Comparing Event Occurrence Across PORs

[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.

 

[GeorgeDishman]

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.

I haven't seen you state it at all which probably means I just missed the message. I've looked at both your diagrams and the associated posts and a few around them and haven't spotted it so can you tell me the message number where you define it.

Basically what i am describing relies on the fact that according to all experiments, light and electric signal always arrive together to clock.

In that case there are two more problems, firstly you haven't shown where there are clocks or cable in your diagram and secondly electrical signals in copper wire travel at about 60% of the speed of light in the rest frame of the wire. The way that transforms between frames will be similar to Fizeau's experiments on light in flowing water.

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?

Well the obvious point I have to make is that you have not done any calculations to create your argument. What you need to do is define the motion of the individual detectors and calculate where and when the flash (or the leading edge of the light being switched on) hits each. Then transform those into craft coordinates using the Lorentz Transforms. If you have electrical cables going to clocks, do the same for those signals. Then calculate the proper time between each signal arrival at each clock and see if there are any differences.

.. 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.

No problem, assume the cables are parallel to the direction of motion and ignore lateral displacement.

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.

If you apply the Lorentz Transforms properly, you will find that everyone measures the same 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.

OK, you can use the rising edge of the light being switched on as equivalent to the flash, you just need something that happens at a well defined instant, not something with a duration.

 

[GeorgeDishman]

I'm just wondering if I have been misreading what you are asking.

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 you first assume that all experiments say that light always has a specific speed in any inertial frame then subsequently assuming two different speeds will contradict what you have assumed about the experimental results. That's an obvious tautology though so I'm not clear on what you are trying to achieve with this.

 

[whosapopstar?]

I'm just wondering if I have been misreading what you are asking.
If you first assume that all experiments say that light always has a specific speed in any inertial frame then subsequently assuming two different speeds will contradict what you have assumed about the experimental results. That's an obvious tautology though so I'm not clear on what you are trying to achieve with this.

This is great! We might be very close to putting the finger on the place that i got it all wrong. If this will not turn out be the case, then i will get back and reply to your previous message.

Let's assume that light and electric signal arrive together, if this will turn out to be the main problem (and that electricity is actually 60% slower), then as said above, i will relate to this later, since it belongs to your previous message.

If you think that, anyway i should add a clearer diagram, let me know and i will draw one.

What i assume, is that light changes its speed when entering spaceship 3. Then i assume that light and signal arrive to clock together aboard spaceship 3, as well, at this point, i assume that the electric signal on spaceship 2 continues all the way at the same speed as light had, before entering spaceship 3, and when light returns to spaceship 2, it returns to its previous speed. Then i prove that this negates the possibility that also aboard spaceship 2, light arrives together with spaceship 2 electric signal to clock. This brings me to the conclusion that there is no change in the speed of light, not only within each frame, but also when moving from one frame (space ship 3) to another (space ship 2).i am aware of the fact, that this is most probably a logical error, but i still don't see the exact details from your explanation, since your write " you first assume that all experiments say that light always has a specific speed in any inertial frame ", but as much as i understand it, this is not what i assume, since i assume something about every frame by its own, and only then arrive at a conclusion that has to do with all the frames together.

Thanks.

 

[GeorgeDishman]

What i assume, is that light changes its speed when entering spaceship 3. Then i assume that light and signal arrive to clock together aboard spaceship 3, as well, at this point, i assume that the electric signal on spaceship 2 continues all the way at the same speed as light had, before entering spaceship 3, and when light returns to spaceship 2, it returns to its previous speed. Then i prove that this negates the possibility that also aboard spaceship 2, light arrives together with spaceship 2 electric signal to clock. This brings me to the conclusion that there is no change in the speed of light, not only within each frame, but also when moving from one frame (space ship 3) to another (space ship 2).

OK, here's another way to help people understand what you're saying. Suppose ship 3 is filled with water. When the light enters it, we know it really will change it's speed. Would your ergument prove that is impossible?

i am aware of the fact, that this is most probably a logical error, but i still don't see the exact details from your explanation ...

My problem is that I don't understand what you are trying to achieve. If the light travels in vacuum everywhere, there is no reason why it should change speed and if it does change as in my question above, your experiment shouldn't prove it doesn't. Again, it appears to be a tautology.

 

[whosapopstar?]

The reason is that i understood, since long ago, that in special relativity, even if the FoRs are moving at constant speed, there is no actual meaning to trying to find a phenomenon that is not dependent on choosing a FoR in advance, furthermore, all this, even if we relate to light, which all special relativity starts from.

That is why i ask about the validity of a way to prove, that actually light speed constancy is a phenomenon that is not dependent on choosing a FoR. It seems that when you are saying that "there is no reason why it should change speed and if it does change as in my question above…" you mean that light cannot change its speed, is true, you only mean that this notion has no meaning or is not defined; therefore it is true only as a vacuous truth.

But i am questioning if there is a possibility to well define a meaning for "light does not change its speed" in a way that will deliver a true meaning of independent FoR definition of light speed constancy, and not just as something that is a result of a vacuous truth. i am asking if, what i propose in the main paragraph of the previous message, do not present a possibility that light does not change its speed, independently of FoRs - as a matter of definition.

You say tautology, but i need you to help me to see these logical details, relating to why this is a tautology or a vacuous truth or any other kind of mistake, to really understand why it is so.

i think that i tried to ask why it is not a tautology, in the main paragraph of my previous message, by repeating the idea, while trying to shed off any redundant words that are not clear. Is it possible somehow to 'dissect', so to speak, that paragraph, in order to show me why it is a tautology or a vacuous truth or any other kind of mistake?

 

[GeorgeDishman]

But i am questioning if there is a possibility to well define a meaning for "light does not change its speed" in a way that will deliver a true meaning of independent FoR definition of light speed constancy, and not just as something that is a result of a vacuous truth. i am asking if, what i propose in the main paragraph of the previous message, do not present a possibility that light does not change its speed, independently of FoRs - as a matter of definition.

It's very difficult to understand what you mean but I'm going to take it as you have said it. Why are you talking about light "changing speed"? What relativity says it that the speed measured by ship 2 has the same numerical value as is measured by ship 3. There is no suggestion of any change of speed seen by either ship but that's not the point. That is unlike Newton's mechanics where you would expect the values to dffer by the speed of one ship as measured by the other.

 

[whosapopstar?]

Can you assure me that it is correct to say (?):

1. That there is no kind of transformation, at constant speed, that says: Yes, we measure light to be 300000kmps in our FoR, but if we transform something from another FoR we conclude that 'his' light is faster or slower the 'our' light?

2. Furthermore, that even numerically, according to SR (at constant speed), the speed of light has the same value for all FoRs, and that this is not something meaningless, true only in a vacuous way, tautological, or just mistake...?

 

[GeorgeDishman]

Can you assure me that it is correct to say (?):

1. That there is no kind of transformation, at constant speed, that says: Yes, we measure light to be 300000kmps in our FoR, but if we transform something from another FoR we conclude that 'his' light is faster or slower the 'our' light?

2. Furthermore, that even numerically, according to SR (at constant speed), the speed of light has the same value for all FoRs, and that this is not something meaningless, true only in a vacuous way, tautological, or just mistake...?

You are close but there are some details that could be clearer. Both ships are measuring the same flash (or rising edge) of light so there is no "his light" or "our light", just "the light".

To be pedantic, the value of c is 299,792,458 m/s and let's suppose that ship 2 is moving past ship 3 at 792,458 m/s. One ship measures the value 299,792,458 m/s. If they then apply the Lorentz transform, they will predict that the other ship will also measure that same numerical value for the speed of the same light. On the other hand, if they apply the Galilean Transform, they will predict that the other ship will measure a speed of 299,000,000 m/s. Experiments are therefore required to distinguish which occurs in reality and the answer is that the Lorentz Transform gives the correct prediction.

For that reason, it is not a tautology. In your previous posts you started by assuming that the speed would be the same and then went on to prove that the speeds would be the same which is just the same as the assumption.

 

[whosapopstar?]

Can anyone please read only the opening message of the thread: "synchronized clocks with respect to rest frame" and answer me this:

When the train returns, we can see that somthing happened, e.g. we have time dilation on the clock, and we agree that at least part of that time dilation was produced by constant speed (CS). There is evidence of say "nature 1" that somthing happened there.

Now regarding the clocks that are not synchronized, although they are both on the same train (but apart from each other): is there an experiment that can be done, which will show us this difference of de-synchroniztion between them, after the clocks will return to the station (nature 1), and not by sending signals when the train is on the move (say we call this kind nature 2)? if not, how come one clock can bring back evidence to the station of a phenomenon (CS time dilation on a single clock of nature 1), while another phenomenon, the de-synchronization of two clocks, is not somthing that can be brought back as evidence (of nature 1 type but only of nature 2 type)? or is such an experiment plausible, after all, for two clocks? or is this de-synchronization, a result of accelerating and de-accelerating and not of constant speed?

Thanks.

 

[ghwellsjr]

Consider two synchronized clocks at rest with respect to each other. Merely accelerating one clock does not de-synchronize it. You could instantly accelerate a clock to some high speed and then just as instantly decelerate it back to its original condition and the time will not have changed on it at all. Accelerating one clock causes it to be at a different speed than the other clock which causes it to tick at a different rate than the other clock but it has to remain at that different speed for some time in order to accumulate a different elapsed time when brought back to the other clock that experienced no acceleration.

I think the easiest way to address your concerns is to think about the Doppler effect and what it would be like if there were no relativity. I encourage you to look up "Doppler effect" in wikipedia. There you will see some formulas to involving the observed frequency f and the emitted frequency f₀. But instead of thinking about frequencies, just think about how each clock views the other one. Specifically, look at this formula where c is the speed of light in a fixed ether medium, v_r is the velocity of the receiver through the ether and v_s is the velocity of the source through the ether:

Just look at the part of the formula inside the parentheses. Let's say, just to get familiar with the formula, that the source clock is moving away from the receiver clock at 10% of c through the medium but the receiver clock is stationary in the medium. That means that the stationary clock will see the moving clock ticking slower than itself by a factor equal to:

c/(c+0.1c) = 1/1.1 = 0.90909

Now let's say instead that the source clock is stationary in the medium but the receiver clock is moving in the other direction at the same speed of 10%c. Now the source clock will see the receiver clock as ticking slower than itself by a factor of:

(c-0.1c)/c = 0.9/1 = 0.9

And you could calculate how the other clock views the first clock in each situation.

Clearly, there is a difference in how each clock sees the other one ticking, based on their speeds relative to the fixed medium, even though the relative speed between them is the same. If there were no relativity, then this difference in the observed tick rates between two clocks in relative motion would change depending on how they are moving through the ether.

But that is not what actually happens. What actually happens is that both clocks see the other one as ticking at the same rate. Please look up the wikipedia article called "Relativistic Doppler effect". Now we have a new formula where f_o is the observed frequency, f_s is the source frequency and β is the relative speed as a fraction of the speed of light:

Just look at the square root part of the formula. For our example of 10%c, β = 0.1 and:

√[(1-0.1)/(1+0.1)] = √[0.9/1.1] = 0.904534

This value is somewhere between the two values that we got before and more importantly, it is the factor that each clock sees the other one ticking at compared to their own. This is really quite an amazing and surprising result because it means that what we observe does not depend on a medium to propagate that observation and any attempt to identify one is doomed to frustration. If we could identify one, then we could take into account the light propagation time to determine the actual time displayed on the remote clock at each location as it moved away from us. Instead, it is not possible to arrive at a conclusion in a determinate way.

Prior to Einstein, scientists believed that the light propagation time was fixed according to an absolutely stationary medium, even if they could not determine its state but Einstein figured out that you could assume any fixed state to be the one in which light propagated at c and this is the basis for Special Relativity.