Why do galaxies take on the shape they happen to take on? What I am wondering is that if space was a vacuum, and gravity has infinite range, then galaxies of course should really respond to each other or collectively I guess to all the gravities of galaxies per say operating at once. It would seem as if this is not true. That’s not really my question though. Is it purely gravity that causes the shape of a galaxy, or is it a mix of various natural phenomena, such as gravity, electromagnetic and thermal effects operating at once? I am just wondering if you get so far from a galaxy, which I know we cant do, if you would detect no gravity really. I know that’s not at all the mainstream idea, but how do we know for sure that gravity does not exist only by bodies with mass? I mean if a galaxy for instance cannot feel the effects of another galaxies gravity, is it merely moving according to how spacetime is being morphed? Such as one galaxy makes a certain shape in it(temporal) in which other temporal shapes other bodies like galaxies make can come to react or push against each other. Like using weight to displace melting plastic… I am trying to get a good enough of an example going is all.

 

So I guess its two questions.

 

1) Is gravity the only influence on a galaxies shape.

 

2) How do we know for sure that outside of bodies with mass(to a certain scale outside a body of mass) gravity exists at all, and if not is galaxy movement really just a product of mass distorting spacetime?

There is believed to be a "cloud" of dark matter around galaxies that "relaxes" and allows matter to clump together. There is certainly a distortion to spacetime (it gets bent by the mass -gravity). We can see a lot of the matter in galaxies because it interacts with light. Dark matter doesn't. They're looking for gravity waves and if this can be done we might be able to "see" dark matter this way.

Why do galaxies take on the shape they happen to take on?

Gravity propegates with the speed of light.

 

The causes for galaxies shapes is a mix of all natural phenomena, but gravity is the primary force.

 

Gravity acts on energy and energy causes gravity too.

 

We have the same model for gravity which fits how bodies behaves on Earth, in the Solarsystem, inside the Milky Way and for interaction between galaxies close to each other. We don't know how gravity behaves on very large scales, but it's reasonable to assume that it continues even on larger scales.

 

The force of gravity drops off very fast with distances, far enough and the force will be weakened to almost zero.

 

On large scales galaxies behave as single bodies, if it's movement changes it's influenced by gravity.

 

In General Relativity the distorsion of spacetime is gravity.