Curvature of space and dark matter

[moronthat]

Assuming gravity is matter curving space as Einstein says, isn't our theory of dark matter just an assumption that because more gravity is required to explain galaxy formation that it must be caused by unseen matter? Why do we assume that the curvature of space required must be caused by matter?

Another question, using a slinky as an analogy. Everyone is familiar with stretching one and observing traveling pressure waves along it. Those pressure waves are like space curvatures caused by mass. But in a slinky the high pressure waves are also accompanied by low pressure waves to compensate, sort of an equal and opposite reaction. Has anyone ever thought that the curvature of space caused by gravity has a similar effect of less curved space near it to compensate? If that's true, wouldn't that act like dark energy?

 

[Ich]

Why do we assume that the curvature of space required must be caused by matter?

There is a Wikipedia article with 3570 words on observational evidence. If you don't understand something in it, maybe you could ask a specific question?

Has anyone ever thought that the curvature of space caused by gravity has a similar effect of less curved space near it to compensate?

Sounds like gravitational waves. But these are a bit more complicated than pressure waves.

 

[phyzguy]

We know that all matter causes a gravitational pull, as described by Newton's law of gravity. Many observations tell us that there is more gravitational pull out there than can be ascribed to ordinary matter. Whatever is causing the extra gravity is "matter", almost by definition. Since we don't know what it is, and it doesn't emit light, we call it "dark matter". What else would you like to call it?

 

[rwmp]

I graduated more decades ago than I like to admit but I got curious and after some research I am blocked by these questions. It seems like the whole evidence for our universe expansion accelerating is that photons which travel a very long space time path arrive with less energy than expected (more red shift and less luminosity). We can detect no direction which seems to point to the center or edge of the universe. If I frame this problem in 2 dimensions I find this only matches objects all on the surface of an expanding sphere. Is there a 3-D analog where all visible objects are on the surface of an expanding extra dimensional sphere? Is this ruled out due to evidence I can't find through reviewing information on the web? There are a number of searches going on for a graviton. If there was a force mediating bosun wouldn't it be captured within a black hole and cause a black hole to not have any gravitational effect outside of its event horizon?