# Event question

1. Mar 8, 2012

### whosapopstar?

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

Last edited: Mar 8, 2012
2. Mar 8, 2012

### Matterwave

Re: Even question

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.

3. Mar 8, 2012

### whosapopstar?

Re: Even question

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).

4. Mar 8, 2012

### ghwellsjr

Re: Even question

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.

5. Mar 8, 2012

### Matterwave

Re: Even question

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.

6. Mar 8, 2012

### ghwellsjr

Re: Even question

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

7. Mar 8, 2012

### Passionflower

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

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

8. Mar 9, 2012

### 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.

9. Mar 9, 2012

### Passionflower

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.

10. Mar 9, 2012

### 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 dont understand.

11. Mar 9, 2012

### whosapopstar?

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

12. Mar 9, 2012

### Passionflower

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

13. Mar 9, 2012

### whosapopstar?

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

14. Mar 9, 2012

### Passionflower

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

15. Mar 9, 2012

### whosapopstar?

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

Last edited: Mar 9, 2012
16. Mar 9, 2012

### Passionflower

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

17. Mar 9, 2012

### 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?

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18. Mar 9, 2012

### 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.

19. Mar 9, 2012

### Matterwave

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

20. Mar 9, 2012

### 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.