On 5 December 2013 06:58, John Clark <johnkcl...@gmail.com> wrote:

> On Mon, Dec 2, 2013 at 4:14 PM, LizR <lizj...@gmail.com> wrote:
>> > the 1919 eclipse data is actually somewhat equivocal, despite
>> catapulting Einstein to fame.
> Back then the measurement was made right at the limit of what was possible
> with 1919 technology, since then it has been repeated many times with
> vastly greater precision and Einstein has always passed the test with
> flying colors.

That's right, yes. Indeed the most accurate measurement ever made is, I
believe, a test of GR involving gravity waves from a binary neutron star.
My point was that the eclipse result wasn't - apparently - quite as cut and
dried as it was presented, but the person who made it (was that Eddington?)
was keen to show Einstein correct.

>> > someone predicted black holes way before Einstein, too, on the basis of
>> Newtonian gravity and the measurement of c - although without realising the
>> full implications ... Mitchell???).
> The earliest reference I can find is 1783 by John Michell, he  called them
> "dark stars", however it had very different properties from  a modern Black
> Hole. If I was far from one of Michell's Newtonian dark stars I could not
> see it, but unlike a real Black Hole, I could obtain a picture of it and
> print it in the newspaper, I'd just have to get closer in a powerful
> spaceship. I could even land on the classical dark star, get a sample of it
> and then return it to Earth, that sort of thing would be impossible with a
> real Einsteinian Black Hole.

That's the one. It was used in a story by Brian Aldiss, I guess before
black holes became widely known about in SF circles (which was probably
thanks to Larry Niven). Of course one could only "land" on it if one could
withstand the gravity, and only take off if one could travel faster than
light - but although those would have been ridiculous goals in Newtonian
theory, they weren't considered physically impossible.

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