Talk:Spacetime/Archive 4

Self-contradictory source

The source for the statement

N = 1 and T = 3 has the peculiar property that the speed of light in a vacuum is a lower bound on the velocity of matter; all matter consists of tachyons.^[16]

appears to be self-contradictory. To quote the source (Max Tegmark):

Since a mere minus sign distinguishes space from time,

the remaining case (n,m) = (1, 3) is mathematically equivalent to the case where (n,m) = (3, 1) and all particles are tachyons [14] with imaginary rest mass. Also in this case, an observer would be unable to make any predictions, since as described in more detail in [15], wellposed problems require data to be specified in the nonlocal region outside the lightcones. If two cases are mathematically equivalent (i.e. indistinguishable), one cannot then distinguish them on mathematical grounds as producing wildly (and hence observably) different predictions. All that would happen is that the three "timelike" dimensions become equivalent to spacelike dimensions and the "spacelike" dimension becomes a timelike dimension (and the supposed tachyons become standard non-tachyons with timelike worldlines inside the light cones with this relabelling), supporting the indistinguishability statement. Blindly quoting an obviously invalid (or naïvely misinterpretable) assertion from a source should be excluded or clarified correctly. — Quondum 17:48, 11 October 2012 (UTC)

From 2 to 3 dims

For example, on the globe the latitude and longitude are two independent coordinates which together uniquely determine a location.

That sentence could be expanded to include altitude which brings the reader from 2 to 3 coordinates which is the next logical stepping point on to the fourth which includes time. Damotclese (talk) 02:56, 15 October 2012 (UTC)

Spacetime References

I'm new, but I don't see how to edit the References on this wiki page. The Ehrenfest article is in Annalen der Physik volume 366, not volume 61 as listed both in the References and in the External Links. (The page number is correct, as is the year.) This can be verified by following the Bibcode link in the References (Reference 14) or by surveying Annalen der Physik. (The original article is in German.) An English version (not sure whether it is a strict translation) can be found in the Proceedings of the Amsterdam Academy listed under the same Reference 14. Giarcea (talk) 04:34, 29 November 2012 (UTC)giarcea

You'll need to edit the section referencing the footnote, in this case, Spacetime#Privileged character of 3+1 spacetime. You may then have to search for a snippet of the reference to locate the actual text to edit, e.g. Annalen der Physik. — Quondum 06:08, 29 November 2012 (UTC)

Continuous creation of space-time

The article does not mention different views/theories about space-time; such as the ones in this article (http://www.alfonsoleonguillen.net/Spacetime56.pdf).

In addition to that, it should be stated somewhere in the article that, space-time has been continuously being created/added since the beginning of the universe: http://www.youtube.com/watch?v=vJayxpt482g Logos5557 (talk) 19:16, 3 February 2013 (UTC)

Spacetime intervals

"The interval s² between two events is defined as s² = Δr² − c²Δt², where c is …, and Δr and Δt …"
Why is s squared? Why not simply call it X or Y or I or S ? --Jerome Potts (talk) 17:09, 13 March 2013 (UTC)

This is really a question for the reference desk (wp:Reference desk/Science) - see wp:talk page guidelines. Good luck over there! - DVdm (talk) 18:07, 13 March 2013 (UTC)

The grinch is correct. But the short answer is that the thing on the left hand side of the = has units of area if you express it without a square, and that's not very intuitive. Better to make it a length. And yes, "space-time separation" would have been a better term for it, since "interval" suggests time units. And in fact the other term is sometimes used. I dunno why the worse one won out. Maybe Einsten or Minkowski used the German equivalent of "interval" for this invariant quantity. SBHarris 18:33, 13 March 2013 (UTC)

That's Mr. Grinch for you ;-) - DVdm (talk) 19:25, 13 March 2013 (UTC)

What is spacetime?

Isn’t it important to distinguish between spacetime as a mathematical model and spacetime as an object in an external world? One is a thought inside an observer’s brain and the other is an object outside an observer's brain.Lestrade (talk) 22:41, 10 April 2013 (UTC)Lestrade

I can't think of any cases in which the lack of distinction would be confusing. It seems to me that the mathematical model is meant to represent the real world entity, and so any discussion thereof addresses the real world entity by describing it in terms of a mathematical model. Although, maybe I just haven't been able to think of any examples where the lack of distinction would cause genuine confusion; please mention any specific instances you can think of.

Crazyeirishman (talk) 15:05, 17 June 2013 (UTC)

Everyone tells me that spacetime is a real world entity, but I have yet to see or feel it in my daily comings and goings. I guess that the distinction between what is inside the brain (mathematical model) and what is outside the brain (real world entity) is some old, outdated notion that belongs in the dustbin of history.Lestrade (talk) 15:58, 17 June 2013 (UTC)Lestrade

Perhaps, but this is the place where we discuss the article, not the subject — see wp:talk page guidelines. If you have questions about the subject, you can go to our wp:reference desk/science. Good luck. - DVdm (talk) 06:19, 18 June 2013 (UTC)

I merely suggested that it is important for the article to distinguish between spacetime as a mathematical model and spacetime as a physical object. One is inside of someone's brain and the other is outside of someone's brain.Lestrade (talk) 15:04, 18 June 2013 (UTC)Lestrade

This would be trying to capture perception and subjectivity. This is more a topic of philosophy, and does not apply only to this example. Your contention is also debatable, and you'd need references anyway. The article should not cover meta-issues like this. — Quondum 15:56, 18 June 2013 (UTC)

In an article on “spacetime,” the definition of spacetime is a meta-issue? The difference between spacetime as a mathematical concept in someone’s mind might be different from spacetime as a physical entity that is curved, becomes warped when matter is near it, and is, itself, located in space. In this way, some naïve reader of the Wikipedia article may think that there are two kinds of spacetime: one a private idea in a mathematician's brain, and the other a curved, warped, public, physical object that is similar to a fabric or rubber sheet. Such a situation would lead to ambiguity and misunderstanding.Lestrade (talk) 00:36, 19 June 2013 (UTC)Lestrade

The article claims that spacetime is a mathematical model, not a physical entity. Is the concept of spacetime analogous to the concept of the electromagnetic field?Lestrade (talk) 15:15, 1 August 2013 (UTC)Lestrade

I don't see a problem. The first lede sentence does indeed define "spacetime" as a mathematical model. However, the very next sentences state that

From a Euclidean space perspective, the universe has three dimensions of space and one of time. By combining space and time into a single manifold, physicists have significantly simplified a large number of physical theories, as well as described in a more uniform way the workings of the universe at both the supergalactic and subatomic levels.

Which means that while "spacetime" may be a mathematical model, that model describes quite well the workings of the actual physical universe in which we reside. The only other possible way to state this that I can come up with is that "spacetime" is a physical attribute of the universe, but which is best explained using mathematical models. I don't see a substantive difference either way. — Loadmaster (talk) 00:05, 2 August 2013 (UTC)

I would think that an encyclopedia article on spacetime would tell a reader what spacetime is. Is it a mathematical model (inside your head) or a physical entity (outside your head)?Lestrade (talk) 02:55, 2 August 2013 (UTC)Lestrade

It is the former, a mathematical model, which is used to model the latter, the physical structure of our universe. As I said above, that is fairly clear from the first lede paragraph. — Loadmaster (talk) 22:25, 5 August 2013 (UTC)

Spatial density and the timing of velocity are directly linked to each other, because if one value changes, the other one will change at a uniform rate. The link between the two is not understood, but it is known to exist, so to give the link between space and time a name, spacetime. There is various literature that accompanies theories about spacetime... counting dimensions, travelling without moving, time as an individual object, even Einsteins paper called "Space-time" talks about matter showing up where it cannot based on the fact that it cannot and the three lines of a triangle being a single straight line for no physical reason and basically, spacetime is the unexplained link between space and time while most of the stuff that goes with it is what they call a load of ole rubbish, but don't quote me or I will never pass my doctorate in physics! ~ R.T.G 17:28, 19 August 2014 (UTC)

Block quote format

Some of the quotes under 'Spacetime in literature' seem too long not to be block quotes, especially the one from William Rowan Hamilton, since it includes single-quoted passages. The only reason I bring this up is because I was quickly scanning the article, saw a passage that didn't look very wikipedia-like, and had to look up and down several lines before I found any indication that it was from a quote. Has anybody else noticed this? Crazyeirishman (talk) 14:59, 17 June 2013 (UTC)

Necessity of the "privileged character of 3+1 spacetime" section

Hi all, I'm currently working on this article in my sandbox in the very early steps of attempting to bring it to FA, and I believe that the section mentioned in this section header goes off on a tangent and distracts from the rest of this article; it doesn't really belong here. I'd like to hear some further opinions on this, and what should be done with this section if people don't think it should stay. Thanks! StringTheory11 (t • c) 02:58, 17 July 2013 (UTC)

The section isn't entirely bs, but I agree, it doesn't belong here as it stands. Try to shorten it down to a minimum and rinse out the more or less philosophical stuff. Statements like "The inverse square law doesn't produce stable orbits unless 3+1" and "EM theory looks different in other dimensions" are true and can be backed up rigorously.

Also, be warned! I don't think this article will make FA status ever. Try to get it to B+ or even A. That would be an accomplishment. YohanN7 (talk) 08:12, 17 July 2013 (UTC)

We can try :). StringTheory11 (t • c) 21:41, 20 July 2013 (UTC)

No ideas for now but looking forwards to StringTheory11 advancing the article up to FA, since he's an expert in the topic. Right now I'm editing articles related to spacetime on four vectors and in relativistic quantum mechanics, not to mention symmetries in quantum mechanics involving the Lorentz group and Poincaré group. M∧Ŝc²ħεИ_τlk 10:19, 17 July 2013 (UTC)

Eh, I'm not really an expert in the topic; I don't (yet) have a formal physics or astronomy education; everything I know is self-taught. But yeah, I'd be happy to work on one of those articles, if necessary. StringTheory11 (t • c) 05:51, 18 July 2013 (UTC)

Since nobody seems to have any objections, I'll get to work trimming it. StringTheory11 (t • c) 21:41, 20 July 2013 (UTC)

I agree with the other comments, but I would put it even more strongly: this article is not the place for what is essentially a summary of meandering supposition and, no doubt, circular reasoning. This entire section appears to be aimed at motivating/explaining/debating the necessity of this particular configuration of observed spacetime. I suggest removal of the section from the article, leaving at most a see-also link (if it is moved elsewhere, else simply delete it). If the content seems to have value, an article could be created for it, but IMO it'd take a lot of work to make it withstand an AfD. It makes for interesting speculative reading, but so does science fiction; it does not strike me as encyclopaedic material. It might, for example, belong better as a subsection of Anthropic principle#Applications of the principle if trimmed and properly sourced. — Quondum 01:16, 21 July 2013 (UTC)

Article on time correction

Dear Editors,

I have an article on time correction that explains the dimension of time as a parameter for several special relativity calculations. I am hoping to add to basic concepts and add to some of my topics to space time if you can look over it. I am wondering if an editor can look at my article and suggest additions for space time please?

https://en.wikipedia.org/wiki/Wikipedia_talk:Articles_for_creation/Time_correction

Magravat (talk) 21:35, 19 February 2014 (UTC)MAgravatMagravat (talk) 21:35, 19 February 2014 (UTC)

Hi Magravat. I have added a header for your new section. I think your best bet is to go to Wikipedia talk:WikiProject Physics/Taskforces/Relativity with this. But do note that we cannot add our original research (see wp:NOR) to articles. For anything we like to add anywhere, we need solid reliable secondary sources (see wp:secondary sources). Good luck and cheers - DVdm (talk) 21:57, 19 February 2014 (UTC)