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Thread: Timey-wimey Wibbly-wobbly Stuff

  1. #31
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    Quote Originally Posted by Grimble View Post
    But when one has an observer who is moving relative to a Frame of reference, that movement is reciprocal, relative movement. <snip>If two events are simultaneous they happen at the same point on the time dimension - because it is a dimension.
    Let's consider this, relating to Time Dilation. Let's say you and I are whizzing past eachother, such that gamma works out at 60 (or is that 1/60th?) This means you see your clock ticking normally, and see my clock ticking so slow that it your clock advances one minute before you see mine advance one second. All well and good.

    So, you draw up a space-time diagram, with 3 dimensions of space and one of time. The time dimension is really easy - you simply graduate it in your minutes, and also mark off each of my seconds (at your minute marks). Two events then happen - were they simultaneous? Simply check the time scale.

    The trouble is, as you noted above, that everything must be reciprocal. If you see my clock ticking 60 times slow, then I see yours ticking 60-times slow relative to mine (ie. my clock advances a minute in the time it takes me to see yours advance a second). Remember, my view is every bit as "valid" or "real" as yours. Equally, I can also draw up my space-time diagram, graduated with my units.

    So, lets combine yours and mine space-time diagrams into a "God's-Eye" view. How would we draw up the axis for the time dimension such that it accurately captures the fact that one of my seconds equates to one of your minutes, together with one of your seconds equates to one of my minutes?

    Clearly, this is impossible - which means the concept of a global time axis is also impossible. This, in turn, means it is impossible to give a unique global (ie. over all frames) time coordinate to an event. This renders the attempt to state that two events have the same "time" coordinate across all frames as futile.

  2. #32
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    Quote Originally Posted by Shaula View Post
    As I said, proper intervals are fine. But you made the leap from the concept of a proper length/distance/time to absolute time. Which is not a valid leap to make.
    That is an easy judgement to make. Can you substantiate it?

    You originally said you do not need a frame to measure that distance - in this latest post you are then showing that you do. In every frame there is proper length/time - and all are equally valid. There is no absolute underlying frame we can point to in order to define unambiguously 'simultaneous'.
    No, I am not showing that one needs a Frame of reference to measure a distance all one needs is a scale to measure it with.
    All measurements, however they are made are comparisons against a scale, it is how measurements work.

    Two points in space have the same separation whether they are measured or not. Measuring that separation does not change it. It is something that exists. Using a Frame of reference enables one to place that distance within Spacetime with respect to some other point, it is mapping what is there.

    In spacetime two events are simultaneous if they are at the same mark on the time scale, at the same place in the time-like dimension. That, after all, is what the time-like dimension is. It is the definition of what a dimension is.

    How can simultaneity be anything other than the same place in a dimension?

    If two events, at the same point in a time-like dimension are not simultaneous how can that possibly work? It would be making nonsense of the concept of a dimension!

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    How can simultaneity be anything other than the same place in a dimension?
    Because the concept of simultaneity is not what you seem to think it is. All it means is that two events appear to occur at the same time in a frame of reference. It is not an absolute concept, it is a relative one.

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    I'm sorry but that is going against the whole concept of having dimensions!

    Every event in spacetime has a particular location, a particular time - that is after all what makes it an event.

    A Frame of reference is merely a way of showing a single view of Spacetime it changes nothing.

    A Frame of reference is no more than the name says - a framework against which times and locations can be referred.

    If you like the most basic, ultimate Frame of reference is spacetime itself! In that frame of reference one can take all space and time and relate it to any known event. Each and every view is relative to a fixed point - but that is all they are - views.

    And yes all times and locations are relative - together they make a whole - a whole that is spacetime.

    If one were to look at two poles, A & B, and one, A, is nearer to you in your frame of reference, then to another observer on the far side of them, B will B the nearer pole. Going from one view to the other changes the relationship to the viewer, not their relationships in Spacetime.

    This is exactly as described by Minkowski's 'Space and Time (1920)' http://en.wikisource.org/wiki/Space_and_Time and Einstein's 'Relativity: The Special and General Theory (1920)' http://www.bartleby.com/173/9.html.

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    I'm sorry but that is going against the whole concept of having dimensions!
    No, it is going against your concept of 'having dimensions' as meaning embedded in some special, universal frame of reference.

    If you like the most basic, ultimate Frame of reference is spacetime itself!
    That is the problem - according to current theory it is not. No frame is more special than any other. There is no absolute spacetime underlying everything. There has been some interesting but so far speculative work on how spacetime is 'stitched together' from microframes.

    If one were to look at two poles, A & B, and one, A, is nearer to you in your frame of reference, then to another observer on the far side of them, B will B the nearer pole. Going from one view to the other changes the relationship to the viewer, not their relationships in Spacetime.
    Two events, A and B. One observer says A happened before B, another says B happened before A, and an observer in the same frame as the events said they happened together. All equally valid views, equally real.

  6. #36
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    This thread seems to have gotten away from simple Q&A and more into a discussion (and some of that has been dangerously close to ATM). Discussions are better handled in S&T so...

    Thread moved.
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  7. #37
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    Quote Originally Posted by Shaula View Post
    No, it is going against your concept of 'having dimensions' as meaning embedded in some special, universal frame of reference.


    That is the problem - according to current theory it is not. No frame is more special than any other. There is no absolute spacetime underlying everything. There has been some interesting but so far speculative work on how spacetime is 'stitched together' from microframes.


    Two events, A and B. One observer says A happened before B, another says B happened before A, and an observer in the same frame as the events said they happened together. All equally valid views, equally real.
    I don't think that you can have ever looked at a Frame of reference as to what it is, rather than how it works.

    It defines nothing it it merely a different perspective.

    Either two things happen simultaneously or they don't. However that might seem from different perspectives.

    And two things simultaneous will appear to be simultaneous from each and every frame of reference, when viewed as they appear within that frame of reference and observed by an observer within that same frame of reference.

    You are mixing that up wit the fact that they will not appear to be simultaneous from an observer looking at them in another frame of reference.

    Show me an example where that is not true. Show me something that is simultaneous when existing and observed from within the one frame of reference, that appears not to be simultaneous when we see how it appears in another frame of reference when observed from within that frame of reference.

    I believe that your problem understanding what I am saying arises from this diagram: http://upload.wikimedia.org/wikipedi...aneity.svg.png

    Where we see that only the green frame sees simultaneity. But that is because the blue and red frames are being observed by the observer in the Green Frame of reference.

    If that same situation were observed by the red observer it is the red frame that would show simultaneity, and if by the blue observer then it would be the blue frame and in neither of those cases would the green frame show simultaneity!

    Onw has to be sure of both what is being observed and where it is being observed from.

    The simople logic of this has screamed at me ever since I first saw it! Please do the scientific thing and Think about it before automatically deciding based on prejudice.

    It really is very simple and that is why I question where I am going wrong if someone can show me where I am misunderstanding it, what is wrong with my logic, I will be satisfied.

    But merely saying 'that is wrong' without any reasoning proves nothing.

    All I want is calm reasonable cold logic!

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    Quote Originally Posted by Grimble View Post
    I don't think that you can have ever looked at a Frame of reference as to what it is, rather than how it works.
    I'm sorry, but it is you who doesn't understand. Your claims are in conflict with predictions and observations of relativistic effects.


    Quote Originally Posted by Grimble View Post
    Either two things happen simultaneously or they don't. However that might seem from different perspectives.
    Simultaneity is purely local, it is not definable globally.


    Quote Originally Posted by Grimble View Post
    You are mixing that up wit the fact that they will not appear to be simultaneous from an observer looking at them in another frame of reference.
    No, they will not be simultaneous in all frames.


    Quote Originally Posted by Grimble View Post
    Show me an example where that is not true. Show me something that is simultaneous when existing and observed from within the one frame of reference, that appears not to be simultaneous when we see how it appears in another frame of reference when observed from within that frame of reference.
    The classic example is Einstein's train. It's described in detail in a variety of places.


    Quote Originally Posted by Grimble View Post
    Onw has to be sure of both what is being observed and where it is being observed from.
    No. It's not an illusion caused by viewing a system from another frame. Two observers can start out in a shared frame, part ways and take different paths through spacetime, rejoin each other, and find that they have experienced different amounts of time. We have actually done this experiment, and must take it into account when dealing with high precision clocks.


    Quote Originally Posted by Grimble View Post
    The simople logic of this has screamed at me ever since I first saw it! Please do the scientific thing and Think about it before automatically deciding based on prejudice.
    Do you really think people are prejudiced to believe that time and space are relative? You are the one clinging to your preconceptions and intuitive understanding.


    Quote Originally Posted by Grimble View Post
    It really is very simple and that is why I question where I am going wrong if someone can show me where I am misunderstanding it, what is wrong with my logic, I will be satisfied.
    As you've already been told many times, you're assuming a preferred reference frame. That is the fundamental flaw in your logic...there isn't a preferred reference frame.


    Quote Originally Posted by Grimble View Post
    But merely saying 'that is wrong' without any reasoning proves nothing.

    All I want is calm reasonable cold logic!
    You're not being logical. You're rejecting anything that doesn't agree with your existing intuitive understanding, in spite of a great deal of observational evidence that your understanding is wrong.

  9. #39
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    And two things simultaneous will appear to be simultaneous from each and every frame of reference, when viewed as they appear within that frame of reference and observed by an observer within that same frame of reference.
    In which case, by your definition, all events are simultaneous. Because give me 2 events and I can find a frame in which they are simultaneous.

    cjameshuff has done a good job on the rest of the post. I see no need to repeat it.

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    Quote Originally Posted by cjameshuff View Post
    The classic example is Einstein's train. It's described in detail in a variety of places.
    But in Einstein's train everything, that is the embankment and the train, is observed from the Embankment! If you look at how it would be when observed from the train - he answers that - "vice versa".

    This just proves my point; although it would take a brave person to look at it with an open mind rather than repeating What they have been told is there

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    This just proves my point; although it would take a brave person to look at it with an open mind rather than repeating What they have been told is there
    Actually when we did SR modules at Uni we went through a range of examples, worked through the basics and found we agreed with 'what we have been told is there'. The train example certainly doesn't prove your point, it disproves it.

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    Quote Originally Posted by Grimble View Post
    But in Einstein's train everything, that is the embankment and the train, is observed from the Embankment! If you look at how it would be when observed from the train - he answers that - "vice versa".

    This just proves my point; although it would take a brave person to look at it with an open mind rather than repeating What they have been told is there
    Yes. Your misunderstanding of the classic train thought experiment (you've been through this before on BAUT) shows you are arguing against current science. Thread moved to ATM. 30 days starts from the original opening of this Q&A stealth ATM thread.
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    Time to get serious

    Quote Originally Posted by pzkpfw View Post
    Yes. Your misunderstanding of the classic train thought experiment (you've been through this before on BAUT) shows you are arguing against current science. Thread moved to ATM. 30 days starts from the original opening of this Q&A stealth ATM thread.
    Grimble, please supply us with observations (NOT assertions) and math (from the observations) to support your claim that there is an absolute frame of reference.

    Thanks, John M.
    Last edited by John Mendenhall; 2012-May-08 at 09:07 PM. Reason: Clarity
    I'm not a hardnosed mainstreamer; I just like the observations, theories, predictions, and results to match.

    "Mainstream isnít a faith system. It is a verified body of work that must be taken into account if you wish to add to that body of work, or if you want to change the conclusions of that body of work." - korjik

  14. #44
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    Quote Originally Posted by Grimble
    Show me something that is simultaneous when existing and observed from within the one frame of reference, that appears not to be simultaneous when we see how it appears in another frame of reference when observed from within that frame of reference
    Quote Originally Posted by Grimble View Post
    But in Einstein's train everything, that is the embankment and the train, is observed from the Embankment! If you look at how it would be when observed from the train - he answers that - "vice versa".

    This just proves my point; although it would take a brave person to look at it with an open mind rather than repeating What they have been told is there
    Let's see the vice-versa quote in context from your own link at http://www.bartleby.com/173/9.html (bold mine):
    Observers who take the railway train as their reference-body must therefore come to the conclusion that the lightning flash B took place earlier than the lightning flash A. We thus arrive at the important result:
    Events which are simultaneous with reference to the embankment are not simultaneous with respect to the train, and vice versa (relativity of simultaneity).
    First off, please explain how Einstein's quote above "proves your point" that "two things simultaneous will appear to be simultaneous from each and every frame of reference".

    Let's examine the train scenario a bit closer. An extremely long train is passing a 200m embankment left-to-right. We'll extend the analogy a bit (sorry Albert!) by saying that the lightning strikes leave scorch marks where they hit, on both the embankment and the train.

    Now, we all agree that the observer in the middle of the embankment says that the strikes were simultaneous. What's the definition of simultaneous? In this case, that he receives light from both strikes at the same time AND that he is equidistant from each spot where the strikes happened. Where did the strikes happen? At each end of the embankment, of course - where the scorchmarks are.

    OK, how about the observer on the train. Like the observer on the embankment, he gets the light from both strikes at the same time. Is he equidistant from where the strikes happened?

    NO !

    The scorch marks on the embankment are moving relative to him - the one on the left is moving away, the one on the right is coming towards him. This means they are not in his frame of reference. To try to use the embankment's scorchmarks would be as silly as using the train's scorchmarks for the observer on the embankment. For the train observer, the lightning strikes happened at the scorchmarks on the train. They are the ones stationary relative to him. So, was he equidistant to those? No - he can't be. When the strikes happened, a certain amount of time passed until the light reached the middle of the embankment. During that time, the train was moving, bringing that observer level towards the middle - which means that observer must have been closer to the left at strike-time. So, when he measures the distance to each scorchmark, he'd find, say, that it's 80m towards the back, and 120m towards the front. Since he received the light from both at the same time, then for him, the front-strike MUST have hit earlier than the back.

    So I've got a question for you now You wake up in a railway carriage and glance out the window, and notice you're directly opposite a man at the middle of a 200m embankment. Just at that moment, you get the light from two lightning strikes front and back. You get up and measure the distance to the scorchmarks of each strike - they're both 100m away from you.

    QUESTION: Did the strikes happen simultaneously for the observer on the embankment?

    Oh, I forgot to mention whether the train was moving or not. Not to worry - I'll do that after you've posted your reply

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    The lightning strikes, A & B, are two events in spacetime.

    The light from them will meet at event P situated midway between them in space and at a time t later than Events A & B.

    An observer who is stationary at the location of P will determine that those two events are simultaneous.

    Any and every Frame of reference will be stationary to an observer within that Frame of Reference.

    Observed from the Embankment's Frame of Reference A & B are points on the railway. The observer WHO IS STATIONARY AT POINT P is the embankment Observer at point M in his Frame of reference. He will say that in the Embankment's Frame of Reference the lightning strikes are simultaneous but that the Passenger on the train who passes point P as the lightning strikes will not see simultaneity as his motion will have taken him away from P by the time the light reaches there.


    From the Train's Frame of Reference, A & B are points on the Train, and the observer WHO IS STATIONARY AT POINT P is the passenger Observer at point M' in her Frame of Reference. He will say that in the Train's Frame of Reference the lightning strikes are simultaneous but that the Observer on the Embankment, standing at M, passes point P as the lightning strikes and so will not see simultaneity as his motion will have taken him away from P by the time the light reaches there.

    You see it is all due to each Frame of Reference being stationary to themselves and moving to all the others.

    As for a preferred frame of reference No there is none as Einstein said.

    But then Frames of reference are mental constructs that we use to map Space time.

    Spacetime exists. times and locations exist within spacetime, what spacetime lacks as far as being a Frame of Reference is coordinates.

    We give spacetime coordinates when we define frames of reference. And that is all they are a way of locating and defining our mapping coordinates.

    That is why we can have no preferred frame of reference.

    Time and space in spacetime are fixed, isotropy and homogeneity. Relativity is all about how we relate those different 'maps' of spacetime.

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    Quote Originally Posted by Grimble View Post
    Any and every Frame of reference will be stationary to an observer within that Frame of Reference.
    I don't know if this obviously wrong statement is part of the source of your confusion or if you have just thrown it out there to confuse the issue. Clearly, only frames of reference which are stationary with respect to the observer will be stationary with respect to the observer. Frames of reference which are in motion relative to the observer will not be stationary with respect to the observer.

    Observed from the Embankment's Frame of Reference A & B are points on the railway. The observer WHO IS STATIONARY AT POINT P is the embankment Observer at point M in his Frame of reference. He will say that in the Embankment's Frame of Reference the lightning strikes are simultaneous but that the Passenger on the train who passes point P as the lightning strikes will not see simultaneity as his motion will have taken him away from P by the time the light reaches there.

    From the Train's Frame of Reference, A & B are points on the Train, and the observer WHO IS STATIONARY AT POINT P is the passenger Observer at point M' in her Frame of Reference. He will say that in the Train's Frame of Reference the lightning strikes are simultaneous but that the Observer on the Embankment, standing at M, passes point P as the lightning strikes and so will not see simultaneity as his motion will have taken him away from P by the time the light reaches there.
    What you seem to be saying is that both observers will see the lightning as simultaneous but will think that the other does not. Is that correct?

    As you want to base your argument on "logic" rather than the mathematics of relativity, let's try this:

    Let us consider the case where the observer on the train has a little electronic device that has a light detector on each side. If it detects a flash simultaneously (1) on each side, it will light a green LED display saying "YES", if the flashes are not coincident then the display shows "NO" in red. Now, according to your reasoning above, the observer on the train will see a green "YES" and the observer on the platform will see the same display show a red "NO".

    How do you explain that?

    (1) For practical purposes, we will obviously need to allow a small tolerance in the detection of the flashes but we will make sure that this is much smaller than the difference in simultaneity predicted by relativity.

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    Time and space in spacetime are fixed, isotropy and homogeneity. Relativity is all about how we relate those different 'maps' of spacetime.
    So what happens near a black hole? Or in the simpler case of gravitational lensing? And how does cosmic expansion work if space is fixed, isotropic and homogeneous?

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    Quote Originally Posted by Grimble View Post
    ... As for a preferred frame of reference No there is none as Einstein said. ...
    But it is you who is putting a preferred frame of reference on the Universe, by saying there's an absolute frame of reference where the events at A and B occur at the same time - for all observers.

    Quote Originally Posted by Grimble View Post
    ...
    Observed from the Embankment's Frame of Reference A & B are points on the railway. The observer WHO IS STATIONARY AT POINT P is the embankment Observer at point M in his Frame of reference. He will say that in the Embankment's Frame of Reference the lightning strikes are simultaneous but that the Passenger on the train who passes point P as the lightning strikes will not see simultaneity as his motion will have taken him away from P by the time the light reaches there.


    From the Train's Frame of Reference, A & B are points on the Train, and the observer WHO IS STATIONARY AT POINT P is the passenger Observer at point M' in her Frame of Reference. He will say that in the Train's Frame of Reference the lightning strikes are simultaneous but that the Observer on the Embankment, standing at M, passes point P as the lightning strikes and so will not see simultaneity as his motion will have taken him away from P by the time the light reaches there.
    ...
    The embankment observer will know A and B occured at the same time, if the light reaches him or her from A and B at the same time.
    But if this does occur, the embankment observer will not see the light reaching the train observer, from A and B at the same time.

    The train observer will know A and B occured at the same time, if the light reaches him or her from A and B at the same time.
    But if this does occur, the train observer will not see the light reaching the embankment observer, from A and B at the same time.

    So the two situations are contradictory. The two events A and B can not be considered simultaneous by both the train and embankment observers.

    It's not just that each sees the others situation differently. If the light from A and B reaches one observer simultaneously, the light from A and B can't reach the other observer simultaneously.
    Last edited by pzkpfw; 2012-May-10 at 08:01 PM. Reason: 2nd quote
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    Quote Originally Posted by pzkpfw View Post
    The embankment observer will know A and B occured at the same time, if the light reaches him or her from A and B at the same time.
    But if this does occur, the embankment observer will not see the light reaching the train observer, from A and B at the same time.

    The train observer will know A and B occured at the same time, if the light reaches him or her from A and B at the same time.
    But if this does occur, the train observer will not see the light reaching the embankment observer, from A and B at the same time.

    So the two situations are contradictory. The two events A and B can not be considered simultaneous by both the train and embankment observers.

    It's not just that each sees the others situation differently. If the light from A and B reaches one observer simultaneously, the light from A and B can't reach the other observer simultaneously.
    You know, when you put it like that, it is just so obvious.

    So obvious that I expect Grimble to come back and say, "Oh, I see what you mean. I've got it now".

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    Quote Originally Posted by Strange View Post
    You know, when you put it like that, it is just so obvious.

    So obvious that I expect Grimble to come back and say, "Oh, I see what you mean. I've got it now".
    I do like your addition:

    Quote Originally Posted by Strange
    Let us consider the case where the observer on the train has a little electronic device that has a light detector on each side. If it detects a flash simultaneously (1) on each side, it will light a green LED display saying "YES", if the flashes are not coincident then the display shows "NO" in red. Now, according to your reasoning above, the observer on the train will see a green "YES" and the observer on the platform will see the same display show a red "NO".
    If both the embankment and train observer have such a device the contradiction will become very clear.

    Observer X will see the two flashes from A and B reflect off observer Y. Observer X will also see observer Y's detector flash the "YES" or "NO".
    Observer X can't see the two flashes from A and B hit Y simultaneously, while also seeing observer Y's device flash "NO".
    Observer X can't see the two flashes from A and B hit Y non-simultaneously, while also seeing observer Y's device flash "YES".
    If observer X's detector flashes "YES", because the A and B flashes hit X at the same time (according to X's frame of reference), then X will note that the flashes didn't hit Y at the same time... and Y's detector will flash "NO".
    X and Y can be embankment/train or vice-versa.

    So again, it's not just about seeing something occur differently for the other observer; each observer has their own reality of whether the events A and B were simultaneous.

    (It occurs that, if anything, there is one true frame of reference - the speed of light. Everything else (time and distance) bends to keep that "frame" fixed.)
    I don't see any Ice Giants.

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    Quote Originally Posted by Grimble View Post
    As for a preferred frame of reference No there is none as Einstein said.
    Well, if you accept that, you've answered your own OP question, "Is time absolute?" - Clearly, the answer is "no." Is there any point to continuing this thread?

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    Quote Originally Posted by Strange View Post
    Quote Originally Posted by pzkpfw View Post
    The embankment observer will know A and B occured at the same time, if the light reaches him or her from A and B at the same time.
    But if this does occur, the embankment observer will not see the light reaching the train observer, from A and B at the same time.

    The train observer will know A and B occured at the same time, if the light reaches him or her from A and B at the same time.
    But if this does occur, the train observer will not see the light reaching the embankment observer, from A and B at the same time.

    So the two situations are contradictory. The two events A and B can not be considered simultaneous by both the train and embankment observers.
    You know, when you put it like that, it is just so obvious.

    So obvious that I expect Grimble to come back and say, "Oh, I see what you mean. I've got it now".
    Yes, really nice summary - so long as we remind Grimble that he specified that we're only considering observers at the midpoint between A and B in their respective frames of reference.

    I must admit that, on first reading, I got confused thinking "Hang on, in the original example from Einstein, the observer on the train got the light from both sides at the same time". Of course, there was no simultaneity, since that observer was not at the midpoint (between the scorchmarks in my extension).

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    Quote Originally Posted by Strange View Post
    I don't know if this obviously wrong statement is part of the source of your confusion or if you have just thrown it out there to confuse the issue. Clearly, only frames of reference which are stationary with respect to the observer will be stationary with respect to the observer. Frames of reference which are in motion relative to the observer will not be stationary with respect to the observer.
    Any observer's 'map' of Spacetime, the Frame of reference and its coordinates that he is using to 'map' spacetime will always be stationary in spacetime. That is what a Frame of Reference is. An observer's mapping of spacetime and it will of necessity be stationary as it cannot be moving relative to itself.
    The observer, however may be moving within that Frame of reference while the coordinates he is using are st



    What you seem to be saying is that both observers will see the lightning as simultaneous but will think that the other does not. Is that correct?[/quote]

    Yes, Correct!

    As you want to base your argument on "logic" rather than the mathematics of relativity, let's try this:

    Let us consider the case where the observer on the train has a little electronic device that has a light detector on each side. If it detects a flash simultaneously (1) on each side, it will light a green LED display saying "YES", if the flashes are not coincident then the display shows "NO" in red. Now, according to your reasoning above, the observer on the train will see a green "YES" and the observer on the platform will see the same display show a red "NO".

    How do you explain that?.
    No, of course not! What a daft idea!

    The light will be green as it is in the trains frame. It will be seen as green from the embankment. The observer on the embankment however will be adamant that it should have been red as the lights did not meet there.

    It really is not that difficult.

  24. #54
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    Quote Originally Posted by pzkpfw View Post
    I do like your addition:



    If both the embankment and train observer have such a device the contradiction will become very clear.

    Observer X will see the two flashes from A and B reflect off observer Y. Observer X will also see observer Y's detector flash the "YES" or "NO".
    Observer X can't see the two flashes from A and B hit Y simultaneously, while also seeing observer Y's device flash "NO".
    Observer X can't see the two flashes from A and B hit Y non-simultaneously, while also seeing observer Y's device flash "YES".
    If observer X's detector flashes "YES", because the A and B flashes hit X at the same time (according to X's frame of reference), then X will note that the flashes didn't hit Y at the same time... and Y's detector will flash "NO".
    X and Y can be embankment/train or vice-versa.

    So again, it's not just about seeing something occur differently for the other observer; each observer has their own reality of whether the events A and B were simultaneous.

    (It occurs that, if anything, there is one true frame of reference - the speed of light. Everything else (time and distance) bends to keep that "frame" fixed.)
    In which frame of reference are observer's X and Y?

  25. #55
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    Quote Originally Posted by Strange View Post
    You know, when you put it like that, it is just so obvious.

    So obvious that I expect Grimble to come back and say, "Oh, I see what you mean. I've got it now".
    Yes, well, of course I see it, and I have seen it like that for some time and seen the error in it.

    One cannot have a 'preferred Frame' and your embankment is a preferred frame. If there is no preferred frae then ALL frames MUST make the same judgement about simultaneity. So simultaneous in one REQUIRES simultaneity in each.

    Note in EACH not ALL!

    Just as one seeing simultaneity means each must see simultaneity, the one seeing that it is the only one to see the simultaneity means each will come to the same conclusion.

    Each will see it and deny that all others will.

    The simultaneity exists in Spacetime and will be recognised by any observer stationary in Spacetime. That can happen in each and every frame of reference.

    A frame of reference is merely a mapping of Spacetime from one perspective. That is why none can be preferred and what happens in one happens in each.

    Look at Minkowski's "Space and Time (1920)" http://en.wikisource.org/wiki/Space_and_Time and you will come to exactly the same conclusion as described by Minkowski and thoroughly backing up what Einstein wrote. He is the one who describes simultaneity in Spacetime.

  26. #56
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    Quote Originally Posted by Grimble View Post
    If there is no preferred frae then ALL frames MUST make the same judgement about simultaneity. So simultaneous in one REQUIRES simultaneity in each.
    No, that is not what a "preferred frame" means.

    The simultaneity exists in Spacetime and will be recognised by any observer stationary in Spacetime.
    Now that is a preferred frame. Suggesting that someone can be "stationary in Spacetime" implies some sort of absolute reference (otherwise, what are they stationary relative to).

  27. #57
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    Quote Originally Posted by Grimble View Post
    AThe light will be green as it is in the trains frame. It will be seen as green from the embankment. The observer on the embankment however will be adamant that it should have been red as the lights did not meet there.
    So you would discard reality (i.e. cause and effect) in order to preserve your warped view of special relativity?

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    Quote Originally Posted by Grimble View Post
    In which frame of reference are observer's X and Y?
    Each in their own.
    I don't see any Ice Giants.

  29. #59
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    Quote Originally Posted by Grimble View Post
    The observer, however may be moving within that Frame of reference while the coordinates he is using are st
    No. Every observer considers themselves at rest (since we're in SR), and a Frame of Reference is the system of coordinates relative to themselves. Multiple objects not moving relative to eachother do, by definition, share the same Frame of Reference. Also by definition, observers do not move within their Frame of Reference (which is, after all, based on their position, and they are at rest). Please note that this is NOT a matter for opinion or discussion; In a technical forum, you must use terms according to their official definition, since doing otherwise causes confusion. More to the point, however, if you have been following a different meaning of terms like Frame of Reference, you'll get an inconsistent understanding of what Relativity's saying.

    Quote Originally Posted by Grimble View Post
    Yes, well, of course I see it, and I have seen it like that for some time and seen the error in it.
    OK, then show us the error.

    Quote Originally Posted by Grimble View Post
    One cannot have a 'preferred Frame' and your embankment is a preferred frame.
    No, we do not have a preferred frame. Everything we say about the embankment frame is entirely symmetrical and consistent with the Train frame.

    Quote Originally Posted by Grimble View Post
    If there is no preferred frae then ALL frames MUST make the same judgement about simultaneity. So simultaneous in one REQUIRES simultaneity in each. Note in EACH not ALL!
    No, they don't. In fact, expecting all frames to make the same judgement on simultaneity implies that all frames must be making that judgement based on the same global time dimension - and guess what? That's just another name for a preferred frame.

    Look, you said it yourself :

    Quote Originally Posted by Grimble View Post
    From the Train's Frame of Reference, A & B are points on the Train, and the observer WHO IS STATIONARY AT POINT P is the passenger Observer at point M' in her Frame of Reference. He will say that in the Train's Frame of Reference the lightning strikes are simultaneous but that the Observer on the Embankment, standing at M, passes point P as the lightning strikes and so will not see simultaneity as his motion will have taken him away from P by the time the light reaches there.
    In other words, when A and B are simultaneous in the Train Frame of Reference, then they are not simultaneous to the Embankment's. ( I know you were using the labels A and B to try and make it seem like the same occurrence as the simultaneous-in-the-embankment example in your previous paragraph, but it can't be the same so let that go). ALL we have are measurements and observations. If the embankment observer does not see Simultaneity, THEN THERE IS NO SIMULTANEITY IN THAT FRAME. End of story.

    To finish up, a couple of points :
    - Remember my Scorch-mark example. Yes, each lightning strike was an event, happening at a specific coordinate in time and space - but look what happened afterwards! The Space location of the strikes (the scorchmarks) changed or diverged in the different frames of reference. Is it so strange that the time location should change similarly?
    - You seem sure that everybody shares the same 3 space dimensions, and single time dimension. In Relativity, this is NOT the case. Yes, every observer at rest has the 3 + 1, with the clock ticking steadily, but it's not as simple as that. But "One man's space is another man's time" as Sir J.Jeans put it. So not everybody shares the same clock ticking at the same rate. There is no global clock, so no global simultaneity.

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    Let me thank you one and all for your confirmations of my understanding.

    Special Relativity has no hidden mystery but is a plain straightforward piece of mechanics following Einstein's Postulates.
    There are no deep mysteries and certainly no counter intuitive phenomena. Everything happens just as it logically should and as Einstein and Minkowski described.

    I have a thorough understanding of your Special Relativity what it means and how it works. But it is interesting to see how confused you can be by a few simple questions.

    It is worth noting that you seem to be unable to read what is written without making it read what you have already decided it says.

    I am fortunate in my background of finding faults in technical writing and computer programming to see where and how such confusion arises and to have found the true simplicity of Relativity.

    Thank you once again for confirming my theories.

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