Physics Help Forum What makes gravity pull on an object?

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Aug 2nd 2014, 05:30 PM   #11

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 Originally Posted by johns123 There's a common sense theory that is quite old .. and may either be Mach's Principle, or based on Mach's Principle. It goes something like stars at a great distance constitute infinite mass. In other words we exist at the center of a sphere of infinite mass. And each of those star-points in that sphere are emitting a "dust" but we don't know what it is. But if it hits you, it will push on you. Coming from infinite distance, you are located at the exact center of that dust collision all around you, so you are in balance. But, if you are on the side of, or near a large body .. like the earth .. that body shields you from the dust collision on that side, and the two bodies are pushed together by the dust collisions on the other side of each of you. Now that's common sense, but Einstein said his theory of gravity was based on Mach's Principle .. I think Einstein even coined the name, "Mach's Principle". And that common sense theory even clearly explains why a photon going past a star is moved towards the star. It might even explain Doppler shifting of light from a star in line with the path back to the star. And that would say NO! to the expanding universe .. the Universe is infinite. And no Big Bang :-)
See here.

I don't know a whole lot of the history but Einstein was a big supporter of Mach's Principle, in fact he tried to incorporate it directly into GR, but it turns out GR says that Mach's Principle is wrong but not totally wrong.

Mach's Principle is an attempt to understand the way inertia works. His (Mach's) idea was to directly link the overall mass distribution of the Universe to inertial reference frames. That is to say the distribution of mass in the entire Universe explains how an apple falls out of a tree and knocks Newton in the head. Again I'm sketchy with the details here but GR does incorporate some of this idea but says the local geometry is more influenced by the local mass distribution.

I've heard an idea that links things to Quantum Mechanics as well. It's pure speculation at this point in time, but if the Universe actually was a point particle at the Big Bang then all particles in the Universe were once in contact....which brings up the idea of quantum entanglement which means that all particles in the Universe are, to some extent, connected which means that local space-time geometry is in fact influenced by the large scale mass distribution in the Universe! (It's fun to think about, but as I said it's nothing more than speculation.)

-Dan
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 Aug 4th 2014, 07:28 PM #12 Junior Member   Join Date: Mar 2014 Posts: 14 I think what is easy to miss in Mach's Principle is that the infinite mass is pretty much at infinite distance .. maybe not quite, but it doesn't "matter". What happens in a condition like that is you really do have a fixed frame of reference ... even though the individual masses at that distance might change position wrsp to your motion .. the only thing that applies is the totally smooth central force that you are contained at the exact center of unless you move fast enough so it cannot correct its own influence on you. I'm not saying that well, but the rate of "correction" of the totally smooth fixed frame is probably found in Einstein's corrective equations. And Inertia really is Newtonian .. and is the "rate of correction" of the infinite mass influence at essentially infinite distance. I think Mach's Principle deserves another look !
 Aug 4th 2014, 08:02 PM #13 Forum Admin     Join Date: Apr 2008 Location: On the dance floor, baby! Posts: 2,776 It's always a good thing to take a step back and re-evaluate. The only problem here is that the Einstein field equations cannot really be solved for such a thing...masses at infinity and all that. I'm not saying it can't be done, just that it might be possible. We'll have to wait until we get better Mathematical tools to work with. GR is very nasty to work with in many cases. That being said GR has been proven correct for the last 100 years or so. Mach's Principle and GR do not predict the same things and we've been able to verify GR. So Mach's Principle is pretty much hosed unless we have to abandon GR. -Dan __________________ Do not meddle in the affairs of dragons for you are crunchy and taste good with ketchup. See the forum rules here.

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