How does gravity curve spacetime?

[MeJennifer]

GR1) An object in circular orbit is moving inertially, its velocity relative to itself (an inertial observer) is always zero, so its acceleration relative to a local inertial observer (itself) is zero.

Not just circular orbits.

 

[gravityblock]

Thanks to all who have taken the time to post a reply to my questions. I am sure I will not always ask meaningful questions when it comes to physics, but at least I'll be learning how to formulate better questions in these discussions.

Thanks

 

[jambaugh]

T[...] but at least I'll be learning how to formulate better questions [...]

Asking the right questions is the most important skill you can learn, even --I dare say-- more so than the mathematics.

 

[chis]

Gravity and Time are the same force.
Spacetime as Einstien intended it is merly a name for the matter dimention. The matter dimention is the one we percive ourselfs in. We see our environment in 3D, these dimentions are Antimatter, light and our dimension matter. Imagine a blind person reading brail where their hands are the matter dimention and the brail bumps are antimatter encapsulsted in light. The blind persons hands exert a presure on the brail bumps (gravity) and repeated presure would erase the bumps or in other words they would decay (time).

 

[Naty1]

Don't look for the mechanism by which "space-time is curved" but rather understand space-time as a mathematical construct we make prior to expressing the dynamics of an object.

But that is exactly what I wanted to do...to see if anyone yet understands a physical mechanism. I guess not yet.

 

[mehul ahir]

d

r stars & matter & energy in space infinite or finite?

 

[mehul ahir]

r stars & matter & energy in space infinite or finite?

 

[Hurkyl]

But that is exactly what I wanted to do...to see if anyone yet understands a physical mechanism. I guess not yet.

What do you mean by 'physical mechanism'? As I would understand such a phrase, our best theory of gravity says that matter* curving space-time is a 'physical mechanism'.

*: more accurately, stress-energy

 

[Phrak]

What do you mean by 'physical mechanism'? As I would understand such a phrase, our best theory of gravity says that matter* curving space-time is a 'physical mechanism'.

*: more accurately, stress-energy

Hey, Hurkyl. Not to disagree with you, but there are always the why questions, like "why should matter curve space?", which every once in a few hundred years leads to a deeper understanding. Or maybe matter doesn't curve space. Maybe matter is curved space.

 

[jtbell]

But that is exactly what I wanted to do...to see if anyone yet understands a physical mechanism. I guess not yet.

How would you distinguish a "physical mechanism" from a mathematical model? When we find the True Physical Mechanism for gravity, how will we know it?

 

[Naty1]

But that is exactly what I wanted to do...to see if anyone yet understands a physical mechanism. I guess not yet.

Math explains what happens, not necesarily why.

I simply wondered if there was an additional detail of understanding. Newtons laws explained a lot pretty well until Einstein came along and offered some deeper insights...but relativity is not the final answer either. Maybe magnetism would be an analogy...I think we understand pretty well why some materials are strongly magnetic and others are not...

Why SHOULD matter stress/energy curve space? Einstein had several different formulations...until the equivalence principle enabled him to discard the ones that did not fit...maybe we'll gain an understanding when we find out what "space" is...for now envisioning space time as a mathematical construct will have to do..but that doesn't mean it is the best we can do.

 

[jtbell]

I simply wondered if there was an additional detail of understanding.

We simply don't know yet, as far as I'm aware. Maybe a theory of quantum gravity will take us to a deeper understanding, if we can find one that can be verified experimentally. I'm not qualified to speculate in this area.

 

[Hurkyl]

Math explains what happens,

A slight correction: physics explains 'what happens'. Math tells us about math. e.g. while math might tell us that the kinds of 'particles' that are symmetric under 'infinitessimal rotation' can be categorized by half-integral 'spin', it's physics that tells us that particles exist and are (generally) symmetric under infinitessimal rotation.

not necesarily why.

What does "why" mean, really? In the operational sense, the question "why?" is a request to take a particular fact, and express it as a consequence of other facts. So, in order for the question "why?" to even make sense, you have to have accepted some category of facts in terms of which you will accept 'explanations'. This begs a question -- if the elements of our foundational scientific theories aren't acceptable as building blocks for 'explanation', then what is? And what is the justification for using those, rather than scientific ones?

 

[Hurkyl]

Just to make it clear: I'm not trying to marginalize imagination and innovation -- exploring for new ideas is an important part of science. But by the same token, one shouldn't marginalize the existing foundations of knowledge we do have -- it's not really fair to characterize it as merely something that will 'have to do'.

I get the feeling that you are leaning towards doing the latter, which is why I said something; if I am mistaken, then I apologize.

 

[atyy]

Newtons laws explained a lot pretty well until Einstein came along and offered some deeper insights...but relativity is not the final answer either. Maybe magnetism would be an analogy...I think we understand pretty well why some materials are strongly magnetic and others are not...

Why SHOULD matter stress/energy curve space? Einstein had several different formulations...until the equivalence principle enabled him to discard the ones that did not fit...maybe we'll gain an understanding when we find out what "space" is...for now envisioning space time as a mathematical construct will have to do..but that doesn't mean it is the best we can do.

Newton's gravity incorporates the equivalence principle. So can we describe it as spacetime curvature?

On Newton-Cartan Cosmology
Christian Rueede, Norbert Straumann
http://arxiv.org/abs/gr-qc/9604054

The main difference between Newton and Einstein is not curvature, but special relativity?