Talk:Light-dragging effects

Expert needed: Mach vs. gtr (and competitors)

It would greatly improve this article if various more precise Mach principles were stated (it's terribly important to emphasize at every opportunity that there are many Mach principles, not just one Mach's principle; see the article by Bondi on the ArXiV for a list of about a dozen versions), and if the discussion made clear exactly which of the effects mentioned are even qualitatively realized by gtr. E.g. light bending in Kerr vacuum (and exterior field of other rotating objects, such as a disk) includes an angular momentum dependence, so this could be said to exhibit qualitatively "dragging" of light. It would be good to write and link to another article discussing quantitatively the rotation of a thin spherical shell in gtr. This could mention the case of counter-rotating cylinders, often taken as anti-Machian.

Even better, one could finish the job by discussing Machian effects (or absence of them) in some of the simpler competitors of gtr. By the time this work is finished, you'd have several fine articles. I could do it, but my hands are full with other matters, so invite anyone interested to have a go.---CH (talk) 05:23, 1 September 2005 (UTC)

Nope. This page was meant for SR people

The intention of the page was not to get into analysis of Mach's Principle and what it means, or make a "Mach vs GTR" page, but simply to list the situations in whch we might expect light-dragging to occur. Nice and simple and short and factual. If you want to set up a stub "Mach's Principle and GR" page that might be a very useful thing to have, but this ain't it. I think that perhaps your interest in MP is pulling you slightly off the page's intended topic.

This page wasn't meant to be aimed at GR people, it was meant to politely point out to those particular SR enthusiasts who still go around teaching that we "know" that it's experimentally proved that moving matter does NOT drag light (because it's supposedly "proved" that the speed of light is independent of the source), that they are wrong.

DeSitter and Brecher's double-star observations showed that lightspeed was not globally dictated by the motion of the source, their use of the word "independent" to mean "not (wholly) dependent on" was perhaps unfortunate.

Perhaps I could reword the page slightly to make its original intent more obvious, but this would involve saying explicitly that some claims made for SR are not true - I was trying to keep the controversy levels down by not actually coming out and saying that.

I know - what if I swap the two sections around and put the particulate-medium dragging effects first and the frame-dragging section afterwards, would that make it more clear that I was referring to the general existence of an effect, and not trying to write a page on general relativity? I'd hoped that the single sentence intro ("In physics ...") would have made it clear that I was trying to be as general as possible, but perhaps starting with the "Mach/GR" stuff threw you off.

I'll reorder. ErkDemon 00:28, 9 September 2005 (UTC), redited ErkDemon 22:15, 11 September 2005 (UTC)

Okay, sorted

Perhaps when I originally wrote this page I did get a little carried away and went into more detail about Machian arguments than I needed to, when all I really had to do was to point out that the effects existed under current theory and provide links. So I've stripped out the material that Chris objected to so much, and hopefully the page is now less objectionable and more focussed.

"Moving matter is expected to drag light in various situations, despite statements to the contrary." Examples and links. End. ErkDemon 23:04, 11 September 2005 (UTC)