# Measuring Speed of Light with A Ruler in Expanding Space

At $$t_0$$, we have a ruler which has two tick marks (one at each end) with one labeled "$$0$$" and the other labeled "$$L$$" (it is $$L$$ units long). Suppose at that time we also have two point objects which are a certain distance apart. Suppose that, by $$t_1 > t_0$$, space has uniformly expanded so that the two point objects are twice as far apart. Would the ruler also have expanded, by $$t_1$$, so that the two tick marks are now twice as far apart, since the space that the ruler occupied doubled, or would the distance between the two tick marks stay the same, because of the forces holding the ruler material together? In the former case, length $$L$$, as measured by the tick marks on this ruler, means something different at the two different times, since the ruler has expanded between those times.

If the answer is that the ruler would have expanded, then, I have a follow-up question: if at $$t_0$$, the speed of light is measured to be $$nL/sec$$, by the ruler as it is at $$t_0$$, then, at $$t_1$$, is the speed of light still measured to be $$nL/sec$$, by this ruler as it is at $$t_1$$ (expanded), even though $$L$$ means something different at $$t_1$$ than it does at $$t_0$$?