Known physics defeated by simple puzzle?
in [Relativity]
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From: Ste on 5 Apr 2010 16:47 On 5 Apr, 17:37, PD <thedraperfam...(a)gmail.com> wrote: > On Apr 4, 12:24 pm, Ste <ste_ro...(a)hotmail.com> wrote: > > > But you don't explain Peter. Quite often, you don't even know what I'm > > asking. And even when you do, you generally just make assertions - > > like the one about the ladder fitting in the barn, and when I ask > > further questions about it, you don't understand what I mean by words > > like "real". And by the looks of it, we're also approaching an > > argument about the meaning of "the sky" and "the colour". > > > Even if you do have some understanding Peter, you are very poor at > > communicating it, and despite ostensibly speaking English you appear > > to have no comprehension of fairly simple questions. And it's not just > > you. Even Paul Draper, who claims to be a teacher for heavens sake, is > > just as bad. > > :>) > > This is in the camp of "Well, there's certainly nothing wrong with me, > so if I'm not understanding it properly, it must be your fault." Indeed. > It does not occur to you, apparently, that effective learning and > teaching does commonly involve concessions and compromises for the > sake of effective communication by both parties. Usually, by the way, > it is the student who makes the most concessions, because it is the > student that is desiring the most change in the state and contents of > his mind. I'm happy to make concessions, but I have to be able to ask questions and get meaningful answers. The ladder in the barn is a prime example. I'm told "the ladder contracts to fit in the barn". And I ask "so a person riding the ladder would see the barn expand", and the answer comes back "no, no, the person riding the ladder would see the barn *contract*". So I say, "well clearly in the latter case the ladder cannot possibly fit with both doors shut, so it must be a visual effect". "No, no" comes the reply, "the ladder *really* does fit according to a person standing in the barn, and it *really* doesn't fit according to the person riding the ladder". And I say, "well, it can't do both at once", and the reply that is merely asserted in response is "well, it does!". And that sums up thousands of words in probably hundreds of posts exchanged between me and a quite a few posters on the ladder and barn paradox. It always comes back to a plain assertion that "this is how it works", but there is no attempt to explain *why*, or any attempt to show how a mere visual explanation would not suffice for some or all of the observed effects.
From: paparios on 5 Apr 2010 16:59 On 5 abr, 16:47, Ste <ste_ro...(a)hotmail.com> wrote: > On 5 Apr, 17:37, PD <thedraperfam...(a)gmail.com> wrote: > > > I'm happy to make concessions, but I have to be able to ask questions > and get meaningful answers. The ladder in the barn is a prime example. > I'm told "the ladder contracts to fit in the barn". And I ask "so a > person riding the ladder would see the barn expand", and the answer > comes back "no, no, the person riding the ladder would see the barn > *contract*". So I say, "well clearly in the latter case the ladder > cannot possibly fit with both doors shut, so it must be a visual > effect". "No, no" comes the reply, "the ladder *really* does fit > according to a person standing in the barn, and it *really* doesn't > fit according to the person riding the ladder". And I say, "well, it > can't do both at once", and the reply that is merely asserted in > response is "well, it does!". > > And that sums up thousands of words in probably hundreds of posts > exchanged between me and a quite a few posters on the ladder and barn > paradox. It always comes back to a plain assertion that "this is how > it works", but there is no attempt to explain *why*, or any attempt to > show how a mere visual explanation would not suffice for some or all > of the observed effects. There are plenty of places where this so called "paradox" is explained. For instance, http://hyperphysics.phy-astr.gsu.edu/HBASE/Relativ/polebarn.html The relevant part is that the fact that two events are simultaneous in one frame of reference does not imply that they are simultaneous as seen by an observer moving at a relativistic speed with respect to that frame. Miguel Rios
From: PD on 5 Apr 2010 17:10 On Apr 5, 3:47 pm, Ste <ste_ro...(a)hotmail.com> wrote: > On 5 Apr, 17:37, PD <thedraperfam...(a)gmail.com> wrote: > > > > > On Apr 4, 12:24 pm, Ste <ste_ro...(a)hotmail.com> wrote: > > > > But you don't explain Peter. Quite often, you don't even know what I'm > > > asking. And even when you do, you generally just make assertions - > > > like the one about the ladder fitting in the barn, and when I ask > > > further questions about it, you don't understand what I mean by words > > > like "real". And by the looks of it, we're also approaching an > > > argument about the meaning of "the sky" and "the colour". > > > > Even if you do have some understanding Peter, you are very poor at > > > communicating it, and despite ostensibly speaking English you appear > > > to have no comprehension of fairly simple questions. And it's not just > > > you. Even Paul Draper, who claims to be a teacher for heavens sake, is > > > just as bad. > > > :>) > > > This is in the camp of "Well, there's certainly nothing wrong with me, > > so if I'm not understanding it properly, it must be your fault." > > Indeed. > > > It does not occur to you, apparently, that effective learning and > > teaching does commonly involve concessions and compromises for the > > sake of effective communication by both parties. Usually, by the way, > > it is the student who makes the most concessions, because it is the > > student that is desiring the most change in the state and contents of > > his mind. > > I'm happy to make concessions, but I have to be able to ask questions > and get meaningful answers. The ladder in the barn is a prime example. > I'm told "the ladder contracts to fit in the barn". It contracts to fit the barn in the rest frame of the barn, which is why the ladder makes no marks on the barn doors when the doors are shut at the same time. In the rest frame of the ladder, the ladder does not contract and indeed does not fit inside the barn at all. In the rest frame of the ladder, the reason why there are no marks on the barn doors when they are shut is that they were not shut at the same time in this frame. What is observationally verifiable and consistent across both accounts is that the ladder passed through the barn, that the doors where shut and reopened, and that there were no marks on the doors. However, it is a false expectation that "fitting in the barn" is a statement that applies to both reference frame, as is "doors shut at the same time". This is not a visual effect. It is a real, physical effect. Both accounts are fully consistent with the laws of physics, and neither of them is more "real" than the other. I've given this account to you already before, and now you act as though you've never heard of it before, giving the summation below that hundreds of posters have somehow given you the impression that "the ladder fits in the barn" is a frame-independent statement, which you naturally and rightfully would be something that would confuse you, if in fact that was indeed the summation that was given to you. Now, I advise you to please reread the few paragraphs by me above a few dozen times, so that the next time you are tempted to say that you were told that the ladder fits in the barn and yet the barn contracts to be shorter than the ladder, you will remind yourself that this is Stinking Thinking and Poor Recollection. > And I ask "so a > person riding the ladder would see the barn expand", and the answer > comes back "no, no, the person riding the ladder would see the barn > *contract*". So I say, "well clearly in the latter case the ladder > cannot possibly fit with both doors shut, so it must be a visual > effect". "No, no" comes the reply, "the ladder *really* does fit > according to a person standing in the barn, and it *really* doesn't > fit according to the person riding the ladder". And I say, "well, it > can't do both at once", and the reply that is merely asserted in > response is "well, it does!". > > And that sums up thousands of words in probably hundreds of posts > exchanged between me and a quite a few posters on the ladder and barn > paradox. It always comes back to a plain assertion that "this is how > it works", but there is no attempt to explain *why*, or any attempt to > show how a mere visual explanation would not suffice for some or all > of the observed effects.
From: Sue... on 5 Apr 2010 17:19 On Apr 5, 4:59 pm, "papar...(a)gmail.com" <papar...(a)gmail.com> wrote: > On 5 abr, 16:47, Ste <ste_ro...(a)hotmail.com> wrote: > > > > > On 5 Apr, 17:37, PD <thedraperfam...(a)gmail.com> wrote: > > > I'm happy to make concessions, but I have to be able to ask questions > > and get meaningful answers. The ladder in the barn is a prime example. > > I'm told "the ladder contracts to fit in the barn". And I ask "so a > > person riding the ladder would see the barn expand", and the answer > > comes back "no, no, the person riding the ladder would see the barn > > *contract*". So I say, "well clearly in the latter case the ladder > > cannot possibly fit with both doors shut, so it must be a visual > > effect". "No, no" comes the reply, "the ladder *really* does fit > > according to a person standing in the barn, and it *really* doesn't > > fit according to the person riding the ladder". And I say, "well, it > > can't do both at once", and the reply that is merely asserted in > > response is "well, it does!". > > > And that sums up thousands of words in probably hundreds of posts > > exchanged between me and a quite a few posters on the ladder and barn > > paradox. It always comes back to a plain assertion that "this is how > > it works", but there is no attempt to explain *why*, or any attempt to > > show how a mere visual explanation would not suffice for some or all > > of the observed effects. > > There are plenty of places where this so called "paradox" is > explained. For instance,http://hyperphysics.phy-astr.gsu.edu/HBASE/Relativ/polebarn.html > > The relevant part is that the fact that two events are simultaneous in > one frame of reference does not imply that they are simultaneous as > seen by an observer moving at a relativistic speed with respect to > that frame. < Einstein's relativity principle states that: All inertial frames are totally equivalent for the performance of all physical experiments. In other words, it is impossible to perform a physical experiment which differentiates in any fundamental sense between different inertial frames. By definition, Newton's laws of motion take the same form in all inertial frames. Einstein generalized this result in his special theory of relativity by asserting that all laws of physics take the same form in all inertial frames. >> What is simultaneous in one inertial frame is simultaneous in a relativity moving frame. The ad hoc definition you are trying to use is stated to have no physical significance: <<There is only one demand to be made of the definition of simultaneity, namely, that in every real case it must supply us with an empirical decision as to whether or not the conception that has to be defined is fulfilled. That my definition satisfies this demand is indisputable. That light requires the same time to traverse the path A > M as for the path B > M is in reality neither a supposition nor a hypothesis about the physical nature of light, but a stipulation which I can make of my own freewill in order to arrive at a definition of simultaneity.>> http://www.bartleby.com/173/8.html Now wondering why I bother writing to someone who has already stated it is a matter of religion for him, but why waste keystrokes. send. Sue... > > Miguel Rios
From: Ste on 5 Apr 2010 17:29
On 5 Apr, 17:51, PD <thedraperfam...(a)gmail.com> wrote: > On Apr 4, 12:36 pm, Ste <ste_ro...(a)hotmail.com> wrote: > > > As I've said before, the easiest definition of "simultaneous events" > > is "those events which would have occurred at the same time if > > information about their occurrance had travelled instantaneously > > across space". This is basically the common sense definition that > > people use anyway. > > This is the common sense definition that YOU use. Please do not > presume to speak for "people" who, through different assumptions and > perhaps a bit more openness, would arrive at a different definition > entirely. Indeed, in my experience, students usually intuitively > arrive at a definition that is a lot closer to the one that is used by > physicists than the one you use. Then what definition *do* they use? > > If I sit with family at 7 o'clock the evening and I ask "what time did > > you have breakfast this morning", I'm not interested in when the > > information is actually conveyed to me (i.e. long after breakfast > > time). That is, I would not expect to be told "I've just had > > breakfast", and when I query this I would not expect to be told that > > "I had breakfast 5 seconds ago, when information of its occurence > > first reached your ears". > > > What I would expect to be told, when I ask "when did you have > > breakfast", is "I had breakfast at 9 o'clock this morning". > > This has nothing to do with simultaneity. It has to do with comparison > of an event against a local clock. If I asked you what time you had > breakfast, and you told me at 9:00 this morning, and I asked you how > you knew that, you might say "Because I looked at my watch while I was > doing it." You would not say, "Because had a signal from the National > Bureau of Standards had reached me instantaneously, it would have told > me 9:00." Indeed, but implied in the question is that "what time..." means "what time by a clock that is presupposed to be accurate...". And anyway, my intention is not to go on a long drawn out debate about the meaning of words again. It is simply to make a single point, that it is commonly held that events can happen before you know about them (in other words, before the information has reached you). The other definition of "simultaneous", that of "information about two events being received at the same time", is an unworkable definition, because it means nothing ever happens before you know about it (in other words, no one ever has breakfast until they tell you about it, and the time at which they ate breakfast was at the time they told you about eating it, not at the time that the food was actually consumed). I find it more convenient to make a distinction between "when something really happens" and "when you find out something happens/ when something apparently happens". > > The problem with this nonsense definition of simultaneity that the > > physics community seem to be using is that nothing is held to have > > ever happened until you actually measure it, and because it takes time > > for information to travel, that means not everyone necesarily measures > > the same event at the same time. And according to this definition of > > simultaneity, the family member above had breakfast at 7pm in the > > evening, because it took until 7pm for the information to reach me! > > You still don't get it. Simultaneity is determined AFTER accounting > for the transit time of the signal. I think we may be using a different definition of "simultaneity" Paul. > If two signals arrive at the same time, at 17:01:34, one does not say > that the events that generated the signal were simultaneous at > 17:01:34. One asks, how long did the signal take to get here from the > first event? How long did the signal take to get here from the second > event? If the answer to both those questions is 00:00:17, then you > know the events both occurred at 17:01:17, and since they both > happened at the same time, they were simultaneous. Yes, indeed. > On the other hand, if another observer sees a signal from one event at > 17:01:34 and a signal from the other event at 17:01:37, then you still > need to ask, how long did the signal take to get here from the first > event? How long did the signal take to get here from the second event? > If the answer to both those questions is 00:00:17, then you know the > first event occurred at 17:01:17 and the second event at 17:01:20, and > they were not simultaneous. > > And here is the interesting thing: We have real cases where there are > two and only two events, and one observer will see signals from them > both at 17:01:34, and another observer will see one signal at 17:01:34 > and the other signal at 17:01:37. Then BOTH observers will figure out > the time of transit of the signals and deduce that the transit times > where 00:00:17 in all cases. The conclusion one draws from this set of > circumstances is obvious. Then we need to discuss this scenario. I do not see how this can work, unless the clocks themselves fall out of synchronisation (and hence are not actually measuring the same periods of time as each other). |