On 12/2/2013 1:14 PM, LizR wrote:
On 2 December 2013 20:14, meekerdb <meeke...@verizon.net <mailto:meeke...@verizon.net>> wrote:

    On 12/1/2013 7:35 PM, LizR wrote:
    On 2 December 2013 16:16, Richard Ruquist <yann...@gmail.com
    <mailto:yann...@gmail.com>> wrote:

        MOND is an alternative explanation that replaces Dark Matter by 
modifying gravity.

    Yes (hence the flippant remark about bolt on extras)

        Dark Matter results when gravity is not modified. (pure Newtonian)

    Or rather Einsteinian, I don't think Newtonian gravity predicts 
gravitational lensing?

    Sure it does, but only half as strong as GR.

Ah yes, that's right. I believe that's why the 1919 eclipse data is actually somewhat equivocal, despite catapulting Einstein to fame. (And 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???).

Mind you, I think my correction above is still pertinent - that is, it's still truer to say that "dark matter is what results when gravity is not modified (pure /Einsteinian/)".

Dark matter would be implied by the same observations even assuming Newtonian gravity. Just the amount would be different. I don't know if Fritz Zwicky even used relativistic calculations of rotation curves of galaxies to infer dark matter - it wouldn't have been necessary since the motions are not that fast.

Incidentally I met Zwicky at a party once and he regalled me with the story of how he and a NACA team had actually beaten the Russians into space by launching an artificial satellite *before* Sputnik. When I expressed surprise that I had never heard of this satellite, he explained that it was launched from a B-50 flying at 50kft over the equator using a two stage rocket. When the second stage reached it's apogee, it fired a shaped charge which sent a molten mass of metal into orbit around the Earth.


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