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Mainstream treatment for relativistic Doppler effect under accelerated motion? 
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#1
Jan2007, 09:47 PM

P: 329

I would need a pointer to a mainstream treatment of the general relativistic Doppler effect when source and receiver are accelerated wrt each other. Book/paper/wiki . No crank papers , please (i.e. no Apeiron and such). Thank you.



#2
Jan2007, 10:28 PM

P: 997

Authors: Rothenstein, Bernhard; Popescu, Stefan The uniformly accelerated reference frame described by Hamilton, Desloge and Philpott involves the observers who perform the hyperbolic motion with constant proper acceleration gi. They start to move from different distances measured from the origin O of the inertial reference frame K(XOY), along its OX axis with zero initial velocity. Equipped with clocks and light sources they are engaged with each other in Radar echo, Doppler Effect and Radar detection experiments. They are also engaged in the same experiments with an inertial observer at rest in K(XOY) and located at its origin O. We derive formulas that account for the experiments mentioned above. We study also the landing conditions of the accelerating observers on a uniformly moving platform. Comment: 15 pages, 8 figures, includes new results on radar detected times and distances If you consider arXiv among "such" then delete my thread. If not please have a critical look at my paper you can download from arXiv. sine ira et studio 


#3
Jan2107, 09:06 AM

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P: 2,340

Hi, nakurusil,
So let me restate the question as: "what are some mainstream treatments of frequency shift phenomena, involving a source and an receiver, when either the source or the receiver (or both) are accelerating"? Some obvious places to begin are the first edition of Taylor and Wheeler, Spacetime Physics, or another book which treats the kcalculus (IIRC, there is one by Rindler which does so), then Section 2.8 and Chapter 6 of Misner, Thorne & Wheeler, Gravitation (MTW) for two scenarios featuring accelerating observers and or sources. Then you can see "Frame fields in general relativity", "Rindler coordinates", "Born coordinates", "Ehrenfest paradox", "Bell's spaceship paradox" in the versions listed at http://en.wikipedia.org/wiki/User:Hillman/Archive; these have citations to published review papers where you can find many more references. Books like Nakayama, Geometry, Topology, and Physics, might be useful in following the first article; there is also some material on frame fields in MTW, and you can find these techniques treated in standard monographs such as Hawking & Ellis, The Large Scale Structure of SpaceTime. Note well! Wikipedia is inherently unstable, and that articles in this specific area have been dogged in the past year by a single cranky dissident who managed to chase out of WP least one contributor with a Ph.D. in physics, plus myself (Ph.D. in mathematics), who incorrectly maintains in the face of all evidence that the mainstream view is his view. For this reason, current versions of the articles I mentioned may be better than the last ones I contributed to, or they may be much worse, so I recommend that you start with the ones I cited and compare carefully with subsequent editions. To repeat something I find myself saying with distressing frequency at PF: I will not "discuss" physics with specific cranks or their supporters; it should not be neccessary to for me to explain why not and I will not do so. Ultimately, you are on your own in terms of evaluating specific versions of specific WP articles; it will not always be easy to tell simply from obvious clues whether or not the article faithfully and accurately reflects the current scientific mainstream. Ultimately, only someone who has read the literature with adequate insight and understanding may be able to tell. And don't overlook the obvious: MTW itself has a huge bibliography which you can use to find some older but still important, useful, and relevant papers. Note well! Everyone should be aware that published papers vary widely in quality; as you yourself obviously already appreciate (good!), some "journals" seem to function as trashcans which collect papers rejected by more rigorous journals. In addition, while the arXiv is an invaluable resource, it does not yet function as a refereed journal. The "endorsement" system is only analogous to "moderation" in a newsgroup; it cannot and does not prevent cranky eprints from being posted to the arXiv. Thus, the quality of eprints posted there varies even more widely than does the quality of papers in the published literature. So you should be cautious about anything you read outside a highly reputable and widely used textbook such as MTW until you know more. Unfortunately, I must add a specific caveat. I and others have noticed that the arXiv is particularly uneven in the case of papers on alleged "foundational issues" centering around relativistic physics, and I emphatically intend to include the treatment of accelerated observers as a known "problem area" in the arXiv where eprints have a better than even chance of being partially or completely incorrect. It is crucial to understand that most physicists (at least those who often deal with relativistic physics), upon being asked to pick out the bad eprints, would have little trouble doing so; there is fact wide concensus on right and wrong ways to treat these problems, but a small group of noisy dissidents came sometimes create an incorrect impression which might fool casual observers unfamiliar with standard mathematical techniques. Let there be no mistake: the appropriate mathematical techniques are very well known and widely used outside of these particular problems; the issues in questions come down to computations and there is no ambiguity about the fact that the incorrect claims are in fact mathematically incorrect. [EDIT: having just noticed another post in this thread, perhaps I should caution against "guessing games" about which specific arXiv eprints I might have in mind. That would be profitless and in selfdefense I will not respond to queries of that sort.] You can also search PF for a recent thread (last two weeks or so) in which I posted some computations of frequency shift phenomena for various pairs of observers, including some accelerating receivers, in the Schwarzschild vacuum solution. 


#4
Jan2107, 09:47 AM

P: 329

Mainstream treatment for relativistic Doppler effect under accelerated motion?
"general" in the sense of arbitrary orientation (i.e. arbitrary angle [tex]\theta[/tex] and arbitrary relative motion between source and receiver). Sorry about confusing you. I will look for your posts on "some computations of frequency shift phenomena for various pairs of observers, including some accelerating receivers, in the Schwarzschild vacuum solution.". A pointer from you would be welcome. 


#5
Jan2107, 10:56 AM

P: 329

The paper you quote does not appear to be correct since it is an attempt to plug in variable [tex]v[/tex] into the relativistic Doppler formulas. The oobjections I have to the paper are that: 1. It does not derive the relativistic Doppler effect from base principles. 2.Instead, it uses the formulas derived for nonaccelerated motion and it plugs in the values computed for hyperbolic motion Looking thru your papers, I think this one is better The objections are smaller: 1. It is not clear what are the improvements over reference [3] 2. It deals only with sourcereceiver angle of motion [tex]\theta=0[/tex], i.e. is not general enough. 


#6
Jan2107, 01:28 PM

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While no particular papers come to mind, the required technique seems fairly straightforwards to me. Since Chris has already given you some suggestions for papers, I'll just add in my $.02 on the techniques I'd suggest.
You have a source, moving through some specific path through spacetime, that emits signals as a constant time interval [tex]d\tau_1[/itex]. The signals themselves follow null geodesis You have a destination, moving through some specific path through spacetime, that receives the signals. We are interested in the interval between pulses (null geodesics) as a function of time. Note that the notion of simultaneity will, in general, depend on the coordinate system one uses, of course. If you happen to be in flat spacetime, regardless of whether or not your observers are acclerating, the answer is easy enough to compute using inertial coordinates, for the null geodesics will be straight lines in any inertial coordinate system. This approach will basically demonstrate, when carried to its conclusion, that there is no doppler shift due to acceleration as long as one works in an inertial frame. There is only SR doppler shift in inertial frames in flat spacetime, any other doppler shift comes from the choice of coordinates. I.e. pick a frame momentarily comoving with the transmitter. Draw the null geodesics in this frame. The time interval between reception will depend entirely on the velocity of the receiver relative to the inertial frame we defined, the "angle" at which the receiver's wordline "cuts across" the congruence of null geodesics. By computing the null geodesics for other geometries (say the FRW expanding universe  I've seen this partricular case done in textbooks for cosmological redshift and could probably dig up a reference in MTW), one can compute the doppler shift for those nonflat geometries as well. Rescaling the metric to "conformal time" can help this process a lot, greatly simplifying the geodesic equation. [tex] \frac{d^2x^\lambda }{dt^2} + \Gamma^{\lambda}_{~\mu \nu }\frac{dx^\mu }{dt}\frac{dx^\nu }{dt} = 0 [/tex] It's a lot easier to pick suitable coordinates to simplify the above equation than it is to solve it in the general case. Most particularly one can often simpolify this equation greatly by by rescaling time so that T = f(t)  i.e. "conformal time". This will often make light cones "straight lines", at least if one starts out with spatial coordinates that are the same in all directions (i.e. isotorpic coordinates for the Schwarzschild metric). The next most useful trick in dealing with geodesics is to take advantage of conserved quantities  every Killing vector in the source geometry generates a conserved quantity. The least useful technique is to attempt to solve the differential equations above by "brute force". 


#7
Jan2107, 02:41 PM

P: 997




#8
Jan2107, 02:54 PM

P: 997

You have a source, moving through some specific path through spacetime, that emits signals as a constant time interval [tex]d\tau_1[/itex].
That is the problem. What you propose is known as very small period assumption Most papers I know treat the problem making that assumption which obscures some peculiarities of the Doppler Effect. 


#9
Jan2107, 03:11 PM

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One way of looking at doppler shift geometrically is that there is some function that maps [itex]\tau_1[/itex], the proper time of the emitter of some signal when that signal is emitted, into [itex]\tau_2[/itex], the proper time of the receiver when that same signal is received. The slope of that curve can be regarded as the doppler shift, ie [tex]\frac{d\,\tau_2}{d\,\tau_1}[/tex] (or perhaps the inverse). 


#10
Jan2107, 05:06 PM

P: 2,050




#11
Jan2107, 05:08 PM

P: 329




#12
Jan2107, 05:10 PM

P: 329




#13
Jan2107, 11:32 PM

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P: 2,340

Another technique which can be useful is group analysis, in which one starts with a system including some undetermined function, and looks for particular choices which ensure that the system acquires extra symmetries, which often leads to exact solutions of special cases. Stephani has some remarks about this. Further introducutions to symmetries and differential equations include: 1. Peter J. Olver, Applications of Lie groups to differential equations, Springer, 1993. 2. Bluman and Kumei, Symmetries And Differential Equations, Springer, 1989. 3. Brian J. Cantwell, Introduction to symmetry analysis, Cambridge University Press, 1992. 4. Nail H. Ibragimov, Elementary Lie group analysis and ordinary differential equations, Wiley, 1999, and CRC handbook of Lie group analysis of differential equations, CRC Press, 1994. I'd recommend reading all of these. Incidently, Killing equations are very simple to attack by CAS. In Maple, the key command is "casesplit", which carries out the triangularization mentioned above (as in linear algebra, this can be tedious for humans, but computers enjoy such mindless tasks). 


#14
Jan2107, 11:34 PM

P: 997




#15
Jan2107, 11:43 PM

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One "wrinkle" I glossed over  under some circumstances, it's possible to view a point source via multiple paths. Each of these paths can have its own associated doppler shift.



#16
Jan2207, 12:11 AM

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Interesting, thanks for the info and references. I've done enough with the problem to appreciate how messy solving the geodesic equations can be, so I'm glad to hear about new techniques and methods. 


#17
Jan2207, 12:15 AM

P: 329




#18
Jan2207, 12:43 AM

P: 997




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