I think you need to reconsider what you just said. Please Register or Log in to view the hidden image! Light in the embankment view is what is being considered and not the fact that the phtotodetector and light source are comoving. From the embankment view the light is clearly blue shifted and the light is chasing the moving engine which is a case of red shift.
Thanks 2inquisitive! I think this talk about red and blue shifting filters is confusing. Neither frame needs to red or blue shift the filter since there is no Doppler effect involved. The only relevant effect to this scenario is the time dilation. -Dale
This is not a physics response. You are denying that to the embankment observer the light is blue shifted? You are denying that in the embankment frame that the light is shasing the engine and takes longer to reach thephtotodetector; hence MUST be red shifted? Try again. You cannot just blow off these issues because they make you uncomfortable.
You are correct, it is not a physics response. You are demonstrating your ignorance of the Doppler effect, so what is needed is an educational response not a physics response. You are not going to learn anything from what I say, so I suggest that you go back and re-learn the Doppler effect for yourself. Both frames agree that the Doppler effect occurs for light going from the flash to the embankment. Both frames agree that the Doppler effect does not occur for light going from the flash to the detectors. -Dale
It's a matter of symmetry. The doppler effect applies to light emitted in a moving frame ... it also applies to light received in a moving frame. If someone in the embankment frame stuck out a measurement device and intercepted the light, yes, it would be red/blue shifted. But the detectors on either side of the carriage aren't in the embankment frame. Viewed from their frame, there is no doppler effect. Viewed from the embankment frame, there is doppler on emission and doppler on reception which cancels it out.
And I suggest you tone it down. Your post still does not address the issue and it is not MY ignorance but perhpas yours that is starting to show. The issues was the view from the embankment and that the light flash is blue shifted but that the light going to the detector is red shifted. You chose to ignore this issue. Afraid not. If the embankment sees the light blue shifted it MUST see it as red shifted relative to the detectors. Does not the embankment see the light take longer to reach the detectors than from the train frame? Yep. Otherwise there would be no simultaneity shift. Does not that mean the light MUST be red shifted? Yep. The embankment sees the light flash blue shifted and it's relation to the detectors red shifted. According to the embankment the light flash cannot trigger the bombs. You stand corrected. Speak of your own ignorance in the future. Please Register or Log in to view the hidden image!
If you insist on calculating in a frame other than that of the target, then doppler affects the target as well as the source. I think CANGAS saw this a page back?
Please Register or Log in to view the hidden image! LOL, that is hillarious coming from you MacM. Anyway, I see you are already setting up your usual "I haven't gotten any physics responses" rant quite nicely. Please, don't let my earlier analysis slow you down. -Dale
The last sentance of your post has been discussed already. Consider the circumstance where the observer on the embankment frame is behind the departing train. The photons from both filters will be redshifted in the embankment frame, as both are moving away from his location behind the train. Will the photons from the flash also be red shifted in both directions according to the embankment observer? Does the embankment observer subtract the relative velocity of the train from BOTH forward travelling and rearward travelling flashes to cause a red shift in both directions?
Ah, sorry. If the light takes a different path (e.g. via an observer behind the train), then that's another matter. I was thinking of the case where the observer was stationary w.r.t the embankment but was pretty much 'in between' the flash and the detector in question. If you're talking about different directions though, then there's no single doppler shift for a 'frame'. There would be some kind of doppler function for every point in the frame. I'm fairly sure using points in the line where the light is travelling anyway would make no difference since you'd have an effect going from one frame to another and the reverse effect returning to the original frame, but unless you use a mirror there is no reason for the light to pass through any other point, e.g. behind the carriage. And that isn't a problem specifically with SRT. I think you'd find the same change at low (compared to c) speeds when dealing with, say, dopplered sound, if you calculate an indirect path.
No, there are two Doppler shifts to worry about in the embankment frame, as discussed at length in previous posts by myself and Zephyr. Time dilation hasn't realy come up here, since the only issue being discussed has been the colors of the photons from various perspectives, not when they arrive at certain locations.
No, the blue and red shifts cancel eachother out, and the flash triggers the bombs. I and Zephyr have already explained this at length, in this thread.
Right, nothing discussed in this thread has anything to do with SRT. You could do the exact same experiment with sound waves and acoustic filters instead of light pulses and optical filters, and calculate the results with Galilean relativity, and obervers in the embankment frame would see the exact same Doppler effects. The only difference would be that there would be no disagreement over simultaneity; however, again, that hasn't been an issue in this thread anyway.
No problem so far. Mac M, This statement is just not conformable with the laws governing the motion of light. There is no way, for even in Hell, can the a photon that is moving completely independent of the motion of the source of the light reach the forward bomb - the bomb is moving away from the light trying to catch up -- . the same time it arrives at the caboose end of the train -moving antiparallel or in a collision course with the photon. The train observer located at the point of emission of the light has the inalienable right to believe that the train is not moving and that it is the embankment that is moving. Here is the gist of the fallacy of the statement: The distance between the bombs and the midpoint are, by definiotion the same. So the rearward moving light has reach the rear bomb in time t after traveling a distance ct. in time t, the rear bomb has moved a distance vt. The forward moving light has also moved only the distance ct from the point of emission, though the observer on the moving frame does not see the frame moving and it escapes him that the midpoint has moved with respect to the original point of emission. Draw a simple sketch. of the bombs the midpoint and the light being emitted. Now without moving the frame, draw the distance the light travels to the rear, stopping short of the rear bomb.. Now draw the formward companion photon the same length in the forward direction. |-----<============|============>-----|. Notice, when the light reaches the rear bomb and we have inserted an idestructable mirror (such that when reflected see below, some of the light is reflected back to the source, the forwartd moving light and the companion light are, very briefly, moving in the same direction, hence a loss of anti-parallel symmetry). Now, move the frame to the right without moving the photons until the rear bomb just touches the rearward moving light. Simply shift the frame to the right. Now the right bomb is located vt + vt from the right moving photon. This step wise motion does not introduce ambiguities. The most important lesson here is that the light positions do not, cannot depend in any way on the motion of the frames. The observer that is considering his motion at rest wrt the train, is tied fatally to the motion of the train, that with no induced stress, just doesn't analyze it own motion. Let us educate this observer and have him conduct 20,000 tests as seen from the embankment where all the tests are conducted when the frame at rest wrt the embankment. Now, the director of "Test Operations" orders 20,000 tests where the only condition changed is the frame is now moving at velocity v wrt the embankment. Like you said, the embankment observer will now see the lights arriving sequentially, first at the rear, then at the forward end of the train. The test crew now places bombs in the embankment frame at those locations where the foprward and rearward bombs are seen to explode in the moving frame tests. The bobmbs are removed from the train completely. If there is anything approaching time dilation or frame contraction (from any causes) then the dilation and contraction must be symmetrical to the rear and forward spaces separating the bombs and the light motion and the midpoint of the bombs. Assume the observer is now qualified to conduct the tests while riding along on the train. The bombs will explode sequentially even though they are at rest wrt the embankment. The light motion is oblivious to the placement of the bombs, whether the bombs are moving wrt the embankment or are at rest wrt the embankment. Unless you have ommitted something I missed, I do not see any possibility of the lights arriving simultaneously at the bombs on the moving frame. I think I missed that lump in your cheek where you stated above the bombs arrived simultaneously in the moving frame. Further, the lump in your other cheek, also missed, as I am replying on the run, is the implication that what the observer "sees" from the train, somehow operates to manipulate the cosmos and that while SRT theorists disdain the concept of rational observations and are hence coached into accepting SRT (they do intend to have jobs after the educational phase of their life is completed), what you see is what you manipulate and something i have been apparenbtly missing is the sheer power of the mind to make the universe as they believe, with what they see of course. Geistkiesel
Your analysis would be necessary for sound or other waves that propagate through a medium. To calculate the Doppler shift for such waves you take the difference between the velocity of the source relative to the medium and the velocity of the detector relative to the medium. However, for light or other waves that do not propagate through a medium all that is important is the velocity of the source relative to the velocity of the detector. That is zero in this example, regardless of the frame. In any case, you are getting the right answers by using the approach for sound. You are just doing more work than you need to. The first paragraph of the Wikipedia entry summarizes it clearly: http://en.wikipedia.org/wiki/Doppler_effect -Dale
You are mixing what is observed,as you see it, with what is occuring. By developing a state of mind conformable to SRT, as you are saying, Doppler effects disappear. Of course you realize that your conclusions require a cooperating light pulse that is supposedly independent of the frame motion, do you not.? geistkiesel
You're right in that normally you wouldn't bother with any frames other than source or target for light. But since relativity isn't an emission theory, if you imagine a device that measures a light pulse and then immediately reproduces it in the same direction at the same magnitude and frequency, it makes no difference to the overall picture. So for the sake of MacM's idea of 'looking at the light in the embankment frame' you could imagine such a device in that frame. In which case you'd have two Doppler effects which would cancel each other - first moving from train frame to embankment frame, being re-emitted by the device, then moving back. Of course this only makes sense if the device is in the light path anyway. Unless it changes the direction of the light, placing it behind the carriage is useless since light in that direction never reaches the bombs anyway. If you make it change direction it will act like a mirror, and a moving mirror causes Doppler changes anyway.
DaleSpam, Now I get it, I think. When we say that light motion is independent of the motion of the source of the light then, as far as SRT goes, we must abandon that postulate for the simple reason that not doing so destroys SRT. Geistliesel
