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Gravity only illusion due to expansion of universe? 
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#37
Jan2909, 03:19 PM

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Yes. This might be easier to visualize of you substituted a moon for a cannonball. In an "Earthfeather system", your total mass (and thus your total gravitational attraction) is equal to 1 Earth + 1 feather. In an "Earthmoon system", your total mass (and thus your total gravitational attraction) is equal to 1 Earth + 1 moon. It becomes intuitively obvious now that the EarthMoon system should make contact in less time. 


#38
Jan2909, 06:55 PM

P: 645

The influence is, of course, related to the mass of the total system. We usually are talking about systems like "Earth" and "feather" where M>>m and we can approximate and simplify by saying (M+m)=M. The question then arises, is the OP's original question related to crackpottery if we consider the mass of the total system, ie the whole universe, rather than just considering local (and open) subsystems. Naturally, we would need to carefully consider what we would treat a mass and I would suggest that we look at a mass as a concentration of energy (or concentration of massenergy, if you prefer) rather than a point mass notionally located at a body's centre. A body's concentration of massenergy falls away as you move away from that body (the rate at which the concentration falls away is easily calculated). If you can visualise the effects of two concentrations of massenergy in an expanding universe, accept that concentrations of massenergy would resist expansion in proportion to the concentration of massenergy (if they didn't the gravitational "illusion" would never eventuate) and do the sums, you will find that the effects would be the same as gravity (and G would be related to a coefficient of "expansion resistance" which would in turn be inversely related to the speed of light squared. If planck units are used, the coefficient of "expansion resistance" resolves back to unity). The equations are available, but as it is not considered to be mainstream physics this is not the correct forum for providing them or even posting links to them. Even if it were mainstream physics, you would still be left with the questions: what causes the expansion? (an answer is available, but may not be mainstream) and what causes the resistance to expansion of concentrations of massenergy? (Although, to be fair, without gravity or some similar phenomena which leads to the "illusion" of gravity, the universe would be smooth and there would be no lumpy bits like ourselves to ponder the question.) cheers, neopolitan 


#39
Jan3109, 08:18 PM

P: 1

I did not undestand the last line ' multiply by inertia..... Can you kindly give me some link or reference where I can learn more about this point of view.... Thanks 


#40
Jan3109, 09:42 PM

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#41
Feb109, 05:03 AM

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#42
Feb109, 06:41 AM

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#43
Feb109, 03:58 PM

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Here's what Peter Bergmann (a student of Einsteins) had to say about gravity and electromagnetism in THE RIDDLE OF GRAVITATION (1992) :



#44
Feb109, 06:04 PM

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Out of curiosity, since the universe is expanding isotropically how could that be the explanation for gravity which points down rather than being isotropic?



#45
Feb109, 06:38 PM

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#46
Feb109, 06:54 PM

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The FriedmannLemaîtreRobertsonWalker (FLRW) metric
[tex]\Large{c^2 d\tau^2 = c^2dt^2  A(t)^2 d \Sigma^2}[/tex] This looks suspiciously as if it gives preferencial treatment to particular inertial frames, nominally at rest with the cosmic background radiation, perhaps. Does anyone know? 


#47
Feb109, 07:34 PM

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#48
Feb109, 11:09 PM

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When you say gravity "points down" you are thinking of it as a force, I thought the whole idea of the OP was that it is an illusion. Expansion of the universe may be isotropic (specifically in all directions), but it is not smooth. It it were smooth, we'd not notice it because we are largely empty space ourselves. What we see expanding are the gaps between masses, or concentrations of massenergy. What then gets difficult to explain is why we see expansion between big lumps (galaxies) and not so much between smaller lumps (planets in the solar system). It could be that the universe would expand both isotropically and smoothly, if it weren't for mass (or concentrations of massenergy). Concentrations of massenergy seem to do something, it could be that they bend space or it could be that they resist expansion, the overall effect would be the same. If concentrations of massenergy did resist expansion, then gravity would then "point" along a line of increasing concentration, ie towards the (other) mass. Put two masses close enough to each other and you will see a line of maximum resistance to expansion linking them, because the centre of their combined mass (combined massenergy) lies on that line. How would this differ from "normal" gravity? Not much, it just wouldn't be a force, it would be a phenomenon  and you wouldn't, therefore, have a gravity field or gravitons. Gravity lensing would still happen if a photon passed through a region of resistance to expansion. Space would still seem to be bent. Oh, and some physicists would be upset since it would play havoc with some pet theories. cheers, neopolitan 


#49
Feb109, 11:44 PM

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#50
Feb209, 02:24 AM

P: 1,162

That the acceleration is always going to be a result of reciprocal interaction but if inertial mass is actually equivalent to gravitational mass, this shouldnt make any difference. But subsequent posts seemed to question this so now I am curious as to which is correct. 


#51
Feb209, 06:31 AM

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#52
Feb209, 06:38 AM

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#53
Feb209, 08:31 AM

P: 645

If there are reputable push gravity theories, I may be interested, but it seems they replace gravity with a repulsive force which is not what the OP here seemed to be considering and certainly not what I was hypothesizing about  I was thinking of whether the force could be an illusion in entirety, not replaced by another, rather more counter intuitive force. Try thinking of this: one consequence of relativity, the one that really messed with Einstein's head is that it implies expansion, he worked tirelessly to try to get around that and later described that effort as his greatest blunder (and that is ok, science benefits enormously from blunders). Is it so unreasonable to ponder what would have happened if Hubble's work had come earlier than Michelson and Morley, and we knew that the universe was expanding but not that there was something odd about some of our late 19th century assumptions which included aether? Could we get from this universal expansion back to relativity and the understanding that aether is unnecessary, as opposed to from relativity to expansion? I think you should be able to. For me the first step is to realise that the universe is expanding, but not all of it ... why is that? It may be difficult to try the exercise properly, since there are huge temptations to take the shortcuts we know are there, but it might be worth the effort if we get the whole picture  well, maybe more of the picture or a different perspective on the same piece of the picture we already have cheers, neopolitan 


#54
Feb209, 11:37 AM

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I just fail to see (1) how this idea relates to established theories (2) what the motivation for this idea is. 


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