General Relativity: Angular Momentum, Gravity & Questions

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• manolo-mm
In summary, the conversation discusses a YouTube video about general relativity and how gravity bends spacetime, redirecting angular momentum into the center of gravity. However, the validity of this information is questioned and it is suggested to seek reliable sources such as textbooks and peer-reviewed papers. The use of videos from well-known universities is also mentioned as a potential source of accurate information. The difficulty of explaining complex scientific concepts in a simple yet accurate manner is acknowledged.
manolo-mm
Hi everybody

I saw quite a nice Youtube vid about general relativity and how gravity bends spacetime and therefor redirects angular momentum into the center of gravity. I thought the first time I begun to understand the concept but immediatly the questions poped up.

The video basically says that curved spacetime redirects angular momentum into the gravitational center. Ok there is no no difference in gravity on northpol to southpol. so all external angular momentum forces are redirected in full. And all objects in our solar system are moving in the same speed along with the sun through the universe. And there is no gravitational differences on other bodys in our solar system as far as we know. So they all redirect the angular momentum of traveling through the universe to their center of gravity. To why do we have different amounts of gravity on the different bodys in our solar system? The only answer i can imagine is that its not angular momentum that is redirekted through curved space time but another force. But that's just a guess. Anybody has a solid answer for me?

manolo-mm said:
how gravity bends spacetime

No, stress-energy bends spacetime; "gravity" is just another name for the effects of bending spacetime.

manolo-mm said:
and therefor redirects angular momentum into the center of gravity

This sounds like nonsense to me. I have not watched the video but I am skeptical that it is a reliable source. [Edit: It looks like the problem is with the OP's misunderstanding something, not the video itself--see follow-up post below.] YouTube videos in general are not a good place to be looking if you want to learn actual physics. You should be looking at textbooks and peer-reviewed papers.

vanhees71
manolo-mm said:
The video basically says that curved spacetime redirects angular momentum into the gravitational center.

And now having watched the video, I don't see where it says this anywhere. What it does say actually looks OK to me, though of course it only barely scratches the surface of GR. But I don't see it saying anything like this. Where are you getting this from?

vanhees71 and Motore
Thats how I understood and interpreted this vid.

weirdoguy and Motore
manolo-mm said:
Thats how I understood and interpreted this vid.
Which of the seven levels mentioned angular momentum?

PeterDonis said:
YouTube videos in general are not a good place to be looking if you want to learn actual physics. You should be looking at textbooks and peer-reviewed papers.
I think, what are pretty reliable videos is if they come from lectures at well-known universities, often also appearing at youtube (e.g., the online lectures from MIT). It's of course easier to produce reliable videos on the natural sciences when addressed to students of the subject rather than to the public. To "explain science as simple as possible but not simpler" is among the most difficult tasks for a scientist!

vanhees71 said:
I think, what are pretty reliable videos is if they come from lectures at well-known universities, often also appearing at youtube (e.g., the online lectures from MIT).

Yes, these are something of a special case, since as course materials they have to meet certain standards that a random YouTube video does not.

vanhees71
Of course, the random Youtube video is more likely to be unreliable. It's a kind of 2nd law applied to "web content" ;-).

1. What is general relativity?

General relativity is a theory of gravity proposed by Albert Einstein in 1915. It describes how the force of gravity arises from the curvature of space and time caused by the presence of matter and energy.

2. What is angular momentum in general relativity?

Angular momentum is a measure of the rotational motion of an object. In general relativity, it is a conserved quantity that describes the amount of rotation of a massive object in a curved spacetime.

3. How does general relativity explain gravity?

General relativity explains gravity as the result of the curvature of spacetime caused by the presence of massive objects. This curvature affects the motion of objects in space, causing them to move towards each other.

4. What is the difference between general relativity and Newton's theory of gravity?

The main difference between general relativity and Newton's theory of gravity is that general relativity takes into account the curvature of spacetime, while Newton's theory considers gravity as a force acting between two objects. General relativity also predicts the bending of light and the existence of black holes, which are not explained by Newton's theory.

5. Can general relativity be tested?

Yes, general relativity has been extensively tested and confirmed by numerous experiments and observations. Some of the most famous tests include the bending of starlight by the sun, the precession of Mercury's orbit, and the detection of gravitational waves. General relativity has passed all tests with remarkable accuracy, making it one of the most successful theories in physics.

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