Comparing Event Occurrence Across PORs

[ghwellsjr]

I might need to add some kind of 'intergalactic dust' to my diagram, in order to be able to ask what i want to ask, but still there is probably a distance to make, before i am sure, the scenario i want to represent, is coherent.

In order for that to happen, what i want to ask now, is this:
Regarding slow transport:
I do not understand how to separate into categories three 'kinds' of 'explanations' or 'terms' which are: 'slow transport', 'coordinate system', 'proper time' and 'rest frame':

1.It is a mathematical error to assume there is a rest frame.
2.There is no mathematical problem assuming a rest frame, but experimentally this rest frame never appears.
3.Under the mathematical description used by SR, which interprets experimental results, the term 'rest frame' has no meaning.

The biggest problem i might have, when trying to understand this, is related with number 3 and with the notion (that is probably an error of understanding on my side), that there is a legitimate situation where one can say: this or that question has no meaning, under such and such terms, conditions or situations.

I am saying all that, because i want to ask: under what 'kind' of explanation (1,2,3 or another or a combination) would this question fall:

Is the speed of light the same or is it not the same when moving 'between' the frames or reference? Does the speed of light change or does it not change when it is moving from one FOR to another?

Somehow, i had the notion, that the answer to that question is number 3: 'This question has no meaning', since a rest frame does not appear in experiments, or for other reasons. If this is the case, i don't understand what 'has no meaning' means, and i have to put some intergalactic dust in my diagram, so i can ask the question in more coherent terms.

These more coherent terms, are supposedly relevant, since they are, supposedly (and probably by error) able to bring up a scenario that proves, that you can only say: 'Yes light speed changes when moving between FORs' or you can say: 'No, light speed does not change when moving between FORs', and most important, that there is no 'middle' possibility e.g. to say that there is 'no meaning' to this question.

Just like your original question about Point of View can have different meanings depending on context, the term "rest frame" can have different meanings and I'm not sure what you are asking about so I will try to give a bunch of different answers and you can figure out which one applies.

Between the time of Maxwell's equations and Einstein's theory of Special Relativity, scientists believed that light traveled at c only in a single rest frame that they assumed was fixed in space and absolutely at rest and they developed the Lorentz Ether Theory around this idea. There is nothing mathematically or experimentally wrong with this theory except, as you point out, it's impossible to identify that state of absolute rest but, almost assuredly, we are never at rest in it.

Einstein turned this all around and said you could consider any inertial state to be just like the elusive ether rest frame in which light propagates at c. This enables him to build up a consistent coordinate system involving both time and distances in which to describe and analyze any scenario we desire. As a result of this, it has become common practice to use the term "rest frame" to mean a frame in which an inertial observer is at rest. Nowadays, when someone uses that term, that is what they mean. So you will see people say, "In Alice's rest frame, Bob is moving at 0.5c," for example. Then they might say, "In Bob's rest frame, Alice is moving at -0.5c." But note that Alice and Bob are in both frames. We don't mean that Alice's rest frame is owned by Alice or exclusive to Alice in any way or that it gives her more insight into what she can see or measure.

Einstein also established a way to calculate how the coordinates for events in one inertial frame can be transformed into the coordinates for the same events in a second inertial frame moving with respect to the first frame but you only use one frame at a time. This process is called the Lorentz Transformation. You shouldn't think of an observer starting out in one inertial frame and then moving to another inertial frame. An observer can start out at rest in one inertial frame and then accelerate up to some speed, but he is still in that same frame.

So now getting to your questions about the speed of light in different frames. Just like you shouldn't think of an observer moving from one frame to another frame just because he accelerates, you shouldn't think about light moving from one frame to another frame. Remember, Einstein's concept of a Frame of Reference is one in which light is defined to propagate at c. So there is no question about the speed of light in any frame, it is c by definition. So when you start with one FoR to describe and analyze a bunch of events in a scenario, light is traveling at c in that FoR. If you use the Lorentz Transformation to transform the coordinates of all those events into a second FoR moving with respect to the first one, the speed of light is c in that second FoR.

The bottom line is that in Special Relativity, the speed of light in a frame has meaning because we give it meaning through a definition and, as such, it is not subject to experimental proof. Of course, if it didn't comport with reality, then it would be a useless theory, but that hasn't happened.

 

[whosapopstar?]

Let me also ask this: what exactly 'happens' in the slow transport technique, that doesn't enable to establish a coordinate systems and the c definition?

You use 'definition', which i interpret as 'mathematical definition', which i ascribe as possibility no.1, but then isn't it actually possibility no.2? e.g. experimental results? But you explicitly write:

"Once we adopt Einstein's theory of Special Relativity, we can see that the slow transport of clocks does not result in the same time on them as what we need for Coordinate Time except in a particular rest frame."

This means what? that possibility no.1 must always come before possibility no.2? isn't time dilation, an experimental result that can be established also with the slow transport technique? which you say that does not enable to establish a coordinate system? where is the heads and where is the tails here?

 

[yoron]

"1.It is a mathematical error to assume there is a rest frame.
2.There is no mathematical problem assuming a rest frame, but experimentally this rest frame never appears.
3.Under the mathematical description used by SR, which interprets experimental results, the term 'rest frame' has no meaning."

Nice thinking W (with the very long name that I now shorten to W)

You are right in that it is a arbitrarily made definition in Relativity, as long as we're not discussing local 'accelerations' in where you always will be able to define 'who did what'. But it has a, very local, meaning. Just as you are free to define the 'uniform motion' to you, you can, in part, or for the whole define it to your 'counterpart' when measuring.

And to measure a 'time' you need the 'local clock'. As that is the 'clock' you tick by, for real, or at least as 'real' as we can get it. You could ignore your own arrow of time of course, instead measuring by using other 'frames of references' clocks, but that would become a conceptual exercise, leaving yours undefined as long as you don't know all gravitational settings and the 'relative motion' of all involved.

As for relative motion it has no relevance to what you measure lights speed as. You can take how much 'time' you like to get from A to B and your local measurement using your local clock will always give you 'c' as far as I see.

In Relativity an acceleration is equivalent to 'gravity', and just as with the NIST experiments we know that different 'gravity' will deliver different 'clock rates' relative the observer studying those clocks. That's also the reason why in a two way experiment you can get different values for lights speed in a vacuum, as you will have a constantly varying 'gravity' in any (non-uniform) acceleration, as well as different time rates, depending on the clocks 'elevation' inside the spaceship, just as Earthside relative a clock in the atmosphere.
==

You can assume a uniform constant acceleration of course, at one gravity for example. But then you still will have that 'elevation', giving different clock rates, to consider when measuring the speed of light. Find a way to make a 'one way' measuring of lights speed in a vacuum and that problem should disappear, as I think of it :)

Or maybe not :
I really need to think about this one.

 

[whosapopstar?]

Please note that in this thread, including the diagram at the beginning and all of the text, personally i never refer to acceleration, but only to constant speed.

 

[yoron]

NP :)

But your original question has been answered, hasn't it?
"Is it possible for an event to occur in one POR and never occur in another POR?"

That has to do with lights speed in a vacuum. If you get no information from an event then there is no way you can validate that it happened. As long as nothing stops that light from reaching you you will be able to observe it.

You can if you like take a philosophical stance here and ask yourself what defines SpaceTime. Is it all of it? Even those places wherefrom no information can be got, or should we define it to what we experimentally can observe?

Relativity defines it from observations based on experiments proving them. Even though I can imagine/assume 'places' and 'events' that won't exist for us observing, they become superfluous in any description based on what we actually can observe.

But philosophically it's a very valid question.

 

[whosapopstar?]

Did not get yet to the scenario i wanted to represent, that brought me to ask the initial question about an event.
i need first to understand very clearly a few things:
let's go back again to George writing:

"Once we adopt Einstein's theory of Special Relativity, we can see that the slow transport of clocks does not result in the same time on them as what we need for Coordinate Time except in a particular rest frame."

Does it mean that time dilation can be proved to exist, without having a coordinate system?
i conclude this, because of "does not result in the same time on them as what we need for Coordinate Time", does it mean that time dilation can be proved to exist, without having a coordinate system and 'although' (so to speak) we are regarding only a particular rest frame and also as well, are using a slow transport technique?? and yet can observe this phenomenon of time dilation?

 

[ghwellsjr]

Did not get yet to the scenario i wanted to represent, that brought me to ask the initial question about an event.
i need first to understand very clearly a few things:
let's go back again to George writing:

"Once we adopt Einstein's theory of Special Relativity, we can see that the slow transport of clocks does not result in the same time on them as what we need for Coordinate Time except in a particular rest frame."

Does it mean that time dilation can be proved to exist, without having a coordinate system?
i conclude this, because of "does not result in the same time on them as what we need for Coordinate Time", does it mean that time dilation can be proved to exist, without having a coordinate system and 'although' (so to speak) we are regarding only a particular rest frame and also as well, are using a slow transport technique?? and yet can observe this phenomenon of time dilation?

You don't need a coordinate system to prove that accelerating a clock will result in less time accumulating on it after you bring it back to an identical clock that remained inertial. You also don't need a coordinate system to prove that accelerating a clock will result in a position change with respect to time. But in both cases, unless you establish a coordinate system, you will have a hard time making accurate calculations or precise predictions about what that clock is doing or will do, both in terms of its changing location and in terms of its displayed time.

Einstein's theory of Special Relativity meets that need both in terms of precisely and consistently defining the meaning of coordinate space and the meaning of coordinate time for a particular Frame of Reference and it does this by assigning the propagation of light to be c in that frame. The slow transport of a clock that starts out at rest with coordinate time on it will deviate by a known small calculable amount from the coordinate time in a new location, as we learn from SR.

Let's think about an observer who is measuring the round-trip speed of light using a single clock colocated with a light source and a mirror some measured distance away. No matter what his state of inertial motion in our particular Frame of Reference, we know from experiment and from theory that he will get c. But we also know from theory that his clock is dilated as a result of his motion in that frame and that he is totally unaware of this fact and also of the fact that the light is not taking the same amount of time to go from his clock to his mirror as it takes to come back from his mirror to his clock. So if he uses the slow transport of a clock to determine the time that the light arrives at the mirror, he will get the wrong answer.

 

[Passionflower]

Let's think about an observer who is measuring the round-trip speed of light using a single clock colocated with a light source and a mirror some measured distance away. No matter what his state of inertial motion in our particular Frame of Reference, we know from experiment and from theory that he will get c.

It won't be c in curved spacetime.

 

[whosapopstar?]

Let's put aside acceleration for a moment.
Let's put aside slow transport for a moment.

I think this is important for me to understand at this point:

Can time dilation at constant speed (not acceleration) be proved to exist, without the need for a coordinate system?

 

[ghwellsjr]

Let's put aside acceleration for a moment.
Let's put aside slow transport for a moment.

I think this is important for me to understand at this point:

Can time dilation at constant speed (not acceleration) be proved to exist, without the need for a coordinate system?

Of course, the muon experiment was the first but since than many experiments done in particle accelerators prove time dilation without any consideration for establishing a Frame of Reference.

 

[whosapopstar?]

i might be ready to ask the question:
Here is the diagram again, this time with hypothetical gas or dust (assume spread even etc..) that enables every spaceship in the group 'spaceship x' to see the light beam sent from Earth to spaceships 1,2,3.

If light would have changed it's speed when 'moving' or 'changing' FOR's (and no matter what is the FOR first to observe this change), wouldn't that be considered an event? If so, wouldn't the spaceships in 'spaceship x' group, be able to observe this event as well?

Now, maybe i am adding at this point one more error on top other errors,
anyway, i will assume that no one of the spaceships in 'spaceship x' group will observe any such event.

So this must exclude the possibility that light changes its speed in any circumstance or combination. Doesn't it?

Now to add one more error on top of that, i ask, something changing its speed is excluded, how come we will still be left with two options: not defined and does not change its speed, and not only with the option : does not change its speed. If up to this point by some miracle i don't have errors, than how come this last possibility could exist? Does it take us back to a coordinate system oriented problem somehow?

Thanks.

 

[ghwellsjr]

i might be ready to ask the question:
Here is the diagram again, this time with hypothetical gas or dust (assume spread even etc..) that enables every spaceship in the group 'spaceship x' to see the light beam sent from Earth to spaceships 1,2,3.

I'm assuming the light beam is turned on at some point in time and it's the progress of this turn-on transient that the different spacecraft are measuring, correct? So how does dust provide any more information? All it will do is diffuse and scatter the light after the turn-on transient but it won't help the timing at all.

If light would have changed it's speed when 'moving' or 'changing' FOR's (and no matter what is the FOR first to observe this change), wouldn't that be considered an event? If so, wouldn't the spaceships in 'spaceship x' group, be able to observe this event as well?

You have described one FoR. That's what your diagram is, correct? Where are these other FoR's? If you also want to have each spaceship define their own FoR, they have to do it before the flash of light gets to them, long before. Then in each of those FoR's, they will have their own synchronized clocks at both detectors but each of those FoR's will extend out to include all the other spaceships and the Earth and the flashlight and they will each have their own coordinates for what is happening. All these coordinates in each FoR will be different but the speed of light will be constant in each FoR because that's how we define a FoR. You can't avoid that or get around that. It is a mistake to analyze a problem where you have different FoR's for different parts of the scenario which is what you are attempting to do. So the light never switches between FoR's. To do it properly, you should start with your original FoR and then transform all the events into each of the other FoR's and see what happens but the Lorentz Transform guarantees that the speed of light is a constant in each FoR so it will be a lot of work to prove what we already know to be the case.

Now, maybe i am adding at this point one more error on top other errors,
anyway, i will assume that no one of the spaceships in 'spaceship x' group will observe any such event.

So this must exclude the possibility that light changes its speed in any circumstance or combination. Doesn't it?

Now to add one more error on top of that, i ask, something changing its speed is excluded, how come we will still be left with two options: not defined and does not change its speed, and not only with the option : does not change its speed. If up to this point by some miracle i don't have errors, than how come this last possibility could exist? Does it take us back to a coordinate system oriented problem somehow?

Thanks.

Please go back and study my responses to you in the other thread, I have already explained everything in detail there. You might also explain why you think dust makes any difference.

 

[whosapopstar?]

i was assuming that the dust would scatter the light across the universe and out of the beam path. i was assuming that no matter if a spaceship within the path can calculate or observe under certain conditions an event of light changing its speed, a spaceship outside the path, no matter the transformation to be calculated, will never observe or calculate this event of light when changing its speed.

On the other hand, if you tell me that at constant speed, no FoR, with or without using a transformation, will observe any chage in light speed, it just 'short-cuts' the scenario to the same question: how come this does not prove the one way speed of light to be constant? i guess you will reply that the answer was already given. Well, i am having trouble understanding this. But it is probablly only because i am having trouble making the transformation, so to speak, from spoken words and imagined visualisations to mathematics and vice versa.

b.t.w i did understand your very clear explanation at the other thread, and you are probably correct to say that what i am trying is to "...analyze a problem where you have different FoR's for different parts of the scenario which is what you are attempting to do." but i seem to have a problem understanding by which physical and mathmatical rules: "You can't avoid that or get around that. It is a mistake to analyze a problem where..".

 

[ghwellsjr]

i was assuming that the dust would scatter the light across the universe and out of the beam path. i was assuming that no matter if a spaceship within the path can calculate or observe under certain conditions an event of light changing its speed, a spaceship outside the path, no matter the transformation to be calculated, will never observe or calculate this event of light when changing its speed.

But all your spaceships are inside the path so can we forget about the dust?

On the other hand, if you tell me that at constant speed, no FoR, with or without using a transformation, will observe any chage in light speed, it just 'short-cuts' the scenario to the same question: how come this does not prove the one way speed of light to be constant? i guess you will reply that the answer was already given. Well, i am having trouble understanding this. But it is probablly only because i am having trouble making the transformation, so to speak, from spoken words and imagined visualisations to mathematics and vice versa.

There is no proof that the one-way speed of light is constant in all reference frames. It doesn't need a proof. It only needs to be shown that it is consistent with all the experimental evidence. In Lorentz's Ether Theory, the one-way speed of light is not constant in all reference frames, it is only constant in the rest state of the ether. There is also no proof for that idea. It only needs to be shown to be consistent with all the experimental evidence, which it is. There is no proof that will help us determine which of the two theories, SR or LET (or some other theory) is true and all others false. We cannot know how light propagates because we don't have anything faster than light to enable us to track its progress. So, based on our implicit or explicit assumptions, we can build a consistent theory. LET assumes that light travels at c only in the fixed ether and arrives at the conclusion that since we are never at rest in the ether, our rulers are contracted in some unknown way and our clocks are dilated by some unknown amount. SR boldly asserts that light travels at c in any inertial frame and concludes that if we are stationary in that frame then our rulers are not contracted and our clocks are not dilated. You get to choose which theory you like, there is no proof one way or the other.

b.t.w i did understand your very clear explanation at the other thread, and you are probably correct to say that what i am trying is to "...analyze a problem where you have different FoR's for different parts of the scenario which is what you are attempting to do." but i seem to have a problem understanding by which physical and mathmatical rules: "You can't avoid that or get around that. It is a mistake to analyze a problem where..".

 

[whosapopstar?]

OK.
There is a reason for differentiating spaceships 123 from group x and hence adding this nagging dust stuff. Perhaps a wrong reason, but i need to understand why it is wrong. i will try to explain my thoughts again later, perhaps this issue needs a few days of rest.

 

[whosapopstar?]

The reason for differentiating between: 1. the straight path of light from 'Erath' to spaceships 1,2,3, and: 2.'Spaceship X' group, is simplification.

If we want to discuss some kind of constellation (FoR or other), where light can change its speed, we should use, only the straight path of the main light beam, and the straight path of spaceships 1,2,3 inside this main-straight light path. On the other hand, if we want to discuss this event, of light changing its speed, it is a binary question: Did this event occur or did it not? Hence in that case, we will use 'space ship x' group and the hypothetical-artificial-imaginary dust, that enables the events that occur inside the straight path, to reach 'space ship x' group. Because this group deals only with a binary question (event occurred or not), we will not have to bother ourselves with angel calculations of light reaching there (these calculations will be made only inside the straight path). This is why my first question in this thread was: Is it possible for an event to occur in one FoR and never occur in another FoR?

Was this question that i am asking, already been asked by me before? i don't think so.

If i already got the answer for this very question, in the near past, in this forum, and so many times before, maybe that explanation can improve, since i seem to 'restart' the whole issue every other day, and cannot seem to recall a stable answer.

Please, only someone that can explain this to me very patiently.

Thanks.

 

[ghwellsjr]

if we want to discuss this event, of light changing its speed, it is a binary question: Did this event occur or did it not? Hence in that case, we will use 'space ship x' group and the hypothetical-artificial-imaginary dust, that enables the events that occur inside the straight path, to reach 'space ship x' group. Because this group deals only with a binary question (event occurred or not), we will not have to bother ourselves with angel calculations of light reaching there (these calculations will be made only inside the straight path). This is why my first question in this thread was: Is it possible for an event to occur in one FoR and never occur in another FoR?

You are misusing the word "event".

In Special Relativity, "event" only has meaning within the context of the very specific definition of a Frame of Reference and refers to a point in spacetime consisting of three coordinates of space and one coordinate of time. In other words, it refers to an instant of time at one point in space. When you transform the four coordinates defined in one FoR into the four coordinates of a second FoR moving with respect to the first one, you will get a different set of numbers but it's the same event. There is no event that you can specify in the first FoR that can't be transformed into any other FoR moving with respect to the first FoR.

So "event" is more restrictive than our popular use of the term "event" which would be more appropriately called a "happening" such as a football game or a trip to Disneyland that takes place over an extended period of time and covers a broad region of space.

So when you ask about the "event" of light changing its speed, I have to ask what the coordinates are for this "event" and what Frame of Reference you are using?

If you give me some coordinates for an event, such as, t=35224, x=43435, y=63345, z=2975 in one FoR and you want to know what the coordinates are in a second FoR moving along the x-axis at v=0.2346c, then I can run these numbers through the Lorentz Transform and tell you that the coordinates in the second frame are t'=25752.9 x'=36181.2, y'=63345, z'=2975 for that same event. There are no numbers that you can give me that won't transform, provided that v is less than c.

But I have to reiterate something that I have said over and over again in this thread (post #31, #33, #37, #42, and #44) and answered to your satisfaction in post #14 in your other thread: in Special Relativity, the speed of light is defined to be c in any Frame of Reference you choose.

So please don't misuse the term "event" and whether an event in one FoR can exist in another FoR if you are trying to understand why the propagation of light is defined to be c in all Reference Frames. And if that is what you really want to know, then tell me why you were satisfied with my answer in post #14 of your other thread and now you are not satisfied.

 

[Mentz114]

Is it possible for an event to occur in one FoR and never occur in another FoR?

It depends how you define 'event' ( as George says above).

If you define an event in terms of the relationship between worldlines, then if it happens in one FoR it happens in all.

I'm not sure if 'light changing speed' can be described in those terms.

 

[whosapopstar?]

The explanation that George gave was indeed very clear.

But my question departs from the rest of your explanation, exactly where you show that having a result of light-speed as ∞, is a problem.

i see how this problem that you describe, to measure a numerical value for the one way speed of light, appears.

But on the other hand i ask, why is this not a great opportunity to prove that, although without regard to a specific numerical measurement value, still, a speed measurement of ∞ for light, in that very configuration presented by George, enables us to prove that there is no change in the one way speed of light.

How can it be possible to exclude a change of speed, without regarding a specific numerical value, you might ask? Well, why should it be wrong to say this:

Let us assume that light changes its speed when traveling inside the boundaries of detectors 1 and 2 of spaceship 3. Then, within the boundaries of spaceship 2, we will use the exact same method that George explained with wires and one clock, but using the configuration that gave us ∞ speed (clock always at the end). Now, we will not get an ∞ result any more, as the measurement of light speed made inside the boundaries of detectors 1 and 2 of spaceship 2. When assuming such a scenario, that light changed its speed between the two detectors of spaceship 3, we will measure a negative or a positive result for light speed (depends if we assume faster or slower light speed inside the boundaries of spaceship 3).

But we know from experiments, that we will always get ∞, as a measurement result for the speed of light within the boundaries of spaceship 2. Hence this initial assumption, that the one way speed of light can change, is wrong. Hence there is always an implicit assumption, that light never changes its one way speed, although we cannot measure a numerical value for that one way speed.

Where is the error in this chain of arguments?

Thanks.

 

[GeorgeDishman]

I think this is important for me to understand at this point:

Can time dilation at constant speed (not acceleration) be proved to exist, without the need for a coordinate system?

The "time dilation" factor is the ratio of the coordinate time between two events in one frame and that between the same events in a different frame which means time dilation is only defined if you have a minimum of two different coordinate systems.

 

[whosapopstar?]

The "time dilation" factor is the ratio of the coordinate time between two events in one frame and that between the same events in a different frame which means time dilation is only defined if you have a minimum of two different coordinate systems.

Apparently there is a disagreement here. Please refer to a muon experiment, brought up earlier in this thread.

 

[GeorgeDishman]

The "time dilation" factor is the ratio of the coordinate time between two events in one frame and that between the same events in a different frame

Apparently there is a disagreement here. Please refer to a muon experiment, brought up earlier in this thread.

There are no details in the previous mention but I guess it is referring to the fact that the rest frame lifetime is 2.2us while it is longer if they are moving at high speed. The dilation factor is their lifetime in the lab frame relative to that in their rest frame.

If you are using some alternative definition of "time dilation", please let me know, I'm assuming the usual terminology.

 

[whosapopstar?]

There are no details in the previous mention but I guess it is referring to the fact that the rest frame lifetime is 2.2us while it is longer if they are moving at high speed. The dilation factor is their lifetime in the lab frame relative to that in their rest frame.

If you are using some alternative definition of "time dilation", please let me know, I'm assuming the usual terminology.

i guess, this means there is no need to consider reults of any other measurement lab moving at constant speed, besides your own lab, in order to prove the existence time dilation.

 

[GeorgeDishman]

i guess, this means there is no need to consider reults of any other measurement lab moving at constant speed, besides your own lab, in order to prove the existence time dilation.

If the universe were Galilean invariant, there would be no time dilation effect, the ratio would always be 1, so you do need experiments to confirm it. The definition is based on the relationship between two coordinate systems either way so I think you just need to be clear as to what question you are asking.

 

[ghwellsjr]

The explanation that George gave was indeed very clear.

For the sake of others reading this, the explanation you are referring to is here.

But my question departs from the rest of your explanation, exactly where you show that having a result of light-speed as ∞, is a problem.

i see how this problem that you describe, to measure a numerical value for the one way speed of light, appears.

But on the other hand i ask, why is this not a great opportunity to prove that, although without regard to a specific numerical measurement value, still, a speed measurement of ∞ for light, in that very configuration presented by George, enables us to prove that there is no change in the one way speed of light.

How can it be possible to exclude a change of speed, without regarding a specific numerical value, you might ask? Well, why should it be wrong to say this:

Let us assume that light changes its speed when traveling inside the boundaries of detectors 1 and 2 of spaceship 3. Then, within the boundaries of spaceship 2, we will use the exact same method that George explained with wires and one clock, but using the configuration that gave us ∞ speed (clock always at the end). Now, we will not get an ∞ result any more, as the measurement of light speed made inside the boundaries of detectors 1 and 2 of spaceship 2. When assuming such a scenario, that light changed its speed between the two detectors of spaceship 3, we will measure a negative or a positive result for light speed (depends if we assume faster or slower light speed inside the boundaries of spaceship 3).

But we know from experiments, that we will always get ∞, as a measurement result for the speed of light within the boundaries of spaceship 2. Hence this initial assumption, that the one way speed of light can change, is wrong. Hence there is always an implicit assumption, that light never changes its one way speed, although we cannot measure a numerical value for that one way speed.

Where is the error in this chain of arguments?

Thanks.

Even if the speed of light changed between the two detectors of spaceship 3, we have to assume that the speed of the electrical signal traveling down the cable changes by exactly the same amount (electrical signals and light are both electromagnetic phenomenon obeying the same laws) and that this happens for both spaceships which means they will both still measure ∞ for the speed of light. Remember, a speed of ∞ simply means that the light traveled from detector 1 to detector 2 in the same amount of time that the electrical signal traveled the same distance. It really doesn't matter what the actual speeds are or even if they change as long as they are the same and change the same.

 

[ghwellsjr]

The "time dilation" factor is the ratio of the coordinate time between two events in one frame and that between the same events in a different frame which means time dilation is only defined if you have a minimum of two different coordinate systems.

Apparently there is a disagreement here. Please refer to a muon experiment, brought up earlier in this thread.

There is no disagreement here.

When Einstein defined the meaning of τ (tau, which is Proper Time) in the middle of section 4 of his 1905 paper, he used two coordinate systems. But later in the section, when he applied that definition to his introduction of the Twin Paradox, he used only one coordinate system.

So time dilation is the ratio of t (Coordinate Time) to τ (Proper Time) for a clock moving in a single coordinate system. You can also arrive at the same conclusion by going back to the original definition involving two coordinate systems in which the Proper Time for the clock moving in one coordinate system becomes the Coordinate Time for the clock at rest in the second coordinate system.

But I was making the point in post #37 that time dilation can be proven without establishing any coordinate system, simply by enacting the twin paradox--two synchronized clocks at mutual rest, one takes a trip and comes back with less accumulated time on it.

 

[whosapopstar?]

What i meant was that,
Let's assume that while both the electric cable signal and light aboard spaceship 3, move at the same rate and reach spaceship 3 clock together, the electric signal in the cable on spaceship 2 (regard, another separate cable), always moves at another constant rate, all the way from the detector to the clock on spaceship 2, even when the electric signal is moving 'under' spaceship 3. i assume that its only light that changes its rate, while on a single path- e.g. when in spaceship 2 and outside spaceship 3, its speed is constant, equal in both sides and different from its constant speed between the detector and clock of spaceship 3. Then i prove that this is not possible, and then i conclude that light does not change its speed as a result of the difference of constant speed between spaceship 2 and spaceship 3.

 

[GeorgeDishman]

There is no disagreement here.

True.

So time dilation is the ratio of t (Coordinate Time) to τ (Proper Time) for a clock moving in a single coordinate system. You can also arrive at the same conclusion by going back to the original definition involving two coordinate systems in which the Proper Time for the clock moving in one coordinate system becomes the Coordinate Time for the clock at rest in the second coordinate system.

Exactly, proper time is just coordinate time in the rest frame of the clock (barring acceleration of course).

But I was making the point in post #37 that time dilation can be proven without establishing any coordinate system, simply by enacting the twin paradox--two synchronized clocks at mutual rest, one takes a trip and comes back with less accumulated time on it.

Ah, good point. Given the mention of muons, I was thinking of something like the evidence provided by the Ives-Stilwell experiment but Hafele-Keating (ignoring gravitational effects) can prove the existence of the effect without a coordinate system as such.

 

[GeorgeDishman]

.. i conclude that light does not change its speed as a result of the difference of constant speed between spaceship 2 and spaceship 3.

I've come into this thread late so sorry if I've picked it up wrongly but you seem to be saying that none of the ships are accelerating so no speeds are going to "change" for any ship.

Can I suggest a change to your diagram that might make the meaning of some terms clearer. Replace your light source with a camera flash bulb, and assume the light lasts for a negligible time, i.e. it can be detected at a specific instant but its duration is too short to measure. An "event" is then the flash hitting a ship's detector and the speed of the light is the distance between any two detectors when illuminated by the flash divided by the time between the events. Of course both numbers must be expressed in the same coordinate system to get the speed in that system or "frame".

 

[whosapopstar?]

I've come into this thread late so sorry if I've picked it up wrongly but you seem to be saying that none of the ships are accelerating so no speeds are going to "change" for any ship.

Can I suggest a change to your diagram that might make the meaning of some terms clearer. Replace your light source with a camera flash bulb, and assume the light lasts for a negligible time, i.e. it can be detected at a specific instant but its duration is too short to measure. An "event" is then the flash hitting a ship's detector and the speed of the light is the distance between any two detectors when illuminated by the flash divided by the time between the events. Of course both numbers must be expressed in the same coordinate system to get the speed in that system or "frame".

What i ask is, to assume that light changes its speed, and then to prove this possibility wrong.

i think that i describe clearly what i mean by light changing its speed, isn't it so? If i did not describe very well what I call 'light changing its speed', please let me known and I will try to make it as clear as possible.

Basically what i am describing relies on the fact that according to all experiments, light and electric signal always arrive together to clock. Now if we assume a different speed for light and electric signal in spaceship 3, with respect to the electric signal that moves just under them, in spaceship 2, then in spaceship 2 the physical law that says that light and signal arrive together, will not preserve itself anymore, in contradiction to every possible experiment. Hence it is not possible.

If I have an error in this chain of arguments, where is it? please let me understand. If i need to describe better what i mean by: to assume that there is a difference of speed between light and signal in spaceship 3 and the signal under them in spaceship 2, i think i can, and there will be no need for any angle calculation, since i will put spaceship 3 very close over spaceship 2 floor and electric cable, at a negligible height.

i think that if i describe in an accepted way, what does light changing its speed mean, and then i negate this possibility, what i gain is the definition of light not changing its speed.

Since it took me a lot of effort to get to that scenario, i'd rather not change it and rather try to find an error in it so i will understand things in the way that i think of them, if logically right or wrong.