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Originally Posted by nutant gene 71
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Originally Posted by worzel
I don't think I've seen the actual value of G used anywhere in this thread, only the symbol. Doesn't that suggest to you, mutant gene, that the actual value is irrelevant to your argument, depsite your argument being about its value changing?
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Worzel, I treat this question as "hypothetical" because to date no hard evidence had been found to doubt Newton's G, which is G = 6.67E-11 Nm^2 kg^-2 (or m^3 kg^-1 s^-2). As far as we know, that is what G is, so the question of measurement in any kind of variable kilograms had not come up before, to my knowledge.
What is being explored is that IF Earth's G were instead tenfold, i.e., G' = 66.7E-11 Nm^2 kg^2, |
Well simply quoting the number over and over now doesn't change my point. You haven't used the value in any of your arguments.
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what would be the equivalence (inertial) mass of a cubic decimeter of water in kilograms? Would that same cube, which would not change in size, still be the same kilogram as before
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Depends on what you mean by kilogram. If you mean the amount of mass then yes, if you mean how much does it weigh then no. The former is the correct usage of the term kilogram, the latter is a convenience because we live in an almost constant gravitational field where a 1kg "weight" is the amount of mass that happens to weigh 9.8N.
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and still maintain the equivalence principle?
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In Newtonian mechanics it was a bit of mystery why the inertial mass equals the gravitional mass - but given that they're equal, I don't see any reason to suppose they wouldn't be if G changed because that would require a big coincidence: that they are equal now!
Einstein's resolution was that spacetime is warped so that free falling masses are following Newton's first law (they keep going in a straight line) as best they can in warped spacetime (they follow geodesics). For the equivalence to break there would have to be a different warping of spacetime for different masses starting out on the same geodesic.
As I see it, a more interesting question would be: if
intertia is resistance to the gravitional field of the universe as a whole (Mach, Lense Thirring), then is there even any meaning to the quesion "what if G changed?" ?