Talk:Spacetime/Archive 18

Removing self-references per WP:SRTA and WP:CLICKHERE

I'm in the process of fixing the text accompanying the links between the sections and their summaries. The Transhumanist 23:11, 19 August 2017 (UTC)

Your edits, while well intentioned, completely ignore the fact that over 40% of users access through mobile devices, and can become utterly confused by limitations of these devices unless forewarned. The mobile interface is buggy and I have an outstanding bug report on phabricator. The extensive notes and instructions are there for a purpose. Ignoring the limitations of mobile devices is a major disservice to a very large minority of our users. Stigmatella aurantiaca (talk) 00:17, 20 August 2017 (UTC)

Three months pageviews summary shows about 45% access through the mobile web, of which we can probably assume are mostly through phones. To save screen space and data usage, Wikipedia mobile collapses sections when displaying on a phone screen. The target of an internal link does not exist unless the section where it is located has been expanded at least once and cached. Phone users need to be warned of this fact.

The phabricator bug report has to do with the "<" back button on mobile devices, which under certain conditions goes completely haywire.

The recommendations on WP:SRTA and WP:CLICKHERE were developed by desktop users who are largely ignorant of mobile limitations.

Stigmatella aurantiaca (talk) 00:37, 20 August 2017 (UTC)

The standard notes that its application "is best treated with common sense, and occasional exceptions may apply." The Spacetime article, far more than other articles on Wikipedia, binds main article and section summaries into a seamless whole, the smooth union of which would be disrupted by your edits, especially on mobile devices. Stigmatella aurantiaca (talk) 00:48, 20 August 2017 (UTC)

I don't know what you're doing, but if you need many call-outs for "mobile users do this to read the article", you're doing it wrong. Power~enwiki (talk) 02:44, 20 August 2017 (UTC)

@Power~enwiki, claiming absurdity of an obviously researched phenomenon is not very helpful, as well as the dry judgement of doing something wrong. For the sake of the article I hope you can contribute something better. I can't, but simply this single, one reversion. Purgy (talk) 06:59, 20 August 2017 (UTC)

This is not a generic web hosting service, it is an encyclopedia. Format the article in a way that works for the other 5 million articles, or host it somewhere else. Power~enwiki (talk) 15:32, 20 August 2017 (UTC)

The mission of the encyclopedia is to be accessible and useful to as wide an audience as possible. This is a long article on a technical topic. We have attempted, using (1) an extended, detailed lede and (2) closely integrated section summaries to make a multilevel document that is understandable by everybody from middle school students to first year college students. Unfortunately, the mobile web interface presents serious challenges in terms of its design as well as its unresolved bugs. Only 3% of users use the mobile APP as opposed to the mobile WEB. If mobile users all used the mobile APP, perhaps I wouldn't be so resistant to your suggestions. Stigmatella aurantiaca (talk) 17:35, 20 August 2017 (UTC)

I feel that all the "See also: Section summary below" and "Return to Introduction" should be removed entirely. Having a separate "Introduction to Spacetime" article (if a page title can be agreed on) is a better way of solving the technical issues that you are concerned about. Simply shoe-horning mountains of device-specific text into the page is clearly not a good approach here. Power~enwiki (talk) 16:01, 20 August 2017 (UTC)

"Introduction to" articles have, with only a few exceptions, historically failed in their mission. For example, see the talk page of the former "Introduction to special relativity" which was ultimately deleted. The discussion leading to deletion and the aforementioned talk section outline many problems with the "Introduction to" approach. Stigmatella aurantiaca (talk) 17:12, 20 August 2017 (UTC)

Do we not have a method, such as {{Selfref}} for example, by which we can automatically format all these self-references so that they won't show up in paper versions of articles? I think this may be a good compromise. -- œ^™ 00:56, 20 November 2017 (UTC)

{{selfref inline}}? {{repeat|p|3}}ery (talk) 01:07, 20 November 2017 (UTC)

Yes, and {{Unprintworthy inline}}. @Stigmatella aurantiaca: would you consider formatting the page using these templates so that we may have consistency across ALL platforms including print? -- œ^™ 01:19, 20 November 2017 (UTC)

Missing sitation

The article says: "The fundamental reason for merging space and time into spacetime is that space and time are separately not invariant ..." Is there some reference for this?

Please, add new sections at the bottom, and, please sign your contributions.

This appears so obvious to most, that nobody searched for it? Purgy (talk) 05:28, 18 September 2017 (UTC)

I agree it may be obvious. I still would appreciate having a reference for it 18:27, 23 September 2017 (UTC)

Relativity

According to Einstein the speed of an observer effects how time effects that observer. Then one can infer that because we are all move thru space at different speeds, time is relative to each observer. Then my question is "when is "Now" occurring ? Russcnj (talk) 01:35, 24 November 2017 (UTC)

"Now" is just a convenient time coordinate, specifying a time tick in the frame you are in, and transferable via Lorentz to other frames. Please, take your questions to more appropriate places (reference/help desks?). Purgy (talk) 07:01, 24 November 2017 (UTC)

First section: motion of observer

From the Explanation section: However, Albert Einstein's 1905 special theory of relativity postulated that the speed of light through empty space has one definite value—a constant—that is independent of the motion of the light source.
I think we should add independent both of the motion of the light source and of the motion of the observer. Independence from the observer's motion is the really striking and unintuitive part. --Arnaudf (talk) 07:58, 8 January 2018 (UTC)

While from some outside POV (from an additional, new frame of reference) a motion of the observer might be worth mentioning, I think it is important to emphasize that -intentionally- obervers -wrt their motion- are identified with a frame of reference, in which they are at rest, and so they have no motion wrt this frame, in which they observe the speed of light. The really striking and unintuitive fact in STR is that all observers, in their relatively moving frames agree on the observed speed being the very same. Personally, I dislike the separation of observers and frames. Purgy (talk) 10:43, 8 January 2018 (UTC)

@Arnaudf: I have addressed your concerns. Please let me know if the point has been clarified to your satisfaction. Prokaryotic Caspase Homolog (talk) 06:40, 2 April 2018 (UTC)

Sorry, I missed this reply, and directly edited the article. I am convinced that setting relative motion and Einstein's postulate on equal footing generates more confusion than less. Einstein himself, addressed in a comment, just -wisely!- mentioned movement of the source. Many of the troubles in SRT result from unluckily separated terms "observer" and "frame of reference". Please, note the emphasis on "at rest" in my above rp. Purgy (talk) 13:08, 2 April 2018 (UTC)

This symmetry of movement of source/observer is no consequence of the postulate, but of the relativity principle. The counterintuitivity lies in the postulate, exactly as it is formulated (without "moving observers"!) by Einstein, in that it denies the linear additivity of velocities (v_observed = v_light ≠ v_light ± v_source!). The ± covers an approaching and a receding source.

I think Arnoudf got Einstein's statement only incompletely. To talk about a "moving observer" (no observer anymore!) requires another "observer", since each observer is per definition at rest in his frame of reference. This leads to the misleading situation that the "observedly moving observer" (being not at rest!) is not an observer anymore, ... The constancy of speed of light is made up by all observers (at their respective rest!) agreeing on its value.

Since "moving (non!-)observers" are not relevant for the constancy of speed of light, it would be best to again get fully rid of them. I regret not having eliminated completely your effort to (additionally) answer Arnoudf's question, and you seem to have overlooked my rp to Arnoudf above. I do not want to get into some reverting frenzy, but the current phrasing is logically wrong.

My suggestion below is to essentially return to the status before introducing an inappropriate "moving observer", in an effort to explain a question that is better answered by "the difference between what one measures/observes versus what one sees", since genuine observers are constantly at rest. Other notions of being at rest are just confusing in SRT.

 Einstein's equations describe important consequences of this fact: While the spatial distances and the temporal differences between two events, as measured by different observers, do not agree, there is a new invariant measure established, that connects the two events, the spacetime interval.

I am unsure whether to mention here the specs about inertial frames, which I omitted. Perhaps consensus should be achieved on this before moving on to Einstein/Minkowski. I hope you are OK with me splitting this. Purgy (talk) 09:49, 3 April 2018 (UTC)

1. In terms of its historic content, your suggested paragraph, which I presume you intend to insert after the paragraph ending "... (separate vantage points that aren’t being subjected to g‑forces but have different velocities)", gives the false impression that the spacetime interval played an important part in Einstein's original kinematic formulation of special relativity. He was, of course, aware of the relationship, but it was Minkowski who raised the spacetime interval to a central theme in his geometric reformulation.
2. In terms of its scientific content, the paragraph says little that is not stated in the paragraph beginning, "In 1908, Hermann Minkowski—once one of the math professors of a young Einstein in Zürich..."
3. Much of the detail about observers and reference frames that you go into above is detail that should go into the main body of the article, not the lede. Ledes are customarily written without references, because they are supposed to reflect what is covered in the main body of the fully referenced article. Expanding the lede to cover your points would convert the lede into an unreferenced personal essay.
4. We therefore need to decide where in the main body of the article you wish to insert your discussion. I would suggest that it be in the text accompanying Figure 1-1.
5. Yes, when I wrote below about Einstein's preference for "Theory of Invariance", I had in mind page 164 of Miller.
6. You wrote, "I do not want to get into some reverting frenzy, but the current phrasing is logically wrong." As you can see from this diff, the current phrasing represents my minimal retouching of your words to fix the grammar.

Prokaryotic Caspase Homolog (talk) 11:21, 3 April 2018 (UTC)

(1) My suggestion was intended to replace the sentence "Einstein's equations ...", that you suspended, and the whole rest of this paragraph (starting with "Because physics ...", especially the sentence about different physics, thereby omitting the mentioned inertial frames and their g-forces). The reasons are, first (re (6)), that your edit moved the property of "counterintuitivity" from the really counterintuitive postulate to a "plain" consequence, which is not primarily implied by the postulate, but by physics not depending on frames (not specific for STR), and second, for getting rid of these "moving observers" as explained above. I am perfectly fine with tracelessly removing the current sentence ("Because physics ..."), and leave out the "Einstein' equations ...", too. Please, make your suggestion, preferably without moving observers. ;)

(3+4) I do not think that my above ranting about "moving observers" and their potential of confusion is of encyclopedic value, so I see no place for it, certainly not in the lead. Let me know if you think there is useful content in and a meaningful place for it.

(2+5) I don't know Miller's p.164, and I am not sufficiently erudite to discuss the origin and the epiphany of the "invariant spacetime interval". I try hard to correct misleading thoughts within existing sentences, under the condition of keeping most of them. This way I repetitiously always end with the central theme of STR: the invariant spacetime interval. Maybe, it is not too bad to mention it every once in a while? Cheers, and thanks for correcting my typoed quotes. Purgy (talk) 19:13, 3 April 2018 (UTC)

I'm a little confused. Can you show me how you want to rewrite this section? Make your edits directly to the text.

Until the turn of the 20th century, the assumption had been that the three-dimensional geometry of the universe (its description in terms of locations, shapes, distances, and directions) was independent and distinct from a one-dimensional time (the measurement of when events occur within the three-dimensional universe). However, Albert Einstein's 1905 special theory of relativity postulated that the laws of physics are the same in all inertial frames of reference (i.e. the principle of relativity), and that the speed at which light propagates through empty space has one definite value –a constant– that is independent of the motion of the light source. Because physics should not depend on different observers (principle of relativity), this postulate The combination of these two postulates has the counterintuitive consequence that the constant speed of light is also independent of the motion of the observer. constant regardless of the frame of reference in which it is measured. Furthermore, the distances and times between pairs of events vary when measured in different inertial frames of reference.

Thanks, Prokaryotic Caspase Homolog (talk) 20:56, 3 April 2018 (UTC)

I made a few changes. Feel free to add more or to undo anything that I've done. Prokaryotic Caspase Homolog (talk) 12:09, 4 April 2018 (UTC)

More changes to work around your issue with moving observers. As before, feel free to make additional edits. Prokaryotic Caspase Homolog (talk) 12:37, 4 April 2018 (UTC)

I just had an edit conflinct, I don't think I'll use a shared edit zone anytime soon. :) Please, see my suggestion below:

Until the turn of the 20th century, the assumption had been that the three-dimensional geometry of the universe (the where, as spatially perceived in terms of locations, shapes, distances, and directions) and the one-dimensional time (just measuring the temporal when of events within three spatial dimensions). However, Albert Einstein postulated 1905 in his special theory of relativity that the speed at which light propagates through empty space has one definite value –a constant– that is independent of the motion of the light source.

This postulate, upsetting the linear additivity of velocities, not only inseparably joins together the four dimensions, hitherto assumed as independent, of space and time, but also has many spectacular and counterintuitive consequences. Einstein framed his theory in terms of kinematics (the study of moving bodies) by devising fundamental thought experiments (trains and flashes) involving known lengths and signalling via light flashes. These showed that distances and even temporal ordering (simultaneity!) of pairs of events change, when measured in different inertial frames of reference. Einstein's theory was a breakthrough advance over ...

Removed for reasons given above:

Because physics should not depend on different observers (principle of relativity), this postulate has the counterintuitive consequence that the constant speed of light is also independent of the motion of the observer.

Removed from elder versions and my contributions:

... (separate vantage points that aren’t being subjected to g‑forces but have different velocities). Einstein's equations, derived from these experiments, describe the important consequences in detail, and establish a new quantity, the spacetime interval between two events, each described by its "where" and "when", as invariant with respect to change of observers.

To state that I would want to rewrite the section in the above way, is way too much. It's just a way that I do not object for the moment, and that contains my suggestions. Sorry for having been incomprehensible. Purgy (talk) 12:46, 4 April 2018 (UTC)

Hmmm... I'll see how to merge your ideas and my ideas. Right now I'm off to work. Prokaryotic Caspase Homolog (talk) 13:21, 4 April 2018 (UTC)

Let's try this:

Until the turn of the 20th century, the assumption had been that the three-dimensional geometry of the universe (its spatial expression in terms of coordinates, distances, and directions) was independent of one-dimensional time. However, in 1905, Albert Einstein postulated in his special theory of relativity that (1) the laws of physics are the same in all inertial frames of reference (this is the principle of relativity), and (2) the speed at which light propagates through empty space has one definite value—a constant—that is independent of the motion of the light source.

A logical consequence of these postulates is the inseparable joining together of the four dimensions, hitherto assumed as independent, of space and time. Many other counterintuitive consequences emerge: in addition to being independent of the motion of the light source, the speed of light is constant regardless of the frame of reference in which it is measured; the distances and even temporal ordering of pairs of events change when measured in different inertial frames of reference (see relativity of simultaneity); and the linear additivity of velocities no longer holds true.

Einstein framed his theory in terms of kinematics (the study of moving bodies). Einstein's theory was a breakthrough advance over ...

I specifically excluded the following because there is no coverage in the main article of Einstein's thought experiments. The article is devoted to development of the geometric interpretation of relativity, not the kinematic. Perhaps this sentence should go into the Special relativity article, along with specific examples. Currently Special relativity gives no coverage of these thought experiments, which, although they never appeared in any of Einstein's formal publications, played a large role in Einstein's popular and semi-popular writings, as well as in his personal visualization.

by devising fundamental thought experiments (trains and flashes) involving known lengths and signalling via light flashes.

I also thought that words like "spectacular" and the use of exclamation points was non-encyclopedic. Prokaryotic Caspase Homolog (talk) 03:00, 5 April 2018 (UTC)