robinpike Posted July 8, 2014 Author Share Posted July 8, 2014 Although the maths is useful (and exact), I do find it easier to discuss from a descriptive point of view. However I can see from my opening post, that using the term 'frame of reference' has a specific meaning in physics: that is, reference from a single observer's point of view; and this isn't actually what I meant. The question I meant to ask is: Does the constant speed of light suggest that there is 'universal framework' that light moves to? Yes it could be said that from a trivial point of view, photons moving side-by-side, are in fact are at rest with respect to each other, but photons in general must of course be moving across space. Also, the observation that we do not detect any change in our relative motion to light's motion, would seem to be a separate point of discussion. Link to comment Share on other sites More sharing options...
Delta1212 Posted July 8, 2014 Share Posted July 8, 2014 Also, the observation that we do not detect any change in our relative motion to light's motion, would seem to be a separate point of discussion. That's not a separate point of discussion. That's what the constant speed of light means. It is constant with respect to any frame. Rather than being an indicator of some "universal framework" as it pertains to motion, the constant speed of light is what caused us to drop the idea that such a thing exists in the first place. Link to comment Share on other sites More sharing options...
robinpike Posted July 8, 2014 Author Share Posted July 8, 2014 That's not a separate point of discussion. That's what the constant speed of light means. It is constant with respect to any frame. Rather than being an indicator of some "universal framework" as it pertains to motion, the constant speed of light is what caused us to drop the idea that such a thing exists in the first place. But the constant speed of light can be noted by observing that two photons moving side-by-side, stay together. That is all that is needed. Why does any other observation, such as our relative motion to light being constant, have to be mentioned? Link to comment Share on other sites More sharing options...
xyzt Posted July 8, 2014 Share Posted July 8, 2014 Yes it could be said that from a trivial point of view, photons moving side-by-side, are in fact are at rest with respect to each other, but photons in general must of course be moving across space. Also, the observation that we do not detect any change in our relative motion to light's motion, would seem to be a separate point of discussion. You cannot associate a frame of reference to photons. I am quite sure you have been told this before. Link to comment Share on other sites More sharing options...
swansont Posted July 8, 2014 Share Posted July 8, 2014 But the constant speed of light can be noted by observing that two photons moving side-by-side, stay together. That is all that is needed. Why does any other observation, such as our relative motion to light being constant, have to be mentioned? A bit of sloppiness in the terminology. The speed of light is invariant, which carries with it more than saying it is constant. Not only does it have a constant value, it has the same value for any two observers moving relative to each other. There cannot be a preferred/universal frame, if all observers get the same answer. Link to comment Share on other sites More sharing options...
robinpike Posted July 8, 2014 Author Share Posted July 8, 2014 A bit of sloppiness in the terminology. The speed of light is invariant, which carries with it more than saying it is constant. Not only does it have a constant value, it has the same value for any two observers moving relative to each other. There cannot be a preferred/universal frame, if all observers get the same answer. Swansont, that is the part that I do not understand. If the speed of light is invariant to all observers, why isn't the first step in achieving that, that all photons move to a universal frame? I appreciate that there will be other steps, but how can that first step not remain in place? Link to comment Share on other sites More sharing options...
Delta1212 Posted July 8, 2014 Share Posted July 8, 2014 Swansont, that is the part that I do not understand. If the speed of light is invariant to all observers, why isn't the first step in achieving that, that all photons move to a universal frame? I appreciate that there will be other steps, but how can that first step not remain in place? Why would it be that? It doesn't require a universal frame to obtain that result and attempting to extrapolate what a frame based on the speed of light would look like leads to some nonsensical results (e.g. distance not existing and no passage of time) which is why you can't build a frame from the perspective of a photon, and certainly not a universal frame. Link to comment Share on other sites More sharing options...
swansont Posted July 9, 2014 Share Posted July 9, 2014 Swansont, that is the part that I do not understand. If the speed of light is invariant to all observers, why isn't the first step in achieving that, that all photons move to a universal frame? I appreciate that there will be other steps, but how can that first step not remain in place? How can you have a universal frame? That implies one single frame of reference. But there are an infinite number of frames that give you this answer. Plus, as you've been told, there is no frame of reference for photons. Link to comment Share on other sites More sharing options...
robinpike Posted July 9, 2014 Author Share Posted July 9, 2014 How can you have a universal frame? That implies one single frame of reference. But there are an infinite number of frames that give you this answer. Plus, as you've been told, there is no frame of reference for photons. Yes, different frames for different observers - but for the photons themselves, do they move relative to their own universal frame? If they do not move to a universal frame, how can the following be explained... Using starlight thousands of years old and created in a different part of the galaxy to us, if it happens to reach us, then we can create some light and compare the two by directing the newly created light so that it is moving parallel to the path of the older starlight. If we were to do this, then we would find that the new light moves at the same speed as the old light. How is this result explained if light does not move to a universal frame? Link to comment Share on other sites More sharing options...
imatfaal Posted July 9, 2014 Share Posted July 9, 2014 Robin - what do you mean by "universal frame"? Because the standard definition - which has been mentioned above - is strictly ruled out by current theory. Link to comment Share on other sites More sharing options...
swansont Posted July 9, 2014 Share Posted July 9, 2014 Yes, different frames for different observers - but for the photons themselves, do they move relative to their own universal frame? "The photon's frame" makes no sense in physics. There are no equations to describe what happens in that frame — our equations all diverge at v=c. We are not photons; what we care about is describing photons in our own frames of reference. Even if we had some idea of describing that frame, we couldn't get into that frame and test it. How is this result explained if light does not move to a universal frame? The speed of light is invariant. I have no explanation of why that is so, but that's not what physics is meant to do. It observed to be true, and we can use that information to see how nature behaves. 2 Link to comment Share on other sites More sharing options...
Strange Posted July 9, 2014 Share Posted July 9, 2014 (edited) If the speed of light is invariant to all observers, why isn't the first step in achieving that, that all photons move to a universal frame? If there were a universal frame of reference then any object's velocity (and position) could be defined with reference to that frame of reference. How do you compare either your velocity or position to "light" (the universal frame of reference)? Your speed "relative to light" would always be c (in as much as the concept means anything). But the same is true of every other object in the universe, regardless of their state of motion relative to you. Therefore, you cannot treat light (or the speed of light) as a reference. Unless you assume that all motion is an illusion, or some other weird psychological/philosophical excuse. Also, if light was moving relative to some universal/absolute frame of reference, then we would measure its speed differently depending on our state of motion relative to that universal frame. And that isn't what we observe. Edited July 9, 2014 by Strange Link to comment Share on other sites More sharing options...
Delta1212 Posted July 9, 2014 Share Posted July 9, 2014 Yes, different frames for different observers - but for the photons themselves, do they move relative to their own universal frame? If they do not move to a universal frame, how can the following be explained... Using starlight thousands of years old and created in a different part of the galaxy to us, if it happens to reach us, then we can create some light and compare the two by directing the newly created light so that it is moving parallel to the path of the older starlight. If we were to do this, then we would find that the new light moves at the same speed as the old light. How is this result explained if light does not move to a universal frame? Because it moves at c in every frame. You don't need to have a universal frame in which it is moving at c when it moves at c in every frame. 1 Link to comment Share on other sites More sharing options...
jajrussel Posted August 7, 2014 Share Posted August 7, 2014 When photons move through empty space, they are found to always move at the same speed, i.e. that of the speed of light. This property of 'a single speed' can be demonstrated by the situation of several photons moving parallel to each other, side-by-side, always staying abreast to each other. This is regardless as to how the photons were created, or when they were created. In order for this to be the case, does this mean that light - no matter where it is in the universe and when it was created - is moving to an absolute frame of reference? I have found this conversation to be confusing. This confusion may show up in my questions. I thought that absolute frame of reference specified an objects location based on arbitrary bearings? Are you saying that c should be regarded as an absolute frame of reference? I do notice that the term universal is used rather than absolute later in the conversation, but the two words are not the same even if a / is drawn between to two words. If the old light and the new light are moving through the same medium, would you expect them to be different? If the term vacuum is necessary to define c then I would assume that where it is stated that they will be found to be moving at the same speed, does not necessarily mean c. I realize that my own ignorance plays a large part in my confusion, but I do have another question. You state in, I believe it was post number 5, something to the effect that c is not relevant. That it only matters that the photons are grouped together. Not your exact words, I know, my short term memory is terrible, but if the photons speed is not c and could possibly vary what exactly is to be considered as absolute? Link to comment Share on other sites More sharing options...
between3and26characterslon Posted August 12, 2014 Share Posted August 12, 2014 But the constant speed of light can be noted by observing that two photons moving side-by-side, stay together. That is all that is needed. Why does any other observation, such as our relative motion to light being constant, have to be mentioned? First of all the frame of reference in which the observation is made is one we are at rest in, the speed of light measured in this frame is always c, regardless of which frame you choose to make your measurement in. If light travelled relative to a universal frame we would measure the speed of light to be other than c in the frame in which we make the measurement. This is the principle of relativity. You are the one making unecessary additional (universal) frames. Second, you ask "if two photons are travelling side by side how can this not lead to the conclusion that they are travelling relative to a universal frame" My question to you would be how does it lead to the conclusion there is a universal frame? Does it lead to any conclusion? Can you disprove a negative or just collect enough evidence to show a diferent answer is more likely? Thirdly, This universal frame you are insisting on must by definition be absolutely at rest, what is the frequency of light in this frame. We know the speed of light is constant in all frames but its frequency changes depending on your motion relative to its source so what would the frequency of light be in a universal frame, zero or infinite? (keeping wiht the theme) Fourthly, the point everyone is trying to make is that two photons travelling side by side does not lead to the conclusion there is a universal frame nor does it lead to the conclusion there is not a universal frame... But everthying else we know tells us there is not a universal frame, as many people have explained in many different ways. Link to comment Share on other sites More sharing options...
JesuisSean Posted August 14, 2014 Share Posted August 14, 2014 (edited) If you analyze the idea of motion occurring within an absolute 4 dimensional Space-Time environment, you eventually end up with a full understanding of Einstein's theory of Special Relativity. You also end up producing all of the equations that are related to Special Relativity as well. Meaning, you start with a universal frame of reference, and you place motion within it. But when you fully realize what "motion" actually is, this leads you to some remarkably odd outcomes, meaning, relativistic outcomes. A step by step analysis of motion can be found at http://goo.gl/fz4R0I ( Nine short videos, total 1 hour 39 minutes ) The analysis also reveals that all objects are constantly moving at the speed of light within the 4 dimensional Space-Time environment. ( As mentioned by physicist Brian Greene in his book The Elegant Universe, see The_Elegant_Universe-B.Greene.pdf Motion Through Space-Time pages 26 and 27, all objects are constantly on the move within Space-Time at the speed of light. ) Thus the speed of light is in the picture, so to speak, no matter what. Anyhow.....a step by step analysis of motion, as seen in the few examples above, soon produces all of the equations and so forth. Edited August 14, 2014 by JesuisSean Link to comment Share on other sites More sharing options...
robinpike Posted August 15, 2014 Author Share Posted August 15, 2014 First of all the frame of reference in which the observation is made is one we are at rest in, the speed of light measured in this frame is always c, regardless of which frame you choose to make your measurement in. If light travelled relative to a universal frame we would measure the speed of light to be other than c in the frame in which we make the measurement. This is the principle of relativity. You are the one making unecessary additional (universal) frames. Second, you ask "if two photons are travelling side by side how can this not lead to the conclusion that they are travelling relative to a universal frame" My question to you would be how does it lead to the conclusion there is a universal frame? Does it lead to any conclusion? Can you disprove a negative or just collect enough evidence to show a diferent answer is more likely? Thirdly, This universal frame you are insisting on must by definition be absolutely at rest, what is the frequency of light in this frame. We know the speed of light is constant in all frames but its frequency changes depending on your motion relative to its source so what would the frequency of light be in a universal frame, zero or infinite? (keeping wiht the theme) Fourthly, the point everyone is trying to make is that two photons travelling side by side does not lead to the conclusion there is a universal frame nor does it lead to the conclusion there is not a universal frame... But everthying else we know tells us there is not a universal frame, as many people have explained in many different ways. Perhaps it would help if I reverse the question... If two objects are side by side, and remain so, is it possible that they are NOT in the same reference frame? If it is possible that they are not in the same reference frame, then I will re-assess my conclusion. Link to comment Share on other sites More sharing options...
xyzt Posted August 15, 2014 Share Posted August 15, 2014 (edited) Perhaps it would help if I reverse the question... If two objects are side by side, and remain so, is it possible that they are NOT in the same reference frame? If it is possible that they are not in the same reference frame, then I will re-assess my conclusion. If they are side by side and there is no relative motion, the two objects are at rest in the same reference frame. Do not try (again) to apply the above to light beams, it doesn't apply. Edited August 15, 2014 by xyzt Link to comment Share on other sites More sharing options...
imatfaal Posted August 15, 2014 Share Posted August 15, 2014 Perhaps it would help if I reverse the question... If two objects are side by side, and remain so, is it possible that they are NOT in the same reference frame? If it is possible that they are not in the same reference frame, then I will re-assess my conclusion. I understand frame of reference as meaning a set of coordinates that allow me to make measurements of position, direction, and changes to those under time. What do you understand frame of reference to mean? You are imbuing frame of reference with properties and characteristics (an almost concrete existence which an object either has to be within or not) that the standard definition does not include. Link to comment Share on other sites More sharing options...
robinpike Posted August 15, 2014 Author Share Posted August 15, 2014 I understand frame of reference as meaning a set of coordinates that allow me to make measurements of position, direction, and changes to those under time. What do you understand frame of reference to mean? You are imbuing frame of reference with properties and characteristics (an almost concrete existence which an object either has to be within or not) that the standard definition does not include. I appreciate that I am probably not using the term correctly. I am trying to argue that, because light moves at a constant speed in all frames of reference, this means that light must first be moving at a constant speed to a 'universal frame of reference', as a first requirement to produce that result. Detecting such a 'universal frame of reference' is another question, and shouldn't be used as a blocker to stop the first point being discussed / decided. Link to comment Share on other sites More sharing options...
Delta1212 Posted August 15, 2014 Share Posted August 15, 2014 I appreciate that I am probably not using the term correctly. I am trying to argue that, because light moves at a constant speed in all frames of reference, this means that light must first be moving at a constant speed to a 'universal frame of reference', as a first requirement to produce that result. Detecting such a 'universal frame of reference' is another question, and shouldn't be used as a blocker to stop the first point being discussed / decided. Why does it need to be moving at a constant speed with regard to a universal frame if it has the exact same behavior in every frame? Additionally, two objects moving at the same speed but in different directions are not in the same rest frame. Since light can move in different directions, even if you could establish a frame for light, which you can't, all light would not be in the same frame. Link to comment Share on other sites More sharing options...
swansont Posted August 15, 2014 Share Posted August 15, 2014 I appreciate that I am probably not using the term correctly. I am trying to argue that, because light moves at a constant speed in all frames of reference, this means that light must first be moving at a constant speed to a 'universal frame of reference', as a first requirement to produce that result. Detecting such a 'universal frame of reference' is another question, and shouldn't be used as a blocker to stop the first point being discussed / decided. Why is there a "first requirement"? Why does such a hierarchy need to exist? Link to comment Share on other sites More sharing options...
Strange Posted August 15, 2014 Share Posted August 15, 2014 I am trying to argue that, because light moves at a constant speed in all frames of reference, this means that light must first be moving at a constant speed to a 'universal frame of reference', as a first requirement to produce that result.. If there were an absolute frame of reference, then that frame of reference would see the same speed of light as every other frame of reference. However, there is no reason to think that there is any such absolute frame, is there? Link to comment Share on other sites More sharing options...
Endy0816 Posted August 15, 2014 Share Posted August 15, 2014 (edited) This might be of some help to better understand what happens as you approach c(and in turn the issue with taking measurements at c). http://hyperphysics.phy-astr.gsu.edu/hbase/relativ/muon.html#c3 Edited August 15, 2014 by Endy0816 Link to comment Share on other sites More sharing options...
JesuisSean Posted August 15, 2014 Share Posted August 15, 2014 (edited) Does the single speed of light mean an absolute frame of reference?To clear the picture......1) Yes light moves at a constant speed in all frames of reference.2) But, light does not move at the same speed in all frames of reference.3) Light is, however, still measured as being the same speed in all frames of reference.Light moves across space at the velocity of 300,000 kps.However, if it passes through a hollow tube that is moving across space at say 260,000 kps, that does not mean that the light will be moving relative to the tube at 300,000 kps. But if those in the tube frame of reference measured the speed of the light passing through, they too would measure, 300,000 kps even though the speed of the light is only 40,000 kps relative to the tube. This is due to the tube, at this velocity, having contracted from a 300,000 km length to 150,000 km, and clocks 2A and 2B are now ticking at half speed, and clock 2A is ahead of clock 2B by 0.866 of a second. Thus when they use their measurements instruments ( The clocks, and the tube used as a ruler. ) to measure the speed of light, they get the usual result of 300,000 kps. This occurs no matter which way the light passes through the tube. Edited August 15, 2014 by JesuisSean Link to comment Share on other sites More sharing options...
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