If we synchronise two clocks, and have one stationary, and the other moving at near c for a long time then they will be out of time due to time dilation. If we consider from the stationary clock, then the other clock appears to be moving at near c and should run slower. If we consider from the moving clock, then the stationary clock appears to be moving at near c, and so it should run slower. I think what I'm trying to say is that if two clocks are comoving, how do we tell which one experiences time dilation?
Hi cckieran Firstly, comoving means "moving together", or "in the same frame of reference", or "stationary with respect to each other". Now. The scenario is symmetrical. Each clock considers the other one to be running slowly. This can only be possible if there is no universal now. Two events that happen in a particular order from one point of view might actually happen in the reverse order from another point of view. This means that it's not possible to unambiguously compare the time on two clocks in different reference frames, unless they are in the same location (ie in the instant that they pass each other).
I am not the expert but I can tell you that they are going to claim that one clock must accelerate to establish the relative velocity. During such acceleration it is no longer an inertial system But frankly that appears to me to be a strawman arguement. 1 - Suppose that the period of acceleration is varied for a series of tests. a - Accleration is 1 year. Constant velocity is for another year. Time dilation = x b - Acceleration is for 1 second and constant velocity is for another year. Time dilation = x 2 - Or accelerate both clocks for the same period and constant velocity for the same added period. a - In opposite directions. b - Comoving. Now try and make sense of "Time-Dilation" claims. Please Register or Log in to view the hidden image!
I think you have mis-stated something here. If they are co-moving (i.e. - at relative rest to each other) they do not see each other as having slowed time. Time dilation is only between clocks with relative motion to each other.
That's irrelevant to the question which was asked. True, but, as I said, irrelevant. If you mean "x" to be the same value here, you are incorrect. And so... ? I'm still trying to make sense of the point you're trying to make here.
I don't follow this comment. What isn't relevant?. 1 - I am not an expert? 2 - One clock accelerates and the other doesn't?. This issue has been raised so many times in the twins paradox that it is a standard cut and paste response. How so?. I know for a fact that not only have every Relativists here (including you) argued that acceleration of one twin is the key to time dilation, the fact of linear (constant) relative velocity is as he has described "mutually applied to each clock" such that there can be no net actual change in time between clocks in the final analysis. I don't want to hear about GR and gravity fields, etc., because that is only a diversionary issue in specific cases and is not at issue as to the "Relative Velocity" issue between clocks and time dilation. Well, this really is quite simple. The issue he raises has been raised several times. "Relative" means "Simultaneously Mutual" and reversable. If it doesn't meet those requirements then it is not "Relative". If it meets those requirements then it can have no net affect in the final analysis. Only the arguement regarding acceleration can possibly have any merit. These examples are to show that fact when "x" is calculated. The duration of "Constant Relative Velocity" will have no impact on the ultimate "Round Trip" net clock affect. Take a case where two identical clocks were formed instantaneously by the Big Bang and coming into existance had a relative velocity of .9 c with respect to each other. Assuming 1 million years from the enception somehow this unusual BB event occured so as to cause the clocks motion to result in their ultimate near head on collision. As they pass each other in the night, what accumulated time will be recorded on each clock? Recall they were synchronized by "Stipulation" via the concept of enception. They are the only clocks in the universe. There was no period of acceleration. What is the accumulative affect on each clock in terms of time dilation due to their 1 million year "Constant Relative Velocity" to each other? I should hope the above has done that. We shall wait and see.
cckieran , thats a genius question. How does the dam moving clock know that it is moving relative to the stationary one. Does this mean that by moving in a certain direction where time is fastest is infact the direction towards the center of universe or the origin of BigBang ?
It is obvious from the context that cckieran means two clocks that are not comoving, and I have responded accordingly.
I am not disagreeing with your assessment nor the fact that he intended to say something different. I was merely trying to clarify the record as to what was meant. :m:
I'm sorry, but that makes no sense at all! There is no "direction" where time is fastest- If A is moving in any direction at relativistic speed relative to B, then B will observe A's time as "slow". Of course, A will also observe B's time as "slow".
The interesting thing is that in all this relative time we still have a zero frame of reference. How is one clock deemd to be "slow" and another "faster" if the reference is not deemed absolute. Is the zero or absolute reference a mathematical construct or is the time dilation a mathematical construct or are both a mathematical construct.......
Mac, the history of the clocks makes absolutely no difference to the cckeiran's question. The resolution of cckieran' problem is easy - the time difference between the clocks depends only on the reference frame in which they are compared, and the manner in which they were synchronized. For example, let's synchronize the clocks as they pass each other. This is good because the synchronization is then frame independent - at that instant, both clocks agree that the other clock reads the same time. Now at an arbitrary time in the future: In A's reference frame, clock B's time is less than clock A's time. In B's reference frame, clock A's time is less than clock B's time. In the average reference frame (in which A and B are moving at the same speed in opposite directions), clock A's time is the same as clock B's time. Now, your scenario is very interesting, and poses a real puzzle for me! Firstly, I'll consider the objection that the Big Bang happened at a single point, so the clocks must have been at the same point at that instant. I think this objection may be dismissed - it is my understanding that according to the GR model the Big Bang singularity (assuming for the moment that it had a physical reality) was not necessarily of zero size. So... two clocks, initially separated by some distance, at an instant specified by the Big Bang. I'm afraid I have more questions than answers. It seems to me that the problem is in specification of the Big Bang as a Universal instant, simultaneous in all reference frames - something that defies the relativity of simultaneity. This seems a bit suspicious to me... the BB does have an associated frame of reference (that in which the average kinetic energy of all mass/energy in some large region is zero, which I think corresponds to the CMBR frame). Does that mean the BB was not simultaneous in a different reference frame? Would it matter if it wasn't? Does it even make sense to consider simultaneity across the BB singularity? It's a spacetime singularity after all, so time comparisons might not be meaningful? Is there a GR resolution to this problem? Thinking about real consequences, is the CMBR of the same age in all areas of our sky? The CMBR is a dipole (red shifted on one side, blue shifted on the other), so is the CMBR actually younger on one side than it is on the other?
We agree except I don't have the problem that most seem jto by stipulating clock synchronization. It is a thought experiment is it not. It seems synchronization can be stipulated. If so then one can set up several interesting scenario's. I agree and I anticipated that complaint. But one could argue for thought experiment purposes that two virtual particles should appear in the universe some distance apart and that this event is stipulated to be simultaneous, ergo an observer located mid-way between them. Further that these particles, unlike most such particles but are real as does occur when a Black Hole absorbs one of these particles in a virtual pair, that they survive sufficently long and are moving towards each other at speeds equal ergo the observer. If we now claim that they do have a decay rate (hence can be viewed as a form of clock). You can have the same situation I stipulated at the outset. So go from there. I believe that situation is deamed to be anisotropy or caused by motion relative to the background motion of the CMBR.
First, some clarifications to bring the language and assumptions of your scenario into alignment with SR (feel free to raise objections, and I'll start again!): ...these events are... The word event has a specific meaning in the framework of relativity. An event is a single point in space-time. For any reference frame, an event is a specific point in space at a specific point in time. ...ergo an observer with the average velocity of the two particles. In the SR model, the location of the observer has no relevance to the simultaneity of events, only the observer's velocity. ...at equal speeds relative to the observer. Clarification only. I'm almost certain this is what you meant, but I was confused by your wording (sorry!) OK! In this case there's no problem, because we have a specific reference frame (that of the observer) in which our two 'clocks' were synchronized. For our observer of average speed the time dilation of the two 'clocks' is equal, so they say that the two particles are the same age when they collide or pass each other. (I'm using 'age' to mean the proper time experienced by the particle in its own reference frame). Now consider an observer comoving with one of the particles (particle A) - according to SR, what does that observer say about the ages of the particles at the instant that they pass each other or collide? I was going to answer this, but it's a good opportunity for testing. Mac, What do you think that SR suggests that an observer comoving with particle A sees as the particles pass each other? a) A and B are of the same age b) A is older than B c) B is older than A d) other (?!) cckeiran, you could have a go at this as well if you're still around and are following the scenario.
No objections. Clarifications appreciated. We agree. The problem however is the issue of time dilation as seen by observers comoving with each particle (which if I read it correctly is your next question). They see each others clocks as running slower, hence they are getting older faster than the observed particle. But now you have Relativity predicting multiple time intervals for the same particle. All cannot be correct. Only the one associated with their frame of rest is correct, which in this case means time dilation did not actually result in a physical change in age. Time dilation is exposed as a perception and not a reality. I have to assume this is a second observer exclusive of the observer used to synchronize clocks. Further this observer is comoving with i.e "A" toward "B". Ans: "A" is older, For an observer comoving with "B" he would conclude the opposite. That is he is older in that "A's" clock appears to be running slow.
Did you consider that for an observer comoving with A the two initiating events were not simultaneous? The correct answer is that SR suggests that for an observer comoving with A: 1) B appears before A 2) B ages slower than A A and B are of the same age when they pass each other So for the observer comoving with A: particle B has been in existence for longer than A but is the same age as A, and time dilation is seen to be a reality!
You are mixing apples and oranges and getting applesauce. I am quoting time dilation based on clock rates. You are introducing simultaneity of "A's" view of when "B" comes into existance. "A's" view of that is superflous in that upon arriving at the common spatial ordinates their onboard clocks will have accumulated the same amount of time but appear to each other as having ticked at different rates. You are actually making my point. Relavistic views are not reality. The only reality is the one at rest to the clock. Its natural tick rate. If I die at the age of ninety I do not die at different ages. Even shifted by simultaniety such that my death may be claimed to have been percieved at a different time, I was still ninety when I died. I did not die at 80 or 100 just because you thought I died at some other time or thought my clock was running at some other speed. Make sense?
Mac, If your point is that proper times (natural tick rates) are invariant, then duh! That's what SR says too! Do you think it doesn't? You are welcome to believe that this is the only reality if you like, but that seems to me to be an article of faith or philosophy. My point is that the SR model suggests otherwise, and consistently so. You don't have to believe in it's reality, but I don't see how you can claim that it is not self-consistent. In the scenario in question, the special relavity model suggests that for the observer comoving with A, particle B has actually been in existence for longer than particle A. The event of particle B's appearance happened before the event of particle A's appearance. Don't get tied up with the age concept - age is invariant! The time dilation question is that of the time separation between two events in a given reference frame.
Here's an extension to that scenario in an attempt to illustrate the reality of time dilation according to SR: The two particles pass each other. Some time later, particle A perishes, and in doing so triggers the appearance of particle C. From its inception, particle C is approaching particle B, and eventually collides with it. Question: At the collision, is the age of particle B more, less, or the same as the sum of the age of particle A when it perished and the age of particle C at the collision? What does the SR model suggest? According to SR, would different observers give different answers?
