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Author Topic: Are inertial forces real?  (Read 11680 times)

Offline yor_on

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Re: Are inertial forces real?
« Reply #25 on: 27/11/2013 09:55:03 »
true Pete, but what it made me think about was actually electrons 'orbitals'.
 

Offline Pmb

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Re: Are inertial forces real?
« Reply #26 on: 27/11/2013 10:22:39 »
Quote from: yor_on
true Pete, but what it made me think about was actually electrons 'orbitals'.

Where did you mentionor indicate that you were thinking about orbitals? Or did you? You wrote
Quote
A charged particle moving in a circle, is that a geodesic? If it isn't, then it is a acceleration. And if it accelerates it must lose 'energy'.
Electrons in orbitals are not moving in circles and are not accelerating. Those are classical ideas which don't belong in the realm of quantum mechanics.
 

lean bean

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Re: Are inertial forces real?
« Reply #27 on: 27/11/2013 16:39:03 »
The laws of physics don’t require the existence of gravitational objects for gravitational waves to exist.
Trying not to take your opening question too of course here, but...
Can you explain something of what you mean there.
I stuck with thinking of either mass or energy or momentum as having something to do with the origin of gravitational waves. Or are you saying not to worry about the origin of the waves?
« Last Edit: 27/11/2013 16:55:19 by beany »
 

Offline Pmb

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Re: Are inertial forces real?
« Reply #28 on: 27/11/2013 17:02:30 »
Quote from: beany
Or are you saying not to worry about the origin of the waves?
Yes. Anytime I've ever had to calculate the force exerted on a particle I never had to know the source of the field. All I had to know was the field.
 

lean bean

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Re: Are inertial forces real?
« Reply #29 on: 27/11/2013 17:20:19 »
Quote from: beany
Or are you saying not to worry about the origin of the waves?
Yes. Anytime I've ever had to calculate the force exerted on a particle I never had to know the source of the field. All I had to know was the field.
Ok, now I know what you mean, but, I do think you could have worded that better... confused for a moment thinking what other laws, if not those of physics, do you require to make G waves. :)

 

Offline yor_on

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Re: Are inertial forces real?
« Reply #30 on: 27/11/2013 20:16:34 »
I know that Pete, on the other hand you have 'photographic evidence', although created by taking several images/snapshots, of something called a particle (electron) in that Swedish experiment (think it was Lund's university). So we have both in some weird way, or not so weird if propagation can be questioned, instead using the idea of a field, keeping a local 'constant' arrow for any observer, allowing this 'particle' to be depicted through repeated 'snapshots'. It's the way my mind works Pete :) Also called galloping senility.
=

(As well as thinking of it as if a 'acceleration' can be translated to something at a particle level, we do it with a planet, do we not? Earth 'accelerates', so the question I started to ask, and still ask, myself is if one could apply the same sort of view on a atom and its constituents. Accelerations versus uniform motion. )
=
And to come a little clearer :) Not talking about a acceleration as something 'spending a energy' for this. As far as I know Earth do not spend any 'energy' by 'constantly uniformly accelerating' at about one gravity
==

Maybe you can express it this way. If Earth is 'accelerating', then it is in no measurable direction for us. Instead we find a uniform motion that we can measure, through the universe. And that motion is a geodesic as I understands it, spending no 'energy', never mind how much matter, neutron stars, etc, I involve in Earths path.

That one gives me one headache, no 'friction', the other is what a 'acceleration' can be, if I define Earth as accelerating. And then we have particles, they should have a gravitational field too, shouldn't they? And they, just as Earth, should then 'accelerate'.
==

Maybe the question could be. Do a acceleration spend 'energy'? I sort of automatically have assumed it must do so, it seems the reasonable assumption to me. But what about the equivalence principle then, and Earth 'accelerating'?
« Last Edit: 27/11/2013 21:07:27 by yor_on »
 

Offline alancalverd

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Re: Are inertial forces real?
« Reply #31 on: 27/11/2013 23:38:55 »
Quote
one body generates a field and it’s the field that interacts with objects to exert forces on them. So all we need to know, and all that needs to exist, is the field, not the source. The laws of physics don’t require the existence of gravitational objects for gravitational waves to exist.

Spot the selfcontradiction.

If you can generate a gravitational field  without a source object, you can have all the Nobel prizes at once. But until then, I think anyone observing the effect of a gravitational field will (rightly) infer the existence of a massive object. That is, after all, how astronomers conduct their business, and to date, they have been right every time.

Not sure how the laws of physics determine the existence of gravitational waves. Scientific laws are discovered by observation, not imposed by Brussels.

Quote
In Einstein's theory of general relativity, gravity is treated as a phenomenon resulting from the curvature of spacetime. This curvature is caused by the presence of mass.

But what did Einstein know about relativity? My friend pmb says you don't need mass. So there.
« Last Edit: 27/11/2013 23:42:44 by alancalverd »
 

Offline Pmb

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Re: Are inertial forces real?
« Reply #32 on: 27/11/2013 23:57:25 »
Quote from: beany
Ok, now I know what you mean, but, I do think you could have worded that better... confused for a moment thinking what other laws, if not those of physics, do you require to make G waves. :)
Well I can't be good at everything. :)   But could have worded what exactly, better?
 

Offline yor_on

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Re: Are inertial forces real?
« Reply #33 on: 28/11/2013 12:34:48 »
It's a really tricky one Alan. But think of 'energy' for it. If there is a equivalence between energy and mass, then 'energy' should be enough for making a defined 'container of a universe, even in the absence of matter, as long as we assume gravity to have a relation to 'mass'. Light can be referred to as having mass too. So you're right in that we need a relation, but what that relation need to be? Then there is the way you can translate away a 'gravity' by changing your reference frame. If I imagine a gravitational field as a defined color, then this statement is the same as saying that the color disappear just by me changing some parameter 'inside' it, as stopping my acceleration, free falling. And if we involve different frames of reference, then me on earth may define a satellite as 'free falling' inside a gravitational field, but for the satellite itself there is no gravitational field to be measured. Or if we define it as some sort of grid lines, then me accelerating either becomes a very local experience of 'gravity or, assuming gravity's infinite reach, those locally created 'field lines' reach forever, as long as I keep accelerating.
 

Offline alancalverd

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Re: Are inertial forces real?
« Reply #34 on: 28/11/2013 20:41:59 »
Quote
then me on earth may define a satellite as 'free falling' inside a gravitational field, but for the satellite itself there is no gravitational field to be measured

Oh yes there is! The observer on the satellite will note that he is accelerating towards a massive object, and deduce that he is therefore in a convergent gravitational field.
 

Offline Pmb

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Re: Are inertial forces real?
« Reply #35 on: 28/11/2013 22:22:41 »
Quote from: alancalverd
Quote
then me on earth may define a satellite as 'free falling' inside a gravitational field, but for the satellite itself there is no gravitational field to be measured
Oh no there isn’t
Oh yes there is! yor_on was attempting to explain Einstein’s equivalence principle to you. That principle states that at any event in spacetime it’s possible to transform the gravitational field away. And likewise it’s possible to create a gravitational field at any point in spacetime. If you really want to learn Einstein’s general theory of relativity then you should pick up a GR textbook and read it rather than making all of these false assumptions about it attempting to prove it wrong. Start here The Foundation of the General Theory of Relativity by Albert Einstein (1916), Annalen der Physik, 49. See
http://hem.bredband.net/b153434/Works/Einstein.htm
Quote
It will be seen from these reflexions that in pursuing the general theory of relativity we shall be led to a theory of gravitation, since we are able to "produce" a gravitational field merely by changing the system of co-ordinates.

Quote from: alancalverd
The observer on the satellite will note that he is accelerating towards a massive object, and deduce that he is therefore in a convergent gravitational field.
That’s a misinterpretation of what yor_on said. He didn’t say that it’s possible to transform the gravitational field away at all events. He actually meant that at even event you an transform it away. However in a curved spacetime like that around earth it can’t be transformed away everywhere. In this case the observer on the satellite will not be in a gravitational field if he stays close to the (small) satellite. However in this case it’s the earth that is in free fall in his frame of reference. I.e. the earth is in the gravitational field now, not the satellite.

« Last Edit: 28/11/2013 22:38:24 by Pmb »
 

Offline CPT ArkAngel

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Re: Are inertial forces real?
« Reply #36 on: 28/11/2013 22:24:09 »
If you are in a box or an elevator, maybe the walls are hiding the truth...

Nice article Pete!
 

Offline alancalverd

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Re: Are inertial forces real?
« Reply #37 on: 29/11/2013 00:24:17 »
So you are saying that according to GR, gravitational fields exist in the absence of mass.

Now here's a fine mess, because one principle of all non-newtonian physics is that it must approximate to the newtonian at the mesoscopic level, because that is what we observe and we don't like arbitrary discontinuities in our theories. So where does the mass of the bodies come from, in our carefully measured "Gm1m2/r^2" forces? 
 

Offline Pmb

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Re: Are inertial forces real?
« Reply #38 on: 29/11/2013 04:36:51 »
Quote from: alancalverd
So you are saying that according to GR, gravitational fields exist in the absence of mass.
It's certainly allowed by the field equation, that's for sure.

Quote from: alancalverd
Now here's a fine mess, because one principle of all non-newtonian physics is that it must approximate to the newtonian at the mesoscopic level, because that is what we observe and we don't like arbitrary discontinuities in our theories.
This is what I've been talking about. If you actually sat down and chose to learn general relativity then you'd no longer make mistakes like this.

In this case you're confusing the notion of incommensurate theories with the correspondence principle and then you thought you found a problem but the problem doesn't exist. The problem is with your poor knowledge of GR.

What you're trying to refer to is the correspondence principle in general relativity that is described here -
http://en.wikipedia.org/wiki/Physical_theories_modified_by_general_relativity

That principle demands that the weak field approximation of GR be what Newtonian gravity predicts. This is one of the things you'd learn correctly if you actually took our word for it and studied GR formally by picking up a good GR text and hitting it hard. Perhaps you don't have the math skills? Is that why you've been refusing to learn it? The math is something you learn as part of learning physics. It's not a roadblock to it but part of the education.

Or what is the reason that you refuse to learn GR before you continue to claim that it’s wrong?

However the correspondence principle doesn't apply to this. For example; in Newtonian gravity there are no gravitational waves so in this respect the correspondence principle doesn't apply. Then there's the fact that frames of reference in a freely falling frame are non-inertial frames in Newtonian mechanics but are inertial frames in GR. Also a place where the correspondence principle doesn't apply.

Quote from: alancalverd
So where does the mass of the bodies come from, in our carefully measured
"Gm1m2/r^2" forces? 
That's the problem. You're wondering where the mass of the bodies comes from but
don't even ask yourself what body is it that you're referring to. In Newtonian gravity all
gravitational fields had massive bodies as sources. However that's Newtonian gravity,
not general relativity. Again you're confusing the two theories.

You also don't seem to be able to understand anything except the gravitational fields outside of planets and stars. This is how you're stuck in Newtonian gravity. If you learned GR then you'd learn the error in making such assumptions.

Are you familiar with Mach's principle? I don't believe so since if you did then you wouldn't have made such a statement. Please learn about it at http://en.wikipedia.org/wiki/Mach's_principle

It explains things like this. E.g. suppose you were in a frame of reference that's rotating relative to an inertial frame of reference. In the rotating frame there'd be gravitational fields. However this is only true in GR and not in Newtonian mechanics where those forces are referred to as "inertial forces" and go by names such as the Coriolis force and the centrifugal force. In GR those are gravitational forces. The source of those  gravitational forces is the matter from the distant stars. Consider how Einstein viewed such forces/fields. The following comes from an article that Einstein wrote which appeared in the February 17, 1921 issue of Nature
Quote
Can gravitation and inertia be identical? This question leads directly to the General Theory of Relativity. Is it not possible for me to regard the earth as free from rotation, if I conceive of the centrifugal force, which acts on all bodies at rest relatively to the earth, as being a "real" gravitational field of gravitation, or part of such a field? If this idea can be carried out, then we shall have proved in very truth the identity of gravitation and inertia. For the same property which is regarded as inertia from the point of view of a system not taking part of the rotation can be interpreted as gravitation when considered with respect to a system that shares this rotation. According to Newton, this interpretation is impossible, because in Newton's theory there is no "real" field of the "Coriolis-field" type. But perhaps Newton's law of field could be replaced by another that fits in with the field which holds with respect to a "rotating" system of co-ordinates? My conviction of the identity of inertial and gravitational mass aroused within me the feeling of absolute confidence in the correctness of this interpretation.
You could learn more about this if you really wanted to learn about GR by looking at http://home.comcast.net/~peter.m.brown/gr/inertial_force.htm
Search for the term inertial induction.

I've had you in my kill file for a very long time. Do you want to know why? If so then it's because of the fact that you refusing to learn GR means that you keep making mistakes and when I saw a mistake I felt compelled to correct it. Since there are so many mistakes and it takes a lot of work to correct you and you have no desire to go out and learn this for yourself it's a waste of my time.

Since this is getting to be way to much work again to keep correcting your mistakes I'm putting you back in mh kill file. Sorry but this is supposed to be a two way street, not just one way. You have to be willing to learn and you're not willing to read a good book on GR
 

Offline alancalverd

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Re: Are inertial forces real?
« Reply #39 on: 29/11/2013 09:39:15 »
Relax, man. I haven't questioned the validity of GR, nor would I bother to do so. I'm concentrating on the question of whether gravitation is an inertial force, that is, one that exists between two bodies.   
 

Offline Pmb

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Re: Are inertial forces real?
« Reply #40 on: 29/11/2013 12:50:47 »
Quote from: alancalverd
Relax, man.
I am relaxed. This isn't a question of me not being relaxed either. Also please try to understand that I'm not saying these things to be a jerk or to come off as being arrogant. I'm truly and honestly trying to help you get to learn everything it is that you're seeking to learn and I know as fact and from experience that all of our answers are found by learning general relativity. So you can imagine my confusion at your absolute refusal to learn the theory which was created to answer just the kinds of questions that you're seeking answers to.  :-\

Quote from: alancalverd
I haven't questioned the validity of GR, nor would I bother to do so. I'm concentrating on the question of whether gravitation is an inertial force, that is, one that exists between two bodies.
Inertial forces are not defined as a force between two bodies. An inertial force is defined here http://home.comcast.net/~peter.m.brown/gr/inertial_force.htm 

An inertial force is a force which is proportional to the mass of the object the force is acting on just like the Coriolis and censtrifugal force. Those have nothing to do with a source body. And my point here is that all of this is explained in any decent GR text. After all that's exactly what the theory is explaining to you. So your choosing not to go directly to the source of where your answers are designed to be found in. Why is that?
« Last Edit: 29/11/2013 13:10:01 by Pmb »
 

Offline Mike_Fontenot

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Re: Are inertial forces real?
« Reply #41 on: 29/11/2013 21:06:22 »
My question for you is  - Do you believe that the gravitational force cannot be thought of as a "real" force and must therefore be called, at best, a pseudo force? Or to phrase it another way - How many of you believe that if a particle is accelerating under the action of a field for which the 4-acceleration on the particle is zero that any attempt to define a "force" on the particle must imply that it should be thought of/defined as a pseudo-force?

As to your first phrasing of the question, I think real gravitational fields are those that are caused by specific, identifiable masses (and not by "the masses at infinity", as in Mach's explanation of inertia).  I think the spatially-uniform gravitational field that one gets, when the equivalence principle is used to explain the perspective of a traveler who is being accelerated by a rocket (and who is far from any large masses), is a FICTITIOUS gravitational field.

As to your second phrasing of the question, it's been too long since I've studied GR, and 4-acceleration in particular, for me to comment on that specific question. But I will just say that I think the two very different concepts of acceleration in GR vs SR cause a HUGE amount of misunderstanding in many discussions I've witnessed. For example, the notion, that someone at rest on the surface of a (non-rotating and non-orbiting) earth, "is accelerating", and that someone who is free-falling into a deep hole in the earth "is not accelerating", is quite different from the notion that masses accelerate when there is a net force on them, and otherwise they don't accelerate. I don't remember if that difference is purely due to the difference between the concepts of spatial acceleration (3-acceleration?) vs 4-acceleration, or not.

Also, I certainly don't take seriously the notion that, if I were floating in empty space (far from any significant masses), and if I decided to turn on my rocket at some thrust level and direction, that a spatially-uniform gravitational field would suddenly come into existence, which exactly counteracts my rocket thrust, preventing me from accelerating, and causing all the other masses (anywhere in the universe) to accelerate. Such a notion has, in my opinion, little or no value in explaining the twin "paradox" ... its value lay in pointing the way to GR, by constraining the results that GR must give, and also as a verification of the resulting GR theory.
 

Offline Pmb

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Re: Are inertial forces real?
« Reply #42 on: 29/11/2013 21:46:32 »
Quote from: Mike_Fontenot
As to your first phrasing of the question, I think real gravitational fields are those that are caused by specific, identifiable masses (and not by "the masses at infinity", as in Mach's explanation of inertia). etc
Mike - You already answered this question in my forum so you don't need to repeat it here unless you're doing so for the benefit of sharing your point of views with the other members here? If so then it’d make sense to repeat yourself here.  Otherwise it's redundant.
 

Offline Pmb

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Re: Are inertial forces real?
« Reply #43 on: 29/11/2013 22:08:14 »
Quote from: MikeFontenot
It's been too long since I've studied GR, and 4-acceleration in particular, for me to comment on your specific question.  But I will just say that I think the two very different concepts of acceleration in GR vs SR cause a HUGE amount of misunderstanding in many discussions I've witnessed.
What are these misunderstandings that you’re referring to?

Quote from: MikeFontenot
   For example, the notion, that someone at rest on the surface of a (non-rotating and non-orbiting) earth, "is accelerating", and that someone who is free-falling into a deep hole in the earth "is not accelerating", is quite different from the notion that masses accelerate when there is a net force on them, and otherwise they don't accelerate.
That’s not a quite precise way to describe what’s going on. It certainly isn’t how Einstein perceived the situation. Here’s how he phrased it. From The Foundation of the General Theory of Relativity by Albert Einstein, Annalen der Physik, 49, (1916) which can be found at http://hem.bredband.net/b153434/Works/Einstein.htm
Quote
Let K be a Galilean system of reference, i.e. a system relatively to which (at least in the four-dimensional region under consideration) a mass, sufficiently distant from other masses, is moving with uniform motion in a straight line. Let K' be a second system of reference which is moving relatively to K in uniformly accelerated translation. Then, relatively to K', a mass sufficiently distant from other masses would have an accelerated motion such that its acceleration and direction of acceleration are independent of the material composition and physical state of the mass.
Does this permit an observer at rest relatively to K' to infer that he is on a "really" accelerated system of reference? The answer is in the negative; for the above-mentioned relation of freely movable masses to K' may be interpreted equally well in the following way. The system of reference K' is unaccelerated, but the space-time territory in question is under the sway of a gravitational field, which generates the accelerated motion of the bodies relatively to K'.
So in Einstein’s viewpoint it’s valid to refer to a body sitting on the surface of the earth to be considered to be at rest. It’s only accelerating if you state with what it’s accelerating with respect to. If you’re in a free-fall frame then the body at rest on the surface of the earth is accelerating with respect to your free-fall frame.
Quote from: MikeFontenot
Also, I certainly don't take seriously the notion that, if I were floating in empty space (far from any significant masses), and if I decided to turn on my rocket at some thrust level and direction, that a spatially-uniform gravitational field would suddenly come into existence, which exactly counteracts my rocket thrust, preventing me from accelerating, and causing all the other masses (anywhere in the universe) to accelerate.
I believe that the reason you reject what general relativity says on this point is because you’re trying to use the Newtonian theory of gravity to interpret what’s being described with general relativity. You’re stuck in the Newtonian frame of mind where all gravitational fields have a definite source to that is close by and used to calculate what’s happening to a body in the field. You haven’t gone over to general relativity as a result of being stuck with the Newtonian thought process. If you don’t study the reasons for this radically different viewpoint how can you justify rejecting it? You’re stuck with old definitions and interpretations and haven’t made the transition to GR.

Do you actually know why Einstein said what he said? What was on his mind? What was he thinking? What was his justification for it?

Quote from: MikeFontenot
  Such a notion has, in my opinion, little or no value in explaining the twin "paradox" ... its value lay in pointing the way to GR, by constraining the results that GR must give, and also as a verification of the resulting GR theory.
You already stated your opinion on this in my forum so there’s no reason to put it here too. Especially out of context like this since nobody here knows what you’re talking about.
 

lean bean

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Re: Are inertial forces real?
« Reply #44 on: 30/11/2013 11:15:33 »
Pete, You may remember this pdf found at the Mit site
Don't know if this has relevance on this thread, but...

From pdf here  http://ocw.mit.edu/courses/physics/8-224-exploring-black-holes-general-relativity-astrophysics-spring-2003/assignments/
Pick pdf “How Gravitational Forces Arise from Curvature” Page 2.

It say’s 
Quote
1. Introduction: Extremal Aging and the Equivalence Principle
These notes supplement Chapter 3 of EBH (Exploring Black Holes by Taylor and Wheeler).
They elaborate on the discussion of the Principle of Extremal Aging and the motion of massive bodies in curved spacetime.
Do you agree with the idea that the acceleration of a rock near earth, is just the outward appearance of the rock following a path of maximum aging on its wristwatch (rock’s proper time) in an altered spacetime near mass. Maximum aging defining the geodesic path of rock.

Quote
However, according to general relativity it still works out that the correct path is the one that maximizes proper time!
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.
My bold.
:)
« Last Edit: 30/11/2013 11:44:14 by beany »
 

Offline Pmb

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Re: Are inertial forces real?
« Reply #45 on: 30/11/2013 12:36:58 »
Quote from: beany
Pete, You may remember this pdf found at the Mit site
Don't know if this has relevance on this thread, but...
Yes. I remember it very well since the premise is wrong, i.e. curvature is not a necessary condition for the presence of a gravitational force on a body in a gravitational field.

Quote from: beany
Do you agree with the idea that the acceleration of a rock near earth, is just the outward appearance of the rock following a path of maximum aging on its wristwatch (rock’s proper time) in an altered spacetime near mass. Maximum aging defining the geodesic path of rock.
Only if the rock is in free fall is that true. But yes, of course I agree.
 

lean bean

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Re: Are inertial forces real?
« Reply #46 on: 30/11/2013 17:22:37 »
Yes. I remember it very well since the premise is wrong, i.e. curvature is not a necessary condition for the presence of a gravitational force on a body in a gravitational field.
Are you saying it is not possible to transform away the gravitational field even locally ?
Do you need to transform away the field completely for it to not effect the test point/particle?


Is it this part you don’t agree with…
From link given in my last post.
Quote
What then is the path of a freely-falling body in the presence of gravity? According to Newtonian physics, the answer is given by solving ~F = m~a = md2~x=dt2 as a differential equation for ~x(t).
Gravity causes acceleration, and one might expect therefore that the maximal-aging result breaks down. A body obviously accelerates in a gravitational field, and so an unaccelerated path cannot be the correct one. However, according to general relativity it still works out that the correct path is the one that maximizes proper time!
equation symbols don’t copy correctly.

Besides spacetime curvature / space curvature and time dilation/gravitational redshift, what other evidence shows the presence of a field? Also how does this other evidence of field effect the Equivalence Principle if at all?

Have you let the MIT people know that their premise is wrong?
Given MIT are ‘teaching’ this, you would be doing them a service informing them.  Does E. Taylor still ‘reside’ at MIT?

Only if the rock is in free fall is that true. But yes, of course I agree.
Yes, the rock is un-powered and following a geodesic, defined by maximum aging on the rock’s watch and the spacetime metric, and so giving the appearance of acceleration when moving through an altered spacetime near mass. Why is the spacetime altered near mass? Don’t know.
What is the mechanism of an attracting ‘force’? Don’t know. Both being convenient models of observations.

From “Exploring Black Holes” Pick chapter titled “Diving” PDF page 2
Here…http://exploringblackholes.com/
Quote
Newton says a “force of gravity" leads to the parabolic trajectory. But  Einstein declares that Newton's “force of gravity" does not exist. Instead spacetime shouts, “Go straight!" The free stone obeys. What does “straight" mean?  Straight with respect to what? We know the answer: The path of the stone is straight with respect to every local free-fall (inertial) frame through which it passes.

I don’t know why I’m telling you this pete? I know you were one of those who proof read EBH or perhaps still are the 2nd edition. :)
« Last Edit: 30/11/2013 17:30:47 by beany »
 

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Re: Are inertial forces real?
« Reply #47 on: 30/11/2013 23:53:31 »
Quote from: beany
Are you saying it is not possible to transform away the gravitational field even locally ?
No. How did you get that from what I said?

Quote from: beany
Do you need to transform away the field completely for it to not effect the test point/particle?
No. So long as the particle isn’t charged. For a charged particle the field is part of the charge and that acts to “probe spacetime.” A charged particle does not follow a geodesic in a curved spacetime.

Quote from: beany
Is it this part you don’t agree with…
No. As I said above, the part that is wrong is that the gravitational force is not a manifestation of spacetime curvature since you can have a gravitational force with no spacetime curvature.

Quote from: beany
Besides spacetime curvature / space curvature and time dilation/gravitational redshift, what other evidence shows the presence of a field?
If a particle subjected to no other than the gravitational force accelerates then there is a gravitational field present. If the particle does not accelerate then there is no gravitational field. The presence of spacetime curvature can be detected by looking for geodesic deviation, i.e. when two particles in free-fall accelerate relative to each other.

Quote from: beany
Have you let the MIT people know that their premise is wrong?
Edwin knows that it’s wrong. I don’t think he’ll tell the man who wrote it though, i.e. Bertschinger. I personally don’t like Bertschinger. To me he’s kind of a snob. He gives me the impression that I’m not important enough to want to know or talk to. That’s why I really don’t like that guy at all. I hear he’s like that with a lot of people. That’s why I have no respect for him whatsoever.

Quote from: beany
Given MIT are ‘teaching’ this, you would be doing them a service informing them.
That’s their problem, not mine. I do my service by proof reading the text that they’re learning out of.

Quote from: beany
Does E. Taylor still ‘reside’ at MIT?
He still has an office there, yes. He’s retired. He teaches when he has the time and energy.

Quote from: beany
Newton says a “force of gravity" leads to the parabolic trajectory. But  Einstein declares that Newton's “force of gravity" does not exist.
Einstein never said that and the author knows that. He wrote it in there anyway. I wasn’t too happy about it.

Quote from: beany
I don’t know why I’m telling you this pete?
Perhaps you feel the need to cover all your bases? :)

Quote from: beany
I know you were one of those who proof read EBH or perhaps still are the 2nd edition. :)
Yep. I’m starting over from chapter 1 which I’m finishing up this weekend.
Yes. I remember it very well since the premise is wrong, i.e. curvature is not a necessary condition for the presence of a gravitational force on a body in a gravitational field.
Are you saying it is not possible to transform away the gravitational field even locally ?
Do you need to transform away the field completely for it to not effect the test point/particle?


Is it this part you don’t agree with…
From link given in my last post.
Quote
What then is the path of a freely-falling body in the presence of gravity? According to Newtonian physics, the answer is given by solving ~F = m~a = md2~x=dt2 as a differential equation for ~x(t).
Gravity causes acceleration, and one might expect therefore that the maximal-aging result breaks down. A body obviously accelerates in a gravitational field, and so an unaccelerated path cannot be the correct one. However, according to general relativity it still works out that the correct path is the one that maximizes proper time!
equation symbols don’t copy correctly.

Besides spacetime curvature / space curvature and time dilation/gravitational redshift, what other evidence shows the presence of a field? Also how does this other evidence of field effect the Equivalence Principle if at all?

Have you let the MIT people know that their premise is wrong?
Given MIT are ‘teaching’ this, you would be doing them a service informing them.  Does E. Taylor still ‘reside’ at MIT?

Only if the rock is in free fall is that true. But yes, of course I agree.
Yes, the rock is un-powered and following a geodesic, defined by maximum aging on the rock’s watch and the spacetime metric, and so giving the appearance of acceleration when moving through an altered spacetime near mass. Why is the spacetime altered near mass? Don’t know.
What is the mechanism of an attracting ‘force’? Don’t know. Both being convenient models of observations.

From “Exploring Black Holes” Pick chapter titled “Diving” PDF page 2
Here…http://exploringblackholes.com/
Quote
Newton says a “force of gravity" leads to the parabolic trajectory. But  Einstein declares that Newton's “force of gravity" does not exist. Instead spacetime shouts, “Go straight!" The free stone obeys. What does “straight" mean?  Straight with respect to what? We know the answer: The path of the stone is straight with respect to every local free-fall (inertial) frame through which it passes.

I don’t know why I’m telling you this pete? I know you were one of those who proof read EBH or perhaps still are the 2nd edition. :)

 

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Re: Are inertial forces real?
« Reply #48 on: 01/12/2013 13:23:33 »
Quote from: beany
Are you saying it is not possible to transform away the gravitational field even locally ?
No. How did you get that from what I said?
I don't know, that just entered my head at the time. :)

the part that is wrong is that the gravitational force is not a manifestation of spacetime curvature since you can have a gravitational force with no spacetime curvature.
If a particle subjected to no other than the gravitational force accelerates then there is a gravitational field present. If the particle does not accelerate then there is no gravitational field. The presence of spacetime curvature can be detected by looking for geodesic deviation, i.e. when two particles in free-fall accelerate relative to each other.
LATE MODIFICATION...Is your ‘cavity’ inside a large mass an example of gravitational field without curvature?  If so, In the cavity, from what direction does the force act on a test particle to accelerate it.
Or, are you saying the forces in the cavity cancel each other? If so, where’s the  evidence of the presence of a gravitational field if there is no acceleration of a test particle?


Quote from: beany
Newton says a “force of gravity" leads to the parabolic trajectory. But  Einstein declares that Newton's “force of gravity" does not exist.
Einstein never said that and the author knows that. He wrote it in there anyway. I wasn’t too happy about it.
Pete, I’m not sure it is Bertschinger’s total doing…

 There is a figure and caption on page 2-5 of “Exploring Black Holes” edition one only, The references at the end of the chapter state the figure plus caption are taken from the book “Gravitation” back in 1979, By Misner, Wheeler and thorne.

Part of the caption reads…
Quote
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. Its instructions are simple: “Go straight! Follow the straightest possible worldline (geodesic).” Physics is as simple as it could be locally. Only because spacetime is curved in the large do the tracks diverge or converge.
And in “Exploring Back Holes” edition one, page 3-4 there is…
Quote
So what is new about relativity? On the theory side, Einstein says that you can do away entirely with Newton’s gravitational force.
That edition is just J.Wheeler and E.Taylor, not Bertschinger.
So, these othes are wrong too? :)


« Last Edit: 01/12/2013 17:59:45 by beany »
 

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Re: Are inertial forces real?
« Reply #49 on: 01/12/2013 21:15:26 »
Quote from: beany
LATE MODIFICATION...Is your ‘cavity’ inside a large mass an example of gravitational field without curvature?
Yes. In fact that’s the entire purpose of the example.

Quote from: beany
If so, In the cavity, from what direction does the force act on a test particle to accelerate it.
Construct vector whose tip is at the center of the body and whose tail is the center of the cavity. The force is parallel to and in the direction of this vector.

Quote from: beany
Pete, I’m not sure it is Bertschinger’s total doing…
It doesn’t matter. He should know better. Thinking in terms of spacetime curvature is what leads people to make mistakes like this.

Quote from: beany
There is a figure and caption on page 2-5 of “Exploring Black Holes” edition one only, …. That edition is just J.Wheeler and E.Taylor, not Bertschinger.
So, these othes are wrong too? :)
Yes. It doesn’t matter though. Neither of these two men should be making an error as careless as this. They should know better. Thinking in terms of spacetime curvature is what leads people to make mistakes like this. They might be justifying it to themselves by saying that tidal forces are a result of gravitational force and that’s how they can justify claiming that force is a manifestation of spacetime curvature but not only is it wrong its very misleading. As you know from the cavity example you can have a gravitational force without spacetime curvature.
 

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Re: Are inertial forces real?
« Reply #49 on: 01/12/2013 21:15:26 »

 

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