yknot Posted October 7, 2012 Posted October 7, 2012 The optical Doppler effect is defined as follows: "A change in the observed frequency of light or otherelectromagnetic radiation caused by relative motion of the source and observer." The problem with this definition is the fact that the light is no longer connected to the source by the time the former is viewed (by observers). In fact, the source could be long gone or even utterly destroyed by the time its light is finally seen. I see this light as being analogous to a simple picket fence that is floating in space whilst observers in various (inertial) frames pass by. The fence does not (and cannot) change (no accelerations here, we are talking special relativity only), so the only thing that can cause a different view of its "frequency" (the passing of its posts) is different observer motions relative to the fence. In the case of light, the same thing happens, that is, observers in different (inertial) frames see the light differently (different colors) because they are passing the light differently. And since relative motion is reciprocal, this means that the light is passing the observers differently. But now we have the problem that this last fact runs counter to special relativity theory. At least, that's *my* conclusion. What say ye?
ACG52 Posted October 7, 2012 Posted October 7, 2012 Whether the emitter is still there or not is imaterial. If we are heading towards where the emitter is or was, we will see the light as being blue-shifted, as compared to the spectrum when it was emitted. If headed away from the original position at the time of emission, we see it as red-shifted. And since relative motion is reciprocal, this means that the light is passing the observers differently. But now we have the problem that this last fact runs counter to special relativity theory. No it doesn't. All observers measure the speed of light as c. The frequencies will be different due to relative motion, but this in no way violates SR.
Ronald Hyde Posted October 7, 2012 Posted October 7, 2012 We see red shifted galaxies from billions of years ago and our telescopes were not even built then. Obviously there is something wrong with your assumptions, facts or reasoning.
yknot Posted October 7, 2012 Author Posted October 7, 2012 To ACG52: My point about the source was that motion relative to it cannot be involved if the source is no longer there. The only things that are involved are the light rays and the observers. They pass each other in the night. My point about light's passing speed still stands because no one has ever measured light's passing (or one-way) speed. Can you possibly show how such a measurement can be even be made? To Mr. Hyde: I am unsure of your point. Could you possibly clarify?
Ronald Hyde Posted October 8, 2012 Posted October 8, 2012 To Mr. Hyde: I am unsure of your point. Could you possibly clarify? Well, one assumption that is wrong is that something that happens to the source or sink of the light during transit does affect the lights progress.
EquisDeXD Posted October 8, 2012 Posted October 8, 2012 The optical Doppler effect is defined as follows: "A change in the observed frequency of light or otherelectromagnetic radiation caused by relative motion of the source and observer." The problem with this definition is the fact that the light is no longer connected to the source by the time the former is viewed (by observers). In fact, the source could be long gone or even utterly destroyed by the time its light is finally seen. I see this light as being analogous to a simple picket fence that is floating in space whilst observers in various (inertial) frames pass by. The fence does not (and cannot) change (no accelerations here, we are talking special relativity only), so the only thing that can cause a different view of its "frequency" (the passing of its posts) is different observer motions relative to the fence. In the case of light, the same thing happens, that is, observers in different (inertial) frames see the light differently (different colors) because they are passing the light differently. And since relative motion is reciprocal, this means that the light is passing the observers differently. But now we have the problem that this last fact runs counter to special relativity theory. At least, that's *my* conclusion. What say ye? Mathematically you can think of it as this: If you move towards light, you run into the "bumps" or sign changes in a sine wave faster, and if you move away from light, you run into the sign changes at a slower rate, though the actual measurement of light is an instant process, but it might have to do with relative kinetic energy as well.
yknot Posted October 8, 2012 Author Posted October 8, 2012 Mathematically you can think of it as this: If you move towards light, you run into the "bumps" or sign changes in a sine wave faster, and if you move away from light, you run into the sign changes at a slower rate, though the actual measurement of light is an instant process,but it might have to do with relative kinetic energy as well. Since I am still confused re Mr. Hyde's remarks, I shall go ahead and address Mr. EquisDeXD's. Here is a quick question that may help: As far as relative motion per se is concerned, is there really any difference between that of a passing asteroid and that of a light ray? (Yes, I know that the ray may be traveling a lot faster, but that is beside the point.) It seems to me that there is no difference at all, and this tells us that light's relative motion is no different from that of any other entity, such as a neutrino or a baseball. This is probably why no experiment has ever shown a variance in light's one-way speed per two clocks. The optical Doppler effect is just another example of light's varying one-way speed. At least that's the way I seeze it. How about you guyzz??
Ronald Hyde Posted October 8, 2012 Posted October 8, 2012 It isn't just that the light ray's speed is faster, it is that it is invariant. It's direction may change, and therefore it's velocity, but not its speed.
EquisDeXD Posted October 8, 2012 Posted October 8, 2012 (edited) Since I am still confused re Mr. Hyde's remarks, I shall go ahead and address Mr. EquisDeXD's. Here is a quick question that may help: As far as relative motion per se is concerned, is there really any difference between that of a passing asteroid and that of a light ray? (Yes, I know that the ray may be traveling a lot faster, but that is beside the point.) It seems to me that there is no difference at all, and this tells us that light's relative motion is no different from that of any other entity, such as a neutrino or a baseball. This is probably why no experiment has ever shown a variance in light's one-way speed per two clocks. The optical Doppler effect is just another example of light's varying one-way speed. At least that's the way I seeze it. How about you guyzz?? No, I'm pretty sure there's experiments that you can easily do, like let's say you have a light source. One has a stationary measuring device and there's another one moving away. We'd measure the stationary one has having no frequency change while we measured the moving away one as being red-shifted. This may also be due to the warping of space as an object travels through it, or the passage of time. Actually, based on black hole theories, isn't probably time. As light approaches a black hole, it get's red shifted since time slows the more you approach a black hole, but time moves more slowly the faster you travel, so that could be an explanation as well, since time slowing would technically lower the number of oscillations per second, but with the directional thing I'm not quite sure, because if you move towards light it get's blue shifted even though time is still slowing down. Someone with a greater knowledge of relativity should probably address this. Edited October 8, 2012 by EquisDeXD
IM Egdall Posted October 8, 2012 Posted October 8, 2012 (edited) The Doppler shift affects our observation of the frequency of light. It does not affect our observation of the speed of that light. To model how our relative motion affects the speed of light and the speed of other thing, Einstein came up with a clever formula. See link: http://math.ucr.edu/...R/velocity.html Per this formula, the speed of light is always the same value, c (about 670 million miles an hour), no matter what the speed of the light source or the speed of the observer. The speed of a particle with mass (and objects which they are made up of) is always less than the speed of light, c. And per Einstein's formula, no matter what your speed or the speed of such an object, the combined speed is always less than the speed of light. In other words, no matter what your point of view, your (uniform) reference frame, you will measure the speed of light as the same value c. And no matter what your reference frame, you will measure the speed of particles with mass as less than c. My website: http://www.marksmodernphysics.com/ Edited October 8, 2012 by IM Egdall 1
yknot Posted October 9, 2012 Author Posted October 9, 2012 The Doppler shift affects our observation of the frequency of light.It does not affect our observation of the speed of that light. To model how our relative motion affects the speedof light and the speed of other thing, Einstein came up with aclever formula. See link: http://math.ucr.edu/...R/velocity.html Thanks for the replies, folks! I don't mean to sound argumentative, but I must stay with the facts, wherever that may lead! One fact that pertains to the above is that Einstein's composition of velocities formula was based on his _assumption_ of one-way light speed invariance. Not surprisingly, given this, we end up "getting" "c" for the speed of light (and less than c for all other entities). (Neither Einstein nor anyone else ever actually _measured_ light's one-way speed between two clocks.) Another fact that also pertains to the above is that one-way invariance is an invalid assumption because it cannot occur experimentally (or even theoretically). Although this second fact may be difficult to believe, it is fairly easy to demonstrate by the following simple challenge: Show on paper how light's one-way speed between two clocks can be c experimentally in any inertial frame or frames.
Ronald Hyde Posted October 9, 2012 Posted October 9, 2012 Another fact that also pertains to the above is that one-way invariance is an invalid assumption because it cannot occur experimentally (or even theoretically).Although this second fact may be difficult to believe, it is fairly easy to demonstrate by the following simple challenge: Show on paper how light's one-way speed between two clocks can be c experimentally in any inertial frame or frames. Please explain to me this fixation on the notion that the 'one way speed of light' is immeasurable or different than the two way speed? If you send a radio signal to a spacecraft orbiting Mars and request that it radio back, you don't get a two way signal back, it's only a one way signal because it's transmitted and not reflected back. But the timing is in full agreement with the speed being C in both directions. And if you want you can put a clock on the spacecraft. And if you do all the math, which is only just above high school algebra level, it's in complete agreement with the Special Theory of Relativity. So all your arguments, yes you are being argumentative, just fall on their face.
yknot Posted October 10, 2012 Author Posted October 10, 2012 To Hyde: Please point out my argumentative stuff; I do not intend to be so. To explain my "fixation" on light's one-way speed, and why and how it differs fundamentally from the round-trip speed, I turn to Einstein's own words, since you seem to think that mine are somehow "argumentative." (I really should not have to use Einstein's words to explain SR because they have been readily available to everyone for decades, but since you asked....) The one-way and round-trip cases are different. One-way light speed "invariance" had to be given by definition, whereas round-trip speed invariance was given prior to special relativity via experiment, as Einstein said in his 1905 paper . "In agreement with experience we further assume the quantity 2AB/(t'a-ta) = c to be a universal constant - the velocity of light in empty space." http://www.fourmilab...in/specrel/www/ [Einstein's "In agreement with experience" means "In agreement with experiment." (The Michelson-Morley experiment - MMx) Einstein's "2AB" means "a round-trip from A to B and back." Einstein's time period "ta'-ta" is the round trip time per one clock. (Einstein had to use the word "assume" because the MMx did not use a clock. Later, the Kennedy-Thorndike experiment did use a clock, and also got c for light's round-trip speed. Yes, there were two round-trip null results, meaning that the first one did _not_ prove round-trip invariance.)] But Einstein was _unable_ to point to a one-way light speed experiment because none existed, and this is still the case. As I said, all he could do was to define "invariance," as is seen clearly by the following from Einstein's SR paper: "Any ray of light moves in the "stationary"' system of co-ordinates with the determined velocity c, whether the ray be emitted by a stationary or by a moving body. Hence velocity = light path/time interval where time interval is to be taken in the sense of the definition in § 1." Since the definition in §1 forces clocks to obtain the value "c" for light's one-way speed (by presetting them to read the same time for both one-way trips purely by stipulation), it is clear that this "invariance" is neither a postulate nor assumption, but merely a convention like the rather trivial convention that 12"= 1'. The problem with Einstein's definition is that it causes clocks to be asynchronous. This is why SR has relative time, which is really just a euphemism for incorrect time since everyone knows that SR's clocks are not absolutely synchronous. SR does not have absolute time only because Einstein decided to force clocks to "get" "c" as he wished. To repeat: No experiment has ever said this (or ever will). Even though Einstein preferred his asynchronous clocks (because they seemed to give him what he thought he needed, namely, one-way "invariance," he was unable to prove that truly synchronous clocks cannot exist because negatives cannot be proved. In fact, Einstein mathematically stated that observers who use the absolutely synchronous clocks of classical physics will get a _variable_ one-way light speed. [Quoting Einstein:] "w is the required velocity of light with respect to the carriage, and we have w = c - v. The velocity of propagation of a ray of light relative to the carriage thus comes out smaller than c. But this result comes into conflict with the principle of relativity.... For, like every other general law of nature, the law of the transmission of light in vacuo must, according to the principle of relativity, be the same for the railway carriage as reference-body as when the rails are the body of reference." http://www.bartleby.com/173/7.html This is not a closing velocity because Einstein claims that it conflicts with the principle of relativity, and a closing velocity would not do this. Also, no mere closing velocity could have given Einstein a headache. And no mere closing velocity could have caused the creation of the theory of special relativity. All of the above tells us that even though the round-trip light speed case was closed (experimentally) prior to SR, the one-way case remains open. All we need are a pair of (truly) synchronous clocks to get a variable one-way light speed (w = c ± v, per Einstein himself), which would detect our absolute motion, just as happened in Einstein's own example/experiment above. So, if you think that I am just being "argumentative," or that my arguments are merely "falling flat," then maybe you will listen to Einstein's own words.
Ronald Hyde Posted October 10, 2012 Posted October 10, 2012 But Einstein was _unable_ to point to a one-way light speed experiment because none existed, and this is still the case. This is totally false, I just gave you an example of a dual 'one way speed' experiment that is probably performed daily by people who track interplanetary spacecraft. This isn't some highfalutin obscure theory that people don't know about, it's something that some people use every day in their line of work.
yknot Posted October 10, 2012 Author Posted October 10, 2012 First of all, it is funny that Einstein did not mention your "one-way experiment," and second of all, it is not possible to measure light's one-way speed without using two clocks, and third of all, why did you ignore Einstein's simple equation saying that given the clocks of classical physics, light's one-way speed must vary with frame velocity? And please show the math (you said it was simple math) for your experiment to show how light's one-way speed can be c in any inertial frame. Your claim that my above was "totally false" is itself totally false, as you will soon discover by trying to do the math.
Ronald Hyde Posted October 10, 2012 Posted October 10, 2012 First of all, it is funny that Einstein did not mention your "one-way experiment," and second of all, it is not possible to measure light's one-way speed without using two clocks, and third of all, why did you ignore Einstein's simple equation saying that given the clocks of classical physics, light's one-way speed must vary with frame velocity? And please show the math (you said it was simple math) for your experiment to show how light's one-way speed can be c in any inertial frame. Your claim that my above was "totally false" is itself totally false, as you will soon discover by trying to do the math. I'm not aware of any probes that were orbiting Mars or the Moon in Einsteins time. And Einstein was in the process of proving that the classical notion of time as displayed by moving clocks was not correct.
IM Egdall Posted October 10, 2012 Posted October 10, 2012 I think the first verification of the absolute speed of light was by DeSitter in 1913. He examined binary star systems ( two stars revolving around a common center of gravity). His observations and analysis agreed with Einstein's prediction. And this was a one-way light experiment. See for example http://en.wikipedia.org/wiki/De_Sitter_double_star_experiment 1
swansont Posted October 10, 2012 Posted October 10, 2012 Wouldn't GPS fail if there was a variable sped of light? The time of flight from the satellites would be off, leading to a positioning error.
yknot Posted October 10, 2012 Author Posted October 10, 2012 To Mr. Hyde: Let me for a minute return to my original post. What do you, Mr. Hyde, think causes observers to see different colors when viewing the same passing light ray? Since the light itself cannot and does not change color, we are left with only one answer, namely, the different speeds of the observers relative to the passing light. This simple experiment alone is enough to prove that light's speed relative to observers varies. But let me also return to Einstein's simple equation, w = c - v. Regardless of your statement that Einstein was in the process of "proving" that classical time was incorrect, he _did_ in fact derive the equation w = c - v. Can you show us how he derived it? And as for your statement that there were no Mars or Moon probes in Einstein's day, this is irrelevant because Einstein could have used a thought experiment, as he often did (even in the "important" case of his derivation of the relativity of simultaneity.) Perhaps if you just show how Einstein derived his equation w = c - v, you will see what I have been talking about (non-argumentatively). But I _will_ give you the following little hint: Einstein did not really prove that the clocks of classical physics were wrong, but simply discarded such clocks in lieu of the really wrong clocks (asynchronous clocks) of special relativity. As we know, he replaced good clocks with bad clocks (absolutely synchronous clocks with absolutely asynchronous clocks) in order to (try to) get all clocks to record "c" for the one-way speed of light. Of course, he very conveniently did _not_ show how this can be done experimentally. But you, Mr. Hyde, are welcome to try. Well, I have blabbered enough for now. (Oh, I almost forget to mention that you have yet to show how your probe experiment yields the value "c" for light's one-way speed.) I think the first verification of the absolute speed of light was by DeSitter in 1913. He examined binary star systems ( two stars revolving around a common center of gravity). His observations and analysis agreed with Einstein's prediction. And this was a one-way light experiment. See for example http://en.wikipedia....star_experiment Well, this is only about light's source independency, not its one-way speed. Wouldn't GPS fail if there was a variable sped of light? The time of flight from the satellites would be off, leading to a positioning error. All clocks today are synchronized per Einstein's definition, and this definition assumes "c" for light's one-way speed. Obviously, truly or absolutely synchronous clocks would be better for GPS, but it can get by with Einstein's slightly-off clocks because of the following: On the satellite side, timing is almost perfect because they have incredibly precise atomic clocks on board. But what about our receivers here on the ground? Remember that both the satellite and the receiver need to be able to precisely synchronize their pseudo-random codes to make the system work. If our receivers needed atomic clocks (which cost upwards of $50K to $100K) GPS would be a lame duck technology. Nobody could afford it. Luckily the designers of GPS came up with a brilliant little trick that lets us get by with much less accurate clocks in our receivers. This trick is one of the key elements of GPS and as an added side benefit it means that every GPS receiver is essentially an atomic-accuracy clock. The secret to perfect timing is to make an extra satellite measurement. That's right, if three perfect measurements can locate a point in 3-dimensional space, then four imperfect measurements can do the same thing. By using an extra satellite range measurement and a little algebra a GPS receiver can eliminate any clock inaccuracies it might have. If you, Mr. Swan..., think that GPS clocks are absolutely synchronous, then please tell us how that was done. According to current theory, it cannot be done, and should not be done ("cause time is relative, not absolute per Albert E). What you all are overlooking here is the simple fact that Einstein himself said mathematically that the one-way light speed will vary given the clocks of classical physics, clocks which he was unable to obtain probably because he wanted to discard them.
ACG52 Posted October 11, 2012 Posted October 11, 2012 Since the light itself cannot and does not change color, we are left with only one answer, namely, the different speeds of the observers relative to the passing light. This simple experiment alone is enough to prove that light's speed relative to observers varies. The different FREQUENCY of the light relative to the observers, not the speed.
Ronald Hyde Posted October 11, 2012 Posted October 11, 2012 To Mr. Hyde: Let me for a minute return to my original post. What do you, Mr. Hyde, think causes observers to see different colors when viewing the same passing light ray? Since the light itself cannot and does not change color, we are left with only one answer, namely, the different speeds of the observers relative to the passing light. This simple experiment alone is enough to prove that light's speed relative to observers varies. But let me also return to Einstein's simple equation, w = c - v. Regardless of your statement that Einstein was in the process of "proving" that classical time was incorrect, he _did_ in fact derive the equation w = c - v. Can you show us how he derived it? And as for your statement that there were no Mars or Moon probes in Einstein's day, this is irrelevant because Einstein could have used a thought experiment, as he often did (even in the "important" case of his derivation of the relativity of simultaneity.) Perhaps if you just show how Einstein derived his equation w = c - v, you will see what I have been talking about (non-argumentatively). But I _will_ give you the following little hint: Einstein did not really prove that the clocks of classical physics were wrong, but simply discarded such clocks in lieu of the really wrong clocks (asynchronous clocks) of special relativity. As we know, he replaced good clocks with bad clocks (absolutely synchronous clocks with absolutely asynchronous clocks) in order to (try to) get all clocks to record "c" for the one-way speed of light. Of course, he very conveniently did _not_ show how this can be done experimentally. But you, Mr. Hyde, are welcome to try. Well, I have blabbered enough for now. (Oh, I almost forget to mention that you have yet to show how your probe experiment yields the value "c" for light's one-way speed.) http://www.fourmilab.ch/etexts/einstein/specrel/www/ This is a reference to Einsteins first paper, I can't find your little formula in it, maybe you can point it out or quote it. The color of the light and also it's energy depends on its frequency, it's speed is independent of its color. Another replier has already told you this. This is pretty basic stuff, I can't imagine it being left out of a high school science book. The satellite experiment works because they are tracking the satellite and can predict its exact position and speed relative to the transmitting and receiving antennas. Einstein was right and you are wrong, simple as that. And you are the one obligated to prove your assertions in a case like this where you are saying that well established theories are wrong.
LaurieAG Posted October 11, 2012 Posted October 11, 2012 Long-slit Spectroscopy provides a 90 degree twist on the doppler effect. http://en.wikipedia.org/wiki/Long-slit_spectroscopy in an expanding universe?
yknot Posted October 11, 2012 Author Posted October 11, 2012 The different FREQUENCY of the light relative to the observers, not the speed. You must have forgotten about or somehow overlooked my fence analogy (given in my first post). Let's say that a picket fence is floating in space (inertially, no acceleration). Let's say that you and I see different frequencies for this fence. That is, we observe different numbers of fence posts passing us each second. Is not the only way that this can occur is for us to be moving at different speeds relative to said fence? And, as I said in my original post, since relative motion is reciprocal, we must say that the fence is moving at different speeds relative to each of us. Methinks that you fellows are (for some reason that I cannot yet fathom) fighting too strongly against the simple equation w = c - v. It's time to face the facts and get on with life.
Ronald Hyde Posted October 11, 2012 Posted October 11, 2012 Methinks that you fellows are (for some reason that I cannot yet fathom) fighting too strongly against the simple equation w = c - v. It's time to face the facts and get on with life. You've never provided us with the context that equation is used in. Why are you wasting people's time with this post? Why are you wasting you own time, if you study and understand Einstein's paper you will have the correct view, and not the erroneous one that you are espousing? Nature simply doesn't choose to work according to your line of reasoning, so your reasoning is just plain wrong.
ACG52 Posted October 12, 2012 Posted October 12, 2012 You must have forgotten about or somehow overlooked my fence analogy (given in my first post). Let's say that a picket fence is floating in space (inertially, no acceleration). Let's say that you and I see different frequencies for this fence. That is, we observe different numbers of fence posts passing us each second. Is not the only way that this can occur is for us to be moving at different speeds relative to said fence? And, as I said in my original post, since relative motion is reciprocal, we must say that the fence is moving at different speeds relative to each of us. Methinks that you fellows are (for some reason that I cannot yet fathom) fighting too strongly against the simple equation w = c - v. It's time to face the facts and get on with life. Except that light is not a fence post. The speed of light is invarient in all inertial frames, regardless of their relative motion. You do not seem to have heard about Relativity.
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