The discussion revolves around the light clock problem in special relativity (SR), particularly focusing on the interpretation of light clock diagrams and the paradoxes they may present. Participants explore the implications of these diagrams on our understanding of time dilation, the behavior of light, and the nature of measurements in different frames of reference.
Participants express a range of views, with no consensus on the interpretation of light clock diagrams or the implications of the light clock problem in special relativity. Disagreements persist regarding the nature of light paths, the validity of the diagrams, and the application of time dilation.
Participants note that the discussion involves complex interpretations of light behavior, measurement challenges, and the foundational principles of special relativity, which may not be fully resolved within the thread.
altergnostic said:It is real in all frames, but an "observer" can't assign coordinats of events he is not aware of. Those light paths are not seen by a distant observer, so he can't diagram them. If you want him to know the times of the reflections, you have to send him a signal at each reflection event. As it is, the light clock diagram assumes he can actually see those light paths, which easily leads to paradoxes. Also notice that if he really sees those light paths at an angle he will actually measure light going faster than c, and only after the transforms will he have a dilated time and the speed of light normalized to c. But SR and experiment shows that no observer can measure light going faster (or slower) than c. That's why he should use light that reaches him directly, which he will directly measure going at c, to do the transforms in the first place.
bahamagreen said:OK... so I think what you are saying is that the light clock diagram must be viewed as an inferred and possibly flawed interpretation of what is remotely happening, not an existential representation.
If so, and the paradox stems from the current diagram, can the diagram be saved by altering it or is there no proper diagram possible for representing the remote behavior of the light path?
marty1 said:Please explain how photons are never given momentum from the source but a change in frequency due to the momentum of the source yet can be given the lateral momentum of the sideways motion of the source to cause them to continue across the moving lab and still hit the mirror and come back to the detector.
marty1 said:Please explain how photons are never given momentum from the source but a change in frequency due to the momentum of the source yet can be given the lateral momentum of the sideways motion of the source to cause them to continue across the moving lab and still hit the mirror and come back to the detector.
marty1 said:But it not just the maximum they cannot exceed in the direction of travel. They also cannot be slowed down when emitted from a source moving away. They are instead red shifted. Momentum in every other direction seems to be completely Newtonian. Do they "know" which direction they are heading and follow different laws? Do they have a head and a tail?
Sure, but I have a hard time taking this as a serious objection. That should be an obvious and trivially understood part of the operation of any clock. Any clock has an oscillator of some sort (Caesium atom, quartz crystal, pendulum, etc.) and a mechanism for signalling the results (dial with hands, digital display, broadcast signal, paper printout, etc.). When you analyze the physics of a specific clock, you analyze the oscillator part, as is traditonally done with a light clock. It is understood that the oscillation can be reported in any number of ways.altergnostic said:It is real in all frames, but an "observer" can't assign coordinats of events he is not aware of. Those light paths are not seen by a distant observer, so he can't diagram them. If you want him to know the times of the reflections, you have to send him a signal at each reflection event.
No true paradoxes have been found in over a century of careful scrutiny by the most brilliant minds in the world. All that have been found are unintuitive things which confuse students, many of which are hyperbolically advertised as paradoxes.altergnostic said:As it is, the light clock diagram assumes he can actually see those light paths, which easily leads to paradoxes.
Austin0 said:The result is the vector is tilted forward in the direction of motion in the lab frame.
Austin0 said:This is not correct. The observed diagonal paths in HarryLin's proposed set up would always produce c as a direct calculation of the distance and detection times (D/dt5) in the LAB frame.
No transformation whatsoever required in that frame.
Exactly as would be the case if the mirror was removed and the photon continued on to a detector at rest in the lab frame.
Nugatory said:We scatter observers, at rest relative to each other and carrying synchronized clocks, throughout space. Whenever anything happens right under an observer's nose, so only local considerations apply, the observer writes down what happened and the time it happened on a slip of paper. At some later time, we collect all the slips of paper and piece together a complete global picture.
We do all of this, and where's the paradox? The local angle each observer reports is exactly what you get by Lorentz-transforming from what observers at rest relative to the mirrors see.
marty1 said:Ok I understand how that all works out nice mathematically, but a photon changing direction of emission depending on velocity of source?
marty1 said:Again you are imparting the sideways momentum of the lab onto the photon (sideways meaning the labs toward direction which is sideways to the sideways fired photon). That is where I get lost.
altergnostic said:I don't know if I have followed your reasoning, are you saying that the final diagram will agree with the stationary frame diagram?
DaleSpam said:Sure, but I have a hard time taking this as a serious objection. That should be an obvious and trivially understood part of the operation of any clock. Any clock has an oscillator of some sort (Caesium atom, quartz crystal, pendulum, etc.) and a mechanism for signalling the results (dial with hands, digital display, broadcast signal, paper printout, etc.). When you analyze the physics of a specific clock, you analyze the oscillator part, as is traditonally done with a light clock. It is understood that the oscillation can be reported in any number of ways.
Once you know that the detection occurred then you may use any reference frame to analyze the clock. There is no requirement to use a frame where the clock or the observer is at rest. Everything else follows.
No true paradoxes have been found in over a century of careful scrutiny by the most brilliant minds in the world. All that have been found are unintuitive things which confuse students, many of which are hyperbolically advertised as paradoxes.
marty1 said:So the emitted photon does carry the momentum of the source in its movement 90 degrees from its direction of travel.
I think you are right in that the fact that the speed of light is independent of the motion of the source should be expanded to include the fact that the direction of propagation is not also independent. With the elaboration of its effects, the relativistic aberration, that is certainly relevant to the light clock and it's understanding.altergnostic said:Well, it should be obvious, but (as you point out at the end of your post) many "less brilliant" minds don't find it so obvious, so why not diagram the setup more realistically? Einstein usually tried to do so, and usually using many different thought problems and examples to explain the same thing. He is the one who said that if you can't explain something to a six year old, you have not understood it yourself. The point is that the propagation of the signals, or, the times of observations of each tick of the clock from the moving frame point of view, must enter the equations. As it is, they are left out. There's no consideration of the distance between the light clock and the observer in the moving frame, and neither any consideration of the time it takes for each event to be observed by the moving frame. As it is, the observer is assumed to instantaneously see each event, which is very not-SR.
Exactly! So exactly at what x,y,z,t coordinates does the observer know the detection (reflection in the light clock) has occurred? In other words, at what time and relative position does the observer actually observes the events? Is this irrelevant to this problem? Why is it irrelevant here and relevant in problems like the train and embankment?
I actually almost agree with this. There is no true paradox if you remember to send signals to the observer, since the final result is correct regardless. But as it is the assumptions are unreal and impossible. You can't diagram unseen light, it is simple as that. Of course you are bound to find a lot of unintuitive things and confused students since the diagram is unintuitive and confused to start with. It is at least incomplete, and it is never diagrammed realistically and complete. We never see any analysis of how the observer knows about those paths, how he sees them, from what distance, and at what times, etc. Even though we have a lot of confused students, we keep the diagram incomplete. Why? Why not remember them that they need to signal the events to the observer somehow? Why do we allow students to wonder how the motion of the emitter can affect the direction of the beam without changing the beam's velocity (very counter-intuitively), in seemingly contradiction with the postulate of SR that the motion of emitter doesn't affect the speed of light? How are they not to get confused? We have many animations on the web showing how the motion of an emitter compresses the frontal waves and stretches the trailing waves, creating Doppler, and those diagrams show no change in the direction of the emitted light due to the motion of the source, so how are they to believe both diagrams without confusion?
You admitted that we need to send signals at each tick of the light clock if we want the observer to diagram anything. So if just remembering that reflection events are not seen directly helps to make some sense of the diagram, why not do so? If you actually need to signal the reflection events to the moving observer, those signals have to travel some distance until they reach the observer, after some time from the moment of emission. The students would immediately relate the problem to the famous train and embankment, for example, and it would be easier to comprehend. And also, the moving observer wouldn't diagram those diagonal paths in such a setup at all. You would apply the transforms on the incoming signals and the light clock's beam would be diagrammed straight up and down. No angles. No confusion.
If you still think the diagram is perfect and it is the students that fail, you are not trying to make a comprehensive diagram, or to make SR easier to understand, you are just trying to flunk them.
Austin0 said:Yes. If it is emitted at 90 deg. relative to motion in the source frame the forward momentum will result in the path pointing at some angle forward in an observing frame.
Nugatory said:The final diagram will agree with the stationary frame diagram if the speed of all these observers happens to be the speed of the light clock. Otherwise it will agree with one of the moving frame diagrams.
But nothing prevents me from doing this "scatter observers, at rest relative to each other and carrying synchronized clocks" thing multiple times using a different speed for each flock of observers... And I can still gather up all those slips of paper and correlate them. So I'll get to see the exact same light-hits-mirror event as reported from both the stationary frame and as many different moving frames as I please.
I cannot say this strongly enough: get hold of and understand the relevant chapter of that Taylor/Wheeler book. It will extract you from the "what's a frame?" quagmire that you've fallen into like nothing else can.
Austin0 said:I think you are right in that the fact that the speed of light is independent of the motion of the source should be expanded to include the fact that the direction of propagation is not also independent. With the elaboration of its effects, the relativistic aberration, that is certainly relevant to the light clock and it's understanding.
As for the rest; you may have a certain point but it should be clear that certain unrealistic aspects of most thought experiments are not really relevant to their aid as constructs for understanding. IMO
marty1 said:So I post my question again. What is special about the "sides" of a photon that permit the source to give it momentum but any attempt to do that in the direction of propagation results only in red or blue shift?
It seems that from the side a photon is no different from any other particle.