Comparing Event Occurrence Across PORs

[whosapopstar?]

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

 

[Matterwave]

POR? You mean FOR frame of reference?

It sort of depends on what you mean by "event occurs in a FOR".

The constantly acclerated observer's "reference frame" (accelerating forever), for example is disconnected from some portions of space-time (creating an event-horizon like surface, called the Rindler Horizon). Some events cannot even send light signals to this observer. In that sense, you could make some case for the event "not occurring" in this accelerated observer's reference frame. Perhaps more appropriate, however, would be to say that the accelerated observer's coordinates do not cover the entire manifold (it's only a coordinate patch), and so it really has more to do with the coordinates being local coordinates rather than global coordinates.

Similar things occur in the Schwarzschild solution for events inside the event horizon and observers outside the event horizon.

 

[whosapopstar?]

I meant in FORs that move at constant speed (i took Point Of View and Frame Of Reference and 'meshed' them together, are they the same? LOL).

 

[ghwellsjr]

I meant in FORs that move at constant speed (i took Point Of View and Frame Of Reference and 'meshed' them together, are they the same? LOL).

There's no precise and standard definition for PoV like there is for an inertial FoR in Special Relativity so you can never tell when someone talks about a PoV if they really mean a FoR in which an observer is at rest or if they mean what the words imply--what someone can actually see. A FoR does not in any way improve on what an observer can actually see because he still has to wait some time for the image of remote events to propagate to him at the speed of light. Furthermore, if the observer ever accelerates, then he is no longer at rest in his initial inertial FoR and once again, there is no precise and standard definition for a non-inertial FoR.

So if I could control the vocabulary, I would reserve PoV to mean what an observer can actually see and not allow it to be equal to FoR, but since I don't, you will have to figure out from the context or ask what a person means when they use the term PoV.

But to answer your original question, in Special Relativity, there is no event that can occur in one FoR that does not occur in any other FoR you wish to choose. The Lorentz Transform has no limits on it for the events it can handle, just the limit on the value of v--it has to be less than c.

 

[Matterwave]

ghwells, it seems you are restricting frames to global inertial reference frames, isn't that too restrictive? Surely, what an accelerating observer can measure by putting rigid rulers and clocks in his accelerating rocket should still count as a reference frame...albeit a local one.

 

[ghwellsjr]

ghwells, it seems you are restricting frames to global inertial reference frames, isn't that too restrictive? Surely, what an accelerating observer can measure by putting rigid rulers and clocks in his accelerating rocket should still count as a reference frame...albeit a local one.

I am restricting it to what the Lorentz Transform can handle which is what I thought the OP was asking about.

 

[Passionflower]

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

Sure, that's is because there are event horizons.

Similar when the Sun is beyond a horizon it can no longer be seen. :)

 

[whosapopstar?]

OK, at this point I will take the answer as "No, if you, 'the measurer', move at constant speed, and an event occurred, it is not possible that you will never be able to observe that event." My intent is to take the question further, to perhaps another direction. To be continued soon, or aborted if not able to ask more in what seems coherent terms.

 

[Passionflower]

OK, at this point I will take the answer as "No, if you, 'the measurer', move at constant speed, and an event occurred, it is not possible that you will never be able to observe that event."

I told you you are wrong it appears you simply ignore what you do not like. What is the point in asking if you ignore the answers.

 

[whosapopstar?]

Here we go with the emotional stuff. Yes, i read what you wrote and if you had not wasted the time berating me, but instead jut repeat again and again as much as needed, probably i would already get it. Yes, since i already read what you wrote please try to rephrase it or let other people explain what i don't understand.

 

[whosapopstar?]

OK, i will stop asking until I will be sure i understand the answer to the first question.

 

[Passionflower]

One example is events that take place inside a black hole outsiders cannot observe these.

 

[whosapopstar?]

Great, and besides black holes? Any other example that exclude a black hole scenario? thanks.

 

[Passionflower]

Great, and besides black holes? Any other example that has nothing to do with a black holes? thanks.

Sure because our universe is expanding certain events cannot be observed as well namely those that are outside the observable universe.

 

[whosapopstar?]

OK so we have: outside the observable universe and black holes. This still enables me to ask further, i think. Any other possibilities?

 

[Passionflower]

OK so we have: outside the observable universe and black holes. This still enables me to ask further, i think. Any other possibilities?

Apart from possibly more exotic situations that pretty much covers it.

 

[whosapopstar?]

OK. Please look at the attached diagram. Will any spaceship from the group 'spaceship x', observe any change in light speed, before or after light enters detectors d1 and d2, located on spaceship3?

 

[Matterwave]

The three common "event horizons" to appear are those for black holes, the one for the observable universe, and the Rindler's horizon for accelerating observers.

None of these can really be fully dealt with using only special relativity. In the Rindler's case, one can do some of the analysis using only SR. One can, for example, deduce that constantly accelerated observers travel on hyperbolas.

 

[Matterwave]

All local measurements of the speed of light will result in c. This is true also in general relativity.

 

[ghwellsjr]

But since whosapopstar clarified his original question with more information from post #3 saying he meant a Frame of Reference moving at a constant speed (with respect to another FoR), I gave my answer in post #4 from the context of Special Relativity. In SR, the Lorentz Transform can handle any event. It's important for whosapopstar to understand the different ways his question can be interpreted. In the context of SR and LT the answer to his original question is no. In other contexts, such as General Relativity, the answer could be yes, but then, I don't know why he brought up the issue of constant speed.

 

[ghwellsjr]

OK. Please look at the attached diagram. Will any spaceship from the group 'spaceship x', observe any change in light speed, before or after light enters detectors d1 and d2, located on spaceship3?

I thought we resolved your questions with regard to your diagram in posts 10 through 15 of Why is light speed constant in all reference frames?

 

[whosapopstar?]

This question goes further. But Indeed, first i need to be as sure as possible, of the meaning, of what i am asking, for the answerers may render the rest of the question redundant.

 

[whosapopstar?]

I thought we resolved your questions with regard to your diagram in posts 10 through 15 of Why is light speed constant in all reference frames?

I was totally unable to say, even what I don't unserstand, when it got at that thread, to post #16.

 

[ghwellsjr]

I was totally unable to say, even what I don't unserstand, when it got at that thread to post #16.

Post #16 was not addressing your question so you don't have to understand it. You did say in post #15 that you understood my explanation in post #14. Are you now reconsidering?

 

[whosapopstar?]

Post #16 was not addressing your question so you don't have to understand it. You did say in post #15 that you understood my explanation in post #14. Are you now reconsidering?

When i read that answer i felt satisfied, but now i read it again and i am totally lost. i guess i will read it again and again now for a while, although i do think that i am asking things differently.

Thanks and will be back shortly, if not back to an understanding point.

 

[whosapopstar?]

Yes,
Did connect again with the explanation, and now, might know what kind of questions popped up in my mind afterwards, which boiled some months later to what i actually want to ask today:
1. What about, 'slow transport'? Which means as much as I understand, that each detector has already a clock, that was synchronized at one point, and then they where moved very slowly to their places at detector 1 and 2.
2. Is the reason that i can see a laser, when standing at point C, while the laser is actually pointed from point A to B, is that there is refraction with the air and smoke etc...or does it also occur in space? e.g. that i can observe the laser 'from the side'? (Space e.g. no gravity, no air etc...)

 

[ghwellsjr]

Yes,
Did connect again with the explanation, and now, might know what kind of questions popped up in my mind afterwards, which boiled some months later to what i actually want to ask today:
1. What about, 'slow transport'? Which means as much as I understand, that each detector has already a clock, that was synchronized at one point, and then they where moved very slowly to their places at detector 1 and 2.

Einstein was well aware of slow transport of clocks and he rejected it in favor of his prescribed convention for establishing Coordinate Time. A clock keeps Proper Time. What we want is Coordinate Time. 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. In other frames, the slow transport of clocks does not correspond with the Coordinate Time.

2. Is the reason that i can see a laser, when standing at point C, while the laser is actually pointed from point A to B, is that there is refraction with the air and smoke etc...or does it also occur in space? e.g. that i can observe the laser 'from the side'? (Space e.g. no gravity, no air etc...)

Yes, the laser beam illuminates particulate matter floating around in the air which scatters the light so that you can see it. In a vacuum, either in space or in a vacuum chamber on earth, you won't be able to see the beam. When the astronauts were walking on the moon, the sky was black. The could not see any sunbeams or effects from their silhouettes casting shadows.

 

[Mentz114]

Here we go with the emotional stuff. Yes, i read what you wrote and if you had not wasted the time berating me, but instead jut repeat again and again as much as needed, probably i would already get it. Yes, since i already read what you wrote please try to rephrase it or let other people explain what i don't understand.

If you define an event as a relationship between worldlines then it will be observable in all frames without exception.

For instance, the ringing of a bell is the confluence of the WL of the bell and the WL of the clapper. If this happens in one frame, it happens in all.

Similarly, if two WLs are approaching then they will be seen to be approaching all frames.

 

[whosapopstar?]

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 or 'kinds of explanations' some 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.

 

[Mentz114]

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.

Different frames of reference use different coordinates. The speed of ligh measured with non-local coordinates can change. But in any frame, using local coordinates the speed of light is always the same.

The term 'rest frame' is not meaningless. If you are considering a scenario with many inertial observers you can nominate anyone of these to be your rest frame. It makes no difference which one you choose, the physics is the same. So it is not meaningless, it is irrelevant.

 

[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.