
#1
Feb1612, 11:04 PM

P: 183

I fully understand time dilation if I already could believe it, but I am not convinced yet.
What is the most convincing argument for you, that you are sure time dilation exist and so duration is different in locations (when duration is always the same, I believe in time dilation too, that's not the problem, its just a definition of Simultaneity)? 



#2
Feb1612, 11:08 PM

Mentor
P: 16,473

My favorite is the muon lifetime experiments: "They stored muons in a storage ring and measured their lifetime. When combined with measurements of the muon lifetime at rest this becomes a highly relativistic twin scenario (v ~0.9994 c), for which the stored muons are the traveling twin and return to a given point in the lab every few microseconds. Muon lifetime at rest: Meyer et al., Physical Review 132, pg 2693; Balandin et al., JETP 40, pg 811 (1974); Bardin et al., Physics Letters 137B, pg 135 (1984). Also a test of the clock hypotheses (below)." 



#3
Feb1712, 05:35 AM

Mentor
P: 21,999

My favorite is GPS.




#4
Feb1712, 01:36 PM

Emeritus
Sci Advisor
PF Gold
P: 5,500

What are your best arguments for time dilation, so duration is different ?
The HafeleKeating experiment has the most charisma.




#5
Feb1812, 03:07 AM

P: 500

Are you looking for experimental evidence that confirms time dilation in the data, or are you looking for an explanation of how time dilation could be an existential reality?
The data received indicates dilation; but that data is always received locally, the interpretation of this data and extension of its implications to the existential state of the source of the data is a theoretical process. I think most probably take the "philosophy" that the data represents the receiving observer's local existential reality, and use SR principles to infer the local existential reality of the data source in it's own reference frame... not much else to work with unless or until new experimental evidence could indicate otherwise... ? 



#6
Feb1912, 04:48 PM

P: 183

Thanks all for the answers I go to read them all.
@bahamagreen In fact I understand since yesterday what time dilation is, its not what I expected. Its just local time or remote time. The time you loose is the time from light being overbridged (or just time). That C is always constant is something I already understand in fact (but now for sure). So I was looking for data (and shall read the articles) but in fact I will not expect that C is not found. The last problem is, time dilation is really to understand in the moving direction, but in the other directions is it still mysterious. I would expect: 1) in other directions is no time dilation because there is no length contraction and so your ruler is not smaller 2) in other directions is length contraction as well, and so the same time dilation 



#7
Feb1912, 06:19 PM

PF Gold
P: 4,521

If you go on to read the rest of his paper, he eventually gets to the dilation of time on a moving clock, that is, a clock moving with respect to the coordinate system, that is, a clock moving in the Frame of Reference. The time on the moving clock is called Proper Time. The ratio of the Proper Time on a clock moving with respect to the clocks displaying Coordinate Time is the reciprocal of gamma. It's as simple as that. So please don't say the time dilation is just local time or remote time. You should say that time dilation is what happens to a moving clock (Proper Time) compared to a stationary clock (Coordinate Time). 



#8
Feb2012, 06:41 PM

P: 183

Yes you are right, sometimes I will mix the concept or definitions (not a professional in physics, but not on my website, I shall check it all again because I finish this subject and rewrite my blog and website), but I understand it very well. Besides I gave you an answer in the other thread (deleted and written again a time ago). So there you don't find this confusion anymore .. 



#9
Feb2112, 06:59 AM

P: 3,178

http://physicsforums.com/showthread.php?t=575332&page=2 (you can start reading the comments by ghwellsjr, dalespam and myself from post #30 which describes time dilation without a definition of simultaneity). The first positive detection of time dilation was the IvesStilwell experiment: http://en.wikipedia.org/wiki/Ives%E2...ell_experiment It makes use of the fact that "relativistic Doppler" is the combined effect of classical Doppler and time dilation. Also interesting was the first indirect experiment as it was completely independent of relativity of simultaneity: http://en.wikipedia.org/wiki/Kennedy...ike_experiment Harald 



#10
Feb2112, 10:25 PM

P: 183

If I consider only my own example to make it simple (for my own) I just see with length contraction the car and ruller are smaller in frame B, but they both arrive at the same moment in as well frame B and A. But if there is communication between measuring persons between frame A and B, and B would give a light signal with his position to frame A and that signal arrives at the same moment the car arrived on time t in frame A, the car was on 1/γ . t in frame B. So I see it now, its just a measuring problem. And that time of the light signal, we call it time dilation. You can say there is also time dilation when there is no length contraction, but you need a clock and ruler to prove that, and do you have in fact than length contraction too while measuring ? Than you can say a moving clock runs slower, thats not only because it moves. Its just the moments you compare with a stationary clock. So in my example I could say send the time in the signal, it would be 1/γ. t from frame B when the light signal arrives on t in frame A. So the clock does not run slower, its just a measuring problem because you need it to be sure what the location is from the moving person (and vice versa). You can make 1000 of errors in thinking with time dilation I guess .... who is right, I think the future and better experiments with expensive equipment impossible to have in your kitchen ... 



#11
Feb2212, 01:27 AM

P: 3,178





#12
Feb2212, 01:01 PM

P: 183

Maybe you have not seen that thread, so in frame A a car drives between start and endpoint and takes t in time (measured in frame A), seen from frame B on a specified moment it is on 1/γ . t (because of length contraction), but on that time it is also on 1/γ . t in frame A. Strange in all this theory is the fact how long it takes before it is clear, because everybody comes with the same examples, time after time and yet its not clear for me ... I am curious to your answer ... Suppose the car is in frame A 1 meter long, its speed is 10m / s, so ten cars after each other in 1 second, in frame B ten cars of 1/γ m after each other since the start point, but remember the car was already shorter in frame A but measured with the unit 1 m, in frame B with the unit 1/γ m ... Maybe it is better to answer in this thread : http://www.physicsforums.com/showthread.php?t=576717 



#13
Feb2212, 01:24 PM

P: 3,178





#14
Feb2212, 02:05 PM

PF Gold
P: 706

Then when you see the Galilean transformation, and compare it to the Lorentz Transformation, and compare the two to the rotation transformation. Since the Lorentz Transformation looks just like rotation, but with hyperbolic sines and cosines instead of circular sines and cosines, there's a certain symmetry to it that just "seems" right. The most convincing argument, to me, is neither logical nor experimental; it's more aesthetic. 



#15
Feb2212, 08:09 PM

P: 183

I have a little question for you (if you want to answer), if a car is driving in frame A where somebody standing still (its rest frame A) is measuring its speed, than you have length contraction in the cars rest frame B. Is the car already smaller in frame A while measuring its speed because going smaller is something really physical or is this not real ? 



#16
Feb2212, 09:55 PM

PF Gold
P: 4,521

If a car is driving in frame A where somebody standing still (its rest frame A) is measuring its speed, then you don't have length contraction in the cars rest frame B, the car has length contraction in the rest frame A.
In the car's rest frame B, the person "standing still" is length contracted. Pick one frame from which to define lengths. When you use a different frame, with its own definition of lengths, things have different lengths. 



#17
Feb2212, 10:23 PM

P: 1,555

To me time dilation is the situation where different observers measure a different duration between two events even after they discount the effect of light travel time.




#18
Feb2212, 10:29 PM

P: 183

So in frame A is the unit 1 meter and is the rest frame A for a person measuring the car when it was standing still. Suppose the car was 2 meter long. Now the car has a speed in rest frame A, with speed v = x / t (x = distance in t seconds). There is no time dilation for the car in frame A but a length contraction 1/γ. In the rest frame B where the car is standing still (same car driving in the measuring persons rest frame A), there is time dilation 1/γ . t, suppose a ruler in the car, 1 meter is now 1/γ meter and the car is 2/γ meter long. Or is the car length contracted in A and has same new length in B ? What is the lenght from the car in frame B ? What is the new unit in frame B for as well time as length expressed in units from frame A ? 


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