Properties of a preferred frame, an inertial frame in SR and
in [Relativity]
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From: Daryl McCullough on 18 Jul 2010 10:34 JT says... > >On 18 Juli, 15:10, stevendaryl3...(a)yahoo.com (Daryl McCullough) wrote: >> There is one universe, but there are many different coordinate >> systems that can be used to describe that universe. Whether two >> events are simultaneous or not is relative to a coordinate system. >> Whether one event occurs before or after another is relative to a >> coordinate system. >> >> If you assume that ordering of events is independent of observers, >> then that means *either* that you are assuming an unobservable absolute >> time (a preferred coordinate system), or you are assuming the existence >> of signals of unbounded speed. >No that is simpy not correct, you can pick any cordinate, all >cordinate system it will still describe the same universe same event >period it is just a matter of picking point of origin. The question is not describing the same events---every coordinate system describes the same events---the question is the temporal *ordering* of events: which events occurred before which other events. Coordinate systems disagree about that. Look at a particular example, which I've gone over before. You have two pairs of clocks, C1 and C2, which are at rest relative to one another, and are lined up left to right, with C1 to the left of C2. You have another pair of clocks, D1 and D2, which are at rest relative to one another, with D1 to the left of D2. The clocks D1 and D2 are moving left-to-right at speed 0.866 c relative to clocks C1 and C2. We note the following events involving the clocks: e1. When clock D1 passes C1, both clocks show time 12:00. e2. When clock D2 passes C2, D2 shows time 11:50 and C2 shows time 12:10. e3. When clock D1 passes C2, D1 shows time 12:10 and C2 shows time 12:20. These same events occur in every coordinate system. But in a coordinate system in which C1 & C2 are at rest, e1 occurs before e2, which occurs before e3. In a coordinate system in which D1 & D2 are at rest, e2 occurs before e1, which occurs before e3. -- Daryl McCullough Ithaca, NY
From: Daryl McCullough on 18 Jul 2010 10:41 JT says... >No that is simpy not correct, you can pick any cordinate, all >cordinate system it will still describe the same universe same event >period it is just a matter of picking point of origin. Setting up a coordinate system is not just a matter of picking an origin. A coordinate system assigns a time to each event that happens. If you have a collection of clocks that are all at rest in some frame, then you need to know how to set each clock in order to give a time to events occurring at that clock. We can always pick some clock to be the reference clock, and arbitrarily declare some moment to be the zero of time (at which we set the clock to 12:00). But then how do you specify when distant clocks should be set to 12:00? The only way I know of is if you have some signal travel from the reference clock to the distant clock, and you know how long the signal took to travel that distance. But how do you know that? Knowing all the events that take place is *not* sufficient to know which events occurred before which other events. -- Daryl McCullough Ithaca, NY
From: JT on 18 Jul 2010 10:52 On 18 Juli, 16:34, stevendaryl3...(a)yahoo.com (Daryl McCullough) wrote: > JT says... > > > > >On 18 Juli, 15:10, stevendaryl3...(a)yahoo.com (Daryl McCullough) wrote: > >> There is one universe, but there are many different coordinate > >> systems that can be used to describe that universe. Whether two > >> events are simultaneous or not is relative to a coordinate system. > >> Whether one event occurs before or after another is relative to a > >> coordinate system. > > >> If you assume that ordering of events is independent of observers, > >> then that means *either* that you are assuming an unobservable absolute > >> time (a preferred coordinate system), or you are assuming the existence > >> of signals of unbounded speed. > >No that is simpy not correct, you can pick any cordinate, all > >cordinate system it will still describe the same universe same event > >period it is just a matter of picking point of origin. > > The question is not describing the same events---every coordinate > system describes the same events---the question is the temporal > *ordering* of events: which events occurred before which other > events. Coordinate systems disagree about that. > > Look at a particular example, which I've gone over before. > > You have two pairs of clocks, C1 and C2, which are at rest > relative to one another, and are lined up left to right, with > C1 to the left of C2. You have another pair of clocks, D1 and > D2, which are at rest relative to one another, with D1 to the > left of D2. The clocks D1 and D2 are moving left-to-right at > speed 0.866 c relative to clocks C1 and C2. We note the following > events involving the clocks: > > e1. When clock D1 passes C1, both clocks show time 12:00. > e2. When clock D2 passes C2, D2 shows time 11:50 and C2 shows time 12:10. > e3. When clock D1 passes C2, D1 shows time 12:10 and C2 shows time 12:20. > > These same events occur in every coordinate system. But in a coordinate > system in which C1 & C2 are at rest, e1 occurs before e2, which occurs > before e3. In a coordinate system in which D1 & D2 are at rest, e2 occurs > before e1, which occurs before e3. > > -- > Daryl McCullough > Ithaca, NY Take the existensial determinism of a two stars relative at rest going supernova are you that deluded that you think, it is undecidable which star did first go out of existence? Do you really think it is a matter of observer which did go out of existence first....... I feel very sorry for you if can not determine the way temporal order in which they dissapeared indeed you must have some logical impairment. Temporal order of spatial separated events is absolute........ and there can be no doubt about it, for relative moving objects at difference distance you have to account transmission delays, and if you want to know which supernova that had longest period you would also have to know at which velocity they travel and if they are approching or receding. JT
From: Daryl McCullough on 18 Jul 2010 11:05 kenseto says... >When you compare two clocks in relative motion the following >possibilities exist: >1. A is running faster than B then B is running slower than A. >3. B is running faster than A then A is running slower than B. > >At no time the bogus concept of mutual time dilation that: from A's >point of view B is running slow and from B's point of view A is >running slow. Strictly speaking, it's not that one clock runs slow relative to another clock; one clock runs slow relative to a *coordinate* system. A coordinate system is not a single clock, it is a system of *synchronized* clocks. Let's go through an example: Suppose in one frame we have two synchronized clocks at rest, C1 and C2, lined up left-to-right, with C1 to the left of C2. In another frame, we also have two synchronized clocks at rest, D1 and D2, that are also lined up left-to-right. Clocks D1 and D2 are traveling at 0.866c relative to clocks C1 and C2, and their velocity is left-to-right. They are traveling so that D1 & D2 pass very close to C1 and C2. So here are some events involving these two pairs of clocks: e1: D1 passes C1, and they both show time 12:00 e2: D2 passes C2, and D2 shows time 11:50, while C2 shows time 12:10 e3: D1 passes C2, and D1 shows time 12:10, while C2 shows time 12:20 If we assume that C1 and C2 are synchronized, then we explain the events this way: (1) At time 12:00, D1 shows time 12:00, while D2 shows time 11:45; D1 & D2 are not synchronized. (2) At time 12:10, clock D2 has advanced 5 minutes, to 11:50, while clocks C1 and C2 have advanced 10 minutes, to 12:10. So it is running at 1/2 the speed of C1&C2. At this time, D1 shows time 12:05. (3) At time 12:20, clock D2 has advanced another 5 minutes, to 12:10. Clock C2 has advanced another 10 minutes, to 12:20. So if we assume that C1 and C2 are synchronized, we conclude that D1 and D2 are running slow, and that they are not synchronized (D1 is 15 minutes ahead of D2). On the other hand, if we assume that D1 and D2 are synchronized, we explain the events this way: (1) At time 11:50, clocks D1 and D2 show time 11:50. Clock C2 shows time 12:10, while clock C1 shows time 11:55. (2) At time 12:00, clocks D1 and D2 have advanced 10 minutes, to 12:00, while clock C1 has only advanced 5 minutes, to 12:00, and C2 has also advanced 5 minutes, to 12:15. (3) At time 12:10 clocks D1 and D2 have advanced another 10 minutes, to 12:10. Clock C1 has advanced 5 minutes, to 12:05. Clock C2 has advanced 5 minutes, to 12:20. So if we assume D1 and D2 are synchronized, we conclude that C1 and C2 are running slow, and that they are not synchronized (C2 is 15 minutes ahead of C1). So mutual time dilation is *not* a comparison of two clocks alone; it is a comparison of 4 clocks, together with assumptions about synchronization. Just comparing two clocks, you cannot possibly say whether one clock is running slower than the other. -- Daryl McCullough Ithaca, NY
From: eric gisse on 18 Jul 2010 16:09
kenseto wrote: [...] Are you going to do this until the day you die, Ken? |