Talk:Spacetime/Archive 6

"Usually" in the lead

Why is the word "usually" in quotes in the first sentence of the lead? If no one is opposed, I will amend this. Mr Ernie (talk) 16:49, 11 February 2016 (UTC)

The scare quotes were put there with this edit. A good reason i.m.o., but the thing is sitting there most ugly, so I tagged it for clarification. Good find. - DVdm (talk) 17:52, 11 February 2016 (UTC)

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Encyclopedia is to provide information not to mislead

We should provide correct not misleading information to users.

I have corrected a slightly misleading description, but the editor of my latest correction is clearly interested in spreading misinformation.

Look at this sentence:

Mathematically it is a manifold consisting of "events" which are described by some type of coordinate system.

Manifold is not consisting of events because "n-dimensional manifold is a topological space M for which every point x ∈ M has a neighbourhood homeomorphic to Euclidean space Rn" Therefore manifold consists of points not events. Even if you put events in quotes, what quotes mean to anyone is anyone's guess. This is lacking precision required in encyclopedias.

The problem is a widespread negligence of equating events with their coordinates. The difference is not very subtle:

1. An event is a physical state change not some abstract set of coordinates. For one event there is an infinite set of coordinates from an infinite set of possible coordinate systems, while an event is unique in the whole universe history.

2. For the same set of coordinates there may be more then one event. Note Einstein's descriptions of two non distant events:

If at the point A of space there is a clock, an observer at A can determine the time values of events in the immediate proximity of A by finding the positions of the hands which are simultaneous with these events.

• We shall not here discuss the inexactitude which lurks in the concept of simultaneity of two events at approximately the same place, which can only be removed by an abstraction. - Einstein means co-located events which are nearly impossible to have in practice

3. If an event is a state change, then this cannot be a part of an abstract space although an abstraction from an event can be associated with the point of space

4. While events may or not happen, the coordinates at which they may happen are unconditional.

5. Finally if logical arguments are not sufficient, here is the authority taking events:

It is neither the point in space, nor the instant in time, at which something happens that has physical reality, but only the event itself A.Einstein, The Meaning of Relativity, Princeton: Princeton University Press, 1988 page 30. 

— Preceding unsigned comment added by AndrewWutke (talk • contribs) 08:31, 7 August 2016 (UTC)

Please sign all your talk page messages with four tildes (~~~~). Thanks.

Note that your version "Mathematically it is a manifold consisting of points which are coordinates of possible events." is wrong. In mathematics, points are not coordinates. Points can have coordinates. Confusion between points and their coordinates w.r.t. some coordinate system (—and between vectors and their components w.r.t. some basis—) is all too common. Let's avoid it. Yes, as you say in your edit summary, precision is required. Spacetime as a set of points, called "events", is standard. See, for instance [1].

As for Einstein's statement: indeed, "neither the point in space, nor the instant in time", but "only the event itself", in other words, something in a combination of space and time. The quote in context:

"It was not observed that the true element of the space-time specification was the event specified by the four numbers x1, x2, x3, t. The conception of something happening was always that of a four-dimensional continuum; but the recognition of this was obscured by the absolute character of the pre-relativity time. Upon giving up the hypothesis of the absolute character of time, particularly that of simultaneity, the four-dimensionality of the time-space concept was immediately recognized. It is neither the point in space, nor the instant in time, at which something happens that has physical reality, but only the event itself."

Look at the past tense in "It was not observed". That was in Newtonian mechanics, as opposed to now in relativity. You seem to present Einstein's description as a direct contradiction of your own view. - DVdm (talk) 09:26, 7 August 2016 (UTC)

Causal field vs space-time

The Lorentz transformation dictates that the causal field (or causality field, or field of causality) is fundamental and spacetime isn't.

Why the non fundamental spacetime has an article and the fundamental causal field hasn't? I don't ask for lazy excuses. We must slowly create a new article. — Preceding unsigned comment added by 2A02:587:4110:E400:D8F0:821D:19CE:EA10 (talk) 01:27, 12 October 2016 (UTC)

we have this one (gauge theory) but we should create a more generic one which will mention the gauge fields — Preceding unsigned comment added by 2A02:587:4110:E400:D8F0:821D:19CE:EA10 (talk) 01:31, 12 October 2016 (UTC)

Spacetime goes along with the book Spacetime Physics for undergrads. There isn't yet a book Causal Field Physics for undergrads. Gah4 (talk) 17:20, 26 February 2017 (UTC)

This article needs a complete redo

I've been on Wikipedia for quite some time, and this is just about the worst article I've seen. For starters, the lede paragraph isn't appropriate for a general-interest encyclopedia. It launches straight into speciality lingo like “manifolds”, without anything so much as a simple explanatory parenthetical, like (a topological space) to make the lede more accessible to a general-interest readership.

Like so many of Wikipedia’s mathematical- and science-related articles, this one too appears to be suffering from a protracted period where authors were more anxious to demonstrate to other wikipedians just how smart-smart they are than to explain the subject matter using clear, non-pretentious prose that A) doesn't call attention to itself, B) uses plain-speak and explanatory parentheticals that doesn’t demand “click more links to learn the essential basics,” and C) has a lede and early sections that are appropriately accessible to a general interest readership.

Equally important are the graphics and illustrations, or lack therefore. One would reasonably expect that what graphics are in the article would actually help, but alas, no. Take the topmost graphic in the lede. The article is spacetime, yet the illustration primarily illustrates a tangential, secondary effect regarding how gravity distorts spacetime. Such a graphic needs to be placed later in the article, at the relevant subsection.

I'm not trying to dump on anyone; Wikipedia is an all-volunteer effort and no volunteer with good faith should be ripped for contributing. And I'm not sufficiently knowledgeable about the subject matter to help in a meaningful way… and even if I was, I’m too busy right now. I am encouraging that those who are active here need to take a step back and make a fresh assessment of what this page has grown into. Greg L (talk) 00:42, 10 October 2016 (UTC)

Won't happen while there are trigger-happy reverters. I've seen this story before. It's near impossible to "write one level down", as per WP guidelines because somebody will get butthurt if their technical jargon word isn't in the article, or their own POV way of having learned the material. Revert city. It's a waste of everybody's time and effort, and I've gotten to the point where I don't care if WP is crap anymore. WP needs a git-like fork where everyone can have their say, but ultimately, consensus goodness survives, not just individual vetos. WP is now a veto chamber with very high impedance. 75.139.254.117 (talk) 05:19, 15 March 2017 (UTC)

It's indeed frustrating that this has become the them of many mathematical Wikipedia pages. The Lie derivative page is a prime example of jargon-abuse leading to an incomprehensible resource. I have always followed Feynman's mantra that the true measure of ones understanding is their ability to explain the topic through non-technical language. A fork system is a fantastic idea, without it I fear it will be impossible to remedy pages like this one that essentially need a full rewrite. It's a shame that so many mathematical gatekeepers have taken to filling these pages with jargon. PhysicsSean (talk) 01:25, 21 March 2017 (UTC)

spacetime or space-time

Should this article be titled spacetime or space-time? Personally, I am happy with spacetime, but it seems that it isn't (yet) in the OED. I probably think it should be, but then it isn't my say. I am not voting to change it, but wondering what others think of the name. Gah4 (talk) 03:05, 17 February 2017 (UTC)

There is a Request for Comment (RFC) on a relativity-related article

Notice. An RFC (poll, of sorts and discussion area) is ongoing on a relativity-related article here at Talk:Twin paradox. It is easier to discern a true consensus when more wikipedians thoughtfully weigh in.

Graphics

@Greg L: I find the hardest thing about animation is not the scripting/computer programming, although the effort there can be considerable. It's working out the storyboard: how much to show, when to show it, and how you show it.

Much of that is true of graphics in general. What colors do I want, how thick the lines, etc. There are a lot of compromises. For example, I may very much want to display grid lines, but their presence may make a graph too busy. My length contraction animation has undergone significant tweaking even after I uploaded a presentation that I thought was going to be a final version. My latest tweak to the animation was deciding that a small displacement of the "1" on the x axis was too distracting, so I've placed it where it is permanently bisected by the magenta curve. The result is slightly uglier, and the difference is mostly on a subliminal level, but not having a jump of the "1" means one less thing for the viewer to puzzle over.

Someone once said that you know that negotiations have gone well when both sides walk away from the negotiating table a bit unhappy. Well, I've got this right side of the brain and this left side of the brain that are unhappy with each other... Stigmatella aurantiaca (talk) 06:07, 9 April 2017 (UTC)

There are still a few things to do before I can consider myself as finished with the introduction. Most important is to explain the meaning of the term "observer" in special relativity. The Wiki article on the observer in special relativity has no graphics, nor do I see any suitable illustrations in Commons.

The next logical enhancement would be to provide an "Introduction (part 2)" to extend the spacetime description to weak gravitational fields. I don't really see how I can do this properly without having an intermediate section introducing the Lorentz transformation to show the relationship between my graphical descriptions and the math. I don't particularly like the existing Wiki articles on this subject. Too advanced for my target audience. Unfortunately, if I tackle this subject, I will be writing at too advanced a level for my target audience. No way I can win. Stigmatella aurantiaca (talk) 14:23, 10 April 2017 (UTC)

My two cents: Your work on the graphics is very helpful and well done. The introduction is now very thorough and each subsection goes into quite some depth.

Taking the example of Encyclopædia Brittanica (which I own and am quite familiar with it), the extremely complex subject of spacetime could really benefit from a Micropædia before taking the reader to an in-depth Macropædia. Said another way, I propose not delving next into a deeper “part 2”, but instead tackling an overview-like “part ½”—a primer that bridges the lede and what you currently have. I'm thinking something on the order of 1000–1500 words and maybe two well chosen graphics.

Doing what I am proposing would be double-tough; I can think of no more difficult technical writing challenge than trying to make the subject of spacetime accessible in a Micropædia to a certain segment of a general-interest target readership. In this case, I propose that such a target readership be defined as A) having a technical aptitude, B) having an education level of as little as 12th grade, and C) having an I.Q. of as little as 115 (+1 σ above average). Given the subject matter, writing to even that readership segment would be quite a challenge. Greg L (talk) 22:33, 10 April 2017 (UTC)

Hmmm... I was thinking that your lede would be the Propædia, the Introduction section would be the Micropædia, and some to-be-written sections would constitute the Macropædia. I believe that the lede and Introduction sections, as currently written, are accessible to an intelligent middle-school/early high school science student, say 10th grade or so, who is willing to put in a bit of work. My envisioned Lorentz transformation section probably would require a 12th grade level of mathematical sophistication, while my envisioned Weak gravitational fields section would need 12 grade AP physics/math.

Side note: In 1974 I sold 15th-edition Britannica when it first came out, to earn money before going off to graduate school. So I, too, am reasonably familiar with its organization. :-) Stigmatella aurantiaca (talk) 10:50, 11 April 2017 (UTC)

Coincidentally, I sold World Book in the late 70s. I sure didn't make much money; the marketing scheme was based essentially around looking for Big Wheels and other kids’ toys sitting around in front of a house and making a pitch directed to “doing what's good for children” to an audience that was cash strapped.

This is your article for the moment and, as a volunteer effort, the authoring process must be engaging and interesting to you or you'd never go through the exercise. But consider this:

I think the lede introduces what spacetime is, but doesn't explain it in any detail to speak of. Currently, the Introduction is nearly 5000 words that begins with Definitions, which a reader would assume they must bone up on before wading further. The meat & potatoes of the Intro section currently resides in four subsections: Spacetime interval, Reference frames, Light cone, and Relativity of simultaneity. That's four sections of rather intimidating heavy verbiage that a visitor would logically assume they must pull all together into a intertwined whole; I'm sure many visitors don't go there due to the time and energy commitment.

I'm suggesting that the article would be visited more frequently and readers would spend more time if it had a primer that summarized those four subsections in a 1000-word executive summary at a Nova-level technical difficulty. I try to think of readers as some of the business managers I've had to deal with: I provide something really simple to start with. Greg L (talk) 18:11, 11 April 2017 (UTC)

I'll think about the executive summary idea, but I still haven't finished cleaning up the Introduction yet. There are a lot of tweaks still to do. (I don't own a Rubik's cube, for instance...) There is a danger in oversimplifying Einstein, but I try as best as I can. Stigmatella aurantiaca (talk) 14:50, 12 April 2017 (UTC)

Another drive-by tagging by an anonymous IP user. Only way to stop the "Son of Ref" tagger is to quickly add a bunch of references. I've been WORKING on them!!! :-( Stigmatella aurantiaca (talk) 20:35, 12 April 2017 (UTC)