EPTDirect Proof of Dark Matter Found! - Page 6
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Braavos36390 Posts
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maoam
United Kingdom444 Posts
On August 23 2006 15:30 micronesia wrote: I think the problem has been that from the beginning you claimed that you are very knowledgable then haven't really backed that up. You dropped some fancy terms to sound like you know what you are talking about, but stopped the moment you needed to show a deep understanding of the topic. I don't claim to be an expert on physics (I have a degree in mathematics, though), or even on GR. I have done a graduate course on it, and I've read about this subject before (to be precise, about how the GPS system uses relativity). That is why I referenced the article on John Baez's site. I don't recall using any fancy terms, but if I did, I should certainly have used simple ones instead; however, as I have said several times in this thread, I don't see why I should be expected to reproduce the figures or calculations myself, when it's unlikely that the people I will be presenting them to have sufficient knowledge of physics. Perhaps I should've taken the time to explain, in detail, exactly why GPS require GR, and exhibit a deep knowledge of the subject in the process. But I thought that people might take the word of a mathematical physicist (well, a guy with a PhD in mathematics who has published papers on GR) over mine, how can I explain it better? | ||
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testpat
United States565 Posts
But that was a really cool article maoam, i'm much more impressed with the other adjustments they make in the gps systems. | ||
micronesia
United States24761 Posts
On August 23 2006 18:16 testpat wrote: GPS does adjust for gr, but i think the compound errors are grossly overstated since they can be easily corrected right? If every x seconds the satellite asked for the proper time from a land base system, the maximum error would then be limited to the change over the x seconds rather than a day . Yes, that is accounting for special relativity. The point is that there is a need to acknowledge the effects of relativity, whether or not he reason behind these effects is even understood. | ||
Bill307
Canada9103 Posts
On August 23 2006 04:25 Cascade wrote: I do not know exactly how the GPS works, but I'm quite positive it involves sending light speed signals and then making time measurements to measure postion. So i ASSUME that if the satelites are a time t wrong, then the you will get an error in position of the order t*c. Using the figure in Bills quote 38.6*10^-6 (In the US, 38,600 means 38 thousand 6 hundred?) seconds per day, that would give around 38.6*10^-6 * 3*10^9 = 115.8 10^3 meters. That is: after just one day ignoring general relativity, you would get an error of about 100km. Ahhh. This is the kind of quantitative example I was waiting for  . Even though your figure my disagree with that other one posted (11 km), I am starting to understand why the tiny difference in frequency can cause a monumental error. I didn't realize the frequency played such an important role. I'm also in awe of the accuracy of these instruments. | ||
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