# Clock hypothesis, gravity time dilation and Equivalence Principle

• I
You're right then. Do you see a problem with that?
No problem. The time dilation of that longitudinal light clock consists of two time delays. We may call the time delays Doppler shifts too. A Doppler shift is a quite large effect, while time dilation is quite small effect, at low speeds, and so is length contraction. How small effect is then such time dilation that is caused by length contraction. It's a very very very small effect at low speeds.

You have this backwards
Right! Thanks! :0)

Inertial acceleration is indeed equivalent to gravitational acceleration. Locally (no tidal effects), the clock at the lower potential runs slower by an amount determined by the difference in the potential.
I still don't see where the potential difference lies. For an observer inside the ship, the two clocks are accelerated at the same rate, whereas in a gravitational field, they are not....

...wait a minute, I think I get something: time dilation applies to moving clocks, and those in the ship are accelerating, so they are necessary dilated more when they receive the light than when they send it, which means that they always see the other clock as less dilated. Is that it?

If so, it's still a bit different than with gravitational acceleration, where it is always the higher clock that is less dilated.

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Dale
Mentor
I still don't see where the potential difference lies.
Locally the PE = mgh, so the potential is gh. It doesn’t matter if g is the gravitational acceleration or the fictitious force’s acceleration in a non inertial reference frame. Either way, the time dilation depends on gh, not just g.

If you don't mind of course, I prefer to study the way light would travel instead of studying the math. In my previous message, I was saying that the two clocks in the ship had to be more dilated at detection than at emission, and you did not comment. Do you agree?

vanhees71
Gold Member
2019 Award
How do you study the way light would travel without math? An "antimathematical" attitude towards physics is not helping in understanding the subject!

Dale
Hi Vanhees,

I finally understood relativity out of a simulation, so I prefer those to maths. I'm actually learning JavaScript to be able to make them myself. I'll try to make one about that accelerating ship, meanwhile, here is <off topic content deleted by moderator>

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Dale
Mentor
I prefer to study the way light would travel instead of studying the math.
If you are uncomfortable with math like PE = mgh then you have no business studying relativity.

I was saying that the two clocks in the ship had to be more dilated at detection than at emission, and you did not comment. Do you agree?
It is neither correct nor relevant.

vanhees71
so I prefer those to maths.
You can't learn properly physics without the maths. Period. It's like studying japanese poetry without knowing japanese.

Dale and vanhees71
vanhees71
Gold Member
2019 Award
It's a contradiction! You cannot simulate anything that you haven't fully understood. There's no simulation without math!

weirdoguy
PeterDonis
Mentor
2019 Award
You cannot simulate anything that you haven't fully understood. There's no simulation without math!
Exactly. A simulation is not an alternative to math. It's just one way of doing the math.

vanhees71 and weirdoguy
PeterDonis
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2019 Award