A Challenge to Special Relativity?

[Curious6]

Please consider this simple, but very interesting interpretation of the nature of space in special relativity.

Space is both relative AND absolute. Why? Let's take a very simple example.

The Eiffel Tower is 10,000 miles East from City X and 2,000 miles East from City Y. Michael is in City X, Tim is in City Y. If we were to plot everything that exists for Michael and for Tim on an imaginary map, Michael would disagree with Tim on where the Eiffel Tower is; for Michael it would be 10,000 miles East, for Tim it would be 2,000 miles East. Space in this case is relative; Michael and Tim disagree on what they find at 10,000 miles East and they disagree on what they find at 2,000 miles East. However, when Michael takes into account that Tim is where he is (i.e., 8,000 miles away from him) he now understands how Tim sees the Eiffel Tower as being only 2,000 miles East. Space here is absolute; they now both agree on where the Eiffel Tower is.

Is this distinction made at all in special relativity? I think it is a very important one. Basically, space is relative until we take into account the position of others, then space ceases to be relative. The same could be said for time (possibly challenging the notion of the relative simultaneity of events). Any insights would be much, much appreciated!

 

[atyy]

Yes, spacetime is absolute, and the events in spacetime are absolute. The relative thing is that different reference frames assign different numbers to the same event. Relativity tells us how the numbers of different reference frames are related.

 

[Curious6]

atty, thanks for your answer. I do know that special relativity says spacetime is absolute, but I haven't brought time into the picture in my example above, which shows a case where space is relative and space is absolute. I am not saying I am right or anything; on the contrary, I am hoping someone can point out the flaw in the reasoning above that leads to the seemingly paradoxical result.

 

[atyy]

atty, thanks for your answer. I do know that special relativity says spacetime is absolute, but I haven't brought time into the picture in my example above, which shows a case where space is relative and space is absolute. I am not saying I am right or anything; on the contrary, I am hoping someone can point out the flaw in the reasoning above that leads to the seemingly paradoxical result.

I didn't know what you said is wrong, I read it quickly and it made sense to me. I'll read it more carefully now.

 

[Curious6]

A further point. If, as in my example, space can be conceived of as relative and absolute, then a further step shows that 'absolute' space is the 'correct' way to conceive of existing things. Why? Well, if Michael says the Eiffel Tower is 10,000 miles East, and Tim says it is 2,000 miles East, and Marie says it is 5,000 miles North of her, then the Eiffel Tower is in effect existing in all these places. But we know there is only ONE Eiffel Tower. Therefore, once Michael, Tim, and Marie take into account their relative perspectives, they all agree there is only one place the Eiffel Tower exists in (thereby conceiving of space as being absolute).

Again, I am not saying I am right, I am just trying to share this thought with you all so that I have a better chance at seeing where the possible mistake lies.

 

[atyy]

atty, thanks for your answer. I do know that special relativity says spacetime is absolute, but I haven't brought time into the picture in my example above, which shows a case where space is relative and space is absolute. I am not saying I am right or anything; on the contrary, I am hoping someone can point out the flaw in the reasoning above that leads to the seemingly paradoxical result.

OK, I'm confused. What is paradoxical about what you said? There are relative and absolute descriptions of events in spacetime. The only thing that seems unconventional to me is that you say space is relative, whereas most people would say reference frames are relative, but that seems to be just terminology.

 

[matheinste]

Hello Curious6.

But how do you tell anyone where the Eiffel Tower is without refrerring to some other point and so on?

Matheinste.

 

[Curious6]

Hi, matheinste. Well, I don't think it's necessary to refer to another point to say where the Eiffel Tower is. You can just say: 'it's 200 miles due South of where I am' or 'it's 10,293 miles NE of where I am'.

 

[Doc Al]

If we were to plot everything that exists for Michael and for Tim on an imaginary map, Michael would disagree with Tim on where the Eiffel Tower is; for Michael it would be 10,000 miles East, for Tim it would be 2,000 miles East.

Without a common reference point, of course they would "disagree". But such a "disagreement" is trivially handled: Both agree that the Eiffel Tower is 10,000 miles east of Micheal and 2,000 miles east of Tim.

I don't see what this has to do with Special Relativity.

 

[Doc Al]

Hi, matheinste. Well, I don't think it's necessary to refer to another point to say where the Eiffel Tower is. You can just say: 'it's 200 miles due South of where I am' or 'it's 10,293 miles NE of where I am'.

That's good enough. Both will agree on this. Disagreement has magically vanished.

(I seriously hope you aren't troubled by the fact that Michael refers to himself as "I" while Tim refers to himself as "I".)

 

[Curious6]

Doc Al, they would disagree because from their perspectives on space differ, that is, their perspectives on space are relative to where they are. Nevertheless, they can find common ground and agree on where a specific object is (i.e., the location of the Eiffel Tower). The Eiffel Tower's position is therefore defined in absolute terms. There seems to be a contradiction. I posted this in the special relativity forum because it is chiefly concerned with our perception of space as being relative.

 

[Curious6]

That's good enough. Both will agree on this. Disagreement has magically vanished.

(I seriously hope you aren't troubled by the fact that Michael refers to himself as "I" while Tim refers to himself as "I".)

After posting it I realized that adding the 'where I am' bit might cause some controversy. Nevertheless, I don't see how that affects my main point.

 

[Doc Al]

Doc Al, they would disagree because from their perspectives on space differ, that is, their perspectives on space are relative to where they are. Nevertheless, they can find common ground and agree on where a specific object is (i.e., the location of the Eiffel Tower). The Eiffel Tower's position is therefore defined in absolute terms. There seems to be a contradiction.

What contradiction? The same object can certainly be a different distance and direction from different reference points. So what? How does that "contradict" anything?

 

[Curious6]

The same object can certainly be a different distance and direction from different reference points.

That is exactly the point. The same object appears to be at different distances and directions from different reference points, which suggests it has different locations in space (locations dependent on one's reference point), but in actuality it only has one location in space.

 

[JesseM]

That is exactly the point. The same object appears to be at different distances and directions from different reference points, which suggests it has different locations in space (locations dependent on one's reference point), but in actuality it only has one location in space.

What is "location in space"? Is it separate from its distance from other objects, or from position relative to a certain coordinate grid? If so, how do you measure it?

 

[Curious6]

What is "location in space"? Is it separate from its distance from other objects, or from position relative to a certain coordinate grid? If so, how do you measure it?

JesseM, I think your question is another way of asking what I am trying to get at. What I proposed is that there are two ways to think of 'location in space': one relative, one absolute, as explained briefly below.

'Location in space' is an imaginary grid where you can place where objects are with respect to you. In the example that started this thread, each person has an imaginary grid where they position their objects. For instance, Michal's grid positioned the Eiffel Tower 10,000 miles East from him whereas Tim positioned it only 2,000 miles East from him. Therefore, what Tim would find 10,000 miles East from him on his grid is different than what Michael finds 10,000 miles East from him on his grid (Michael finds the Eiffel Tower). In this sense then, 'location in space' is relative; Michael and Tim have different perceptions of objects' locations in space.

'Location in space' however also refers to an object's actual position on a universal grid. What I mean by this is a grid like for instance the geographic coordinates used to give positions of objects on Earth. By this definition of 'location of space' the Eiffel Tower has just one location, whereas we just saw above that it has various locations. Who's grid are we to trust therefore? Clearly, it does not appear to be any individual's grid (an object could be located at potentially an infinite number of places). There seems to be a universal grid on which objects can placed. That is what I mean and what I'd like further insights on.

 

[matheinste]

Hello Curiou6.

One point in empty space is indistinguishable from any other point and has no "position" and nothing to define it without reference to some object, such as yourself or the Eiffel Tower. I suppose using your own position as a reference point is a natural thing to do and is as valid as any other way.

Matheinste

 

[ZapperZ]

There seems to be a universal grid on which objects can placed. That is what I mean and what I'd like further insights on.

Then you are assuming that there is an 'absolute space' and an absolute reference point. Care to tell me what evidence that you have to know that such a thing exist?

Zz.

 

[Curious6]

Hello Curiou6.

I suppose using your own position as a reference point is a natural thing to do and is as valid as any other way.

I agree with that and so does special relativity, but there does appear to be a sense in which an object occupies a certain position within absolute space, i.e., there are certain coordinates in the entirety of space occupied by certain objects; this is the opposite case to our relative perception of space.

 

[Curious6]

Then you are assuming that there is an 'absolute space' and an absolute reference point. Care to tell me what evidence that you have to know that such a thing exist?

Zz.

I have no evidence for that besides my thought experiment outlined above. I am actually not assuming there is an absolute space; my example derives absolute and relative space as notions. Clearly, from the thought experiment there seem to be relative and absolute reference points.

 

[ZapperZ]

I have no evidence for that besides my thought experiment outlined above. I am actually not assuming there is an absolute space; my example derives absolute and relative space as notions. Clearly, from the thought experiment there seem to be relative and absolute reference points.

How is that? All you have shown in your example is the ability to transform from one reference point to another. Translational symmetry. This is your "evidence" for the existence of "absolute space"? Why haven't all the most brilliant physicists stumbled upon that?

Zz.

 

[matheinste]

Quote:-
----I agree with that and so does special relativity, but there does appear to be a sense in which an object occupies a certain position within absolute space, i.e., there are certain coordinates in the entirety of space occupied by certain objects; this is the opposite case to our relative perception of space.-----

Of course an object occupies a certain unique position in space but there is nothing about about that point that tells us where it is. I think it was Eddington who said that the only way to tell someone which location in space you wish to indicate without reference to another location was to actually point to it.

Matheinste.

 

[JesseM]

I agree with that and so does special relativity, but there does appear to be a sense in which an object occupies a certain position within absolute space, i.e., there are certain coordinates in the entirety of space occupied by certain objects; this is the opposite case to our relative perception of space.

Keep in mind that when people talk about things being relative to one's choice of reference frame, they are usually talking about different coordinate grids in motion relative to one another, not just coordinate grids with their origins at different locations. For example, if I am on a spaceship moving at constant speed relative to a space station, there could be one coordinate grid centered on the ship, and naturally in this grid the ship is at rest while the space station is moving. So, from one time to another the ship occupies the same space coordinate, while the space station's space coordinate is constantly changing. On the other hand, there could be another coordinate grid centered on the space station, and in this system the reverse would be true. Do you believe there must be a real truth about whether the ship or the station (or neither) is remaining at a fixed point in space while the other is moving? Even if there was a "real truth" about this in some metaphysical sense, relativity says it would be impossible to determine experimentally which was at rest in absolute space and which wasn't, because all the laws of physics work the same way in both coordinate systems, which negates the idea that there is an experiment either the ship or the station could do to determine their velocity relative to absolute space (since if they both perform the same experiment, they must get the same results if all the laws of physics are the same in both coordinate systems).

 

[atyy]

The Eiffel Tower's position is therefore defined in absolute terms.

Of course an object occupies a certain unique position in space

Both statements seem right and equivalent to me. Am I misunderstanding something?

In Newtonian physics, the position in space of the Eiffel tower is absolute. In special relativity, it would be the worldline in spacetime of the Eiffel tower which is absolute. (I suppose there's the detail about isometry.)

 

[atyy]

Is the discussion related to eg. Giulini's "the points that constitute M, which for the time being we think of as recognizable entities, as mathematicians do. (For physicists these points are mere ‘potential events’ and do not have an obvious individuality beyond an actual, yet unknown, event that realizes this potentiality.)" http://arxiv.org/abs/gr-qc/0603087

 

[atyy]

The preamble here may also be relevant: "Do we think of spacetime points as “determined well-distinguished objects of our intuition or of our thinking”?"

The Rich Structure of Minkowski Space
Domenico Giulini
http://arxiv.org/abs/0802.4345

 

[Dale]

There is nothing even remotely parodoxical in this. All you have said is:

1) Different coordinate systems assign different values for the coordinates of a given object

2) There exists some transformation between coordinate systems

 

[matheinste]

Hello atyy

Saying that a point occupies a unique position in space is really just saying that it exists as one object at one location but says nothing about its location.

Matheinste.

 

[atyy]

Saying that a point occupies a unique position in space is really just saying that it exists as one object at one location but says nothing about its location.

Doesn't it say that it's location is where it is? The fact that there is something there (say the Eiffel tower) distinguishes that location.

Or is that what you mean, ie. if there were nothing there, then empty space is all the same, we cannot give directions to a point in totally empty space.

Or do you mean that even with the Eiffel tower at some place and me at another place, we still have to lay out a grid between the the tower and me, so we can give it and the intervening points some addresses before I can get directions on how to get there?

What I'm trying to figure out is whether you are saying something different from Curious6, and if so, what is the difference? Or do you agree with him, and are just rephrasing what he's saying for clarity? I'm thinking Curious6 is right that absolute location exists (in Newtonian physics), otherwise how can we even say that I am here and the Eiffel tower is there in a coordinate independent sense? In special relativity, it would have to be the location of events in spacetime that is absolute, because simultaneity is conventional. The part I disagree with Curious6 about is not that absolute location exists, but that there's any paradox in having many different coordinate systems being able to describe the same absolute things.

 

[matheinste]

Hello atyy

The point I am making is that if you have an object then it occupies a location in space. If there was nothing else in space to refer it to, you cannot describe to me where it is, without my being able to see it or detect it some other way. That means the description of a space location is relative.

Matheinste.

 

[alxm]

I'm thinking Curious6 is right that absolute location exists (in Newtonian physics), otherwise how can we even say that I am here and the Eiffel tower is there in a coordinate independent sense?

Because your position relative the Eiffel tower is the same regardless of how you define your coordinate system. There's no paradox in the fact that you can describe something in different ways and arrive at the same result.

In special relativity, it would have to be the location of events in spacetime that is absolute, because simultaneity is conventional.

'Absolute' would imply that there's some fixed point everyone can measure against. There isn't.

If you find one, tell Archimedes. He's promised to move the world if you do :)

 

[Saw]

The approach proposed by Curious6 is, in my view, very interesting. It does not “challenge” SR, but it may serve at least to clarify its concepts.

SR is right, but it plays with some obscure concepts, at least at the level of pure English. Its mathematics and its geometry may be undisputable, but it is my impression that when you try to put it in plain words, problems arise. (Hence the “paradoxes”.)

To try to solve this, I would propose this challenge, not for SR but for our discussion skills:

1) start with this rudimentary example, which only deals with objects stationary wrt each other and hence excludes time;

2) give a sound account of what it conceptually means for you, handling the concepts of what “space” is, what is “absolute” and “relative”, what a “measurement” means and so on;

3) in particular, always within the boundaries of this elementary example, explain the transition from a Galilean viewpoint to the Einsteinian one (this may sound strange, since here there is no motion, but it may be possible, if you hit on the right analogy…) and

4) only then introduce the complication of motion and apply your concepts to this new context, “mutatis mutandi” (changing what needs to be changed and leaving unaltered what does not need to be changed).

In this exercise, it’d be fundamental not to skip step 3: you would have to fully explain SR within the constraints of the situation described by Curious6 (a pure example of distances), so that, when you shift into the domain of motion, the meaning of SR shines up effortlessly, causing an Aha! of instantaneous comprehension in all your listeners…

Would anyone take the challenge? I would, but I can’t (I am still looking for the right analogy...)

 

[Dale]

SR is right, but it plays with some obscure concepts, at least at the level of pure English. Its mathematics and its geometry may be undisputable, but it is my impression that when you try to put it in plain words, problems arise. (Hence the “paradoxes”.)

This is like knowing that Tolstoy is a great author but the English translations are lacking. The solution is not to do yet another English translation which cannot express all the artistry of the original, but the solution is simply to learn Russian.

Same here, learn Minkowski geometry. Then the SR concepts are elegantly unified and clear. English words are too ambiguous and flexible to serve this purpose well.

 

[Naty1]

Dalespam said it all in post #27.

I tried to skim all posts and no one seemed to mention that space may not have always existed, is expanding due to the cosmological constant...also no one pointed out that space becomes time at the center of a black hole...those things rather smother "absolute" space whatever that might be...
Curious is entirely right to think in different ways about space, but I can't find anything insightful there...

 

[Curious6]

Hi. Thanks for all the posts. I have taken a look at them and have thought some more about what I said yesterday. I am a little bit in a rush right now but I will address some of the points raised later on.

 

[Saw]

This is like knowing that Tolstoy is a great author but the English translations are lacking. The solution is not to do yet another English translation which cannot express all the artistry of the original, but the solution is simply to learn Russian.

DaleSpam, you adhere to Galileo's view, when he suggested something like "the universe is written in mathematical language". Another view: the universe is what is and the human intellect may "represent" or "reproduce" it in any language, whether mathematical, geometrical (a different language, after all, even if akin to the mathematical formulation), conventional (English just being one of this subset...) or even emotional! I agree that mathematical and geometrical rules are far more effective..., when it comes to drawing consequences from axioms. But if you doubt about the axioms, you may need some pre-mathematical discussion... in plain English or Russian words... or in the mathematical language of a superior culture who has pushed mathematical terminology farther than your own! For instance: in ancient mathematics, when they did not handle the concept of "convergence of infinite series", how did mathematicians discuss over the proposal to include such new concept in the list of approved terms? By exchanging formulas with mysterious symbols of unknown meaning or in some conventional language?

Anyhow, this is a side-matter and the crucial aspect of my proposal was: can you do step 3, in any language you prefer, mathematical if you prefer? But, sorry, because I start writing and cannot stop. Maybe this is the subject for another thread. Please forget this parenthesis and continue your discussion.

 

[atyy]

3) in particular, always within the boundaries of this elementary example, explain the transition from a Galilean viewpoint to the Einsteinian one (this may sound strange, since here there is no motion, but it may be possible, if you hit on the right analogy…)

Maybe with Escher's famous picture:
http://www.geom.uiuc.edu/graphics/images/medium/Special_Topics/Hyperbolic_Geometry/escher.gif

And mathematically by the new metric given by Eq 1 here:
http://mathworld.wolfram.com/PoincareHyperbolicDisk.html

?

 

[Curious6]

How is that? All you have shown in your example is the ability to transform from one reference point to another. Translational symmetry. This is your "evidence" for the existence of "absolute space"? Why haven't all the most brilliant physicists stumbled upon that?

Zz.

No, translational symmetry is not what I am referring to. Translational symmetry refers to the mapping of one's coordinates upon the others, so that they both agree. This refers to one's coordinates taking into account the other's coordinates to understand why they have different coordinate systems and come to the realization there is actually only one real coordinate system (objects can be found in one place).

 

[Dale]

DaleSpam, you adhere to Galileo's view, when he suggested something like "the universe is written in mathematical language".

Yes, and you are kidding yourself if you believe that you can understand it without putting in the effort required to learn the math. I have had this discussion before, and frankly the anti-math position always seems lazy to me.

Another view: the universe is what is and the human intellect may "represent" or "reproduce" it in any language

The difference is that math is the only language where illogical statements are gramatically incorrect.

 

[Curious6]

Of course an object occupies a certain unique position in space but there is nothing about about that point that tells us where it is. I think it was Eddington who said that the only way to tell someone which location in space you wish to indicate without reference to another location was to actually point to it.

Matheinste.

I agree that there is nothing about a point that tells us where it is. We need to look at it with respect to other points in order to know where it is. Take point X. Point X's position cannot be known by just looking at point X. However, if you now take another point, point Y for instance, then you can say point X is 5 metres South of point Y. Point X is also 5 metres East of point Z. Point X is at different points on point Y's and point Z's respective coordinate systems; space is relative. Nevertheless, in reality point X is just at one single point; a position both point Y and point Z will agree upon (that's why we agree upon where objects are located; e.g., we agree the Eiffel Tower is in Paris); space is in this sense absolute.

 

[Curious6]

Keep in mind that when people talk about things being relative to one's choice of reference frame, they are usually talking about different coordinate grids in motion relative to one another, not just coordinate grids with their origins at different locations. For example, if I am on a spaceship moving at constant speed relative to a space station, there could be one coordinate grid centered on the ship, and naturally in this grid the ship is at rest while the space station is moving. So, from one time to another the ship occupies the same space coordinate, while the space station's space coordinate is constantly changing. On the other hand, there could be another coordinate grid centered on the space station, and in this system the reverse would be true. Do you believe there must be a real truth about whether the ship or the station (or neither) is remaining at a fixed point in space while the other is moving? Even if there was a "real truth" about this in some metaphysical sense, relativity says it would be impossible to determine experimentally which was at rest in absolute space and which wasn't, because all the laws of physics work the same way in both coordinate systems, which negates the idea that there is an experiment either the ship or the station could do to determine their velocity relative to absolute space (since if they both perform the same experiment, they must get the same results if all the laws of physics are the same in both coordinate systems).

Good insight. I agree with that. What I would like to suggest though, and this differs from special relativity and is therefore controversial, is that one object IS actually moving whereas the other one is remaining stationary. Please take one minute to read the reasoning behind this statement, and then point out where it's wrong because it clearly differs from what SR says and I'd therefore appreciate it if someone could point out any flaw which I have overlooked. Take any empty field. You have two people, Mike and Jane, at rest with respect to each other, and Tim, who is about 100 meters away riding on his bicycle. Now Tim rides past Mike on his bicycle. Mike records him as being in motion. Tim records Mike as being in motion. Each other's positions change on their relative coordinate systems; each observer's reference point is equally valid - this is SR. However, Jane also notes Tim's position as changing on her coordinate system; she doesn't see Mike's position changing on her coordinate system. Not only for Mike, but for Jane, Tim has moved as well. Now you may argue that both Mike and Jane are in the same frame of reference so that doesn't matter. However, you could say that for every other object in the field, the only position that has changed is that of Tim; the relative positions between the other points in the field have remained the same. Taking it one step further, all the remaining positions of points in the Universe with respect to other points have staid the same; only Tim's relation to other points in the Universe has changed. It can therefore be said Tim is in motion.

Any comments on the above?

 

[Curious6]

The approach proposed by Curious6 is, in my view, very interesting. It does not “challenge” SR, but it may serve at least to clarify its concepts.

SR is right, but it plays with some obscure concepts, at least at the level of pure English. Its mathematics and its geometry may be undisputable, but it is my impression that when you try to put it in plain words, problems arise. (Hence the “paradoxes”.)

To try to solve this, I would propose this challenge, not for SR but for our discussion skills:

1) start with this rudimentary example, which only deals with objects stationary wrt each other and hence excludes time;

2) give a sound account of what it conceptually means for you, handling the concepts of what “space” is, what is “absolute” and “relative”, what a “measurement” means and so on;

3) in particular, always within the boundaries of this elementary example, explain the transition from a Galilean viewpoint to the Einsteinian one (this may sound strange, since here there is no motion, but it may be possible, if you hit on the right analogy…) and

4) only then introduce the complication of motion and apply your concepts to this new context, “mutatis mutandi” (changing what needs to be changed and leaving unaltered what does not need to be changed).

In this exercise, it’d be fundamental not to skip step 3: you would have to fully explain SR within the constraints of the situation described by Curious6 (a pure example of distances), so that, when you shift into the domain of motion, the meaning of SR shines up effortlessly, causing an Aha! of instantaneous comprehension in all your listeners…

Would anyone take the challenge? I would, but I can’t (I am still looking for the right analogy...)

Very interesting proposal. I'd like to take it up but given that I have raised objections to SR which I'd like to see debunked I'd like someone else to try it.

 

[JesseM]

Good insight. I agree with that. What I would like to suggest though, and this differs from special relativity and is therefore controversial, is that one object IS actually moving whereas the other one is remaining stationary. Please take one minute to read the reasoning behind this statement, and then point out where it's wrong because it clearly differs from what SR says and I'd therefore appreciate it if someone could point out any flaw which I have overlooked. Take any empty field. You have two people, Mike and Jane, at rest with respect to each other, and Tim, who is about 100 meters away riding on his bicycle. Now Tim rides past Mike on his bicycle. Mike records him as being in motion. Tim records Mike as being in motion. Each other's positions change on their relative coordinate systems; each observer's reference point is equally valid - this is SR. However, Jane also notes Tim's position as changing on her coordinate system; she doesn't see Mike's position changing on her coordinate system. Not only for Mike, but for Jane, Tim has moved as well. Now you may argue that both Mike and Jane are in the same frame of reference so that doesn't matter. However, you could say that for every other object in the field, the only position that has changed is that of Tim; the relative positions between the other points in the field have remained the same.

But you've stacked the deck by including a bunch of objects at rest relative to one another and only one object in motion relative to these other objects. And all the objects at rest relative to one another are just at rest relative to the surface of the Earth which carries them--unless you are a geocentrist, why would you think the Earth is "really" at rest in an absolute sense? The point is that although some frames may seem more "natural" to use as rest frames than others because their happen to be more objects at rest in that frame in your local neighborhood, that doesn't justify the idea that these frames represent a state of absolute rest, since after all the laws of physics say that even if there was an absolute rest frame in a metaphysical sense, this frame would not be privileged as far as the laws of physics are concerned so a group of observers would make exactly the same observations regardless as to whether they were at rest in absolute space or moving at 99% the speed of light in absolute space.

Taking it one step further, all the remaining positions of points in the Universe with respect to other points have staid the same; only Tim's relation to other points in the Universe has changed. It can therefore be said Tim is in motion.

What are "positions in the universe"? Are they measurable things, so that you have an experimental way to decide whether something is at a fixed position in the universe or has a changing position in the universe? If not, then once again, you are talking about a metaphysical idea which may or may not be true, but even if it is true it would have no relevance to physics if it made no difference to the outcomes of any experiments/observations.

 

[Curious6]

But you've stacked the deck by including a bunch of objects at rest relative to one another and only one object in motion relative to these other objects. And all the objects at rest relative to one another are just at rest relative to the surface of the Earth which carries them--unless you are a geocentrist, why would you think the Earth is "really" at rest in an absolute sense? The point is that although some frames may seem more "natural" to use as rest frames than others because their happen to be more objects at rest in that frame in your local neighborhood, that doesn't justify the idea that these frames represent a state of absolute rest, since after all the laws of physics say that even if there was an absolute rest frame in a metaphysical sense, this frame would not be privileged as far as the laws of physics are concerned so a group of observers would make exactly the same observations regardless as to whether they were at rest in absolute space or moving at 99% the speed of light in absolute space.

OK, I see what you mean; you're right - the laws of physics don't differentiate between frames of reference. Nevertheless, it seems to me that if we were to imagine a still Universe then if something within that Universe would move it would only be partially right to say both the person is moving as well as the Universe is moving. This is only true if you consider the reference frame of the person moving. From all other objects or points in the Universe, it is the person who is moving though, whereas the other objects are at rest to each other. The laws of physics don't differentiate, but our common sense and intuition does. Perhaps it is a metaphysical question, but as one bearing on the nature of our reality, an important one nevertheless.

What are "positions in the universe"? Are they measurable things, so that you have an experimental way to decide whether something is at a fixed position in the universe or has a changing position in the universe? If not, then once again, you are talking about a metaphysical idea which may or may not be true, but even if it is true it would have no relevance to physics if it made no difference to the outcomes of any experiments/observations.

Positions in the Universe are basically fixed points in the fabric of space (i.e., the coordinates we can agree upon to specifically state where an object is) which are not dependent upon your point of observation. Again, perhaps a metaphysical point as you rightly pointed out. I do think though that here it comes down to your perspective on science: if physics can only tell us so much about the nature of reality, should we use our reasoning to probe deeper or should we content ourselves with what physics tells us we can know?

 

[matheinste]

Hello Curious6.

For clarification, what is your definition of absolute space?

Matheinste.

 

[Mentz114]

Curoius6 is coming at this from the wrong direction. Space is only defined by the objects in it ( in physics anyway). There's no 'absolute space' and no such thing as 'position' except as perceived by observers. I wish absolutists would stay away from this relativity forum, especially those who think they have found something that contradicts SR. What a chimera.

Who said 'everything got to be somewhere' ? ( Popeye ? )

 

[JesseM]

Positions in the Universe are basically fixed points in the fabric of space (i.e., the coordinates we can agree upon to specifically state where an object is) which are not dependent upon your point of observation. Again, perhaps a metaphysical point as you rightly pointed out. I do think though that here it comes down to your perspective on science: if physics can only tell us so much about the nature of reality, should we use our reasoning to probe deeper or should we content ourselves with what physics tells us we can know?

Perhaps this thread should be moved to the philosophy section then? As I said, relativity doesn't rule out the idea of an "absolute space" with absolutely no empirical consequences, but just from a philosophical point of view, I don't see what "reasoning" compels us to believe in such a thing, or to think of space as a "fabric" with identifiable points which persist over time. Do you also believe in an absolute coordinate grid, so that there is an absolute truth about what an object's "real" x-coordinate is at a given moment? If not, what makes the idea of an absolute truth about whether an object is moving or at rest any more compelling?

 

[atyy]

Point X is at different points on point Y's and point Z's respective coordinate systems; space is relative. Nevertheless, in reality point X is just at one single point; a position both point Y and point Z will agree upon (that's why we agree upon where objects are located; e.g., we agree the Eiffel Tower is in Paris); space is in this sense absolute.

Yes. Let's stick to Newtonian physics. The location of an object is absolute. The description of where the object is relative.

Let's have 2 objects for convenience. The vector pointing from one object to the other is absolute. But you can represent that vector in many ways. If you fix one set of axes, that vector will be some set of 3 numbers {rx,ry,rz}. If you use a set of axes rotated, the same vector will be described by a different set of 3 numbers {sx,sy,sz}. In Newtonian physics, there is an absolute number called the distance d between the two objects that can be obtained from either one of the relative descriptions:

d=sqrt(rx²+ry²+rz²)=sqrt(sx²+sy²+sz²)

 

[Curious6]

Hello Curious6.

For clarification, what is your definition of absolute space?

Matheinste.

Hi, my definition of absolute space is simply based on the observation that we can all agree on where specific objects are, that is, they occupy only point in space. Even though an object can appear at different points on different coordinate grids, taking into account one another's position yields agreement on where the object is in an absolute sense. I think the numerical example I gave about point X, point Y, and point Z clarifies the above sentence.

 

[Doc Al]

Perhaps this thread should be moved to the philosophy section then?

Sounds more appropriate to me.