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Einstein, again

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IamSmooth

Mon Nov 16 2009, 08:08PM

Registered Member #190 Joined: Fri Feb 17 2006, 12:00AM
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It has been awhile since someone has touched on the subject. I have read about the perihelion of Mercury and how the general theory of relativity predicted this motion. I believe it is the result of the Sun's gravitational pull affecting the curvature of spacetime. Is there any reference that goes deeper than this "blanket statement", and derives the precession based on the curvature?

Edit: I may have found something which I will start to read.

Dr. Slack

Mon Nov 16 2009, 09:07PM

Registered Member #72 Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659

You could try a famous free collaborative on-line encyclopedia. "Advance of Mercury's perihelion" is quite short, but "Kepler problem in general relativity" has what looks like a derivation (I'm not qualified to say whether it's good or not) of the precession of Mercury which goes on for pages.

That's the thing about wikipedia, it's usually pretty poor for engineering articles (we engineers are too busy doing stuff to post much), but the theory-heavy sciences are well represented (there are far too many students and post-grads sitting around at 2am with a computer and nothing else to do).

Mon Nov 16 2009, 11:14PM

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A cool general relativity thing is accurate clocks. When comparing accurate clocks they have to take into account the elevation difference between the clocks. Even if they are in the same building but on different floors, which I think is pretty cool.

Nicko

Tue Nov 17 2009, 06:33AM

Registered Member #1334 Joined: Tue Feb 19 2008, 04:37PM
Location: Nr. London, UK
Posts: 615

dugg wrote ...

A cool general relativity thing is accurate clocks. When comparing accurate clocks they have to take into account the elevation difference between the clocks. Even if they are in the same building but on different floors, which I think is pretty cool.

We think we're odd - however, there is a group of enthusiasts called "Time Nuts" who build networks of some of the most accurate clocks in the world - 1uS per year or better...

Tom van Baak (

) is one of those - in 2005 he took his kids on a practical demonstration of Einstein's general theory of relativity - see

- home page for this experiment is at

He also has the world's most accurate wrist watch

Dr. Slack

Tue Nov 17 2009, 08:07AM

Registered Member #72 Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659

Tom van Baak summed up his road trip with "that's the best extra 22nS I've ever spent with the kids!"

Dennis Rogers

Tue Nov 17 2009, 11:09PM

Registered Member #1837 Joined: Tue Dec 02 2008, 02:20PM
Location: NYC
Posts: 65

General Relativity can be very involved, and the Maths get intense. The perihelion of Mercury was a great experiment for GR, but understand the combination of gravitational red shift, doppler effect of measurement and time dilation/length contraction. Everything in a defined orbit is on a constantly changing course, gravitational effects approach limits based on location in orbit and other nearby bodies. Gravitational red shift has always been the hardest to measure, but of course is proved. You may be interested in the Vessot/Levine experiments.

Dennis

IamSmooth

Tue Nov 17 2009, 11:21PM

Registered Member #190 Joined: Fri Feb 17 2006, 12:00AM
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The link I posted explains the derivation, but I never studied this math in college. My physics course just covered special relativity. I looked up the derivation of the Schwarzchild metric on Wikipedia

I didn't understand the assumptions, diagonalizing and the notation that is used for the derivation. Did anyone study this that could clear this up? It is a bit complex.

Proud Mary

Tue Nov 17 2009, 11:40PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Wasn't it a Mercury demomstration of the Special Theory?

Health Hazard: in respect to the Eddington experiment, I may well have confused the
General Theory with the Special Theory - but it's as best as I can do!

Dennis Rogers

Tue Nov 17 2009, 11:41PM

Registered Member #1837 Joined: Tue Dec 02 2008, 02:20PM
Location: NYC
Posts: 65

I only have limited knowledge of the maths of GR. I know this forum is not a place for speculation but if no one else chimes in I would say you should look at it as vector mathematics. The diagonalization appears to be a tensor or vectored value of many variables, which makes sense considering the factors involved in GR. My biggest complaint with physics/math is not that it is so difficult, but that it is nearly impossible to find someone who truly understands the concepts that can explain it satisfactorily.

PS. Stella, this is considered a test of general relativity. It is a motion of mercury that doesn't make sense in Newtonian physics. It is a discrepancy with where Mercury "should" be, later explained by curved spacetime.

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