## Why do we use light signals to measure time?

why do we use light signals to measure time?
In flat spacetime

Let's say we have two observers in one's rest frame the other one has velocity v. We suppose each of them sent light signals to other one with time seperation of Δt(their proper time) and measure time accordingly.we see time dilation here. so far everything is ok for me.

But I think I'm missing something and I do not get that. Do we have to use light signals?

In the same situtation what if observers throw rocks with velocity w again with time seperation Δt. Both should see the rocks thrown from other one with velocity w' with different signs.Shouldn't this method measure time dilation with same accuracy? if it can , can't we built this method to build coordinate lattices?

I assumed that we know Lorentz transformations and limiting speed.
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 Recognitions: Science Advisor Staff Emeritus We use clocks to measure time - though one can, in principle, define a "light clock" given a ruler, there's no special need to use this particular sort of clock - and in fact we usually use other sorts of clocks, atomic clocks being the most accurate. We use light signals to synchronize clocks. We could use other means, but light signals are easy. If you're familiar with the limiting speed concept, you can see that we could use ultra-relativistic particle beams to synchronize clocks too, but why bother when we know they'll travel at the same speed as the more easily generated light beams.
 i got the point.. I see it was a silly question .Thanks for the answer.

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