# Time dilation: most recent & precise experiments

1. Mar 28, 2009

### lalbatros

I would like to know about the most precise or most recent experimental tests of time dilation.
Either based on particle lifetimes or on atomic clocks.

Thanks

2. Mar 28, 2009

### robphy

Last edited by a moderator: Apr 24, 2017
3. Mar 29, 2009

### bernhard.rothenstein

The formula that accounts for the Doppler shift has a very good experimental support. Deriving it we first derive the classical Doppler shift formula and involve the formula that accounts for the time dilation effect in order to transform the coordinate time intervals in proper ones.
Could we consider that the Doppler shift formula is a good confirmation of the time dilation effect?

4. Mar 29, 2009

### clem

Time dilation is precisely verified daily, so I would have to say the most recent is when I started typing this. Muons are accelerated to high velocities in high energy accelerators.
The muon lifetime is extended by time dilation, making the experiments possible.
The initial and final beam intensity is carefully measured and agrees with the SR formula.

5. Mar 29, 2009

### jefswat

I suppose they are always updating the GPS satillites to get them as accurate as possible. I'd have no idea where to look to see how precisely they measure time dialation within their calculations.

6. Mar 29, 2009

### Staff: Mentor

7. Mar 29, 2009

### Staff: Mentor

Not just muons, but all other unstable particles. When I was a grad student thirty years ago, one of my friends worked on an experiment that used beams of sigma and xi hyperons (as I recall). Given the beam energy, without time dilation, the beams would have decayed within a few miilimeters. With time dilation, the beams were a few meters long, and the detectors were designed accordingly.

Without time dilation, they wouldn't have been able to do the experiment because the beams wouldn't have reached the detector!

8. Mar 29, 2009

### Saw

But please clarify this to me. It is my understanding that, logically, since simultaneity in SR is relative, the muon's lifetime is found to be extended ONLY from the perspective of the lab, as per the lab's simultaneity line. But from the perspective of the muon-frame, as per the muon's simultaneity line, it is the lab the one that suffers time dilation. Thus, for example, if a muon is created at rest with the lab at the same time, as measured in the lab frame, as the travelling muon:

- the judgment in the lab-frame will be that the the travelling muon's clock is time dilated and that is why it has made it to the target and
- the judgment in the muon-frame is that the lab muon has decayed because it was created earlier as "himself", but if another lab muon had been created right when "he" was born, that second lab muon would not have decayed and would in fact outlive "him", because its time is dilated.

Is this understanding right? Or, on the contrary, do any experiments prove that lab muons live less in an "absolute" sense?

9. Mar 29, 2009

### Mentz114

Mainly right. Essentially, the muon will appear to live for more ticks of the labs clock than on its own (identical) clock.
Not sure what's happening so I can't answer.

No, no, no. There's no 'absolute', only Lorentz invariant quantities.

You must be clear about 'time-dilation' and the elapsed time on clocks. All observers agree on elapsed times ( when clocks are brought together ) but time-dilation is frame dependent. This makes a lot of people mad.

Do you want to see a space-time diagram of the muon scenario ?

10. Mar 29, 2009

### Saw

Well, if we are sure about "something" with regard to the lab-frame, then we must be as sure as to the same "something" with regard to the muon-frame. It's just a question of applying the rules of the theory to the other perspective.

That is OK. No problem with that.

I had myself drawn this one. It'd be nice to hear your comments. Obviously in mine the numbers are not realistic, since I use v=0.5 c, an Earth atmosphere (the red frame in the drawing) of 1 ls and a half-life of the muon of 1.8 s, just because I'm used to calculations with this sort of numbers, but I'd be glad to see another diagram with the real magnitudes.

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11. Mar 29, 2009

### Mentz114

Hi saw,
those pics are a bit cluttered but I can see the life of one muon in the lab frame and in the muons frame and that looks OK. I'm not sure why the atmosphere is there. I guess you've answered your own question.

M

12. Mar 30, 2009

### lalbatros

Clem,

I would be so happy with a (t,v) curve of that:
Would you know where to find it together with a description of how that was measured?

13. Mar 30, 2009

### lalbatros

Doppler shift is nice of course, but it is not as direct as a real clock measurement.
Particles lifetime is nearly as direct as clocks.
I would be interrested in the most naïve yet precise experiment.
I think clocks are probably the most naïve test but it is also possible.