On Thursday, July 23, 2020 at 8:56:03 PM UTC-6, Alan Grayson wrote: > > > > On Thursday, July 23, 2020 at 11:59:59 AM UTC-6, Brent wrote: >> >> >> >> On 7/23/2020 4:41 AM, Lawrence Crowell wrote: >> >> On Thursday, July 23, 2020 at 5:56:32 AM UTC-5 [email protected] wrote: >> >>> >>> >>> On Saturday, July 18, 2020 at 6:31:23 AM UTC-6, Alan Grayson wrote: >>>> >>>> >>>> >>>> On Saturday, July 18, 2020 at 6:18:28 AM UTC-6, Lawrence Crowell wrote: >>>>> >>>>> The tortoise coordinates is found from the Schwarzschild metric >>>>> >>>>> ds^2 = (1 - 2m/r)dt^2 - (1 - 2m/r)^{-1}dr^2 - r^2dΩ^2 >>>>> >>>>> where for a signal leaving a point near the black hole with ds = 0 >>>>> (null path) and propagating radially out, dΩ = 0, we have dt = dr/(1 - >>>>> 2m/r) which then leads to >>>>> >>>>> T = t - t0 - 2m ln|r - 2m|. >>>>> >>>>> That is the tortoise coordinate. Please look this up to read further. >>>>> I can't spend beaucoup time going over this for weeks to come. >>>>> >>>>> LC >>>>> >>>> >>>> You don't have to. We're done. But you should IMO address Brent's >>>> objection, maybe on another thread. AG >>>> >>> >> I don't know what objection you're referring to. LC is just showing why >> it takes a distant observer forever to see an infalling object reach the >> event horizon of a black hole. >> >> Brent >> > > Your words: > > I wonder about the use of cicumlocutions like "from the perspective of an > outside observer". In special relativity it it is often said that a moving > object will looked shortened along the direction of motion. But as Terrell > pointed out that's not at all how they look. It is more accurate to say > that *measuring* a moving a object will show that it is shortened along > the direction of motion; the difference being that the measurement corrects > for the fact that you want the difference in arrival time of photons that > left the ends of the object at the same time (an ill defined concept), > instead of the image formed by photons that arrived at the same time. But > then I think, why not correct for the Lorentz contraction too in the > measurement and arrive at what we might call "the proper length". That's > just as "measured" as either of the other two. > > By the same reasoning, you're really saying the visual impression of a > distant observer is that infalling stuff appears to be on the surface of > the event horizon. Which is because it takes forever for photons to reach > him. But why should he be so naive. He knows what he's seeing is > arbitrarily far in his past; so what he should be said to "measure" or > "calculate" is that the stuff has already been annihilated at the > "singularity" in his reference frame. > > ----------------------------------------------------- > > I forget why LC brought up this particular coordinate system. He had some > point in response to a comment I made. I'll have to review my comments; > maybe that the gravitational field due to a BH, external to the event > horizon, has an objective reality. AG >
I just reviewed LC's comments. He was claiming that tortoise coordinates show the existence of the gravitational field due to a BH, external to it. He wasn't limiting his argument, which you apparently objected to, to how long a distant observer would have to view an infalling mass, to see it disappear. AG > > > >> >> >>> When it comes to GR, you're a genius; no question about it. I wouldn't >>> want to waste your valuable time. But consider this; the Schwartzschild >>> metric applies to NON-ROTATING masses. Do you really think a massive >>> contracting star which forms a BH will be non-rotating? Obviously, it will >>> be RAPIDLY rotating, like an ice skater who contracts her arms. Brent also >>> had some substantive questions about your model. But I see you prefer your >>> illusions than to address his objections. AG >>> >> >> The result is similar, but more complex. The same calculation can be done >> for the Kerr solution. It is just a lot more complicated mathematically. >> >> LC >> >> -- >> You received this message because you are subscribed to the Google Groups >> "Everything List" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to [email protected]. >> To view this discussion on the web visit >> https://groups.google.com/d/msgid/everything-list/5b3752f7-55da-4c90-bc8b-11e1b8f42344n%40googlegroups.com >> >> <https://groups.google.com/d/msgid/everything-list/5b3752f7-55da-4c90-bc8b-11e1b8f42344n%40googlegroups.com?utm_medium=email&utm_source=footer> >> . >> >> >> -- You received this message because you are subscribed to the Google Groups "Everything List" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/everything-list/28206371-de23-4dfd-9e2b-978ad5dbcec2o%40googlegroups.com.
