Talk:Spacetime

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Not satisfied with the lead

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)

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)

Misleading statement

I find the paragraph `Spacetime interval` misleading, it introduces pythagoeran distance, and calls it invariant

``Although two viewers may measure the x, y, and z position of the two points using different coordinate systems, the distance between the points will be the same for both (assuming that they are measuring using the same units). The distance is "invariant".``

while the sentence is technically true for euclidean geometry, in newtonian spacetime, distance between events is not invariant for moving observers if the events are separated by time, i think this paragraph should highlight what was introduced by special relativity, not what was introduced by addition of time. Lorentz contraction can be mentioned separately, here maybe its better to highlight time itself as the invariant variable in newtonian physics. Ondrosaurus89 (talk) 11:49, 18 September 2023 (UTC)

Geometry of 'common sense'?

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)

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

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)

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)

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

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)

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)