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.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.
Which is completely at odds with Einstein and relativity.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.
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.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.
"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
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.
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.
Thank you, members of cosmoquest forum, you are a part of my life I value.
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:
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.
I understand perfectly what you are saying. That is how I know it is wrong.Yes, yes yes, I think you are beginning to understand what I am saying
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.)If so how?
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Just because you don't like the term?
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.
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.
And it still fails. Thus illustrating both the unintuitive nature of relativity and your misunderstanding of it...
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.
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
Then you should have no problem with the fact that simultaneity can not be universal.
So far as this makes any sort of sense, it just shows you once again stuck in a mindset with a special rest frame.
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.
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.
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?
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.
I am reading what you wrote.
But that is exactly how SR works!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.
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: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.Originally Posted by Einstein, chapter IX
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
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.
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?
Thank you, members of cosmoquest forum, you are a part of my life I value.
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?
Last edited by RobA; 2012-May-21 at 12:12 PM. Reason: Ask agreement, and oops, fixed up y coords
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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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.I believe that it is best to let Einstein himself answer whether this has anything to do with Relativity
Edit: Plus read the last bit I quoted again. Are you really using a quote from Einstein to try to justify this conclusion?
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:
There's more, but I don't want to breach "fair use" rules on a copyrighted work.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 system^{1}, 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 astonishing^{3} 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^{2} ...
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.
Thank you, members of cosmoquest forum, you are a part of my life I value.
Yes. Because each will deny that the other sees them as simultaneous.
Yes. As seen from that observer's frame.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.
Hmmm!That can't contradict what that other observer experiences for themself!
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.
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.Thus the flashes won't be simultaneous for that other observer (whichever way around it is).
agreed.(* 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.)
Yes, yes, yes! I think you are getting what I am saying. Reciprocity.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.
Answer 1: GreenHere'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 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
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.
No, not at all, it agrees exactly with that assertion.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.
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.
Which is exactly what I am saying2. 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.the two frames will actually disagree about whether event were simultaneous.the authors opinion, not a scientific judgement3. Note how the result is described as "astonishing".I find it astonishing that each thinks that only they can see the simultaneity.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 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?