At rest in Einsteinian relativity

[mangaroosh]

By being more specific and to-the-point concerning laws of physics you could discuss some of these matters here. But yes, I think that the more "fuzzy" type of discussion belongs in the philosophy forum.

[EDIT] as is undoubtedly obvious [/EDIT] I'm not that well versed in the use of some of the specific terminology, so when I present my understanding of things it tends to come across sounding "fuzzy"; I'll start one in the philosophy forum, and see how it goes.

Cheers Harry.

 

[Dale]

The use of the term "moving" represents the idea of absolute motion, which is the deduction.

Exactly, you persistently assume the thing you want to deduce, that is a fallacy.

Just taking the example of the two lone observers who start off at rest relative to each other; they then start moving relative to each other - here we only consider relative motion, or velocities.

The deduction we can make on that basis, as far as I can see, is that in order for relative motion to occur, at least one has to start moving. We cannot determine which one moves - as per the principle of relativity; but we can deduce, surely, that one of them has to have moved.

Note all of the references to absolute motion. In SR none of these terms are defined (see "flubnubitz" above). You have made them, simply assuming that they are well-defined, without proving it. To be well-defined this paragraph should be written:

"In order for relative motion to occur, at least one has to start moving relative to any given inertial frame. We can determine which one moves relative to any inertial frame - as per the principle of relativity; and we can deduce, surely, that one of them has to have moved relative to any inertial frame."

If you say the word "move" or "rest" without saying the frame you have not said anything with meaning. If you consistently say what frame you are talking about then you will always get statements that are meaningful and logically self-consistent.

 

[Dale]

mangaroosh, here is a physical example that may help. If I say "the door is open" what I am actually talking about is the relationship between the door and its frame. If you have a door without a frame it doesn't make sense to say that it is either open or closed. Similarly, if I say "X is moving" what I am actually talking about is the relationship between X and a reference frame. If I have X without a frame it doesn't make sense to say that it is either moving or at rest.

The difference between door frames and reference frames is that each door has at most one door frame, while X can have an infinite number of reference frames. But in each case the frame is something which essential for defining the state, and statements about the state are meaningless without the frame.

 

[Dale]

Well, the fact of the matter is that at least some of them held that their conclusions were experimentally justified and it corresponds to a currently discussed interpretation of QM (one alternative model has that reality doesn't exist!). Apparently you think that their logic must be illogical because you cannot follow their logic

The equations of mechanics, EM, and QM are all relativistic (either Galilean or Special). The only way for their conclusions about absolute space to be experimentally justified would be to find experimental violations of the principle of relativity (i.e. experiments that violate the coresponding relativistic equations). None of them did that. If you believe that I am incorrect about that then please find a reference where one of them found a violation of the principle of relativity, because I am unaware of it.

I am sorry if my statements bother you, but I do not think that it is a matter of opinion which needs to be qualified by a IMO.

 

[harrylin]

The equations of mechanics, EM, and QM are all relativistic (either Galilean or Special). The only way for their conclusions about absolute space to be experimentally justified would be to find experimental violations of the principle of relativity (i.e. experiments that violate the cooresponding relativistic equations). None of them did that. If you believe that I am incorrect about that then please find a reference where one of them found a violation of the principle of relativity, because I am unaware of it.

I am sorry if my statements bother you, but I do not think that it is a matter which needs to be qualified by a IMO.

None of your statements bother me.

However, to give just one clear example, you just wrote that: "The equations of [Galilean] mechanics[..] are [..] relativistic [..]. The only way for their conclusions about absolute space to be experimentally justified would be to find experimental violations of the principle of relativity".

As Newton's mechanics uses Galilean relativity, your claim implies that he should have found an experimental violation of his theory of mechanics to justify his absolute space postulate - and I trust that you agree that that doesn't make any sense. So, I'm sorry if that bothers you; and as this isn't the right place for such a discussion, you could bring it up as a separate topic in the appropriate group - I will abstain from further off-topic comments here.

 

[Dale]

As Newton's mechanics uses Galilean relativity, your claim implies that he should have found an experimental violation of his theory of mechanics to justify his absolute space postulate

Yes, exactly.

 

[D H]

As Newton's mechanics uses Galilean relativity, your claim implies that he should have found an experimental violation of his theory of mechanics to justify his absolute space postulate

Yes, exactly.

Newton argued that we mere mortals cannot sense absolute time or absolute space. For the most part all we can sense are relative time, relative distance, relative motion. However, Newton also argued that we can catch a glimpse of this absolute time and space in the concave surface of a rotating bucket of water and in the equatorial bulge of a rotating planet.

 

[mangaroosh]

mangaroosh, here is a physical example that may help. If I say "the door is open" what I am actually talking about is the relationship between the door and its frame. If you have a door without a frame it doesn't make sense to say that it is either open or closed. Similarly, if I say "X is moving" what I am actually talking about is the relationship between X and a reference frame. If I have X without a frame it doesn't make sense to say that it is either moving or at rest.

The difference between door frames and reference frames is that each door has at most one door frame, while X can have an infinite number of reference frames. But in each case the frame is something which essential for defining the state, and statements about the state are meaningless without the frame.

Sticking with the door analogy, which is quite helpful:

Let's say that we have a door and a frame, and the door is at rest relative to the frame in the open position. How can the door change to the closed position without either the frame or the door moving; surely we can deduce that either the door, or the frame, or both, actually move so that the door goes from being open to closed?

If we imagine that, in the open position, the door is at a right angle to the frame; if we then define a reference grid such that the frame runs along the X-axis and the door along the Y-axis. If, subsequently, both the door and the frame run along the X-axis when in the closed position, would we not conclude that it was the door that moved towards the frame; if both ran along the Y-axis would we not conclude that the frame moved towards the door; if they met at different co-ordinates would we not conclude that both of them moved?

 

[Mentz114]

Sticking with the door analogy, which is quite helpful:

Let's say that we have a door and a frame, and the door is at rest relative to the frame in the open position. How can the door change to the closed position without either the frame or the door moving; surely we can deduce that either the door, or the frame, or both, actually move so that the door goes from being open to closed?

Without reference to a third frame of reference, you cannot say which of them moved.

If we imagine that, in the open position, the door is at a right angle to the frame; if we then define a reference grid such that the frame runs along the X-axis and the door along the Y-axis. If, subsequently, both the door and the frame run along the X-axis when in the closed position, would we not conclude that it was the door that moved towards the frame; if both ran along the Y-axis would we not conclude that the frame moved towards the door; if they met at different co-ordinates would we not conclude that both of them moved?

Now you've introduced another frame of reference ( your grid) and you can tell which one moved relative to that frame. Your movements are always expressed realtive to some frame. It's not possible to define movement except as relative movement.

 

[harrylin]

Newton argued that we mere mortals cannot sense absolute time or absolute space. For the most part all we can sense are relative time, relative distance, relative motion. However, Newton also argued that we can catch a glimpse of this absolute time and space in the concave surface of a rotating bucket of water and in the equatorial bulge of a rotating planet.

I'll copy-paste this discussion in a new thread in the classical physics forum. Thus that fork of the discussion can proceed here: https://www.physicsforums.com/showthread.php?p=3871579#post3871579

 

[Dale]

Let's say that we have a door and a frame, and the door is at rest relative to the frame in the open position. How can the door change to the closed position without either the frame or the door moving; surely we can deduce that either the door, or the frame, or both, actually move so that the door goes from being open to closed?

You completely missed the point of the analogy. The point is that the designation of a door being open or closed doesn't even make sense without comparison to the door frame.

Tell me, in your opinion, if there is no door frame, can the door be considered to be open or closed?

 

[Aurin]

I'm sure I'll violate all sorts of precision in my choice of words, so please forgive me in advance.

As I understand it, being at rest isn't a separable entity of kinematics. It's just a "special case" of motion where velocity is equal to 0 and that value is no more or less significant than a non-zero value of velocity. For any given object we can attribute a frame providing it any value for its velocity we choose.

As I also understand it, an object relative to a frame that suddenly changes direction, moving opposite to its original path, had at one instantaneous point attained a velocity equal to zero and thus may have been at rest in that frame for a moment. By extension, other frames never witnessed the object changing direction, but only a change in speed witnessed as speeding up or slowing down.

So if asked "what does it mean to be at rest in SR?" like this thread's original purpose, my response would surely be that an object's velocity is equal to 0 relative to the frame that provides that velocity. Is there a disjoint in that answer?

 

[russ_watters]

I see how the logic works now:

1. Start with the assumption that absolute motion and rest exist.
2. If two objects are at rest relative to each other, they may be in absolute motion or absolute rest.
3. If one starts moving relative to the other, now we can be certain that at least one is in absolute motion since you can't simultaneously have both in absolute rest.
4. Conclude therefore that absolute motion and rest exist.

The line of logic is absolutely fine in the middle, but the conclusion is #3, not #4. #4 is just an echo of the starting assumption and the test does not delve into the issue of if the starting assumption is correct.

It also frustrates me that people cling so dearly to the assumption of absolute motion/rest, particularly when every waking moment of our lives we deal in relative motion and often even multiple simultaneous relative velocities in several frames at once (ie, when driving or playing sports). None of our experiences mandate the existence of an absolute reference frame, so I have trouble even understanding where the default assumption of an absolute reference frame would come from. Perhaps it comes from the thought of a fish-tank universe with God looking through the glass. Perhaps he's there, but whether he is or not, there is no basis for assuming he is nor any value in making the assumption. If one acknowledges that he and his frame are completely undetectable, then speculation about his existence is of no value in a scientific setting. It is purely a religious belief.

But...at the risk of confusing things, I will point out that there are objective, absolute realities that have to be acknowledged here. Consider the case of a rocket launching off the earth. The rocket burns fuel, so it must be said that it is moving (accelerating) away from the Earth and not the other way around. But the absoluteness of the fuel burning doesn't require an absoluteness of motion/rest.

 

[harrylin]

[..]None of our experiences mandate the existence of an absolute reference frame, so I have trouble even understanding where the default assumption of an absolute reference frame would come from. Perhaps it comes from the thought of a fish-tank universe with God looking through the glass. Perhaps he's there, but whether he is or not, there is no basis for assuming he is nor any value in making the assumption. If one acknowledges that he and his frame are completely undetectable, then speculation about his existence is of no value in a scientific setting. It is purely a religious belief. [..]

That comment seems to be a direct attack on Newton. So, if you like, I'll add your comment to the new thread that I just started on that topic.

 

[yoron]

My take on it :)

Can you define a 'motion'?
Do you need another frame of reference to do it?

If you are on 'something' being in a uniform motion, lifting/accelerating from it, does it matter what speed it has? For what acceleration/lift you need from that object?

Think about that one for a while before answering.

If uniform motion, as measured relative something else, doesn't crave any more 'energy/momentum' relative, or if you like, no matter what 'speed/velocity' you define it to have, or make you expend more energy accelerating from it, what is a 'uniform motion'?

Einstein differed between two things, 'uniform motion' and accelerations. He called one 'relative motion', the other a 'gravity'.
=

To simplify, define a speed/velocity of something (relative some 'inertial' definition). Accelerate from it. find the energy expended. Then make the object you accelerate/lift from beget double the speed/velocity, relative that same inertial frame of reference, to then become in a 'uniform motion' again. Then lift/accelerate from it again..

Will the energy expended by you accelerating/lifting differ between those two scenarios? If it won't, what do you think a uniform motion means?

 

[Mentz114]

This statement

It is not posible to distinguish between a state of rest and uniform motion

has been wrongly interpreted by the OP as meaning that a body is in one of these states or the other. But that is not what it means. It means they are the same state.

It may be said that a body is either in a state of uniform motion or accelerated motion, and that covers it.

What the statement above is saying is that we should abandon the idea of 'rest'.

The OP keeps insisting that there is actual motion, and I think he is referring to accelerated motion, which is certainly 'actual' in the sense that it can be detected.

 

[mangaroosh]

Without reference to a third frame of reference, you cannot say which of them moved.

But you could presumably conclude that one of them did, in fact, move, no?

Now you've introduced another frame of reference ( your grid) and you can tell which one moved relative to that frame. Your movements are always expressed realtive to some frame. It's not possible to define movement except as relative movement.

Is it not more accurate to say that you cannot measure movement except relative to some frame?

I would have thought that "absolute motion" would be a simple "yes" or "no" answer to the question, "did X move"? Measurement is, by necessity, relative, so I think the idea of measuring absolute motion would be a contradiction in terms, no?

If an absolute reference frame could be detected, which of course it can't, it might be possible to define something as "absolute velocity", which would simply be velocity relative to the "absolute frame".

But getting back to the door and the frame; if we imagine an infinite number of reference frames in the universe, wouldn't all observers agree which one actually moves i.e. the frame or the door; and could they not deduce that one of them, has to actually move in order for the door to go from being open, to being closed?

 

[Dale]

But you could presumably conclude that one of them did, in fact, move, no?

Good example of the logical fallacy "begging the question".

http://www.fallacyfiles.org/begquest.html

Your question presumes that the word "move" without any qualifiers has meaning. This is the very point under dispute, so you cannot assume it.

To make your question not fallacious you would need to qualify the word "move" in the question by specifying what it is moving relative to since both sides of the argument agree that relative motion is well defined and meaningful.

 

[mangaroosh]

You completely missed the point of the analogy. The point is that the designation of a door being open or closed doesn't even make sense without comparison to the door frame.

Tell me, in your opinion, if there is no door frame, can the door be considered to be open or closed?

I understood the analogy but I don't think it fully addressed the question. I agree with the point being made, and would say that a door cannot be considered open or closed in the absence of a frame.

But we're taking the example where there is a door and a frame; the door starts off in the open position and then subsequently changes to the closed position.

In your opinion, how can the door go from being open to closed without either the frame moving or the door moving; surely one of them, at least, has to move in order for the door to close?

We may not be able to determine which one moves, and in the doors frame of reference it might be the frame that is labelled as moving (although it cannot be determined if that is the case), and in the frames reference it might be the door that is labelled as moving (although that too cannot be determined); surely though we can agree that one of them, at least, has to move for the door to close?

 

[mangaroosh]

I see how the logic works now:

1. Start with the assumption that absolute motion and rest exist.
2. If two objects are at rest relative to each other, they may be in absolute motion or absolute rest.
3. If one starts moving relative to the other, now we can be certain that at least one is in absolute motion since you can't simultaneously have both in absolute rest.
4. Conclude therefore that absolute motion and rest exist.

The line of logic is absolutely fine in the middle, but the conclusion is #3, not #4. #4 is just an echo of the starting assumption and the test does not delve into the issue of if the starting assumption is correct.

#1 above can be dropped.

2. Two objects are at rest relative to each other e.g. a door and a door frame

3. The door is in the open position.

4. The door changes to the closed position.

5. Either the door or the frame, or both, moved.

It also frustrates me that people cling so dearly to the assumption of absolute motion/rest, particularly when every waking moment of our lives we deal in relative motion and often even multiple simultaneous relative velocities in several frames at once (ie, when driving or playing sports). None of our experiences mandate the existence of an absolute reference frame, so I have trouble even understanding where the default assumption of an absolute reference frame would come from. Perhaps it comes from the thought of a fish-tank universe with God looking through the glass. Perhaps he's there, but whether he is or not, there is no basis for assuming he is nor any value in making the assumption. If one acknowledges that he and his frame are completely undetectable, then speculation about his existence is of no value in a scientific setting. It is purely a religious belief.

It does appear as though people seem to be hung up on the idea of an absolute reference frame; I would have thought that the question of absolute motion was a simple "yes" or "no" question that didn't require an absolute reference frame e.g. "is X moving"?

You mention that we deal with relative motion every waking moment of our lives, but for most people - and this is where part of my struggle comes from - it makes perfect sense to ask "am I moving", without necessarily asking "relative to what?".

Take the example of walking down the street; most people would be able to engage in a conversation to answer the question "is it me that is moving, or is the Earth moving beneath my feet?". We would all measure the movement relative to the street, that isn't a problem, but the question of "which one is actually moving?" is a question that most people would, at least, agree makes sense to ask. They wouldn't say, "what do you mean 'actually moving', that doesn't make sense!", they would usually answer uneqivocaly, "don't be stupid! I'm actually moving, of course". If it were explained to them that it cannot actually be determined that they are moving, then they would presumably agree that either they must be moving, or the ground beneath them, and all the buildings, must be moving.

But...at the risk of confusing things, I will point out that there are objective, absolute realities that have to be acknowledged here. Consider the case of a rocket launching off the earth. The rocket burns fuel, so it must be said that it is moving (accelerating) away from the Earth and not the other way around. But the absoluteness of the fuel burning doesn't require an absoluteness of motion/rest.

But surely the fact that there is relative motion demonstrates that something must actually be moving, in some absolute sense - not necessarily relative to an absolute reference frame. The motion will always be measured relative to something, but either the Earth or the rocket has to be moving.Just to re-iterate the real life example of walking down the street, because I think it helps to anchor the question in everyday terms, and might help clarify where my issue lies.

If you are walking down the street, or even just walk across the room you are in; as you notice your motion relative to the objects in the room or on the street, ask yourself, is it me that is moving, or is the street, or the floor, moving beneath my feet like a treadmill?

 

[Mentz114]

But you could presumably conclude that one of them did, in fact, move, no?
Is it not more accurate to say that you cannot measure movement except relative to some frame?

I would have thought that "absolute motion" would be a simple "yes" or "no" answer to the question, "did X move"? Measurement is, by necessity, relative, so I think the idea of measuring absolute motion would be a contradiction in terms, no?

If an absolute reference frame could be detected, which of course it can't, it might be possible to define something as "absolute velocity", which would simply be velocity relative to the "absolute frame".

But getting back to the door and the frame; if we imagine an infinite number of reference frames in the universe, wouldn't all observers agree which one actually moves i.e. the frame or the door; and could they not deduce that one of them, has to actually move in order for the door to go from being open, to being closed?

So you've deduced that in order for something to change its state of motion a force must be applied.

How is this relevant to distinguishing 'rest' from unaccelerated motion ? Even if you knew the entire acceleration history of two comoving bodies in uniform motion, it does not alter the fact that now it does not matter to which we ascribe motion. They are now in a reciprocal state connected by a Lorentz transformation.

I don't think you like relativity and you cannot understand what it is and what it is used for. You are horribly misinterpreting the theory. Have you seen my post#106 ?
Do you agree with Newtons laws of motion ?

Finally, by your definition of 'actually moving', anything that has ever experienced acceleration is 'actually moving'. That probably includes all the matter in the universe so it is a useless concept, without any deductive or physical significance, and I wish you'd stop going on about it.

 

[Dale]

I agree with the point being made, and would say that a door cannot be considered open or closed in the absence of a frame.

And by analogy, an object cannot be considered moving or at rest in the absence of a reference frame.

But we're taking the example where there is a door and a frame; the door starts off in the open position and then subsequently changes to the closed position.

And by analogy there is motion and a reference frame.

In your opinion, how can the door go from being open to closed without either the frame moving or the door moving; surely one of them, at least, has to move in order for the door to close?

Has to move relative to what? As we have discussed neither the door nor the door frame can be considered moving or at rest in the absence of a reference frame. Until you specify that, your question is incomplete.

If you specify some inertial frame then at least one of them moved relative to the inertial frame. You could instead simply specify that they moved relative to each other. Of course, if you specify some non-inertial frame then you may find that neither moved relative to that frame. You have to specify what the motion is relative to otherwise the question is meaningless. Not only is it meaningless, but it is fallacious.

 

[russ_watters]

In your opinion, how can the door go from being open to closed without either the frame moving or the door moving; surely one of them, at least, has to move in order for the door to close?

As always, your formulation - by saying "move" without qualifiers - assumes the existence of absolute motion. It isn't necessary. The door and frame have to move relative to each other in order to open or close, but there is no need or value for assuming one or the other is the "one" to move in an absolute sense. Or, both could be moving with respect to a 3rd frame and the door may not necessarily close. You've assumed the existence of this third frame, that it is the universal frame and that one is stationary relative to it and the other is moving. None of that is necessary.

#1 above can be dropped.

2. Two objects are at rest relative to each other e.g. a door and a door frame

3. The door is in the open position.

4. The door changes to the closed position.

5. Either the door or the frame, or both, moved.

Again, with #5, stating "moved" without qualifiers. Indeed in order to close, one must move relative to the other. This allows us to conclude nothing about an absolute frame other than that it isn't necessary for this thought experiment. Pile up enough thought experiments where it isn't necessary and you have pretty good circumstantial evidence that it doesn't exist and no evidence whatsoever that it does.

It does appear as though people seem to be hung up on the idea of an absolute reference frame; I would have thought that the question of absolute motion was a simple "yes" or "no" question that didn't require an absolute reference frame e.g. "is X moving"?

Since motion requires comparison of reference frames, absolute motion must therefore require an absolute reference frame be one of those frames. That's by definition. That's what "absolute motion" means!

You mention that we deal with relative motion every waking moment of our lives, but for most people - and this is where part of my struggle comes from - it makes perfect sense to ask "am I moving", without necessarily asking "relative to what?".

As I said earlier in the thread, the reason it is rarely ever stated in everyday life is that people just intuitively understand it. Our brains are programmed to "get" it and use it. That's the reason I am so incredulous that you don't. In my thought experiments with the police officer measuring the speed of a car, the two different methods of measuring the speed of a car would never, ever, ever confuse anyone: There's three "observers" and two different speed measurments happening in both cases, but no one would ever get confused about which one is being referred to.

Take the example of walking down the street; most people would be able to engage in a conversation to answer the question "is it me that is moving, or is the Earth moving beneath my feet?". We would all measure the movement relative to the street, that isn't a problem, but the question of "which one is actually moving?" is a question that most people would, at least, agree makes sense to ask. They wouldn't say, "what do you mean 'actually moving', that doesn't make sense!", they would usually answer uneqivocaly, "don't be stupid! I'm actually moving, of course". If it were explained to them that it cannot actually be determined that they are moving, then they would presumably agree that either they must be moving, or the ground beneath them, and all the buildings, must be moving.

Doubt it. Simply by pointing out that the Earth is rotating - which everyone knows - would anyone be able to be convinced that the relative motion of a person and the Earth wrt each other truly is relative.

But surely the fact that there is relative motion demonstrates that something must actually be moving, in some absolute sense ...

I can't fathom a way you could have worded that any more exactly self-contradictory other than to cut out intermediate words. Do that and you just said 'relative = absolute'. Wow.

...in some absolute sense - not necessarily relative to an absolute reference frame.

Double wow. Now you're saying 'absolute is not necessarily absolute.' Honestly, I'm having a lot of trouble taking you seriously now.

If you are walking down the street, or even just walk across the room you are in; as you notice your motion relative to the objects in the room or on the street, ask yourself, is it me that is moving, or is the street, or the floor, moving beneath my feet like a treadmill?

And if you are truly being honest here and not trolling us, you would conclude: it doesn't matter.

 

[yoron]

Motion is always relative something, an acceleration can be seen as displacements of a infinite assemble of 'uniform motions', but it is also the single definition in where you can 'prove' a motion in that you locally will find something new coming into play, a 'gravity' :)

What you seem to mean is that as there is something called a motion, there must also be a absolute reference frame from where it exist, a 'gold standard' of it. The easiest way to define such a notion would be to turn it around, don't you agree?

If there is no 'motion', then why can we displace ourselves relative something else?

That's a really interesting question.

 

[harrylin]

[..]
It also frustrates me that people cling so dearly to the assumption of absolute motion/rest, particularly when every waking moment of our lives we deal in relative motion and often even multiple simultaneous relative velocities in several frames at once (ie, when driving or playing sports). None of our experiences mandate the existence of an absolute reference frame, so I have trouble even understanding where the default assumption of an absolute reference frame would come from. Perhaps it comes from the thought of a fish-tank universe with God looking through the glass. Perhaps he's there, but whether he is or not, there is no basis for assuming he is nor any value in making the assumption. If one acknowledges that he and his frame are completely undetectable, then speculation about his existence is of no value in a scientific setting. It is purely a religious belief.

Concerning classical mechanics I now answered your remark in the new thread on Newton's relativity. You could similarly start a topic about Bell's assumption of such a frame which he based on his theorem in the QM forum (note that he confusingly called it a "preferred frame" without suggesting disagreement with SR). As far as relativity is concerned, Langevin (I doubt that he was religious) gave his SR-based arguments (in 1911 it was still called "relativity") for the existence of a Lorentz ether here, starting from p.47:
http://en.wikisource.org/wiki/The_Evolution_of_Space_and_Time

[..] I will point out that there are objective, absolute realities that have to be acknowledged here. Consider the case of a rocket launching off the earth. The rocket burns fuel, so it must be said that it is moving (accelerating) away from the Earth and not the other way around. [..]

I also mentioned that fact of observation in post #88. Perhaps Mangaroosh did not understand what I wrote, but will understand what you wrote.

 

[bahamagreen]

The first eight derivatives of position are:

velocity
acceleration
jerk (jolt, surge, lurch)
jounce (snap)
crackle
pop
lock
drop

With acceleration we have the first "absolute" in terms of qualitative existence, but the quantitative value will be measured differently by observers in various inertial FOR.

What about the higher derivatives? Will there never be one where all the absolute attributes become quantitatively universal for all inertial FOR?

If acceleration is the "floor" for finding even a qualitative absolute presence, is there a way to demonstrate that this is the result and expectation from dimensional geometry?

 

[Dale]

With acceleration we have the first "absolute" in terms of qualitative existence, but the quantitative value will be measured differently by observers in various inertial FOR.

Well, acceleration is a vector quantity, so you will always have disagreement about the components of vectors. However, you can make it into an invariant by making a scalar (rank 0 tensor) from it. The invariant quantity is called the proper acceleration. It is the magnitude of the 4-acceleration in any frame and is equal to the magnitude of the 3-acceleration in the momentarily co-moving inertial frame.

 

[mangaroosh]

I've recently been accused of trolling, with specific reference to this thread, so I just wanted to clarify where I'm coming from, and hopefully dispell that perception, because I think it can have a negative overall effect on the discussion.

Where I'm coming from
I'm really just hoping to give an honest representation of my understanding, and discuss any potential issues with it, because this issue represents one of the stumbling blocks I have to learning relativity. It is essentially something I would have taken to be common sense, and something I believe the majority of lay people would also take to be common sense. I know this doesn't mean that it is correct, but hopefully it might clarify why there is resistance to the idea that it is incorrect. Essentially, because there is a deeply ingrained belief which was taken to be self-evident, which is now being challenged as incorrect.

Representative
I would also be fairly confident that my understanding is highly representative of the vast majority of lay people out there; if you ask them about their experience of walking down the street, and ask them "are they actually moving, or is it the ground and buildings that are actually moving, while they 'walk on the spot' (as on a treadmill)", I have no doubt whatsoever that the vast majority of people will not respond by saying "actually moving" doesn't make sense; instead, they will unequivocally reply, that they are the ones who are "actually moving".

For the vast majority of people, this would be taken as common sense, regardless of its accuracy; but this represents just one of the stumbling blocks to learning relativity for lay people. It is a genuine block to learning relativity, because it requires discarding a deeply ingrained belief. Personally I find that a reasoned discussion, based on logic is the best way to circumnavigate, or unlearn erroneous beliefs. A certain level of self-awareness is also required to identify the level of attachment that one holds to their beliefs also.

Even Salvestrom's comment, in this thread, indicates that I am not alone in my understanding of this

if it depends on our point of view shouldn't we perhaps be move cautious in proclaiming "actually moving" has no meaning? I'm pretty sure my fingers are moving as I'm typing

I think we all know what it is like discussing things on an internet forum; it is easy to get a little wound up when you think someone is trolling, or just being intentionally dense; as part of the human condition we tend to get a little wound up when our accepted beliefs are perceived to be challenged. I know that I have let the frustration get the better of me at times, and it will undoubtedly do so again, but hopefully we can all look beyond that to the logic in the posts and discuss the issue primarily on that basis.


(Why can't we all just get along? )

 

[mangaroosh]

Good example of the logical fallacy "begging the question".

http://www.fallacyfiles.org/begquest.html

Your question presumes that the word "move" without any qualifiers has meaning. This is the very point under dispute, so you cannot assume it.

To make your question not fallacious you would need to qualify the word "move" in the question by specifying what it is moving relative to since both sides of the argument agree that relative motion is well defined and meaningful.

Hopefully I can type this in such a way as it doesn't come across confrontational, because that isn't my intention. I think this might repersent a good starting point though, because it addresses some fundamental issues.


Essentially the question is about whether or not "actual movement", or "move without any qualifiers" makes sense; it could probably be classified as asking whether or not "absolute motion" makes sense or exists.

You mention that it must be speficied, relative to what "movement" occurs, in order for the question not to be fallacious, but I think that is assuming the conclusion that "absolute motion" doesn't make sense and that only "relative motion" does.

My understanding is that "absolute motion" would be a simple "yes" or "no" answer to the question "is X moving"; if it must be specified relative to what it is moving then that would be "relative motion", not absolute. Motion will always be measured relative to something, but the question of which object is moving doesn't require that specification.


Real world example
Take a walk down the street, or across the room; notice the ground moving beneath your feet, and the scenery moving by; then stop walking and notice the difference; start walking again and notice the chages.

To me, and I dare say, the majority of people out there, we would conclude that "I am the one who is doing the moving".

Now, my understanding of the PoR is that we cannot actually determine who is doing the moving i.e. we cannot determine the absolute nature of the motion; we can even define reference frames which label either one or the other as movin; again, I just see this as an extension of the same principle i.e. we cannot tell who is doing the moving.

But I think we have to conclude that one, or the other, is actually doing the moving.


Clarification
You'll have to forgive me for this, because the idea is very intuitive to me, and almost self-evidently true, so I'm trying to see if you can relate to what I am getting at.

I presume you've been on a treadmill before, and know the experience of jogging on the spot while the band moves beneath your feet; if you contrast this with walking down the street where you wouldn't really say that the ground, and the scenery are moving as though on a conveyor belt; you would presumably say that you are the one causing the relative motion between you, the ground and the surrounding environment.

Again, we could define reference frames which label either one or the other as moving, but surely we cand deduce that one of them has to be "causing the relative motion" or "doing the moving" - apologies, I'm searching for a term that might adequately describe what I am trying to say.

 

[Austin0]

Well, acceleration is a vector quantity, so you will always have disagreement about the components of vectors. However, you can make it into an invariant by making a scalar (rank 0 tensor) from it. The invariant quantity is called the proper acceleration. It is the magnitude of the 4-acceleration in any frame and is equal to the magnitude of the 3-acceleration in the momentarily co-moving inertial frame.

Hi what is 3 acceleration regarding an inertial frame? On the face of it ,it seems to be a contradiction of terms.
Are you saying that it is possible for all inertial frames to calculate a shared quantitative value for an observed accelerating system?
Thanks