Why Argue Semantics?

n scientific usage gravitation and gravity are distinct. "Gravitation" is the attractive influence that all objects exert on each other, while "gravity" specifically refers to a force which all massive objects (objects with mass) are theorized to exert on each other to cause gravitation. Although these terms are interchangeable in everyday use, in theories other than Newton's, gravitation is caused by factors other than gravity. For example in general relativity, gravitation is due to spacetime curvatures which causes inertially moving objects to tend to accelerate towards each other.

Okay.  Generally, people who come here are LAYpeople, right?  Not people with PhDs in physics.  Not always people who have even sat in on a physics class once in their lives. 

So, if gravity and gravitation are interchangeable in everyday use, why not let it slide when new people use the term "gravity?"  Maybe tell them the difference, then go on to discuss whatever point they were trying to make?  It only serves to piss people off when you treat them like morons.  Seriously, why?



PS, I think that if you keep going on about "there is no such thing as gravity," you should just shut up about the UA as a force.  Both are theoretical.  One isn't true just because you say the other is false.

They both could be same or different, depending on which definition are you referring to. In terms of similarity, they both cause acceleration. In terms of difference, however, one is the cause (gravity)and the other is the effect (gravitation). Either way, gravity and gravitation are related.

Using gravity in the layman's term would simply cause problems in understanding the functions of the FE acceleration. Explaining the differences, or at least, providing statements in such a way as to promote self-education are generally what is done.

And as stated by Jack, gravity is a cause, not a result.

Quote from: http://en.wikipedia.org/wiki/Gravity

n scientific usage gravitation and gravity are distinct. "Gravitation" is the attractive influence that all objects exert on each other, while "gravity" specifically refers to a force which all massive objects (objects with mass) are theorized to exert on each other to cause gravitation. Although these terms are interchangeable in everyday use, in theories other than Newton's, gravitation is caused by factors other than gravity. For example in general relativity, gravitation is due to spacetime curvatures which causes inertially moving objects to tend to accelerate towards each other.

Okay.  Generally, people who come here are LAYpeople, right?  Not people with PhDs in physics.  Not always people who have even sat in on a physics class once in their lives. 

So, if gravity and gravitation are interchangeable in everyday use, why not let it slide when new people use the term "gravity?"  Maybe tell them the difference, then go on to discuss whatever point they were trying to make?  It only serves to piss people off when you treat them like morons.  Seriously, why?



PS, I think that if you keep going on about "there is no such thing as gravity," you should just shut up about the UA as a force.  Both are theoretical.  One isn't true just because you say the other is false.

Because its not arguing about the word, its trying to help them understand it.  If they choose to be ignorant and mad there is nothing we can do.

Hold on now. Slow down.

The importance of separating "gravity" from "gravitation" MAY not be important in everyday life (though many would argue it is still), but in the sake of this debate it's very, very important. The Earth in the flat Earth theory HAS gravitation, that's why we stay to the ground. But it does NOT have gravity (the supposed force that keeps us stuck to the ground in some theories). Thusly, to use them interchangeably would be oxymoronic. In this debate, it simply doesn't work. Therefore, it's not allowed.

As for UA and gravity, that's just silly. UA is, of course, theoretical, but it actually makes a remote amount of sense. Gravity on the other hand, has been proven to be false, and not just by flat Earth scientists, but by credible round Earth believers as well (like, you know...Einstein?). UA hasn't been proven, but it hasn't been conclusively disproven, as gravity has, and that's why we still talk about whereas gravity we argue is false conclusively.

As a semi-related sidenote, don't tell us not to treat people like morons, OR not to piss people off. If they're dumb enough to believe some of the crap they're talking about, then they deserve to be treated like morons, and if people get pissed off, then it just makes them funny to watch. Don't be so silly.


~D-Draw

Hold on now. Slow down.

The importance of separating "gravity" from "gravitation" MAY not be important in everyday life (though many would argue it is still), but in the sake of this debate it's very, very important. The Earth in the flat Earth theory HAS gravitation, that's why we stay to the ground. But it does NOT have gravity (the supposed force that keeps us stuck to the ground in some theories). Thusly, to use them interchangeably would be oxymoronic. In this debate, it simply doesn't work. Therefore, it's not allowed.

As for UA and gravity, that's just silly. UA is, of course, theoretical, but it actually makes a remote amount of sense. Gravity on the other hand, has been proven to be false, and not just by flat Earth scientists, but by credible round Earth believers as well (like, you know...Einstein?). UA hasn't been proven, but it hasn't been conclusively disproven, as gravity has, and that's why we still talk about whereas gravity we argue is false conclusively.

As a semi-related sidenote, don't tell us not to treat people like morons, OR not to piss people off. If they're dumb enough to believe some of the crap they're talking about, then they deserve to be treated like morons, and if people get pissed off, then it just makes them funny to watch. Don't be so silly.


~D-Draw

Please, may I see a document or something where he proves that? 


(^---Not me being a smartass, I'm honestly curious)

It's too late for me to look up specific documents, but if you're genuinely curious, look up General Relativity.

Oh, and...Good luck...

~D-Draw

Let me grab my collection of stuff.

I'm SO not a physicist.  Is there any document you could point me to that I can actually understand, which would make it clear to me?   

I'm SO not a physicist.  Is there any document you could point me to that I can actually understand, which would make it clear to me?   

Not really. Basically, it says gravity (as in the force) is bullshit, gravitation warps spacetime, acceleration creates gravitation (thus acceleration warps spacetime), and a bunch of other shit that I'm not going to explain because I'm tired and cranky.


~D-Draw

The first chapter or two of A Brief History of Time, perhaps.

From a post of mine:

"gravity exists, but it is not a real force. Matter curves spacetime which causes gravitation (acceleration), which causes objects (us) to follow geodesics, which are stopped by the Earth, which is then thought to be a force (gravity).

This means that gravity is a manifestation of curved spacetime, NOT THE OTHER WAY AROUND. This means that curved spacetime + an incorrect assumption (our non-inertial FoR being thought to be inertial) causes the force of gravity. Again, gravity is an effect, not a cause. [not as commonly thought]

This means that gravity = the feeling of the Earth's mechanical resistance to gravitation and our following of geodesics."

Quote from: L0gic on October 24, 2007, 07:50:22 AM

What part of General Relativity says gravity isn't real?!

As TheEngineer said earlier in this thread, "Gravity is a pseudo force that only arises by taking a non inertial frame of reference to be inertial.   Gravitation is a consequence of the deformation of space, no force between objects necessary."

Since our FoR is non-inertial, there is no need for gravity. It, as a force, doesn't exist.

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"All fictitious forces are proportional to the mass of the object upon which they act, which is also true for gravity. This led Albert Einstein to wonder whether gravity was a fictitious force as well. He noted that a freefalling observer in a closed box would not be able to detect the force of gravity; hence, free falling reference frames are equivalent to an inertial reference frame (the equivalence principle). Following up on this insight, Einstein was able to show (after ~9 years of work) that gravity is indeed a fictitious force; the apparent acceleration is actually inertial motion in curved spacetime. This is the essential physics of Einstein's theory of general relativity." - http://en.wikipedia.org/wiki/Fictitious_force

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"Is Gravity A Fictitious Force?

...

The strange and in some ways disturbing answer to this supposition is that the phenomenon of gravity (the fact that things fall, and have weight) is real, but the force of gravity, as described by Newton, is not a real force, but a fictitious force."
- http://cseligman.com/text/physics/fictitious.htm

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"With general relativity, Einstein managed to blur forever the distinction between real and fictitious forces. General relativity is his theory of gravity, and gravity is certainly the paradigmatic example of a "real" force. The cornerstone of Einstein's theory, however, is the proposition that gravity is itself a fictitious force (or, rather, that it is indistinguishable from a fictitious force)." - http://www.sciam.com/askexpert_question.cfm?articleID=ABE57453-E7F2-99DF-32538FF7C7B37F20

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"You have it essentially right

mdivito@cevo.com wrote:
> user_email -- mdivito@cevo.com
> question -- I was just looking for some clarification of a few things in regards to gravitation.
>
> GR basically showcases that gravity as a force doesn't exist, correct?
>
> Now, as I understand it, gravity only needs to exist as a force in Euclidean spacetime, and since GR states that spacetime is non-Euclidean, what we feel on Earth is therefore gravitation, and not gravity?
>
>
>
>   

--
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F. Todd Baker
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Email: tbaker@physast.uga.edu
Phone: 706-546-xxxx
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Web: http://www.ftoddbaker.com/
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"This is analogous to what mass does to the structure of space-time. It causes a depression to form so that if an object  rolls toward it, it falls into the pit and is captured. (This, by the way, is how Einstein envisioned how gravity works. Mass distorts the space-time causing particles to roll toward the mass. Note that the objects follow the shape of the space-time and in this sense are following an unforced motion! That is, there is no gravitational force, objects are simply following their natural motions.)" - http://zebu.uoregon.edu/~imamura/122/lecture-2/gw.html

Quote from: Wiki on GR

One of the defining features of general relativity is the idea that gravitational 'force' is replaced by geometry. In general relativity, phenomena that in classical mechanics are ascribed to the action of the force of gravity (such as free-fall, orbital motion, and spacecraft trajectories) are taken in general relativity to represent inertial motion in a curved spacetime. So what people standing on the surface of the Earth perceive as the 'force of gravity' is a result of their undergoing a continuous physical acceleration caused by the mechanical resistance of the surface on which they are standing.

Quote from: Wiki on Non Inertial Frames of Reference

An apparent exception would seem to be the force of gravity, which is also proportional to the mass upon which it acts. Although gravity can be considered a "real" physical force for the purposes of calculations in classical mechanics, Albert Einstein showed in his theory of general relativity that gravity itself can also be considered a fictitious force. In his theory, the free-falling reference frame is equivalent to an inertial reference frame (the equivalence principle). By contrast, Einstein noted that observers standing on the Earth are experiencing an unrecognized acceleration from the normal force pushing up on their feet and, thus, are in a non-inertial (accelerated) reference frame. Further details may be found under general relativity.

If you need anything clarified, just ask.

Quote from: questions on November 14, 2007, 10:34:56 PM

I'm SO not a physicist.  Is there any document you could point me to that I can actually understand, which would make it clear to me?   

Not really. Basically, it says gravity (as in the force) is bullshit, gravitation warps spacetime, acceleration creates gravitation (thus acceleration warps spacetime), and a bunch of other shit that I'm not going to explain because I'm tired and cranky.


~D-Draw

Is it that it invalidates gravity, or that it doesn't touch on it and explains acceleration, warping of space-time, etc. via methods which have nothing to do with gravity?  Because those are two very separate things.

Quote from: Diego Draw, Tamer of Beasts on November 14, 2007, 10:37:13 PM

Quote from: questions on November 14, 2007, 10:34:56 PM

I'm SO not a physicist.  Is there any document you could point me to that I can actually understand, which would make it clear to me?   

Not really. Basically, it says gravity (as in the force) is bullshit, gravitation warps spacetime, acceleration creates gravitation (thus acceleration warps spacetime), and a bunch of other shit that I'm not going to explain because I'm tired and cranky.


~D-Draw

Is it that it invalidates gravity, or that it doesn't touch on it and explains acceleration, warping of space-time, etc. via methods which have nothing to do with gravity?  Because those are two very separate things.

You mean energy warps spacetime Diego.

It invalidates gravity.

It invalidates gravity because there are situations where the calculations for gravity don't work but the calculations of GR still hold up.

gravitation warps spacetime, acceleration creates gravitation (thus acceleration warps spacetime), and a bunch of other shit that I'm not going to explain because I'm tired and cranky.


~D-Draw

Eh, gravitation is the result of the curvature of space-time. Matter warps space-time. Energy/mass/momentum warps space-time, and any object that has these can do the same. Light, for example, has energy and momentum; therefore, light warps space-time. I rather use the word "curve" instead of "warp", though.

So, gravity and GR are both theories? 


I'm not saying this to be an ass, but hear me out (I need to know for myself):

Is it possible that GR is correct except where it relates to gravity?  Or that GR isn't correct at all?

It invalidates gravity because there are situations where the calculations for gravity don't work but the calculations of GR still hold up

Like what situation?

General relativity explains gravity in a different perspective.

So, gravity and GR are both theories? 


I'm not saying this to be an ass, but hear me out (I need to know for myself):

Is it possible that GR is correct except where it relates to gravity?  Or that GR isn't correct at all?

Quote

It invalidates gravity because there are situations where the calculations for gravity don't work but the calculations of GR still hold up

Like what situation?

I'm really not an expert on this but I know that there are situations where the calculations for gravity don't work.  Look up gravity in Wikipedia for a better idea (you'll find, interestingly enough, that there is no page for gravity and it will redirect you to gravitation).

Sorry, it's way too late for me to be still debating here.  

That and I'm no physicist either, I simply dabble in all of this stuff.

Is it possible that GR is correct except where it relates to gravity?  Or that GR isn't correct at all?

No. Well, yes, but no. The accuracy in which General Relativity predicts things pretty much validates it entirely. It's proven at nearly every corner.


~D-Draw

Ahhhhh.  Well, thanks guys.

But that still brings me around to this question:

If there is no such thing as "gravity," and laypeople believe gravity/gravitation to be some force which attracts things to each other, then why can't the term gravity be used?

I think the simplest thing to say.. just to clarify what people are 'upset about' regarding gravity is to think of the concept of gravity as we remember growing up with... most people think that in laymen's terms - Gravity is caused by the mass of an object attracting other objects to it, according to it's size - or 'massiveness!'

General Relativity 'produces' gravity - if you will - by the fact that Mass (amongst other things) curves space time.

Simplest way I can think of to put it is this... get a trampoline out.. that's space. Set a bowling ball in the middle of it... that's now a large object curving space time around itself. Now try to roll a marble or some other object in a straight line past it... you can't. Because of the curvature in space-time created by the bowling ball, anything passing near it, that doesn't "outweigh it" will just be pulled right into it. Larger bowling ball - as it passes by, it will pull the already existing one into it, but since heavier, will keep on track. Works both ways back and forth and in between.

I don't know if this is even close to what you are looking for, but I hope this helps some. Just remember that the trampoline is a 2D representation of space itself and the objects upon it are "distorting space" therefore the trampoline is simply a way to observe what WOULD be happening all around the object.

So Newtonian Gravity as described by General Relativity is what causes that little marble to sway back into the bowling ball - Not ONLY because of it's greater mass, but it's effect on space time also. The latter being specific to GR.

I hope I didn't just make it muddier, but I tried.

Take care,
John

So, gravity and GR are both theories? 


I'm not saying this to be an ass, but hear me out (I need to know for myself):

Is it possible that GR is correct except where it relates to gravity?  Or that GR isn't correct at all?

Quote

It invalidates gravity because there are situations where the calculations for gravity don't work but the calculations of GR still hold up

Like what situation?

For example, Newton thought gravity is instantaneous. However, Einstein calculated the speed of gravity, limiting it to the speed of light. Thus, there are some situations that cannot be calculated using Newton's gravity. In most cases, Newton's laws still produce great approximation, just not as accurate as GR.

I think the simplest thing to say.. just to clarify what people are 'upset about' regarding gravity is to think of the concept of gravity as we remember growing up with... most people think that in laymen's terms - Gravity is caused by the mass of an object attracting other objects to it, according to it's size - or 'massiveness!'

General Relativity 'produces' gravity - if you will - by the fact that Mass (amongst other things) curves space time.

Simplest way I can think of to put it is this... get a trampoline out.. that's space. Set a bowling ball in the middle of it... that's now a large object curving space time around itself. Now try to roll a marble or some other object in a straight line past it... you can't. Because of the curvature in space-time created by the bowling ball, anything passing near it, that doesn't "outweigh it" will just be pulled right into it. Larger bowling ball - as it passes by, it will pull the already existing one into it, but since heavier, will keep on track. Works both ways back and forth and in between.

I don't know if this is even close to what you are looking for, but I hope this helps some. Just remember that the trampoline is a 2D representation of space itself and the objects upon it are "distorting space" therefore the trampoline is simply a way to observe what WOULD be happening all around the object.

So Newtonian Gravity as described by General Relativity is what causes that little marble to sway back into the bowling ball - Not ONLY because of it's greater mass, but it's effect on space time also. The latter being specific to GR.

I hope I didn't just make it muddier, but I tried.

Take care,
John

This is actually very helpful.

I'm still confused as to why it really matters if someone refers to gravity, since the effect of GR and of "just gravity" is kinda similar/almost the same?  (At least as it relates to FE/RE debate)

Simplest way I can think of to put it is this... get a trampoline out.. that's space. Set a bowling ball in the middle of it... that's now a large object curving space time around itself. Now try to roll a marble or some other object in a straight line past it... you can't. Because of the curvature in space-time created by the bowling ball, anything passing near it, that doesn't "outweigh it" will just be pulled right into it. Larger bowling ball - as it passes by, it will pull the already existing one into it, but since heavier, will keep on track. Works both ways back and forth and in between.

Ah, the rubber-sheet experiment.

If there is no such thing as "gravity," and laypeople believe gravity/gravitation to be some force which attracts things to each other, then why can't the term gravity be used?

The point is that there is no force. The term gravity can be used, but the common notion of what it is and such are incorrect. The objections seen on this forum more so outline affecting people's ignorance to it than anything else. That and educating them.

I think it might be a good idea to sticky some kind of "gravity/gravitation" explanation in the FAQ (or stickied in the forum).  This helped me to see it a lot more clearly.

I agree with the aforementioned statement about force being what a lot of the confusion is about. And as I said we all grew up with certain notions and terminologies, so it gets cumbersome.

Think of it this way.. in either model.. is the Earth "forcing itself" into you? In RE the closest thing you could say would be you're being pulled into it, and on FE the Earth is accelerating towards you so to speak.

The definition of the word "force" In physics, is that which tends to cause a body to accelerate.

So as you said - it is playing with semantics, but ohhhh so nasty of them. lol

Let's see if I can muddy this up some.

The term 'gravity' specifically refers to the classical sense of it, the way Newton described it.  He observed that two masses attracted each other and concluded a force must be acting on them.  Newton did not know the cause of this force nor did he attempt to limit its speed, as this caused his equations to break down.  This presents two problems:  This applies only to objects with mass and the universal speed limit, the speed of light, is violated.

What we see on the earth is that the apple falls from the tree and accelerates to the ground.  We assume we are not moving, since it sure looks that way.  Therefore, there must be some force acting on the mass to cause this acceleration (F=ma).

What Einstein realized is that we are not at rest.  Space is curved, as in the trampoline example from before.  All objects move in space, and thus we follow the curvature of it.  The apple is following this curvature to the center of the Earth.  When it reaches the ground, it can't go any further since the Earth is in the way.  The apple is constantly accelerating into the ground, but the ground pushes back on the apple.  This is what gives us weight. 

No force is needed in order for the apple to accelerate towards the ground, since F=ma does not apply in our accelerating frame of reference (we are constantly accelerating into the ground and the ground pushes back on us).  Gravity can be thought of like this:

Imagine you are driving in your car, you take a ball and toss it up towards the roof.  You quickly turn the steering wheel and watch the ball fly out towards the passenger door.  From where you are sitting, there is not much movement going on.  You are stationary in your car but the ball just shot towards the door, so there must have been some force acting on it.  However, if you looked at it from a point of reference that was not accelerating (as in outside the car), you would see the ball going in a straight line and it was the car that moved towards the ball, thus, no force was necessary.

This is what happened with gravity.  We are in this accelerating reference frame that we claim to be still.  This gives rise to imaginary forces (gravity, Coriolis, centrifugal), just like the one the driver sees acting on the ball inside the car.  If you remove yourself to a frame that is still, you would see there is no force at all.

Einstein's General Theory of  Relativity completely changed what we thought happened to the apple.  Gone were the forces and in their place was simple geometry of space.  These deformations of space would carry at the speed of light and would be caused, not only by mass, but also energy and momentum.  It would affect every object that traveled through this spacetime. 

There is evidence GR is correct, it predicts the gravitational time dilation, in that time slows in higher gravitational fields, light (which has no mass) will be affected by objects with mass in space, and, because the limit on the gravitation is the speed of light, it correctly calculates the precession of the perihelion of Mercury.

So in the end, gravity is not a force, it only appears to us as one, because we are not looking at ourselves in the correct reference frame.

I sure hope that made sense, it's late. 

I think I'll add that to my little collection for future use.