Physics Stack Exchange is a question and answer site for active researchers, academics and students of physics. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

General Relativity posits that matter curves spacetime, such that geodesics point towards the object in question, hence, gravity. Now, how does matter do this? What is spacetime "made of", anyway, such that it should interact with matter, being bent by it and forcing it to accelerate (via gravity)?

share|cite|improve this question
up vote 6 down vote accepted

The image of space being bent is just an analogy, it is not meant that anything is actually being deformed. Gravity distorts the notion of distance on spacetime, i.e. the presence of matter somehow causes the metric to change. A way to visualize this is to think of spacetime being bent, as you say, but really, spacetime is not made of anything, the idea of an ether has been laid to rest for a hundred years now, with good experimental reasons.

Spacetime interacts with matter since matter exists within (or on, in some terminology) it, and when the notion of distance changes, the behaviour of objects relying on that notion changes.

As for why the presence of matter itself influences the metric...well, this is the defining property of having mass/energy, just as generating (or reacting to) an electric field is the defining property of having an electric charge - in a manner of speaking, mass could be seen as the charge of gravity, though, since we do not fully understand gravity (yet), this is necessarily vague.

share|cite|improve this answer
So... then, how do we separate space from the metric defined upon it? – silvascientist Jun 17 '14 at 16:17
Short answer: We don't. Slightly longer answer: On the same "spacetime", which is really just what one would call a (smooth) manifold, there are many different possible metric structures one could define. The one that is realized in nature is given by the solution of the Einstein field equations, where the solution is mainly dependent on the energy-momentum tensor, which arises from the distribution of energy/matter. Spacetime without metric is (likely) just $\mathbb{R}^4$. – ACuriousMind Jun 17 '14 at 16:38
Relevant xkcd: – DanielLC Apr 22 '15 at 9:51

Conventional theory calls it spacetime, which I would assume refers to an unidentified amount of space over an unidentified amount of time but both distance and time are measurements of properties of matter and are dependent upon relative matter, example. Time is the measurement of relative movement, thedistance the sun can travel in a second is different than the distance an atom could due to a difference in the motion of each. Should there be no motion, there can be no "time" as there would be no cycles taking place. 1 earth cycle=1day. Motion=time. In the interest of answering your question with the understanding I have I would have to say space is made of a medium of extreme density, so much so that the substance that comprises it doesn't give any energy (exert a force) as it doesn't require loss of energy to travel through. (when you throw something in space it goes on until acted upon by another force=no drag) there must be some medium by which matter can interact/propagate because it is difficult to believe that spacetime doesn't exist and isn't real or that it's empty yet it's able to react to gravity to influence light...

share|cite|improve this answer

Space is the canvas on which the Universe is painted. Space is created when a Higgs wave (dark energy) intersects dark matter. When this happens, three things are created. Matter, energy and a whole lot of SPACE. Space has two known properties. First, Dr. E. tells us it can be warped. Second, I tell you it cannot be compressed. That being said, this reaction is still occurring and therefore the Universe continues to expand at an accelerated rate. This also explains the Big Bang. Prior to it the Universe had no dimension as the two darks were both waves and did not require space to exist. A quantum foundation caused the dark energy to produce the cascading Higgs wave which produced the matter energy and SPACE.

Hope that clears things up.

L. Stewart Hearl

share|cite|improve this answer
No, that really doesn't clear much of anything up. – Jon Custer May 31 at 23:45

protected by Qmechanic Jun 1 at 4:24

Thank you for your interest in this question. Because it has attracted low-quality or spam answers that had to be removed, posting an answer now requires 10 reputation on this site (the association bonus does not count).

Would you like to answer one of these unanswered questions instead?

Not the answer you're looking for? Browse other questions tagged or ask your own question.