# I Time Dilation (Clock specific)

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1. Feb 22, 2017

### Maaruk

Hi, I went ahead and read through all the similar discussions and none are on this particular topic so I'll go ahead and shoot. I did find this topic as well, but my question is pretty simple.

I think I understand how time dilation works, I read through the explanation here, this jives with the explanation provided in this World Science Festival panel in this video (it starts at around 11:30 if the link didn't work). This is the light clock thought experiment where it shows why a light particle in the moving clock is bouncing slower than the one in the stationary clock. This makes sense to me, and I wondered if the Hafele-Keating experiments which use a cesium beam atomic clocks work on the same basic principle described?

2. Feb 22, 2017

### DaveC426913

Why would they behave any differently?

3. Feb 22, 2017

### Staff: Mentor

Hi Maaruk, welcome to PF, and thank you for taking the time to dig around a bit and come with a thoughtful question!

So the hypothetical clock which is a pulse of light bouncing back and forth is called a light clock. It is primarily meant to be an easy to analyze teaching tool. As far as I know there is not any such clock built that actually works that way. However, assuming that the principle of relativity is true then if a light clock slows down in a reference frame then so must all other comoving clocks.

Edit: I just had a thought that you could consider the microwave cavity to be a kind of mirror arrangement

4. Feb 22, 2017

### Maaruk

From the description of the atomic clock used in the H-K experiment it wasn't clear to me whether the cesium clock uses the same metronomic principle as the light clock.

Thank you for the welcome.

I definitely appreciated how easy the light clock concept was to understand, and why movement would affect its measurement of time. I just wasn't clear on whether the atomic clock in the H-K experiment operates with roughly the same principle and something very similar to the light clock thought experiment is happening in the H-K experiment. Maybe more clearly, are the mechanisms of the light clock and the cesium clock roughly the same? I think I see what you are saying about the microwave cavity, I read through 5 different descriptions of the cesium clock and I still wasn't sure so I thought I would find someplace to ask

5. Feb 22, 2017

### Staff: Mentor

Cesium clocks are not light clocks, but they have been compared to light clocks in various reference frames: They are equivalent.

6. Feb 22, 2017

### Maaruk

Thanks guys, very helpful. Asking accurate questions is very helpful, and I know sometimes I do not ask accurate questions. Plus it doesn't help that I am usually a mess of terminology but I generally know what I mean by something. Thanks again.

7. Feb 22, 2017