[yor_on]

Maybe one could turn it around and state that as I feel a gravity, standing on earth, then that too must be a proof for a preferred direction, or geodesic, existing. And if matter tells space how to 'bend', and space tells matter how to 'move' then we all are in a geodesic, having a preferred direction, defined by all matter in a universe, or locally defined (earth) if one want, defined by the matter close to me. But if gravity has a infinite reach the first statement should be more correct I think?

[Pmb (OP)]

Fictitious force is a very nice description of it Pete. As you can transform it away by a free fall.

Here's the problem with that. It has given the false impression that such a field cannot be caused by matter, which is false. People think that if it's fictitious then it can't be caused by a gravitational source. That's what happens when you label things as fictitious. You can call it what you like. I prefer to call it real because it is real. You can't tell the difference. Calling it fictitious because you can transform it away is like saying that an electric field is fake because you can transform that away too.

[lean bean]

Fictitious force is a very nice description of it Pete. As you can transform it away by a free fall.

Here's the problem with that. It has given the false impression that such a field  cannot be caused by matter, which is false. People think that if it's fictitious then it can't be caused by a gravitational source. That's what happens when you label things as fictitious. You can call it what you like. I prefer to call it real because it is real. You can't tell the difference.

Pete
 What do you mean by field here "It has given the false impression that such a field cannot be caused by matter, which is false.''

Are you saying...the region of altered spacetime in the vicinity of mass is real, but locally it can be transferred away?
 To make it clearer for me, and if it helps others, is this field you refer to Newton's gravitational force of attraction or a region of altered spacetime? Evidence of this altered region of spacetime being accelerations and the converging together of test particles (originally on parallel paths) as they move towards the centre of mass of a planet?

[Pmb (OP)]

Pete
 What do you mean by field here "It has given the false impression that such a field cannot be caused by matter, which is false.''

I’ve been discussing general relativity with people for over a decade now. It seems that people think of spacetime curvature as being what we normally think of as a gravitational field (i.e. things fall when we drop them at a rate which is independent of their mass). However that is not the case. But people have come to expect that when there is a body falling from the gravitational acceleration caused by a planet it is due to spacetime curvature (Riemman tensor) when actually it’s due to what’s called the affine connection. Since people have the wrong idea about it I’ve found that in almost all circumstances people have expected spacetime curvature where there shouldn’t be any. The example I always use is the uniform gravitational field. Such a field is actually defined as having no spacetime curvature yet since people are always associating spacetime curvature with gravity they also expect there to be spacetime curvature in a uniform gravitational field. And I’m not talking about the layman. I’m talking about experts. This occurred in the American Journal of Physics as well as in Gravitation by Misner, Thorne and Wheeler (MTW). In the case of MTW they wrongly assert that gravitational redshift implies spacetime curvature, which it doesn’t. In fact the very first calculation of gravitational redshift, by Einstein of course, used flat spacetime!

Are you saying...the region of altered spacetime in the vicinity of mass is real, but locally it can be transferred away?

Not just locally but in a finite region of spacetime. The term local means a small region. The region need not be small when the field is a uniform gravitational field. However the equivalence principle states that the gravitational field (the affine connection) can always be transformed away whereas spacetime curvature cannot.

To make it clearer for me, and if it helps others, is this field you refer to Newton's gravitational force of attraction or a region of altered spacetime?

You seem to be indicating that there is a difference between Newton and GR in this area and there isn’t. The area of physics where Newton differs from Einstein is not the gravitational force, because that also exists in GR (see http://home.comcast.net/~peter.m.brown/gr/grav_force.htm). Its in the area of the field e equations and the fact that Newton’s gravitational field acts instantaneously with no delay in propagation time between a change in the distribution of matter to a change in the gravitational field.

Evidence of this altered region of spacetime being accelerations and the converging together of test particles (originally on parallel paths) as they move towards the centre of mass of a planet?

That exact same thing happens in Newtonian physics too you know?

Am I wasting my time asking direct questions of you?

I'm sorry but I don't understand this question. Why would it be a waste of time? Don’t you think I'm capable of answer your questions?

[galaxysim]

ref What do you think? And than you for your thoughts in advance.

I think you should make the effort to make a series of video shorts, or at the very lest build up a link of video shorts you can send people off to watch. Assuming your mission is education of the many ?

pages of text and diagrams is not only dry but a poor communication medium...it might suit some people in some circumstances but people tend not to posses the mindset of a low grade bank clerk...which is what you would have to have to enjoy wading through reams of dry text and line drawings

Far too many intellectuals have poor multi media and communication skills
Thus much of that knowledge remains buried in books or the halls of academia

The mind that can understand deeply is often hampered by the inability to communicate widely

We are much like ants, and the intrinsic complexity of the universe and our finite brain capacity means overspecialization has its downsides.

Sagan, Feynman & Neil deGrasse Tyson the exception rather than the rule....i think thats a great shame for all of us

Dr. Neil DeGrasse Tyson: A fascinatingly disturbing thought

Dawkins & Tyson on Intelligent Aliens

communication the other half of the 'lack of wisdom problem'

[lean bean]

You seem to be indicating that there is a difference between Newton and GR in this area and there isn’t.

There is a difference between the Newton and Einstein when it comes to field.
Newton is action at a distance with force of attraction, wheeler says moving orders are from local spacetime right where the partical is. Read on for Newton quote and wheeler.

Why do people like E. Taylor and J. Wheeler give  ''These notes supplement Chapter 3 of EBH (Exploring Black Holes by Taylor and Wheeler).''

It seems astonishing that a result from special relativity carries over directly to general relativity without modification. The key is that, in the paradigm of general relativity, free-fall motion arises not from acceleration but from the effects of spacetime curvature. As we will see, the appearance of acceleration arises naturally from extremal paths in a curved spacetime.
We say “appearance of acceleration" because ordinary acceleration depends on the motion of one's reference frame. In an inertial reference frame in Newtonian gravity, a body moves at a constant velocity if no forces act on it. In Newtonian theory, an inertial reference frame can be extended over all of spacetime. But we have already argued in the first set of notes that there are no global inertial reference frames in curved spacetime. Consequently the notion of acceleration is ambiguous! Acceleration depends on frame, and if there are no preferred frames, there is no preferred concept of acceleration.

Pick the pdf titled ‘How Gravitational Forces arise from Curvature’
From http://ocw.mit.edu/courses/physics/8-224-exploring-black-holes-general-relativity-astrophysics-spring-2003/assignments/

So, above quote as Taylor and co  saying the appearance of acceleration arises naturally from extremal paths in a curved spacetime.
-------
 Newton is force and attraction...
Here’s a quote from Newton’s ''Philosophiæ Naturalis Principia Mathematica’’

For by the propositions mathematically demonstrated in the first books, we there derive from the celestial phenomena, the forces of gravity with which bodies tend to the sun and several planets.

Please don’t ask me to link to that…it’s in google books and the page just doesn’t present itself when I link to it.

Also.
In the book EBH you have Taylor and Wheeler saying…

In Newtonian theory this effect is ascribed to gravitational force acting at a distance from a massive body. According to Einstein a particle gets its moving orders locally, from the geometry of spacetime right where it is.

So there is the difference between the Newton and Einstein.

So, Newton has a force of attraction and Wheeler saying it’s local spacetime geometry giving the moving orders. In fact, wheeler says elsewhere it’s the local spacetime metric and maximum aging of rocks wristwatch that  selects the geodesic path through spacetime

Now this is the nub...

I'm sorry but I don't understand this question. Why would it be a waste of time? Don’t you think I'm capable of answer your questions?

It’s hard to answer that without it seeming personal, I have read articles of people  mis-understanding GR even though they may be able to ‘do the math’, because of that I’m very suspect of most things on the web, especially forums. I know you wrote the glossary of the first book, but I seem to be getting different understandings of GR from the book’s authors and you??
And I have to say this, I'm rubbish at math, so have to rely on acknowledged ‘experts’. Don’t get down pete, It’s my own defence against the web. I try to use university research sites and acknowledged ‘experts’ own sites for info. Trying to avoid a bun fight here.

[Pmb (OP)]

And I have to say this, I'm rubbish at math, so have to rely on acknowledged ‘experts’. Don’t get down pete, It’s my own defence against the web. I try to use university research sites and acknowledged ‘experts’ own sites for info. Trying to avoid a bun fight here.

Let me make something very clear to you LB. I respect you, plain and simple. If you have something to say to me then I’ll listen and that includes criticism from you. I’m man enough and confident enough in myself to believe that we can work through our differences so that we can either get to a point where I can help you understand something or you can help me understand something. I’m man enough to admit when I’m wrong my good man.

[galaxysim]

There are so many complications and paradoxes it is not easy for ANYONE to wrap there head round.

Which is why a series of video shorts would be the best method of communication.

[niebieskieucho]

It's a double rubbish. Spacetime is a sick idea. It's just space that has nothing to do with time (of what BTW?), as time spontaneously does not exist.

From these comments its clear that you don’t know what spacetime is. Please learn about these things before you make another attempt at commenting on them. I.e. please study what spacetime is. I created the following for this purpose
http://home.comcast.net/~peter.m.brown/sr/spacetime.htm [nofollow]

You are living in an antiquated, hermetic world of “official” science that stuck to their myths cherished for over a century and is deaf for a down to earth physics offered by number of independent scientists and researchers. Well, I'll have to use the same arguments in the discussion because there are produced the same counterarguments. Please note that those who claim that understood relativity automatically admit that understood nonsense. Thank you for the links but it's wild goose chase. Do you really think that I do not know “scientific” explanation of spacetime? Sorry, I cannot treat it seriously. Minkowski talked about time as if it were an independent physical entity. May I in turn submit you my article about time. I would be grateful for your kind leaning over it, and letting me know if you find anything that seems to you untrue. 
http://www.eioba.com/a/33e7/why-time-cannot-dilate [nofollow]

Whether spacetime is curved or not is not up for debate. It’s an observable fact. It’s a measurable phenomena.

Nonsense. Nothing of the kind.

But until you learn what it really is as opposed to what you think it is (which you’ve proven that what you think it is is wrong) you won’t be able to understand that very simple fact.

Among other things, I did it by the above article. There is no scientific proof to support what you claim.

If you had chosen to first learn about the subject that you’re criticizing then you wouldn’t have made these mistakes. I showed you where to read about it online. Please do so before you make another attempt to argue that it’s wrong.

You have referred to material that is nothing new to me.

Quote from: niebieskieucho
As to the second rubbish, i.e. alleged curvature of space, it's simply impossible. Space does not undergo deflection, is indestructible, does not expand, is of the same volume as it was before origin of matter.
These comments also tell me that you don’t know what space curvature is. You incorrectly assumed that it meant that space is deflected. It doesn’t.

Really? So, I'll have to remind you artistic vision of the (allegedly) curved spacetime in the vicinity of massive bodies (something like a trampoline):
http://cosmicshipmedia.net/spacetime/Spacetime_curvature.png [nofollow]

It has to do with the measured distance between various points in space. The amount of deflection of star light by the sun is a measure by how much space is altered by the sun’s gravitational field.

No way! Nothing can influence on deflection of space. Which are you talking about is just contents of space. Beam of light can be curved, but not space.

My impression is that many people believe that spacetime curvature refers to the curving of a worldline in spacetime caused by a gravitational field. Am I close?

I don't know what others think. I do not accept spacetime or its alleged curvature (see the image above).

No. You’re way off. A charged particle moving in flat spacetime in an electric field will have a worldline that curves. That in no way shape or form means that the spacetime is curved.

I do not honour spacetime. Space is a physical reality whereas time does not autonomously exist, moreover, it's an abstraction as it is mathematical notation. Please try to couple for example 1 hour with space. Could you? It doesn't matter whether it is electric field or any object or particle. Any of them is in constant motion or is timing, thus time is property of matter but not space. Nevertheless, nobody hit upon the idea to call it mattertime.

If the particle’s worldline is a geodesic (i.e. the 4-force on it is zero – only inertial forces are acting on it) and it curves then all that tells you is that you’re observing the motion of the particle from a non-inertial frame of reference. Spacetime curvature pertains to the divergence of two geodesics which start out parallel and deviate. See
http://home.comcast.net/~peter.m.brown/gr/geodesic_deviation.htm [nofollow]

If you say spacetime you by this talk about non-existent entity. I do not honour spacetime. Matter is matter. It doesn't mean if it is some object or particle. They undergo the same laws of nature.

Quote from: niebieskieucho
The only curvature of space I can accept is due to spherical shape of the (finite) universe.
Then why not choose to learn about it and learn what it really means as opposed to what you think it means.

I know what is said in this question. Let's quote Wikipedia, http://en.wikipedia.org/wiki/Spacetime [nofollow]
Nonsense follows nonsense. I could make a list of them but it can't afford to spend hours to do it.

If you really want to learn what spacetime curvature is then read Exploring Black Holes at http://exploringblackholes.com/ [nofollow]

There is no spacetime. Spacetime is absurdity. Black Holes are contained in the universal space and they cannot curve it. All they can do it's absorption of spatial contents.

Or read
http://home.comcast.net/~peter.m.brown/sr/sr.htm [nofollow]
http://home.comcast.net/~peter.m.brown/gr/gr.ht [nofollow]

You are recommending false theory as such one is Relativity.

I know it’s a lot but nobody said that learning about spacetime curvature could be easy to learn.
Unless you really don’t want to learn it?

I like learning, but not scientific rubbish – no offence. To let you know my point of view on space, kindly see my article: http://www.eioba.com/a/3dm8/how-to-comprehend-space [nofollow]
My quality is lack of faults and my fault, is nothing but qualities
In addition, I trace - unfortunately - scientific absurdities

I'm sorry if I come across as being rude to you. I don't mean to be.

Not at all. You weren't.

I simply get irritated when people claim that things are wrong when it's also clear that they've never learned what it is in the first place.

Maybe some do so. But I am aware enough what I am talking about.

[Pmb (OP)]

It’s hard to answer that without it seeming personal, I have read articles of people  mis-understanding GR even though they may be able to ‘do the math’, because of that I’m very suspect of most things on the web, especially forums. I know you wrote the glossary of the first book, but I seem to be getting different understandings of GR from the book’s authors and you??

This part is absolutely true. The authors and I see things a bit different. However that doesn't make things wrong by any means. I see things the way that Einstein did and they see things the way that Wheeler did, which is consistent with the way that Max Von Laue saw things. My viewpoint is consistent with the way that John Stachel, Professor Emeretus at Boston University sees things which is also the way Einstein saw things.

Einstein saw the existance of a gravitational field in terms of the non-vanishing of the affine connection whereas myself, Einstein and Dr. Stachel see the non-vanishing of the gravitational field as the non-vanishing of the components of the affine connection.

Note: Dr. Stachel was the editor of the previous editor of the Einstein Papers Project.

[yor_on]

First of all. "I think you should make the effort to make a series of video shorts, or at the very lest build up a link of video shorts you can send people off to watch."

No GS.

Never liked that. The difference between TNS and some u-tube movie, is that you can think for yourself, we're not stuffing 'food down your mouth', you are free to argue your ideas and questions, even refuse it

As for " Assuming your mission is education of the many ?" I think Pete want to share what he find to be the essence of Relativity, and as long as he accept that there will be arguing, (it always is, btw:) I think the journey will be worth it, for all of us.

[yor_on]

And Pete "The example I always use is the uniform gravitational field. Such a field is actually defined as having no spacetime curvature yet since people are always associating spacetime curvature with gravity they also expect there to be spacetime curvature in a uniform gravitational field."

Then you say "Einstein saw the existance of a gravitational field in terms of the non-vanishing of the affine connection ...

...whereas myself, Einstein and Dr. Stachel see the non-vanishing of the gravitational field as the non-vanishing of the components of the affine connection."

So, 'affine connection'? And what do you mean by the above?

My very own view is that a metric must be there, but it doesn't need to 'curve' for a observer. Although it 'must' be there to make sense, to a lot of things, as a 'closed universe' for example, like that ball shaped one.

[Pmb (OP)]

So, 'affine connection'? And what do you mean by the above?

Take a look at the page I created for the uniform gravitational field at
http://home.comcast.net/~peter.m.brown/gr/uniform_force.htm

The capital gamma's in Eq. (5) are the affine connection, aka the connection coefficients. They are also referred to as the Christofell symboks.

Please readhttp://www2.warwick.ac.uk/fac/sci/physics/current/teach/module_home/px436/notes/lecture9.pdf

I will too so that we're on the same page.

Wish me luck or say a prayer for me today folks, depending on your theological bent. This morning is the morning that I finally have cataract surgery for my left eye. Then I'll see just like a real person does again.

[lean bean]

Wish me luck or say a prayer for me today folks, depending on your theological bent. This morning is the morning that I finally have cataract surgery for my left eye.

Best of luck pete...no gravitational lens jokes please

[Pmb (OP)]

Wish me luck or say a prayer for me today folks, depending on your theological bent. This morning is the morning that I finally have cataract surgery for my left eye.

Best of luck pete...no gravitational lens jokes please

Thanks buddy. All went well. I didn't even have to have an eye patch over the eye after suergery. I was sitting waiting for them to take me into surgery and then they told me it wsa all over. That freaks me out to no end. Lol!!

[Pmb (OP)]

You are living in an antiquated, hermetic world of “official” science that stuck to their myths cherished for over a century and is deaf for a down to earth physics offered by number of independent scientists and researchers.

In this forum we see quite a few people who don’t have any real understanding of science, never mind physics, that you’ve demonstrated such a large lack in. We don’t waste our time with people claim to know everything but whose posts demonstrate that they actually know nothing. Had you chosen to learn relativity and what the terminology means then you’ve have learned that the term curvature when applied to spacetime is used as an analogy and not used erroneously as you have obviously done and to be taken as a literal meaning. And this is all already explained quite clearly to anyone and everyone who wants to know it. But you’ve chosen not to learn the truth since you ignored http://exploringblackholes.com/

Anyone who’s studied general relativity and actually knows what they’re talking about knows this as one of the most basic of all truths of physics. However since you’ve instead chosen to take this as an opportunity to criticize general relativity rather than to learn it you’re going to remain ignorant. That this is the case is apparent from your choice to ignore the online text on GR by Bertschinger, Taylor and Wheeler which explains that curvature is a term used as an analogy just goes to show how little you’re willing to learn.

Good lord! It’s amazing on how much you’ve droned on about things you have absolutely no idea what they are. On this forum we only spend time talking to people who actually want to learn and either know what they’re talking about or ware willing to learn about it.

I’ve cut the rest since its of no worth to anyone.

In a way I feel sad for you. But not that sad since you could learn but have chosen not to.


Come on folks! Why do we allow trash to be posted in this forum by people who have absolutely no idea about what they're talking about? I mean this is just a little too overboard for my taste.

[yor_on]

Hope it worked out for you Pete, with the operation and all. As you forgot to link Einstein’s gravitational field. which gives a more digestible introduction (for us laymen) to your thoughts, I took upon me the liberty of linking it .

As for people not trusting relativity.
Well, everyone has his own ideas. That's why we discuss, and as they say, 'don't get mad, get even'.

[Pmb (OP)]

Hope it worked out for you Pete, with the operation and all. As you forgot to link Einstein’s gravitational field. which gives a more digestible introduction (for us laymen) to your thoughts, I took upon me the liberty of linking it .

Thank you my friend. How do you like thar article by the way?

[yor_on]

I enjoyed it. It was very readable, and I agree to that a earths gravitational field is there, even when I am in a 'free fall', if we by that refer to tidal forces? Although it seem to clash with the idea of a geodesic to me, as a geodesic, per definition and as I read it, exist everywhere you have a free fall, and a geodesic should be without 'gravity'?

[yor_on]

Then again, you have this example with a uniform gravitational field that you would be welcome to expand on, preferably without mathematics,

You say " This expression gives the local acceleration of an object whose velocity is v. Observers at different positions z in the field system will not measure the same local value of acceleration. Not only will the object’s acceleration depend of position but also on velocity. This is contrary to what one would normally assume for a uniform gravitational field. "

If it is a uniform field, me reading that as it should have a same value at all positions, then what gives those, lets say two, observers different accelerations? You give their initial velocity (uniform) as one reason, the other being where they are positioned in it. Can you find a way to define it without mathematics?
=

I am assuming that the observers are identical to each other, preferably able to be defined as being 'at rest' with each other, although at different positions.   

(Eh, better add that I totally agree on that gravity should be everywhere, no matter how one define the space, as flat or not.)