Excellent work, 2inq! You've determined a test to distinguish between your hypothesis and other theories. Your hypothesis says that the laser must be aimed exactly at the reflector array, and that the return beam will be detected in exactly the same place, from exactly the same direction. Special relativity (if I've figured it out correctly) says that the return beam will be deflected forward by the moon, and will not return exactly the same place as it left. I think the difference should be about a few hundred metres.
But, several hundred metres won't make any difference, will it, if the return beam is spread over 20km. Perhaps we should look at laser ranging of corner reflectors on fast satellites?
Hi Pete, 2inquisitive An array of recievers on the ground around the transmitter would determine the return pattern.
Already have, Pete. Fast satellites with retroreflectors attached to them are used for many tasks, such as Earth crustal motions, sealevels and measurements of the ice at the poles. Like the lunar method, the receiving telescope is mounted at the same location as the laser used to send the signal. Like in the lunar system, the retroreflectors send the beam back to the same location it was emitted. If the short laser pulse carried the forward momentum of the satellite it was reflected off, the beam would shift in the direction of the satellite's motion. The laser beam acts if it hit a stationary target, reflecting back to the emitter. Many pulses are emitted by the laser during a flyby of a satellite overhead, but all the pulses are returned to the emitting location, whether the satellite is approaching the laser location or receding from it. The photons do not retain the forward motion of the reflector, instead acting as if the reflector was stationary. The photons propagate through the 'ether', not retaining the motion of the reflector. Sorry, I use layman's language to explain things as I have said before, I am not a physicist. I did, however, used to be an amature astronomer, so I conceptually know celestial motions.
Interesting... do you have a reference? My own quick search found the opposite result. Do the satellites you found use a prism or some kind to deflect the return beam?
Yes, the satellites I am speaking about carry a retroreflector very much like the ones on the moon. When a signal strikes them, the signal is returned in the exact same path it was received. Of course, since the satellites are moving through the ether, they have to 'lead' the satellite when the laser pulse is fired, then the satellite will intercept this path due to the satellites motion. The laser pulse is then reflected back toward the emitter along the exact same path. The outgoing path and the returning paths do not diverge. No forward motion due to the satellites motion through the ether is imparted to the pulse. Here is a link to a paper by NASA, I believe it was. There are many more links I could give for different satellites and missions. http://ilrs.gsfc.nasa.gov/reports/d...eProspect/SLR-CurrentStatusFutureProspect.pdf
No, I apologise. Bare retroreflectors are indeed used on satellites when the beam isn't too tight. But... Development of the Portable Satellite Laser Ranging System (Master's Thesis) Chapter 2, Mark A. Broomhall One other consideration when choosing retroreflectors is the velocity aberration induced by the high perpendicular velocity of a satellite with respect to the propagation direction of a laser pulse. As the velocity increases the aberration also increases. If the FFDP (far field diffraction pattern) is angularly small then it is possible that the velocity aberration will cause the return signal from the retroreflector to fall outside the field of view of the receiver optical system even with perfect telescope pointing. Velocity aberration becomes a problem with LEO satellites where the tangential velocity is high due to the low orbit. In such cases it is necessary to increase the FFDP of the retroreflectors on the satellite. This is generally done by increasing the dihedral angles of the retroreflector by less than two arcseconds or even grinding a lens into the face of the retroreflector (Degnan, 1993). This is known as 'spoiling' of the retroreflector.
See also: Conceptual Design of the retroreflector, photodetector, and optical beacon payloads for the Photon target satellite (Google Cache), Florida Space Institute (Images found in this related PowerPoint presentation) Velocity aberration An interesting effect that occurs when using a moving retroreflector is known as the velocity aberration. This term originates in the field of astrometry, where it is used to designate the difference between the true angle to a star and the observed angle to a star, induced by the relative velocity between the observer and the star. In the context of an orbiting retroreflector, another term for this effect might be point-behind error. It is fairly intuitive to expect that in order to hit a moving target one must point slightly ahead of the target along its trajectory. This is the case when aiming a laser beam at a satellite in low earth orbit, where the spacecraft is orbiting at a velocity on the order of 7 km/s. This point-ahead error can be incorporated in the control system that points the ground station's beam director. It is perhaps less intuitive that, in the spacecraft's frame of reference, it is the ground station that is moving at 7 km/s in the opposite direction. Thus, in order to hit the ground station, the spacecraft should point the reflected beam 'ahead' of the ground station (i.e. in a direction opposite that of the spacecraft's velocity; in that sense behind the ground station). But the property of a retroreflector is that it will reflect the beam back in exactly the same direction that it entered, so this point-behind error is not accommodated. Thus, by the time the beam reaches the ground station, it arrives slightly in front of the ground station, as illustrated in Figure 6: Please Register or Log in to view the hidden image! Figure 6: Velocity aberrationThe angle of the velocity aberration q is given by: Please Register or Log in to view the hidden image! Where v is the tangential velocity, f is the elevation angle of the beam from the ground station, and c is the speed of light. For a satellite in a 400 km altitude orbit, the return beam will be centered on a point about 19 m from the optical transmitter. One solution to this problem would be to locate the ground receiver at this offset location. But each orbital pass visible from the ground station may have different ground tracks, so the direction of this offset may be different for each orbit. A more practical solution in most cases is to diverge the return beam such that the optical receiver is included within the beam. For a small retroreflector (< ~2 cm) diffraction will diverge the beam sufficiently. In the case of a larger retroreflector, the retroreflector should be deliberately 'spoiled'. The retroreflectors for the Relay Mirror Experiment (RME), had vertex angles slightly different from the nominal 90°, and incorporated a cylindrical lens. The RIS experiment on ADEOS also spoiled the angles, but curved one of the mirrors rather than adding a cylindrical lens. The Photon retroreflector design will be similar to that used for the RIS.You can read more about the Photon satellite here: The Florida Space Institute's Photon Satellite Bus (pdf)
Pete, thanks for the link. It is clear and well written, with not too much maths and a few pictures. Please Register or Log in to view the hidden image! You are absolutely correct that for my hypothesis to be correct, there must be no forward momentum to the photon carried over by the emitter/reflector. That is what separates my model from Special Theory. You had me a little worried by the quote in your post to begin with. But I think I have it figured out now that I read the dissertation. The velocity aberration the paper is referring to is caused by the laser pulse entering the retroreflector array at a angle due to the motion of the corner prisms. It is like the standard description of starlight aberration down a tube. The tube is moving perpendicular to the path of the light beam, causing the beam to move to the side due to motion of the tube itself. What is happening with the high speed satellites is the same effect. The laser path travels through the retroreflector array at an angle. The return path follows this same angle. The path to the retroreflector is a straight line, which is then 'bent' as it moves through the prism itself. That causes the retroreflector to emitt the laser beam not exactly back along the same path it travelled from emitter to the surface of the prism. It is within the prism itself that the velocity induced aberration is produced. Again, the photon does not retain the forward motion of the satellite. It is just reflected back on a different path from which it travelled from emitter to satellite. Yes, it is easy to prove my hypothesis wrong. It can also be distinguished from other theories by the actual path a photon travels when emitted from a moving source. I will have to read more before I can absolutely confirm if my thinking is correct. But it won't make any difference to anyone but me personally, because I know standard theory is not going to be junked because of some anonymous internet poster with no physics training. I just hoped maybe someone might see some potential and decide to run with it. Please Register or Log in to view the hidden image!
Hi 2inq, A light beam entering the retroreflector at any angle is reflected back along the same path when the retroreflector is stationary. That's the whole point of a retro-reflector. It is only when the reflector is moving that aberration occurs.
I've got evidence that says otherwise, CANGAS. What have you got, besides yawns, insults, and bad spelling?
Yes, the point is that the 'when the retroreflector is moving'. The aberration is internal within the prism, causing the returned beam to be sent back not along the same path it arrived on, but the motion causes the beam the be reflected toward a different location. There is no transverse component to the photon's motion, it is just returned to a different location. Easy to understand for me. Junk your 'rest frames' for moving objects and you will see it too. I fully agree with aberration Pete, but it is evident only in the moving frame, as this one.
You appear to have convinced yourelf that your hypothesis once again produces a result in agreement with relativity. Interesting. 2inquisitive, is there any result that would indicate to you that your hypothesis is false?
Remember this exchange? Want to think through it again? Pete, Pete, 2inquisitive, Pete, You have convinced yourself that your theory is correct, again. Would you be willing to admit your theory is incorrect if I showed you that you are mistaken?
OK... It's not my theory, it's Einstein's special relativity. And as far as "convincing" anyone goes, all I've done is dig up experimental evidence for you that you specifically denied existed, and that would disprove your theory if it did. But go ahead. If you show me that I'm mistaken, then I'll admit that I'm mistaken. And I really need an answer to this question (rephrased more specifically): 2inquisitive, what experimental result would indicate to you that your hypothesis is false? You said before that aberration of light reflected from a moving satellite would do it... but then changed your mind.
Hi Pete Thanks for the links and info. As I understand it: Ground station fires a pulse at the satellite's future position (leading the target). From the moving satellite's point of view (reference frame) the light pulse is seen (from aberration of light) to come from a point in front of the ground based emitter. The reflector prism sends the light pulse back to this point in front of the emitter. The "in front of" is relative to the satellite's motion with respect to the ground emitter. Please Register or Log in to view the hidden image!
Pete, No, You did not dig up experimental evidence that disproved my hypothesis. You only used ST's 'relative velocity' explaination to explain the evidence. My hypothesis doesn't agree with ST's explaination. I gave you my explaination, based on Bradley's method, which I believe to be the correct method. Now to your statement: Let's use two objects, 'A' and 'B' to represent the problem. Imagine a string stretched between A and B. Now let the two objects move at speed perpendicular to the string (sideways motion). According to ST and you, a photon emitted from A towards B will travel parallel with the string, according to observers on both A and B. First, do you realize the implication of this? The observer at A would determine B was at the same apparent location as its true location. No aberration, no difference between apparent and true locations. What ST postulates is that a stationary observer at a third location would see the photon travel an angled trajectory. Now does the photon still travel parellel to the string as the A-B system passes by? No, the above is not my proof. I just want to see if you and all other relativists agree with my scenario. See if you can understand on your own if any aberration can be detected in the gedanken. I can offer proof the scenario is wrong.
Allow me to recap. We established that SR says that light from a moving source has aberration, and that your hypothesis says it doesn't. You said this meant that according to SR, moonlight should have aberration to Earth observers. I agreed. You then said that the lunar laser ranging experimental evidence indicated otherewise, and that your hypothesis was proven and SR disproven. I investigated, and showed that the SR prediction of aberration wasn't large enough to show up on said experiment, and suggested that bouncing lasers off fast-moving satellites might be a distinguishing experiment. You agreed, and maintained that there was no aberration of lasers bouncing off fast-moving satellites, which supported your hypothesis and disproved SR. I investigated, and found that you were mistaken, and that the evidence does indeed show that lasers reflected from fast moving satellites has aberration. You then changed your mind, and said that your hypothesis did actually predict aberration of lasers bounced off moving satellites after all. In brief: you suggested an experiment to distinguish between your hypothesis and SR. The experiment gave the result that you agreed was predicted by SR.
Correct. Correct. This is a statement of the case in A and B's rest frame. B's photon launching tube will be aimed directly at A, and A's photon receiving tube will be aimed directly at B. No. This is the string's rest frame. In this frame: The light leaving B has aberration (moving source), so its path is at an angle to B's photon launching tube. The light arriving at A also has aberration (moving receiver), so A's receiving tube is at an angle to the light path.
