Talk:Observer (special relativity)

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[edit] Disclaimer

While I am the first in the page history, I have no association to its content: a mere cut and paste move. `'Míkka>t 03:29, 13 May 2008 (UTC)

[edit] Major problem

This article is a good idea, I think, but the content is very wrong. An observer is more like a coordinate system than anything else. The analogy with the camera angle is bad since any observer (ignoring issues in general relativity like horizons) has all the information there is to have. A given reference frame does not need to be supplemented by the info from other reference frames. By using the Lorentz (or more generally, the Poincare) transformations one can derive what measurements would be to another observer. It also isn't really subjective. That being said, I'm simply deleting the last two paragraphs. Joshua Davis (talk) 01:41, 13 May 2008 (UTC)

I wrote the original content. I would point out that, as the CG rendering analogy said, a program rendering a camera angle viewpoint also has all of the data about the scene and the objects in it. This was why I chose a CG analogy in particular - exactly because it's a situation where all of the information for the scene is possessed and the rendering process is just mathematically highlighting a subset of that information.

The original content was in what was basically a philosophy article or at least one that was catering to empiricism, so I tried very hard to write to the audience of a non-mathematician and non-physicist. (I have a mathematical background, by the way, and I am a software engineer.) I think that some good information has been added to the article but the changes have been made with little respect to the writing style or to an audience trying to understand what the term "observer" means in an S.R. textbook (I'm thinking high school students or adults completely unfamiliar with relativity). As a result I think it's now completely opaque and much of the usefulness to anyone trying to understand S.R. from a beginner perspective has been eliminated. In particular I'm going to move the G.R. and quantum mechanics stuff out of the introduction and into its own subsection. (The title of the article specifies that it's about S.R. and I think that introducing G.R., etc. that early can only be confusing.) --❨Ṩtruthious ℬandersnatch❩ 17:07, 13 May 2008 (UTC)
While the camera angle analogy is not all bad, there were statements in the text that read to me as if one was trying to say that an observer does not have all the information. This is incorrect. So I simply deleted some things but haven't added to the article yet. Joshua Davis (talk) 18:04, 13 May 2008 (UTC)
Hmmm. I understand what you're saying in that if the term "observer" was being used to refer to a sapient being, and that sapient being understood special relativity, had precise measurements of all phenomena as they appeared within its own reference frame, and was able to run computations accurately, it would from the information available to it be able to deduce what sapient beings or recording devices within other reference frames would perceive. But I do think that part of what the SR concept of "observer" is trying to convey is specifically what the non-Lorentz-adjusted (non-Poincare-adjusted, etc.) perceptions of an sapient being or recording device within a particular frame would be if it had a sort of limited omniscience constrained within a particular reference frame. That's what I was trying to convey by talking about it connoting an "information-limited" perspective or a subjective perspective.

Note that the term "subjective" does not mean "untrue" nor does it strictly imply an inability to deduce other viewpoints or synthesize viewpoints into objectivity - all that word literally means is viewing things from a particular viewpoint. That's what I was trying to get across - yeah, technically every observer in every reference frame has access to all the same information but I think the entire point of distinguishing between these different observers is that they're viewing the same information from different viewpoints. But "information-limited" was a poor choice of vocabulary, I should have said "information-contextual" or "contextual-information" or something. --❨Ṩtruthious ℬandersnatch❩ 07:45, 14 May 2008 (UTC)

[edit] Level of language

Sentences such as "Reference frames are inherently nonlocal constructs, covering all of space and time or a nontrivial part of it; thus it does not make sense to speak of an observer (in the special relativistic sense) having a location." need to be rewritten in simpler language. If you don't know what an observer is (in relativity), then chances are you have a hard time grasping what "inherently nonlocal construct" means or why a region of space needs to be refered to as "nontrivial", implying that there are trivial regions (Hell I'm in physics and I can't think of a reason why one would need to say "this region is non-trivial"). Headbomb (ταλκ · κοντριβς) 13:45, 13 May 2008 (UTC)

I don't like that part either (and I wrote it). I didn't want to say that coordinate systems cover all of spacetime since that isn't always true, but people do (I think) commonly think that observers have a location within the system, which is wrong and ought to be explicitly corrected somewhere. The coordinate system may not extend off to infinity but it's large enough to cover the events that you care about, and therefore doesn't have a location "that you care about". Maybe it's obvious enough from the rest of the article. -- BenRG (talk) 14:03, 13 May 2008 (UTC)

I was under the impression that observers were are at the origin of their reference system, since you describe events relative to the origin. Headbomb (ταλκ · κοντριβς) 15:32, 13 May 2008 (UTC)

I concur with BenRG's statement that talking about an observer having a particular location is wrong; this is what was conveyed to me when I studied SR and GR in college. Part of the way I had addressed this in the original content was by pointing out that to use the term "observer" does not necessarily hypothesize the existence of an actual person or machine making (standard English) observations, but that note has since been removed from the article.

Stephen Hawking, for example, because he's wicked smart and articulate and intimately understands SR and all its intricacies, would probably only ever specifically say "observer" if he was really actually talking about an individual (standard English) observer. But I don't think Stephen Hawking's use of the term would be notable enough for an article; I think this article should describe the way that textbooks and high school teachers (often clumsily) use the term at odds with the standard English use of the term. --❨Ṩtruthious ℬandersnatch❩ 17:07, 13 May 2008 (UTC)

What is wrong then? If anything it an observer not having a specific location that seems wrong. If you change the origin (4-D location of the observer), you change the description of your system. Observer A and observer B will not describe the same phenomena in the same way unless they are at the same location (4-D). Headbomb (ταλκ · κοντριβς) 12:23, 14 May 2008 (UTC)

What you say is true if one is talking about "observer" in the standard English sense of a sapient being perceiving objects and events but my understanding within SR has been that the primary use of the term "observer" here is to distinguish between the difference in relativistic effects between two different rest frames. Distinction between observers is almost never used to illustrate, for example, the differences in timing that would be caused by two observers being in different spatial locations; in my experience, if a reader interprets the perceived timing differences of different observers in an explanatory SR scenario as being caused by differing physical locations of the observers, it usually means that the reader has misinterpreted the scenario. (Remember we're talking about textbook and other explanations of SR here, not GR.) The same goes for if a reader interprets the source of differing perceptions between two SR observers to be misunderstanding or miscalculation on the part of individual observers, classical doppler effect, etc. or any difference other than the relativistic effects between different rest frames.

In any case, though, you're totally right that the article needs to be written in simpler English, Headbomb. --❨Ṩtruthious ℬandersnatch❩ 01:18, 15 May 2008 (UTC)