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#37
Mar2904, 01:39 PM

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#38
Mar2904, 01:49 PM

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quoting Integral:
quoting Integral: quoting Integral: quoting Creator: quoting Integral: quoting Integral: quoting jdavel: quoting russ_watters: 


#39
Mar2904, 01:54 PM

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#40
Mar2904, 02:00 PM

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#41
Mar2904, 02:17 PM

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Suppose I were to define a standard volume of water as the amount of water in a certain bucket. Then using that bucket I measure the volume of several other buckets to be 5 standard buckets. One day I see a new shiny bucket that I would rather use as my standard. When I use my new standard to measure the amount of water in one of the previously measured buckets I find that it now holds 6 standard buckets. Are you telling me I should ignore this discrepancy or should I assume that all buckets have somehow changed? Clearly, if it is indeed used, a change in a standard will be noticed. If the meter were never used to measure anything but the speed of light we would indeed never notice the change. But as soon as we apply the standard to something else we will certainly notice if the standard changes. Suddenly all previous measurements will be wrong according to our standard. 


#42
Mar2904, 02:21 PM

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What is a "known distance"? A distance is known only when compared to the standard of length. The meter is the standard. If the distance to London was 50km and it is now 60km, then the distance to London changed. The meter is still one meter.
Yes I am well aware that GR allows aribtrary coordinates systems. I didn't want to get into that. You can't talk about a constant speed of light in GR. 


#43
Mar2904, 02:38 PM

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Precisely, none. General Relativity allows expression of physical laws independent of the coordinate system. "the speed of light is constant because the meter is defined in terms of the wavelength of light? and "The meter is expressed in terms of the wavelengths of light because the speed of light is constant" 


#44
Mar2904, 02:49 PM

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What if we measured the amount of some water in terms of the number of standard shiney buckets full, and found it to be six one say, and then, the next day, the the amount was only five. Well, then we'd have to discard our conservation of water law, right? No, because, just in the nick of time, a genius comes along with an incredible breakthrough. He (or she; there have been female geniuses, too) declares that the amount of water is not determined by the volume, but by the weight. Now, whenever the water is measured, on whatever day, the weight is always found to be 8.3 standard shiney buckets. Hooray for the inovative minds on the standardization committee! 


#45
Mar2904, 03:09 PM

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I feel that there is a issue with the distance changes between cities, if standards mean anything, when I measure a distance in meters it had better read the same today as it did yesterday or next year. That is the whole point of a standard. When London is moving at .5c wrt to Paris then I would expect the distance to change. As long as they are stationary the distance must remain the same. The distance is a physical quantity it does not change with the units you measure it in. 


#46
Mar2904, 03:18 PM

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By what, I mean the trivial issue of the standard itself. By how, I mean the more significant issue of the method used to compare to the standard. I support the second statement, but it is not an answer to the original post. 


#47
Mar2904, 03:37 PM

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Turin,
I am failing to see the point of your posts or your arguments. 


#48
Mar2904, 03:43 PM

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#49
Mar2904, 03:43 PM

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#50
Mar2904, 03:53 PM

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The fact is with modern technology I believe it is easier to get a precise measurement of c then [tex] \epsilon_0[/tex] so it may well be that it is now defined it terms of c then the other way round. That does not change the fact that [tex] \epsilon_0[/tex] is a basic property of space time which is a factor in the propagation of EM waves. Which is the "more" fundamental constant. I personally do not know. 


#51
Mar2904, 03:54 PM

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Turin,
You are now arguing semantics, can we get this thread back on topic. 


#52
Mar2904, 04:14 PM

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Integral,
Can you please, then, reword this question (the appropriate topic of this thread, I'm assuming) to elliminate any semantic ambiguity: Perhaps you mean we should now address this question? 


#53
Mar2904, 04:24 PM

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DrMatrix, don't you see that you're now saying that a kilometer and .62 miles are different lengths? The number changes, the distance is the same because the number (I thought we had already established this) is arbitrary. DrMatrix seems to be trying to argue that due to our current definition of a meter, there is no way to prove that C is constant. He is incorrect, but either way, this has nothing to do with that question. 


#54
Mar2904, 04:59 PM

P: 40

I know that when I compare two lengths one of them may be longer than, shorter than or equal to the other one. I can choose one of them as a static reference length and use it to measure other lengths (including other reference lengths). It doesn't matter which one I use unless I want to discuss my measurements with other people. Furthermore, I can say that any length maybe used as a reference length. But some choices are impractical. Because some choices for a reference length make discussion impossible or their use impractical we need to choose a practical standard. If we agree on one as a standard and _everyone_ agrees on the given choice then it is universal by definition. The speed of light, however, must be defined as: [tex]c = \frac l { t }[/tex] where [tex]l[/tex] is a proper unit of length and [tex]t[/tex] is a proper unit of time. It is a quotient! And it is a quotient! And it is a quotient! IOW, c is constant iff this quotient is a constant. Standards do not make this any truer or falser. It doesn't matter _how long_ a unit of proper length or proper time are. The quotient is what matters. (I've read a paper where the authoer uses a quotient of metics (topological) as his measurement primitive.) So, going back to my example of two electrons defining the endpoints of a reference length... You _can_ choose these two distinguishable objects for your static reference length and from the above quotient choose some observable dynamic as the proper unit of time (the dynamic is impied by the quotient  what is it?). As Einstein said, there are no prefered frames. But there are frames where EMR mignt not exist & so you really need to know how to work in those frames (electron frame?) in a general way? Objections? 


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