Simultaneous events and Einstein's absolute time
in [Relativity]
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From: DSeppala on 31 Jan 2010 09:47 In his theory of relativity, Einstein includes implicit use of absolute time. This makes his notion of simultaneous events undefined for many scenarios. Here's a simple example that demonstrates the problem. Let there be two identical devices that emit a pulse once a second. I'll call these devices PL1 and PL2. Let these two devices have zero relative velocity, and be at the same coordinate on the x-axis, and be synchronized such that they each emit pulses at the same time. The simple question is, each time they emit a pulse are these simultaneous events per Einstein's theory? I presume most will say yes. But with Einstein's theory, the answer is indeterminate. There is not enough information given to answer that question. For those who think that answer is wrong we add a third identical device along the x-axis to the right of PL1 and PL2. I'll call this device PR1. Now let there be an inertial frame moving along the x- axis relative to these devices. Let this frame turn on PL1 and PR1 simultaneously and let the velocity and distances be such that these simultaneous events in the moving frame occur one second apart in the rest frame of these devices. Now per Einstein, when each pulse is generated from PL1 and PR1 the moving frame observer says these events occur simultaneously. Do the rest frame observers say these events occur simultaneously? I presume most in this group would say no. Those events are not simultaneous, they occur one second apart as measured in the rest frame. If anyone thinks that is the correct answer, we go back to our original two devices PL1 and PL2. If I tell you PL2 was turned on and started emitting pulses one second after PL1 started emitting pulses, do you now say pulses emitted from PL1 and PL2 are no longer simultaneous events, as you did for PL1 and PR1? And do you now agree that there was insufficient information to determine the answer to the first question in this posting? Einstein in his theory of relativity actually implicitly includes a notion of absolute time in each problem, and there seems to be an implicity redefinition of that in problems like the twins problem and other problems. David Seppala Bastrop TX
From: Dirk Van de moortel on 31 Jan 2010 11:56 DSeppala <dseppala(a)austin.rr.com> wrote in message a945196e-ccbc-426a-a813-789838b1e9f4(a)h2g2000yqj.googlegroups.com > In his theory of relativity, Einstein includes implicit use of > absolute time. "On The Electrodynamics Of Moving Bodies", Einstein, 1905: | Now we must bear carefully in mind | that a mathematical description of this kind has no physical meaning unless | we are quite clear as to what we understand by "time." | ... | It might appear possible to overcome all the difficulties attending the definition | of "time" by substituting "the position of the small hand of my watch" for | "time." And in fact such a definition is satisfactory when we are concerned with | defining a time exclusively for the place where the watch is located; but it is no | longer satisfactory when we have to connect in time series of events occurring | at different places, or-what comes to the same thing-to evaluate the times of | events occurring at places remote from the watch. | ... | The "time" of an event is that which is given | simultaneously with the event by a stationary clock located at the place of | the event, this clock being synchronous, and indeed synchronous for all time | determinations, with a specified stationary clock. | ... | It is essential to have time defined by means of stationary clocks in the | stationary system, and the time now defined being appropriate to the stationary | system we call it "the time of the stationary system." "On The Electrodynamics Of Moving Bodies", Einstein, 1905 Dirk Vdm
From: eric gisse on 31 Jan 2010 15:53 DSeppala wrote: > In his theory of relativity, Einstein includes implicit use of > absolute time. This makes his notion of simultaneous events undefined > for many scenarios. Here's a simple example that demonstrates the > problem. What part of 'this is too hard for you' do you not understand? You've been doing this since 1995 and you still do not understand. How many years of not-understanding does it take for you to acknowledge that YOU DO NOT UNDERSTAND AND NEVER WILL? [snip rest, unread]
From: artful on 31 Jan 2010 16:39 On Feb 1, 1:47 am, DSeppala <dsepp...(a)austin.rr.com> wrote: > In his theory of relativity, Einstein includes implicit use of > absolute time. No .. it would help if you knew what SR actually says before posting about it > This makes his notion of simultaneous events undefined > for many scenarios. But there is no absolute time, and simultaneity is always well defined within an inertial frame > Here's a simple example that demonstrates the > problem. There is no problem > Let there be two identical devices that emit a pulse once a second. > I'll call these devices PL1 and PL2. Let these two devices have zero > relative velocity, and be at the same coordinate on the x-axis, and be > synchronized such that they each emit pulses at the same time. I assume you are referring to the frame whose where you are taking x- axis coordinates > The simple question is, each time they emit a pulse are these > simultaneous events per Einstein's theory? In the frame where you say they happen at the same time .. yes > I presume most will say > yes. But with Einstein's theory, the answer is indeterminate. No it is not .. with the information you have given. If things happen at the same time, they are, by definition, simultaneous. If they are not simultaneous, they do not happen at the same time > There > is not enough information given to answer that question. Yes .. there was. > For those who think that answer is wrong we add a third identical > device along the x-axis to the right of PL1 and PL2. I'll call this > device PR1. Now let there be an inertial frame moving along the x- > axis relative to these devices. Let this frame turn on PL1 and PR1 > simultaneously and let the velocity and distances be such that these > simultaneous events in the moving frame occur one second apart in the > rest frame of these devices. Now per Einstein, when each pulse is > generated from PL1 and PR1 the moving frame observer says these events > occur simultaneously. Do the rest frame observers say these events > occur simultaneously? I presume most in this group would say no. That is correct. events simultaneous in one frame are not simultaneous in another. > Those events are not simultaneous, they occur one second apart as > measured in the rest frame. You are overly verbose > If anyone thinks that is the correct answer, we go back to our > original two devices PL1 and PL2. If I tell you PL2 was turned on and > started emitting pulses one second after PL1 started emitting pulses, > do you now say pulses emitted from PL1 and PL2 are no longer > simultaneous events, as you did for PL1 and PR1? The n'th pulse of PL1 is not simultaneous with the n'th pulse of PR1. But it is simultaneous with another pulse from PR1. So there are simultaneous pulses from those clocks. > And do you now > agree that there was insufficient information to determine the answer > to the first question in this posting? No > Einstein in his theory of relativity actually implicitly > includes a notion of absolute time in each problem, No > and there seems to > be an implicity redefinition of that in problems like the twins > problem and other problems. No
From: Paul B. Andersen on 1 Feb 2010 06:49
On 31.01.2010 15:47, DSeppala wrote: [..] > Let there be two identical devices that emit a pulse once a second. > I'll call these devices PL1 and PL2. Let these two devices have zero > relative velocity, and be at the same coordinate on the x-axis, and be > synchronized such that they each emit pulses at the same time. > The simple question is, each time they emit a pulse are these > simultaneous events per Einstein's theory? I presume most will say > yes. [..] > If anyone thinks that is the correct answer, we go back to our > original two devices PL1 and PL2. If I tell you PL2 was turned on and > started emitting pulses one second after PL1 started emitting pulses, > do you now say pulses emitted from PL1 and PL2 are no longer > simultaneous events, as you did for PL1 and PR1? And do you now > agree that there was insufficient information to determine the answer > to the first question in this posting? Good grief! :-) I and my wife are two persons who eat dinner once a day. My wife and I are synchronized so that the events "she eats dinner" and "I eat dinner" occur at the same time and place. The simple question is, are these simultaneous events per Einstein's theory? If I tell you that I started eating dinner three years before my wife, do you now say dinner eaten by my wife an me are no longer simultaneous events, and do you now agree that there was insufficient information to determine the answer to the simple question above? -- Paul http://home.c2i.net/pb_andersen/ |