
#1
Sep2411, 03:10 PM

P: 344

Let’ say; “A” can see and measure a stone falls to the earth let’s say 10 meter per 1 Earthsecond.
“B” lives at Mercury and can see the same thing. But “B” would do not see the exactly the same, because seen from “B’s” viewpoint time / distance is not the same as for “A”. Let us say time at Mercury would tick half so fast compared to a clock at the Earth. B would not agree it took the stone 1 second to move 10 meter – but have seen that the stone only was moving ½ mercury second. B will therefore also not see the stone falling 10 meter (as A saw it was falling in one Earthsecond), but only that the stones was falling 5 Mercurymeter. It must matter whether the stone was falling 10 meter (from A’s viewpoint) in a certain period,  or only 5 meter (B’s viewpoint),  So the problem is now, how can all laws of nature be the same for all observers. If distances not are changing proportional the same rate as time,  A and B would not agree of the speed of light. Hence distance always must change proportional with time, right?. Both A and B would therefore observe the “same” speed of the stone,  even though a process on Mercury would take relative double so long time measured with a Earthclock. It is simple math to understand that the speed of the stones anyway “seems” to be the “same” for both of A+B,  but in fact it is not, simply because time is different, and distance too. For example if we on Earth (A) see a photon traveling from the Moon to the Earth, and it take 1 second,  the same event (according to the example) would seen from Mercury only take ½ second. But because distance seen from the Mercury viewpoint (between the Moon and the Earth) is only the half compared to the earth viewpoint,  a photon would hence after one Mercurysecond have travelled the double distance meassured 1 second,  with a Earthclock. Which mean that after 1 Mercury second the photon must have traveled 600,000 Earthkm measured in 2 second with a Earth clock. (Since 2 Mercurysecond = 1 Earthseconds) Let’s return to the real world to make that more clear. After 1 orbit of the Milkyway, a clock at Mercury (B) would REALLY have “lost” 6 years compared to a clock at the Earth (A). The point is that when time/distance not is the same for A and B, how can the laws expressed by Newtonian and Keplerian equations be the same everywhere. At least the gravity constant “G” seems to must be adjusted all the time, since distance is changing all the time. Otherwise the result of gravity will not be right by our feeds compared to ours noses. How can a person that not share ours timedistances share (our) gravity constant (G) ? For example; A person living at mercury and another at the Earth could never agree about the distance  our Sun  travels the MilkyWay,  simple because time is not the same these two places. Evidence is atomic clock wouldn’t lie on these two planets. When 2 such observers cannot agree about distances /radius/ diameter of the Milkyway,  how is it possible for both to use the excact same gravity equations ? If we exaggerate and say that a clock on Mercury ticks half so fast as on Earth,  this would mean that after 1 orbit of the Milkyway we on earth have travels 377,000 Light years, but a person living at Mercury would say the orbit only is the half. Therefore 2 such observers must also get two different result of how strong gravity of the Milky way really is ? How can we then say that the laws of Newtonian/Keperian gravity are the same for both observers? 



#2
Sep2411, 04:51 PM

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P: 4,525

When we say the same laws apply, we're talking about formulas but the numbers we plug into those formulas and the results can be
different on each planet, except everone will measure the same value for the speed of light. 



#3
Sep2511, 02:43 AM

P: 344

The Point is that the gravity constant "G" cannot be the same, at different planets (etc), even not the same by your feed as by your nose, since time and distance not are the same.
I you would live on Mercury you would also measure the "same" speed of every motion included light, but when you would compared such speeds, with how an observer on earth would see the same event these are not the same speed because distances of Mercury are shorter. For example according to the example mentioned above,  after 1 Mercurysecond the photon must have traveled 300,000 Mercurykm  but at the same time (period) it have travel 600,000 Earthkm This is because 2 second measurement with a Earth clock is 1 Mercurysecond measurement with a Mercury clock . The observer on Mercury would hence say 600,000 Earth km is only 300,000 Mercurykm, and therefore in fact the photon must REALLY be moving double so far measured with a EarthMeter stick compared to a Mercury meterstick. ( but still the "same" speed/ distance seen from the perspective of both observers (without comparing). This must mean that the observer plays the "primary role",  the Universe plays a secondary role. Or that;  the Universe is like the eyes (clocks) see it, and not opposite. 



#4
Sep2511, 09:21 AM

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P: 4,525

Are laws of nature really the same in all reference frames?
You are right, the gravity constant, "g", is not the same on different planets, it's not even a constant on earth but changes slightly from location to location due to differences in the mass density of the earth at different locations and due to changes in elevation, but the gravitational constant, "G", does not change due to any local considerations. I would suggest you look up the articles in wikipedia on these two "constants" if you want to learn about them. But these issues have nothing to do with different laws at these different locations.
You have expressed concerns about the effects of gravity on measurements which is a very complex subject and requires an understanding of General Relativity. I would suggest that you focus first on understanding Special Relativity because that is so much easier and I think that once you can see how different observers traveling with respect to each other (no gravity involved) can both measure the speed of light to be the same, even though they each measure the other one's clocks and rulers to be different than their own. That, after all, is what this forum is for, understanding relativity. Are you interested in learning and understanding Special Relativity? In the meantime, I'd like you to think about your comment regarding seeing a photon traveling from the moon to the earth and I would like to ask you, how can anyone see a photon? This has bearing on your last comment: This must mean that the observer plays the "primary role",  the Universe plays a secondary role. 



#5
Sep2511, 03:36 PM

P: 344

The essence is 2 clocks are ticking differently, ; this is all we so fare need to know. We have 2 clock and 2 different observers. One observer could be you,  the other a man and a clock on Mercury. How long distance would the Sun travel seen from the perspective of these two observers (in 377,000 years / orbit the MW)  and wich distance is the “right distance” ?. After 1 orbit of the Milkyway (MW) these 2 observers could impossible agree about what the radius / diameter circumference or the MW is. If time is different and speed of light must be the "same” for all observers  left is only that distances not can be the same. It seems to me to be a simple mathematic necessity. So why make this simple event more difficult as is possible can be? Doesn’t matter whether the reason to the different time rate is GR or SR,  distances cannot be the same, and hence the Keplerian and Newtonian laws of gravity ,  yes are the same,  but G cannot be,  since distances is the main factor of gravity. The principle is what count. When time not is the same distances can also not be,  and hence "G" can also not be. On the one hand speed seems to be the same for both observer,  on the other hand,  so soon you compare how the distance difference (measured by 2 different relativistic observers) is , the observer with the slow clock must measure a shorter comparable distance,  in a certain period common for both. So on the one hand, any observer will see (measure) light (a photon) travels 300,000 km/h, but only because of distances not can be the same,  on the other hand that picture is wrong so soon you compare what have happen in a certain period. I think we shall be carefully not to use relativity as a junkyard for things that not make sence, and allow export to such junkyard so soon something is “so complex” that probably nobody has understood it. So fare I see this question, there MUST be a simple logical mathematical explanation, doesn’t, matter whether the clock ticks different due to gravity (GR) or fast motion (SR).. “If you can't explain it simply, you don't understand it well enough”. Albert Einstein 



#6
Sep2511, 09:34 PM

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You have stated that you believe you know a lot about SR but yet you have said:




#7
Sep2511, 09:39 PM

P: 848

Bjarne,
Why not try approaching it with a simpler comparison. Have A and B initially together in the same inertial reference system (on earth, out in space away from everything..., you pick it), and each is furnished with a laboratory on separate identical space ships. They can perform any of the basic experiments historically used to describe our physical laws. Now, they take off in opposite directions at relativistic speeds (it really doesn't matter whether they go at the same speeds relative to the original rest frame or not). Each one performs a number of different experiments and then return to their original rest frame to compare their results. Their results will be the same. So, yesthe laws of physics are the same in all inertial reference frames. Also, if you have them land on distant planets (ignoring the inhabitable environments) and perform experiments, they will come up with the same results such as Newton's law of gravitation; they will find that masses attract with a force inversely proportional to r^2 with the same Newton gravitation constant, G. They will both find F = ma. The ratio of e/m will be the same, etc. They probably won't have any more luck with experiments aimed at unification of general relativity and quantum mechanics than anyone has had so far. 



#8
Sep2611, 12:52 AM

P: 344

The fact is that a clock on board on Mercury really is ticking slower as one at Earth. Hence an observer (a clock) on Mercury must have "lost" 6 years due to GENERAL relativity, (compared to a clock at the Earth) after one MW orbit of the solar system. This give you 2 simple possibilities 1.) An observer on Mercury must have seen the Sun (orbit the MW) faster as an observer at the Earth have observed the same event (faster as the 250 km/s  the speed we on Earth observe the Solar system (the Sun) is orbiting the MW)  I don't believe you can sell that to anyone because that would in the end violate that “c” always is the same. 2.) That distance is not the same for both observers.  This is logic math since an observer on Mercury would see the Sun complete 1 orbit of the MW in less time (6 years less) as seen from the Earth. 



#9
Sep2611, 02:24 AM

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You have stated: 



#10
Sep2611, 04:18 AM

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#11
Sep2611, 08:49 AM

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P: 1,376

Now you say that inertial frames are not extendable globally. To me this statement seems equivalent to the statement that physical laws are not the same globally. 



#12
Sep2611, 09:54 AM

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#13
Sep2611, 09:58 AM

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#14
Sep2611, 03:34 PM

P: 344

My concern is mainly if ALL laws of nature (equations) ALWAYS the same for all observer. OR is (for example) gravity  and here I mean G (the gravity constant) an exception´. Above you wrote; "G", does not change due to any local considerations" I am now not sure what you really mean,  Is "G" ALWAY constant.  Yes or no ? Yes of no ? If the answer is no, then try to explain how 2 observers located in different spacetime (caused by gravity) obviously not would be able to agree how long time one MW orbit take,  and therefore logical also not agree what the radius of the MW really is ,  and therefore also not agree what G really is ?  What I mean is;  there are no common answers. G cannot be a constant  OR WHAT ? So fare according to this context I believe a clock (observer) on Mercury don't care why time ticks slower,  exactly as we don’t care why our clock is slower as a clock on Neptune, I mean how much time dilation is due to GR and SR  the point will still be is G ALWAYS constant ? Yes or no. 



#15
Sep2611, 04:41 PM

P: 3,543





#16
Sep2611, 04:49 PM

P: 42

EDIT: Actually, consistency is the wrong word. What I suppose I meant was that globally there is local continuity of physical laws, instead of locally there being global continuity of physical laws. That's, as far as I understand it, rather the entire point of SR. 



#17
Sep2611, 04:51 PM

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P: 4,525

Is the reason that you think GR is easier than SR because things like time dilation and length contraction are not reciprocal? 



#18
Sep2711, 02:50 AM

P: 344

Let us forget everything about SR and only consider the consequence of GR and hence time dilation caused by gravity for 2 observers orbiting the MilkyWay. These 2 observers, one on the Earth and one on Mercury measure the orbit of the Sun round the Milkyway, by multiplying time and speed. Now... The observer on Earth will claim 1 orbit of the MilkyWay took exactly 1,19E16 Earthsecond. But the observer on Mercury would say that the orbit toke 194,000,000 s (6 earthyear) less according to his clock. This time difference is only caused by GR... Time dilation on Mercury relative to the Earth = 0,000000016 s. ( due to GR) Time per year = 60*60*24*365 = 31,153,000 s. Orbit of the MW = 314,000 Light Years (at the periphery). EarthTime to orbit the MW (250 km/s) = 377,000,000 years. (at the periphery). Total Earthsecond to 1 MW orbit = 377,000,000 * 365*24*60*60 = 1,19E16 seconds. Lost" of Mercurytime in years = 1,19E16 s. * 0,000000016 s. = 194,000,000 s. So after 1 MikyWay orbit the clock on Mercury have "lost" 194,000,000 seconds ( = 6 earthyears) relative to a clock on the Earth. Now here is the simple question. Is the circumference of the Milkyway the same for these 2 observers, so long we only speak about the mentioned time dilation due to GR ? If the answer is yes,  how is this possible when the rate of time not is the same ? This only can mean a mathematical meltdown, right ? I mean since speed multiplied with the time one orbit takes must result to = Distances. The only possible outcome I can see is that distance not can be the same,  so how can the law of gravity / the equations (and G) be the same? I don’t understand why it is necessary to complicate that simple question  more as necessary,  . Distances cannot be the same so far I can understand this simple logic ,  this is to me the only logical answer,  and this must mean G have a problem. It is not enough to say this is wrong, I must know why it should be wrong.



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