by Chris Peterson » Sat Apr 03, 2010 4:15 pm
mark swain wrote:How can Gas and dust, be affected by gravity, from 28 thousand light years away?
The real question is, in the context of everything we know about gravity, how could gas and dust
not be affected by gravity? Gas and dust have mass, and everything with mass is affected by gravity. Nobody has ever found an exception. You can look at the behavior of our galaxy in terms of Newtonian mechanics, where gravity is treated as a force, or in terms of GR, where the gravity is seen as distorting spacetime. Either way, the behavior predicted by these theories is precisely what we observe.
In the case of our galaxy, the dust and gas (or stars) are not being affected by gravity from 28 thousand light years away. They are being affected by the gravity of a distributed mass. There's nothing special about the center of the galaxy, or its center of mass, except as a mathematical abstraction. The actual force (or distortion of spacetime) doesn't come from a single point.
Or is the space/time in our galaxy also spinning with us?
No, it isn't (except for the predicted phenomenon of
frame dragging, which is a much more subtle distortion of spacetime than I think you are referring to.)
[quote="mark swain"]How can Gas and dust, be affected by gravity, from 28 thousand light years away?[/quote]
The real question is, in the context of everything we know about gravity, how could gas and dust [b]not[/b] be affected by gravity? Gas and dust have mass, and everything with mass is affected by gravity. Nobody has ever found an exception. You can look at the behavior of our galaxy in terms of Newtonian mechanics, where gravity is treated as a force, or in terms of GR, where the gravity is seen as distorting spacetime. Either way, the behavior predicted by these theories is precisely what we observe.
In the case of our galaxy, the dust and gas (or stars) are not being affected by gravity from 28 thousand light years away. They are being affected by the gravity of a distributed mass. There's nothing special about the center of the galaxy, or its center of mass, except as a mathematical abstraction. The actual force (or distortion of spacetime) doesn't come from a single point.
[quote]Or is the space/time in our galaxy also spinning with us?[/quote]
No, it isn't (except for the predicted phenomenon of [url=http://en.wikipedia.org/wiki/Frame-dragging]frame dragging[/url], which is a much more subtle distortion of spacetime than I think you are referring to.)