Expert: Philip A. Stahl - 8/9/2007

Question
Hello I'm a musician from Puerto Rico and I saw an illustration explaining gravity in space as an elastic fabric in which a heavy ball (planet) forms a small cone on the fabric pulled down by it's weight and a smaller ball (moon) rotates in the cone as a coin spins in a funnel in an amusement park. First who came up with this theory and since moons and planets for that matter dont often rotate on the same axis how does that theory explains it. I think that then space must be a solid spheric blanket that covers every angle and vector but then how is a planet able to bend it in one direction for one moon and at the same time bend it at another angle to accomodate different trayectories for additional moons. I hope you get what im saying eitherways you're the astrophysicist. Thanks

Answer
Hello,

I think, from your answer - you are really confusing an actual theory (General Relativity) which describes the warping of space-time in the vicinity of massive objects- with a "cartoon" illustration of the theory.

I have also seen the fabric "bending" demo you describe, I believe in a video of the Stephen Hawking book 'A Brief HIstory of Time'.

Einstein's general theory of relativity has do with
the large scale structure of the universe. To put it conceptual terms, the general theory of relativity is really a theory of gravity in 4 dimensions(x,y, z and t or 3 of space, one of time). In particular, the force of
gravitational attraction arises around large, massive bodies because *space-time* is warped or distorted in their vicinity. A 'well' of gravity is thereby formed, and any smaller or less massive objects move around it. This "well" applies to the fabric illustration you noted.

In practical terms, experiments conducted (since 1919) during the time of total solar eclipse have found that the light from stars sppearing in the (background)
is slightly bent or deflected as it passes close by the Sun. This is a direct indication of the warping of the space-time around the Sun. This effect was indeed, predicted by Einstein in his theory.

In terms of the demonstration you saw, it is important to remember this is only a crude portrayal and NOT an exact replication of the REAL THEORY!  For example, the demonstration is only being done in THREE dimensions, NOT four! Also it is limited by the fact that a TWO-dimensional surface (fabric) is being used to illustrate the distortion. The rotation of any objects in the vicinity for the demonstration is therefore neither here nor there. These have nothing to do with the point of the general theory - which is explicitly HOW space-time deforms. Not how moons or planets rotate in the vicinity of the deformation.

I believe your questions to do with rotation axes (for moons and planets)  are either mistakenly taken from the wrong context (in the fabric illustration), or from another theory you may have referenced. You may wish to clarify that - if you think I am "not getting it".

Also, you said you "think space must be a solid spherical blanket that covers every angle and vector".

Do you wish me to give a response here to what YOU think, or to the Einstein theory? I am not clear on this. If you wish a response to what YOU think - you will have to take your time and explain it, express it much more clearly.

It seems to me, as if you have some complaint about the given (Einstein) theory of deforming space, and are trying to come up with your own version to it. However, bear in mind Einstein's theory has been tested numerous times and WORKS! Some of the best minds (e.g. Carl Brans, Robert Dicke) have tried to overthrow it but so far no one has succeeded.

General relativity has met all its prediction tests and then some, including accounting for the oblateness of the Sun (the ratio of its equatorial to its polar diameter).

I hope this addresses your question. If not, please rephrase or re-do your question and make sure I am understanding what you want me to.