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According to the theory of general relativity 'space' can be bend like a fabric.

Objects with a lot of mass bend spacetime like a well or a bowling ball on a stretched blanket.

It (images) always look like spacetime is being 'pushed' downwards thus objects swirl around the more massive object (if their velocity is fast enough to not getting pulled into the singularity).

So I seriously ask myself, is it possible for objects / matter in the universe to push / bend spacetime 'upwards?'

Upwards in the sense that the ball in the picture (above) is bending spacetime in the other direction (vertical).

Though one problem arrises in my head already, wouldn't objects be invisible to our eyes since ,just like with the bowling ball and the blanket, it would be a layer under the actual play field <-- Instruments should be able to detect their impact right?

Info: I'm just a hobby astrophysics learner, not a physicist or a professional student in this field, so anything I've written down could be non-sense / false. Correct me if that's the case.

  • $\begingroup$ I think you may have meant 'spacetime' in a few places, instead of just 'space'. $\endgroup$ – user191954 Jul 16 '18 at 13:07
  • $\begingroup$ Those pictures with space (note: space!) bent down around massive objects are not really helpful in terms of thinking about spacetime curvature, I think. $\endgroup$ – tfb Jul 16 '18 at 13:16
  • $\begingroup$ Not sure what to include other than that. If I type into google 'Spacetime curvature', I get exactly those kinds of images. $\endgroup$ – stringExchange Jul 16 '18 at 13:21
  • $\begingroup$ You will need to bite the bullet and learn the math.:) The pictures are giving you the wrong idea that you,or anybody, can visualise 4 D space-time. $\endgroup$ – user198207 Jul 16 '18 at 13:31
  • 1
    $\begingroup$ If by "bending space upward" you're referring to creating gravitational repulsion, then no, there is currently no way to do that. That said, there are a few theories that predict gravitational repulsion. For example, domain walls (essentially, boundaries between two vacuums of different energies, see e.g. arxiv.org/pdf/gr-qc/9306005.pdf) are known to create a repulsive gravitational field, but we have no evidence that they exist. We also don't know how gravity acts on antimatter, so it's possible that antimatter "falls up"; measurements are ongoing, but they're difficult. $\endgroup$ – probably_someone Jul 16 '18 at 13:37

You refer to "embedding diagrams" where the "squares" of space or spacetime retain their size, but buckle out into an "embedding dimension." Compare this to the 2-dimensional surface (not volume) of the Earth being embedded in a 3-dimensional space. There is no "up" or "down" in the embedding dimension.

An alternative approach to embedding diagram is to simply deform the "squares" of spacetime in place, in the two dimensions of a map rather than an Earth globe. Feynman has a lecture on a "hot plate" that demonstrates this approach. Kip Thorne also describes measuring rods that bend and stretch in his pop-science book "Black Holes and Time Warps."

  • $\begingroup$ so we are actually talking about 3 dimensional spacetime? If so then my question is pointless. Though why are pictures of black holes impact on spacetime always like a well / 'downwards' ? $\endgroup$ – stringExchange Jul 16 '18 at 13:44
  • $\begingroup$ @stringExchange Because we haven't thought of a way to portray the deformation of a 3-D space (well, really, a 4-D spacetime) in a 2-D image. $\endgroup$ – probably_someone Jul 16 '18 at 13:51
  • $\begingroup$ -1: Your answer would be correct, if the diagrams in question were in fact embedding, but clearly they are not. Embedding general relativity requires at least 5 dimensions (with a cosmological constant) or more. Even if we could depict a projection, it would not be intuitive or revealing. Instead the diagram simply shows the gravitational time dilation on the vertical scale, the essential cause of gravity per the least action principle. Thus clearly "up" and "down" directions are there depicting the speed of the proper time near a heavy object. $\endgroup$ – safesphere Jul 17 '18 at 2:54
  • $\begingroup$ @stringExchange Your question is not "pointless", you simply selected a wrong answer. The diagrams clearly show the "up" and "down" directions that have a simple and logical interpretation. It is a shame that such a simple matter is so widely misunderstood and misinterpreted by the "experts". $\endgroup$ – safesphere Jul 17 '18 at 3:02
  • $\begingroup$ Do a Google image search for "embedding diagram general relativity" and find many diagrams similar to the one shown in the image above. It's true that if our 4d spacetime is embedded in an external dimension, that would make for 5d. But how to draw a 5d graph? What physicists often do is to suppress the time dimension and one space dimensions, leaving two dimension, then use the third for embedding. At hands-on science museums you can find 3d funnels (with a 2d surface) as an analog of the spacetime outside a planet. Then in a 2d image the 3d funnel is sketched as in the image above. $\endgroup$ – bernander Jul 17 '18 at 6:52

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