ago by posting under a handle that was obviously feminine but I had to cancel the experiment because it didn't really work due to my posting style being too abnormal.
- prawn 13y ago
  I never noticed gender come into it on the public side, at least. A good number of people wouldn't have even been aware she was female. (Think of the Groklaw thread the other day and many assuming PJ is male.) There was an abrasive way RRC responded to some that fired up discussions and I got the impression that this ultimately frustrated her into ending her participation. I've seen that abrasive style/response feedback loop develop with males just the same.

vehementi 13y ago

That... doesn't contradict anything.

diminoten 13y ago
> 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).
- vehementi 13y ago
  This: >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.
  - diminoten 13y ago
    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.
    - vehementi 13y ago
      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.

pdonis 13y ago

The linked article directly disagrees with this post (except the last paragraph, which itself disagrees with the rest of the post) Actually, Baez's article disagrees with the last paragraph of RRC's post; in so far as it talks about what's in the rest of RRC's post, it basically agrees with it (the part at the beginning about the Wile E. Coyote stuff isn't really talked about in Baez' article, except in so far as it's supposed to illustrate that a static gravity field doesn't have to "propagate" at all). Baez' article, and the paper by Carlip that is referenced in it (and by RRC) basically say that measurements like the binary pulsar show that this statement from RRC's post is, strictly speaking, false: all the aberrations you might expect because of a finite speed of light end up canceling out, so gravity acts like it's instantaneous The cancellation is not exact; that's why binary pulsar systems can lose energy by emitting gravitational waves. But it's very close to being exact, closer than the analogous cancellations for electromagnetism; that's why we don't observe "aberration" in the direction of the gravitational force to the same extent that we do for the electromagnetic force.