At rest in Einsteinian relativity

[harrylin]

I don't see why this should be seen as an issue, because I think we can deduce that, at least, one observer has to be actually moving (or in "absolute motion") from a scenario where observers are moving relative to each other, even inertially. It doesn't necessarily require a change in relative motion, I just think it is easier to highlight.

OK, probably you already clarified that elsewhere; if so, sorry and thanks for doing it again.

So, with "actually moving" you mean something similar as "true motion" in Newton's model?

To be honest, I'm not sure which one is the relevant theory; I'm just offering the examples which illustrate my understanding. I thought it was a more straight forward question than that though; is the Earth rotating or not?

As I stated, the answer is different in SR than in 1916 GR; but I think that Einstein was forced to change his mind about it by 1920. So, your term "in Einsteinian relativity" is too poorly defined for a straightforward answer.

[..] Just on the link you provided; I'm familiar with the Twin Paradox; [..] It isn't a paradox according to GR because of the equivalence principle i.e. either gravitation or acceleration resolves the paradox.

In contrast, according to the link that I provided, Einstein's solution of induced real gravitational fields doesn't seem to make much sense to most people.

It might be helpful to state it in terms of the test of the principle of relativity, as mentioned earlier.

Yes, especially which relativity principle do you refer to? Einstein's general relativity principle which has nearly been forgotten, or the special one as he formulated it?

The test says that the absolute nature of motion cannot be determined by a co-moving experiment; I think we can deduce that the nature of the motion has to be absolute.

Where absolute is used in its usual sense of "without reference to anything", so "absolute motion" would be motion without reference to anything.

Certainly not! That expression can be used to mean different things, but not "motion without reference to anything" - one popular modern meaning is instead "motion with reference to all inertial reference systems".

This can perhaps be clarified with contextual examples:
- can you move i.e. are you capable of movement?
- have you ever been in a moving car?
- have you ever stood still on an escalator and still moved? [..]

All those expressions relate to relative motions, such as a car relative to the road and the elevator relative to the building. So, I'm afraid that you are indeed bringing this discussion back to the ancient times of Greek philosophers.

 

[mangaroosh]

'The point' has nothing to do with the PoR. Special relativity does not require the history of the frames under consideration. SR is constituted so it does not matter which inertial frame 'actually moved'.

The Lorentz transformation does not have any terms for the 'who actually moved' thing.

I do wish you could see that what you're insisting over and over has nothing to do with relativity.

It does have to do with learning relativity though; I've been trying to outline my understanding, which I believe I have done in a fairly logical manner. There is some contention over the notion of "actual" or "absolute" motion, but it is something that, to me, seems almost self-evident; two other posters in the thread also seemed to suggest something similar. I do genuinely believe that a large proportion of people would be of the same opinion also.

It seems that my understanding does not correspond to relativity, so I'm trying to see how the issue is addressed through relativity; I don't fully undertsand how the theory can be formulated such that it doesn't matter, because I think there might be certain deductive consequences that probably do matter.

 

[harrylin]

[..]
3) The relative velocity between A and B subsequently changes to a value greater than 0.
4) Therefore either A or B moved.

For the third (or fourth) time, you must mean: Therefore either A or B accelerated. Do you disagree? This is what has been stressed in most of my last posts as well as those of several others. As long as you insist on confounding inertial motion with acceleration, no sensible discussion is possible. Motion is not the same as change of motion.

 

[Mentz114]

It does have to do with learning relativity though; I've been trying to outline my understanding, which I believe I have done in a fairly logical manner.

I can't believe you can think that. All you have done is repeat that you think there is some notion of 'actually moved' without being able to define it.

There is some contention over the notion of "actual" or "absolute" motion, but it is something that, to me, seems almost self-evident;

Where is the contention ? You are misguided if you think absolute motion has supporters on this forum.

It seems that my understanding does not correspond to relativity, so I'm trying to see how the issue is addressed through relativity;

It has no relevance in relativity whatever so you're wasting your time.

I don't fully undertsand how the theory can be formulated such that it doesn't matter,

Learn special relativity and you'll see.

because I think there might be certain deductive consequences that probably do matter.

There aren't any, as even an elementary understanding of SR would tell you.

I think you have to stop waving your hands and get down to defining what you're trying to say in a proper scientific manner.

 

[mangaroosh]

You keep on repeating the same thing. If we can deduce that one has "actually moved", then "actually moved" must have a clear definition. You haven't been able to give one.

I've never really had to define it before, it was something that I genuinely believed, and believe, is self-evidently true. I was hoping that by giving contextual examples it would become clear what was meant; again, examples I genuinely believed were fairly easy to comprehend.

The easiest way to think about it might be to think about it personally; imagine that you and a friend are standing about 2 feet apart, facing each other. Make a bet with your friend that the first person who moves loses the bet, and owes the other $50. Let's say your friend takes a step to the side, would you be within your rights to claim the $50?

You keep repeating this, but offer no evidence. I sincerely do not think that "most people" would understand what you are getting at, but that is in any case beside the point. Here you are having a discussion with some particular people, most of whom have spent considerable time reflecting on the concepts of relativity and motion. If you can't make your ideas on motion clear to us, you need to have a think about why.

It might be worth aksing a few friends who don't have a background in science; if you are walking with them, ask them if both of you are actually moving; tell them that it isn't a trick question, it's a genuine question. Just see what answer they give.

I have thought about why people are having so much trouble understanding what I believe are very simple ideas; there are a number of reasons, some of which attributable to me, some of which attributable to those that can't understand, and some of which are attributable to the nature of the subject itself.

No, the movement is always thought of with respect to the assumed frame. The idea of "actual movement" without a reference frame simply makes no sense. You could talk about "actual movement" if it was agreed that there was an absolute rest frame, in which case the term would mean "movement relative to the absolute rest frame", but without any reference frame the term has no meaning that I can discern, nor have you been able to define any such meaning.

The idea isn't necessarily "actual movement" without a reference frame; it is inevitbale that movement will take place in a reference frame, it's an unavoidable fact of the universe. The idea is that "actual movement" can be deduced from the motion within that reference frame.

The idea that movement is always thought of with respect to an assumed frame is not, I believe, entirely true; people, I would say, primarily think about the body doing the moving. They believe that they are the agent of the motion, in most cases.

I'm not sure if it clarifies the issue to speak about "the act of moving" i.e. the body which "does the action", as opposed to the passive object.

When walking down the street, there would be relative motion between you and the street, but you would be the active agent in the scenario, while the street would be the passive agent.

It's just as nonsensical as saying that the term "distance" has a meaning when applied to one object: you can measure the distance between two objects, or the distance of one object from a specified reference point, but the "actual distance" of a single object is not a meaningful concept.

While you could measure the distance between two points on a single object, the it's not the same issue at all.

Indeed, distance is a factor in the example; two objects a given distance from each other, then the distance begins to increase; at least one of them has to be an active agent in causing that distance to increase.

You're still repeating the same argument. You still don't give your definition of what "actually" means in this context.

as the truth or facts of a situation:
we must pay attention to what young people are actually doing

http://oxforddictionaries.com/definition/actually?q=actually

Each observer see the other's clock as running slower than their own. The situation is symmetric and does not permit us to define in an absolute sense that one of the clocks as "moving" and the other as "at rest": for each observer, their own clock is at rest and the other clock is moving.

I understand that point about ER, but just address the question you asked

Let's say it's "really" me that is moving. How is this situation different from the one where the car is "actually moving" and I am stationary? How does this difference manifest itself?

It might be more intuitive to say that it is the car that is actually moving.

If we assume that you and the clock are both on the earth, without assuming the nature of motion of the earth, either way; if you have a light clock and the observer in the car has a light clock, then the path length of the photon will have a pre-established path length, depending on the motion of the earth, wouldn't it?

That is, if you and the car were at rest on the earth, then the photon in the light clock would have a path length dependent on the motion of the earth, wouldn't it?


If we assume that the car is actually moving, such that you and the car are moving inertially, relative to each other, then the path length of the photon will be different to the path length of the photon in your clock. Meaning that it will either tick faster or slower, depending on the motion of the earth, no?

 

[mangaroosh]

I can see we have a long way to go. The qualifier "infinitely" is important. If I have a finite plane, say in the shape of a square, it's very easy to define the centre of it. How would you go about defining the centre of an infinite plane?

I was thinking the qualifier "infinitely" was important, but if the plane is in the shape of a square then presumably you could have infinitely long lines disecting the angles of the square, which would naturally meet in the middle.

EDIT: of course, it might make more sense to ask how an infinite plane can have the shape of a square.

 

[Mentz114]

The idea that movement is always thought of with respect to an assumed frame is not, I believe, entirely true;

But it is the basis of special relativity. If you don't accept special relativity you have no business in this forum.

people, I would say, primarily think about the body doing the moving. They believe that they are the agent of the motion, in most cases.

Again, this is not relevant to special relativity.

I'm not sure if it clarifies the issue to speak about "the act of moving" i.e. the body which "does the action", as opposed to the passive object.

When walking down the street, there would be relative motion between you and the street, but you would be the active agent in the scenario, while the street would be the passive agent.

Not relevant to SR. These ideas belong elsewhere.

 

[mangaroosh]

OK, probably you already clarified that elsewhere; if so, sorry and thanks for doing it again.

No hassle at all; I don't think I mentioned it to yourself, I think it came up with Dale, but I wouldn't have stressed the point because I didn't think it wasn't aware that it might be an issue, and thinking about it, I don't think it should be.

So, with "actually moving" you mean something similar as "true motion" in Newton's model?

Unfortunately I can't say, I'm not overly familiar with Newton's model; my familiarity extends only as far as the idea that there is an absolute referecne frame against which absolute, or perhaps, true motion can be measured.

That would appear to be a contradiction in terms, to me though, to suggest that absolute motion is relative.

I'm not sure if it helps to clarify the difference between an active and a passive agent, in relative motion; for example, if you are walking down the street, there would be relative motion between you and the road, but you would be the active agent i.e. "doing the moving".

As I stated, the answer is different in SR than in 1916 GR; but I think that Einstein was forced to change his mind about it by 1920. So, your term "in Einsteinian relativity" is too poorly defined for a straightforward answer.

Apoloigies.

Just in the context of the question "Is the Earth rotating or not?", do the two theories provide different answers; what is the contemporary answer; and what is your own thinking on it?

In contrast, according to the link that I provided, Einstein's solution of induced real gravitational fields doesn't seem to make much sense to most people.

I don't doubt that.

Yes, especially which relativity principle do you refer to? Einstein's general relativity principle which has nearly been forgotten, or the special one as he formulated it?

I was referring more to the test of relativity, as it is often presented, and the often stated consequences.

Certainly not! That expression can be used to mean different things, but not "motion without reference to anything" - one popular modern meaning is instead "motion with reference to all inertial reference systems".

I was actually thinking about that, and was thinking that if something does actually move then presumably all reference frames will label it as moving, unless something else is moving inertially to it; this would bring us back to the question of which one is moving, but again, I think we could deduce that it must be one or the other.

The adjective, "absolute", however, which qualifies the noun, does mean without reference to anything; it would presumably be a kind of fundamental motion; again, a "yes or no", or "either, or" question.

I was wondering about the idea of inertial reference systems actually, and was wondering how you could determine if a system is inertial; presumably there will always be an accelerating reference system; and presumably it would always be possible to define a reference frame in which it isn't accelerating, where the accerlationg is attributed to every other object in the universe.

All those expressions relate to relative motions, such as a car relative to the road and the elevator relative to the building. So, I'm afraid that you are indeed bringing this discussion back to the ancient times of Greek philosophers.

None of them make reference to relative motion; they simply make reference to motion i.e. it is the car that is moving.

 

[mangaroosh]

For the third (or fourth) time, you must mean: Therefore either A or B accelerated. Do you disagree? This is what has been stressed in most of my last posts as well as those of several others. As long as you insist on confounding inertial motion with acceleration, no sensible discussion is possible. Motion is not the same as change of motion.

I would agree that either A or B accelerated.

But I would still think we can deduce that either A or B has to actually, or absolutely, be moving, even from inertial, relative motion.

 

[HallsofIvy]

Just in the context of the question "Is the Earth rotating or not?", do the two theories provide different answers; what is the contemporary answer; and what is your own thinking on it?

Rotation involves acceleration, it is not a constant velocity.

I don't understand why, after 189 posts, you are still simply asserting "
But I would still think we can deduce that either A or B has to actually, or absolutely, be moving, even from inertial, relative motion." Even though you have been repeatedly told that is NOT true and repeatedly told why it is not true.

 

[mangaroosh]

I can't believe you can think that. All you have done is repeat that you think there is some notion of 'actually moved' without being able to define it.

I have repeatedly tried to give contextual examples that a lot of people would have no trouble understanding. It might be possible to drop the contentious term "actual movement" and try and deduce the answer in another way.

Make a bet with your friend; stand opposite each other, facing one another, a short distance apart; make the provision of the bet that the first person to move owes the other $50. Do you think that it is possible for anyone to win the bet?

Where is the contention ? You are misguided if you think absolute motion has supporters on this forum.

The contention is manifest in this thread. Also, salvestrom's post earlier in the thread (#47 I think it was) and bahamagreen's comments seem to suggest that they at least understand the contention being made.

It has no relevance in relativity whatever so you're wasting your time.

I would presume that something which potentially has deductive consequences, has, at least, some relevance to relativity.

Learn special relativity and you'll see.

Contrary to popular belief, I am learning about relativity; there is more than one way to skin a cat.

I understand that the theory is formulated with the idea that it doesn't matter, but I struggle to see how it can be formulated such that something which might have deductive consequences doesn't matter.

There aren't any, as even an elementary understanding of SR would tell you.

I think you have to stop waving your hands and get down to defining what you're trying to say in a proper scientific manner.

I'm not the one waving hands here. The examples I've given are very straight forward, and would undoubtedly make senes to an awful lot of people. I would genuinely suggest asking someone from a non-scientific background, and perhaps even people from a scientific background, whether or not actually moving makes sense.

Try going for a walk, and ask them if they are actually moving; tell them it isn't a trick question, tell them it is a straight forward question and you're looking for a straightforward answer; just to see what they say.

Genuinely, I'm not trying to be elusive, I've never actually had to try and explain this before, so that may be why I am struggling to clarify it sufficiently, but I think it is a fairly intuitive - not that that makes it right - idea.

Again, the clarification of an active and passive agent might help some bit; as you are walking down the road there will be relative motion between you and the road; you, however, would be the active agent, while the road, the buildings etc. would be passive agents. If you pass someone walking the other way, they too would be active agents in the relative motion between you and them.

Hopefully that helps to clarify it some bit.

 

[mangaroosh]

But it is the basis of special relativity. If you don't accept special relativity you have no business in this forum.

Woudl you say that I understand relativity?

I'm guessing the answer is no.

In that case, I'm not sure how I can possibly accept something I don't understand; if I were to accept it, then the thing I would be accepting wouldn't be relativity, it would be a misunderstanding of it.

I'm here to learn about relativity, to explore it logically and rationally; once I understand it and if I find it stands up to reason then I can accept it; presumably you don't accept things you find don't stand up to reason.

Again, this is not relevant to special relativity.

But it is relevant to learning relativity, becaues it represents an existing belief that has to be unlearned.

Not relevant to SR. These ideas belong elsewhere.

Are issues with potential, deductive properties not relevant to SR?

 

[Mentz114]

I have repeatedly tried to give contextual examples that a lot of people would have no trouble understanding. It might be possible to drop the contentious term "actual movement" and try and deduce the answer in another way.

And repeatedly failed to demonstrate why this has any relevance to a theory based on relative velocity.

Make a bet with your friend; stand opposite each other, facing one another, a short distance apart; make the provision of the bet that the first person to move owes the other $50. Do you think that it is possible for anyone to win the bet?

That is just silly. You are moving the goalposts. We are talking about scientific definitions involving velocities.

The examples I've given are very straight forward, and would undoubtedly make senes to an awful lot of people. I would genuinely suggest asking someone from a non-scientific background, and perhaps even people from a scientific background, whether or not actually moving makes sense.
Try going for a walk, and ask them if they are actually moving; tell them it isn't a trick question, tell them it is a straight forward question and you're looking for a straightforward answer; just to see what they say.

Physics is not a democracy.

Genuinely, I'm not trying to be elusive, I've never actually had to try and explain this before, so that may be why I am struggling to clarify it sufficiently, but I think it is a fairly intuitive - not that that makes it right - idea.

You won't be able to explain it better. There is no scientific way of defining a useful concept that requires absolute motion.

Again, the clarification of an active and passive agent might help some bit; as you are walking down the road there will be relative motion between you and the road; you, however, would be the active agent, while the road, the buildings etc. would be passive agents. If you pass someone walking the other way, they too would be active agents in the relative motion between you and them.

The 'active/passive' notion can only be scientifically expressed as 'non-inertial/inertial' because there are no other states of motion.

 

[mangaroosh]

Rotation involves acceleration, it is not a constant velocity.

Is it not possible to rotate at a constant velocity, no?

I don't understand why, after 189 posts, you are still simply asserting "
But I would still think we can deduce that either A or B has to actually, or absolutely, be moving, even from inertial, relative motion." Even though you have been repeatedly told that is NOT true and repeatedly told why it is not true.

And I've sought to address the whys, and the discussion has grown organically. I could just as easily say that I've explained why it is true, but I recognise the fact that it is not as straight forward as I thought it might have been.

The reasons being put forward for why my understanding is wrong, is to say that motion can only ever be relative to something; I have outlined that in each case of relative motion there are, at least, two possible scenarios which can account for the relative motion. Each one involves one or another object actually moving.

The response seems to be that relative motion occurs because objects move relative to each other; that just seems to be a tautology which allows us to posit the two different scenarios again.

Bet
Just to address the bet scenario to yourself; if you stand face to face with a friend, and make a bet with the provision that whoever moves first owes the other $50; do you think it is possible for anyone to win the bet?

 

[mangaroosh]

And repeatedly failed to demonstrate why this has any relevance to a theory based on relative velocity.

Apart from having potential deductive consequences, which I presume would be relative to any theory, it is relevant to the process of learning relativity, because it represents an existing belief that would have to be unlearned, or sufficiently rationalised, to allow for the assimilation of information pertaining to relativity theory.

Conflict between existing beliefs and new ideas are one of the main stumbling blocks in the learning process.

That is just silly. You are moving the goalposts. We are talking about scientific definitions involving velocities.

How is it moving the goalposts; it's simply a continuation of the existing discussion but taking a different approach, because the current approach seems to be going round in circles.

Again, it is a fairly simple scenario which shouldn't really cause that much difficulty to answer, but might allow us to make certain deductions.

Physics is not a democracy.

I didn't think it was, although it was suggested earlier that definitions are formed on the basis of consesus.

Physics is an approach to explaining empirical experiences, and such a walk would represent an empirical experience.

You won't be able to explain it better. There is no scientific way of defining a useful concept that requires absolute motion.

That may explain why it is so difficult to explain something which is, for many people, self-evidently true; or at least, which appears to be.

The 'active/passive' notion can only be scientifically expressed as 'non-inertial/inertial' because there are no other states of motion.

Active and passive are farily well understood terms; they could easily be used as adverbs to describe a type of non-inertail/inertial motion.

 

[mangaroosh]

Wanna bet?

As is abundantly clear to all here, the discussion appears to be going round in circles. For that reason I just wanted to put something out for general consideration, as opposed to the individual discussions that have been going on. It might help to clarify the issue, it might not, but here's hoping. I've referred to it in a few posts to individuals already, but in the hope to maybe resolve the issue, I just want to post it as a general question.

The bet
If you are standing face to face with your friend, and you make a bet, with the proviso, that the first person to move owes the other $50; do you think it is possible for anyone to win the bet?

 

[Mentz114]

Apart from having potential deductive consequences,

You like this phrase "deductive consequences" but it is empty if you cannot demonstrate one.

... it is relevant to the process of learning relativity, because it represents an existing belief that would have to be unlearned, or sufficiently rationalised, to allow for the assimilation of information pertaining to relativity theory.

Physical theories don't require belief. They stand or fall on their internal consistency and agreement with experiment.

Conflict between existing beliefs and new ideas are one of the main stumbling blocks in the learning process.

In your case more of a towering wall. Would you go on a maths forum and declare you are learning arithmetic but don't understand what numbers are ?

I think you should ask for this thread to be moved to the philosophy forum. There are lots of clever people there who might grasp what mere physicists cannot.

 

[phinds]

If you are standing face to face with your friend, and you make a bet, with the proviso, that the first person to move owes the other $50; do you think it is possible for anyone to win the bet?

If they don't understand physics, yes, because they don't understand what they are ACTUALLY betting on, as you clearly do not.

If they understand physics, no.

 

[Dale]

I'm not sure where the disagreement lies, if you agree that the Earth is "actually rotating". Given your responses thus far in the thread, I have to ask the question what you mean by "actually rotating". If you hadn't argued so vehemently against it I would have assumed we were in agreement, but would you say that the Earth is rotating in an absolute sense?

Yes. Rotation is non-inertial motion, and it can be measured without respect to any external body simply by using an accelerometer. Furthermore, if two objects are rotating relative to each other, it is possible to experimentally identify which of the two is rotating. Rotation is empirically different from inertial motion, so examples showing that rotation is absolute will not show that inertial motion is absolute.

Your disagreements, thus far, have effectively taken the form of "only motion relative to something makes sense", which is why I was saying you were assuming the conclusion - I'm not sure what the formal name is, but when you attempt to disprove something by proving something else, which is contradictory to be true?

That is called proof by contradiction, or proof by counter-example. However, pointing out a flaw in a proof is not itself a proof by contradiction. Pointing out a flaw in a proof simply invalidates the proof, but does not give any information about the truth of the conclusion. I.e. you may use faulty logic in an attempt to prove a true proposition.

Interestingly, there is a fallacy called the fallacy fallacy, which is one of my favorite fallacies. Basically, the fallacy fallacy is when someone makes the claim that the conclusion of a fallacious argument is false because the argument is fallacious.
http://www.fallacyfiles.org/fallfall.html

I appreciate your highlighting the logical fallacy that you believe is, and may perhaps be, being committed, because it helps to highlight where the issue lies. I was hoping the contextual examples would help to illucidate the point, as it seems to have done for bahamagreen, and salvesrom (although I would suspect they didn't require "my" examples to illucidate it).

I understand your point. The problem isn't a communication problem, it is a logic problem. You have clearly "illucidated" your erroneous reasoning. Further contextual examples serve no purpose.

I am indeed interested in learning SR, but I think an issue might lie in the preconceptions that people might have about the learning process. A horribly contrived expression I've come across in my own teacher training is the term "expectation violation", which can be a major obstacle to effective teaching and indeed learning; where the teacher has expectations about the learning/teaching process, which do not come to fruition, it can cause frustration and anger, which can affect the overall process.

I'm not sure how my profile as a learner compares to others who visit the site, but I don't doubt that, given enough research we could all be broadly categorised. I'm approaching this as a mature learner, with a pre-existing worldview which I believe to be fairly reasonable; there are undoubtedly subconscious beliefs thrown in there, and subconscious attachment to other beliefs, that younger learners have, perhaps, not yet developed. I do try to develop self-awareness and non-attachment to those beliefs, but it isn't a simple case of switching them off, as I'm sure you can appreciate.

I can appreciate the difficulty of learning SR, it took me 7 years of occasional study. However, in my experience working with other people to learn it is clear that a person who continues to argue an incorrect point (particularly one which has been clearly shown to be incorrect) is either unwilling or unable to learn until they change their attitude. For me, that was the case, and I have seen it other times. My motivation for changing my attitude was to read and understand the overwhelming experimental evidence:
http://www.edu-observatory.org/physics-faq/Relativity/SR/experiments.html

I am interested in learning and developing an understanding of ER that extends, primarily, to its foundational assumptions; I want to explore them and question them to see do they stand up to reason, and if they do, then I will be in position, psychologically, to accept it; unfortunately not before - as I'm sure you will agree, it is not possible to accept something that you do not understand, or that you haven't subjected to rational enquiry.

I am looking forward to your subjecting SR to rational enquiry. So far, I have seen only evidence of personal biases and prejudices supported by fallacy. And despite the fact that the fallacious reasoning has been clearly identified you seem to cling to it anyway. It makes it quite difficult to believe that you are really interested in rational enquiry instead of personal validation.

 

[Michael C]

I was thinking the qualifier "infinitely" was important, but if the plane is in the shape of a square then presumably you could have infinitely long lines disecting the angles of the square, which would naturally meet in the middle.

If the plane is a finite square, there's no problem finding the middle. But what does an infinite square look like? Where are the corners? I thought I'd hit on a good analogy here but I'm afraid it's only raising more questions.

My recommendation: you really need to learn more about basic concepts in maths and classical mechanics before adventuring into relativity.

 

[Michael C]

The bet
If you are standing face to face with your friend, and you make a bet, with the proviso, that the first person to move owes the other $50; do you think it is possible for anyone to win the bet?

This is getting really silly. A commonplace, imprecise use of the word "move" does not in any way help us here. In this case it will probably be assumed that the verb "move" applied to a person means something like "produce a discernible relative motion between different parts of the body", but that really has no bearing on the present discussion.

 

[Dale]

Even the language in the above formulation suggests an underlying assumption that the act of moving can be ascribed to one or the other; "one of them has to move", with the qualification "relative to the other".

Exactly. With the qualification "relativie to the other" it is clear which one the motion is ascribed to.

To say that the objects move relative to each other because they move relative to each other, doesn't explain why the relative motion occurs. It's logically self-consistent, but it is merely tautological.

Correct, it is tautologically true and self-consistent. That is the reason you cannot use the existence of relative velocity to prove that absolute velocity exists. You have to make the fallacious assumption of absolute velocity, otherwise you are simply left with a tautological truth about relative velocity.

As to "why" the relative motion occurs, that is a different question. Either it is a given boundary condition in the scenario or it occurs because of some dynamics which are a result of the given boundary conditions in the scenario.

 

[Dale]

1) Consider two inertially moving objects, A and B, with a relative velocity of 0.
2) If neither A nor B moves, their relative velocity will remain 0.
3) The relative velocity between A and B subsequently changes to a value greater than 0.
4) Therefore either A or B moved.

This is non-inertial motion, so this scenario is not relevant to the dispute.

If something is absolute, or not relative, then it presumably isn't measureable, so I would imagine that it wouldn't have any measurable consequences, but would have deductive consequences.

No. Something which is absolute is agreed upon by all reference frames. I.e. it is frame invariant. There are many absolute or frame invariant quantities which are measurable. E.g. proper time, proper acceleration, spacetime interval, invariant mass, etc.

EDIT: note, this usage of the word absolute may not be standard. Others believe that "absolute" is not the opposite of "relative" but rather refers to quantities in a preferred frame. In which case proper acceleration (including rotation) would not be "absolute", but would instead be frame invariant. I am looking for a good reference on the term "absolute".

 

[Dale]

The bet
If you are standing face to face with your friend, and you make a bet, with the proviso, that the first person to move owes the other $50; do you think it is possible for anyone to win the bet?

Again, this is non-inertial motion. It is not relevant to the disagreement.

 

[harrylin]

I would agree that either A or B accelerated.

But I would still think we can deduce that either A or B has to actually, or absolutely, be moving, even from inertial, relative motion.

Obviously, IF absolute motion exists, THEN at least one of the two has to be in absolute motion. There is nobody who has any issue with that logic. However, by far not all people have that postulate; and the mere fact that A and B are moving relative to each other, doesn't tell you anything else.

It's just as with creation: if we observe different species, we could deduce that one of them must have been created before the other - IF we base our reasoning on a certain hypothesis of creation.

But surely all these things have been explained to you many times by now. What is left to discuss?

 

[russ_watters]

This I don't understand.

My understanding is that neither can verify that they are the ones "actually moving", but they could deduce that, at least, one of them has to be.

Not your understanding, your belief. That's what this ultimately comes down to. The POR is saying that "actually moving" has no meaning in that context. You choose to believe that either the POR is wrong or that no one but you understands it.

 

[Dale]

Mangaroosh, given some physical object X do you believe that the phrase "X is moving" give any physical information other than that which is already implied simply by the fact that X is an object?

 

[Austin0]

I have repeatedly tried to give contextual examples that a lot of people would have no trouble understanding. It might be possible to drop the contentious term "actual movement" and try and deduce the answer in another way.

The contention is manifest in this thread. Also, salvestrom's post earlier in the thread (#47 I think it was) and bahamagreen's comments seem to suggest that they at least understand the contention being made.

I would presume that something which potentially has deductive consequences, has, at least, some relevance to relativity.

I understand that the theory is formulated with the idea that it doesn't matter, but I struggle to see how it can be formulated such that something which might have deductive consequences doesn't matter.

Genuinely, I'm not trying to be elusive, I've never actually had to try and explain this before, so that may be why I am struggling to clarify it sufficiently, but I think it is a fairly intuitive - not that that makes it right - idea.

Hopefully that helps to clarify it some bit.

Hi I certainly understand your contention and the logic leading to it.
and certainly the attempt to apply the deductive process is worthwhile and has a long tradition. Newton, Mach ,Einstein, to name a few, applied it to this and similar questions. I suggest you look up Newtons bucket for an instructive example of both logical reasoning and its limits as far as a definite determination.
While the effort of deduction may be worthwhile I think you may be impeding your own learning process by focussing on that and not recognizing the limits of knowledge in this regard.
Until you truly understand the viewpoint that has been presented to you by those here, your resistence and reasoning is based on incomplete knowledge. If you gain that understanding you may still choose to infer a concept of actual motion but at least it will be based on a real foundation.
You should also realize that such a concept is not actually in conflict with the theory itself.
The theory makes no statements about the actuality, or not , of motion. But rather is based on the empirical reality, that it is impossible to determine the "actual" state of a system in inertial motion.
Newton also believed in absolutes but had no choice but to proceed on the basis of relativity. Of which he had a complete understanding, of course.

So the question of real motion or not, is not relevant to the study or applicability of SR.

SR is a fundamental principle of the workings of reality and anyone who really wants to try and understand that reality, should not ignore it. Certainly not because they think there is conflict between it and their intuitions , without learning enough to make a real judgement.
IMO

BTW I also happen to "believe", intuit, deduce there is an objective reality, independent of our ability to measure it. But that does mean there is necessarily a logical argument in support of that view and I am forced to recognize these concepts may in fact be wrong..
On the other hand, to positively assert there is no real motion ,or propagation medium or that a photon has no intrinsic frequency, appears to me an equally unwarrented belief , unsupported by logic or evidence. IMHO
I hope some of this might help.

 

[harrylin]

[..] I suggest you look up Newtons bucket for an instructive example of both logical reasoning and its limits as far as a definite determination.
[..] Until you truly understand the viewpoint that has been presented to you by those here, your resistence and reasoning is based on incomplete knowledge. If you gain that understanding you may still choose to infer a concept of actual motion but at least it will be based on a real foundation.
You should also realize that such a concept is not actually in conflict with the theory itself.
The theory makes no statements about the actuality, or not , of motion. [..] the question of real motion or not, is not relevant to the study or applicability of SR.

SR is a fundamental principle of the workings of reality and anyone who really wants to try and understand that reality, should not ignore it. Certainly not because they think there is conflict between it and their intuitions , without learning enough to make a real judgement.
[..] I hope some of this might help.

Great summary Austin; as the discussion was starting to sound like a stuck record, such a different reply may help indeed.

And to continue your attempt: learning SR and GR (but first the basics of classical mechanics and optics!) could be useful to develop an argument about "the actuality, or not, of motion".
It may be frustrating, but one cannot logically reach a conclusion from arguments that are based on the understanding that one doesn't yet have.

 

[Mentz114]

My understanding is that neither can verify that they are the ones "actually moving", but they could deduce that, at least, one of them has to be.

Another repitition of the absolutist fallacy.

Why is this thread still open ? Clearly nothing is going to convince the poster that his ideas are not scientific and have been rejected after close scrutiny.

 

[Dale]

So the question of real motion or not, is not relevant to the study or applicability of SR.

I have made this point to him multiple times on multiple threads. He consistently ignores it.

 

[Mentz114]

So the question of real motion or not, is not relevant to the study or applicability of SR.

I've made the same point but he insists it is relevant.

 

[Chestermiller]

Mangaroosh,

I have an experiment for you to perform. Get in your car and go out on a long, straight, smooth road. Set your cruise control to a constant speed, say 100 km/hr. Now try to imagine that, rather than you and your car moving along the highway relative to the surrounding landscape, your and your car are stationary, and it is the highway and surrounding landscape that are moving backwards relative to you. I've done this experiment many times on the New Jersey Turnpike. It's a weird feeling, but I know you can do it. Now try to think of an experiment you can do within the cabin of your car to prove that you are the one that is moving at constant speed in a straight line, and not the surrounding landscape. You can't do it. You and your car are at rest relative to one another. The trees and houses and highway are at rest relative to one another. But you are moving at a constant speed in a straight line relative to the landscape, and the landscape is moving at constant speed in a straight line relative to you. That's basically all that these guys are trying to tell you.

Chet

 

[bahamagreen]

I think some of you are being a little hard on the OP; you have the advantage of having studied relativity to the point where it seems "normal".

In Minkowski's famous 1908 lecture, the "...with this valiant piece of chalk..." one, he begins with Newton's equations and their two fold invariance... that the physical laws hold for any change of position, and that they hold for any uniform motion of translation.
He mentions how these two kinds of invariance denote two different groups of transformations for the differential equations of mechanics... then goes on to say:

"We look upon the existence of the first group as a fundamental characteristic of space. We always prefer to punish the second group with contempt, so as to get over the fact with a light heart, that we can never decide from physical considerations whether the space, which is supposed to be at rest, may not finally be in uniform motion."

I gather that everyone attending the lecture was of the belief that space is either at rest or in some kind of uniform motion...?

 

[Dale]

I think some of you are being a little hard on the OP

Hundreds of posts and multiple threads ago we were not being so hard on the OP. Gentleness is generally the default position on this forum, but it has already been tried with mangaroosh and it has failed.