Talk:Spacetime/Archive 9

Looking good

I'm rather busy but just did a drive-by reading on Time dilation and length contraction. I think you've done an absolutely fabulous job on that bit. Bravo! Greg L (talk) 19:42, 20 April 2017 (UTC)

Thanks! Getting the illustrations right was key to getting an understandable explanation. A lot of thought went into the stop-motion graphics illustrating the spacetime diagram for length contraction. My first animation went straight through without pause and was hard to follow. Then I saw Princess Fiona's "bullet time" fight scene in Shrek, and I realized that I could improve the presentation with appropriately positioned freeze-frames. Working out the "storyboard", so that the images would be minimally cluttered and only essential detail would be shown at any moment, took a lot of trial and error. I was still bothered by the timing. Things seemed too rushed between event C and events O/B. Going back to the Princess Fiona versus Robin Hood's Merry Men, I realized that freeze-framing wasn't the only animation technique that I could adopt. Most of the frames are on the screen for 60 milliseconds apiece. But I've slowed the frames between event C and events O/B to 80 milliseconds each. Paradoxically, making the frames slower for these seven frames smooths out the animation. There's some sort of psychological "time dilation" effect here... :-) Stigmatella aurantiaca (talk) 12:27, 21 April 2017 (UTC)

I had been promising to explain to you about the essential difference between Einstein pre- and post-Minkowski. Einstein liked thinking in terms of clear visual images, many of which he shared with the public in his popular writings. The evidence is that Einstein really did visualize time dilation with the help of imagined light clocks, trains and so forth. His vivid mental images always came first, and the math came later.

Minkowski's geometric presentation was of an entirely different nature. The mental imagery associated with the geometric approach is actually a bit dull and abstract, compared with the kinematic approach. When Einstein first learned of Minkowski's take on special relativity, he was not impressed because Minkowski showed him absolutely nothing that he had not already worked out. What good was it?

Honestly, given a choice between Figure 10 and its lines drawn on an invariant hyperbola, versus an illustration of a light clock swooping through space, which image has a better chance of sticking in a student's mind?

If this were an article on special relativity, I might give a balanced approach showing different ways of thinking about time dilation, length contraction, twin paradox, etc. Since this is not an article on special relativity, but one about spacetime, I limit myself to the spacetime way of visualizing things.

Stigmatella aurantiaca (talk) 19:02, 21 April 2017 (UTC)

Parking some material that I removed

Does anybody have any objections to my removal of this material?

Spacetime in special relativity

The geometry of spacetime in special relativity is described by the Minkowski metric on R⁴. This spacetime is called Minkowski space. The Minkowski metric is usually denoted by $\eta$ and can be written as a four-by-four matrix:

$\eta _{ab}\,=\operatorname {diag} (1,-1,-1,-1)$

where the Landau–Lifshitz time-like convention is being used. A basic assumption of relativity is that coordinate transformations must leave spacetime intervals invariant. Intervals are invariant under Lorentz transformations. This invariance property leads to the use of four-vectors (and other tensors) in describing physics.

Strictly speaking, one can also consider events in Newtonian physics as a single spacetime. This is Galilean–Newtonian relativity, and the coordinate systems are related by Galilean transformations. However, since these preserve spatial and temporal distances independently, such a spacetime can always be decomposed into spatial coordinates plus temporal coordinates, which is not possible for general spacetimes.

Stigmatella aurantiaca (talk) 22:08, 3 May 2017 (UTC)

I found a use for the Summary!

@Greg L: Check out the back-and-forth cross-linking between each subsection in the Introduction and the brief summary! Stigmatella aurantiaca (talk) 08:31, 5 May 2017 (UTC)

---

@Stigmatella aurantiaca:

I think cross-linking to summary material is, broadly, a good concept. However, the implementation falls a bit short because doing links in that fashion runs afoul, in my opinion, with the “principle of least astonishment” (additional thoughts on this subject here on my userpage). Links should not be novel, surprise Easter eggs; they can waste users’ time as many will click just to find out what the nature of the link is. I propose linking like this:

Reference frames (click here for a glossary definition)

Now the reader knows what what to expect were they to click the link.

Also, instead of forking to another article, I suggest you transplant the material from the forked article to a Glossary near the bottom of the primary article.

There's a good reason to adopt these suggestions. Whenever there are new, unusual, or rather novel implementations on Wikipedia (I’ve tried them in the past… and always for good reason), other editors who dislike change and value project-wide conformity will eventually wade in and do a drive-by shooting to make an article conform to familiar conventions. You will doubtlessly not feel like embracing others’ solutions, which can be draconian and not well thought out.

Your return link from the glossary sub-heading back to the article should be similarly formatted, where the link is a parenthetical “(click here here to return)”.

BTW, did you note how my two links in the first paragraph of this reply behaved in a largely predictable and unsurprising manner?

Greg L (talk) 22:37, 6 May 2017 (UTC)

There are several problems:

1. I do not want to have the parenthesized instructions "(click here for a glossary definition)" at the same font size as "Reference frames", and trying to adjust fonts is incompatible with the semantics of the "=== ===" markers. Believe me, I tried to find a workaround. However, I have reformatted the return links so that the clickable area of the subsection header has been expanded. [Note added Sunday morning: In addition, the syntax/semantics of "=== ===" is such that I had found no way of adding "(click here for a glossary definition)" without it showing up in the TOC. Stigmatella aurantiaca (talk) 07:53, 7 May 2017 (UTC)]
2. Reiterating an abridged form of the Introduction section at the end strikes me to be as much a surprise as having it in a separate article.
3. By the time I finish "Basic mathematics of spacetime", the article will be up to maybe 120,000 characters, and I absolutely do not want to bloat it with non-essential material. If decide to carry through with my plans to give an elementary introduction to curved spacetime (I don't know if I really want to or not), the article may be up to 240,000 characters in a year. There will be people insisting that the article should be split, but my vision for the article is far too tightly integrated for it to be split. Note, for instance, the cross-referencing between the numbered figures and distant sections of the text. There will be more in the future. Better to split out what can be split out ahead of time.
4. If you haven't noticed, I have had absolutely no problem with the article watchdogs. You, PhysicsSean, and 75.139.254.117 had earlier complained about how "WP is now a veto chamber with very high impedance" etc. Well, that is just not so, not if you have established a bit of a reputation. Stigmatella aurantiaca (talk) 00:45, 7 May 2017 (UTC)

If I can't figure out a way to explain Riemannian manifolds, one-forms and tensors in a manner understandable to a first-year Calculus student, all that I will be able to do will be to make some blah, blah, jabber jabber general remarks about the equivalence principle, wave my hands in "...and then a miracle occurs" fashion, and present Einstein's field equations providing the student with essentially zero understanding. In other words, I will not in any way have improved on articles already on Wikipedia like the General relativity article or any number of popular books. That cop-out is not for me. It's been done already.

There are only two moments in "Basic mathematics of spacetime" that I have required more than high school algebra (when I twice invoked dr/dt = 0 when discussing transverse Doppler shift). Thinking of ways to present curved spacetime in a fashion understandable to someone with one year of Calculus is a major challenge. Stigmatella aurantiaca (talk) 01:10, 7 May 2017 (UTC)

Just wanted to comment on your remarks about establishing a "reputation". That's all well and good, and I'm glad that works for you, but I feel you are losing sight of what "assume good faith" means if you feel that is a requirement. And you might also keep in mind that what works for you may not work for everyone. Your comments aren't even practicable for me as an IP editor, for example. 47.32.217.164 (talk) 01:15, 17 May 2017 (UTC)

I was also thinking of using the interlinked-separate-glossary idea for a separate "Notes" article which, unlike the existing <ref group=blahblah> feature, would have full-sized text and could incorporate figures. The links would not be at the subsection level, but at the level of individual terms. The article title might be

Spacetime (Introduction to curved spacetime section) notes

and could potentially be as long as the current "Spacetime" article. Again, this is all speculative, since I'm still stuck on the technical difficulties of creating a first-year-calculus explanation. Stigmatella aurantiaca (talk) 08:20, 7 May 2017 (UTC)

MOS Freaky Links?

Which part of the MOS spells out how to do the freaky links in this article, like for Spacetime Interval? I've never seen that before. Why is the article inconsistent, with some freaky links, but not all? 47.32.217.164 (talk) 05:42, 17 May 2017 (UTC)

redirect

Should relativistic spacetime link here? — Preceding unsigned comment added by 47.32.217.164 (talk) 07:39, 17 May 2017 (UTC)

My vision of what the article needs to be

To 47.32.217.164:

My vision has been for an article that everybody from middle-school students to first-year physics students can read with profit. An interested individual of almost any level of mathematical sophistication should be able to read straight through from easy to more advanced material until the reading gets too heavy going, at which point they should be able to stop and not feel that they have been cheated. The article that you revised and rearranged had an almost completely non-mathematical Introduction, followed by an algebra-based section dealing with Flat Spacetime (Special Relativity). In the future, I had hoped to follow with a calculus-based section dealing with Curved Spacetime.

Your actions have included consolidation of sections that I had deliberately segregated into non-mathematical Introductory treatments and mathematical reiterations requiring algebra.

Your edits are incompatible with my vision of an article accessible to all levels. Advanced and introductory material is all mushed together in your rearranged article. Stigmatella aurantiaca (talk) 18:27, 22 May 2017 (UTC)

Ok, so you have a point of view. I get it. I have one too, and it doesn't match yours. I do agree that making the article simpler to understand is a good thing, but that's not a license to do anything you feel like.

You seem to be pursuing two lines of thought together, one of "increasing development of the topic" and one of "increasing development of the mathematics"; I'd rather not conflate the two.

Yet somehow finding a means to serve the broadest possible readership has repeatedly been stated in multiple guides on Wikipedia as a highly desirable goal. Stigmatella aurantiaca (talk) 22:38, 22 May 2017 (UTC)

I see. You have the monopoly on how to appeal to the broadest possible readership. There's no need for discussion about that. — Preceding unsigned comment added by 47.32.217.164 (talk) 23:48, 22 May 2017 (UTC)

Both of those are value judgments. While I can see justifying the first for the sake of writing a coherent article, I don't see the necessity of the second. I believe a good article can be written without forcing a progression of the mathematics within the article.

And therein lies the fundamental difference in our viewpoints. Readers who want a non-mathematical treatment of spacetime should be able to access a non-mathematical treatment. Readers who are not afraid of algebra should be able to access an algebraic treatment. And readers who are comfortable with basic calculus should be able to access a calculus-based treatment. This necessarily implies a progression of the mathematics. Stigmatella aurantiaca (talk) 22:38, 22 May 2017 (UTC)

Yes. That is the difference in our viewpoints. I notice you're resorting to "should" statements now, though. I was hoping for something more constructive. 47.32.217.164 (talk) 23:36, 22 May 2017 (UTC)

Would you care to point out where you think the mathematics is "mushed", and see if we can't come up with a solution? 47.32.217.164 (talk) 19:24, 22 May 2017 (UTC)

Can I also ask that you stay away from "should" statements? That feels like you are talking down to me. 47.32.217.164 (talk) 19:28, 22 May 2017 (UTC)

I give up

I see where you are headed with this article.

You actually want to load up the "Early philosophy" section with cruft that is totally irrelevant to 99% of users of this article? You've already wrecked my non-mathematical introduction to spacetime.

Goodbye. Stigmatella aurantiaca (talk) 01:43, 23 May 2017 (UTC)

Wow. You nailed me. My evil plan has been thwarted. 47.32.217.164 (talk) 02:52, 23 May 2017 (UTC)