# Comparing Event Occurrence Across PORs

• whosapopstar?
In summary, the answer is "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."
whosapopstar?
Is it possible for an event to occur in one POR and never occur in another POR?

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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.

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).

whosapopstar? said:
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.

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.

Matterwave said:
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.

whosapopstar? said:
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. :)

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.

whosapopstar? said:
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.

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.

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

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

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

whosapopstar? said:
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.

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

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whosapopstar? said:
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.

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?

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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.

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

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.

whosapopstar? said:
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?

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.

ghwellsjr said:
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.

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whosapopstar? said:
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?

ghwellsjr said:
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.

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...)

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whosapopstar? said:
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.
whosapopstar? said:
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.

whosapopstar? said:
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.

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.

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whosapopstar? said:
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.

whosapopstar? said:
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.

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?

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"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 :

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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.

NP :)

"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.

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