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Thread: Timey-wimey Wibbly-wobbly Stuff

  1. #91
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    Quote Originally Posted by Grimble View Post
    May I refer you to a blog that makes sense to me?

    It has a very erudite reading of just what Einstein wrote, considered in full without taking partial quotes to remove their context.
    So you have found someone who shares your lack of understanding. So what?

  2. #92
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    One of Einstein's major breakthroughs was the concept of the Relativity of Simultaneity. That, as one observer measured events, those that she would measure, as simultaneous, would be simultaneous only to her.

    But, does that mean that only that observer would measure that simultaneity?

    If so it would mean that they were privileged, would it not? That one could take her Frame of Reference as being a special one; that events had to be more complicated for all other Frames of reference.
    I stopped there. Clear lack of understanding of what is meant by a special frame of reference. Relativity says precisely nothing about the perceived 'complexity of events' - plus assuming non-simultaneous events are somehow more complex is nonsensical.

    And we can extrapolate from this particular conclusion and say simultaneous events in Spacetime, will be simultaneous to a stationary observer in any and every Inertial Frame of Reference; and equally, that such an observer will conclude that they cannot be simultaneous in any other Inertial Frame of Reference.
    Which is completely at odds with Einstein and relativity.

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    From the blog:
    Again this is emphasising that it is from the perspective where M' is travelling toward lightning flash B. This is the case only when considered from the embankment. For in the Frame of Reference of the observer on the train at M', she is stationary between the points A & B on the train.
    It's important to remember that from the train observer frame of reference as at rest, the lightning flashes occupy two separate frames, one being in motion towards the observer on the train and the other being in motion away.
    "There are powers in this universe beyond anything you know. There is much you have to learn. Go to your homes. Go and give thought to the mysteries of the universe. I will leave you now, in peace." --Galaxy Being

  4. #94
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    Quote Originally Posted by Grimble View Post
    No, absolutely, precisely, each will think their flashes were simultaneous and that the other's weren't! You are agreeing exactly with what I am seeing!
    No. If the flash is seen as simultaneous by one observer, it won't be seen as simultaneous by the other. It is simply getting childish now, that you "agree" with what one of us writes, but then say we are saying what we are not.

    Quote Originally Posted by Grimble View Post
    One has to take into account that each is seeing the light travel with the speed of light in their rest frame

    So N will see the light from a and B, travelling at c in her frame reach her simultaneously, as will M see the light from C and D in his frame.
    N will also see the light from C and D move at C but M will appear to move toward C while M sees the light from A and B move at C but N will be moving toward B.
    No, because you make a contradiction.

    One observer can't see the flashes of light reach themself at the same time, while the other observer sees the flashes of light reach that observer at different times. You are mis-reading the situation. The initial flashes of light, regardless of what frame you look at, will reach some observer at some time. The same two flashes of light can't reach an observer M at the same time, according to observer M, and reach observer M at different times according observer N.

    If two cars crash into the same lamp post, at the same time, all observers will agree that they crashed at the same time. There's no observer who can see/measure/calculate that one of the cars hit the post 30 seconds before the other.

    But if those lamp posts are physically separated, one in London and one in Moscow, then we can have observers who in their own frame of reference think the crashes were siumultaneous or not. They actually can't agree.

    In the lights/train/embankment thought experiment, everyone will agree whether the flashes hit an observer at the same time or not. But that doesn't mean the two observers M and M' will both experience the same thing.

    The flashes being generated, is the equivalent of the cars hitting the separate lamp posts. The flashes of light hitting an observer are the equivalent of the cars hitting the same lamp post.

    No observers can disagree that the cars hit the same lamp post at the same time. You can't have one observer say "well, the lamp post was moving relative to me, so the blue car must have hit it first". That just can't happen. If one observer sees the cars hit the same lamp post at the same time, then all observers must.

    Similarly, you can't have an observer see the two flashes of light hit them at the same time, while another observer sees them hit at different times. This is the nonsense of your idea that the flashes are simultaneous for all observers, but observers may simply "think" or "see" the flashes hit other observers at different times. That just can't work.
    I don't see any Ice Giants.

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    Quote Originally Posted by Grimble View Post
    May I refer you to a blog that makes sense to me?http://fromtheretohereandonward.blog...-sideways.html

    It has a very erudite reading of just what Einstein wrote, considered in full without taking partial quotes to remove their context.
    He's simply making the same mistake as you, misunderstanding what Einstein wrote. It's a fringe view.
    I don't see any Ice Giants.

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    I wrote yet another point-by-point answer to this. But then realised it was a waste of time and deleted it.

    I will just say this:

    Quote Originally Posted by Grimble View Post
    No, no, no. All I am assigning are relative positions. Each is only defined by its relationship to the others. So I can say exactly that.
    Without defining the frame of reference, you can't even say that. The fact that you don't understand that is the root of your problem.

    Yes, yes yes, I think you are beginning to understand what I am saying
    I understand perfectly what you are saying. That is how I know it is wrong.

    If so how?
    This is what people have been explaining to you over and over. (This is where I realised the entire enterprise is futile. I'm out.)

  7. #97
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    Quote Originally Posted by Grimble View Post
    One has to take into account that each is seeing the light travel with the speed of light in their rest frame
    What is the rest frame of the observer on the moving train? The frame that defines the coordinates when the train is at rest with respect to the embankment?
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  8. #98
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    Quote Originally Posted by Grimble View Post
    Space time exists, in-so-much that it is a description of the matter of the universe and how it is related in space and time. If you don't like the idea that it is fixed in any way, why not call it Wibbley-wobbley Timey-wimey stuff and have done with it.
    Just because you don't like the term?


    Quote Originally Posted by Grimble View Post
    Precisely. But not upon the speed of the Aircraft emitting the sound. It can, after all, travel faster than the sound can.
    The speed of sound measured from the aircraft certainly does depend on its airspeed, and on direction, very much unlike the speed of light. And yes, it can be exceeded, completely unlike the speed of light.


    Quote Originally Posted by Grimble View Post
    Explain. Have you understood what I am saying or have you merely dismissed it out of hand? (Which is of no help to anyone.)
    It is simply wrong. The difference in our understanding is not "about where it is observed from". You have several severe and fundamental misconceptions about relativity, which have already been detailed.


    Quote Originally Posted by Grimble View Post
    So? It was an analogy to show there are better analogies that a bullet.
    And it still fails. Thus illustrating both the unintuitive nature of relativity and your misunderstanding of it...


    Quote Originally Posted by Grimble View Post
    No, I do not see see any universal reference frame. A Reference Frame of any kind is something added. It is a way of defining coordinates, relative to a set point. Spacetime exists, the universe exists, whether we define reference frames or not.
    Your arguments against relativity of simultaneity are the same as arguing for a "special" universal rest frame, as events are quite plainly not required to be simultaneous in all frames.


    Quote Originally Posted by Grimble View Post
    Is that just the time for the acceleration? For , by definition, the time that passes in inertial frames of reference, is the same. That is one of my problems, you cannot just ignore the postulates when making your calculations.
    That question doesn't make any sense, and that is not a postulate of relativity. Here's the list: http://en.wikipedia.org/wiki/Postula...ial_relativity


    Quote Originally Posted by Grimble View Post
    I have no problem whatsoever with time dilation etc.
    Then you should have no problem with the fact that simultaneity can not be universal.


    Quote Originally Posted by Grimble View Post
    those calculations work wonderfully well, we all know that. But it is the measurements that change according to the conditions they are measured under. It is, as has been well established right from the start that it is the observed clock that slows.
    It slows for the stationary observer, which is why we talk of the clock having different readings depending on where it is measured from.
    Some one moving very fast relative to a clock reads the time differently, he does not, cannot affect, the way that time passes for a clock that he has no connection to. Or if there are two moving observers, is their slowing of the clock cumulative?
    So far as this makes any sort of sense, it just shows you once again stuck in a mindset with a special rest frame.


    Quote Originally Posted by Grimble View Post
    Exactly! They will have different coordinates from different frames.
    Yes. Including time coordinates. Events that happen at the same time but different locations in one frame happen at different times in other, equally-valid frames.


    Quote Originally Posted by Grimble View Post
    So please explain “Time is that quantity measured by time-measuring instruments. ”
    Define what you mean by time, because that definition is meaningless!
    It requires no further explanation, and is not meaningless.

    What you are doing is relativity denialism, nothing else. You claim otherwise, but you consistently misinterpret relativity to give an absolute, universal notion of space and time.

  9. #99
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    Quote Originally Posted by RobA View Post
    Quote Originally Posted by Grimble View Post
    Could you explain what my mistake is? What constitutes a Frame of Reference seems to be self evident, but that leaves me confused according to your understanding so could you explain?
    Let's take an example. Alice, Bob and Charlie are all in a room at 3pm. Alice and Bob are standing still talking to eachother. Now Alice (whose watch reads 2:55) likes Cartesian coordinates measured in centimetres from the bottom SouthWest corner of the room. Bob (whose watch reads 2:57) reckons everything in Polar coordinates from the lightbulb in the middle of the ceiling. Charlie (watch at 2:53) is sitting on top of a ramp, so he's using Cartesian coordinates with origin at the top corner of the ramp, and with the XY plane (and the Z axis) tilted at 30 degrees compared to Alice's. Oh, and he measures everything in inches.

    So, 3 totally different coordinate systems describing the room. Each has a unique set of (3 numbers plus a time) to map every point - every Event - in the room.
    Grimble, I've told you before, and I'll tell you again: You are using a different definition of the term "Frame of Reference" from the standard one used in Relativity. This is what's causing all the discussions to go round in circles. It is such an important concept that you'll never understand simultaneity - let alone Relativity - until you get it clear. The first step in working through that is to go through examples to identify points of difference - and that's the point of my question here.

    So, for the third time of asking: How many Frames of Reference are there in the example above?
    Please consider this a DIRECT question.

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    Quote Originally Posted by Luckmeister View Post
    From the blog:


    It's important to remember that from the train observer frame of reference as at rest, the lightning flashes occupy two separate frames, one being in motion towards the observer on the train and the other being in motion away.
    The lightning flashes are events, they happen at a particular time and place. i.e. They cannot be moving

  11. #101
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    Quote Originally Posted by Grimble View Post
    The lightning flashes are events, they happen at a particular time and place. i.e. They cannot be moving
    The space component certainly moves with the Frame of Reference - remember the scorchmarks !

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    Quote Originally Posted by RobA View Post
    Grimble, I've told you before, and I'll tell you again: You are using a different definition of the term "Frame of Reference" from the standard one used in Relativity. This is what's causing all the discussions to go round in circles. It is such an important concept that you'll never understand simultaneity - let alone Relativity - until you get it clear. The first step in working through that is to go through examples to identify points of difference - and that's the point of my question here.

    So, for the third time of asking: How many Frames of Reference are there in the example above?


    Please consider this a DIRECT question.

    Alice has a Frame of Reference where she is at the origin where her coordinate axes are centred.
    Similarly Bob and similarly Charlie. Three separate Frames of Reference with three separate sets of coordinates.
    HOWEVER, as they are each at rest, one with another, they will each be at rest in the other's Frames of Reference.
    If their coordinate axes are aligned, a simple conversion will let their coordinates be referred to one set of coordinates.

    So the answer to your question is four, 3 individual ones or one common one.

    My turn to ask a question, I think.

    When is a Frame of reference any more than a 'mapping' of Spacetime from a particular perspective? (that is giving Spacetime, and what is in it, Coordinates)

    Explained so well by Einstein with his invisible 'rigid framework'.

    So if this is wrong, what is the 'standard definition' used in relativity?

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    Quote Originally Posted by RobA View Post
    The space component certainly moves with the Frame of Reference - remember the scorchmarks !
    Yes, the space component certainly moves, but the lightning flashes, being events, only have a single set of coordinates in whichever frame one observes them.
    Consider if a fly hits the front of the train when they are each travelling, that event has a particular, unique, set of coordinates in both the trains frame of reference and the fly's frame of reference. Those coordinates are fixed in either frame.

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    Quote Originally Posted by pzkpfw View Post
    He's simply making the same mistake as you, misunderstanding what Einstein wrote. It's a fringe view.
    And what Minkowski described?

    Have you actually read it?

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    Quote Originally Posted by Grimble View Post
    Yes, the space component certainly moves, but the lightning flashes, being events, only have a single set of coordinates in whichever frame one observes them.
    And, just to clarify, those coordinates will be different for every frame of reference.

    [I know, I said I was out of here. But I thought it was worth clarifying that for any "lurkers" following this.]

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    Quote Originally Posted by Shaula View Post
    I stopped there. Clear lack of understanding of what is meant by a special frame of reference. Relativity says precisely nothing about the perceived 'complexity of events' - plus assuming non-simultaneous events are somehow more complex is nonsensical.
    I believe that it is best to let Einstein himself answer whether this has anything to do with Relativity:
    Quote Originally Posted by Einstein chapter V, the Principle of Relativity
    If, for instance, our embankment were the system K0, then our railway carriage would be a system K, relative to which less simple laws would hold than with respect to K0. This diminished simplicity would be due to the fact that the carriage K would be in motion (i.e. “really”) with respect to K0. In the general laws of natural which have been formulated with reference to K, the magnitude and direction of the velocity of the carriage would necessarily play a part.
    Last edited by Grimble; 2012-May-23 at 07:44 AM. Reason: formatting

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    Quote Originally Posted by pzkpfw View Post
    No. If the flash is seen as simultaneous by one observer, it won't be seen as simultaneous by the other. It is simply getting childish now, that you "agree" with what one of us writes, but then say we are saying what we are not.
    I am reading what you wrote.

    No, because you make a contradiction.

    One observer can't see the flashes of light reach themself at the same time, while the other observer sees the flashes of light reach that observer at different times. You are mis-reading the situation. The initial flashes of light, regardless of what frame you look at, will reach some observer at some time. The same two flashes of light can't reach an observer M at the same time, according to observer M, and reach observer M at different times according observer N.

    If two cars crash into the same lamp post, at the same time, all observers will agree that they crashed at the same time. There's no observer who can see/measure/calculate that one of the cars hit the post 30 seconds before the other.

    But if those lamp posts are physically separated, one in London and one in Moscow, then we can have observers who in their own frame of reference think the crashes were siumultaneous or not. They actually can't agree.

    In the lights/train/embankment thought experiment, everyone will agree whether the flashes hit an observer at the same time or not. But that doesn't mean the two observers M and M' will both experience the same thing.

    The flashes being generated, is the equivalent of the cars hitting the separate lamp posts. The flashes of light hitting an observer are the equivalent of the cars hitting the same lamp post.

    No observers can disagree that the cars hit the same lamp post at the same time. You can't have one observer say "well, the lamp post was moving relative to me, so the blue car must have hit it first". That just can't happen. If one observer sees the cars hit the same lamp post at the same time, then all observers must.

    Similarly, you can't have an observer see the two flashes of light hit them at the same time, while another observer sees them hit at different times. This is the nonsense of your idea that the flashes are simultaneous for all observers, but observers may simply "think" or "see" the flashes hit other observers at different times. That just can't work.
    But that is exactly how SR works!

    Your summary is firmly set in the world of Galileian Relativity.

    Simultaneity is seen by an observer who is at rest at the mid point between the two lightning strikes. That is Einstein's definition. Right?

    In the embankment Frame of Reference M is permanently fixed at that mid-point, where everything is stationary according to the embankment observer.
    In the Frame of Reference of the passenger, it is the train that is stationary, it is M' that is permanently fixed at the mid-point of points A & B on the train.

    The lightning strikes when A on the train is adjacent to A on the embankment and when B on the train is at B on the embankment:
    Quote Originally Posted by Einstein, chapter IX
    But the events A and B also correspond to positions A and B on the train.
    So where do the lightning flashes meet? They meet at point P in spacetime, that is mapped by the coordinates of M in the embankments Frame of Reference and mapped by the coordinates of M' in the train's Frame of Reference.

    The passenger on the train CANNOT be moving towards one flash and away from the other, in her Frame of Reference, for to do so the light would be travelling at different speeds from the two flashes! No in the train's frame of reference it is the observer M who is travelling in relation to the points A & B on the train.

    Oh, my goodness, why can you not see it? It is simple basic and at the very heart of relativity. It is relative so what one sees is the reciprocal of what the other sees. One can swap the parties and the maths is the same, that is the way relativity works.

    You are not wrong, but limited by how far you are willing to tread along the path of relativity. It is just a short step to realising te full extent of what Einstein and Minkowski were saying.
    Last edited by Grimble; 2012-May-23 at 07:47 AM. Reason: formatting

  18. #108
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    Quote Originally Posted by Grimble View Post
    The passenger on the train CANNOT be moving towards one flash and away from the other, in her Frame of Reference, for to do so the light would be travelling at different speeds from the two flashes!
    Correct* : which is part of why the two observers can't agree on whether the flashes were simultaneous. Where there is one observer for whom the flashes were simultaneous (whichever observer it is), the flashes reach the other observer (in motion relative to that first observer) at different times. That can't contradict what that other observer experiences for themself! Thus the flashes won't be simultaneous for that other observer (whichever way around it is).

    The "vice versa" in the referenced paper means that any observer could be in the situation of knowing the flashes were simultaneous - for them but not for the other observers. It doesn't mean that all observers will see the same flashes as simultaneous but only "see" them as not, for the the other observers. That's a silly contradiction in the actual observations each observer can make, and quite a twisted reading of the paper.

    (* Did you even read my treatment using bullets? This covers the fact that both observers can consider the shots as simultaneous, but this relies on one observer being able to consider the other observers bullets as having speeds +/- according to the relative motion. That can't apply to light.)

    For the train observer to decide the flashes were simultaneous (given a scenario where the flashes were simultaneous for the embankment observer), and given the constant speed of light, and given the train observer can consider their own frame as their own "at rest" frame, then the flashes must have come from A' and B', which are equidistant from M'. But in that case, A is not the same event as A', and B is not the same event as B'. The two observer can not both consider the flashes as simultaneous.

    Quote Originally Posted by Grimble View Post
    No in the train's frame of reference it is the observer M who is travelling in relation to the points A & B on the train.
    Yes, which is why the train observer could see that the flashes were simultaneous, if they were in his or her frame, but in that case the embankment observer won't.


    Here's a very simple set-up, introduced earlier by another member but for which I'd now appreciate very specific answers:
    i) Assume embankment and train, pretty much as described in the referenced paper.
    ii) The observer on the train wears a device that detects the two flashes, and has it's own light that lights up green if the device detects the two flashes at the same time, or blue if it detects one flash before the other.
    iii) Assume the embankment observer detects the two flashes at the same time, and concludes that the flashes were simultaneous with reference to the embankment.
    iv) The light from the device worn by the train observer, is visible (when it lights up) to the embankment observer.

    Question 1: What colour does the embankment observer see the device light up with?
    Question 2: What colour does the train observer see the device light up with?
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  19. #109
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    Quote Originally Posted by Grimble View Post
    So the answer to your question is four, 3 individual ones or one common one.
    Great - thanks for that. However, I think we've identified on cause of the misunderstandings. Whenever we make a statement about Frame of Reference, you have 4 definitions to choose from, and to map the words of our sentence to your understanding. Naturally, with 4 choices, sometimes you'll agree, and then sometimes not - in what, to us, appears an arbitrary fashion.

    So far as everyone else in this discussion is concerned, in Relativity the term "Frame of Reference" unambiguously, ALWAYS, and everywhere refers SOLELY to the COMMON ONE (the others are mere translations of coordinates). So it would greatly help if you can remember that we ALWAYS use it that way, and for you to do so as well - Thanks

    So, to continue the example, let's assume they all choose to use axes as the edges of the room, with origin in the SouthWest corner. So, the NorthEastCeiling corner might be at (100m, 300m, 3m) in some units. So,every point in the room is defined by coordinates (0 <= x <= 100, 0 <= y <= 300, 0 <= z <= 3). (we'll say x is heading North). Also by definition, any point with coordinates outside those ranges is outside the room.

    Quote Originally Posted by Grimble View Post
    My turn to ask a question, I think.
    When is a Frame of reference any more than a 'mapping' of Spacetime from a particular perspective? (that is giving Spacetime, and what is in it, Coordinates)
    Explained so well by Einstein with his invisible 'rigid framework'.
    So if this is wrong, what is the 'standard definition' used in relativity?
    For a single individual (or group stationary relative to themselves), then that's all it is pure and simple. A fixed coordinate system spreading out from some nominated origin.
    The point is, when you introduce someone in motion, then they have their own Frame of Reference (and remember, we're using the unambiguous definition of the term).

    For example, let's say David is moving through the room along the X axis. Hey, we'll also say Edith is with him 2m away. So, David and Edith share the same Frame of Reference (ie. they've agreed a fixed set of coordinates). However, this Frame of Reference is different from ABC's. (remember, unambiguous definition).

    So what does this mean? As D hits the SouthWest corner of the room, he shares the Origin point with ABC. However, for him (and for Edith), the NorthEastCeiling corner is at (90m, 300m, 3m). The point (95m, 300m, 3m) is outside the room.

    Same room. Same Origin. The coordinate systems are different. Do you agree?
    Last edited by RobA; 2012-May-21 at 12:12 PM. Reason: Ask agreement, and oops, fixed up y coords

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    Quote Originally Posted by Grimble View Post
    So where do the lightning flashes meet? They meet at point P in spacetime, that is mapped by the coordinates of M in the embankments Frame of Reference and mapped by the coordinates of M' in the train's Frame of Reference.
    You are still assuming an absolute "spacetime" and that there exists an absolute measure for P. Hint, there isn't one.

    There is no spacetime to define P as an absolute though, there is only what observers see, which is that there is a point P on the embankment frame where they meet (at M), and there's a P' in the frame of the train where they meet (a bit behind M' because for that observer the flashes where not simultaneous).

    Note that the two observers will agree on where in the respective frames P and P' are, as that can be observed by setting up strategically aligned mirrors at P and P' that'll turn one of the flashes so both observers can see that P and P' were the points in the two frames where the flashes arrived simultaneously.
    There is no paradoxical disagreement on where these points are in the frames; both observers can observe that the two flashes arrive at P at the same time and both observers can observe that the two flashes arrive at P' at the same time.
    There will be disagreement on when the flashes arrive a P and P' and for M', the fact that P' is slightly behind her (as defined by the direction of the train's travel relative to the embankment) there's a clear observation that the flashes where not simultaneous.
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    I believe that it is best to let Einstein himself answer whether this has anything to do with Relativity
    The quote you give is not relevant. The blog states that more complex events are the key to the reasoning it uses. Relativity is about the laws that govern them. Events can be arbitrarily complex yet descried by simple laws. So the argument that 'I think things look all complicated' is utterly irrelevant and your quote does not counter that. Read the bit I quoted - it is fundamentally flawed logic.

    Edit: Plus read the last bit I quoted again. Are you really using a quote from Einstein to try to justify this conclusion?

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    Another example (though my questions in post #108 still need to be answered), from "The Evolution of Physics", Albert Einstein and Leopold Infeld.

    My hardcover edition by Touchstone (Simon and Schuster), July 2008. This from page 178:

    Once more, the example of the moving room with outside and inside observers will be used. Again a light signal is emitted from the center of the room and again we ask the two men what they expect to observer, asuming only our two principles and forgetting what was previously said concerning the medium through which the light travels. We quote their answers:
    The inside observer: The light signal traveling from the center of the room will reach the walls simultaneously, since all the walls are equally distant from the light source and the velocity of light is the same in all directions.
    The outside observer: In my system1, the velocity of light is exactly the same as in that of the observer moving with the room. It does not matter to me whether or not the light source moves in my CS since its motion does not influence the velocity of light. What I see is a light signal traveling with a standard speed, the same in all directions. One of the walls is trying to escape from and the opposite wall to approach the light signal. Therefore, the escaping wall will be met by the signal a little later than the approaching one. Although the difference will be very slight if the velocity of the room is small compared with that of light, the light signal will nevertheless not meet these two opposite walls, which are perpendicular to the direction of the motion, quite simultaneously.
    Comparing the predictions of our two observers we find a most astonishing3 result which flatly contradicts the apparently well-founded concepts of classical physics. Two event, i.e., the two light beams reaching the two walls, are simultaneous for the observer on the inside, but not for the observer on the outside2 ...
    There's more, but I don't want to breach "fair use" rules on a copyrighted work.

    Things to note:

    In this book, "CS" means "frame of reference" (via "co-ordinate system").

    1. The view of the outside observer is reported by the outside observer. It's not an assumption for the outside observer by the inside observer. This blows away the Grimble assertion that in the train/embankment version of the thought experiement, that it's all just the view of the embankment observer, of the train observer, and that that train observer would actually themselves see the flashes as simultaneous.

    2. The basic learning of this is exactly what current science expects: "Comparing the predictions of our two observers we find a most astonishing result which flatly contradicts the apparently well-founded concepts of classical physics. Two event, i.e., the two light beams reaching the two walls, are simultaneous for the observer on the inside, but not for the observer on the outside". Again, it's not just about the view of one frame from another, the two frames will actually disagree about whether event were simultaneous.

    3. Note how the result is described as "astonishing". If this whole thing were merely about observation, it'd hardly be more exciting than noting that someone sitting closer to one drum than another, will hear the nearer drum first! It's "astonishing" that (spatially separated) events which are simultaneous for one observer, can't actually be simultaneous for different observers (if in relative motion).
    Last edited by pzkpfw; 2012-May-21 at 09:10 PM. Reason: Inside the quote tags, had to change Italic to Underline.
    I don't see any Ice Giants.

  23. #113
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    Quote Originally Posted by pzkpfw View Post
    Correct* : which is part of why the two observers can't agree on whether the flashes were simultaneous.
    Yes. Because each will deny that the other sees them as simultaneous.
    Where there is one observer for whom the flashes were simultaneous (whichever observer it is), the flashes reach the other observer (in motion relative to that first observer) at different times.
    Yes. As seen from that observer's frame.
    That can't contradict what that other observer experiences for themself!
    Hmmm!
    The observer who sees simultaneity, sees, from his frame that the lights do not reach the other simultaneously. There is a difference in what is seen, in the two frames.
    Thus the flashes won't be simultaneous for that other observer (whichever way around it is).
    Yes, exactly, but only as seen from the first observer. As I say: simultaneous as seen within their own frame but not as seen from the other frame. I.e relative to where they are seen from.

    (* Did you even read my treatment using bullets? This covers the fact that both observers can consider the shots as simultaneous, but this relies on one observer being able to consider the other observers bullets as having speeds +/- according to the relative motion. That can't apply to light.)
    agreed.
    Yes, which is why the train observer could see that the flashes were simultaneous, if they were in his or her frame, but in that case the embankment observer won't.
    Yes, yes, yes! I think you are getting what I am saying. Reciprocity.

    Here's a very simple set-up, introduced earlier by another member but for which I'd now appreciate very specific answers:
    i) Assume embankment and train, pretty much as described in the referenced paper.
    ii) The observer on the train wears a device that detects the two flashes, and has it's own light that lights up green if the device detects the two flashes at the same time, or blue if it detects one flash before the other.
    iii) Assume the embankment observer detects the two flashes at the same time, and concludes that the flashes were simultaneous with reference to the embankment.
    iv) The light from the device worn by the train observer, is visible (when it lights up) to the embankment observer.

    Question 1: What colour does the embankment observer see the device light up with?
    Question 2: What colour does the train observer see the device light up with?
    Answer 1: Green
    Answer 2: Green

    However, the embankment observer will continue to insist that the wrong light was lit as he could see that the two lights were not simultaneous.

    What is seen in each frame depends on the relative motion of both reference frames to the events.
    From each it will appear that the other frame is moving and that, therefore, the fixed point in the other frame M, or M' will be moving away from central point as they determine it in their reference frame.
    Last edited by tusenfem; 2012-May-23 at 09:33 AM. Reason: corrected quote tag

  24. #114
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    Quote Originally Posted by RobA View Post
    Great - thanks for that. However, I think we've identified on cause of the misunderstandings. Whenever we make a statement about Frame of Reference, you have 4 definitions to choose from, and to map the words of our sentence to your understanding. Naturally, with 4 choices, sometimes you'll agree, and then sometimes not - in what, to us, appears an arbitrary fashion.

    So far as everyone else in this discussion is concerned, in Relativity the term "Frame of Reference" unambiguously, ALWAYS, and everywhere refers SOLELY to the COMMON ONE (the others are mere translations of coordinates). So it would greatly help if you can remember that we ALWAYS use it that way, and for you to do so as well - Thanks

    So, to continue the example, let's assume they all choose to use axes as the edges of the room, with origin in the SouthWest corner. So, the NorthEastCeiling corner might be at (100m, 300m, 3m) in some units. So,every point in the room is defined by coordinates (0 <= x <= 100, 0 <= y <= 300, 0 <= z <= 3). (we'll say x is heading North). Also by definition, any point with coordinates outside those ranges is outside the room.


    For a single individual (or group stationary relative to themselves), then that's all it is pure and simple. A fixed coordinate system spreading out from some nominated origin.
    The point is, when you introduce someone in motion, then they have their own Frame of Reference (and remember, we're using the unambiguous definition of the term).

    For example, let's say David is moving through the room along the X axis. Hey, we'll also say Edith is with him 2m away. So, David and Edith share the same Frame of Reference (ie. they've agreed a fixed set of coordinates). However, this Frame of Reference is different from ABC's. (remember, unambiguous definition).

    So what does this mean? As D hits the SouthWest corner of the room, he shares the Origin point with ABC. However, for him (and for Edith), the NorthEastCeiling corner is at (90m, 300m, 3m). The point (95m, 300m, 3m) is outside the room.

    Same room. Same Origin. The coordinate systems are different. Do you agree?
    I think so, assuming that the ABC coordinates are different from DE coordinates? Which I suppose they must be if one takes into account that they are moving?

    And yes, agreed: The point (95m, 300m, 3m) is outside the room.

  25. #115
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    Quote Originally Posted by HenrikOlsen View Post
    You are still assuming an absolute "spacetime" and that there exists an absolute measure for P. Hint, there isn't one.
    So what are the frame of reference referencing? Are you suggesting that they exist separately? What is it that is being observed, where does it exist?

  26. #116
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    Quote Originally Posted by Grimble View Post
    Answer 1: Green
    Answer 2: Green

    However, the embankment observer will continue to insist that the wrong light was lit as he could see that the two lights were not simultaneous.
    Hilarious.

    Does anyone know if there are any experimental results which are directly equivalent to this setup? This might help to demonstrate quite how far from reality Grimble has drifted.

  27. #117
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    Quote Originally Posted by pzkpfw View Post
    Another example ... from "The Evolution of Physics", Albert Einstein and Leopold Infeld.

    My hardcover edition by Touchstone (Simon and Schuster), July 2008. This from page 178:



    There's more, but I don't want to breach "fair use" rules on a copyrighted work.

    Things to note:

    In this book, "CS" means "frame of reference" (via "co-ordinate system").

    1. The view of the outside observer is reported by the outside observer. It's not an assumption for the outside observer by the inside observer.
    Yes, agreed, and it is the outside observer's assertion that the inside observer's test for simultaneity – that the light reaches the two walls simultaneously – fails as observed from the outside.
    This blows away the Grimble assertion that in the train/embankment version of the thought experiement, that it's all just the view of the embankment observer, of the train observer, and that that train observer would actually themselves see the flashes as simultaneous.
    No, not at all, it agrees exactly with that assertion.
    It is the view of the outside observer, of the inside observer.
    The outside observer's version of the test for simultaneity would be whether the lights would have reached the walls simultaneously if the room had not been moving relative to the outside observer.

    2. The basic learning of this is exactly what current science expects: "Comparing the predictions of our two observers we find a most astonishing result which flatly contradicts the apparently well-founded concepts of classical physics. Two event, i.e., the two light beams reaching the two walls, are simultaneous for the observer on the inside, but not for the observer on the outside". Again, it's not just about the view of one frame from another, the two frames will actually disagree about whether event were simultaneous.
    Which is exactly what I am saying
    the two frames will actually disagree about whether event were simultaneous.
    3. Note how the result is described as "astonishing".
    the authors opinion, not a scientific judgement
    If this whole thing were merely about observation, it'd hardly be more exciting than noting that someone sitting closer to one drum than another, will hear the nearer drum first! It's "astonishing" that (spatially separated) events which are simultaneous for one observer, can't actually be simultaneous for different observers (if in relative motion).
    I find it astonishing that each thinks that only they can see the simultaneity.

  28. #118
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    Quote Originally Posted by Strange View Post
    Hilarious.

    Does anyone know if there are any experimental results which are directly equivalent to this setup? This might help to demonstrate quite how far from reality Grimble has drifted.
    I am glad that you can see the humour in this situation, Strange. Because all we are doing is going round and round without having established any common base for our discussions.

    Perhaps it would be better to turn my attention to addressing some very basic concepts?

    Should we start a new thread and leave this one to slowly gyrate on its own?

    I think a look at frames of reference, and what space-time is, what space and time are, and how they relate would be a good starting point.

    What physical properties does a body possess? It has dimensions, mass, density. Are those absolute? If not how do they vary and how do we relate those variations?

  29. #119
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    Quote Originally Posted by Grimble View Post
    Perhaps it would be better to turn my attention to addressing some very basic concepts?
    It might be, but over many threads here (and elsewhere) you have demonstrated that you are unwilling to be open-minded enough to understand the basic concepts.

  30. #120
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    Quote Originally Posted by pzkpfw View Post
    Using guns and bullets instead of light:

    N is on a train moving right. A and B are guns pointing at her.
    The real question is: did the post train get away or did the robbers get their loot?

    Teaching relativity by western movies, there might be something in there...

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