Is Gravity Really Just Curved Spacetime?

[sophiecentaur]

No, you can't. At least not correctly. etc

Thanks for that. I learned sunnink today!

 

[harrylin]

Then we should be allowed to treat centrifugal force as a real force too. In general relativity, you can't have one defined as a real force and not the other.

Edit: that's the beauty of general relativity - you can use whichever coordinate system you want. But this means we must accept that gravity and fictitious forces are one and the same.

Edit again: You could say that the coordinate system comoving with the expansion of the universe is the only true coordinate system, and use this coordinate system to judge what is gravity and what is fictitious force. But this seems like an unnecessary extension to me, without much insight gained.

Strictly speaking GR doesn't identify "real" or "fictitious"; it depends on the used coordinate system and one's interpretation what one calls fictitious and what real. That doesn't mean that gravity and fictitious forces must be one and the same - rather the contrary (see my post #20)!
It probably depends on what one means with "fictitious" in this context. In my world, "fictitious" forces are imaginary (or even occult) forces, without an identified corresponding physical cause (see also the footnote in my post #20).

EDIT: what is your definition of "field" in physics?
As I stated earlier I'm a purist, and consequently very recently due to a discussion here I recently adapted my definition of "field" to the original one, which is more logical.

 

[Nugatory]

It probably depends on what one means with "fictitious" in this context. In my world, "fictitious" forces are imaginary (or even occult) forces, without an identified corresponding physical cause

"Fictitious" is an unfortunate word, although given the history it's easy to see how it came into use and why it persists.

 

[K^2]

It probably depends on what one means with "fictitious" in this context. In my world, "fictitious" forces are imaginary (or even occult) forces, without an identified corresponding physical cause (see also the footnote in my post #20).

The term "fictitious force" is strictly defined in physics. If you misunderstand it, that is your problem and yours alone.

Gravity is a fictitious force under General Relativity by definition of the former. This is not something that deserves an argument.

 

[superbk]

I think that True or False depend on our definition , anything's relative

 

[harrylin]

The term "fictitious force" is strictly defined in physics. If you misunderstand it, that is your problem and yours alone.

http://en.wikipedia.org/wiki/Fictitious_force
As you say, "if you misunderstand it, then that is your problem"; but "yours alone" is not sure as there could be more people who misunderstand it. Importantly, the purpose of this forum is to help each other.

Gravity is a fictitious force under General Relativity by definition of the former. This is not something that deserves an argument.

Anyway, the question of this thread here does not concern "fictitious" but "force"; as someone brought it up it was useful to explain what people mean with it and why, but an argument about it is out of place and distracts from the topic.

 

[harrylin]

I think that True or False depend on our definition , anything's relative

Hi superbk welcome to physicsforums.
I largely agree that if gravity is a force depends on definitions, and many people have explained that here with more details.

Note: Suddenly it strikes me that markf has not come back yet with his feedback - and he already received 36 posts in answer!

markf, can you give feedback? Did you find any answers helpful?

 

[vijendra sing]

as i told you before gravity is not a force it is the property of any thing which has mass

 

[D H]

as i told you before gravity is not a force it is the property of any thing which has mass

Here's what you said before:

really gravity is not a force it is property of object by virtue of an object attract other object

This is pretty much meaningless and doesn't answer the question. The ability of an object to attract another object? That is, in a sense, the definition of a force.


Whether gravity is or is not a (real) force is a matter of point of view. In Newtonian mechanics, objects subject to gravitation undergo acceleration when viewed from the perspective of a Newtonian inertial frame. So gravitation is a real force in Newtonian mechanics. In general relativity, gravitation is not a real force. It's a tautology. Objects that are subject to gravitation only are free-falling. A free-falling frame is a local inertial frame in general relativity, by definition.

As Khashishi said way back in post #8, "I think physicists don't get too worked up about what exactly constitutes a force." Or, quoting Shakespeare, "What's in a name? That which we call a rose by any other name would smell as sweet."

 

[Vierstein]

according to the theory of General Relativity, there is an equivalence to a body falling in free fall to an identical body out in free space traveling at a constant velocity.

what a big mass (like a planet) does is warp or curve space in such a way so that objects flying about freely in this curved space appears to us in our Euclidian space to be following a curve where it just appears that a force is acting on the body that causes its path to be curved toward the center of that big mass.

But it still takes force to escape curved spacetime. So what is curved spacetime? Is it akin to a hole in the ground? Isnt it any more a force, than a barrier in your way is, which you have to break through?

One more question, wouldn't that imply, that there is such a thing as maximum gravity? If we think of gravtiy as curved spacetime, then eventually spacetime reaches a point where it is bent by mass in such a way, that it exercises a maximum pull, with any further alteration of spacetime dimnishing its gravitaitonal pull.

 

[K^2]

But it still takes force to escape curved spacetime. So what is curved spacetime? Is it akin to a hole in the ground? Isnt it any more a force, than a barrier in your way is, which you have to break through?

One more question, wouldn't that imply, that there is such a thing as maximum gravity? If we think of gravtiy as curved spacetime, then eventually spacetime reaches a point where it is bent by mass in such a way, that it exercises a maximum pull, with any further alteration of spacetime dimnishing its gravitaitonal pull.

Verstein, you need to learn a bit about differential geometry. The short answer to both of these is "no", but you need to understand how curvature in general manifolds works to go on further. How are your Calculus and Linear Algebra?