Vera Rubin has died. Age 88

[BaalChatzaf]

Vera Rubin a first tier astronomer  verified a hypothesis made by Fritz Zwicky back in the 1930's that the stars in out portions of galaxies do not move in a purely Keplerian manner.   Zwicky postulated that there was non-visible matter that made the stars in t he outer portion of galaxies  move faster than they "should" have under purely Newtonian gravitation.  Vera Rubin corroborated Zwicky's finding  by computing the motion curves for several galaxies and sure enough they do not move in a Keplerian manner.  It was as though t here was a rigid disk to which which the stars were attached, somewhat like a merry-go-round.  The rigid material is hypothetical "dark matter"  whose composition we do not know,  but which is hypothesized to interact  gravitationally with ordinary matter. 

Zwicky's hypothesis did not catch on at the time he made it for a number of reasons.  One,, in the thirties we did not have all the powerful telescopes we now have.  And second Zwicky was not a charming fellow.  He was irascible and ill tempered and many workers in the astronomy field did not particularly like him.  His lack of charm and very blunt approach did not convince others.  But Rubin's finding  finally convinced the astronomy and cosmological community  that Zwicky was onto something.

Please see:  https://en.wikipedia.org/wiki/Vera_Rubin  and https://en.wikipedia.org/wiki/Fritz_Zwicky

Also see:  https://en.wikipedia.org/wiki/Dark_matter

 

[Brant Gaede]

Does gravity even exist?

--Brant

[BaalChatzaf]

6 hours ago, Brant Gaede said:

Does gravity even exist?

--Brant

That is a damned good question.  Gravity, in Einstein's theory is not a force, but a manifestation of the curvature of the space-time manifold.  In Newtons formulation,  which we know is not quite correct, it is a force which obeys somewhat similar rules to electromagnetic force  except that gravity sucks.;  It only attracts.  But according to the findings made back in the 1990's  there is some kind of an accelerating expansion of spacetime itself which is akin to repulsion. It turns out that Einstein's blunder of adding an antigravitational tensor to has field equations  to  force spacetime not to expand  was not a total mistake.  When Einstein found out from Hubble  that the cosmos is indeed expanding he kicked himself.  He added that expansion tensor to offset gravitation because  he believed the cosmos  was globally static.  Well,  his fudge factor turned out to be useful after all.  If it has the right value it accounts for the recently observed accelerated expansion. So even when Einstein was wrong, he was right.  What a lucky guy!

By the way this global accelerated expansion is not the  gravitation of so-called dark matter that Zwicky postulated and Rubin confirmed. 

Bottom line,  it may turn out the our most favorite and beloved gravitational theories  (essentially General Relativity)  may not be quite right. No not only was Newton off a bit,  so was Einstein.  That is science for you.  There does not seem to be a sure thing theory that explains  Everything.