Timeline for Does the Doppler effect happen instantly?
Current License: CC BY-SA 4.0
14 events
| when toggle format | what | by | license | comment | |
|---|---|---|---|---|---|
| Jun 21, 2019 at 15:51 | vote | accept | Paradoxy | ||
| Jun 19, 2019 at 15:13 | comment | added | Cort Ammon | Thus there is merely "Frame B." But if you happen to choose the behavior of Frame B such that the position of the antenna does not change over time in Frame B, then the calculations done in Frame B translate into meaningful observed results when one looks at the signals received by the antenna. But the presence of an antenna did not actually change the math of the frame transform at all... it merely made the frame transform into a useful one for predicitng what we observe. | |
| Jun 19, 2019 at 15:11 | comment | added | Cort Ammon | This comment series reminds me of one of the more difficult things when it comes to working with frames. Frames are 100% abstract concepts, divorced from any physical object. They are simply a way of measuring real life effects in terms of vectors. The calculations (such as those for Doppler shift) happen regardless of objects in the world -- they happen purely based on transforms between frames. However, if you choose the "right" frame, it becomes easy to convert the vectors measured in that frame to meaningful measurable quantities in the real world. | |
| Jun 19, 2019 at 8:22 | comment | added | Paradoxy | @Harry Johnston, yes of course, but that paradox has nothing to do with our problem here imo because in Andromeda conundrum, spaceship movement doesn't influence our observers, years later they will receive a signal. Here, the movements of observers does influence their observation and it happens instantly | |
| Jun 19, 2019 at 8:18 | comment | added | Paradoxy | @The Photon, I am not completely convinced (antenna doesn't move), but nevertheless i gave you an upvote. | |
| Jun 19, 2019 at 7:46 | comment | added | Harry Johnston | OP, are you familiar with the Andromeda paradox? Your concerns about the star's motion sound similar. | |
| Jun 19, 2019 at 0:59 | comment | added | The Photon | The antenna doesn't "change frames". It exists in both frames at all times. Sometimes it's at rest in one frame and moving in the other. Other times the other way around. The frame, and the behavior of the star in each frame, and the behavior of the waves coming from the star (as measured in each frame) don't depend on what the antenna does. The antenna just lets some operator measure the waves, with the result depending on how the antenna is moving relative to the source. | |
| Jun 18, 2019 at 22:55 | comment | added | Paradoxy | I see no problem with constructing a frame for an accelerated observer (which is done by Rindler and others, as long as you keep acceleration constant though). What you are saying is like after changing of frames antenna will consider star in movement from the very begining of the time, while antenna clearly knows that it's not the case. As a matter of the fact, if it was the case, then every accelerated observers should discard every information they ever had at every moment. not very plausible, and it is not really the case (like in accelerated systems we couldn't solve equations of motion) | |
| Jun 18, 2019 at 22:42 | comment | added | The Photon | RE "there is no 'antenna's frame'", of course what I mean is the antenna's frame is not an inertial frame. Trying to analyze what happens in this non-inertial frame is beyond my knowledge. But you shouldn't expect it to behave like an inertial frame, because it isn't one. | |
| Jun 18, 2019 at 22:33 | comment | added | The Photon | But now that the receiver is at rest in frame B, it will start measuring the frequency of the light from the star as if it were an object at rest in frame B. | |
| Jun 18, 2019 at 22:28 | comment | added | The Photon | There is no "antenna's frame". There is frame A and frame B. The antenna is initially at rest in frame A, then later it is at rest in frame B. When the antenna changes velocity to be at rest in frame B, it doesn't change anything about the star in frame B. The star is still moving in frame B the way it always has been. | |
| Jun 18, 2019 at 22:20 | comment | added | Paradoxy | I had the same answer in my mind before asking the question, however, there is a problem with this. In actual B's frame, star is really moving (because from the begining of the time, it was moving!) however, in antennta's frame who is just moved to B's frame, star would be at the rest, or are you suggesting that a very far star will start its movement in antennta's frame suddenly (which means star had moved 100y ago before antenna even starts its movement that now antenna see its movement?)Another possible answer might be discarding all of information that antenna ever had from A frame,but no! | |
| Jun 18, 2019 at 20:56 | history | edited | The Photon | CC BY-SA 4.0 |
added 271 characters in body
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| Jun 18, 2019 at 20:44 | history | answered | The Photon | CC BY-SA 4.0 |