## Wednesday, July 27, 2011

### 21 Interpretations of Mach's Principle !?

"Many Physicists do not agree that Einstein’s theory of relativity really solved/implemented Mach’s Principle (completely or at a degree)."

### It's nice to see Professor Dantas return to blogging at her new weblog "Toy Universes". Initially she wrote a nice exposition of "Mach's Principle", and how even to this day "interpretations" are controversial, indeed there are 21 different ones!

Steven Colyer said...

Christine's weblog Toy universes is also on this list, which is 50 Awesome Blogs for Physics Geeks.

Well done, Christine! :-)

Neil Bates said...

I don't trust hard-core Machism either. GR can take the "background" of S-T and inertial standards as given (by what, sure that's a good question and challenge ...), and then matter tweaks in the vicinity. Lens-Thirring is often given as an example of Machism, but it really isn't. L-T is basically the magnetic analog for gravity: spinning matter twists space like spinning charge creates magnetic field. But note, it isn't "authentic" Machism because if I spin a mass now, the gravitomagnetic effect spreads at c as it must for causal propagation. Yet the Machian "explanation" of Newton's "spinning" (as we regard it) pail treats the distant masses as if they are whirling around instead.

It's tempting to think, that's really the same thing since mass whirling around would affect the pail. But no, for two reasons:
1. The causality and speed of information issue isn't the same. Even if I could get distant stuff to spin around suddenly, it wouldn't affect the pail right away (?) 2. The spinning stuff has to alter the S-T standard so some of it can go with v > c (which may be fine since gravity does change such standards. 3. It would be a coincidence for the *influence from* the spinning masses to give just the right actual centrifugal acceleration. G needs to have the right value in proportion to the masses and their distribution. Do you really think, even if roughly correct, that the distribution of matter is just right and G just right, that if you spun if at a certain omega around you, the local acceleration generated by L-T would just be the right value of a = r*omega^2? Really, we find "dark matter" around and all of a sudden the average density is several times more, but the implication is really just "so what" for Machian pretensions.

Ulla said...

Einstein recognized the importance of Mach Principle. But he could not explain the Principle. He probably knew that his Field Equation is against the Principle. He must have known that the Equation is a guess at the truth of Mother Nature and might not be true. That resembles the way some people made a guess at the explanation of cosmic redshift. Human’s conscience might have realized that those guesses may be wrong. However, those dictators wanted to take an advantage of the fame of Einstein and Hubble.http://blog.vixra.org/2011/07/28/higgs-combination-and-fits-revisited/#comment-9533

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