Talk:Spacetime

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Not satisfied with the lead[edit]

The lead says spacetime is a mathematical model. But we all live within spacetime, meaning spacetime can't just be a mathematical model. Spacetime is what we live in.

As far as we know, spacetime is a four dimensional thing that generally has everything in it, except for the stuff that is very far away, or very old, or through black holes or across other exotic boundaries.

I think the lead should be updated. 96.227.223.203 (talk) 03:13, 5 September 2023 (UTC)[reply]

Spacetime is a model for representing, describing, and predicting the universe and behavior its astronomical bodies. It's typical in science to use abstracted representations of objects, phenomena, etc. Our understanding of spacetime is not necessarily correct or complete. Basically, we don't necessarily live in our idea of spacetime. But these models can give us some idea of how we can expect things to behave. 2600:1700:D580:8680:CC69:C05D:1BB3:FBDD (talk) 05:59, 30 March 2024 (UTC)[reply]

Geometry of 'common sense'?[edit]

I don't think this terminology is helpful. Can we improve the description of a euclidean geometry please? Thx :) 189.158.98.184 (talk) 14:26, 11 November 2023 (UTC)[reply]

Longitudinal Doppler effect: Unclear, "W = YW' " should be "w = gamma * w' "[edit]

The derivation of the longitudinal Doppler effect is unclear. Either clarify the reasoning, or copy the reasoning from the Wikipedia page "Relativistic Doppler effect". Also: The equation "W = YW' " should most probably be "w = gamma * w' ".

If the current example could be clarified, then that would be a good thing: We would have two different derivations of the longitudinal relativistic Doppler effect. Note that the explanation in the referenced book by Sander Bais, is much clearer. Johanwiden (talk) 08:43, 17 March 2024 (UTC)[reply]

You're right. My original presentation was based closely on Bais. In the intervening years, other editors have "improved" on my original presentation, introducing typographical errors along the way. I won't try to bring it back to my original presentation, but at least I can fix the obvious typos. Prokaryotic Caspase Homolog (talk) 07:02, 30 March 2024 (UTC)[reply]

I have now reviewed the section, after your update. What I complained about has now been fixed. Thank you! Johanwiden (talk) 14:42, 9 May 2024 (UTC)[reply]

Extending momentum to four dimensions: Wrong unit for vertical axis, unclear explanation[edit]

As stated in Wikipedia "Four-momentum", and in the referenced paper by Sander Bais, the vertical axis has units "kg * m / s", but in the section it is implied that the unit is "m" (i.e. c * t). The explanation therefore becomes unclear. An explanation of the units of the axes is also needed: Why they have those units, and why it is OK for relativistic calculations. Johanwiden (talk) 12:09, 17 March 2024 (UTC)[reply]

In contrast to what I wrote above about Longitudinal Doppler effect, I can't blame other editors for infelicities of expression in this section. I'll see what I can do to improve the presentation, which is pretty much unchanged from what I wrote in 2017. Prokaryotic Caspase Homolog (talk) 07:10, 30 March 2024 (UTC)[reply]

I have now changed the figure 3.8 text:

- From: Relativistic spacetime momentum vector

- To: Relativistic spacetime momentum vector. The coordinate axes of the rest frame are: momentum, p, and mass * c. For comparision, we have overlaid a spacetime coordinate system with axes: position, and time * c.

I have no further issues. Johanwiden (talk) 08:41, 10 May 2024 (UTC)[reply]

Moving the "Beyond the basics" section to Special relativity?[edit]

A few days ago, I undid a good faith edit by @OzzyOlly: with the explanation,

"Science articles need to start with general readability topics, leaving technical material for later. However, the topics covered in this section, although special relativity topics, are quite technical, presenting a dilemma: placement before and after the general relativity section are *both* problematical. Hence the warning."

Thinking it over, OzzyOlly did have a point. No matter where in Spacetime you place the "Beyond the basics" section, it appears a bit misplaced. On the other hand, I think that this section naturally fits in Special relativity after the "Dynamics" section. Any thoughts on this? If there are no objections after a week, I will make the move. Prokaryotic Caspase Homolog (talk) 14:29, 26 June 2024 (UTC)[reply]

@Prokaryotic Caspase Homolog I have no objections, and I agree with moving it.

I will say that the reason I removed the message was because I felt it was unencyclopedic to stick a giant warning saying that the section might be too complex for readers. There obviously is {{complex}} but I don't believe that template is appropriate. I was more thinking of removing it per Wikipedia:No disclaimers and I probably should've said that in the edit summary. OzzyOlly (talk) 19:00, 27 June 2024 (UTC)[reply]