Is Length Contraction in SR physical??
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From: PD on 9 Feb 2010 16:02 On Feb 9, 12:26 pm, Ste <ste_ro...(a)hotmail.com> wrote: > On 9 Feb, 17:12, PD <thedraperfam...(a)gmail.com> wrote: > > > > > On Feb 8, 11:19 pm, Ste <ste_ro...(a)hotmail.com> wrote: > > > > On 8 Feb, 16:20, PD <thedraperfam...(a)gmail.com> wrote: > > > > > On Feb 6, 11:33 pm, Ste <ste_ro...(a)hotmail.com> wrote: > > > > > > On 7 Feb, 03:54, PD <thedraperfam...(a)gmail.com> wrote: > > > > > > > On Feb 6, 8:52 pm, Ste <ste_ro...(a)hotmail.com> wrote: > > > > > > > > > The only thing that is required is to note at the detector X or the > > > > > > > > detector Y whether the signals from the events arrive at the same time > > > > > > > > or at different times. This is a point decision. It is a yes or no > > > > > > > > question. "Signal from A just arrived at X. Did signal from B arrive > > > > > > > > at X at the same time? Yes or no." > > > > > > > > If detection is instantaneous (i.e. if a photon is absorbed > > > > > > > instantaneously), then it is possible for A and B to be simultaneous > > > > > > > according to both X and Y. However, if detection is not instantaneous, > > > > > > > then it is *not* possible. > > > > > > > I didn't say "according to both X and Y". What I said in fact was the > > > > > > opposite. Please reread. > > > > > > What I did say is that X is *right* in concluding that A and B are > > > > > > simultaneous, based on the procedure we established as reliable.. > > > > > > But the procedure isn't reliable! I've said that repeatedly. > > > > > It isn't reliable for what? > > > > For driving a consensus between X and Y? Is that a necessary > > > > requirement? Why? > > > > Let's revisit the procedure. > > > > If you were going to try to determine whether two events are > > > > simultaneous, according to a *particular* observer, then our suggested > > > > procedure is as follows: > > > > 1. Position a detector midway between the two events, where "midway" > > > > can be established at any time by directly measuring the length > > > > between the marks left by the events and the mark at the location of > > > > the detector. Let's amend this to say that this can be repeated on two > > > > occasions to determine that the "midway" condition has not changed. > > > > 2. Have the events send a signal known to travel with equal speeds > > > > toward the detector. The equality of the speeds can be established at > > > > any time by reproducing the signal and directly measuring the distance > > > > covered by the signal per unit time. > > > > (Note that (1) and (2) unambiguously determine that the propagation > > > > delay is the same from both events.) > > > > 3. Determine whether the signals from the events arrive at the > > > > detector at the same time or at different times. If the signals arrive > > > > at the same time, then from that information the correct conclusion is > > > > that the original events were simultaneous. If the signals arrive at > > > > different times, then from that information the correct conclusion is > > > > that the original events were not simultaneous. > > > > This works only if neither detector is moving. > > > Moving relative to what? Notice that I said that the "midway" > > determination can be done at ANY TIME, and in fact repeated as > > necessary. Does this establish what you need? > > > > > You agreed earlier that this procedure should be sufficient for > > > > determining the simultaneity of spatially separated events, according > > > > to a particular observer. > > > > > Now you seem not so sure. What's the source of your sudden > > > > reservation? What procedure would you otherwise propose for > > > > determining the simultaneity of two spatially separated events? > > > > The source of my reservation is that equidistance cannot be > > > maintained, nor symmetry maintained, over the detection *interval*, if > > > the two detectors are moving relative to each other. > > > Perhaps it would be best if we moved to an example. I'm going to use a > > modified version of Einstein's codification of these experiments. > > > Two trains are on adjacent tracks, going in opposite directions, > > though I say that only to deliberately reinforce an ambiguity here. It > > doesn't matter whether the trains are going at different speeds, and > > in fact it isn't even important if one of the trains is stopped, or in > > fact whether they are going in the same direction but one faster than > > the other. All that matters is that there is a relative velocity > > between them. > > > Two lightning strikes occur, drawn to the trains because of the > > friction of the air between the trains. In fact, one lightning strike > > leaves a scorch mark (a 1 cm spot, if you want to be precise) on > > *both* trains as it hits. The other strike leaves a scorch mark > > somewhere else on *both* trains. > > > The question now is, were the strikes simultaneous or not? > > > There is an observer on train A, and an observer on train B, and they > > are both looking out the window when the strikes occur. > > > They make the following observations: > > 1. The observer on train A sees the two lightning flashes > > simultaneously. > > 2. The observer on train B sees the flash from the front of his train > > before he sees the flash from the rear of his train. > > > Now, it is not yet possible to determine whether the strikes were > > simultaneous originally. We have more work to do. But I want to see if > > you have a picture in your head of what has transpired. > > I have a basic picture, yes. OK, then. Let's now follow up these two observations above and couple them with more observations. 3. After the strikes, the observer on train A runs a tape measure from his location to the scorch mark of one strike and makes note of the number. Then he runs a tape measure from his location to the scorch mark of the other strike and makes note of the number. These numbers are equal. Note the scorch marks are on his train, but that's an undeniable marker of where the event WAS when the signal propagation began. 4. After the strikes, the observer on train B runs a tape measure from his location to the scorch mark of one strike and makes note of the number. Then he runs a tape measure from his location to the scorch mark of the other strike and makes note of the number. These numbers are equal. Note the scorch marks are on his train, but that's an undeniable marker of where the event WAS when the signal propagation began. 5. The observer on A runs some experiments to measure the speed of light and the isotropy of the speed of light (that it is the same in either direction), and finds that the signal speed is the same. (Note this isotropy would NOT hold if the signal were sound, for example.) 6. The observer on B runs some experiments to measure the speed of light and the isotropy of the speed of light (that it is the same in either direction), and finds that the signal speed is the same. (Note this isotropy would NOT hold if the signal were sound, for example.) Given these *observations* 1, 3, and 5, what would the observer on train A conclude about the simultaneity of the original strikes?
From: kenseto on 9 Feb 2010 17:05 On Feb 9, 4:02 pm, PD <thedraperfam...(a)gmail.com> wrote: > On Feb 9, 12:26 pm, Ste <ste_ro...(a)hotmail.com> wrote: > > > > > > > On 9 Feb, 17:12, PD <thedraperfam...(a)gmail.com> wrote: > > > > On Feb 8, 11:19 pm, Ste <ste_ro...(a)hotmail.com> wrote: > > > > > On 8 Feb, 16:20, PD <thedraperfam...(a)gmail.com> wrote: > > > > > > On Feb 6, 11:33 pm, Ste <ste_ro...(a)hotmail.com> wrote: > > > > > > > On 7 Feb, 03:54, PD <thedraperfam...(a)gmail.com> wrote: > > > > > > > > On Feb 6, 8:52 pm, Ste <ste_ro...(a)hotmail.com> wrote: > > > > > > > > > > The only thing that is required is to note at the detector X or the > > > > > > > > > detector Y whether the signals from the events arrive at the same time > > > > > > > > > or at different times. This is a point decision. It is a yes or no > > > > > > > > > question. "Signal from A just arrived at X. Did signal from B arrive > > > > > > > > > at X at the same time? Yes or no." > > > > > > > > > If detection is instantaneous (i.e. if a photon is absorbed > > > > > > > > instantaneously), then it is possible for A and B to be simultaneous > > > > > > > > according to both X and Y. However, if detection is not instantaneous, > > > > > > > > then it is *not* possible. > > > > > > > > I didn't say "according to both X and Y". What I said in fact was the > > > > > > > opposite. Please reread. > > > > > > > What I did say is that X is *right* in concluding that A and B are > > > > > > > simultaneous, based on the procedure we established as reliable. > > > > > > > But the procedure isn't reliable! I've said that repeatedly. > > > > > > It isn't reliable for what? > > > > > For driving a consensus between X and Y? Is that a necessary > > > > > requirement? Why? > > > > > Let's revisit the procedure. > > > > > If you were going to try to determine whether two events are > > > > > simultaneous, according to a *particular* observer, then our suggested > > > > > procedure is as follows: > > > > > 1. Position a detector midway between the two events, where "midway" > > > > > can be established at any time by directly measuring the length > > > > > between the marks left by the events and the mark at the location of > > > > > the detector. Let's amend this to say that this can be repeated on two > > > > > occasions to determine that the "midway" condition has not changed. > > > > > 2. Have the events send a signal known to travel with equal speeds > > > > > toward the detector. The equality of the speeds can be established at > > > > > any time by reproducing the signal and directly measuring the distance > > > > > covered by the signal per unit time. > > > > > (Note that (1) and (2) unambiguously determine that the propagation > > > > > delay is the same from both events.) > > > > > 3. Determine whether the signals from the events arrive at the > > > > > detector at the same time or at different times. If the signals arrive > > > > > at the same time, then from that information the correct conclusion is > > > > > that the original events were simultaneous. If the signals arrive at > > > > > different times, then from that information the correct conclusion is > > > > > that the original events were not simultaneous. > > > > > This works only if neither detector is moving. > > > > Moving relative to what? Notice that I said that the "midway" > > > determination can be done at ANY TIME, and in fact repeated as > > > necessary. Does this establish what you need? > > > > > > You agreed earlier that this procedure should be sufficient for > > > > > determining the simultaneity of spatially separated events, according > > > > > to a particular observer. > > > > > > Now you seem not so sure. What's the source of your sudden > > > > > reservation? What procedure would you otherwise propose for > > > > > determining the simultaneity of two spatially separated events? > > > > > The source of my reservation is that equidistance cannot be > > > > maintained, nor symmetry maintained, over the detection *interval*, if > > > > the two detectors are moving relative to each other. > > > > Perhaps it would be best if we moved to an example. I'm going to use a > > > modified version of Einstein's codification of these experiments. > > > > Two trains are on adjacent tracks, going in opposite directions, > > > though I say that only to deliberately reinforce an ambiguity here. It > > > doesn't matter whether the trains are going at different speeds, and > > > in fact it isn't even important if one of the trains is stopped, or in > > > fact whether they are going in the same direction but one faster than > > > the other. All that matters is that there is a relative velocity > > > between them. > > > > Two lightning strikes occur, drawn to the trains because of the > > > friction of the air between the trains. In fact, one lightning strike > > > leaves a scorch mark (a 1 cm spot, if you want to be precise) on > > > *both* trains as it hits. The other strike leaves a scorch mark > > > somewhere else on *both* trains. > > > > The question now is, were the strikes simultaneous or not? > > > > There is an observer on train A, and an observer on train B, and they > > > are both looking out the window when the strikes occur. > > > > They make the following observations: > > > 1. The observer on train A sees the two lightning flashes > > > simultaneously. > > > 2. The observer on train B sees the flash from the front of his train > > > before he sees the flash from the rear of his train. > > > > Now, it is not yet possible to determine whether the strikes were > > > simultaneous originally. We have more work to do. But I want to see if > > > you have a picture in your head of what has transpired. > > > I have a basic picture, yes. > > OK, then. > Let's now follow up these two observations above and couple them with > more observations. > 3. After the strikes, the observer on train A runs a tape measure from > his location to the scorch mark of one strike and makes note of the > number. Then he runs a tape measure from his location to the scorch > mark of the other strike and makes note of the number. These numbers > are equal. Note the scorch marks are on his train, but that's an > undeniable marker of where the event WAS when the signal propagation > began. It was stipulated that A is at the middle of the train at equal distance from the ends of the train where the strikes occur when A and B are coincide with each other. > 4. After the strikes, the observer on train B runs a tape measure from > his location to the scorch mark of one strike and makes note of the > number. Then he runs a tape measure from his location to the scorch > mark of the other strike and makes note of the number. These numbers > are equal. Note the scorch marks are on his train, but that's an > undeniable marker of where the event WAS when the signal propagation > began. It was stipulated that B was at the middle of the train at equal distance from the ends of the train. When A and B are coincided with each other the lightning strikes occur simultaneously in the A frame. The speed of light is isotropic in the A frame and therefore A will see the strikes to be simultaneous. The question is will B sees the strikes to be sumltaneous? The answer to this question is a resounding YES. Why? Because the SR postulates says that the speed of light in the B frame is also isotropic. Ken Seto > 5. The observer on A runs some experiments to measure the speed of > light and the isotropy of the speed of light (that it is the same in > either direction), and finds that the signal speed is the same. (Note > this isotropy would NOT hold if the signal were sound, for example.) > 6. The observer on B runs some experiments to measure the speed of > light and the isotropy of the speed of light (that it is the same in > either direction), and finds that the signal speed is the same. (Note > this isotropy would NOT hold if the signal were sound, for example.) > > Given these *observations* 1, 3, and 5, what would the observer on > train A conclude about the simultaneity of the original strikes? - Hide quoted text - > > - Show quoted text -
From: PD on 9 Feb 2010 17:14 On Feb 9, 4:05 pm, kenseto <kens...(a)erinet.com> wrote: > On Feb 9, 4:02 pm, PD <thedraperfam...(a)gmail.com> wrote: > > > > > On Feb 9, 12:26 pm, Ste <ste_ro...(a)hotmail.com> wrote: > > > > On 9 Feb, 17:12, PD <thedraperfam...(a)gmail.com> wrote: > > > > > On Feb 8, 11:19 pm, Ste <ste_ro...(a)hotmail.com> wrote: > > > > > > On 8 Feb, 16:20, PD <thedraperfam...(a)gmail.com> wrote: > > > > > > > On Feb 6, 11:33 pm, Ste <ste_ro...(a)hotmail.com> wrote: > > > > > > > > On 7 Feb, 03:54, PD <thedraperfam...(a)gmail.com> wrote: > > > > > > > > > On Feb 6, 8:52 pm, Ste <ste_ro...(a)hotmail.com> wrote: > > > > > > > > > > > The only thing that is required is to note at the detector X or the > > > > > > > > > > detector Y whether the signals from the events arrive at the same time > > > > > > > > > > or at different times. This is a point decision. It is a yes or no > > > > > > > > > > question. "Signal from A just arrived at X. Did signal from B arrive > > > > > > > > > > at X at the same time? Yes or no." > > > > > > > > > > If detection is instantaneous (i.e. if a photon is absorbed > > > > > > > > > instantaneously), then it is possible for A and B to be simultaneous > > > > > > > > > according to both X and Y. However, if detection is not instantaneous, > > > > > > > > > then it is *not* possible. > > > > > > > > > I didn't say "according to both X and Y". What I said in fact was the > > > > > > > > opposite. Please reread. > > > > > > > > What I did say is that X is *right* in concluding that A and B are > > > > > > > > simultaneous, based on the procedure we established as reliable. > > > > > > > > But the procedure isn't reliable! I've said that repeatedly. > > > > > > > It isn't reliable for what? > > > > > > For driving a consensus between X and Y? Is that a necessary > > > > > > requirement? Why? > > > > > > Let's revisit the procedure. > > > > > > If you were going to try to determine whether two events are > > > > > > simultaneous, according to a *particular* observer, then our suggested > > > > > > procedure is as follows: > > > > > > 1. Position a detector midway between the two events, where "midway" > > > > > > can be established at any time by directly measuring the length > > > > > > between the marks left by the events and the mark at the location of > > > > > > the detector. Let's amend this to say that this can be repeated on two > > > > > > occasions to determine that the "midway" condition has not changed. > > > > > > 2. Have the events send a signal known to travel with equal speeds > > > > > > toward the detector. The equality of the speeds can be established at > > > > > > any time by reproducing the signal and directly measuring the distance > > > > > > covered by the signal per unit time. > > > > > > (Note that (1) and (2) unambiguously determine that the propagation > > > > > > delay is the same from both events.) > > > > > > 3. Determine whether the signals from the events arrive at the > > > > > > detector at the same time or at different times. If the signals arrive > > > > > > at the same time, then from that information the correct conclusion is > > > > > > that the original events were simultaneous. If the signals arrive at > > > > > > different times, then from that information the correct conclusion is > > > > > > that the original events were not simultaneous. > > > > > > This works only if neither detector is moving. > > > > > Moving relative to what? Notice that I said that the "midway" > > > > determination can be done at ANY TIME, and in fact repeated as > > > > necessary. Does this establish what you need? > > > > > > > You agreed earlier that this procedure should be sufficient for > > > > > > determining the simultaneity of spatially separated events, according > > > > > > to a particular observer. > > > > > > > Now you seem not so sure. What's the source of your sudden > > > > > > reservation? What procedure would you otherwise propose for > > > > > > determining the simultaneity of two spatially separated events? > > > > > > The source of my reservation is that equidistance cannot be > > > > > maintained, nor symmetry maintained, over the detection *interval*, if > > > > > the two detectors are moving relative to each other. > > > > > Perhaps it would be best if we moved to an example. I'm going to use a > > > > modified version of Einstein's codification of these experiments. > > > > > Two trains are on adjacent tracks, going in opposite directions, > > > > though I say that only to deliberately reinforce an ambiguity here. It > > > > doesn't matter whether the trains are going at different speeds, and > > > > in fact it isn't even important if one of the trains is stopped, or in > > > > fact whether they are going in the same direction but one faster than > > > > the other. All that matters is that there is a relative velocity > > > > between them. > > > > > Two lightning strikes occur, drawn to the trains because of the > > > > friction of the air between the trains. In fact, one lightning strike > > > > leaves a scorch mark (a 1 cm spot, if you want to be precise) on > > > > *both* trains as it hits. The other strike leaves a scorch mark > > > > somewhere else on *both* trains. > > > > > The question now is, were the strikes simultaneous or not? > > > > > There is an observer on train A, and an observer on train B, and they > > > > are both looking out the window when the strikes occur. > > > > > They make the following observations: > > > > 1. The observer on train A sees the two lightning flashes > > > > simultaneously. > > > > 2. The observer on train B sees the flash from the front of his train > > > > before he sees the flash from the rear of his train. > > > > > Now, it is not yet possible to determine whether the strikes were > > > > simultaneous originally. We have more work to do. But I want to see if > > > > you have a picture in your head of what has transpired. > > > > I have a basic picture, yes. > > > OK, then. > > Let's now follow up these two observations above and couple them with > > more observations. > > 3. After the strikes, the observer on train A runs a tape measure from > > his location to the scorch mark of one strike and makes note of the > > number. Then he runs a tape measure from his location to the scorch > > mark of the other strike and makes note of the number. These numbers > > are equal. Note the scorch marks are on his train, but that's an > > undeniable marker of where the event WAS when the signal propagation > > began. > > It was stipulated that A is at the middle of the train at equal > distance from the ends of the train where the strikes occur when A and > B are coincide with each other. Ken, I am not using Einstein's gedanken exactly as he wrote it. Please pay attention. > > > 4. After the strikes, the observer on train B runs a tape measure from > > his location to the scorch mark of one strike and makes note of the > > number. Then he runs a tape measure from his location to the scorch > > mark of the other strike and makes note of the number. These numbers > > are equal. Note the scorch marks are on his train, but that's an > > undeniable marker of where the event WAS when the signal propagation > > began. > > It was stipulated that B was at the middle of the train at equal > distance from the ends of the train. > When A and B are coincided with each other the lightning strikes occur > simultaneously in the A frame. The speed of light is isotropic in the > A frame and therefore A will see the strikes to be simultaneous. The > question is will B sees the strikes to be sumltaneous? The answer to > this question is a resounding YES. Why? Because the SR postulates says > that the speed of light in the B frame is also isotropic. > > Ken Seto > > > 5. The observer on A runs some experiments to measure the speed of > > light and the isotropy of the speed of light (that it is the same in > > either direction), and finds that the signal speed is the same. (Note > > this isotropy would NOT hold if the signal were sound, for example.) > > 6. The observer on B runs some experiments to measure the speed of > > light and the isotropy of the speed of light (that it is the same in > > either direction), and finds that the signal speed is the same. (Note > > this isotropy would NOT hold if the signal were sound, for example.) > > > Given these *observations* 1, 3, and 5, what would the observer on > > train A conclude about the simultaneity of the original strikes? > > - Hide quoted text - > > > > > - Show quoted text -
From: artful on 9 Feb 2010 17:20 On Feb 10, 9:05 am, kenseto <kens...(a)erinet.com> wrote: > On Feb 9, 4:02 pm, PD <thedraperfam...(a)gmail.com> wrote: > > > > > > > On Feb 9, 12:26 pm, Ste <ste_ro...(a)hotmail.com> wrote: > > > > On 9 Feb, 17:12, PD <thedraperfam...(a)gmail.com> wrote: > > > > > On Feb 8, 11:19 pm, Ste <ste_ro...(a)hotmail.com> wrote: > > > > > > On 8 Feb, 16:20, PD <thedraperfam...(a)gmail.com> wrote: > > > > > > > On Feb 6, 11:33 pm, Ste <ste_ro...(a)hotmail.com> wrote: > > > > > > > > On 7 Feb, 03:54, PD <thedraperfam...(a)gmail.com> wrote: > > > > > > > > > On Feb 6, 8:52 pm, Ste <ste_ro...(a)hotmail.com> wrote: > > > > > > > > > > > The only thing that is required is to note at the detector X or the > > > > > > > > > > detector Y whether the signals from the events arrive at the same time > > > > > > > > > > or at different times. This is a point decision. It is a yes or no > > > > > > > > > > question. "Signal from A just arrived at X. Did signal from B arrive > > > > > > > > > > at X at the same time? Yes or no." > > > > > > > > > > If detection is instantaneous (i.e. if a photon is absorbed > > > > > > > > > instantaneously), then it is possible for A and B to be simultaneous > > > > > > > > > according to both X and Y. However, if detection is not instantaneous, > > > > > > > > > then it is *not* possible. > > > > > > > > > I didn't say "according to both X and Y". What I said in fact was the > > > > > > > > opposite. Please reread. > > > > > > > > What I did say is that X is *right* in concluding that A and B are > > > > > > > > simultaneous, based on the procedure we established as reliable. > > > > > > > > But the procedure isn't reliable! I've said that repeatedly. > > > > > > > It isn't reliable for what? > > > > > > For driving a consensus between X and Y? Is that a necessary > > > > > > requirement? Why? > > > > > > Let's revisit the procedure. > > > > > > If you were going to try to determine whether two events are > > > > > > simultaneous, according to a *particular* observer, then our suggested > > > > > > procedure is as follows: > > > > > > 1. Position a detector midway between the two events, where "midway" > > > > > > can be established at any time by directly measuring the length > > > > > > between the marks left by the events and the mark at the location of > > > > > > the detector. Let's amend this to say that this can be repeated on two > > > > > > occasions to determine that the "midway" condition has not changed. > > > > > > 2. Have the events send a signal known to travel with equal speeds > > > > > > toward the detector. The equality of the speeds can be established at > > > > > > any time by reproducing the signal and directly measuring the distance > > > > > > covered by the signal per unit time. > > > > > > (Note that (1) and (2) unambiguously determine that the propagation > > > > > > delay is the same from both events.) > > > > > > 3. Determine whether the signals from the events arrive at the > > > > > > detector at the same time or at different times. If the signals arrive > > > > > > at the same time, then from that information the correct conclusion is > > > > > > that the original events were simultaneous. If the signals arrive at > > > > > > different times, then from that information the correct conclusion is > > > > > > that the original events were not simultaneous. > > > > > > This works only if neither detector is moving. > > > > > Moving relative to what? Notice that I said that the "midway" > > > > determination can be done at ANY TIME, and in fact repeated as > > > > necessary. Does this establish what you need? > > > > > > > You agreed earlier that this procedure should be sufficient for > > > > > > determining the simultaneity of spatially separated events, according > > > > > > to a particular observer. > > > > > > > Now you seem not so sure. What's the source of your sudden > > > > > > reservation? What procedure would you otherwise propose for > > > > > > determining the simultaneity of two spatially separated events? > > > > > > The source of my reservation is that equidistance cannot be > > > > > maintained, nor symmetry maintained, over the detection *interval*, if > > > > > the two detectors are moving relative to each other. > > > > > Perhaps it would be best if we moved to an example. I'm going to use a > > > > modified version of Einstein's codification of these experiments. > > > > > Two trains are on adjacent tracks, going in opposite directions, > > > > though I say that only to deliberately reinforce an ambiguity here. It > > > > doesn't matter whether the trains are going at different speeds, and > > > > in fact it isn't even important if one of the trains is stopped, or in > > > > fact whether they are going in the same direction but one faster than > > > > the other. All that matters is that there is a relative velocity > > > > between them. > > > > > Two lightning strikes occur, drawn to the trains because of the > > > > friction of the air between the trains. In fact, one lightning strike > > > > leaves a scorch mark (a 1 cm spot, if you want to be precise) on > > > > *both* trains as it hits. The other strike leaves a scorch mark > > > > somewhere else on *both* trains. > > > > > The question now is, were the strikes simultaneous or not? > > > > > There is an observer on train A, and an observer on train B, and they > > > > are both looking out the window when the strikes occur. > > > > > They make the following observations: > > > > 1. The observer on train A sees the two lightning flashes > > > > simultaneously. > > > > 2. The observer on train B sees the flash from the front of his train > > > > before he sees the flash from the rear of his train. > > > > > Now, it is not yet possible to determine whether the strikes were > > > > simultaneous originally. We have more work to do. But I want to see if > > > > you have a picture in your head of what has transpired. > > > > I have a basic picture, yes. > > > OK, then. > > Let's now follow up these two observations above and couple them with > > more observations. > > 3. After the strikes, the observer on train A runs a tape measure from > > his location to the scorch mark of one strike and makes note of the > > number. Then he runs a tape measure from his location to the scorch > > mark of the other strike and makes note of the number. These numbers > > are equal. Note the scorch marks are on his train, but that's an > > undeniable marker of where the event WAS when the signal propagation > > began. > > It was stipulated that A is at the middle of the train at equal > distance from the ends of the train where the strikes occur when A and > B are coincide with each other. Yeup > > 4. After the strikes, the observer on train B runs a tape measure from > > his location to the scorch mark of one strike and makes note of the > > number. Then he runs a tape measure from his location to the scorch > > mark of the other strike and makes note of the number. These numbers > > are equal. Note the scorch marks are on his train, but that's an > > undeniable marker of where the event WAS when the signal propagation > > began. > > It was stipulated that B was at the middle of the train at equal > distance from the ends of the train. > When A and B are coincided with each other the lightning strikes occur > simultaneously in the A frame. The speed of light is isotropic in the > A frame and therefore A will see the strikes to be simultaneous. The > question is will B sees the strikes to be sumltaneous? The answer to > this question is a resounding YES. No > Why? Because the SR postulates says > that the speed of light in the B frame is also isotropic. It is obvious that there is only ONE plane of points that is equidistant from two simultaneous strikes .. it is perpendicular to the line between the strikes. We know the strokes where simultaneous in A's frame, and that A is on that plane. B cannot also be on that same plane when light from the strieks arrives at him, because he moves *away* from that location after the strikes occur. So light cannot arrive both simultaneously at A *and* simultaneously at B. It is physically impossible for the light to arrive a B simultaneously (whether you are talking about SR or not). That is a FACT. From that FACT, SR tells us that we can conclude that the strikes were not simultaneous in B's frame, because the isotropy of light in B means that light took the same time to travel to B from each of the strikes .. so if the two light pulses arrive at B at different times, they must have been emitted at different times. Your argument is refuted, AAFCPS
From: kenseto on 9 Feb 2010 17:25
On Feb 9, 11:30 am, PD <thedraperfam...(a)gmail.com> wrote: > On Feb 8, 3:09 pm, kenseto <kens...(a)erinet.com> wrote: > > > > > > > On Feb 8, 3:09 pm, PD <thedraperfam...(a)gmail.com> wrote: > > > > On Feb 8, 12:38 pm, kenseto <kens...(a)erinet.com> wrote: > > > > > On Feb 8, 11:42 am, PD <thedraperfam...(a)gmail.com> wrote: > > > > > > On Feb 7, 7:34 am, kenseto <kens...(a)erinet.com> wrote: > > > > > > > On Feb 6, 10:57 pm, PD <thedraperfam...(a)gmail.com> wrote: > > > > > > > > On Feb 6, 9:02 pm, Ste <ste_ro...(a)hotmail.com> wrote: > > > > > > > > > On 6 Feb, 17:16, PD <thedraperfam...(a)gmail.com> wrote: > > > > > > > > > > On Feb 5, 8:14 pm, Ste <ste_ro...(a)hotmail.com> wrote: > > > > > > > > > > > On 5 Feb, 16:00, PD <thedraperfam...(a)gmail.com> wrote: > > > > > > > > > > > > On Feb 4, 9:57 pm, Ste <ste_ro...(a)hotmail.com> wrote: > > > > > > > > > > > > > On 5 Feb, 02:48, "Peter Webb" <webbfam...(a)DIESPAMDIEoptusnet.com.au> > > > > > > > > > > > > wrote: > > > > > > > > > > > > > > "Ste" <ste_ro...(a)hotmail.com> wrote in message > > > > > > > > > > > > > >news:3979bca1-a35e-4399-bc71-75d2fc680757(a)21g2000yqj.googlegroups.com... > > > > > > > > > > > > > On 5 Feb, 01:12, artful <artful...(a)hotmail.com> wrote: > > > > > > > > > > > > > > > On Feb 5, 11:49 am, kenseto <kens...(a)erinet.com> wrote: > > > > > > > > > > > > > > > > On Feb 4, 6:04 pm, mpalenik <markpale...(a)gmail.com> wrote: > > > > > > > > > > > > > > > > > On Feb 4, 5:59 pm, "kens...(a)erinet.com" <kens...(a)erinet.com> wrote: > > > > > > > > > > > > > > > > > > It it does violate the PoR. You made the contradcictory claims that > > > > > > > > > > > > > > > > > the pole can fit into the barn physically (materially) an at the > > > > > > > > > > > > > > > > > same > > > > > > > > > > > > > > > > > time you claim that the pole cannot fit into the barn physically > > > > > > > > > > > > > > > > > (materially)......that a violation of the PoR. > > > > > > > > > > > > > > > > > No. The doors are not closed simultaneously in the pole's frame, nor > > > > > > > > > > > > > > > > are the two ends of the pole simultaneously in the barn in the pole's > > > > > > > > > > > > > > > > reference frame. In the barn's frame, the two ends of the pole are in > > > > > > > > > > > > > > > > the barn simultaneously and the doors shut simultaneously. In the > > > > > > > > > > > > > > > > pole's frame, the two ends of the pole are in the barn at different > > > > > > > > > > > > > > > > times and the doors shut at different times.. > > > > > > > > > > > > > > > > Sigh..You are making the contradictory claims: > > > > > > > > > > > > > > > 1. The pole can fit into the barn with both doors close > > > > > > > > > > > > > > > simultaneously. > > > > > > > > > > > > > > > In the frame of the barn > > > > > > > > > > > > > > > > 2. The pole cannot fit into the barn with both doors close > > > > > > > > > > > > > > > simultaneously. > > > > > > > > > > > > > > > In the frame of the pole > > > > > > > > > > > > > > > Two different meanings for 'simultaneously'. So they are not > > > > > > > > > > > > > > contradictory > > > > > > > > > > > > > > > You really are not very good at thinking or arguing logically. > > > > > > > > > > > > > > He seems perfectly reasonable to me. > > > > > > > > > > > > > > He's saying that, if one stands in the middle of the barn equidistant > > > > > > > > > > > > > from the doors on each side, and one closes the doors simultaneously > > > > > > > > > > > > > (i.e. what I would call "absolutely simultaneously", but which for > > > > > > > > > > > > > conveience we'll say "simultaneous according to an observer standing > > > > > > > > > > > > > equidistant from each door), then is it possible that both doors can > > > > > > > > > > > > > appear closed while the ladder is observed to be inside the barn. > > > > > > > > > > > > > > It's a simple question, and the answer is "no!". > > > > > > > > > > > > > > ______________________________ > > > > > > > > > > > > > Its a simple question, and the answer is "yes". It is quite easy to devise > > > > > > > > > > > > > an inertial frame in which the doors both appear closed and the ladder is > > > > > > > > > > > > > fully contained in the barn. > > > > > > > > > > > > > The question wasn't whether "an inertial frame can be devised...". > > > > > > > > > > > > Even I can think of situations where it would *appear* that the ladder > > > > > > > > > > > > was inside and both doors closed. The question is whether this is an > > > > > > > > > > > > artefact of observation, or whether the ladder is actually inside with > > > > > > > > > > > > both doors closed. The answer remains "no, the ladder does not fit > > > > > > > > > > > > inside with both doors closed". > > > > > > > > > > > > There is a simple test. > > > > > > > > > > > We can determine whether the doors closed simultaneously. We do this > > > > > > > > > > > using the test of simultaneity I indicated to you above: > > > > > > > > > > > 1. Have the door-closings generate signals that travel at identical > > > > > > > > > > > speeds from either event. > > > > > > > > > > > 2. Have a detector positioned at equal distance from the barn doors. > > > > > > > > > > > 3. If the detector receives the signals from the barn door-closings at > > > > > > > > > > > the same time, then the two doors closed simultaneously unambiguously. > > > > > > > > > > > You and I have agreed on this procedure. > > > > > > > > > > > If the detector is stationary, then yes we agree that this determines > > > > > > > > > > simultaneity. > > > > > > > > > > > > Secondly, we can determine whether any part of the pole was outside > > > > > > > > > > > the barn when those doors were closed by looking for the marks the > > > > > > > > > > > ends of the pole would have made on the door. In the absence of those > > > > > > > > > > > marks, we can safely conclude that the entire pole was inside the barn > > > > > > > > > > > at the time the doors were closed. > > > > > > > > > > > Agreed. I would expect this test is definitive, were it possible to > > > > > > > > > > carry out. > > > > > > > > > > And this has been tested in equivalent experiment. Documented. > > > > > > > > > Has it really? Which experiment was that, because my sources say that > > > > > > > > length contraction has *never* been experimentally observed.. > > > > > > > > I already told you the answer to that. Please look again. > > > > > > > > > > Seto does not read experimental papers, because he finds them > > > > > > > > > confusing. So instead he believes what makes sense to him, rather than > > > > > > > > > letting experimental results tell him something different.. > > > > > > > > > You have to concede at least the possibility Paul that the reason Ken > > > > > > > > finds them confusing, and so do I, is because *we* can see that they > > > > > > > > rest on certain assumptions. That is, assumptions that you've > > > > > > > > internalised, and assumptions which me and Ken reject. > > > > > > > > In Seto's case, it has more to do with thinking that SR says something > > > > > > > it does not. I haven't yet figured out whether you are in the same > > > > > > > boat. > > > > > > > The only assumptions I make are those that have testable consequences. > > > > > > > Which ones of those do you think I have that you reject? > > > > > > > So are you saying that SR doesn't say that the pole can be completely > > > > > > inside the barn with both doors close simultaneously? > > > > > > SR *certainly* does not say that this statement holds true in both > > > > > barn frame and pole frame. > > > > > If you thought it did, then you never understood what SR says. > > > > > I didn't say that that statement hold true in both barn and pole > > > > frame. > > > > Yes, you did. Two days ago you said just this: "The pole observer have > > > to agree with the barn observer that the pole > > > is completely inside the barn with both door close simultnaeously." > > You said: "The pole observer have to agree with the barn observer that > the pole is completely inside the barn with both door close > simultnaeously." > > You THEN said "So are you saying that SR doesn't say that the pole can > be completely inside the barn with both doors close simultaneously? I > ask this question because that's what I think SR says. > > I told you No, SR does NOT say this, and neither does the PoR. > > You THEN said, "I didn't say that that statement hold true in both > barn and pole frame." I was referring to the obsolete SR interpretation. I disagree with this old SR interprestion. I agree with Tom Roberts interpretation that length contraction is not physical. It is the geometric projection of the physical length of the pole is shorter and this projection is able to fit into the length of the barn. > > SR consistently says the two observers do not have to agree on what > happens. You first say the two observers have to agree, and then you > say they don't. > > Admit it, Ken, you've made contradictory statements when SR made none. > > > > > > > So??? What I said here is that I disagree with the SR assertions that > > the pole is physically contracted in one frame and not physically > > contracted in another frame. Since there is only one pole it is either > > contracted or not contracted....but not both. A physically contracted > > pole cannot suddenly not physically contracted. That's why informed > > physicists such as Tom Roberts reject the idea of physical length > > contraction.... instead he said that the length contraction idea in SR > > is a geometric projection of the pole unto the barn frame. > > > Ken Seto > > > > You said they have to agree. They do not. That does not make a > > > contradiction. > > > > > I said that SR claim that the pole is physically contracted so > > > > that it can fit into the barn and that SR also made the contradictory > > > > assertion that the same pole is not physically contracted so that it > > > > is not able to fit into the barn. > > > > > > > I ask this > > > > > > question because that's what I think SR says. > > > > > > You are wrong about that.- Hide quoted text - > > > > > > - Show quoted text -- Hide quoted text - > > > > - Show quoted text -- Hide quoted text - > > > > - Show quoted text -- Hide quoted text - > > - Show quoted text -- Hide quoted text - > > - Show quoted text - |