Physics Forums (http://www.physicsforums.com/index.php)
-   Special & General Relativity (http://www.physicsforums.com/forumdisplay.php?f=70)
-   -   Event question (http://www.physicsforums.com/showthread.php?t=585082)

 whosapopstar? Mar8-12 03:35 PM

Event question

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

 Matterwave Mar8-12 03:45 PM

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.

 whosapopstar? Mar8-12 04:25 PM

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).

 ghwellsjr Mar8-12 05:03 PM

Re: Even question

Quote:
 Quote by whosapopstar? (Post 3805264) 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 Mar8-12 06:12 PM

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.

 ghwellsjr Mar8-12 06:17 PM

Re: Even question

Quote:
 Quote by Matterwave (Post 3805409) 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 Mar8-12 08:42 PM

Re: Event question

Quote:
 Quote by whosapopstar? (Post 3805203) 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? Mar9-12 01:36 PM

Re: Event question

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 Mar9-12 02:02 PM

Re: Event question

Quote:
 Quote by whosapopstar? (Post 3806733) 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? Mar9-12 02:15 PM

Re: Event question

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.

 whosapopstar? Mar9-12 02:18 PM

Re: Event question

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

 Passionflower Mar9-12 02:22 PM

Re: Event question

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

 whosapopstar? Mar9-12 02:27 PM

Re: Event question

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

 Passionflower Mar9-12 02:30 PM

Re: Event question

Quote:
 Quote by whosapopstar? (Post 3806822) 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? Mar9-12 02:34 PM

Re: Event question

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

 Passionflower Mar9-12 02:41 PM

Re: Event question

Quote:
 Quote by whosapopstar? (Post 3806835) 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? Mar9-12 02:47 PM

Re: Event question

1 Attachment(s)
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 Mar9-12 02:52 PM

Re: Event question

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 times are GMT -5. The time now is 10:18 AM.