Talk:Introduction to general relativity

Suggestion For New Diagram

I would find it helpful if someone made an additional diagram. You've all seen it: It's the one that looks like a mattress with a bowling ball in the middle. The x=constant and y=constant lines are straight near the edge, but curve downward near the middle. This diagram would explain in an intuitive way why a planet orbits the sun: it simply follows a geodesic on the curved surface. MathPerson (talk) 20:37, 18 March 2019 (UTC)

What I meant was something like the output of this Mathematica plot:

Plot3D[-Exp[-.2 (x^2 + y^2)], {x, -5, 5}, {y, -5, 5}, PlotRange -> All, Axes -> None, Boxed -> False, PlotPoints -> {30, 30}] MathPerson (talk) 23:00, 18 March 2019 (UTC)

It would be nice if there was a correct diagram.

I have been searching and searching. Finally I found that the image with the rectangular grid is completely wrong like most images which are used all over the web.

If I'm right; “Relative to an observer at rest far from a black hole, space is compressed (contracted) near the event horizon and time is stretched out (dilated).”.

This means that a grid seen from the point of view looking at the website should have smaller segments closer to the mass opposite to the image of an stretches sheet ( with larger segments ). The solution to do it right would be to show a radial sheet instead of this one.

If the above statement is correct it would also be nice to use it in the text. Everyone always states that clocks are running slow in a gravitational field but generally space is omitted and that was why I was searching. It is correct that clocks are running slow but you have to switch it around to compare it to the way we see space. On time you have to think; slow is more time ... is less grid lines is bigger cell's. Maybe as full sentence with the usual running slower;

“Relative to an observer at rest far from a black hole, space is compressed (contracted) near the event horizon and time is stretched out (dilated / running slower).”.

I believe this would make things much clearer.

The best thing would be to show images with what space does, what time does and what the world lines do in different scenarios; black hole with or without speed or rotation, object falling in with speed or without speed and light. I think that this would really clear things for people with a medium understanding.

Disambiguation in section: From acceleration to geometry

This section states:

"(...)The orbits of moving bodies are curves in spacetime; the orbits of bodies moving at constant speed without changing direction correspond to straight lines."

The use of "curves" in the first part and "lines" in the second one suggests that, in the first case, the article describes a trajectory in Minkowski space that is not straight. A parabola, or a sine wave, for example. I get that the use of the unqualified "curves" means any curve, straight or not. But I find that, in an article titled Introduction to General Relativity, it does not convey clearly enough this meaning.

Two edits possible:

"(...)The orbits of accelerated bodies are curves in spacetime; the orbits of bodies moving at constant speed without changing direction correspond to straight lines."

Or

"(...)The orbits of moving bodies are curves in spacetime; the orbits of bodies moving at constant speed without changing direction correspond to straight curves..."

I believe the first edit conveys the point in a clearer manner.

--Jfbertrand8 (talk) 12:17, 5 November 2020 (UTC)

Theory of general relativity, or general theory of relativity?

I see Britanica got it wrong in their article "Black Hole." Maybe this article could correct a common mistake people make who don't know better. 2600:8801:BE31:D300:350B:FC57:5D61:625E (talk) 21:06, 30 May 2022 (UTC) James

A Commons file used on this page or its Wikidata item has been nominated for speedy deletion

The following Wikimedia Commons file used on this page or its Wikidata item has been nominated for speedy deletion:

• Gravity Probe B.jpg

You can see the reason for deletion at the file description page linked above. —Community Tech bot (talk) 15:38, 30 April 2023 (UTC)