# Space-Time fabric 3D or not?

1. Jul 25, 2014

### Natsirt

I've always been interested in Space-Time fabric and have been trying to get a clear answer to whether or not its an actual fabric that's two dimensional or is that an easier way of understanding it when talking about gravity and matter and how Space-Time is effected. If it really is 2D, why?

Last edited: Jul 25, 2014
2. Jul 25, 2014

### Staff: Mentor

What do you mean by Space-Time fabric? Do you have a reference?

3. Jul 25, 2014

### A.T.

No, its 4D. 3D space + 1D time = 4D spacetime.

But we cannot visualize curved 3D or even curved 3D very well. We can visualize curved 2D well, so illustrations drop 2 of the 4 dimensions. Depending on which dimensions you chose you get different diagrams:

http://www.physics.ucla.edu/demoweb..._and_general_relativity/curved_spacetime.html

4. Jul 25, 2014

### Natsirt

http://space.mit.edu/LIGO/more.html

In an endless amount of articles like this they discuss Einsteins general theory of relativity and describe spacetime as a fabric when explaining gravity but is it a two dimensional sheet or a 3D substance that is everywhere?

5. Jul 25, 2014

### Staff: Mentor

Spacetime is four dimensions: 3 spatial and 1 time dimension.

The two-dimensional rubber sheet analogy is a crude analogy, whose main advantage is that we can visualize it easily.

6. Jul 25, 2014

### phinds

"fabric" is a pop-sci analogy that really doesn't hold much water and is not taken seriously by actual physicists.

7. Jul 25, 2014

### Natsirt

To be clear I know Space-Time has 4 dimensions but when alternate dimensions and universes are discussed, are they being thought as a bunch of pieces of paper side by side or a bunch of 3D dimensions side by side, and are these ways of thinking simply for better understanding or are they actual theories?

8. Jul 25, 2014

### Natsirt

when I think of space time warping I think of a mass with particles focused around that mass on all sides (these particle being gravitons) and if I think of the particles as what space -time is made of so now spacetime is focused around the mass would I be wrong?

9. Jul 25, 2014

### phinds

The analogy of parallel sheets of paper is just that ... an analogy. Since there is zero evidence for alternate/parallel universes, how they might relate to ours cannot be determined so that's just a way to talk about it for those who like to speculate about such things.

10. Jul 25, 2014

### x BlueRobot

If I'm right, then the concept of parallel universes developed from Quantum Mechanics and Superposition of the states of a particle. I have considered Space-Time to be 4-dimensional (4D) with the fourth dimension being Time itself which can be manipulated like the other dimensions in theory.

11. Jul 25, 2014

### Natsirt

And time would be changed with movement correct?

12. Jul 26, 2014

### Bandersnatch

Thinking of dimensions as a fabric is like thinking of distance as a line. Both help with visualisation purposes, but neither is made of anything.

13. Jul 26, 2014

### A.T.

More like thinking of distance as a thread.

14. Jul 28, 2014

### infinity149

The use of the term "fabric" when talking about the fabric of spacetime is to help visualize how spacetime warps in the presence of matter/energy. We usually see examples of this in 2D. A mass is placed on a 2D "fabric" and the weight of this mass causes the fabric to sag in the middle, the 2D fabric being distorted by the mass.
Spacetime is, however, considered to be 4-dimensional, not 2D. We can't visualize what a 4D fabric would look like but your 3D visualization above is not unreasonable. Just don't confuse the issue by using any particular kind of particles like gravitons. Think of space as being marked with dots equally spaced in all 3 directions, like a 3D piece of graph paper. In the presence of mass/energy the dots would be closer together near the mass then they would be farther out.
Not all scientists agree on the actuality of this fabric but spacetime seems to behave as though it were a 4D fabric. If one were to try to describe how this 4D fabric bends and warps in the presence of matter/energy using field equations one would conceivably end up with Einstein's General field equations.

15. Jul 29, 2014

### Bandersnatch

The main issue here is that it doesn't show that. At best it shows the distortion of space; there is no time dimension.