# Thread: Am I understanding relativity correctly? and a simple question...

1. Ok I am not sure if I am interpreting the videos I've watched on relativity correctly, and I would like to scan by you guys/gals. Well Einstein imagined a single layer of space-time right? Then when you put an object with mas on this sheet, it bends space-time, and this bending of space-time is gravity... correct? well my question is if space-time is a single sheet then how come we stars above us? I'm also having trouble imagining four dimensions...

2.

3. Originally Posted by Physicsforall
Well Einstein imagined a single layer of space-time right?
Actually, no he didn't. He visualised space-time as a four dimensional structure: the three space dimensions we are familiar with (which is why we can see stars above us) and one time dimension.

The "rubber sheet" analogy is just a really bad attempt to try and visualise in 2 dimensions what is happening in four.

I'm also having trouble imagining four dimensions...
Don't worry, we all are. (Except, perhaps, the mathematicians.)

4. I think I may understand how it can be confusing. Those videos or images that you may have seen are for illustrative purposes to help us visualize with lines and grids how distances bends/warps when there is an object with substantial mass. While I can see where you are coming from, I am not well versed enough in physics to explain it any better than that. Perhaps someone else with more in-depth knowledge and expertise can weigh in when they have the chance.

5. Originally Posted by scoobydoo1
Perhaps someone else with more in-depth knowledge and expertise can weigh in when they have the chance.
Yeah ... I carefully sidestepped that bit!

6. Originally Posted by Strange
Originally Posted by scoobydoo1
Perhaps someone else with more in-depth knowledge and expertise can weigh in when they have the chance.
Yeah ... I carefully sidestepped that bit!
I used to face the same confusion with Physicsforall, but after a time I've realized that attempting to illustrate on a sheet of paper or even in the form of a video is a lot harder than it appears. Without those lines and grids bending/warping around an object of mass, I do not think I am able to grasp/visualize the bending effect. The only real life example I can think of may be that of a spiraling effect when water flows downwards into a drainage in a sink.

7. Markus found a nice diagram that illustrates it in 3D ... not sure I can find it again...

Edit: here it is: Curved spacetime and multiple planets in orbit : an image of this ?

8. Originally Posted by Strange
Originally Posted by Physicsforall
Well Einstein imagined a single layer of space-time right?
Actually, no he didn't. He visualised space-time as a four dimensional structure: the three space dimensions we are familiar with (which is why we can see stars above us) and one time dimension.

The "rubber sheet" analogy is just a really bad attempt to try and visualise in 2 dimensions what is happening in four.
Ok that makes more sense, and if you where to visualize it wouldn't space-time be bending into the object with mass? not around it?
Nice picture by the way.

9. Originally Posted by Strange
Markus found a nice diagram that illustrates it in 3D ... not sure I can find it again...

Edit: here it is: Curved spacetime and multiple planets in orbit : an image of this ?
never mind... that answered my question!

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