Timeline for Relative clock speeds of two satellites with same but opposite direction orbits
Current License: CC BY-SA 3.0
13 events
| when toggle format | what | by | license | comment | |
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| Dec 28, 2016 at 23:41 | comment | added | rob♦ | Ah, but we seem to be having a discussion (which a moderator will probably remove soon, since that's not what the comments are for). Feel free to use the chat room like Usenet, leaving a message and checking for replies later; I won't re-type my responses here. | |
| Dec 28, 2016 at 23:22 | comment | added | Cheers and hth. - Alf | Uhm, 7 to 10 microsecs, not nanosecs. Sorry. :) | |
| Dec 28, 2016 at 23:14 | comment | added | Cheers and hth. - Alf | Thanks for the offer, but I'm an old Usenet denizen. SO is a question and answer site, not a discussion site. I am merely trying to elucidate whether you believe SR is a valid approximation locally for the satellite encounters, as stated in your answer, or not, as apparently now stated two or three times in the comments? | |
| Dec 28, 2016 at 23:13 | comment | added | rob♦ | Let us continue this discussion in chat. | |
| Dec 28, 2016 at 23:10 | comment | added | Cheers and hth. - Alf | Forgive me if I again mis-interpret your comments, but I think you're now saying that (1) Einstein's thought experiments in his popularization (I read his book as a youth) were valid because because gravity did not affect the material objects; I fail to understand that. And secondly, that because contrary to your answer's assertion you now think SR is an invalid approximation here, that a difference between the A and B tick intervals won't be measurable. Re point (1) I'm not qualified to evaluate, but re point (2), I think we're talking about 7 to 10 nanosecs accumulated clock diff per day? | |
| Dec 28, 2016 at 22:59 | comment | added | rob♦ | … The orbital period of the Sun and its neighbors about the Milky Way is 250 Myr, so for discussions about communications between Earth and nearby stars on human-friendly timescales like 1 Myr can probably neglect the corrections from general relativity. Figuring out when an approximation is useful and when it needs to be discarded is one of the skills that separates professional physicists from beginners; it takes many missteps to get a good feeling for it. | |
| Dec 28, 2016 at 22:59 | comment | added | rob♦ | I don't see a conflict between what I wrote in the answer and my elaboration in the comments. For example, the famous thought experiments that Einstein described in his own popularizations of special relativity had to do with light bulbs on trains, which operate in Earth's gravity — but which move in a direction transverse to the gravitational acceleration, and over a distance that's small compared with the radius of Earth's curvature during the course of the thought experiment. … | |
| Dec 28, 2016 at 18:09 | comment | added | Cheers and hth. - Alf | Uhm, please correct my understanding of your response here. I hear you as saying (1) this answer is incorrect because SR does not apply as an approximation for the satellite encounters in this case, since gravity is involved, and (2) that argument applies also to satellites orbiting other bodies, such as the Sun (which we're orbiting), or the Milky Way galaxy (which we're orbiting), which means essentially, SR is out as an approximation for encounters of any objects in free fall. It feels lonely without SR. | |
| Dec 28, 2016 at 7:00 | comment | added | rob♦ | You're right, nothing has changed: the Earth's gravitational field is an integral part of your thought experiment, so you can't use special relativity. Remove gravity, let the satellites travel in straight lines, and the "paradox" goes away. | |
| Dec 28, 2016 at 1:28 | comment | added | Cheers and hth. - Alf | As I see it nothing can change by just adding measurements, which I did. This isn't a quantum mechanics problem where measurements can affect the experiment. So whatever analysis you did, if you did, if your answer was correct then it is still correct with the measurements added, but if it was wrong, then it is still be wrong but perhaps now more easy to recognize as wrong. | |
| Dec 28, 2016 at 1:20 | comment | added | rob♦ | Now that you've involved a signal relay out of the orbital plane, your entire experiment takes place in the Schwartzchild/Kerr metric around the Earth and you can't use special relativity at all. An explanation is beyond my GR skill, sorry. | |
| Dec 27, 2016 at 23:07 | comment | added | Cheers and hth. - Alf | Re “there'll be a period of time when you may neglect the curvature of their orbits and analyze their clocks using special relativity”, yes that's what I thought originally. But the measurement scheme now described in the question, after you answered, really sharpens the apparent contradiction that the question is about. The local measurements of clock ticks when B passes by A, logically need to be the same rate, as measured in A, as the clock ticks communicated via the fixed length signal path. And the latter needs to be N ticks per orbit, exactly the same as A. How is this explained? | |
| Dec 26, 2016 at 21:33 | history | answered | rob♦ | CC BY-SA 3.0 |